Distribution feeder protection could soon be complicated by nonradial flows of real and reactive power available from high penetration distributed generation and potentially from microgrids. Nondirectional overcurrent protection may not provide necessary security and sensitivity for faults on remote points of the circuit. Directional supervision is necessary to set overcurrent pickups with adequate sensitivity for remote faults. Setting the directional element by traditional means provides a reliability risk at varying VAR flows within reach of specific types of distributed generation. This paper will demonstrate the limitations of nondirectional overcurrent protection and the pitfalls of an improperly configured directional element. A unique solution using directional overcurrent elements further secured by a load encroachment function can solve these problems. This approach has been validated in renewable plant collector circuit protection applications over a wide range of operating conditions.

This paper discusses die goals of routine maintenance testing for protective relays. The paper advances a Markov Probability model diat predicts die optimum test interval for protective relays widi and widiout self-testing capabilities. The model uses known system transition rates and relay failure rates. The probability model shows diat die optimum test interval for a relay widi self-tests is quite long.Digital relay failures can also cause relay misoperations and prevent operation for faults. However, relay characteristics are typically not affected by failures. Failures tend to be significant enough to eidler generate a self-test failure indication or cause dIe user to recognize dIe problem during nonnal operation of dIe relay.

No abstract

No abstract

No abstract