Overcurrent Release Test
The Overcurrent Release Test is used to determine the current which trips the breaker. Overcurrent releases are commonly used together with self-powered overcurrent protection relays.
Current transformer releases are used on breakers in substations where no grid independent supply voltage is available. Quite often the breakers do not have a close coil. Overcurrent releases are activated by a current coming from the tripping transformer, with a typical nominal value of 0.5, 1.0 or 5 A AC. An overcurrent relay feeds the current flow from the tripping transformer to the breaker. The tripping transformer and the overcurrent relay are usually powered by the secondary side of the CTs. In the event of an overcurrent, the relay switches the current of the tripping transformer to the breaker and thus causes it to open the main contacts and isolate the faulty grid part.
During the test, with the breaker in closed position, a current is ramped up in steps until the breaker trips. This is the trip current. Then the ramp ends.
The CIBANO 500 Medium Voltage Package includes an Under-voltage Test and an Overcurrent Test, during which the test device uses its inbuild supply to output a voltage ramp, or a current pulse ramp, respectively.