A Modified MDSC based Phasor Estimation Technique for Power System Protection

Protective relays require fast and accurate extraction of fundamental sinusoidal parameters from fault current signals, which is hindered by decaying DC components (DDCs). This paper proposes a new modification algorithm based on Multiple Delayed Signal Cancellation (MDSC) to estimate the fundamental phasor current signal in faulted power transmission line containing one or more Decaying DC (DDC) components such as a primary DDC, and secondary DDC which are caused by fault signal and current transformer respectively. To obtain accurate estimation of the fundamental phasor current signal, an auxiliary signal based on high frequency modulation is used to estimate DDCs. Then the estimated DDCs are finally subtracted from the original current signal to reduce the disturbances caused by the DDCs. The proposed method is accurate and immune to multiple DDCs. To validate the proposed method, both computer-based tests and simulation tests are implemented and its performance is compared with four related phasor estimation methods. In the presence of multiple DDCs with the hindrance of harmonics and noise, the proposed method performs well and the test results show the effectiveness of proposed method. This method is validated for off-nominal frequency as well.

I. Introduction

In power system protection, a protective relay plays a vital role in detecting the fault in transmission lines. However, the fault current often contains multiple DC components such as primary DDC and secondary DDC. Among these DDCs, primary DDC is more intense when compared with other DDCs. Hence the fundamental phasor estimation error caused by the primary DDC is the major concern in the numerical relays [1].