Generator Differential Protection Using a Hybrid Computer

This paper presents a rea1-time hybrid, analog-digital, computer technique for differential protection of generators. The fault/no fault decisions are based on the amplitude ratio of the "fault"\´ and "average through" currents from a selected generator phase. Analog input data pre-processor, fault monitor and soft-ware segments suitable for valid comparison during the transient period after the inception of a fault are described. Typical examples, from out of approximately 800 case studies, including internal and external faults using a three phase generator are presented.