Load Current Approaches Fault Current

Pickup settings on a phase overcurrent device are normally set below the expected fault current levels on

that line by some margin. Consequently, it is possible for load current to approach (or exceed) the pickup

setting on the relay. This could lead to an undesirable trip for an acceptable load condition.

Weak Infeed Condition

During a period of abnormally low system voltage, leading power factor current above relay pickup can

flow in the non-trip direction of a line. Probable current sources are outlying capacitor banks. This could

cause the current to be sensed as lagging current flowing in the trip direction and leading to an

undesirable trip. (A condition often referred to as weak infeed because the lower voltage system – where

load is present – attempts to correct the undervoltage condition on the higher voltage system.)