A New Protection Scheme for Power Transformers Using Time Frequency Analysis

This paper presents a new approach for power transformer protection based on Hyperbolic S-Transform (HST) which is a very powerful tool for non-stationary signal analysis giving the information of transient currents both in time and frequency domains. Some important characteristics of differential currents in different transformer operating conditions such as normal, transformer energization, over excitation, internal and external faults are extracted based on HST. Two indices are defined for proposed protection scheme. Thereafter, by setting two proper thresholds, the internal fault currents are accurately discriminated from other operating conditions. The suitable performance of this method is demonstrated by extensive simulation of different faults and switching conditions in power transformers using PSCAD/EMTDC software. Simulation results show that the proposed scheme is robust against noisy condition. Copyright (C) 2011 Praise Worthy Prize S.r.l - All rights reserved