Transient analysis of erroneous tripping at Grassridge SVC

Abstract

The research work conducted in this paper is the evaluation of real time values obtained using two OMICRON 356's at two independent locations and implementing them as recorder devices in Eskom's power system. A derived model within DIgSILENT is created and EMT studies are performed and compared to the real time values obtained. Transformers are normally closed via an auxiliary contact. Thus by applying system voltage at a random instant in time on the transformer windings result in a high transient magnetizing inrush current which causes high orders of 2nd harmonic currents to flow under no load conditions. A philosophy to mitigating these currents is to energize the transformer by controlling the circuit breaker closing times such that the magnetic flux produced in the windings corresponds to the prospective flux in the core. Transients produced can cause nuisance tripping's at the particular location where the respective transformers are energized. OMICRON EnerLyzer is the software tool used for the Comtrade recordings at both locations. Two “real time” case studies are evaluated using OMICRON EnerLyzer and TOP software. Results are formulated and then evaluated against a derived Electromagnetic transient model using DIgSILENT software.