A New Modified MDSC based Phasor Estimation Techinque for Decaying DC offset Removal

In power systems, a common issue that arises, particularly during fault conditions such as short circuits or open circuits, is the occurrence of decaying DC offset in the fault current waveform. This decaying DC offset can create challenges for protection and control systems, potentially leading to incorrect operation or system failures. Accurate and swift extraction of fundamental parameters from fault signals is crucial for protective relays. However, the presence of decaying DC components (DDCs) poses difficulties for algorithms based on the Discrete Fourier Transform (DFT) which are commonly used for phasor estimation. In this paper, a novel modification algorithm based on the Multiple Delayed signal Cancellation (MDSC), is proposed to estimate the fundamental phasor current signal in faulted power transmission lines that contain one or more decaying DC (DDC) components. These DDC components may include a primary DDC as well as a secondary DDC caused by the current transformer. To enhance the accuracy of phasor measurement and eliminate multiple DDCs, the proposed method combines full cycle MDSC and even sample set MDSC. By subtracting the full cycle MDSC from the even sample set MDSC, the DDC error can be determined. This approach is immune to multiple DDCs, addressing a significant challenge. To validate the effectiveness of the proposed method, numerical tests and simulation tests are conducted, comparing its performance against four other related phasor estimation methods. Even in the presence of DDCs, harmonics, and noise, the proposed method demonstrates favorable results, achieving fast and accurate phasor estimation. Moreover, the method proves effective in mitigating the influence of secondary DDC caused by the current transformer. Overall, this proposed method offers a solution for addressing the impact of decaying DC offset in fault current waveforms, enabling reliable and precise phasor estimation in power systems.

I. Introduction

Protective relays are critical for fault detection in transmission lines and ensuring power system protection. However, fault currents frequently include multiple DDC components, including primary and secondary decaying DDC components. Of these DDCs, the primary DDC has a more significant impact and is of greater concern in numerical relays due to its higher intensity [1].