Knowing IEC 61000-4-30 Class A

Published by Elspec

Power quality refers to a set of electrical boundaries defined by various documented rules designed to allow electrical equipment to function in its intended manner without significant loss of performance or life expectancy, this includes the steady and stable supply of electricity delivered by the grid. In order to achieve this aim it is necessary to constantly and vigilantly monitor the power conditions within an electrical network. There are a large number of parameters involved in this, but surprisingly, many power quality parameters have not been well defined which forced leading power monitoring device manufactures to develop their own methodologies resulting in incomparable values and rules between different instruments. This where the IEC 6100-4-30 comes in; it standardizes the measurement methodologies and creates the ability to directly compare results from different analyzers.

The IEC 61000-4-30 standard defines the measurement method, accuracy and time aggregation to verity of power quality parameters in 3 performance classes to obtain repeatable and comparable results. Additionally, the IEC 62586-1 defines EMC, safety and environmental requirement for power quality analyzers in different installation conditions and the IEC 62586-2 defines the test and uncertainty requirement to comply with IEC 61000-4-30 class A.

The standard is periodically updated as the industry evolves and new measurement scenarios are discovered or required. Since its introduction in 2003, the standard has been updated several times and is currently on its 3rd Edition.

IEC 61000-4-30 performance classes

The IEC 61000-4-30 defines 3 performance classes as follow:

  1. Class A – must to comply to the highest performances and accuracy level to obtain repeatable and comparable results
  2. Class S – accuracy levels are less stringent. Class S Power quality analyzers can be used for statistical surveys and contractual application where comparable measurement are not required.
  3. Class B (obsolete) – This class was introduced at the 1st and 2nd editions of the standard to avoid making may instrument obsolete. In this class the standard required that the measurement method and accuracy will be defined by the manufacturer in the instrument datasheet. In the 3rd addition, this performance class was removed.
Time Aggregation Intervals

The IEC 61000-4-30 class A defines several aggregation intervals:

  • 10/12 cycles (~200ms) at 50/60Hz respectively. The interval time varies with actual frequency.
  • 150/180cycles (~3sec) at 50/60Hz respectively. The interval time varies with actual frequency.
  • 10min interval begins on an absolute 10min time
  • 2 hours interval begins on an absolute even 2h time.

In the 2nd edition of the standard Re-synchronization technique was introduced to align the frequency based aggregations (10/12 cycles, 150/180 cycles) with time based aggregations (10min and 2 hours). The re-synchronization happens exactly every absolute 10min and deviation of the 10/12 cycles block are overlap as illustrated in the image below:

Time Aggregation Intervals
Power Quality Parameters Defined in the Standard

Following are the parameters defined in the IEC 61000-4-30 standard:

  • Power frequency
  • Magnitude of supply voltage
  • Flicker (by reference to IEC 61000-4-15)
  • Supply dips/swells
  • Voltage Interruptions
  • Voltage unbalance
  • Voltage harmonics (by reference to IEC 61000-4-7)
  • Voltage Inter-harmonics (by reference to IEC 61000-4-7)
  • Mains signaling
  • Under- and over-deviation

In the 3rd addition the following parameter was introduced:

  • Rapid voltage changes
  • Flicker class F1
  • Magnitude of the current
  • Current unbalance
  • Current harmonics (by reference to IEC 61000-4-7)
  • Current interharmonics (by reference to IEC 61000-4-7)

Recording of current along with voltage during events.

Examples of IEC 61000-4-30 Class A Requirements
Power Frequency

Measurement resolution of Power frequency is set to 10sec with uncertainty of 10mHz over measuring ranges of 42.5 – 57.5Hz / 51 – 69Hz at 50/60Hz respectively. Aggregation intervals are not mandatory for this section. In some application the required resolution is not sufficient and higher resolution as 1 cycle (power generation), 10/12 cycles (wind turbines) and 1sec (in some national standard) are required. The image below shows reading variations of the same signal measured in different resolution:

Note that the IEEE C37.118.1 suggest different method to calculate power frequency at higher resolution.

Magnitude of Supply Voltage

The magnitude of the supply voltage is the RMS values over 10/12 cycles (~200msec) time interval for a 50/60 Hz power systems respectively. Aggregations of 150/180 cycles (~3sec), 10min and 2 hours are also required. Measurement uncertainty is set to 0.1% of Udin (the declared input voltage) over the range of 10 – 150 % of Udin.

It is important to note that the standard does not specify any requirement for the recording resolution. Hence, it is highly important to look at the manufacturer specifications to verify its recording capability. In a typical PQA (Power Quality Analyzer) without a continuous waveform recording, the recording period depends on the recording resolution. Therefore, recording of 1 week can be done only at 10min resolution. Increasing the resolution to 10/12 cycle will shorten the recording period to a few minutes only.

It is also important to note that this measurement method is used for quasi-stationary signals and not for the detection of power quality events such dips (Sags), swells, interruptions, transient and RVC (Rapid Voltage Changes).

In The example below: the left side shows 1/2 cycle RMS values (colored in red), the right side shows 10 cycles RMS values (colored in black). Move the handle to see the influence of the resolution on the measurement outputs:

Power Quality Events

Dips (Sags), swells, interruptions, transient and RVC events must be measured in a sliding window of 1 cycle width updated every 1/2 cycle and synchronized to zero crossing as illustrated below:

Events evaluation is made by two parameters: voltage deviation from the reference voltage and duration.

The IEC 61000-4-30 standard doesn’t specify what should be recorded when event happens or the recording duration before and after the event.

When looking at manufacturers’ specification it is important to understand what the instrument recording capabilities are. For instance, low cost PQAs will only record the URMS(1/2) of the effected phase for a very short duration, while more advanced analyzers will record both the URMS(1/2) and IRMS(1/2) of all phases (both phase to phase and phase to ground). Furthermore, in many cases it is important to record the waveform signal itself before during and after the event. In this instance, it is important to understand what the waveform recording resolution capabilities are, and how long such high resolution recording can hold.

Having a power quality analyzer with a continuous waveform recording eliminate the need to set any trigger or threshold to capture the event and recording both RMS1/2 and waveform at high resolution continuously.

Harmonics and Interharmonics

IEC 61000-4-30 adopt the 10/12 cycles gapless harmonic subgroup measurement from the IEC 61000-4-7. It means that the FFT window is 10/12 cycle and the harmonic components output (bins) are at 5Hz resolution. The output component for each 5Hz bin is grouped according to the image below:

It means that the actual output have 50 harmonics values and 50 interharmonics values. Aggregations of 150/180 cycles (~3sec), 10min and 2 hours are also required.

The IEC 61000-4-30 puts special attention to the amount of data generated by this measurement method:

  • “This measurement method generates a large amount of data, which, depending on the application, may need to be stored, transmitted, analyzed, and/or archived. Depending on the application, the amount of data may be reduced. To reduce the amount of data, consider applying statistical methods at the measuring location, or storing only extreme and average values, or storing detailed data only when trigger thresholds are exceeded, or other methods.” [Electromagnetic compatibility (EMC) – Part 4-30: Testing and measurement techniques – Power quality measurement methods. Para 5.8.1 NOTE 2]
  • “To minimize storage requirements, after aggregation has been completed it may be practical to discard the source data (such as 10/12-cycle or 150/180-cycle data) if it is no longer required.” [Electromagnetic compatibility (EMC) – Part 4-30: Testing and measurement techniques – Power quality measurement methods. Para 5.8.4 NOTE]

3 main factors affect the amount of required data:

  1. The number of harmonics to be evaluated. In many application, 50 harmonics are not enough and you can find significate harmonic component up to the 100th.
  2. Recording resolution – the latest edition of the IEEE 519 required a daily and weekly harmonic evaluation of both voltage and current at 150/180 cycles (~3sec) resolution per phase.
  3. Spectral resolution – in some application it is required to record the 5Hz bins (raw data) itself rather than the 50Hz subgrouping output. This multiply the amount of data by 10.

For instance, your application required harmonic evaluation as defined in the IEEE 519-2014 edition. It means that the power quality analyzer required to record 50 harmonics per phase at resolution of 3 seconds for a minimum period of 1 week. Assuming that every sample take 3 Bytes of memory. The required memory space is 3(Bytes/sample) X 50(harmonics) X 6(3 phase voltages + 3 phase currents) X 20(samples/min) X 60 (min/hour) X 24 (hours/day) X 7 (days/week) = ~180Mb/week. For interharmonics this should be double and to have the bins it should multiply by 10.

Conclusions

Standards were created to provide an equal starting point to the power quality analysis and to help meters show the same values. However, in many cases limiting the information to standards prevented the troubleshooting engineer from monitoring the anomalies, not to mention identifying their source. The Elspec BlackBox series, equipped with PQZip compression technology, provides continuous measurement of available information in a 1,024 sample/cycle. There is no limit on the available data, since no thresholds or setups are used. In addition, it measures both in accordance to IEC 61000-4-30 and cycle-by-cycle in order to guarantee a complete view of the electrical network. Furthermore, the evaluation according to the latest IEEE 519 is also achievable due to the continuous waveform recording. Using the Elspec G4400 for power quality analysis assures that anomalies not only be monitored, but their causes also be identified.

Source: https://www.elspec-ltd.com/knowing-iec-61000-4-30-class-a/

Similar Products Power Quality Analyzers

Dranetz HDPQ® Plus & SP Family

What is Harmonic Study and Analysis and Why it is Done?

Published by Carelabs (Carelabz)

Image: Carelabz

The current significant growth in electronic devices focusing providing our installations has given rise to a significant change in the last few years on the type of loads connected to the electrical distribution system. Not so long ago the only concern there was when using electricity at home, in establishments and productive centres was simply the voltage, without giving a thought to anything other than whether the equipment and devices were working or not.

These devices, present equipped electronics which in some way or another provide increased performance in the tasks and productive processes we carry out.

Everyone uses computers for their personal use, for the process, control of any production system with variable speed drives, air conditioning units, lifts which adjust slowly on approaching the destination floor etc. These devices equipped with promoters, modulators and distort the current wave form for them to work properly.

Technical costs are those which bring about a loss of performance on our installation.

  • Loss of capacity on energy distribution line
  • Transformer overload
  • Conductor overload
  • Voltage drop
  • Derating of transformers
  • Losses on lines and machines due to the Joule’s effect
  • Magnetic losses on electrical machines

Normally, all technical cost turn into economic costs. Here is where importance of control in our installation.

Economic costs are those which we can economically quantify, although in some cases it is difficult. These costs can  divide into hidden cost and visible costs.

  • Increased electricity consumption
  • Electricity consumption peaks
  • Surcharge or payment on reactive energy
  • Distribution losses
  • Power and energy loss (due to the Joule effect and magnets)
  • Enlargement of the installations
  • Stoppage of productive process

All these phenomena can find to a lesser or greater extent depending on the installation itself and the loads connected.

The main effects of the voltage and current harmonics in a power system can cited as:

  • The chance for elaboration of some harmonics as a result of serial and parallel resonance.
  • Performance reduction in generation, transport and energy usage systems.
  • The aging of the grid insulation peripherals and as issue, energy reduction.
  • Malfunctioning of the system or some of its elements.

However to understand these effects better we must know the nature of harmonics. Harmonics produced by not-linear loads that absorb non-sinusoidal current. The most common loads, both in industrial surroundings and domestic ones, are the following ones:

  • Frequency / Variable speed drives
  • Discharge lamps (high pressure sodium vapour lamp, mercury vapour lamp, low consumption, fluorescent)
  • Rectifiers
  • AC/DC Converters
  • Arc welding
  • Induction ovens
  • UPS
  • Computers and laptops

Harmonics are contortion of the normal electrical waveform, generally transmitted by nonlinear loads. Switch-Mode Power supplies variable speed motors drives, photocopiers, personal computers, laser printers, fax machines, battery chargers and UPSs are examples of nonlinear loads.

Single phase nonlinear loads existing in modern office buildings, while three-phase nonlinear loads are common in organisations and industrial plants. A great section of the non-linear electrical load on most electrical distribution systems comes from Switch-Mode Power Supplies equipment. For example, all computer systems use Switch-Mode Power Supplies that convert utility Air Conditioner voltage to regulated low-voltage DC for internal electronics.

These non-linear power supplies consume electricity in high-amplitude short pulses that create significant distortion in the electrical and voltage wave shape harmonic distortion, measured as Total Harmonic Distortion. The exaggeration travels back into the power source and affect other equipment connected to the same source. Most power systems can take certain level of harmonic currents but will experience problems when harmonics become a significant element of the overall load. As great frequency harmonic electricity flow through power system, would cause communication errors, overheating and hardware damage such as:

  • Overheating of electrical distribution equipment, cables, transformers, standby generators etc.
  • High voltages and circulating currents caused by harmonic resonance
  • Equipment defect due to excessive voltage exaggeration
  • High internal energy losses in connected equipment, causing component failure and shortened life span
  • False tripping of branch circuit breakers
  • Metering errors
  • Fires in wiring and distribution systems
  • Generator failures
  • Crest elements and related problems
  • Lower system element, resulting in fines on monthly utility bills

A standard transformer is not designed for high harmonic currents produced by non-linear loads. It will overheat and fail early when connected to these loads. When harmonics introduced into electrical systems at levels that showed adverse effects (about 1980), the industry responded by developing the K-rated transformer. K-rated transformers not meant for consonants, but they would handle heat produced by consonant electricity and efficiently used under their K-element value.

K-element ratings range between 1 and 50. A standard transformer designed for linear loads have K-element of 1. The higher the K-element, the more heat from harmonic currents the transformer is able to handle. Making the right choice of K-element is very important, because it affects cost and safety. The table shows proper K-element ratings to use for different percentages of non-linear current in the electrical system.

The K-rated transformer commonly used in electrical industries, have more growth in transformer design that offer better performance in decreasing  voltage exaggeration and power losses due to electric consonants. Eaton’s energy-efficient Harmonic Mitigating Transformer designed to handle the non-linear loads of today’s electrical infrastructures. This transformer uses electromagnetic reduction to deal exactly with the triplen (3rd, 9th, 15th etc.) consonants.

Secondary windings of the transformer arranged to cancel zero sequence fluxes and ignore primary winding circulating currents. This transformer addresses the 5th and 7th consonant by using phase shifting. Using electromagnetic strategies, Eaton Harmonic Mitigating Transformer allows promote in same aspect as their operator designed them, while decreasing impact of consonants to energy losses and exaggeration. Eaton Harmonic Mitigating Transformer exceeds NEMA TP-1 efficiency standards, even when analysed with 100% nonlinear loads.

Wherever a K-rated transformer specified, an equal Harmonic Mitigating Transformer is a direct substitute. Power ware PDUs supplied with Harmonic Mitigating Transformer are efficient and effective at reducing the consonants produced by computer equipment and other nonlinear electronic loads.

Advantages of using Power ware PDUs with Harmonic Mitigating Transformer

  • Prevents voltage flat-topping caused by non-linear loads
  • Reduces upstream harmonic currents
  • Eliminates transformer overheating and high operating temperatures
  • Eliminates primary winding circulating current
  • Saves energy by reducing harmonic losses
  • Maintains high energy efficiency even under severe non-loading conditions
  • Treats power quality harmonic issues that K-rated transformers do not address
  • Suitable for high K-element loads without increasing in-rush current
  • Improves power factor

Source: https://carelabz.com/what-how-harmonic-study-analysis-done/

What is Earth Grounding?

Published by Carelabs (Carelabz)

Image: Carelabz

IEEE defines earth as a conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the Earth, or to some conducting body of relatively large extent that serves in place of the earth. The connection(s) to Earth are done by an assortment of metallic means intended to be employed as a designated grounding electrode. A designated grounding electrode is the device that is intended to establish the direct electrical connection to the earth rod.  The designated grounding electrode might be a water pipe, steel columns of a building or structure, concrete encased steel reinforcement rods, buried copper bus, copper tubing, galvanized steel rods, or semi conductive neoprene rubber blankets.  Gas pipes and aluminum rods cannot be employed as grounding electrode The grounding electrode conductor is the designed conductor that is employed to connect A common designated grounding electrode is often a copper clad or copper flashed steel the grounding electrode(s) to other equipment grounding conductors, grounded conductor, and structure.  

Purpose of Earth Grounding 
  • Limit potential difference of neutral for system stability. 
  • Allow for operation of relays and system protections devices. 
  • Personnel safety. 

Practical Ground Resistance rods have much less than 160 Ω. Typical rod resistances will be less than 25 Ω in most soils because of the existence of proximate utility ground references. 

Low ground resistance (< 10 Ω ) can be achieved with: 

  • Multiple Rods bonded together 
  • Counterpoise system 
  • Coupled rods 

Grounding is thought by many to be synonymous with electrical safety. “If equipment is grounded then it is electrically safe” gives a false sense of security. The process that many consider to be “grounding” can and may minimize the severity of electrical faults when performed with an understanding of what happens during an electrical fault. “Grounding” is very specific; it means a connection to the earth (ground). With respect to systems, such as transformers, generators, or batteries, “grounding” generally means providing a connection from one conductor of the system to an electrode that is buried in the earth. However, not all systems are grounded nor is the electrode always in the earth. When referring to equipment, the term “grounding” can have various meanings. It may mean bonding or it may mean a direct connection to the earth. The term “bonding” sometimes may mean “grounding,” and sometimes, it may mean a short or a long connection. 

Earth Bonding 

“Bonding” is a method by which all electrically conductive materials and metallic surfaces of equipment and structures, not normally intended to be energized, are effectively interconnected together via a low impedance conductive means and path in order to avoid any appreciable potential difference between any separate points.   

The bonded interconnections of any specific electrically conductive materials, metallic surfaces of enclosures, electrical equipment, pipes, tubes, or structures via a low impedance path are completely independent and unrelated to any intended contact or connection to the Earth.   

The common mean to effectively bond different metallic surfaces of enclosures, electrical equipment, pipes, tubes or structures together is with a copper conductor, rated lugs, and the appropriate bolts, fasteners, or screws.  Other effectively bonding means between different metallic parts and pieces might employ brackets, clamps, exothermic bonds, or welds to make an effectively connections. 

In addition to preventing potential differences that may result in hazards, effectively bonded equipment can also be employed to adequately and safely conduct phase-to-ground fault current, induced currents, surge currents, lightning currents, or transient currents during such abnormal conditions.

The principle purposes for an “effectively bonded grounding system via a low impedance path to earth” are intended to provide for the following. 

  • Provide for an applicable reference to earth to stabilize the system voltage of a power distribution system during normal operations. 
  • Create a very low impedance path for ground fault current to flow in a relatively controlled path. 
  • Create a very low impedance path for ground fault current to flow in order for overcurrent protective devices and any ground fault protection systems to operate effectively as designed and intended. 
  • Limit differences of potential, potential rise, or step gradients between equipment and personnel, personnel and earth, equipment and earth, or equipment to equipment. 
  • Limit voltage rise or potential differences imposed on a power distribution system from lightning, a surge event, any phase-to-ground fault conditions, or the inadvertent commingling of or the unintentional contact with different voltage system. 

Source: https://carelabz.com/what-earth-grounding/

FLEX-CORE® Glossary of Terms

Published by FLEX-CORE®, Div. Morlan & Associates, Inc.

Current Transformers

Usually rated on a basis of 5 amperes secondary current and used to reduce primary current to usable levels for transformer-rated meters or transducers and to insulate and isolate them from high voltage circuits.

Current Transformer Ratio

Ratio of primary to secondary current. For a current transformer rated 200:5, the ratio is 200:5 or 40:1.

Current Transformer Burdens

Normally expressed in ohms impedance such as B-0.1, B-0.2, B-0.5, B-0.9, or B-1.8. Corresponding volt-ampere values are 2.5, 5.0, 12.5, 22.5, and 45.

Voltage Transformers

Are used whenever the line voltage exceeds 480 volts or whatever lower voltage may be established by the user as a safe voltage limit. They are usually rated on a basis of 120 volts secondary voltage and used to reduce primary voltage to usable levels for transformer-rated meters, transducers and other loads.

Voltage Transformer Ratio

Ratio of primary to secondary voltage. For a voltage transformer rated 4200:120, the ratio is 4200:120 or 35:1.

Voltage Transformer Burdens

Normally expressed as volt-amperes at a designated power factor. May be W, X, M, Y, or Z. W is 12.5 V.A. @ 0.10 pf; X is 25 V.A. @ 0.70 pf; M is 35 V.A.@ 0.20 pf; Y is 75 V.A. @ 0.85 pf and Z is 200 V.A. @ 0.85 pf. The complete expression for a current transformer accuracy classification might be 0.3 at B-0.1, B-0.2 and B-0.5, while the potential transformer might be 0.3 at W, X, M and Y.

Transformer Ratio – (TR)

Total ratio of current and voltage transformers. For a 200:5 C.T. and 480:120 P.T., TR = 40 X 4 = 160.

Weatherability

Transformers are rated as indoor or outdoor, depending on construction (including hardware).

Accuracy Classification

Accuracy of an instrument transformer at specified burdens. The number used to indicate accuracy is the maximum allowable error of the transformer for specified burdens. For example, 0.3 accuracy class means the maximum error will not exceed 0.3% at stated burdens.

Rated Burden

The load which may be imposed on the transformer secondaries by associated meter coils, leads and other connected devices without causing an error greater than the stated accuracy classification.

Relaying Accuracy of Current Transformers

A relaying accuracy class is designated by two symbols which effectively describe the capability of the transformer as follows:

1. C means the transformer ratio can be calculated, i.e. a window type current transformer with uniformly distributed windings. The C rating refers to a low reactance design.

2. The secondary terminal voltage rating is the voltage which the transformer will deliver to a standard burden at 20 times normal secondary current without exceeding 10% ratio error. Furthermore, the ratio error must be limited to 10% at any current from 1 to 20 times rated current at any lesser burden. For example, relay accuracy class C100 means that the ratio can be calculated and that the ratio error will not exceed 10% at any current from 1 to 20 times nominal secondary current if the burden does not exceed 1.0 ohms (1 ohm X 5 amp X 20 times normal current = 100 volts.)

Continuous Thermal Rating Factor – (TRF)

Normally designated for current transformers and is the factor by which the rated primary current is multiplied to obtain the maximum allowable primary current without exceeding temperature rise standards and accuracy requirements. Example – if a 400:5 C.T. has a RTF of 2.0, the C.T. will continuously accept 400 X 2 or 800 primary amperes with the 5 X 2 or 10 amperes from the secondary. The thermal burden rating of a voltage transformer shall be specified in terms of the maximum burden in volt-amperes that the transformer can carry at rated secondary voltage without exceeding a given temperature rise.

Rated Insulation Class

Denotes the nominal (line-to-line) voltage of the circuit on which it should be used. FLEX-CORE® has transformers rated for 600 volts though 15kV.

Polarity

The relative polarity of the primary and secondary windings of a current transformer are indicated by polarity marks associated with one end of each winding. When current enters at the polarity end of the primary winding, a current in phase with it leaves the polarity end of the secondary winding. Representation of primary marks on wiring diagrams are shown as black squares, black circles, or H1. Secondary marks are shown as black squares, black circles or X1.

Hazardous Open-Circuiting

Operation of C.T.’s with the secondary winding open can result in a high voltage across the secondary terminals which may be dangerous to personnel or equipment. Therefore, the secondary terminals should always be short-circuited before a meter or other load is removed from service. It is recommended that shorting blocks or knife switch shorting assemblies be used with current transformers.

Source: https://www.flex-core.com/engineering-resources/glossary-of-terms/