DISTURBANCE EFFECT ON RELAY

Abstract

The design of protective relays has been changed significantly over the past years, due to. the advancement in microprocessor and signal processing technology. Use of numerical relays in switchgear necessitates that the user to be familiar with their design and functionality. A Digital Distance Relay (MHO) is designed in this work by using TMS32OC10 Processor, for converting both the voltage and current analog signals into Digital Signals, and an 8255 is used to transfer the data to the Personal Computer through Parallel Port. Filtering requirements, for the digital distance relays are critical because they must estimate precisely and quickly the electrical distance to the fault, even highly distorted input signals. All types of Recursive Fourier filters (1 /2 Cycle, 1 Cycle, 2 Cycle, and 3 Cycle), Differential equation based algorithm and the algorithm based on a differential equation combined with ,Fourier transform are implemented. The Fourier algorithms possess good high-frequency characteristics. Also, the computation time can be significantly reduced by using recursive calculations. However, the presence of the exponentially decaying DC component adversely affects the calculation accuracy. The differential-equation-based algorithms exhibit. poor high-frequency characteristics so that significantly time-delaying filters are required.