Troubleshooting of Automatic Trip Curve Test

Condition	Probable causes	Solutions
Circuit breaker trips faster than minimum trip band for instantaneous protection when performing automatic trip curve test on short-time or instantaneous segments of time-current curve and in EPC if test result appears as fail and trip time is less than 10 ms.	Secondary injected fault into trip unit has exceeded one or more of the following circuit breaker protection levels: Instantaneous override Close and latch Selectivity	Make sure that the circuit breaker is always in closed position before beginning secondary injection of each fault. This avoids tripping due to close and latch protection. Does long-time segment of time-current curve pass when performing automatic trip curve test? A. YES For communicating MicroLogic trip units, if Ap trip indicator LED on trip unit turns ON when testing short-time or instantaneous segments of time-current curve, then circuit breaker has tripped on instantaneous override, close and latch, or selectivity protection functions. For non-communicating MicroLogic trip units, no trip indicator LED is available. Check that peak value for signal being injected does not exceed instantaneous override or selectivity protection levels. See published time-current curves. B. NO Contact your field service representative.
Circuit breaker is not receiving ZSI restraint during secondary injection testing, but trips as though it is receiving a restraint signal. Circuit breaker trips according to time delay setting for short time (tsd) or ground fault (tg) instead of tripping with no intentional delay.	This is normal operation for the secondary injection test. The Service Interface ZSI self-restrains the short time and the ground fault protection functions during secondary injection testing.	None - Normal operation

Condition

Probable causes

Solutions

Circuit breaker trips faster than minimum trip band for instantaneous protection when performing automatic trip curve test on short-time or instantaneous segments of time-current curve and in EPC if test result appears as fail and trip time is less than 10 ms.

Secondary injected fault into trip unit has exceeded one or more of the following circuit breaker protection levels:

Instantaneous override
Close and latch
Selectivity

Make sure that the circuit breaker is always in closed position before beginning secondary injection of each fault. This avoids tripping due to close and latch protection.

Does long-time segment of time-current curve pass when performing automatic trip curve test?

A. YES

For communicating MicroLogic trip units, if Ap trip indicator LED on trip unit turns ON when testing short-time or instantaneous segments of time-current curve, then circuit breaker has tripped on instantaneous override, close and latch, or selectivity protection functions.

For non-communicating MicroLogic trip units, no trip indicator LED is available. Check that peak value for signal being injected does not exceed instantaneous override or selectivity protection levels. See published time-current curves.

B. NO

Contact your field service representative.

Circuit breaker is not receiving ZSI restraint during secondary injection testing, but trips as though it is receiving a restraint signal.

Circuit breaker trips according to time delay setting for short time (tsd) or ground fault (tg) instead of tripping with no intentional delay.

This is normal operation for the secondary injection test. The Service Interface ZSI self-restrains the short time and the ground fault protection functions during secondary injection testing.

None - Normal operation