What is Circuit Breaker Testing and How is it Done

Published by Carelabs (Carelabz), Website: carelabz.com


Image: Carelabz – Circuit Breakers

Circuit Breaker Testing is utilised to test the operation of each switching systems and the programming of the entire tripping structure. Circuit Breaker Testing is essential to ensure the safe and reliable performance of this key link in the power asset chain. Circuit breakers perform three main tasks:

  • They should conduct the current as efficiently as achievable, when closed.
  • When open, they must insulate the contacts from one another as effectively as possible.
  • In the event of a malfunction, they must disconnect the fault current as quickly and reliably as possible, thereby protecting all subsequent equipment.

Performing circuit breaker testing is more challenging with comparison to other electrical components like transformer as the short circuit current is greater.  In the US market and regions of frequent earthquakes, the most popular high-voltage circuit breakers are “dead tank” units, whereas in central Europe “live tank” breakers are standard. Elsewhere both circuit breaker types are obtainable.

Why is Testing Circuit Breaker Important?

A circuit breaker might stay idle years, but if a malfunction occurs it has to detach fault currents of huge kiloamps gradually within a few milliseconds. Major errors that happen on circuit breakers are incorrect behavior, short circuits in the coils, damage/wear to the mechanical connections or the insulation material. Therefore, circuit breakers need to be regularly and carefully tested. Circuit breakers perform a vital role in protecting expensive equipment from damage through faults i.e. connecting and disconnecting the electrical power in a reliable way; this requires proving their reliability with on field tests during installation and with regular maintenance tests during its lifetime to prevent costly failures and problems that could even compromising the safety of the substation. Testing the performance of your circuit breakers regularly is therefore an essential and cost-effective part of any maintenance strategy. Circuit breaker testing particularly concentrates on obtaining motion and time values on the units. However, our testing solutions have revolutionized circuit breaker testing. Performing the tests without use of the station battery greatly increases safety throughout the testing process.  

What are the Steps in Circuit Breaker Testing?

Type Tests of circuit breaker

Type tests are organised with the aim of proving the abilities and making sure the rated characteristic of the circuit breaker are exact. Such tests are conducted in the specially built testing laboratory.

  1. Mechanical Test– It is mechanical ability type test involving the repeated opening and closing of the breaker. A circuit breaker must close and open at proper speed and do its allocated job and function without any failure.
  2. Thermal Test– Thermal tests are carried out to check the thermal behavior of the circuit breakers. Due to the streaming of rated current through its pole in a rated condition, the breaker under test undergoes steady-state temperature rises. The temperature rise for rated current should not exceed 40° for current less than 800A normal current and 50° for normal value of current 800A and above.
  3. Dielectric Test– These tests are performed to check power frequency and impulse voltage withstand capacity. Power frequency tests are kept on a new circuit breaker; the test voltage changes with a circuit breaker rated voltage. In impulse tests, impulse voltage of particular value is employed to the breaker. For outdoor circuit dry and wet tests are conducted.
  4. Short -Circuit Test– Circuit breakers are subjected to sudden short-circuits in short-circuit test laboratories, and oscillograms are taken to know the behaviour of the circuit breakers at the time of switching in, during contact breaking and after the arc extinction. The oscillograms are studied with particular reference to the making and breaking currents, both symmetrical and asymmetrical restriking voltages, and switchgear is sometimes tested at rated conditions.
 Routine Tests of a Circuit Breaker

Routine tests are done as per references of standards of Indian Engineering Service and Indian Standards. These tests are performed on the manufacturers’ premises. Routine tests confirm the proper functioning of the circuit breaker. The routine tests confirm the proper functioning of the circuit breaker. Routine testing doesn’t necessarily include complex gear in order to ensure that a circuit breaker is functional. Some guidelines and recommendations for these tests include routine maintenance and verifying that that circuit breaker performance is in line with manufacture’s calibration curves.  It is crucial that these tests are performed under stable conditions at suitable temperature so that there are no variations in the data.  Some of the tests are listed below.

Preventative Maintenance of Circuit Breaker, Inspection, and Testing

Preventative maintenance depend operating conditions for circuit breakers.  Primary inspections of CB (circuit breakers) will look at particulate matter that’s contaminating the inner workings of the CB.  Accumulation of particulates can generally be disposed of by flipping the lathe on the breaker “Off” and “On” switch to clear away the accumulated dust

Circuit Breaker Trip Test

By analysing the current consumed by the trip coil during the circuit breaker’s operation, it is possible to determine whether there are mechanical or electrical issues present. In many cases, such issues can be localised to aid in finding the root cause. Optionally, monitoring the tripping supply’s voltage during the operation can detect issues arising with tripping batteries.

Insulation Resistance Test

For individual breaker resistance testing, load and line conductors should be preferably disconnected. If not detached the test values will also involve the characteristics of the connected circuit.  Resistance testing is crucial for verifying that the insulating material which makes up the molded cases breakers are performing correctly.  In order to test for insulation resistance, an instrument known as a megger is used. A megger instrument applies a known DC voltage to a given wire for a given period of time in order to test the resistance within the insulation on that particular wire or winding.  It is vital that voltage is employed as the resistance checked with an ohmmeter may differ when there are no report of potential differences.  It should also be noted that if you apply a voltage that is too high for that insulation to withstand, then you could potentially damage the insulation.

Connection Tests

Connection testing is important to make sure that an appropriate electrical connection is available and to recognise traces of overheating denoted by colour difference.  It is important that electrical connections are properly installed to the CB to prevent and reduce overheating.

Contact Resistance Test

Normal wear and tear of contacts within the CB emerges after extended usage.  An easy method to identify traces of weakening within the circuit breaker is to quantify the resistance across every pole of the breaker. Indications of abnormal conditions within the CB such as erosion and contamination of contacts are evident if there are excessive millivolt drops across the breaker.  The contact resistance test is important in finding out if or not a circuit breaker is still apt for functioning.

Overload Tripping Test

Overload tripping components of CBs can be tested by inputting 300% of the breaker rating into each pole of the circuit breaker to determine that it will open automatically.  The motive of this is to make sure that the circuit breaker will operate or not.  Refer to NETA standards for trip times that are acceptable for the overload tripping test.  When trying to find out tripping characteristics, it is advisable to consult with manufacturer’s manuals.

Instantaneous Magnetic Tripping

In routine tests, it is relevant to find out that the magnetic feature is functional and will trip the circuit breaker instead of finding the precise value at which the instantaneous magnetic feature functions.

How Testing of Circuit Breaker is Performed?

Different circuit breaker test equipment are used to check the operation and condition of circuit breakers on the power systems. How to test a circuit breaker involves many different test techniques and type of testers. This will define how to test a circuit breaker through different testing tools to be applied to check the equipment under a range of conditions or operation types. Discover how to test a circuit breaker with the different test sets that you can need.

Testing with Different Equipment:

To consider how to test a circuit breaker, it is required a deep knowledge of the breaker itself:

  • How it works
  • Its tolerances,
  • Reference values of previous tests,
  • Initial values with which to compare the actual results, sometimes defined by a rated timing graph,
  • Established settings or initial features given by manufacturer

In this sense, how to test a circuit breaker becomes a trending analysis since test results are not always definitive but have meaning just when compared to previous data or results.

Testing with Circuit Breaker Analyzer

The timing tests of the different open and close operations of the breaker is an efficient way of how to test a circuit breaker, analyzing not only the trip times but also the essential synchronism of the poles in the different operations. This define how to test a circuit breaker through different simulations of its operation, which can be directly commanded from the circuit breaker analyzer, or initiated by an external signal, checking the opening or closing time of each pole, in single or combined operations, and checking the possible difference between poles or mismatch time which may lead to a dangerous lack of synchronism. How to test a circuit breaker with a circuit breaker analyzer depends also on the type of possible problems to be confirmed, which leads to check other features such as the possible bouncing, the proper performance of the pre-insertion resistances, the coils condition, and the mechanical analysis through contact travel speed and acceleration data with the use of the appropriate transducers.

Testing with a Micro-ohmmeter

Circuit breakers generally bear a huge value of current. Greater contact resistance cause greater losses, low current carrying capability and threatening hot spots in the breaker, so that the resistance testing with micro-ohmmeters are other way of how to test a circuit breaker for identifying and avoiding upcoming issues. How to test a circuit breaker with a micro-ohmmeter requires also reliable measurements and a wide injection range with high power that enables for longer test leads, less connections problems, and more accurate measurements.

Testing with a High Current Primary Injection Tester

The analysis of the tripping time characteristics of LV circuit breakers and molded-case circuit breakers is performed using high current injection, as the way to check the entire functionality. How to test a circuit breaker of this type depends on its maximum rated current, the trip protection settings and the inverse curve types which will define the overload and short-circuit trip pickup levels and time delays; all these features must be checked with the appropriate primary injection test set with the capacity to simulate the corresponding high current faults required and capture the answer of the breaker. A system which be easily upgraded in power capacity enables how to test a circuit breaker in the different possible situations and range of breakers; how to test a circuit breaker of this kind also needs a bendable design of the test set to fruitfully attain the certain large current job, and a design that create possible to position it nearer to the breaker, and so decreasing the power needed with smaller test leads; this is the case of the Raptor System, a modular and flexible primary injection system which easily and quickly adapts its power capacity to the several high currents ratings of the different circuit breakers.

Benefits of Circuit Breaker Testing
  • Quick and easy to perform on site
  • Circuits can be tested on or off load
  • Tests performance of whole tripping cycle
  • Tests overall timing of tripping system
  • Identifies need for maintenance
  • Part of a comprehensive diagnostic maintenance program
  • Find early indications of possible problems
  • Avoid issues other than pick up pieces
  • Build up a test record database for trending
  • Pick out the bad actors

Source: https://carelabz.com/what-circuit-breaker-testing-how-circuit-breaker-testing-done/

Published by PQTBlog

Electrical Engineer

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s