Capacity Enhancement of Short Circuit Laboratory using Parallel Operation of Transformers

Abstract

Since capacity of short circuit (S.C.) laboratory depends upon effective impedance of testing transformer and line connecting to the test equipment, which is designed to the optimal level while developing the S.C. Lab but still its fault level is lower. To test higher rating of transformer, a high testing fault level is required. Paralleling of S.C. testing transformer is one of the effective way to reduce the effective impedance and increase fault level of the S.C. Lab. Percentage impedance of the conventional power transformer are found to be rated at 10 to 12% , while in case of S.C. testing transformer, this is much lower. S.C. testing transformer is specially designed transformer due to above aspect. This report targets to study the feasibility of connecting another transformer of similar capacity parallel to existing one and to deal with the phenomena of sympathetic inrush current, circulating current etc. This report discusses simulation in ETAP & PSCAD for fault current estimation for the single S.C. testing transformer and after paralleling of two transformers and also simulate the protection scheme of over current and dual slope differential protection of transformer. Simulation results and mathematical results both are observed identical. In this project we also calculate the switchyard equipment ratings basis on IEC, IS, IEEE and CBIP manual.