Testing of circuit breakers
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This PPT explains about the circuit breaker, and its types. Then about the need and purpose of the circuit breaker. And finally the testing and types of testing of circuit breakers.
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Testing of circuit breakers
- 1. 1 TESTING OF CIRCUIT BREAKERS Presented by, KABILESH. K (15BEE023)
- 2. CONTENTS Circuit Breaker Types of circuit breaker Tests of circuit breaker Dielectric and impulse tests Thermal tests Mechanical tests Short circuit tests 2
- 3. CIRCUIT BREAKER An electromechanical switch that breaks the circuit under fault condition. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset to resume normal operation. To detect a fault condition, and immediately discontinue the electrical flow. 3
- 4. 4 TYPES OF CIRCUIT BREAKER AIR BLAST CB VACCUM CB SF6 CB OIL CB
- 5. NEED FOR TESTING During short circuit fault or any other types of electrical fault these equipment suffer a high stress of fault current which may damage the equipment and networks. For saving these equipments and the power networks, circuit breakers are used, thereby disconnecting the circuit. Hence, the testing of the circuit breakers are essential. 5
- 6. TEST OF CIRCUIT BREAKERS Dielectric tests Impulse tests Mechanical tests Thermal tests (Temperature rise tests) Short Circuit tests 6
- 7. DIELECTRIC AND IMPULSE TESTS Dielectric tests: Consists of over voltage withstand tests of power frequency, lightning and switching impulse voltages Tested for internal & external insulation with CB in both the open & closed position. Voltage in Open position >15% of that of closed position. During test, CB is mounted on insulators above ground to avoid ground flash over. Impulse tests: The test is done with switching over voltage. To asses their performance under over voltages due to switching operation. 7
- 8. THERMAL TEST To check the thermal behaviour of the breakers Rated current through all three phases of the switchgear is passed continuously for a period long enough to achieve steady state conditions Temperature rise must not exceed 40°C when the rated normal current is less than 800 amps and 50°C if it is 800 amps and above Contact resistances between the isolating contacts and between the moving and fixed contacts is important. These points are generally the main sources of excessive heat generation. 8
- 9. MECHANICAL TESTS To ensure the open and closing with out mechanical failure. It requires 500(some times 20,000) operations without failure and with no adjustment of the mechanism. A resulting change in the material or dimensions of a particular component may considerably improve the life and efficiency of the mechanism. 9
- 10. SHORT CIRCUIT TESTS To check the ability to safely interrupt the fault currents. To determine the breaking capacities at different load currents Methods of conducting short circuit tests, Direct tests Using the power utility system as the source. Using a short circuit generator as the source. Synthetic Tests 10
- 11. DIRECT TESTS USING THE POWER UTILITY SYSTEM AS THE SOURCE To check the ability to break in normal load conditions or short circuit conditions in the network itself. Done during limited energy consumption. 11
- 12. PROS AND CONS OF DIRECT TEST USING POWER UTILITY SYSTEMS Advantages: 1. Tested under actual conditions in a network 2. Special cases (like very short line faults etc.,) can be tested 3. Thermal & dynamic effects of short circuit currents and applications of safety devices can be studied Disadvantages: 1. Can be tested only in rated voltage and capacity of the network 2. Test is only at light load conditions 3. Inconvenience and expensive installation of control and measuring equipment is required in the field. 12
- 13. SHORT CIRCUIT TEST IN LABORATORIES To test the CBs at different voltages & different SC currents. The setup consists of, A SC generator Master CB Resistors Reactors and Measuring devices The make switch initiates the circuit short circuit & master breaker isolates the test device from the source at the end of predetermined time. If the test device failed to operate, master CB can be tripped. 13 Back up breaker Short Circuit Testing Gen Reactor Test device CT Making Switch Circuit Capacitance G
- 14. SYNTYHETIC TESTS Heavy current at low voltage is applied Recovery voltage is simulated by high voltage, small current source Procedure: When auxiliary breaker 3 and test circuit breaker T are closed, making switch 4 and master breaker 1 is closed. Hence, Current flows through test CB. At time t0, the test CB begins to operate. 14 1 2 3 4 5 6 Vc Cc C0 Cv IvIc T
- 15. SYNTHETIC TEST (Contd.,) At time t1, just before zero of the gen current, the trigger gap 6 closes and high frequency current from capacitance Cv flows through the arc of the gap At time t2, gen current is zero. Master CB 1 is opened The current from Cv will flow through test CB and full voltage will be available At the instant of breaking, the source is disconnected as the high voltage is supplied by auxiliary CB 4. 15 1 2 3 4 5 6 Vc Cc C0 Cv IvIc T
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