Actual Trends in Development of Power System Protection and Automation 30 May – 3 June 2011, Saint Petersburg
PS1 – S3-02
Detection of High Impedance Fault in MV Distribution System
Sankara SUBRAMANIAN, Krishnakumar VENKATARAMAN ALSTOM Grid UK
[email protected];
[email protected]
KEYWORDS High Impedance Fault, Wavelet, Harmonic, Intermittent, EMTP. INTRODUCTION High impedance fault (HIF) is generally defined as unwanted contact of an electrical conductor on a nonconductive surface like road, tree limb, sod or some other surface or object which restricts the fault current to a level below that can be reliably detected by conventional relays [1]. Undetected HIFs such as downed conductors are rather dangerous for personal safety and property security. The primary objective of clearing a HIF is protection of personnel and property and not the power system. Therefore, HIF detection (HIFD) is of crucial importance for utilities and protection engineers. Detection of HIF has long since been of great challenge as well as interest for industrial and academic research. Generally, ways to detect such kind of fault are mainly focusing on waveform features. Harmonics feature such as 3rd harmonic’s amplitude and phase has been used by early researchers [2], [3]. However, harmonic should not be considered as a feature uniquely for HIF, moreover, the accuracy may be affected by the background harmonic source such as nonlinear loads. Randomness such as intermittence is another straightforward feature [4], [5], yet randomness may not cover all HIF cases either. Due to the complexity of the problem, artificial intelligence such as Neural Network (NN) [6], [7] and expert system [4] becomes the focus of HIFD research, but these methods may need considerable training and setting with stage-tests, and the mechanism of these NN black-box style methods is not so clear either. Arc detection using high frequency component and wavelet is also a focus for HIFD [6], [8]. However, in the distribution system, measurement should be taken to discriminate HIF arc from other high frequency distortion. In a word, due to the complexity of system condition and fault cases, it is a truth that not all kinds of HIF can be fully securely detected [1] by any method. These type of faults are predominant in MV networks in countries like USA, Brazil, Australia, Saudi Arabia, UAE, Thailand, V