Study Of Improved Algorithm And The Influence Of CVT Transient On Distance Protection

Capacitor Voltage Transformer(CTV) is of small size and low manufacturing cost, and can effectively restrain ferromagnetic resonance, it is widely applied to high-voltage transmission line. While CVT consists of dividing capacitor, its transient characteristic is relatively poor, and as primary voltage mutates, secondary voltage is of transient error, which will affect the normal operation of relay protection system.Firstly,in order to analyze the influence of CVT transient on protection, based on the basic structure of CVT, it selects a simplified model and conducts mathematical analysis on it, calculates CVT transfer function and resolves transient noise, and proves the leading role of decaying DC component in transient noise, filtering decaying DC component is the key to solve CVT transient problems. Through simulation it verifies influence of parameters as initial failure phase angle, equivalent capacity and resonance damper on CVT transient characteristic, in addition selects appropriate parameters, and builds CVT simulation model.Secondly, it analyzes the basic principle and hardware structure of microcomputer protection as well as studies the filter performance of fourier algorithm for microcomputer protection, and verifies the fourier algorithm filtering characteristic for high frequency harmonic and decaying DC component by handling composite signal with noise through utilizing fourier algorithm.Then, EMTDC/PSCAD is used to set up the model of line protection, and two kinds of normal distance protection projects are selected to conduct simulation; the influence of CVT transient error on distance protection is quantitatively analyzed through simulation, and it investigates the key reasons of opposite direction export fault protection maloperation and positive direction export fault protection delay. Through constructing short line model, it analyzes the influence of CVT transient on power frequency variation distance protection while fourier algorithm is adopted, which shows that the power frequency variation distance protect transcend phenomenon is affected by SIR value, and when SIR is higher, exceeding phenomenon becomes more serious.This thesis proposes to adopt the improved half-wave fourier algorithm that can filter decaying DC component, thus to solve transient transcend problem of distance protection caused by CVT transient, and the simulation verifies the feasibility of improved algorithm to distance protection. According to the results of simulation, an improved protection project has been put forward, and it shows that this scheme can effectively prevent the delay action and misoperation problems of distance protection in export failure, which is of quickness and reliability, and its operation characteristics conform with the basic action requirement of distance protection from Electric Power Research Institute. At the same time, further applying the improved algorithm to power frequency variation distance protection, the behavior characteristic can meet the same requirements, which can solve the transient transcend problem.Finally, it uses Prony algorithm to handle CVT transient voltage signal. The result shows that Prony algorithm is relatively accurate and quick in fundamental wave identification during CVT transient, which shows great applicable prospect.