Research Journal of Applied Sciences, Engineering and Technology 4(23): 5123-5128, 2012 ISSN: 2040-7467 © Maxwell Scientific Organization, 2012 Submitted: April 04, 2012 Accepted: April 25, 2012 Published: December 01, 2012 Corresponding Author: Hamid Radmanesh, Hamid Radmanesh, Electrical Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran, Tel.: (+98-21) 64543335, Fax: (+98-21) 88212072 5123 Improving Transient Recovery voltage of circuit breaker using Fault Current Limiter 1 Amir Heidary, 2, 3 Hamid Radmanesh, 2 Seyed Hamid Fathi and 1 Hamid Reza Rajabi Khamse 1 Electrical Engineering Department, Islamic Azad University, Zanjan Branch, Zanjan, Iran 2 Electrical Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran 3 Electrical Engineering Department, Islamic Azad University, Takestan Branch, Takestan, Ghazvin, Iran Abstract: This study investigates influence of Fault Current Limiter (FCL) on short-circuits current level of substation bus bar splitter circuit breaker and its TRV. An approach for TRV evaluation is developed and applied for proposed power system as shown in this study. FCL circuit is connected to the power system in order to limit TRV. The limiter circuit consists of two equal windings which are turned around unique magnetic core. One of the windings is connected in series with the power system network and the other is connected to the network via series capacitor and power electronic switches. During normal operating condition, both tyristors are in on state and current of the primary and secondary windings are equal. This causes zero impedance of the limiter. During fault, faults current cause the power electronic switch to turn off which increases the limiter impedance. By increasing the limiter impedance, amplitude of TRV decreases substantially. The novel method presented in this study is a cheap and successful scheme. Keywords: Circuit breaker, fault current limiter, transient recovery voltage INTRODUCTION Transient Recovery Voltage (TRV) represents the transient voltage appearing across the terminals of circuit breakers, following fault currents interruption. The circuit breaker interruption capability is limited by both the fault current and the TRV levels. TRV waveform depends on various factors as: the fault position (Terminal, Short-line or Transformer faults), the fault type (3LG, 2LG or 1LG fault), the parameters of the lines connected to the faulted bus-bars as (IEC56, 1992) define standard envelopes based on the requirements concerning TRV main parameters (Rate-of-Rise and Peak Value). If TRV waveform exceeds the standard envelope, the breaker may fail to interrupt the current, as high values of the Rate-of- Rise or the Peak Value may lead to thermal or dielectric failure in the breaker quenching chamber. In this study an approach for TRV computation is developed and the efficiency of different fault current limiting means (as substation bus-bars splitting) is evaluated from TRV point of view. Then, new suggested FCL is used for decreasing the amplitude of the occurred TRV. Although Circuit Breakers (CBs) in electric power systems are used to switch on and off the continuous load current under normal operation conditions, they are primary designed to break the short circuit current in case a fault occurs. In order to successfully break the current, the CB has to withstand the transient recovery voltage that arises across its terminals when the previous arc column rapidly loses conductivity after current zero. Besides the magnitude of the fault current itself, the TRV waveform is the most significant information needed for choosing the appropriate CB for a given application. In particular, the Rate-of-Rise-of-Recovery-Voltage (RRRV) is the essential parameter. Although manufacturers know the RRRV capability of their switchgear, customers often only have inadequate data about the TRV assigned with their particular application. Especially, the TRV waveform associated with power transformer secondary terminal faults is seldom known by the user with the necessary accuracy. On the other hand, transformers in electric systems are one of the most costly apparatus. To illustrate a typical situation of interest, Fig. 1 shows an equivalent circuit of the power system at an ungrounded phase-to-phase fault. As a worst case, the TRV across the first pole-to-clear of a three-phase CB clearing a terminal fault current is essentially determined by the transformer alone (Harner, 1968). Therefore, the source side is represented by three ideal single-phase voltage sources connected directly to the primary side (inputs). Because of the wye-delta configuration chosen for this example, the neutral of the source side is connected to the neutral bushing of the transformer and to the tank, both connected to ground. Harner and Rodriguez (1972) published a study on TRV associated with transformer secondary faults (Harner and Rodriguez, 1972). They measured the