NON STANDARD OVERCURRENT RELAY FOR HIGH RESPONSE WITH SELF BACKUP PROTECTION

The ABB REF 615 relay model is an overcurrent and earth fault relay used to protect the feeder of the real radial system of 66/11 KV Egyptian Substation NO.7 in 10 th Ramadan. The main objective of this paper is to create non-standard characteristics in overcurrent relays to improve the response and to operate under its failing. In the proposed model, a combined setting is utilized and consists of NI and VI curves. The working area of overcurrent relay is divided into two areas. In the first area, the VI curve is operated as back up of NI curve and in the second area, the NI curve is operated as back up of VI curve. The simulation results are verified by ETAP software. The results prove that the developed model has two advantages. The first advantage is reducing the operating time by 40% over the conventional model. The second advantage is providing self back up protection in the relay and increases the protection level if any setting fails to operate.