Improvement of 132/33KV Transmission Injection Substations Protection in Rivers State Using Short Circuit Analysis Technique

This paper presents the improvement of 132/33KV transmission injection substations protection, mainly short circuit fault on Port Harcourt Mains Zone-2 network and it seeks to correct the irregular tripping sequence, poor discrimination of relays, improper isolation action by the circuit breaker, poor current transformer ratio (CTR) calibration of the system. The 3x60MVA injection substation of the network was modeled. Short circuit analysis technique embedded in Electrical Transient Analyzer tool version 16.0 software was used to determine the tripping sequence of relay to circuit breaker coordination, using data from Transmission Company of Nigeria and Port Harcourt Electricity Distribution Company of Nigeria (PHED).The tripping sequence operation report showed that faults created at respective classified zones: A, B, C and D were analyzed and observed in accordance to the individual relay responsiveness to faults conditions. When a three (3) phase fault created at Zone-B, an irregular relay-tripping sequence was observed in the order of 1, 3, 2, and 4 with a tripping time of 11.5ms. This indicates violation in the relay response to fault conditions. Evidently, a new case of the study was re modelled in order to satisfy the statutory conditions. The current transformer (CT-ratio) of the existing condition of (1200/1 = 1200:1) was modified through short-circuit calculation to (900/5 = 900:5) in order to enhance orderly coordinated sequential tripping of 1, 2, 3 and 4 with a tripping time of 7.1ms. The new case showed improved protection (i.e. the irregular relay tripping sequence in the order of 1, 3, 2 and 4 and tripping time of 11.ms of Zone B with a 3 phase fault was improved to have a regular relay tripping sequence in the order of 1, 2, 3 and 4 and tripping time reduced from 11.5ms to 7.1ms) using short circuit analysis technique through relay coordination of the 132/33KV Port Harcourt Mains Z2 injection Substation in Rivers State.