Design and Implementation of System Protection Scheme for Interlinking Transformers at Thermal Power Station

This research paper designed a system protection scheme (SPS) for two 400kV/220kV interlinking transformer (ILT) installed on thermal power plant (TPP) of a practical utility grid to make these ILTs N-1 compliant. Two SPS logic are designed to avoid tripping of ILTs from the overload conditions and to avoid tripping of one ILT when another ILT is tripped on fault. This is achieved by load curtailment on the nearby 220 kV Grid-substation (GSS) in the region. The overload command taken from over-load/over-current relay and trip command taken from 86-master trip relay of the ILTs is transmitted over power line carrier communication (PLCC) system to the nearby 220 kV GSS to trip the 220kV/132kV transformers for load curtailment to reduce loading on the ILTs at TPP. SPS logic are validated through load flow studies performed on Rajasthan transmission system using MiPower software. The designed SPS is effective to avoid cascade tripping of transformers in a power grid which helps to prevent the large area from dark and also ensure proper power evacuation from a thermal power plant.