Published by Electrical Installation Wiki, Chapter J. Overvoltage protection – Surge protection technical supplements
Lightning protection standards
The IEC 62305 standard parts 1 to 4 (NF EN 62305 parts 1 to 4) reorganizes and updates the standard publications IEC 61024 (series), IEC 61312 (series) and IEC 61663 (series) on lightning protection systems.
Part 1 – General principles
This part presents general information on lightning and its characteristics and general data, and introduces the other documents.
Part 2 – Risk management
This part presents the analysis making it possible to calculate the risk for a structure and to determine the various protection scenarios in order to permit technical and economic optimization.
Part 3 – Physical damage to structures and life hazard
This part describes protection from direct lightning strokes, including the lightning protection system, down-conductor, earth lead, equipotentiality and hence SPD with equipotential bonding (Type 1 SPD).
Part 4 – Electrical and electronic systems within structures
This part describes protection from the induced effects of lightning, including the protection system by SPD (Types 2 and 3), cable shielding, rules for installation of SPD, etc.
This series of standards is supplemented by:
the IEC 61643 series of standards for the definition of surge protection products (seeThe components of a SPD );
the IEC 60364-4 and -5 series of standards for application of the products in LV electrical installations (see End-of-life indication of a SPD)
The components of a SPD
The SPD chiefly consists of (see Fig. J50):
1) one or more nonlinear components: the live part (varistor, gas discharge tube, etc.); 2) a thermal protective device (internal disconnector) which protects it from thermal runaway at end of life (SPD with varistor); 3) an indicator which indicates end of life of the SPD; Some SPDs allow remote reporting of this indication; 4) an external SCPD which provides protection against short circuits (this device can be integrated into the SPD)
Fig. J50 – Diagram of a SPD
Technology of the live part
Several technologies are available to implement the live part. They each have advantages and disadvantages:
• Zener diodes; • The gas discharge tube (controlled or not controlled); • The varistor (zinc oxide varistor).
The table below shows the characteristics and the arrangements of 3 commonly used technologies.
Fig. J51 – Summary performance table
Note: Two technologies can be installed in the same SPD (see Fig. J52)
Fig. J52 – The Schneider Electric brand iPRD SPD incorporates a gas discharge tube between neutral and earth and varistors between phase and neutral
End-of-life indication of a SPD
End-of-life indicators are associated with the internal disconnector and the external SCPD of the SPD to inform the user that the equipment is no longer protected against overvoltages of atmospheric origin.
Local indication
This function is generally required by the installation codes. The end-of-life indication is given by an indicator (luminous or mechanical) to the internal disconnector and/or the external SCPD.
When the external SCPD is implemented by a fuse device, it is necessary to provide for a fuse with a striker and a base equipped with a tripping system to ensure this function.
Integrated disconnecting circuit breaker
The mechanical indicator and the position of the control handle allow natural end-of-life indication.
Local indication and remote reporting
iQuick PRD SPD of the Schneider Electric brand is of the “ready to wire” type with an integrated disconnecting circuit breaker.
Local indication
iQuick PRD SPD (see Fig. J53) is fitted with local mechanical status indicators:
• the (red) mechanical indicator and the position of the disconnecting circuit breaker handle indicate shutdown of the SPD; • the (red) mechanical indicator on each cartridge indicates cartridge end of life..
Fig. J53 – iQuick PRD 3P +N SPD of the Schneider Electric brand
Remote reporting (see Fig. J54) iQuick PRD SPD is fitted with an indication contact which allows remote reporting of:
• cartridge end of life; • a missing cartridge, and when it has been put back in place; • a fault on the network (short circuit, disconnection of neutral, phase/neutral reversal); • local manual switching.
As a result, remote monitoring of the operating condition of the installed SPDs makes it possible to ensure that these protective devices in standby state are always ready to operate.
Fig. J54 – Installation of indicator light with a iQuick PRD SPD
Fig. J55 – Remote indication of SPD status using Smartlink
Maintenance at end of life
When the end-of-life indicator indicates shutdown, the SPD (or the cartridge in question) must be replaced.
In the case of the iQuick PRD SPD, maintenance is facilitated:
• The cartridge at end of life (to be replaced) is easily identifiable by the Maintenance Department. • The cartridge at end of life can be replaced in complete safety, because a safety device prohibits closing of the disconnecting circuit breaker if a cartridge is missing.
Detailed characteristics of the external SCPD
Current wave withstand
The current wave withstand tests on external SCPDs show as follows:
• For a given rating and technology (NH or cylindrical fuse), the current wave withstand capability is better with an aM type fuse (motor protection) than with a gG type fuse (general use). • For a given rating, the current wave withstand capability is better with a circuit breaker than with a fuse device.
Figure J56 below shows the results of the voltage wave withstand tests:
• to protect a SPD defined for Imax = 20 kA, the external SCPD to be chosen is either a MCB 16 A or a Fuse aM 63 A, Note: in this case, a Fuse gG 63 A is not suitable. • to protect a SPD defined for Imax = 40 kA, the external SCPD to be chosen is either a MCB 40 A or a Fuse aM 125 A,
Fig. J56 – Comparison of SCPDs voltage wave withstand capabilities for Imax = 20 kA and Imax = 40 kA
Installed Up voltage protection level
In general:
• The voltage drop across the terminals of a circuit breaker is higher than that across the terminals of a fuse device. This is because the impedance of the circuit-breaker components (thermal and magnetic tripping devices) is higher than that of a fuse.
However:
• The difference between the voltage drops remains slight for current waves not exceeding 10 kA (95% of cases); • The installed Up voltage protection level also takes into account the cabling impedance. This can be high in the case of a fuse technology (protection device remote from the SPD) and low in the case of a circuit-breaker technology (circuit breaker close to, and even integrated into the SPD).
Note: The installed Up voltage protection level is the sum of the voltage drops:
• in the SPD; • in the external SCPD; • in the equipment cabling
Protection from impedant short circuits
An impedant short circuit dissipates a lot of energy and should be eliminated very quickly to prevent damage to the installation and to the SPD.
Figure J57 compares the response time and the energy limitation of a protection system by a 63 A aM fuse and a 25 A circuit breaker.
These two protection systems have the same 8/20 µs current wave withstand capability (27 kA and 30 kA respectively).
Fig. J57 – Comparison of time/current and energy limitations curves for a circuit breaker and a fuse having the same 8/20 µs current wave withstand capability
Propagation of a lightning wave
Electrical networks are low-frequency and, as a result, propagation of the voltage wave is instantaneous relative to the frequency of the phenomenon: at any point of a conductor, the instantaneous voltage is the same.
The lightning wave is a high-frequency phenomenon (several hundred kHz to a MHz):
• The lightning wave is propagated along a conductor at a certain speed relative to the frequency of the phenomenon. As a result, at any given time, the voltage does not have the same value at all points on the medium (see Fig. J58).
Fig. J58 – Propagation of a lightning wave in a conductor
• A change of medium creates a phenomenon of propagation and/or reflection of the wave depending on: • the difference of impedance between the two media; • the frequency of the progressive wave (steepness of the rise time in the case of a pulse); • the length of the medium.
In the case of total reflection in particular, the voltage value may double.
Example: case of protection by a SPD
Modelling of the phenomenon applied to a lightning wave and tests in laboratory showed that a load powered by 30 m of cable protected upstream by a SPD at voltage Up sustains, due to reflection phenomena, a maximum voltage of 2 x Up (see Fig. J59). This voltage wave is not energetic.
Fig. J59 – Reflection of a lightning wave at the termination of a cable
Corrective action
Of the three factors (difference of impedance, frequency, distance), the only one that can really be controlled is the length of cable between the SPD and the load to be protected. The greater this length, the greater the reflection.
Generally for the overvoltage fronts faced in a building, reflection phenomena are significant from 10 m and can double the voltage from 30 m (see Fig. J60).
It is necessary to install a second SPD in fine protection if the cable length exceeds 10 m between the incoming-end SPD and the equipment to be protected.
Fig. J60 – Maximum voltage at the extremity of the cable according to its length to a front of incident voltage = 4kV/us
Example of lightning current in TT system
Common mode SPD between phase and PE or phase and PEN is installed whatever type of system earthing arrangement (see Fig. J61).
The neutral earthing resistor R1 used for the pylons has a lower resistance than the earthing resistor R2 used for the installation.
The lightning current will flow through circuit ABCD to earth via the easiest path. It will pass through varistors V1 and V2 in series, causing a differential voltage equal to twice the Up voltage of the SPD (Up1 + Up2) to appear at the terminals of A and C at the entrance to the installation in extreme cases.
Fig. J61 – Common protection only
To protect the loads between Ph and N effectively, the differential mode voltage (between A and C) must be reduced.
Another SPD architecture is therefore used (see Fig. J62)
The lightning current flows through circuit ABH which has a lower impedance than circuit ABCD, as the impedance of the component used between B and H is null (gas filled spark gap). In this case, the differential voltage is equal to the residual voltage of the SPD (Up2).
Published by Andreas Berthou, EE Power – Technical Articles: The Benefits of High-Voltage Direct Current (HVDC) Power, October 19, 2020
This article highlights ABB as HVDC has emerged as a viable complement to AC power transmission, with the ability to connect asynchronous AC grids and allow power transmission across long distances with minimal losses.
For the past century, alternating current (AC) systems have been the global standard for electrical transmission to businesses, applications, and homes. However, over the last several decades, High-Voltage Direct Current (HVDC) has emerged as a viable complement to AC power transmission, with the ability to connect asynchronous AC grids and allow power transmission across long distances with minimal losses.
This is essential for applications such as offshore wind farms, which can operate at considerable distances from where the power they generate is needed. In this way, HVDC technology is on course to unlock the full potential of Europe’s offshore resources and increase the efficiency and compatibility of energy systems across the world. Andreas Berthou explains the benefits of this transmission system.
Figure 1. Offshore wind
AC vs DC
AC transmission has established itself as the preferred global platform over the past century, due to the convenience of transformers in stepping voltage up or down as needed, as well as being easier to interrupt than DC grids. However, high-voltage AC transmission has a number of limitations, including shorter distance constraints and transmission capacity, as well as the impossibility of connecting two AC power networks of different frequencies.
Owing to a number of innovations over the years, HVDC transmission is now primed to supplant AC transmission, with HVDC offering an improved capacity for distance transmission and higher efficiency over those distances. While AC transmission is impossible between two networks of different existing energy infrastructures. This precise power flow allows new energy sources to be integrated seamlessly into power grids without the volatility that such integration can introduce to frequencies, HVDC transmission can connect networks that operate on any frequency or voltage. This allows renewable energy from various sources to be easily integrated into existing power grids, facilitating an efficient transition to renewable energy sources. HVDC transmission is reliable and easy to control, providing instant and precise control of power flow for new and existing grids. HVDC can expand the energy networks, making them more stable.
HVDC is more environmentally friendly than AC, providing more energy per square metre over greater distances more efficiently than AC systems, as well as lower losses and less space requirements. This increased efficiency reduces the carbon footprint of HVDC compared to AC, with losses being reduced from around 5-10% in AC transmission to around 2-3% for the same application in HVDC.
Figure 2. DC overhead lines
What is HVDC?
HVDC, pioneered by Hitachi ABB Power Grids in the 1920’s, and commercially established in the 50’s, differentiates itself from AC transmission systems through electrical current converter technology, converting AC to DC to more efficiently transmit across large distances with fewer transmission lines needed. HVDC is also commonly used to connect asynchronous AC networks, stabilising the surrounding grid while increasing grid capacity and affording greater control over power flow. HVDC systems use high-power semiconductor valves, tuned specifically by Hitachi ABB Power Grids for their applications.
Figure 3. HVDC light valves
HVDC is the method of choice for subsea electrical transmission and long-distance power transmission, owing to its ability to send large amounts of electricity across greater distances than AC transmission, with minimal losses. Offshore wind is becoming increasingly important, with WindEurope estimating that Europe’s offshore wind capacity will reach 450GW in 30 years, and HVDC transmission is an essential part of connecting remote offshore wind farms to the cities and areas where this electricity is used. To enable this integration with offshore energy, a hybrid HVDC breaker designed by Hitachi ABB Power Grids was recently tested by KEMA Laboratories as part of the EU-funded “Progress on Offshore Meshed HVDC Transmission Networks” project. Using optimized power semiconductors developed in-house by Hitachi ABB Power Grids, this breaker overcomes existing technical limitations by allowing the HVDC transmission system to maintain power flow even if there is a fault on one of the lines, breaking the direct current on the line and isolating the fault.
Another important development is HVDC Light®, a voltage-sourced converter solution pioneered by Hitachi ABB Power Grids in 1997, recently hailed by the World Economic Forum as “one of the greatest global energy innovations” of the last decade. HVDC Light provides more secure power control and quick power restoration, and allows long-distance underground high-voltage transmission, enabling easier transition to renewable energy in urban areas.
The future of HVDC
While AC fulfils an important role for energy transmission across shorter distances and to the end-user, HVDC technology is a more viable energy transmission solution in our increasingly connected global energy ecosystem. HVDC’s efficiency across long distances will be an essential part of global renewable energy solutions, seamlessly integrating clean energy into existing power infrastructures and ensuring that renewable energy is accessible and affordable.
Figure 4. HVDC Classic valves from North East Agra multiterminal link in India
This potential is already being shown through large-scale global developments using HVDC in renewable energy systems. Hitachi ABB Power Grids is supporting China in building the Zhangbei HVDC grid in the Beijing-Tianjin-Hebei area, the first grid installation of its kind in the world. When completed, this grid is expected to provide the area with a consistent supply of renewable energy through the integration of remote wind, solar and hydro energy, and could facilitate the adoption of similar systems in Europe and the US. Just last month Hitachi ABB Power Grids announced a major project with Scottish and Southern Electricity Networks (SSEN) Transmission, part of the UK energy giant SSE plc, to enable Europe’s first multi-link VSC HVDC connection. The link, which will connect Shetland to the UK transmission system for the first time, will enhance security of power supply and help transmit wind power generated on the islands, contributing to the UK’s decarbonization target of bringing all greenhouse gas emissions to net zero by 2050.
Another exciting HVDC project is the Dogger Bank development in the UK, consisting of three wind farm projects in the North Sea. The development will be the UK’s first offshore wind application of HVDC and is expected to power 4.5 million homes when completed in 2030. These developments not only represent the massive potential HVDC has for the future of the energy industry, but they are playing an essential role in strategies to reduce global warming and contributing to the UN Sustainable Development Goal of increasing access to reliable and affordable energy for all.
Author: Andreas Berthou received his Bachelor Of Science in Mechanical Engineering at Chalmers University of Technology, then Master Of Science in Business Management at Napier University. He work as a Senior Vice President, High Voltage Cables at ABB.
Published by Jacek F. GIERAS, University of Technology and Life Sciences, Bydgoszcz
Abstract. The paper discusses the electric power system of the Tu-154M aircraft. After brief introduction to aircraft power systems, the results of reverse design and analysis of the GT40PCh6 wound-field synchronous generator including short circuit have been presented. Electric power distribution and assignment of electric grids (channels) to respective aircraft energy consumers has been discussed. Most important electric loads, i.e., the fuel system with electric motor driven pumps, wing anti-ice electric system and exterior and interior lighting equipment have been described. An example of failure of GT40PCh6 synchronous generator is the fire of the Tu-154B-2 on January 1, 2011 before taking off at Surgut airport (flight 7K348).
Streszczenie. Artykul omawia system elektroenergetyczny samolotu Tu154M. Po krotkim wprowadzeniu do systemow elektroenergetycznych samolotow, przedstawiono wyniki projektowania odwrotnego oraz analizy generatora synchronicznego GT40PCh6 o wzbudzeniu elektromagnetycznym z uzwglednienium przebiegow pradow podczas zwarcia. Opisano dystrybucje energii elektrycznej oraz przyporzadkowanie odbiornikow energii elektrycznej samolotu do poszczegolnych sieci (kanalow). Scharakteryzowano najwazniejsze obciazenia elektryczne, tzn. system paliwowy z pompami napedzanymi silnikami elektrycznymi, system elektryczny zapobiegajacy osadzaniu sie lodu na frontowych powierzchniach skrzydel oraz oswietlenie zewnetrzne i wewnetrzne. Przykladem awarii generatora synchronicznego GT40PCh6 jest pozar Tu-154B-2 w dniu 1 stycznia 2011 przed startem na lotnisku w Surgucie (lot 7K348). (System elektroenergetyczny samolotu pasazerskiego Tu-154M)
Keywords: aircraft electric power system, distribution system, electric loads, electric motor-driven fuel pumps, fuel system, lighting, synchronous generator, Tu154M, wing anti-ice electric system Słowa kluczowe: generator synchroniczny, odbiorniki energii, oswietlenie elektryczne, pompy paliwa napedzane silnikami elektrycznymi, system dystrybucji energii elektrycznej, system elektroenergetyczny samolotow, system odmrazania elektrycznego skrzydel, system paliwowy, Tu-154M
Introduction to aircraft electric systems
The function of the aircraft electrical system is to generate, regulate and distribute electrical power throughout the aircraft [4, 7]. Aircraft electrical components operate on many different voltages both AC and DC. Most systems use 115/200V AC (400 Hz) and 28V DC. There are several different electric generators on large aircraft (Fig. 1) to be able to handle loads, for redundancy, and for emergency situations, which include [4, 7, 8]:
1. engine driven main generators; 2. auxiliary power unit (APU); 3. ram air turbine (RAT); 4. external power, i.e., ground power unit (GPU).
Each of the engines on an aircraft drives one or more a.c. generators (Fig. 2) via special transmission system.
Fig. 1. Aircraft generators: 1 – main generator, 2 – APU, 3 – RAT, 4 – GPU [4].
The electricity produced by these generators is used in normal flight to supply the entire aircraft with power. The power generated by APUs is used while the aircraft is on the ground during maintenance and for engine starting. Most aircraft can use the APU while in flight as a backup power source. RATs are used in the case of a generator or APU failure, as an emergency power source. External power may only be used with the aircraft on the ground. A GPU (portable or stationary unit) provides AC power through an external plug. Aircraft generators are typically three-phase, salient pole, wound-field synchronous generators with outer stator with distributed-parameter winding and inner rotor with concentrated coil winding [4]. The field excitation current is provided to the rotor with the aid of a brushless exciter system consisting of two synchronous machines, i.e., wound-field synchronous exciter and permanent magnet (PM) sub-exciter. The power circuit is shown in Fig. 2. PM brushless generators are rather avoided due to difficulties with shutting down the power in failure modes. There are also attempts of using switched reluctance (SR) generators with no windings or PMs on the rotor. A generator control unit (GCU), or voltage regulator, is used to control generator output. The generator shaft is driven by a turbine engine with the aid of gears or directly by low spool engine shaft.
Fig. 2. Architecture of main wound-field synchronous generator [4].
Typical AC power system of aircraft is 115/200V, 400Hz, three-phase system. Since the speed of an aircraft engine varies from full power speed to flight idle speed (typically 2:1), and frequency is proportional to the generator rotational speed, a device for converting a variable speed to constant speed is necessary [7]. The so called constant speed drive (CSD), i.e., a complex hydromechanical device was common until the late 1980s. Nowadays, solid state converters have replaced unreliable CSDs with variable speed/constant frequency (VSCF) systems.
Typical aircraft have from 16 to 160 km of wire installed such that wire from one system is often collocated with wire from many other systems. Electrical wiring can be classified into power wiring (heavy current) and light current wiring. In modern aircraft, power wires, feeding e.g., electric motors, are not routed through the cockpit. Switches in the cockpit are connected to light current wires (control wires), which activate relays of heavy current circuit.
Table 1. AC power systems of Tu-154M aircraft
.
Fig. 3. Main power distribution systems 115/220V AC and 36V AC of Tu-154M.
1 – rectifiers VU-6A (backup and No 1), 2 – rectifier VU-6A No 2, 3 – right junction box (JB) 115/200 V, 4 – converter PTS-250 No 2, 5 – converter PTS-250 No 1, 6 – JB of kitchenette, 7 – JB of anti-ice system, 8 – right panel of generators, 9 – generator GT40PCh6 No 3, 10 – JB of APU 200V, 11 – generator GT40PCh6 of APU, 12 – generator GT40PCh6 No 2, 13 – generator GT40PCh6 No 1, 14 – external power connector for ShRAP-400-3F GPU, 15 – left panel of generators, 16 – left JB 115/220V, 17 – transformer No 2, 18 – transformer No 1, 19 – right JB 36V AC, 20 – left JB 36V AC, 22 – flight attendant’s switchboard, 23 – converter POS-125Ch [3, 13].
Electric power supply system of Tu-154M
The main power supply system of the Tu154M is a three-phase 115/200V, 3×40kVA, 400Hz, AC system [3, 10, 13]. The three-phase 115/200V AC power is delivered by three GT40PCh6 wound-field synchronous generators. The fourth GT40PCh6 AC generator is the APU generator. The APU is also equipped with 27V DC GS-12TO starter-generator.
The secondary three-phase, 36V, 400Hz, 46.8-A, 2×3kW AC system takes power from the main system via two three-phase 206/37V, Dy, TS330S04B transformers. The primary windings of TS330S04B transformers are fed from the navigation piloting system (NPK) bus bars. The 115/200V AC and 36V AC power systems are shown in Fig. 3 and described in Table 1. The third power system is the 27V, 200A, DC, single-circuit system (Fig. 4), which receives power from the main system via transformer and three VU-6A rectifiers and four 20NKVN-25 batteries.
The emergency 36V AC power system (instead of RAT) consists of two 20-30/36V, 400Hz, 250VA PTS-250 transistor inverters fed from batteries. It feeds among others the gyro horizon AGR-144. Another single-phase 115-V emergency system takes electric power from batteries via POS- 125TCh solid state converter.
The simplified electrical diagram of 115/200V AC power generation system with three main generators and APU generator is shown in Fig. 5. The block diagram of overall electric system of the Tu-154M is shown in Fig. 6.
Fig. 4. Power distribution system 27V DC of Tu-154M.
1 – Rectifier VU-6A No 2, 2 – right panel of protection control, 3 – Rectifier VU- 6A No 1, 4 – Left panel of protection control, 5 – junction box (JB) of kitchen, 6 – left power JB 27 V DC, 7 – electrical panel of flight attendant, 8 – rear JB (in left panel of generators), 9 – JB of APU and batteries, 10 – batteries 20NKBN-25, 12 – JB of batteries, 12 – JB of VU-6A backup rectifier, 14 – backup rectifier VU-6A, 15 – “PT” JB, 16 – electrical panel of household devices, 17 – electrical panel of crew cupboard, 18 – flight attendant’s switchboard [13].
Fig. 5. Simplified schematic of main electric power generation system 115/220V AC when all generators G1, G2, and G3 are in parallel.
1 – contactor TKS133DOD “reconnection of grid No 1 on generator No 3”, 2 – contactor TKS233DOD “switching generator No 1 on grid”, 5 – contactor TKS233DOD “switching APU on grid No 2”, 17 – contactor TKS233DOD “switching generator No 2 on grid”, 20 – contactor TKS233DOD “reconnection of grid No 3 on generator No 1”, 21 – contactor TKS233DOD “switching generator No 3 on grid”, 27 – contactor TKS233DOD “switching APU or GPU on grid No 3”, 38 – contactor TKS233DOD “switching APU on grid” [2].
Electric power distribution
The main three-phase, 115/200V, 400Hz power supply system is a three-channel system (Figs 3, 5 and 6). One GT40PCh6 generator feeds one channel (electric grid).
The generator No 1 mounted on the left turbofan engine No 1 feeds the grid No 1, which in turn feeds the left autonomous bus bars, left bus bar of navigation piloting system (NPK), radio navigation equipment, anti-collision flashing lights SMI-2KM, control systems of slats and stabilizers (motors No 1), fuel pumps No 1,3,5,8,10, rectifiers VU-6B No 1 (No 3), passenger cabins lighting, heaters of windshields of cockpit, hydraulic pumping station NS-46 of the second hydraulic system, and other loads. The total power consumption of the grid No 1 is 23.2kVA, 70A (excluding NS-46).
The generator No 2 of the grid No 2 mounted on the center engine No 2 feeds anti-ice electric heating elements of leading edges of wings (slats). The power consumption is 43.6 kVA, 130 A.
The third grid No 3 powered by the generator No 3 installed on the right engine No 3 is loaded with the right autonomous bus bars, right bus bar of navigation piloting system (NPK), control system of slats and stabilizers (motors No 2), fuel pumps No 2,4,6,7,9,11, fuel control system, rectifiers VU-6B No 2 (No 3), air conditioning system, hydraulic pumping station NS-46 of the third hydraulic system, household equipment and other equipment. The total power consumption is 12kVA, 45A (without household equipment and NS-46). The household equipment needs 13kVA, 60A.
In the case of failure of one of the generators, its grid is automatically reconnected to the operating generators.
The GPU supplies all three electric grids. After starting any turbofan engine and after switching on any GT40PCh6 generator, the first and the third grid is automatically connected to this generator while the GPU feeds only the second grid. If two generators are on, the GPU is automatically disconnected from the aircraft electric power system.
Control and protection devices of the main power system are located on the power panel of the flight engineer. The three-phase 36-V, 400-Hz, two-channel electric power system feeds the Kurs-MP-2 landing navigation and control unit, ARK-15M radio compass, Groza-154 radar, Doppler effect velocity and drift angle measure system DISS-3P, and hydraulic pressure gauge MET-4B. The 36V AC system also supplies the gyro horizon (attitude indicator), but its power is supplied independently of the PTS-250 converter, which receives electrical energy from batteries. The PTS-250 No 1 converter is used as an emergency 36V AC power source (Fig. 6). Connection of the converter to the network is made automatically.
Fig. 6. Block diagram of electric power system of Tu-154M [16].
The on-board 27V DC power system consists of three VU-6A rectifiers, GS-12TO starter-generator mounted on the APU, and two four 20NKBN-25 batteries (Fig. 4). The VU-6A rectifiers are the basic DC power sources. They get the power from the first and third grid (from the main 115/200 V AC system). There are two basic rectifiers and the third rectifier is for redundancy (Fig. 6). The third rectifier is switched on automatically in the case of failure of one of the basic rectifiers and operates in parallel with the remaining rectifiers. There is also provision for “forced” connection of the third reserve rectifier.
The 27V DC GS-12TO APU-mounted starter-generator delivers power to the DC grid after starting the APU on the ground until turbofan engines are started and GT40PCh6 synchronous generators operate. In the case of failure of the main 115/200V power system in the air, rechargeable batteries are used to supply the most important loads and to start the APU on the ground in the absence of GPU. Under normal operation, batteries are connected in parallel to smooth the DC bus voltage ripple. Rechargeable batteries are installed in the rear fuselage under the floor of the technical compartment. They can be accessed through a removable hatch in the floor.
In addition, there is a 27V AC power supply designed for household appliances: electric kettles and electric warmer in the kitchenette-buffet. The system gets its power from the main system through a TS-330S04A transformer connected to the grid No 3 via a switch mounted on the flight attendant switchboard (Figs 3 and 4). The transformer is installed on the right board, near the frame No 35, in junction box (JB) of the kitchenette (Fig. 3).
The single-phase 115V AC, 400 Hz power supply provides electric power to Landish-20 FM radio station, radio system RSBN-2SA of near-range navigation, Kurs-MP-2 navigation and control unit, and other radio equipment, as well 2IA-7A temperature meters of engine exhaust gases [3]. In the case of emergency, the electrical power to these loads comes from the converter MA-100M, which is supplied from batteries. The connection of converter is made automatically.
The cross section of basic distribution wires is:
• 1.93 to 35.0 mm2 for AC systems; • 1.5 to 70.0 mm2 for DC systems.
Synchronous generators
The main generators are three 40-kVA, 115/200V, 400Hz, CSD GT40PCh6 wound-field synchronous generators driven by three D-30KU low-bypass turbofan engines (Fig. 7). Each generator feeds one channel (grid). There is also a reserve 40-kVA, 115/200V, 400Hz power source, the so called APU which consists of GT40PCh6 synchronous generator driven by independent TA-6A turbine engine (Fig. 8).
Fig. 7. Turbofan engine D-30KU.
1 – inlet guide vanes heating collector (VNA), 2 – centrifugal air separator of oil system, 3 – fuel-oil heat exchanger, 4 – main oil pump, 5 – front (main) accessory drive gearbox, 6 – hydraulic pump for thrust reverse, 7 – fuel pump, 8 – sensor of referred revolutions, 9 – place for aircraft hydraulic pumps NP-25 and NP-89, 10 – fuel pump regulator, 11 – temperature sensor, 12 – centrifugal regulator of low pressure (LP) rotor, 13 – rotational speed sensor for the LP rotor, 14 – synchronous generator GT40PCh6, 15 – rear accessory drive gearbox, 16 – constant speed drive (CSD), 17 – mechanism of frequency correction, 18 – air turbine of CSD, 19 – air turbo starter, 20 – overlapping cover of turbo starter, 21 – oil removal pump. http: //ru.wikipedia.org/
Fig. 8. APU with GT40PCh6 synchronous generator and TA-6A turboshaft engine.
1 – fuel pump-regulator, 2 – sensor of tacho generator, 3 – synchronous generator GT40PCh6, 4 – leads of synchronous generator, 5 – air-oil heat exchanger, 6 – adapter, 7 – fan, 8 – stabilizer of oil pressure, 9 – front suspension rigging, 10 – grid of compressor, 11 – radial-circular entrance, 12 – compressor, 13 – gas collector, 14 – combustion chamber, 15 – evaporation tube, 16 – head of flame tube, 17 – snail, 18 – exhaust pipe, 19 – air bypass pipeline, 20 – turbine, 21 – air regulator, 22 – bleed air pipe, 23 – spring, 24 – reducer [3].
The longitudinal section of the GT40PCh6 synchronous generator is shown in Fig. 9. From better packaging point of view, the PM brushless sub-exciter is placed inside the exciter.
1 – armature core of main generator, 2 – armature winding of main generator, 3 – armature winding of exciter, 4 – armature core of exciter, 5 – field winding of exciter, 6 – pole, 7 – field excitation system of exciter, 8 – rotor pole of main generator, 9 – armature of subexciter, 10 – PM, 11 – armature winding of subexciter, 12 – end shield, 13 – nozzle, 14 – housing, 15 – bearing, 16 – hollow shaft of rotor, 17 – shaft end, 18 – flanges, 19 – fan, 20 – field winding of main generator, 21 – point of lubrication. http: //s010.radikal.ru/i314/1010/42/cba147b70185.jp
The GT40PCh6 generator operates smoothly under the following conditions:
1. ambient temperature from +100 to −60 ◦C; 2. cooling air temperature from +60 to −60 ◦C; 3. atmospheric pressure up to 124 mm Hg; 4. effects of frost and dew; 5. shock accelerations up to 6g.
The housing monoblock is made of magnesium alloy with pressed steel sleeve mounted on the drive side around the ball bearing. The bearing nest has a pocket for the collection of waste grease that is removed from it with the aid of a plunger. Lubricant is applied to the bearing on the oil line through the point of lubrication.
There are longitudinal ribs on the inner surface of the housing, which increase its rigidity and form channels for passage of cooling air. Windows in the enclosure at the drive side are designed to exit the air. Titanium flange screwed to the end shield mounts the generator on the engine (Fig. 9). A box on the outer surface of the housing contains a differential current transformer for protection of the generator.
The rotor has two ball bearings. Seals of the bearings are threaded type with extra cuffs. The rotor salient poles, armature of the exciter and PMs of sub-exciter are pressed on the hollow shaft. The rotating passive rectifier consists of six silicon diodes D232A.
Cooling of the generator is accomplished by blowing air at a flow rate varying from 0.1 to 0.3 kg/s.
Dimensions, material data and winding diagrams of the GT40PCh6 synchronous generator are not available [3, 13, 10]. To obtain dimensions, winding parameters and detailed performance characteristics of the GT40PCh6 synchronous generator (Table 2), a reverse design on the basis of available sources [3, 10, 13] has been done. The 2D FEM has been used for electromagnetic analysis and synthesis. The 2D magnetic flux distribution in the cross section of the main generator as obtained from the FEM is shown in Fig. 10.
Fig. 10. Magnetic flux distribution in the cross section of GT40PCh6 synchronous generator as obtained from the 2D FEM.
The open circuit characteristics [3] at synchronous speed ns = f/p = const obtained from analytical calculations and 2D FEM are shown in Fig. 11.
Fig. 11. Open circuit characteristics at synchronous speed ns = const obtained from analytical calculations and 2D FEM.
Short-circuit currents can exceed more than 11 times the nominal current. Figs 12 to 15 shows the armature current Iash = f(t) waveforms for three-phase, line-to-line, line-to-neutral and two lines-to-neutral short circuits of the GT40PCh6 synchronous generator. The most dangerous are line-to-neutral (Fig. 14) and two lines-to-neutral (Fig. 15) short circuits. The obtained short-circuit current waveforms are very important since the subtransient and transient shortcircuit currents help to evaluate the possible damage during the electrical power system failure.
Fig. 12. Armature current Iash at three-phase short circuit of GT40PCh6 synchronous generator. The peak current is 911.2 A at 0.9 ms.
Fig. 13. Armature current Iash at line-to-line short circuit of GT40PCh6 synchronous generator. The peak current is 944.6 A at 0.95 ms.
Fig. 14. Armature current Iash at line-to-neutral short circuit of GT40PCh6 synchronous generator. The peak current is 1108.2 A at 0.95 ms.
Fig. 15. Armature current Iash at two lines-to-neutral short circuit of GT40PCh6 synchronous generator. The peak current is 1130 A at 0.6 ms.
Table 2. Parameters of GT40PCh6 synchronous generator
.
Fuel supply system
Civil transport aircraft use the wing structure as an integral fuel tank to store fuel. In larger aircraft, the fuel is also stored in the structural wing box within the fuselage. A typical wing tank is irregular, long and shallow [7]. The fuel is in direct contact with the outside skin. The Tu-154M has six fuel tanks: one central fuel tank (CWT) No 1, two inner wing tanks No 2, two outer wing tanks No 3 and one additional tank No 4. The Tu-154M fuel tank configuration is shown in Figs 16 and 17. The tanks No 3 are between spars 1 and 3 and ribs 14 and 45 of detachable parts of wings [12].
The CWT tank is generally categorized as hazardous due to the proximity to external heat sources, e.g., air conditioning units [7]. It requires tank inerting with the aid of nitrogen-enriched air from the on-board inert gas generating system. The tanks No 1 and 4 of the Tu-154M are inerted in the case of emergency landing without landing gears. The left and right wing tanks are usually categorized as nonhazardous as there is mostly no proximity of heat sources [7]. The wing leading edge slat section is equipped with anti-ice control system, typically with hot air ducts. These ducts take form of pipes with holes to allow air to heat the inner surface of leading edges. The hot air flow to the outer wing leading edges is controlled by the wing anti-ice valve [7]. The Tu-154M has electric anti-ice control system with heating elements embedded in slats.
The fuel system of the Tu-154M uses electric motor driven centrifugal pumps ECN-319, ECN-323 and ECN-325. Fuel pumps ECN-323 and ECN-325 are driven by 115/220-V AC induction motors (Fig. 18) and fuel pumps ECN-319 are driven by DC 27-V brush motors (Table 3). A flange mounted motor and pump constitute one integral unit (Fig. 19a). The feeding cables in fuel tanks are in aluminum tubes (Fig. 19b). Wiring system that delivers electric energy to fuel pump motors must be protected against electrical arcing and accumulation of static electricity that under some circumstances can cause ignition of the fuel-air mixture in the wing tank [6, 7, 9].
In general, there are two types of fuel pumps on typical aircraft [7]:
• Fuel transfer pumps (e.g., ECN-323, which perform the task of transferring fuel between the aircraft fuel tanks to ensure that the engine fuel feed requirement is satisfied; • Fuel booster pumps (e.g., ECN-319, ECN-325) also called engine feed pumps, which are used to boost the fuel flow from the aircraft fuel system to the engine.
Fig. 16. Tu-154M fuel tank configuration: No 1 – center wing tank (CWT), i.e., collector tank, No 2 – inner left and right wing tank, No 3 – outer left and right wing tank, No 4 – additional tank [12].
Table 3. Fuel pumps of Tu-154M.
.
Commercial aircraft use open vent system to connect the ullage1 in each tank to the outside air [7].
Fig. 17. Tu-154M fuel system layout.
Fuel tanks, fuel pumps, fuel transfer lines, D30KU engine and APU have been shown. 1,2 – feed lines of upper transfer from tanks No 4 and 1 to tank No 2; 3 – faucet of reserve transfer; 4 – antifire faucet; 5 – discharge faucet, 6 – connector for maintenance of engines [12, 16].
Fig. 18. Layout of ECN-323 and ECN-325 fuel pumps.
(a) cross section of fuel pump and induction motor; (b) feeding cable tubing. 1 – grid, 2 – induction motor, 3 – motor housing, 4 – shaft, 5 – tube, 6,7 – sealing rubber rings, 8 – pump housing, 9 – rotor, 10 – cover, 11 – snail, 12 – impeller, 13 – channel, 27 – conduit metal tube, 28 – tubing, 29 – terminal block, 30 – cover, 31 – electric cable. Construction of transfer fuel pump ECN-323 is similar [3, 9, 12].
The Tu-154M is equipped with the vent system. The Tu-154 uses fuel Jet A-1. Jet A-1 is a kerosene grade of fuel suitable for most aircraft turbine engines. It is produced to a stringent internationally agreed standard.
1Space between the fuel surface and upper wall of the tank.
Wing anti-ice system
Most civil aircraft use hot bleed air for anti-ice control of outer wing leading edges [7]. The Tu-154M must use electric resistive heating for anti-ice of the wing leading edge slats, as the turbofan engines are tail mounted and located far away from the wings. This would make the hot air bleed system very heavy and cumbersome.
The Tu-154M has three-phase, 115-V electrical wing anti-ice heating system (Fig. 20) [3, 9, 14]. To save electrical energy, heating elements are fed cyclically by adequate determination of time period. Under cyclic heating a thin layer of ice accumulates on slats which does not deteriorate aerodynamic properties of the aircraft. When the accumulation reaches a thickness threshold and the temperature of skin increases, the ice is taken out by the air stream.
The generator GT40PCh6 No 2 driven by the mid turbofan engine (Fig. 5) feeds only the electric grid 2 dedicated to heating wing slats. The electric apparent power is 43.6kVA at 115V (phase voltage) and ≤ 130A.
Heating elements (composites) of one half of slats are divided into eight sections. The other half of slats has also eight sections. Section are fed in the following sequence:
1st, 2nd, . . . 8th, 1st, 2nd, . . . 8th . . . . Sections are numbered starting from the core part of the wing to the end of the wing. The current is on for 38.5 s and off for 269.5 s for each section.
In the leading part a thermal “knife” is installed along the slats. This part is made of 20-mm wide X20H80 NiCr foil. The thermal “knife” is not fed cyclically – it is steadily under current and is isolated from the outer skin by three layers of glass fiber 3 (Fig. 20). Also, the three layers 5 isolate the thermal “knife” from the heating element. On the inner skin/sheathing of heating element of the slat, thermal switches for cyclic operation of sections and thermal “knife” are installed. Thermal switches protect slats and heating elements against overheating.
Lighting
The lighting equipment of the Tu-154M is divided into external and internal equipment. External equipment is intended for taxiing, takeoff, landing, and indicate the plane in the air space at night. Interior equipment is used for illumination of the cockpit, passenger cabin and other chambers of aircraft, and emergency lighting. The external lighting equipment includes wing navigation (position) lights BANO-57 with 70-W SM-28-70 lamps, 115V SMI-2KM anti-collision flashing lights (45 flares/min), and 27V, 35.5A PRF-4 landing/taxi lights. The cockpit is equipped with a general illumination systems and lamps for lighting control boards, panel of flight engineer, top switchboard, middle console of pilots, aircraft panels, panels of automatic pressure control, workplace of navigator, etc. In addition, each crew member has lamps with a red cylindrical optical filter that allows the light to change from white to red.
General illumination of passenger cabins has been designed in form of central and side fixtures with fluorescent lamps. Each central fixture has two fluorescent lamps contained in the reflector and sealed with milky color plexiglas. Side lights are built-in into the lower panels of luggage bins. Individual passenger lamps equipped with lenses to focus the ligh beam are used at night after turning off the lights of the passenger compartment. Lamps are mounted in the bottom panel of luggage bins. Single-lamp fixtures are mounted in the toilets, hallways, kitchenette and above the mirrors.
Emergency lighting is provided to illuminate the passenger areas on the ground when the power is supplied from the on-board batteries. During flight, the emergency lighting of passenger cabins is turned on at night after turning off the general illumination. Emergency lighting is installed in passenger cabins, lobbies, dressing rooms and toilet passages.
Failures of electric power system
Failures of synchronous generators
The mean time between failures (MTBF) of GT40PCh6 synchronous generators is estimated as approximately 8000 to 8500 flight hours [2, 3, 13, 16].
Fig. 21. Tail part of Tu-154B-2 RA-85588 after fire at Surgut airport on January 1, 2011 [2].
Fig. 22. Closed electric circuit on assumption of abnormal scenario corresponding to 21st contactor TKS233DOD “switching generator No 3 on grid” [2].
There is known at least one case of main generator failure, i.e., the Tu-154B-2 RA-85588 while operating flight 7K 348 on January 1, 2011 from Surgut to Moscow (Domodedovo). The plane was taxiing to the runway while preparing for its takeoff from Surgut when the right engine caught fire on the taxiway (Fig. 21). Three out of 126 passengers and 8 crew members died.
Russia’s Interstate Aviation Committee (MAK) released their final report (in Russian) concluding the probable cause of the accident was the outbreak of fire in the right generator panel located between frames 62 and 64 in the cabin [2]. The generators were connected on the network after the engine start and exit to the idle mode. The cause of the fire was an electrical arcing produced by electrical currents exceeding 10 to 12 times the nominal current when two generators not synchronized with each other were brought online but got connected together instead of being connected to parallel busses (Fig. 22). The unsynchronized operation of the generators can be attributed to:
1. Poor technical conditions of contacts TKS233DOD (Fig. 22) responsible for connecting the generators with the electrical busses, that were damaged by prolonged operation without maintenance. A contact normally open was welded and fractured insulation material moved between contacts that are normally closed. These abnormal contact positions led to the connection between No 2 and No 3 generators (Fig. 22).
2. Differences in the schematic diagrams of generator No 2 and generators No 1 and 3. When the switch is moved from “check” to “enable” with no delay in the “neutral” position, the generator 2 is brought on line without time delay. This leads to increased wear of normally closed contacts in the TKS233DOD unit. The specific design of the electrical systems ensures power supply to each bus from either the APU or engine integrated drive generator.
Failures of other electrical equipment
On September 7, 2010, the Tu-154M RA-85684 Alrosa Mirny Air Enterprise Flight 514 aircraft from Udachny to Moscow suffered a complete electrical failure en route, leading to a loss of navigational systems. The electrically operated fuel transfer pumps were also affected and prevented transfer of fuel from the wing tanks to the engine supply tank in the fuselage.
After emergency decent below cloud level the crew were able to spot an abandoned air strip near town of Izhma (Fig. 23). The abandoned air strip is 1325 m, whereas the Tu- 154 requires a minimum of 2200 m. The aircraft landed at a speed of 350 to 380 km/h, faster than normal, due to the lack of flaps. Although the flaps are powered by hydraulics, the switches operating them are electrical. The impact was damped by the young trees, which have grown since the airport was closed. All nine crew members and 72 passengers evacuated using the aircraft’s evacuation slides. No injuries were reported.
Fig. 23. Emergency landing of Tu-154M RA- 85684 at abandoned air strip near town of Izhma on September 7, 2010. http: //www.airlinereporter.com/wpcontent/ uploads/2011/11/TU154a.jpg
On November 17, 1990, the cargo TU-154M, CCCP- 85664 of Aeroflot Airways was heading through Czech territory with a load of Winston cigarettes from Basel to Moscow. A switched-on cooker in the kitchenette caused a fire on board of the plane and the crew decided to land at the closest possible place. The crew made an attempt of emergency landing on the field near Dubenec village in the East Bohemia. There were only 6 crew members on board, all of them survived the air disaster.
On February 18, 1978, the Tu-154A, CCCP-85087 of Aeroflot Airways was standing on the apron at Tolmachevo Airport, Novosibirsk. The cabin heater was left working unattended between flights. A rag caught fire, which incinerated the cabin. A fire that broke out in the passenger cabin engulfed the rear part of the airframe. The forward fuselage burnt out. There were no fatalities.
Conclusions
The electric system of the Tu-154M aircraft is an outdated system typical for aircraft being designed in the 1960s. There are three GT40PCh6 wound-field synchronous generators driven by D-30KU low-bypass turbofan engines and one GT40PCh6 generator driven by the TA-6A APU turboshaft engine. The APU is also equipped with the 27V DC GS- 12TO starter generator. The Tu-154M is not equipped with a RAT.
Main synchronous generators GT40PCh6 are air cooled generators. Air cooling reduces the rated power and increases the mass of generators. Nowadays, modern VSCF wound-field synchronous generators are oil cooled with rated power up to 250kVA (Boeing 787 Dreamliner).
Reversed design and analysis of GT40PCh6 main synchronous generators deliver important information on steady-state and transient performance of these machines. Transient characteristics, especially short-circuit waveforms are very helpful in investigation of electric power system after malfunction, failure or crash.
BIBLIOGRAPHY
[1] Ellis G.: Air crash investigation of general aviation aircraft, Greybull, WY, USA, Capstan Publications, 1984. [2] Final Report on results of investigation of aviation accident involving the Tu-154B-2, tail number RA-85588, airport Surgut, on January 1, 2011, in Russian, Interstate Aviation Committee (MAK), Moscow, 2011. [3] Electrical equipment of aircraft Tu-154B(M), in Russian, Rilsk, Aviation College of Technology, 2000. [4] Gieras JF.: Advancements in electric machines, London-Boston-Dordrecht, Springer, 2008. [5] Hill R., Hughes W.J.: “A review of flammability hazard of Jet A fuel vapor in civil transport aircraft fuel tanks”, Report DOT/FAA/AR-98/26, US Dept of Transp., Springfield, VA, 1998. [6] Kosvic T.C., Zung L.B., Gersten M.: “Analysis of fuel tank fire and explosion hazards”, Technical Report AFAPL-TR-71-7, Air Force Propulsion Laboratory, WPAFB, Ohio, 1971. [7] Moir I., Seabridge A.: Aircraft systemes: mechanical, electrical and avionics subsystems integration, 3rd ed., Chichester, UK,J. Wiley & Sons, 2008. [8] Ronkowski M., Michna, M., Kostro, G., Kutt, F.: Electrical machines around us, in Polish, Gdansk University of Technology, Gdansk, Poland, 2011. [9] Soshin, V.M.: Aircraft Tu-154M, book 2, ed. Samara State Aerospace University, Samara, 2005. [10] Timofieyev, J.M.: Electrical equipment of Tu-154M aircraft, Federal Air Transport Service of Russia, Academy of Civil Aviation, Sankt-Petersburg, 2000. [11] Tu-154. Catalogue of parts and compilation of units. Chapter 27: Control, in Russian, Avia-Media, 1984, updated 2003. [12] Tu-154M. User’s technical guidance, Chpt. 28. Fuel system. [13] Tu-154B. User’s and technical service manual, Book 7, Part 1. Electric equipment, in Russian, Samara, Aviakor, 1994. [14] Wing of Tu-154 aircraft, in Russian, Virtual cabinet of aircraft construction, [web page] http: //cnit.ssau.ru/virt{_}lab/krilo/index.htm [Accessed on Nov. 28, 2012]. [15] Wood R.H., SweginnisR.W.: Aircraft accident investigation, 2nd ed., Casper, WY, USA, Endeavor Books, 2006. [16] Znichenko V.I: Construction and user manual of Tu-154M aircraft, Federal Air Transport Service of Russia, NLMK, Academy of Civil Aviation, Sankt Petersburg. 1998.
Authors: Prof. Jacek F. Gieras, Ph.D., D.Sc., IEEE Fellow, Department of Electrical Engineering, Electrical Machines and Drives, University of Technology and Life Sciences, Al. S. Kaliskiego 7, 85-796 Bydgoszcz, Poland, email: jacek.gieras@utp.edu.pl
Source & Publisher Item Identifier: PRZEGLA˛D ELEKTROTECHNICZNY, ISSN 0033-2097, R. 89 NR 2a/2013
Published by John Jeter, VYCON, EE Power – Industry Articles: Flywheel Energy Storage System Basics, September 23, 2021
Today, flywheel energy storage systems are used for ride-through energy for a variety of demanding applications surpassing chemical batteries.
Flywheels are among the oldest machines known to man, using momentum and rotation to store energy, deployed as far back as Neolithic times for tools such as spindles, potter’s wheels and sharpening stones. Today, flywheel energy storage systems are used for ride-through energy for a variety of demanding applications surpassing chemical batteries.
A flywheel system stores energy mechanically in the form of kinetic energy by spinning a mass at high speed. Electrical inputs spin the flywheel rotor and keep it spinning until called upon to release the stored energy. The amount of energy available and its duration is controlled by the mass and speed of the flywheel.
In a rotating flywheel, kinetic energy is a function of the flywheel’s rotational speed and the mass momentum of inertia. The inertial momentum relates to the mass and diameter of the flywheel. The kinetic energy of a high-speed flywheel takes advantage of the physics involved resulting in exponential amounts of stored energy for increases in the flywheel rotational speed.
Kinetic energy is the energy of motion as quantified by the amount of work an object can do as a result of its motion, expressed by the formula: Kinetic Energy = 1/2mv2
Anatomy of a High-Speed Flywheel
The main components of a flywheel are a high-speed permanent magnet motor/generator, fully active magnetic bearings, and rotor assembly construction (Figure 1).
1. A high-speed permanent magnet motor/generator incorporates specialized rare earth magnets to minimize rotor heating and maximize efficiency and reliability, allowing flywheel systems to cycle quickly without overheating. This facilitates use in demanding applications with high cycling and long-life requirements. The flywheel’s rotor assembly operates in a vacuum provided by an external vacuum pump. By removing air from the rotating area of the motor, all windage losses from the system are eliminated, thereby increasing electrical efficiency.
2. The flywheel incorporates a steel mass for storage. Because steel is a well-understood, well-supported material, it avoids the technology risks associated with other materials such as composites that may offer higher energy densities but with greater risks of temperature changes and creep that can cause unbalanced loads and degrade operation over time.
3. Based on a permanent magnet motor design, flywheels can continuously cycle rapidly with minimal heat. In contrast, other motor technologies generate significantly more heat during a discharge.
4. A magnetic bearing/levitation system allows the motor rotor assembly to rotate at very high speeds with no physical contact with stationary components, optimizing efficiency and product life. Magnetic bearings virtually eliminate the need for maintenance as there are no contact points within the flywheel – no bearings to replace or repack with lubricant.
5. A built-in power conversion module controller provides high efficiency and maximizes reliability over the flywheel’s operating life with self-diagnostic tools that can proactively prevent failures. For each application, flywheel rotational speed limits can be modified for appropriate cycling demands and other specific conditions.
6. Real-time display provides users with views of the flywheel status, including vital parameters such as rotor speed, charged capacity, discharge event history, and adjustable voltage settings. Additional monitoring and control capabilities are available through a serial interface, alarm status contacts, soft-start pre-charge from the DC bus and push-button shutdown.
Prime applications that benefit from flywheel energy storage systems include:
Data Centers
The power-hungry nature of data centers make them prime candidates for energy-efficient and green power solutions. Reliability, efficiency, cooling issues, space constraints and environmental issues are the prime drivers for implementing flywheel energy storage. Flywheels paired with a data center’s three-phase UPS units provide instantaneous and cost-efficient backup power.
During a power disruption, the flywheel will provide backup power instantly. When flywheels are used with UPS systems (instead of batteries), they provide reliable protection against damaging voltage sags and brief outages. During power disruptions and outages, the flywheel provides the energy required to maintain the load allowing enough time for the emergency generator to start and take on the load. At this time, the flywheel recharges back up to full speed ready for the next event. The leading cause of a UPS failing to support the load is battery failure. Battery life is impacted by the number of cycles, temperature and maintenance. To improve battery life and system availability, flywheels can be combined with batteries to extend battery run time and reduce the number of yearly battery discharges that reduce battery life (Figure 2).
Medical Diagnostics
Many types of medical imaging equipment, such as CT or MRI machines can also benefit from flywheel energy storage systems. Power brownouts, surges and outages can have devastating effects on MRI equipment. Often, electricity from the power substation to a hospital is not consistent for MRI and CT operations as voltage drops or surges in power can damage the unit’s refrigeration systems and prompt a hard shutdown of the MRI equipment.
Flywheels paired with the facility’s three-phase UPS systems deliver clean, reliable power to the imaging suite. If there is a power outage or the power coming in from the utility is “dirty,” the UPS will generate smooth, high-quality power from the flywheels. Besides needing the highest power reliability, space is often a concern. Due to the flywheel’s small footprint and no requirement for dedicated cooling, the UPS and flywheels can reside in the radiology suite. Conversely, a UPS with a bank of batteries would need to be located in a larger environmentally cooled area.
Renewable Microgrids
Microgrids deployed in remote installations such as islands face daunting fuel costs if diesel generators are the power source. Photovoltaic solar panels are typically employed to minimize the need for engine generators to save costs while providing cleaner, quieter power in areas such as remote resorts requiring 200 to 300kW power sources. While solar power has many advantages, solar-powered microgrids are subject to problems during demand surges as well as sags in power due to cloud cover. Adding flywheels to this type of installation can support the entire microgrid or just the solar system to prevent power quality problems resulting from sags and surges. The fluctuating nature of power problems on an unprotected solar installation can cause damage to the connected equipment, sensitive electronics such as computers and various appliances. Because the flywheel will serve as a power conditioner, absorbing these fluctuations, operators will find that connected equipment will be far less likely to fail prematurely.
A Greener Approach to Energy
As energy needs in a broad range of applications become more complex, those responsible for assuring reliable, clean, cost-effective energy supplies within their organizations are constantly looking for solutions that can increase efficiencies while enhancing energy reliability. In many cases, incorporating flywheel technology in a new or retrofit electrical system design can serve as an excellent foundation for achieving the sometimes-conflicting goals of maximizing dependability and reducing operating costs. With the added benefit of providing an environmentally friendly energy source, flywheels with a typical 20-year service life, are a clean, cost-effective solution for any application requiring “always on” power.
Author: John Jeter is the Director of Sales for VYCON, Inc. in Cerritos, Calif. John received his electronics training in the US Navy and holds a B.S. in Business from San Diego State University. He has been involved with power quality solutions for over 40 years with domestic and international experience.
Published by Sergio Panetta, International Association of Electrical Inspectors (IAEI) Magazine, Evolving Technologies – Grounding of Wind Power Systems and Wind Power Generators, May 16, 2010
Power continuity is essential in wind power projects where a tripped overcurrent device due to ground fault can have serious economic or operational consequences. An arcing phase-to-ground fault can totally destroy the equipment. Consequential downtime adds to the economic loss. Four typical grounding methods for generators and power systems are examined for these factors and the article concludes that resistance grounding provides the best protection against arcing ground-fault damage in wind power projects with distribution systems and improves reliability and availability of the power systems.
Photo 1. Wind Turbine Fire
Grounding of Generators
The generators can be ungrounded, high-resistance grounded, low-resistance grounded or solidly grounded. In solidly grounded generators, very high fault currents can flow in the event of a phase-to-ground fault with a possibility of extensive fault damage[4]and consequential loss of revenue. In addition, there is a possibility of high harmonic current flows when the generator and step-up transformers are solidly grounded. Applying low-resistance grounding reduces the potential damage due to phase-to-ground faults, but the generator must be tripped and isolated with a consequential loss of revenue. With high-resistance grounding, a phase-to-ground fault can be annunciated[4]and the generator kept running. An ungrounded generator can be used if the cable length to the step-up transformer is relatively small. With long cable lengths in multiple generator systems, the generator to transformer section becomes susceptible to transient overvoltages in case of intermittent phase-to-ground faults. This could lead to subsequent 2ndphase-to-ground failure elsewhere in the network leading to catastrophic damage.
Power Collection System
Figure 1. Single generator to transformer
The transformer secondary is usually connected in delta and can be 5, 15, or 36 kV for areas which follow ANSI specifications, and 3.3, 11, 20, or 33 kV for areas following IEC specifications.
This arrangement can be a single generator to transformer, as shown in figure 1 or multiple generators to a transformer, as shown in figure 2. Power is collected through many such transformers on a wind farm in the medium voltage (MV) distribution network, and exported to the utility network at the point of common coupling, as shown in figure 3.[2]
MV Circuits
Figure 2. Multiple generators to a transformer
Solidly grounded circuits lead to high-fault currents due to phase-to-ground faults and may cause extensive damage and high-step or touch voltages. Low-resistance grounding thus lowers the phase-to-ground fault current and allows time-current coordinated trips to isolate the faulty circuit. High-resistance grounding is not suggested, since the cable capacitance can be quite high due to the total length of the MV cable at the collection voltage. When the MV network is left ungrounded on the occurrence of a phase-to-ground fault, the voltage on the other two phases to ground rises to phase-to-phase value, but the operation of the wind farm remains uninterrupted.[3]
An ungrounded MV network is subjected to transient overvoltages on the two healthy phases in the case of intermittent or arcing type phase-to-ground faults, due to the capacitive charge build-up in the cables.
MV Electrical Distribution Networks
Wind farm collection networks are simple radial circuits with switching devices for isolation and switching.[1]Balanced 3-phase networks are suitable for connecting large wind generators. The secondary of the generator step-up transformer can be Y- or Delta-connected. In Y-connected transformers the neutral point is directly accessible and hence can be easily grounded. In Delta-connected transformers an accessible neutral point is created by using a grounding transformer as shown in figure 4. The usual practice is to ground the neutral point at one location only.
Figure 3. MV Collection Network
Electrical Protection
With high-resistance grounding of the generator step-up transformer, fast acting ground-fault relays can be applied in the generator circuit. Low-resistance grounding by neutral grounding resistors or artificial neutrals is suggested for the MV network. The fault currents in the MV collection networks can be small due to high source impedance and long lengths of cables. In some cases, fuses cannot be relied upon to quickly clear the fault; hence, ground-fault relays and circuit breakers are required. It is important to isolate the faulted section quickly. Correct discrimination is obtained by the application of ground-fault relays.
Figure 4. MV collection network with artificial neutral
Additional Electrical Protection
Photo 2. Wind Turbine Fire
Conclusion
Ungrounded delta systems have many operating disadvantages, including high transient overvoltages and difficulty in locating faults. Solidly grounded neutral systems limit the system potential to ground, and speed the detection and location of ground faults. However, the system must be shut down after the first ground fault and there is a potential for extensive arcing fault damage. Applying coordinated ground-fault protection is very difficult and almost impossible with multiple generators.
Low-resistance grounded neutral systems limit the magnitude of the ground-fault current so that serious damage does not occur. The system must still be shut down after the first ground fault. This level of resistance grounding is generally used on medium- and high-voltage systems, above 6.9 kV.
If the power system is changed to high-resistance grounding then the ground-fault current can be reduced to 10 A or less, which has significant impact on reducing the equipment damage. In addition, it ensures that the wind power system continues to operate and does not suffer trip-out of a faulted generator.
Published by Electrical Installation Wiki, Chapter J. Overvoltage protection – Surge protection Application examples
SPD application example in Supermarket
Fig. J45 – Application example: supermarket
Solutions and schematic diagram
• The surge arrester selection guide has made it possible to determine the precise value of the surge arrester at the incoming end of the installation and that of the associated disconnection circuit breaker.
• As the sensitive devices (Uimp < 1.5 kV) are located more than 10m from the incoming protection device, the fine protection surge arresters must be installed as close as possible to the loads.
•To ensure better continuity of service for cold room areas: ∙ “si” type residual current circuit breakers will be used to avoid nuisance tripping caused by the rise in earth potential as the lightning wave passes through.
• For protection against atmospheric overvoltages: ∙ install a surge arrester in the main switchboard ∙ install a fine protection surge arrester in each switchboard (1 and 2) supplying the sensitive devices situated more than 10m from the incoming surge arrester ∙ install a surge arrester on the telecommunications network to protect the devices supplied, for example fire alarms, modems, telephones, faxes.
Cabling recommendations
• Ensure the equipotentiality of the earth terminations of the building. • Reduce the looped power supply cable areas.
Installation recommendations
• Install a surge arrester, Imax = 40 kA (8/20 µs) and a iC60 disconnection circuit breaker rated at 40 A.
• Install fine protection surge arresters, Imax = 8 kA (8/20 µs) and the associated iC60 disconnection circuit breakers rated at 10 A
Fig. J46 – Telecommunications network
SPD for photovoltaic applications
Overvoltage may occur in electrical installations for various reasons. It may be caused by:
• The distribution network as a result of lightning or any work carried out. • Lightning strikes (nearby or on buildings and PV installations, or on lightning conductors). • Variations in the electrical field due to lightning.
Like all outdoor structures, PV installations are exposed to the risk of lightning which varies from region to region. Preventive and arrest systems and devices should be in place.
Protection by equipotential bonding
The first safeguard to put in place is a medium (conductor) that ensures equipotential bonding between all the conductive parts of a PV installation.
The aim is to bond all grounded conductors and metal parts and so create equal potential at all points in the installed system.
Protection by surge protection devices (SPDs)
SPDs are particularly important to protect sensitive electrical equipments like AC/DC Inverter, monitoring devices and PV modules, but also other sensitive equipments powered by the 230 VAC electrical distribution network. The following method of risk assessment is based on the evaluation of the critical length Lcrit and its comparison with L the cumulative length of the d.c. lines.
SPD protection is required if L ≥ Lcrit .
Lcrit depends on the type of PV installation and is calculated as the following table (Fig. J47) sets out:
Fig. J47 – SPD DC choice
L is the sum of:
• the sum of distances between the inverter(s) and the junction box(es), taking into account that the lengths of cable located in the same conduit are counted only once, and • the sum of distances between the junction box and the connection points of the photovoltaic modules forming the string, taking into account that the lengths of cable located in the same conduit are counted only once.
Ng is arc lightning density (number of strikes/km2/year).
Fig. J48 – SPD selection
a. ^1 2 3 4 Type 1 separation distance according to EN 62305 is not observed.
Installing an SPD
The number and location of SPDs on the DC side depend on the length of the cables between the solar panels and inverter. The SPD should be installed in the vicinity of the inverter if the length is less than 10 metres. If it is greater than 10 metres, a second SPD is necessary and should be located in the box close to the solar panel, the first one is located in the inverter area.
To be efficient, SPD connection cables to the L+ / L- network and between the SPD’s earth terminal block and ground busbar must be as short as possible – less than 2.5 metres (d1+d2<50 cm).
Safe and reliable photovoltaic energy generation
Depending on the distance between the “generator” part and the “conversion” part, it may be necessary to install two surge arresters or more, to ensure protection of each of the two parts.
Published by Ark Tsisserev, International Association of Electrical Inspectors (IAEI) Magazine, Canadian Perspectives – Grounding and Bonding — New Questions and Answers, July 1, 2021
Although Section 10 of the Canadian Electrical Code, Part I (CE Code), which applies to grounding and bonding, has been re-written in the 2018 edition of the Code, I keep receiving questions from the readers regarding the fundamentals of grounding and bonding.
In this article, I’ll share with the readers eight questions (which is usually enough) on this subject and will provide the answers based on the requirements of Section 10 of the CE Code.
Question #1. What is an “electrical system.”
Answer to question # 1. An electrical system is a complete electrical installation in which the electric energy is provided by a single energy source to the utilization equipment via a distribution network. A typical example of such a source for an electrical system could be a secondary winding of a transformer, a generator, a battery, a photovoltaic module, a fuel cell, a hydrokinetic turbine generator, etc. For example, an electrical installation supplied from a transformer or bank of transformers can be considered an electrical system; installation supplied from a different transformer, or a generator would be considered a different electrical system.
When a 347/600 V electrical system supplies a 600 V:120/208 V transformer, then primary winding (usually “delta” connected) of this transformer represents a load, similarly to a heating or motor load, but the secondary (120/208 V “Wye” connected) winding represents a source of a new 120/208 V electrical system.
A typical single-line diagram of a building electrical distribution system is shown in figure 1.
Figure 1. Typical single line diagram of a building electrical distribution system
Question #2. When is an electrical system required to be solidly grounded?
Answer to question #2. Subrule 10-206(1) of the CE Code states the following:
“10-206(1) AC systems exceeding extra-low voltage shall be solidly grounded if
1. a) by doing so, their maximum voltage-to-ground does not exceed 150 V; or 2. b) the system incorporates a neutral conductor.”
It means that if an electrical system has a voltage to ground not more than 150 V (i.e., a typical 120/240 V, single-phase, 3-wire system, or a typical 120/208 V 3 phase, 4-wire system), then the safety objective for solid grounding connection of such electrical system and objective for bonding of metal non-current carrying parts of electrical equipment supplied by such system, is to protect the users by establishing a low impedance path between the grounded conductor and the non-current carrying conductive parts of the system – to stabilize system voltage and to facilitate the operation of protective devices.
It also means that if an electrical system incorporates a neutral conductor, such a system also must be solidly grounded.
Figure B10-6 from the 2021 CE Code. Courtesy of CSA Group.
Question #3: What is the system bonding jumper?
Answer to question # 3: System bonding jumper — a conductor that interconnects the system grounded point with the non-current carrying metal enclosure of the source and interconnects the neutral conductor coming from the source to the service equipment with the non-current carrying metal enclosure of the service equipment.
Clause 6.9 of the CSA safety standard C22.2 No. 0.19 “Requirements for service entrance equipment” clarifies that the neutral conductor coming from the source of a solidly grounded system to the service equipment would have to be terminated in the neutral assembly, provided with a sufficient number of connectors, and that one of such connectors, must be used for connection of the system bonding jumper to the enclosure of service equipment [see item (d) in Clause 6.9]:
“6.9
Equipment intended to function as service equipment for solidly grounded systems involving a neutral or other grounded service conductor shall be provided with a neutral assembly located within the service-disconnecting compartment. The neutral assembly shall be provided with an adequate number of suitable pressure-terminal connectors, clamps, or other approved means for connecting the following:
(a) the incoming (grounded) neutral conductor; (b) the corresponding outgoing (neutral) conductor, if any required; (c) the grounding conductor; (d) the bonding conductor to the enclosure; (e) the bonding conductor to the metal service raceway.”
Question #4. Is a grounding conductor allowed to be connected to the metal non-current carrying enclosure of the service equipment?
Answer to question #4. In a solidly grounded system, a grounding conductor must be connected only to a grounded service conductor (to a neutral conductor brought to the service equipment from the solidly grounded power supply source). Item 6.9(c) in standard C22.2 No. 019 (see text immediately above) clearly articulates this fact.
Rule 10-210(a) of the CE Code, Part I also provides this requirement as follows:
“10-210 Grounding connections for solidly grounded ac systems supplied by the supply authority (see Appendix B)
The grounded conductor of a solidly grounded ac system supplied by the supply authority shallbe connected to a grounding conductor at one point only at the consumer’s service…. “
Only a system bonding jumper must be connected to the enclosure of service equipment when a solidly grounded system is provided by the supply authority. (see Figure B10-6 of the CE Code, Part I):
If, however, an impedance grounded system or ungrounded system is provided, then a grounding conductor is permitted to be connected to the metal, non-current carrying enclosure of the service equipment (see Figures B10-12 and B10-13 of the CE Code, Part I).
Figure B10-12 from the 2021 CE Code. Courtesy of CSA Group.
Figure B10-13 from the 2021 CE Code. Courtesy of CSA Group.
Question #5: What does a single point grounding mean?
Answer to question # 5: It means that the connection of a solidly grounded system to a grounding electrode via a grounding conductor must be made at a single point only so, that there is no objectionable passage of current over the grounding conductors. Ideally, such single-point grounding should be at the source of every newly derived solidly grounded system. However, when such solidly grounded system is provided by the power supply authority/electric utility (it should be noted that installations by utilities are outside the scope of the CE Code), such single-point grounding of the solidly grounded system must be established (in addition to the grounding of this system by the power supply authority/utility), at the service equipment/service box, see Figure B10-6 and Rule 10-210 of the CE Code:
“10-210 Grounding connections for solidly grounded ac systems supplied by the supply authority (see Appendix B) The grounded conductor of a solidly grounded ac system supplied by the supply authority shall a) be connected to a grounding conductor at one point only at the consumer’s service; b) have a minimum size as specified i) for a bonding conductor; and ii) for a neutral conductor when the grounded conductor also serves as a neutral; c) be connected to the equipment bonding terminal by a system bonding jumper; and d) have no other connection to the non-current-carrying conductive parts of electrical equipment on the supply side or the load side of the grounding connection.“
If in addition to the solidly grounded system supplying a building, another (separately derived) solidly grounded system is created in the building (i.e., if, for example, the 347/600 V solidly grounded system supplies the building, and a new separately derived 120/208 V solidly grounded system is created on the secondary “Y” connected winding of a stepdown transformer), this new, separately derived solidly grounded system must have a single point of grounding at the source of this system, or at the first switch controlling the system. (see Figures B10-7 and B10-8 of the CE Code):
Figure B10-7 from the 2021 CE Code. Courtesy of CSA Group.
Figure B10-8 from the 2021 CE Code. Courtesy of CSA Group.
However, Subrule 10-212(2) allows an exception from this requirement. See Subrule 10-212(2) and Figure B10-11:
“10-212 Grounding connections for solidly grounded separately derived ac systems (see Appendix B)
1) Except as permitted by Subrule 2), the grounded conductor of a solidly grounded separately derived ac system shall
a) be connected to the equipment bonding terminal by a system bonding jumper i) at the source; ii) at the first switch controlling the system; or iii) at the tie point, where two or more systems terminate at a tie point; b) be connected to a grounding conductor at the same point on the separately derived system where the system bonding jumper is connected; and c) have no other connection to the non-current-carrying conductive parts of electrical equipment on the supply side or the load side of the grounding connection.
2) A separately derived ac system operating at 750 V or less shall be permitted to be grounded by the system bonding jumper that is connected to the bonding conductor included in the primary supply.“
If a separately derived solidly grounded system is provided not in addition to the main solidly grounded system supplying the building, but as an alternative to this main system (i.e., provided by a generator), and a neutral is not interrupted by the automatic transfer switch, then the neutral of the solidly grounded system derived by the generator may be connected to the grounding electrode via a grounding conductor established at the service of the main solidly grounded system (see diagram in figure 8):
Figure B10-11 from the 2021 CE Code. Courtesy of CSA Group.
Question #6: How is a system bonding jumper sized?
Answer to question # 6: The size of the system bonding jumper (and the bonding conductor) installed at the service equipment must be based on the ampacity of ungrounded service conductors.
Subrule 10-616(2) clarifies this subject as follows:
“10-616(2) The size of a bonding conductor installed in accordance with Rule 10-604 at service equipment shall not be less than that determined in accordance with Table 16 based on the allowable ampacity of the largest ungrounded conductor.“
Question #7: How to size a grounding conductor?
Answer to question # 7: Sub rule 10-114(1) of the CE Code provides the following requirement on this subject:
“10-114 Grounding conductor size (see Appendix B) 1) Except as permitted by Subrule 2), the grounding conductor shall be sized not smaller than a) No. 6 AWG if of copper; or b) No. 4 AWG if of aluminum.”
Figure 8. From Appendix B Notes on 2015 edition. Courtesy of CSA Group.
Question #8: Why is the size of a grounding conductor smaller than the size of a system bonding jumper?
Answer to question # 8: The system bonding jumper is a part of the bonding system which consists of non-current carrying metal enclosures of electrical equipment, interconnected by bonding conductors which will carry fault current back to the source of the solidly grounded system via a system bonding jumper at the service equipment and the grounded service conductor.
The primary function of the grounding conductor is to establish a common reference to ground and to create an equipotential plane by connecting the grounded service conductor with earth.
The size of a grounding conductor for a solidly grounded system does not have to be larger than No. 6 AWG copper or No. 4 AWG aluminum, as the grounding conductor carries only a very small portion of the fault current back to the source via a parallel fault path, and this small portion of the fault current depends on the total impedance of the grounding circuit, including the earth resistance. As the ampacity of the grounded service conductor (neutral) is sufficient to carry the fault current for the entire duration of a fault, the size of the grounding conductor is almost irrelevant for the purpose of its role in mitigating faults.
Of course, in high voltage installations, where a station ground electrode is required in accordance with Section 36 of the CE Code, sizing of station ground electrode conductors and sizing of conductors connecting all non-current carrying metal equipment and structures to the station ground electrode would have to comply with Rules 36-302 and 36-308 of the CE Code, Part I, as Section 36 supplements or amends general provisions of Section 10.
Hopefully, answers to the posted eight questions clarify this interesting and important subject. However, as usual, the authority having jurisdiction for the administration of the CE Code should be consulted in respect to each installation.
Author: Ark Tsisserev is president of EFS Engineering Solutions, Ltd., an electrical and fire safety consulting company, and is a registered professional engineer with a master’s degree in Electrical Engineering. Prior to becoming a consultant, Ark was an electrical safety regulator for the city of Vancouver. He is currently the chair of the Technical Committee for the Canadian Electrical Code and represents the CE Code Committee on the CMP-1 of the National Electrical Code. Ark can be reached by e-mail at: ark.tsisserev@efsengineering.ca His company web site is: http://www.efsengineering.ca
Published by Anna KOZIOROWSKA1,2, Dariusz SOBCZYŃSKI3, Wiesława MALSKA3 Uniwersytet Rzeszowski, Wydział Matematyczno – Przyrodniczy, Instytut Techniki (1) Uniwersytet Rzeszowski, Centrum Biotechnologii Stosowanej i Nauk Podstawowych (2) Politechnika Rzeszowska, Wydział Elektrotechniki i Informatyki, Katedra Energoelektroniki i Elektroenergetyki (3)
Abstract: Specialized biomedical laboratory equipment, very often use power converters, which are a source of higher harmonics. These devices depending on their functions consist of several additional elements (e.g.: UV lamp, heater),and give the possibility of speed control. These devices are most often used in analytical laboratories and research biomedical and biotechnological laboratories.
Streszczenie. Specjalizowane biomedyczne urządzenia laboratoryjne, bardzo często wykorzystują przekształtniki energoelektroniczne, które są źródłem wyższych harmonicznych. Urządzenia te w zależności od swoich funkcji składają się z kilku dodatkowych elementów (np.: lampa UV, grzałka), a dają możliwość regulacji prędkości. Urządzenia tego typu stosowane są najczęściej w laboratoriach analitycznych oraz w biotechnologicznych laboratoriach naukowo-badawczych. (Badania biomedycznych urządzeń laboratoryjnych pod kątem generacji zakłóceń)
Słowa kluczowe: odkształcenia napięcia i prądu, wyższe harmoniczne, urządzenia laboratoryjne Keywords: Voltage and Current Distortion, Higher Harmonics, biomedical laboratory equipment
Introduction
Converters AC/DC are now widely used in many fields of technology, ranging from households and business services to industry, power generation, ending on telecommunications, the aerospace. The purpose of power converters using in consumer devices is mainly the reduction of energy consumption and lower operating costs. There is also important the construction and appropriate control of power electronic devices that from the point of view of the power supply network reduce the negative impact of this type of power converters on the power supply network [1,2,3,4]. This paper presents the results of measuring tests of influence on supply network of ultracentrifugation and electrophoresis system [5,6,7,8,10,11].
The study was conducted in the laboratory of the Institute of Applied Biotechnology and Basic Sciences University of Rzeszow in Werynia.
Photo 1. Electrophoresis system
Characteristics of laboratory equipment
The phenomenon of electrophoresis is the movement of charged particles relative to the solvent under the influence of the applied electric field. Areas of application of electrophoresis phenomenon are biochemistry of nucleic acids and proteins, molecular biology, and medical diagnostics [9]. An example of the application of this phenomenon is the DNA electrophoresis, which allows separation of particles due to their volume. DNA moves in the electric field and the applied gel resists proportional to particle size. Different particles move at different speeds – small rapidly, and large slowly. There are formed stripes, the groups of molecules of the same size. In the laboratory of Center of Applied Biotechnology and Basic Sciences there is installed the electrophoresis kit, which was tested for the impact of nonlinear devices on the quality of electric energy (photo 1).
Centrifugal extractors are popular devices used in analytical laboratories for the separation of mixtures into components of different densities. They are used in research of genetic engineering. They can be used in microbiology laboratories, biochemical, clinical and industrial applications. Due to the fast rotation of the fluid it is possible to separate the lighter components from the heavier. Heavier components will be located away from the axis of rotation. Due to the speed of rotation centrifugal extractors can be divided into three groups: low speed at up to 5 000 rpm, medium speed – up to 20 000 rpm and ultra speeds of more than 20 000 rpm.
Photo 2. Ultracentrifuge
In the study there was used the centrifuge Thermo Scientific Sorvall Legend. It is dedicated to the cell culture, bioproduction and separation of blood cells. Cooling systems used in the centrifuge allows to control the temperature of the sample and the chamber between -10°C and +40°C. Maximum speed is 12 000 rpm, and the power of 1400 W. There is used brushless induction motor drive in the centrifuge. There were made the measurement tests of currents and voltages of Thermo Scientific Sorvall Evolution and its influence on quality of electric energy. This device is designed for high performance samples and is used very often in specialized laboratories.
Results of measurement tests
In order to analyze the work of selected biomedical laboratory equipment in terms of their impact on the supply network there were measured selected parameters at the Laboratory of Biotechnology in Institute of Applied Biotechnology and Basic Sciences. Laboratory equipment is used for scientific research in the field of biotechnology. As the evaluation measure of harmonic distortion factor there were adopted the factor of harmonic content THD (Total Harmonic Distortion) and individual distortion factor HD (Individual Harmonic Distortion) [8,10].
Individual Harmonic Distortion of centrifuge current (Fig. 2), shown in Figure 1 for standby operating status and temperature inside the centrifuge equal 4°C indicates a not very large deformation of the supply current, and the value of THD for the current is 9.97% (THD value of the voltage is 1.73%).
Fig.1. Individual Harmonic Distortion of current fed the centrifuge (standby operation state)
Fig.2. Individual Harmonic Distortion of current supplying centrifuge (operating state at 12 000 rpm and lowering the temperature inside the centrifuge)
Fig.3. Individual Harmonic Distortion of current supplied centrifuge (fixed operations state, speed equal to 12 000 rpm and a fixed temperature inside the chamber of 4°C)
Figure 2 shows a ratio of HD for operating state with a fixed rotation speed equal to 12 000 rpm and operating of the refrigerator in order to reduce the temperature inside the centrifuge chamber to 4°C. For this case there was measured THD ratio of current equal to 33.8% (the value of the voltage THD was 2.25%). For a fixed centrifuge operation at a speed equal to 12 000 rpm and a fixed temperature of 4°C, there was a significant increase in the HD coefficient – fig. 3, which is also reflected in the current THD – equal in this case 137% (the value of the voltage THD was 2.17%).
Figures 4-6 show the waveforms of RMS current drawn by the centrifuge at different operating conditions, start from preparation to operation, by operation and cooling the chamber to 4°C, and from the start to the normal, stable operation at a speed of 12 000 rpm. Figure 4 shows the course of the RMS current of centrifuge over 170 seconds (start-up from standby to start centrifugation at 12 000 rpm, stop and restart). Waveforms allow for the classification of this biomedical laboratory equipment to a group of “Anxious” receivers.
Fig.4. Course of RMS current of centrifuge within 170 seconds (start-up from standby to start centrifugation at 12 000 rpm, stop and re-start)
Figure 5 shows the course of RMS current centrifuge within 170 seconds – from start-up status to stable operation at a speed of 752 rpm, for operating conditions on the first stage of speed control.
Fig.5. Course of RMS current of centrifuge within 170 seconds (start and work on the first stage of speed control with a maximum speed of 752 rpm)
Figure 6 shows the course of RMS current of the centrifuge within 170 seconds. Lists the states of the centrifuge operation from starting and running the fifth stage of centrifugation speed control, ensures the spin speed 9 000 rpm, then turn off the device, restart, work and stop of the centrifuge.
Fig.6. Course of RMS current of the centrifuge within 170 seconds (start and work on the fifth stage of speed control with rotation of 9 000 rpm, power off, restart, work and stop the centrifuge)
For ultracentrifuge, which provides the spin speed to 60 000 rpm HD-value is very low. There is a low value of current THD too, it is equal 6,32%. For the case of Figure 7 the value of the voltage THD is 1.9%. And for the case of Figure 8 current THD equals 4.76% (the value of the voltage THD was 1.85%), reflecting the reduced negative impact of this type of devices on the power supply. Presented in Figures 7-8 individual harmonic distortion HD of the supply current of the ultracentrifuge confirms the high class of device and very low negative impact on the supply network. Harmonic amplitudes have also low values.
Fig.7. Individual Harmonic Distortion of current supplying the ultracentrifuge (starting of the device)
Fig.8. Individual Harmonic Distortion of current supplying the ultracentrifuge (fixed operating state at a rotation speed 40 000 rpm)
Fig.9. Course of RMS current of the ultracentrifuge within 170 seconds (startup of the device, than set of the speed settings)
Fig.10. Course of RMS current of ultracentrifuge within 170 seconds (gradual starting of the device on the top step of startup decrease of voltage value to 212 V at RMS current 19 A)
RMS current waveforms of the ultracentrifuge from the start operation state and set of the parameters of working up to the start-up and normal operation within 170 seconds are shown in Figure 9 This type of centrifuge is a device with a capacity of 3.5 kW, hence the large value of the current during the operation state.
In Figure 10 there is shown the gradual start-up of the device. On the top step of startup voltage decreased to a value of 212 V at RMS current 19 A. After startup there was a normal stable operation state with maintaining ultracentrifuge speed settings and keeping the recommended temperature inside the chamber.
There is interesting centrifuge stops in safe mode in 93 second of observation at a rotation speed 40 000 rpm restart, and normal operation state, shown in Figure 11.
Fig.11. Course of RMS current of ultracentrifuge within 170 seconds (start-up, normal operation, emergency stop of the centrifuge at a speed of 40 000 rpm, standby and restart)
Fig.12. Course of RMS current of ultracentrifuge within 170 seconds (normal operation at a speed of 40 000 rpm and stop in the normal mode)
Fig.13. Course of RMS current of the ultracentrifuge within 170 seconds (normal operation at a speed of 40 000 rpm and stopping at “Normal” operating mode and restart, work and stopping)
Fig.14. Course of RMS current of electrophoresis system within 170 seconds (normal operation state at voltage 70V and current 93 mA)
Fig.15. Course of RMS current of electrophoresis system within 170 seconds (normal operation state at voltage 200 V and current 300 mA)
Fig.16. Individual Harmonic Distortion of current supply electrophoresis system (normal operation at voltage 200 V and current 300 mA)
Shown in Figure 12 stopping of ultracentrifuge in “normal” mode in 75 second of observation at a rotation speed 40 000 rpm until the stop provides a very good design of control and regulation system. However, Figure 13 shows the course of RMS current of ultracentrifuge within 170 seconds from start-up and normal operation at a speed of 40 000 rpm and stop at “Normal” operating mode, restart, work and stop.
Among the analyzed biomedical laboratory equipment with the lowest power was kit for electrophoresis (photo 1). In Figures 14-15 there are presented the courses of RMS current of the electrophoresis system for two different load levels of the device.
Electrophoresis system dependency of individual supply current distortion in a normal operating state and voltage at 200 V and 300 mA is shown in Figure 16. For these conditions the value of current THD is 23.9% (the value of the voltage THD was 1.74%).
Summary
Based on laboratory tests, using a power meter Yokogawa WT 500 there can be evaluated the level of harmonics generated to the power system by a specialized biotechnological laboratory equipment. The results for ultracentrifuge suggest high class of the device and very low negative impact on the power network. Electrophoresis system has larger negative impact on the supply network, but it is a low-power electrical device which specific work is differs significantly from the dynamic specific work of the ultracentrifuge. Both tested devices affect on parameters of power supply network, but has little effect on other electric devices fed from the same power network. All tests shown in the paper will help to design the filter to reduce the higher harmonics generation
The study was performed within the project Centre of Applied Biotechnology and Basic Sciences supported by the Operational Programme Development of Eastern Poland 2007-2013, NoPOPW.01.03.00-18-018/09.
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[1] Barlik R., Nowak M.: Jakość energii elektrycznej – stan obecny i perspektywy. Przegląd Elektrotechniczny , nr 7-8 2005, [2] Hanzelka Z.: Rozważania o jakości energii elektrycznej. Elektroinstalator nr 9/2001- 2/2002 [3] Malska W., Łatka M.: Wpływ odbiorników nieliniowych na parametry jakości energii elektrycznej, Wiadomości Elektrotechniczne, nr 10, 2007r. [4] Nowak M., Barlik R.: Poradnik inżyniera energoelektronika, WNT, Warszawa 1998 [5] Paice Derek A.: Power electronic converter harmonics, IEEE Press, New York 1996 [6] Piróg S.: Energoelektronika: układy o komutacji sieciowej i o komutacji twardej), Uczelniane Wydawnictwa Naukowo-Dydaktyczne, AGH, 2006 [7] Strzelecki R., Supronowicz H.: Filtracja harmonicznych w sieciach zasilających prądu przemiennego, Postępy Napędu Elektrycznego, 1998 [8] Ustawa z dnia 10 kwietnia 1997 r. Prawo energetyczne. Dz.U. nr 54, poz. 348 z późniejszymi zmianami [9] Kalinowska K., Ogórek R., Baran E. – Diagnostyka mikologiczna: wczoraj i dziś. Od mikroskopu do termocyklera, Mikologia Lekarska 2011, 18 (3): 156-158 [10] Bartman J., Koziorowska A., Kuryło K., Malska W. – Analiza rzeczywistych parametrów sygnałów elektrycznych zasilających układy napędowe pomp wodociągowych – Przegląd Elektrotechniczny, 2011/8, str. 8-11 [11] Norma PN-EN/50160 Parametry napięcia zasilającego w publicznych sieciach rozdzielczych. PKN 1998 [12] Rozporządzenie ministra gospodarki i pracy z dnia 20 grudnia 2004 r. w sprawie szczegółowych warunków przyłączenia do sieci elektroenergetycznych, ruchu i eksploatacji tych sieci. Dz.U. z 06.01.2005 [13] PN-EN 50160:2002 Parametry napięcia zasilającego w publicznych sieciach rozdzielczych. [14] PN-T-03501:1998 Kompatybilność elektromagnetyczna (EMC). Dopuszczalne poziomy. Ograniczanie wahań napięcia i migotania światła powodowanych przez odbiorniki o prądzie znamionowym większym niż 16 A, w sieciach zasilających niskiego napięcia. [15] [10] PN-EN 61000-3-2:1997 Kompatybilność elektromagnetyczna (EMC). Dopuszczalne poziomy. Dopuszczalne poziomy emisji harmonicznych [16] prądu (fazowy prąd zasilający odbiornika mniejszy lub rowny 16 A). [17] PN-EN 61000-3-3:1997/A1:2002 (U) Kompatybilność elektromagnetyczna (EMC). Dopuszczalne poziomy. Ograniczanie wahań napięcia [18] [12] PN-EN 61000-4-7:1998 Kompatybilność elektromagnetyczna (EMC). Metody badań i pomiarow. Ogólny przewodnik dotyczący pomiarowharmonicznych i interharmonicznych oraz stosowanych do tego celu przyrządow dla sieci zasilających i przyłączonych do nich urządzeń. [19] PN-EN 61000-4-11:1997 Kompatybilność elektromagnetyczna (EMC). Metody badań i pomiarow. Badania odporności na zapady napięcia,krotkie przerwy i zmiany napięcia. [20] PN-EN 61000-4-14:2002 Kompatybilność elektromagnetyczna (EMC). Metody badań i pomiarow. Badanie odporności na wahania napięcia.
Autorzy: dr inż. Anna Koziorowska, Uniwersytet Rzeszowski, Instytut Techniki, Centrum Biotechnologii Stosowanej i Nauk Podstawowych al. Rejtana 16c, 35-959 Rzeszów, E-mail: akozioro@univ.rzeszow.pl; dr inż. Wiesława Malska, Politechnika Rzeszowska, Wydział Elektrotechniki i Informatyki, Katedra Energoelektroniki i Elektroenergetyki ul Pola 2, E-mail: wmalska@prz.edu.pl; dr inż. Dariusz Sobczyński, Politechnika Rzeszowska, Wydział Elektrotechniki i Informatyki, Katedra Energoelektroniki i Elektroenergetyki, ul. W. Pola 2, 35-959 Rzeszów, E-mail: dsobczyn@prz.edu.pl
Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 89 NR 11/2013
Published by Electrical Installation Wiki, Chapter J. Overvoltage protection – Installation of Surge Protection Device
Connection of Surge Protection Device
Connections of a SPD to the loads should be as short as possible in order to reduce the value of the voltage protection level (installed Up) on the terminals of the protected equipment.
The total length of SPD connections to the network and the earth terminal block should not exceed 50 cm.
One of the essential characteristics for the protection of equipment is the maximum voltage protection level (installed Up) that the equipment can withstand at its terminals. Accordingly, a SPD should be chosen with a voltage protection level Up adapted to protection of the equipment (see Fig. J38). The total length of the connection conductors is
L = L1+L2+L3.
For high-frequency currents, the impedance per unit length of this connection is approximately 1 µH/m.
Hence, applying Lenz’s law to this connection: ΔU = L di/dt
The normalized 8/20 µs current wave, with a current amplitude of 8 kA, accordingly creates a voltage rise of 1000 V per metre of cable.
ΔU =1 x 10-6 x 8 x 103 /8 x 10-6 = 1000 V
Fig. J38 – Connections of a SPD L < 50 cm
As a result the voltage across the equipment terminals, U equipment, is:
U equipment = Up + U1 + U2
If L1+L2+L3 = 50 cm, and the wave is 8/20 µs with an amplitude of 8 kÂ, the voltage across the equipment terminals will be Up + 500 V.
Connection in plastic enclosure
Figure J39 below shows how to connect a SPD in plastic enclosure.
Fig. J39 – Example of connection in plastic enclosure
Connection in metallic enclosure
In the case of a switchgear assembly in a metallic enclosure, it may be wise to connect the SPD directly to the metallic enclosure, with the enclosure being used as a protective conductor (see Fig. J40).
This arrangement complies with standard IEC 61439-2 and the Assembly manufacturer must make sure that the characteristics of the enclosure make this use possible.
Fig. J40 – Example of connection in metallic enclosure
Conductor cross section
The recommended minimum conductor cross section takes into account:
• The normal service to be provided: Flow of the lightning current wave under a maximum voltage drop (50 cm rule).
Note: Unlike applications at 50 Hz, the phenomenon of lightning being high-frequency, the increase in the conductor cross section does not greatly reduce its high-frequency impedance.
• The conductors’ withstand to short-circuit currents: The conductor must resist a short-circuit current during the maximum protection system cutoff time.
IEC 60364 recommends at the installation incoming end a minimum cross section of:
• 4 mm2 (Cu) for connection of Type 2 SPD; • 16 mm2 (Cu) for connection of Type 1 SPD (presence of lightning protection system).
Examples of good and bad SPD installations
Example 1: Equipment installation design should be done in accordance to installation rules: cables length shall be less than 50 cm.
Example 2 : Positioning of devices should be linked to installation rules: reduce length of cables < 50 cm and keep the loop area rule of reducing impact of magnetic fields created by lightning current.
Fig. J41 – Examples of good and bad SPD installations
Cabling rules of Surge Protection Device
Rule 1
The first rule to comply with is that the length of the SPD connections between the network (via the external SCPD) and the earthing terminal block should not exceed 50 cm.
Figure J42 shows the two possibilities for connection of a SPD.
Fig. J42 – SPD with separate or integrated external SCPD
Rule 2
The conductors of protected outgoing feeders:
• should be connected to the terminals of the external SCPD or the SPD; • should be separated physically from the polluted incoming conductors.
They are located to the right of the terminals of the SPD and the SCPD (see Figure J43 ).
Fig. J43 – The connections of protected outgoing feeders are to the right of the SPD terminals
Rule 3
The incoming feeder phase, neutral and protection (PE) conductors should run one beside another in order to reduce the loop surface (see Fig. J44).
Rule 4
The incoming conductors of the SPD should be remote from the protected outgoing conductors to avoid polluting them by coupling (see Fig. J44).
Rule 5
The cables should be pinned against the metallic parts of the enclosure (if any) in order to minimize the surface of the frame loop and hence benefit from a shielding effect against EM disturbances.
In all cases, it must be checked that the frames of switchboards and enclosures are earthed via very short connections.
Finally, if shielded cables are used, big lengths should be avoided, because they reduce the efficiency of shielding (see Fig. J44).
Fig. J44 – Example of improvement of EMC by a reduction in the loop surfaces and common impedance in an electric enclosure
Published by Chuck Gougler, International Association of Electrical Inspectors (IAEI) Magazine, Electrical Fundamentals – Electrical Power Quality and Harmonic Concerns, December 29, 2015
The Problem of Harmonics
Harmonics are generated by nonlinear components in electrical systems, which distort the sine wave. Increasing usage of power electronics causes a corresponding increase in voltage distortion, or harmonics. Electrical components like variable frequency drives, uninterruptible power supplies, and inverters all introduce harmonics of differing orders into the electrical system. When harmonics are present, they can manifest themselves with short-term and long-term consequences. High harmonic distortion can cause failures or malfunctions of electrical devices. Harmonics also cause a temperature rise in the electrical network and the equipment, resulting in losses and shorter service life. Harmonic filters will help to achieve a reduction or elimination of problematic harmonics, before any damage to the electrical system or equipment can occur.
Figure 1. IEEE 519-2014 current distortion limits (%)
Electrical Power System, Harmonics Overview
In general, harmonic currents are the result of the non-linear behavior of electrical devices. The sources of harmonic currents and thus harmonic voltage in power systems are multiple and vary in size (a few KVA up to several MVA). Typically, devices with magnetic iron cores, like transformers or generators, have been a key area of harmonic concern. Today, with the demand for energy efficiency of power electronic equipment, mitigation or reduction of harmonics continues to be a priority for many commercial, industrial and industry-specific customers, such as water and wastewater treatment and oil & gas.
Numerous facilities need to meet stringent requirements in order to operate reliably and in an environmentally compliant manner. Users need to ensure the availability of the operations on a 24/7 schedule.
As the majority of electrical power supplied to the user comes from a utility source, that is, from the local utility company, most of the power problems experienced at the facility level are really derived from within the operation of the plant itself. Harmonics are commonly present within the facility power network and can present issues ranging from nuisance to catastrophic. Harmonic filtering, which can be accomplished with active or passive solutions, helps to eliminate the harmonic issues while enhancing equipment performance and the overall facility electrical power system.
IEEE-519-2014 is a widely recognized set of recommendations which includes the maximum permissible current and voltage distortion values at the point of common coupling (PCC). The distortion limit is given as a function of the system loading, i.e., the relationship between the maximum short-circuit current (ISC) and the maximum demand load current (IL) at the PCC.
When ECOsine® passive and active harmonic filters and reactors are installed in the electrical system, they will reduce the harmonics to meet the requirements of most International Standards. They unload lines and transformers upstream of the non-linear load (for example, a three-phase diode bridge rectifier) hence reducing the system overall losses and operating temperature. Additionally, the total power factor is significantly improved and will remain close to unity even at partial load.
Figure 2. Harmonic spectrum without active filter
Figure 2a. Voltage and input current without active harmonic filter
Harmonics and Equipment
Frequency inverters are among the most widely used pieces of equipment for AC motor control. Such components are found in virtually every area of industry, in applications as diverse as pumps, fans, blowers, and even HVAC equipment. In the quest for ultra-compact, efficient power conversion, inverter manufacturers employ high speed semiconductor switching and pulse width modulation (PWM) techniques, which can create harmonic problems.
Arc furnaces and welders, including welding robotics, are usually very large power consuming applications. This high power, combined with a highly nonlinear voltage-current, produces substantial amounts of harmonic distortion. From a technical standpoint, arc furnaces operate in different phases (melting, air refining, refining) with different levels of harmonics. Additionally, the equipment has a combination of ignition delays and rapid voltage changes caused by random variations of the arc. This leads to an unusual harmonic spectrum with even and odd multiples of the fundamental frequency.
The electronic components within a CNC machine, for example, are particularly sensitive to “electrical imperfections” found in the power distribution system. Problems here can include malfunction of the equipment or program, along with damage to the parts and material. This can lead to missed deliveries and potential quality issues, unsatisfied customers and financial concerns for a company.
The use of variable speed drives for pumps and fans generates a harmonics content of the current in the supply that can lead to thermal overload of the electrical infrastructure and to malfunctions of sensitive equipment and components. In many water and wastewater treatment facilities, new biological stages working with bacteria are implemented. This leads to the installations of very powerful VFD-driven air compressors as bacteria need air to be able to do the job required. These VFDs are creating very high and unacceptable harmonic distortion.
Harmonics can wreak havoc on the electrical power network, causing circuit boards in PLCs to fail, tripped circuit breakers, blown fuses, overheating of motors and transformers, insulation breakdown, and reduced service life of equipment. Furthermore, production downtime/restart-time and shipment (revenue) loss, along with repair costs may result in reduced company profits.
A harmonic site survey (use of meters/analyzers) or a full engineering study may be necessary to completely determine existing harmonics (and other PQ issues), in order to provide a recommended solution to the user. In many, but not all cases, IEEE 519 (2014) guidelines are followed for the acceptable level of distortion. A complete review of the existing system, new/planned or retrofitted equipment along with any plant expansions should be considered.
Passive Harmonic Filters
One solution to mitigate harmonics would be to utilize passive harmonic filters. Such series-connected filters are typically installed “one-on-one,” in other words—one filter for each VFD. A larger passive filter can be designed to accommodate multiple drives, if required.
The most logical installation point at which to eliminate harmonics is right at the source-individual non-linear load. A passive filter provides a low impedance path for harmonic currents, required, as an example by a rectifier. This significantly reduces the amount of harmonics flowing throughout the electrical power system. The end result is the non-linear load drawing sinusoidal current from the power source/grid.
The installation of passive harmonic filters will be immediately beneficial to the electrical system, since they will help to limit the amplitudes of the current harmonics and thus reduce losses, and to operate equipment more efficiently and reliably. Additionally, they help to maximize utilization of the electric system capacity.
In a typical drive system, the total harmonic current distortion is reduced to acceptable limits and meeting IEEE 519 where applicable. Passive filters should be able to provide optimal performance at both full and lightly loaded conditions.
Passive filters can be found in two design types: 1) <5% THDi and 2) 7-10% THDi. Many times IEEE 519 is followed; however, there are applications where, say, 7 or 8% THDi improvement meet the needs of the end user. As a general “rule,” passive filters tend to be more economical than active filters, though they may not effectively mitigate a wide range of harmonic orders like active filters.
Figure 3. Harmonic spectrum with ECOsine TM Active
Figure 3a. Voltage and input current with ECOsine TM Active as well as the compensation current of the filter
Active Harmonic Filtering Solution
Another solution to mitigate harmonics is the use of active harmonic filters (AHF), power quality devices that permanently monitor the nonlinear load and dynamically provide precisely controlled current, helping to prevent distortion in a power network. This current has the same amplitude of the harmonic current but is injected in the opposite phase-shift, canceling out the harmonic currents in the electrical system. As a result, the current supplied by the power source will remain sinusoidal since the harmonics will negate each other, and the harmonic distortion is reduced to less than 5% THDi, meeting all standards. In addition, the AHF power electronics platform is designed to operate at levels that continuously adapt to rapid load variations. With load conditions creating harmonics up to the 50th order, active filters operate in a wide frequency range, adapting their operation to the resultant harmonic spectrum.
Active harmonic filters can also correct poor displacement power factor by compensating the system’s reactive current. The filter also balances the loads of the phases. These sophisticated devices are equipped with insulated gate bipolar transistors (IGBT) and digital signal processing (DSP) components. Generally, active harmonic filters can be installed at any point in a low-voltage AC network (parallel device), and they usually offer much more functionality than their passive filter counterparts.
Active harmonic filters combine these features with their small physical size and efficient operation, which makes them ideal choices for a wide variety of applications. Active filters can be provided for 3-wire or 4-wire connections (3-wire is the most common in North America). Current transformers deliver a signal to the filter, which can be applied to either the line or load side of the power network.
Active harmonics filters can be applied to a single or a group of nonlinear loads. Possible AHF installations include power factor correction in harmonic-rich environments in which filtering cannot be suitably achieved by the use of capacitors; where both power factor and harmonic correction are required; and where emergency power or distributed generation are present in the electrical network.
In general, active harmonic filters are available in several ratings. These ratings can include individual units for 50, 100, 200, 250 or 300 amperes. Different configurations such as open type, or various NEMA enclosure protection ratings and the ability to parallel multiple active filters, for higher current applications are typical. Installation voltages are mostly 480VAC and 600VAC. The 600VAC requirements can utilize a step-down (600/480VAC) transformer with the active harmonic filter, or use a “purpose built” active filter rated for 600/690VAC, where a transformer is not necessary. Active filters will include keypad controls and operator display communications such as RS485 and TCP/IP Ethernet, along with software for communications and monitoring through a Windows-based product.
Active filter is best utilized with 6-pulse VFDs. These VFD products are the most economical, highly common and readily available. One AHF can be used for multiple drives of any horsepower rating and any manufacturer. Drives of 18-pulse tend to have a much higher price point and, with its transformer, occupy more (valuable) space. Additionally, should an 18-pulse drive fail, it is “out of production,” whereas should an AHF fail or require service, the VFD continues to operate.
Where machinery and equipment are electronically controlled and need to meet exacting production standards, sensitive electronic components need to be protected from harmonics driven by the facility’s electrical power distribution system. The use of active harmonic filters can achieve the reliable functioning of the machinery and assure the process quality, while helping to support the financial bottom line.
Application Example with Active Filters
Power factor correction (PFC) equipment suffered from significant additional losses caused by harmonics. The installation of the AHF with a compensation current of 500 A brought the required electrical and thermal relief to the PFC, which considerably improved power quality and also made it possible for the installation of a backup generator in case of an outage. Adding the generator was previously impossible because of the prevalent harmonic content. The AHF’s unique capability to adapt to the situation of grid and load at any one time ideally helped to guarantee the continuous reliable operation of the wastewater treatment plant.
Where machinery and equipment are electronically controlled and need to meet exacting production standards, sensitive electronic components need to be protected from harmonics driven by the facility’s electrical power distribution system. The use of active harmonic filters can achieve the reliable functioning of the machinery and assure the process quality while helping to support the financial bottom line.
Final Comment
After harmonics have been identified and it’s determined a mitigation solution is required, the proper equipment selection will need to be reviewed and implemented. With the many problems associated with harmonics (equipment failure, replacement and maintenance costs, improper component or system operation, production downtime, etc.), it is suggested to keep records on these costs, to help with the ROI of any future mitigation equipment.
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