Micrologic™ 2.0A, 3.0A, 5.0A, and 6.0A Electronic Trip Units | |
Rev. 01, 07/2012 | Section |
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Zone-Selective Interlocking
Control wiring links several trip units in the distribution network and in the event of a fault, a trip unit will obey the set delay time only if receiving a signal from a downstream trip unit.
If the trip unit does not receive a signal, tripping will be instantaneous (with no intentional delay).
•The fault is cleared instantaneously by the nearest upstream circuit breaker.
•Thermal stresses (I2t) in the network are minimized without any effect on the correct time delay coordination of the installation.
Figure 6 shows circuit breakers 1 and 2 zone- selective interlocked.
•A fault at A is seen by circuit breakers 1 and
2.Circuit breaker 2 trips instantaneously and also informs circuit breaker 1 to obey set delay times. Thus, circuit breaker 2 trips and clears the fault. Circuit breaker 1 does not trip.
•A fault at B is seen by circuit breaker 1. Circuit breaker 1 trips instantaneously since it did not receive a signal from the downstream circuit breaker 2. Circuit breaker
1trips and clears the fault. Circuit breaker 2 does not trip.
NOTE: Use I2t off with ZSI for proper coordination. Using I2t on with ZSI is not recommended as the delay in the upstream device receiving a restraint signal could result in the trip unit tripping in a time shorter than the published trip curve.
NOTE: Setting
Figure 6: Zone-Selective Interlocking
06133376
1 B
2 A
ENGLISH
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