Distribution systems fault analysis considering fault resistance estimation André D. Filomena a,d,⇑ , Mariana Resener b , Rodrigo H. Salim c , Arturo S. Bretas d a Companhia Estadual de Geração e Transmissão de Energia Elétrica (CEEE-GT), Av. Joaquim Porto Villanova 201, Porto Alegre, Brazil b Companhia Estadual de Distribuição de Energia Elétrica (CEEE-D), Av. Joaquim Porto Villanova 201, Porto Alegre, Brazil c Electrical Engineering Department, University of São Paulo (USP), Av. Trabalhador São Carlense 400, São Carlos, Brazil d Electrical Engineering Department, Federal University of Rio Grande do Sul (UFRGS), Av. Osvaldo Aranha 103, Porto Alegre, Brazil article info Article history: Received 18 April 2009 Received in revised form 7 February 2011 Accepted 1 June 2011 Available online 5 July 2011 Keywords: Bus impedance matrix Power distribution systems Fault analysis Fault resistance Power systems protection abstract Fault resistance is a critical component of electric power systems operation due to its stochastic nature. If not considered, this parameter may interfere in fault analysis studies. This paper presents an iterative fault analysis algorithm for unbalanced three-phase distribution systems that considers a fault resistance estimate. The proposed algorithm is composed by two sub-routines, namely the fault resistance and the bus impedance. The fault resistance sub-routine, based on local fault records, estimates the fault resis- tance. The bus impedance sub-routine, based on the previously estimated fault resistance, estimates the system voltages and currents. Numeric simulations on the IEEE 37-bus distribution system demon- strate the algorithm’s robustness and potential for offline applications, providing additional fault infor- mation to Distribution Operation Centers and enhancing the system restoration process. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Electric power systems are daily exposed to service interruption mainly due to faults and human accidental interference. A power system fault is defined as any failure which interferes with the normal current flow [1]. The fault phenomenon affects system’s reliability, security, and energy quality, and can be considered stochastic. Different events such as lightning, insulation break- down and trees falling across lines are common overhead power system fault causes. Power system faults may be classified as temporary or perma- nent. Temporary faults in overhead lines are usually caused by lightning. In this case, system service can be automatically restored after approximately 20 fundamental frequency cycles, with the cir- cuit breakers opened, to allow deionization. However, permanent faults are associated with different events, like trees falling across lines. On these situations, system restoration is maintenance crew dependant. Facility maintenance crew must search and repair the system using a fault location estimate. For non-negligible fault resistances (R F ), which are commonly associated with permanent faults, standard fault location algorithms may present poor perfor- mance [2,3]. Fault analysis methods are an important tool used by protection engineers to estimate power system currents and voltages during disturbances. It provides information for protection system setting, coordination and efficiency analysis studies. Today, three approaches are used in the industry for such analysis: classical symmetrical components, phase variable approach and complete time-domain simulations [4]. Classical fault analysis of unbalanced power systems is based on symmetrical components approach [5,6]. However, in untransposed feeders with single-phase or dou- ble-phase laterals, the symmetrical component methods do not consider accurately these specific characteristics [7]. Hence, sym- metrical components based techniques may not provide accurate results for power distribution systems, which are normally charac- terized by those asymmetries. With industrial computer facilities improvement, the fault anal- ysis phase variable approach has been proposed to substitute the symmetrical components methods on distribution systems [8]. In the phase variable approach, system voltages and currents are re- lated through impedance and admittance matrices based on phase frame representation, considering the typical distribution systems asymmetries. However, fault analysis is still fault resistance dependant [9]. Due to fault resistance stochastic nature, typical fault analysis studies consider the fault paths as an ideal short-circuit. To over- come this limitation, recent studies suggest the usage of fault resis- tance estimation algorithms [10–12]. These works provide a fault resistance estimate using symmetrical components or modal anal- ysis techniques, restricting the application on balanced systems 0142-0615/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijepes.2011.06.010 ⇑ Corresponding author at: Companhia Estadual de Geração e Transmissão de Energia Elétrica (CEEE-GT), Av. Joaquim Porto Villanova 201, Porto Alegre, Brazil. Tel.: +55 51 33825220; fax: +55 51 33824349. E-mail addresses: afilomena@ece.ufrgs.br (A.D. Filomena), mariana@ece.ufrgs.br (M. Resener), rhsalim@usp.br (R.H. Salim), abretas@ece.ufrgs.br (A.S. Bretas). Electrical Power and Energy Systems 33 (2011) 1326–1335 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes