RESTRICTED EARTH FAULT PROTECTION (REF) 64R/87N

RESTRICTED EARTH FAULT PROTECTION (REF) 64R/87N Restricted earth fault protection is used in transformers to detect internal earth faults. In this scheme, the CT secondaries of each transformer phase are connected together. These common terminals are then connected to the secondary of a Neutral Current Transformer (NCT). The name Restricted is derived since the objective of the protection is to detect the earth fault is restricted to the specific zone, starting from the breaker to the machine terminals. In the case of a generator, the machine terminal is the neutral point. In the case of a transformer, the machine terminal becomes the star point of either the primary or secondary winding or both. In the case of delta winding, it is the winding itself.