CIRCUIT BREAKER TESTING

1.TIMING TEST

Timing test is done on circuit breaker for measuring the time required to breaker to make and break the contact i.e. to check the closing and opening time of circuit breaker as specified by manufacturer i.e. O-0.3CO-3CO. It is the duty cycle of circuit breaker. By this test we get the time required for each break of CB and each PIR of CB. The closing time should be less than 100 m secs and opening time should be 25 m secs. PIR should close before 8-10 m secs of main contact and it should open before 8-10 m secs than main contact. The time delay between two poles of CB must not exceed 3.33 m secs during closing and 2.5 m secs during opening. Similarly the time delay between two breaks of CB must not exceed 3.33 m secs during closing and 2.5 m secs during opening. During timing test we generally need to perform 5 operations as follow:

1. Closing
2. Opening at Trip Coil- 1
3. Opening at Trip Coil-2
4. Close-Open
5. Open-Close-open

2.CRM TEST

      The CRM test is done in close condition of circuit breaker so it is called as “Static Contact resistance Measurement Test”. In CRM test of circuit breaker, breaker is made close and current is fed to its contacts of 100 Amps DC. The CRM kit is able to measure the micro ohm resistance of the CB. Actually kit measures the voltage across the close contact and manipulates the resistance of contact by ohms law. This test shows the condition of main contact i.e. whether there any erosion or any misalignment in the contact or not. The contact resistance must not exceed 150 μΩ.

1.CAPACITANCE AND TAN-D TEST 

1. Preparation of test

a. The day selected for testing must be dry for outdoor testing; atmospheric temperature should be in range of 20˚C to 30˚C.

b.Clean the porcelain stacks of the insulator/Bushing properly.

c. Discharge the specimen to be tested before applying voltage.

d. Isolate the bus bar/IPS connected to specimen if possible.

e. Remove the earthing and grounding if possible.

These tests are carried out during pre-commissioning stage to check quality of dielectric medium (i.e. Capacitance) by measuring the power loss in that. For the measurement of capacitance of dielectric medium almost Schering bridge of small capacitance measurement is used. Similarly Tan-δ is measured indirectly by manipulating power factor of dielectric medium.

1. Interpretation of results

a. Power factor at low voltage

The power factor of the insulation at low voltage is an indication of the condition of insulation material. Thus if the power factor at low voltage has increased, it indicates the possibility of moisture or other contamination of the insulation resistance.

b. Power factor TIP-Up

The power factor tip-up is a measure of insulation at higher voltage. Power factor tip-up indicates non linearity’s in the insulation. Tip-up caused by partial discharges activity within the insulation and is undesirable as it causes further degradation of the insulation. With age and deterioration, the tip-up will increase or the same tip-up will be exhibited at a lower voltage.

c. Comparison between phases

The similarity between the readings on equipment can be used to draw certain conclusion even if prior history of the equipment insulation is not available. Thus, if any one of the components shows a marked difference from the others, this should trigger and investigation and perhaps additional test. The capacitance and the power factor of the phase to ground insulation should provide the same, if not identical readings. The same applies to the three phase to phase readings. Even though the phase to ground insulation will exhibit a much different capacitance then the phase to phase insulation, their power factor should be basically the same.

1.DCRM TEST

The DCRM test is done in operative condition of circuit breaker so it is called as “Dynamic Contact resistance Measurement Test”. In DCRM test of circuit breaker, breaker is made open & close and current is fed to its contacts of 100 Amps DC. The operations are made as per the duty cycle of CB i.e. O-0.3CO-3CO. The DCRM kit is able to measure the micro ohm resistance of the CB. Actually kit measures the voltage across the close contact and manipulates the resistance of contact by ohms law. This test shows the condition of arcing contact i.e. whether there any erosion or any misalignment in the contact or not. Similarly one transducer is mechanically connected to the mechanism of the circuit breaker whose output is fed to DCRM kit which further calculates travel of contacts and other parameters like Stroke, Rebounce, and Wipe, over travel etc.

During DCRM test following generally three operations are important i.e.

1. Close

2. Open &

3. Open-300 ms Close-Open.

This operation gives us the signature of circuit breaker which it has to perform during the auto reclose of line. By this we get that whether CB can respond to attempt one cycle of auto reclose properly or not.