PKR39809-02

The Problem

Consider the following possible sequence of events:

  • A fault occurs downstream of two ACR’s in series.

  • Both ACR’s pick up but only the downstream device trips as its Trip 1 time is intentionally shorter than the upstream device’s Trip 1 time.

  • The downstream ACR moves to Trip 2 in its sequence and automatically recloses.

  • The fault is still present and both ACR’s pick up again but the upstream device is still on Trip 1 which is a shorter trip time than the downstream device’s Trip 2 time.

  • The upstream ACR trips and clears the fault for the downstream device which resets before its trip time expires.

This would be a mal-operation causing an unnecessary loss of supply to the load connected between the two ACR’s.

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