Mixed Digital/Analog Testing System for Relay Protection of Power System

This paper introduces a mixed digital/analog testing system for relay protection of power system, which creatively integrates digital simulation and analog testing in one system. The system accepts almost all kinds of power fault data including actual fault data, simulation data and imaginary data and possesses powerful fault analysis function based on accurate basal value calculation using the modified-DFT algorithm. The digital simulation software for relay protection is embedded in the upper-computer of the system, which provides an open, expandable experimental platform for users. A closed-loop configuration and a novel modified algorithm using wavelet neural network (WNN) are applied in the lower-amplifying part of the system, which reduces the non-linear distortion of the output waveform of analog protection test greatly. A prototype of the proposed instrumentation system has already been put into practical operation and the good effects obtained have revealed its practicability and effectiveness.