Circuit breaker test kit by KEP: performance testing

Automatic circuit breaker tester UPA-20

A circuit breaker is a power conducting element of switchgear responsible for discontinuing the current flow should it reach a level considered harmful for the grid, therefore preventing damage to equipment and resulting workplace accidents. In the course of preventive maintenance the utility personal use circuit breaker testers to ensure that the grid’s circuit breakers are capable of interrupting current flow if a fault occurs. Given the vital importance of switchgear for the power industry, the manufacturers of circuit breaker test sets, in their turn, must meet the requirements of reliability, accuracy and efficiency.

Further in the article we report on testing done on the circuit breaker test set UPA-20 by KEP. The testing procedures were divided into two main stages. We started with checking the accuracy of current setting on the Circuit Breaker Test Set UPA-20. For this purpose we set one by one the output current values of 4 кА, 6 кА, 10 кА, 12 кА, and compared the UPA readings with those of the reference meters (the current transformer and the comparator measuring current on the current transformer), making allowance for the measurement error of ± 3% specified by the manufacturer. We then measured the consumption current fed from the switchboard, output current on the voltage regulator RNO and voltage on the voltage regulator. Having made sure the actual values of the current fed by the test set match the ones set by the user, we conducted a sample test of a circuit breaker.

Testing the circuit breaker tester UPA-20 for the accuracy of current setting 

For the first stage we connected the voltage regulator RNO to the UPA control unit with the voltage regulator cable. We then connected the earthing wire to the earthing bus and the control unit. The UPA power cord was connected to the power switchboard. In the calibration circuit we should use a current transformer 10000/5 A and a current meter 5 A (in this case, it was a comparator CA507). The comparator reading of 100% corresponds to a current of 10000 A on the transformer. The peak value we can measure in such a circuit is 12000 A, in which case the comparator will display 120%.
The output voltage of the voltage regulator was measured with a voltmeter, while current on the output of the voltage regulator was measured with a clamp. We used the current transformer as a load, connecting it with eight 1-metre long bus bars, the total cross-section of which was 880 mm2.

The circuit breaker test set UPA has two measurement modes, either in kA up to 20000 A, in which case we'll see 20 kA on the display, or in A in the range from 100 A to 4000 A. Bear in mind that for testing and calibration purposes the UPA performance should be evaluated in conjunction with the voltage regulator RNO. So, we began with setting the voltage regulator switch on zero; after that we set the thyristor module knob on maximum, flipped up the circuit breakers, and pressed the button "Testing" to start feeding current. As explained above, during testing we set in turn the operating modes for 4 kA,  6 kA, 10 kA, 12 kA, and compared the readings of the test set with the readings of the reference meters, the current meter and the comparator, by measuring the consumption current from the switchboard, the output current and voltage on the voltage regulator RNO.

The testing results showed, that in the operating mode of 4000 A we had 8 A on the input in phase two, we did not activate phase one; also, the consumption current fed via the voltage regulator RNO was 39 A. After we returned to the lowest current, we had about 900 A as the cross-section of the bus bars we used for connection was the largest possible. If we took longer bus bars with a smaller cross-section, we would be able to start raising current with 100 A.

In the operating mode of 6 kA we had 74 V on the voltage regulator RNO, 6000 A on the test set UPA, and 20 A on the switchboard. The consumption current fed from the RNO was 55 A.
In the operating mode of 10 kA we had 132 V on the voltage regulator, and 62 A on the switchboard. In this case the current on the voltage regulator was 96 A.

When we started testing the circuit breaker test system UPA in the operating mode 12 kA, the regulator was already set on the current value of 10 kA. We reached the peak current for this circuit, 12 kA, and compared the readings with the reference meters, the current transformer and the comparator. On the output of the voltage regulator RNO we had 114 A, on the switchboard we had 87 A.

When operating the circuit breaker test system UPA in the mode 220 V we can raise current up to the peak value for this voltage. As we had a load of eight bus bars, supplied with the circuit breaker test set, with a length of 1 metre and cross-section of 880 mm2, we made it to the peak value of 16.5 kA with a voltage of 230 V on the source.

To test a situation, in which the operating mode of 220 V does not meet the testing objectives and there is a need to go between 14 kA and 20 kA, we first switched off the power on the circuit breakers, switched off the power switchboard, switched the circuit breaker test set UPA to the mode of 400 V, flipped up the two circuit breakers, and then supplied power from the switchboard. It should be noted that at the point of switching on the lowest current value will be equal to the peak current in the mode 220 V, that is, about 14-16 kA. After the testing started, we gradually raised current to the highest value we can get with this circuit breaker test set, 20 kA, while measuring the consumption current, which at that point was equal to 190 A on the voltage regulator RNO; we had 130 A on the switchboard. During testing the bus bars heated up; this may cause the current to go down slightly, but it can be increased if it is necessary.

Since at the moment of testing we did not have a reference meter for a current value over 12 kA, we tested the UPA-20 performance for the output currents between 12 kA and 20 kA working on eight shorted 1-metre long shorted bus bars with the total cross-section of 880 mm2, connected in parallel. We allowed one minute at the peak current of 20 kA, with the bus burs heating up over a temperature of 100 ⁰С, which was acceptable due to the fact that typically testing at peak currents is only conducted for a fraction of a second. In our test we supplied 20 kA for one minute at a voltage of 300 V on the source to show that the circuit breaker test set UPA-20 by KEP has a voltage reserve (voltage can exceed 400 V).

Testing a circuit breaker

In the end we ran a complete circuit breaker testing cycle with the use of the circuit breaker test set UPA-20. Generally, circuit breaker testing is done in the time of 0.1 seconds to find out at what current value the circuit breaker trips and at what current value it does not trip in that time. Based on the testing results the user can assess whether the circuit breaker has passed the testing or failed it.

The circuit breaker test set UPA-20 has a mode in which the user can set the current to be fed. For this type of testing, the user sets the time duration in which the device will be feeding the set current (the available UPA-20 modes are 100 ms, 200 ms,  400 ms, 600 ms, 800 ms, 990 ms and 10 seconds). Once this time is over, the UPA will stop the current supply. In our sample test the circuit breaker tripped at a current of 8.8 kA and time of 480 ms.
Based on the testing results we can confidently conclude that the UPA-20 by KEP has proved to be a reliable circuit breaker test system with accurate current setting capability and an intuitive user interface. In addition, the test set’s portable design makes it possible to conduct circuit breaker testing with ease and flexibility that are especially valuable for field testing.

About KEP

KEP has been engineering high voltage testing equipment for over 15 years. The company’s product line ranges from portable testers to complex high voltage testing systems; it includes solutions for cable testing and fault location, diagnostics of cable systems, circuit breaker testing, and insulation oil testing. All KEP’s instruments are available with on-screen menu in English as well as in a number of other languages.

Please see the video report on the performed testing below (English subtitles are available).

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua