Abstract — Application of wavelet transform technique to high impedance arcing fault detection in distribution networks is presented. Phase displacement between discrete wavelet coeffi- cients calculated for zero sequence voltage and current signals at natural network frequency is tracked. The developed wavelet based HIF detector has been tested with EMTP-ATP generated signals, proving better performance than traditionally used al- gorithms and methods. The protection method proposed is effi- cient, robust and may be used for HIF detection independently of the network neutral point grounding mode. Index Terms — protective relaying, wavelet transform, distribu- tion networks, high impedance arcing faults, transient analysis. I. INTRODUCTION ETECTION of high impedance faults (HIFs) presents still important and unsolved protection problem, especially in distribution networks. Discrimination of the feeder with arcing ground connection is not trivial since the ground fault current in MV networks is very low, often below load current of the feeder. Several approaches for the detection of HIFs may be found in the literature, applying algorithms monitoring: • low frequency spectrum of the current [4], • incremental variance of even order harmonic power [3], • energy variations in a concerned frequency band [6], • wavelet coefficients of the line currents [1], etc. In this paper the idea of detecting HIFs by comparing phase angles of CWT coefficients, suggested previously in [1] as a pos- sible technique for transmission line level, is thoroughly studied. Its new version expanded for MV networks is presented and the results of its extensive simulative testing are described. The following sections of the paper describe the arc model de- veloped and its application in modeling of MV network events (Sec. II), basic information on the wavelet technique and the HIF detection algorithm itself (Sec. III) as well as scheme testing with various ATP-generated signals (Sec. IV). Conclusions close the paper. II. ARC MODEL AND SIMULATIONS PERFORMED A. The arc model adopted The high impedance ground fault model applied in simu- lation experiments was developed basing on research and considerations presented in [3, 4, 9] but some new features were also included into the model implementation. To obtain dynamic features of the ground fault nonlinear impedance the digital arc model described in [9] was adopted. This model is derived from Hochrainer arc description that is based on en- ergy balance in the arc and is described by the following dif- ferential equation: )) ( ) ( ( 1 ) ( t g t G T dt t dg - = (1) that is equivalent to the transfer function 1 1 ) ( ) ( + = Ts s G s g (2) where: g(t) – time-varying arc conductance, G(t) – stationary arc conductance, T – time constant and r(t)=1/g(t) is time- varying arc resistance. The stationary arc conductance follows as p p l t i R u t i t G ) ) ( ( ) ( ) ( + = (3) where: i(t) – arc current, u p – constant voltage parameter per arc length, R – resistive component per arc length (R=9 Ω/cm), l p – arc length (l p =10 cm). The length of the arc l p as well as the time constant T were considered to be constant in the investigations. MODELS i(t) 3kV 4kV 1e3 sin(2πt-π/2) 1e3 sin(2πt-3π/2) if |i(t)|<1 mA then G(t)=0.54 mS else G(t)= |i(t)| / (u p +R |i(t)| l p ) end; g(s)=G(s)/(Ts+1) where u p =25 V R=9 Ω/cm l p =10 cm T=15 μs r(t)=1/g(t) 3 kΩ Fig. 1. Arc model structure. Marek Michalik, Waldemar Rebizant, Miroslaw Lukowicz Institute of Electrical Power Engineering Wroclaw University of Technology, Poland Wavelet Transform Approach to High Impedance Fault Detection in MV Networks Seung-Jae Lee, Sang-Hee Kang Next Generation Power Technology Center Myongji University, Yongin, Korea D