Endurance Test of Circuit Breaker is conducted to check the healthiness of its mechanical parts i.e. operating mechanism. In this test, Circuit Breaker is operated several times and checked for any damage of its mechanical parts / contacts. The breaker should be in a position to open and close satisfactorily. This test is also called Mechanical Test.
In mechanical tests, the circuit breaker is opened and closed several times (1000). Some operations (about 50) are conducted by energizing the relays, remaining are by closing the trip circuit by other means. Mechanical tests on high voltage AC circuit breakers are conducted without current and voltage in the main circuit. Out of the 1000 operations, about 100 operations are made by connecting the main circuit (contacts) in series with trip circuit.
No adjustment or replacement of parts is permitted during the mechanical tests. However, lubrication is permitted as per manufacturer’s instructions.
After the tests, the contacts, linkages and all the other parts should be in good condition and should not show any permanent deformation or distortion. The dimensions should be within original limits. During repeated operations of the circuit-breaker, the weaker parts in the assembly may fail. The circuit-breaker is then considered to have failed in the mechanical test. The tests are then to be repeated after improvement in the design and manufacture. Successful performance in Mechanical Endurance Tests proves the adequacy of design and also good quality of materials and manufacture.
Though 1000 close-open cycles are specified in the standards, the manufacturer may conduct 10,000 or more operations to ascertain the reliability and for getting design data.