Adaptive ground distance protection for UPFC compensated transmission lines: A formulation considering the fault resistance effect Martín Cruz Rodríguez Paz a,b,⇑ , Roberto Chouhy Leborgne a , Arturo Suman Bretas a,c a Federal University of Rio Grande do Sul, Osvaldo Aranha 103, Room 116, Porto Alegre, Brazil b Federal University of Pampa, Av. M. A. Gomes de Godoy 1650, Room 3125, Bagé, Brazil c University of Florida, 216 Larsen Hall, P.O. Box 116200, Gainesville, FL 32611-6200, United States article info Article history: Received 22 September 2014 Received in revised form 24 March 2015 Accepted 18 April 2015 Keywords: UPFC Distance protection Ground fault Phase components approach abstract This paper presents a mathematical deterministic adaptive distance protection formulation for UPFC compensated transmission lines. The proposed formulation is developed using a phase component approach and considers and compensates for various UPFC operation conditions and non-zero fault resis- tances. The proposed methodology is completely adaptive and independent of system characteristics (such as changes in transmission line impedances) or operating conditions (such as different load condi- tions and controlled reference parameters). Moreover, the proposed formulation uses local and remote end voltage and current signals as input data. The comparative test results demonstrate potential bene- ficial aspects of the proposed formulation for real-time applications. Ó 2015 Elsevier Ltd. All rights reserved. Introduction Increasing transmission capacities is always a difficult task. This is mainly due to environmental and political issues and the increasing difficulties involved in obtaining transmission rights of way. FACTS controllers (Flexible AC Transmission Systems) have been used as an alternative method to increase existing transmis- sion line transmission capacities [1,2]. The FACTS concept is very broad, and prominent FACTS devices include Phase-shifting Transformers (PSTs), Thyristor-controlled Series Capacitors (TCSCs), Static Var Compensators (SVCs), Static Synchronous Compensators (STATCOMs), Static Synchronous Series Compensators (SSSCs) and Unified Power Flow Controllers (UPFCs). UPFCs, which are a combination of SSSCs and STATCOMs, are arguably the most versatile and complete FACTS device [1,2]. FACTS provide many benefits for electric power system opera- tions. They enable the control of power flows and improve tran- sient and steady-state stability [1,2]. However, the use of FACTS can result in various issues, such as the misoperation of transmis- sion line distance protection relays [3], which constitute the main transmission line protection equipment [4–7]. The presence of FACTS devices introduces changes in transient and steady-state voltage and current signals that are not considered in current distance protection formulations. Thus, to provide a proper impedance estimation, the admittance added by the UPFC [3] should be considered. In an attempt to address these issues, the negative effects of using FACTS on transmission line distance protection systems are presented in [3,8–15]. A study of the SSSC effect on distance protection and an adap- tive protection methodology is presented in [11,16]. Similarly, [10,9] presents an adaptive methodology for distance protection in the presence of SVCs. In [15], the author presents an adaptive formulation to protect transmission lines compensated via STATCOM based on synchronized measurements. A study of the effects of UPFC on distance protection and novel adaptive distance protection methodologies is presented in [8,12–14]. All previously cited works were performed using symmetrical components. In these studies, new trip characteristics are gener- ated by searching all possible system operating conditions, FACTS device control conditions and fault resistances. None of them per- forms the fault resistance estimation. Furthermore, any change in operating conditions (such as different load conditions and differ- ent controlled reference parameters) or system parameters (such as changes in transmission line impedances) imply the need to generate new trip characteristics. The work in [15] is the only work that presents an adaptive tripping characteristic without the need to generate new trip characteristic for every change in system operating characteristics. However, this work only considers STATCOM’s compensation at the transmission line mid-point. http://dx.doi.org/10.1016/j.ijepes.2015.04.008 0142-0615/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Federal University of Pampa, Av. M. A. Gomes de Godoy 1650, Room 3125, Bagé, Brazil. E-mail address: martin.paz@ufrgs.br (M.C.R. Paz). Electrical Power and Energy Systems 73 (2015) 124–131 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes