Dynamic performance of the power differential relay for transmission line protection Tamer A. Kawady a, * , Abdel-Maksoud I. Taalab a , Eman S. Ahmed b a Power System Protection Group (PSPG), Electrical Engineering Department, Faculty of Engineering, Minoufiya University, Shebin El-Kom 32511, Egypt b Faculty of Engineering, Kafr El-shikh University, Kafr El-Shikh, Egypt article info Article history: Received 14 September 2007 Received in revised form 31 August 2009 Accepted 6 November 2009 Keywords: Differential relay Power swing MATLAB Transmission line Power system protection abstract Power differential relay was proposed recently as a practical relaying scheme for transmission systems. In this paper, the dynamic behaviour of the power differential relay is thoroughly investigated. These inves- tigations are important to evaluate the overall performance of such relaying functions. For this target, a detailed simulation of a typical transmission system was developed via the MATLAB/SIMULINK package using detailed modeling for each power system element. Both stable and unstable power swings are con- sidered. Moreover, single machine-infinite bus and double machine system operations are considered for all possible faulty and non-faulty conditions. All applied test results confirm the superiority of the power differential relay as an ideal candidate for transmission system protection applications. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction There is no doubt that differential relaying is one of the most important functions for protecting transmission lines. Their extra communication requirements may, however, postpone their expansion into the field. Moreover, requiring perfect synchroniza- tion of phase currents at both line ends arises as a technical diffi- culty [1]. The employment of Global Positioning Systems (GPS) or charging comparison schemes may partially represent solutions for these difficulties. On the other hand, GPS system is sophisti- cated and may suffer from service interruption, which is not under the control of power system protection engineers [2,3]. For elimi- nating most of the aforementioned problems, utilizing Phase Mea- surement Units (PMUs) in Conjunction with GPS systems for protection applications was presented in the literatures. This is, however, faced with the economic perspective. Also, charge com- parison schemes were proposed as a solution for the aforemen- tioned problems. However, depending on the current zero crossings may cause slow response under some fault conditions [4]. Non-conventional methods were also utilized for this target as well. Examples for these contributions were listed in the litera- tures as seen in [5,6]. In sympathy with these methods, a novel power differential concept has been recently proposed as reported in [7,8]. Similar efforts were also proposed using the power (en- ergy) computation for protecting transmission lines as reported in [9,10]. The power differential concept relies on computing the active and reactive power loci during normal operation, switching, nor- mal power swing and internal (external) faults. From these loci, discrimination of internal faults can be achieved. Adaptive setting of the power differential relay was also proposed in [8], providing a detailed description for its operation and features. Capability of the power differential relay to efficiently detect line faults occurring at the swing voltage center is an exclusive feature of this relay partic- ularly at higher values of load angle and fault resistances. These faults may not be detected by any of the existing relay technology including the charge comparison scheme. Moreover, the universal- ity of the proposed setting for different transmission systems has been justified as well. As reported in [7,8], the power differential relay corroborates an optimum performance through all applied steady state tests via the EMTP and MATLAB. Both software packages represent the most widely used simulation software for protective applications [11]. During these steady state conditions, the system operates typically close to their nominal frequency under a balance between the gen- erated and the consumed active power. On the other hand, system faults and disturbances (line switching, generator disconnection, and the loss or application of loads, etc.) force to deviate the elec- trical power from the corresponding mechanical power input to generator. These system disturbances may consequently result in oscillations in machine rotor angle producing severe power swings. Depending on the severity of the disturbance and the actions of 0142-0615/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijepes.2009.11.004 * Corresponding author. Tel.: +20 10 4151345; fax: +20 48 2235695. E-mail address: kawady@pspg-egypt.org (T.A. Kawady). Electrical Power and Energy Systems 32 (2010) 390–397 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes