Power Frequency Test of Circuit Breakers
- Short Circuit Test
- Synthetic Testing of Circuit Breaker
- Dielectric Test or Over Voltage Test
1. Short Circuit Test
The procedure for this test is similar to that of – Rated short time current test and momentary current withstand test on isolator.
The circuit breaker should satisfactorily perform opening and closing operations sequentially for all vales of short circuit currents upto rated short circuit breaking current.
2. Synthetic Testing of Circuit Breaker
The short circuit test should be conducted by considering following conditions :
- During initial period of short circuit, the current should be large and voltage should be low.
- During next few cycles (recovery period), the voltage should be high and current should be low The above conditions occur during short circuit faults.
The circuit breaker behavior can be studied if these two conditions are imposed on it.
For achieving above conditions, two separate sources are used. Source one acts for first condition and source two acts after first condition.
The test set up is shown in Figure
L1, L2, R, C are used to get desired operating condition (transient condition)
Initially S2 is closed and high current (short circuit current) is passed through circuit breaker. Then S2 is closed when this current reaches near zero. Thus high voltage gets applied to circuit breaker. The voltage applied has transient nature due to L1, L2, R, C parameters. Thus desired transient re-striking voltage (TRV) with respective rate of rise of re-striking voltage (RRRV) are obtained by this test.
3. Dielectric Test or Over Voltage Test
This test is performed on both internal and external insulation of circuit breaker. It is performed for two conditions.
- Circuit breaker closed
- Circuit breaker open
(i) Circuit breaker closed :
The tested part is R phase i.e. voltage is applied to R phase pole of circuit breaker and Y phase, B phase and metallic frame structure of circuit breaker is earthed. Same procedure is repeated with Y phase and B phase.
(ii) Circuit breaker open : The test voltage is applied to circuit breaker contacts i.e. R, Y, B poles of circuit breaker are connected to bus bar side and voltage is applied from other side consecutively on each phase.
The reference range of standard voltage to be applied for this test are as below.
|
Rated |
Standard |
Test |
|
3.6 |
45 |
16 |
|
7.2 |
60 |
22 |
|
12 |
75 |
28 |
|
24 |
125 |
50 |
|
36 |
170 |
70 |
|
52 |
250 |
110 |
|
72.5 |
325 |
140 |