Smart Grid and Renewable Energy, 2013, 4, 297-305 http://dx.doi.org/10.4236/sgre.2013.43036 Published Online June 2013 (http://www.scirp.org/journal/sgre) 297 High Impedance Fault Detection of Distribution Network by Phasor Measurement Units Mohsen Ghalei Monfared Zanjani, Hossein Kazemi Karegar, Hasan Ashrafi Niaki, Mina Ghalei Monfared Zanjani Department of Electrical and Computer Engineering, Shahid Beheshti University (SBU), Tehran, Iran. Email: mo.monfared@sbu.ac.ir, h_kazemi@sbu.ac.ir, h.ashrafi@sbu.ac.ir, mi.monfared@iran-transfo.com Received November 18 th , 2012; revised January 2 nd , 2013; accepted January 11 th , 2013 Copyright © 2013 Mohsen Ghalei Monfared Zanjani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT This paper proposes a new algorithm for High Impedance Fault (HIF) detection using Phasor Measurement Unit (PMU). This type of faults is difficult to detect by over current protection relays because of low fault current. In this paper, an index based on phasors change is proposed for HIF detection. The phasors are measured by PMU to obtain the square summation of errors. Two types of data are used for error calculation. The first one is sampled data and the second one is estimated data. But this index is not enough to declare presence of a HIF. Therefore another index introduces in order to distinguish the load switching from HIF. Second index utilizes 3rd harmonic current angle because this number of harmonic has a special behaviour during HIF. The verification of the proposed method is done by different simulation cases in EMTP/MATLAB. Keywords: Fault Detection; High Impedance Fault; Phasor Measurement Units 1. Introduction High-impedance faults on distribution feeders are ab- normal electrical conditions that cannot be detected by conventional protection schemes because of the low fault current due to the high impedance fault at fault point. These faults often occur when an overhead conductor breaks or touches a high impedance surface such as as- phalt road, sand, cement or tree and pose a threat on hu- man lives when neighbouring objects become in contact with the line’s bare and energized conductors. HIF can occur in two cases. In one case, a conductor breaks and fall to ground and fallen phase current de- creases and protection relays cannot detect fault because current is not more than setting current of relays. In other state conductor isn’t break but it touches a high imped- ance thing such as tree limbs. In this state feeder current increase but it is not enough to detect by conventional protection relay. Therefore this type of fault is very dif- ficult to detect also it is very dangerous for human life and necessary to detect. So far, many models have been proposed to show high impedance faults features such as nonlinearity, asymme- try and the low frequency of HIF current. In 1990, a model for HIF is proposed which is based on arc nature when a Conductor breaks or touches a high impedance thing. This model is obtained from laboratory measure- ments and theoretical components [1]. A model Using Two Series Time-Varying Resistances was proposed in 2001 [2]. In 2004, a model was proposed in which two inverse diodes, dc source and resistance were used for modeling. The resistance and dc source changed every half cycle to show asymmetrical current of HIF [3]. A model based on dynamic model of arc was presented in 2008 [4]. Based on Emanuel model, a model was pro- posed in 2010 [5] to show more features of HIF. This model shows that when a broken conductor falls on earth, some arcs occur. These arcs have been shown by several parallel of Emanuel model. Therefore, it is necessary to have a perfect model of HIF to accurately detect it. In the past two decades many techniques have been proposed to improve the detection of HIFs in power dis- tribution systems. They can be roughly divided into two groups: time domain algorithms and frequency-domain algorithms. In the time domain, a ratio ground relay, a proportional relay algorithm [6,7] and a smart relay based on time- domain feature extraction [8] have been proposed. Copyright © 2013 SciRes. SGRE