Identification of Faulted Section in TCSC Transmission Line Based on DC Component Measurement Piotr Mazniewski Wroclaw University of Technology Wroclaw, Poland piotr.mazniewski@pwr.wroc.pl Abstract-«This paper presents an analysis of possibility of detection of a fault position with respect to the compensating bank in a series compensating transmission line. The algorithm designed for this purpose is based on determining the contents of dc components in the distance relay input currents. Fuzzy logic technique is applied for making the decision whether a fault is in front of the compensating bank or behind it. The delivered algorithm has been tested and evaluated with use of the fault data obtained from versatile ATP-EMTP simulations offaults in the test power network containing the 400 kV, 300 km transmission line, compensated with the aid of TCSC (Thyristor Controlled Series Capacitor) bank installed at mid-line. The results of the evaluation are reported and discussed. Index Terms-« ATP-EMTP, digital measurement, distance protective relay, fault simulation, fuzzy logic, power transmission line, TCSC. I. INTRODUCTION The concept of FACTS (Flexible Alternating Current Transmission Systems) was proposed by EPRI (Electric Power Research Institute) in the mid of 1980s. Since the rapid development of microprocessors, microelectronics, electronics and communications in recent years, it is possible to implement FACTS technology now. FACTS is referred to the application of power electronic equipment with one or more functions at certain location transmission systems to regulate and control the electrical parameters (such as voltage, impedance, phase angle, etc.) to realize more reliable, flexible and effective transmission systems [1]. Thyristor Controlled Series Capacitor (TCSC) is an important member of FACTS family and continuous changes of the transmission line impedance. Transmission line can be compensated by Fixed Series Capacitors (FSC) or more effectively by TCSC. It has great application potential in accurately regulating the power flow on a transmission line, damping inter-area power oscillations, mitigating subsynchronous resonance (SSR) and improving transient stability. However, the employment of series compensation creates certain problems for its protective relays and fault locators using conventional techniques because of the rapid changes introduced by the associated TCSC control actions in primary systems parameters such as line impedances and load currents [2]. The compensating bank affect both, the steady state and transient conditions of the distance relay measurements. Jan Izykowski Wroclaw University of Technology Wroclaw, Poland jan .izykowski@pwr.wroc.pl SY. TEMA A FA CTS A Fig. 1. Schematic diagram of series compensated line for considering distance protection: FA - fault in front of compensating banks, Fe - fault behind compensating banks. If a series compensated line suffers a fault behind the SCs as seen from the relaying point (fault F B in Fig. 1), a fault loop measured by a distance relay contains, depending on a type of fault, one (for single phase faults) or even two (for inter-phase faults) compensating banks. As a consequence, the operating conditions for protective relays become unfavourable and include such phenomena as voltage and/or current inversion, subharmonic oscillations, high frequency oscillations due to MOVs [4]. The most important singularity of a series compensated line as the object to be protected, lays, however, in the fact that the positive sequence impedance measured by a traditional distance relay is no longer an indicator of the distance to a fault. The aforementioned problems with protective relaying for series compensated lines are being extensively explored as a series of studies performed [5]-[10] . Protection of networks with series compensated lines is considered as one of the most difficult tasks. There is still much room for developing efficient protective relaying for such networks. The approach presented in this paper is one of the attempts for realizing that. II. TCSC MODEL AND STEADY STATE OPERATION The TCSC is composed of a series compensating capacitor in parallel thyristors controlled reactor (Fig. 2). The TCSC is constructed similar to the TSSC if the impedance of the reactor is significantly smaller than the impedance of capacitor. If this is the case the TCSC can be operated in a similar on/off manner as the TSSC [3]. The thyristor controlled series reactor operating at the fundamental system frequency behaves like a continuously variable reactive impedance, controllable by a delay angle a. 978-0-947649-44-9/09/$26.00 ©2009 IEEE