High Voltage Series-Compensated Transmission Line - Evaluation of New Distance Protection Eugeniusz Rosolowski, Jan Izykowski Piotr Pierz Wroclaw University of Technology, Wroclaw, Poland eugeniusz.rosolowski@pwr.wroc.pl jan.izykowski@pwr.wroc.pl piotr.pierz@wp.pl Marek Fulczyk Przemyslaw Balcerek ABB Corporate Research Center Krakow, Poland marek.fulczyk@pl.abb.com przemyslaw.balcerek@pl.abb.com Murari Mohan Saha ABB AB Västerås, Sweden murari.saha@se.abb.com Abstract—This paper investigates a new distance protection principle for a transmission line compensated with 3-phase capacitor banks installed in the middle of the line. Series Capacitors (SCs) equipped with Metal-Oxide Varistors (MOVs), when set on a transmission line, create certain problems for its protective devices. Direct application of the classic distance protection (designed for traditional lines) to series-compensated lines results in considerable shortening of the first zone reach and also in poor transient behaviour. In order to overcome these difficulties the new distance protection principle for the first zone has been developed. The detailed model of considered transmission lines including the SCs&MOVs banks as well as the measurement channels has been developed. Using this model, the reliable fault data has been generated for evaluation of the new distance protection principle under variety of fault conditions. The study has shown considerable improvement of series-compensated line protection as a result of applying the developed new principle. I. INTRODUCTION The problems with protective relaying for series compensated lines are being extensively explored as a series of studies have been performed by relay vendors and utilities [3]–[7]. The new distance protection concept relies on determining the conditional impedances and comparing them with three characteristics specially shaped on the impedance plan by additional first zone logic module. For the considered transmission line one can distinguish the following conditional impedances: – impedance without compensation (Z), – impedance with compensation (Zc). The respective “compensated” impedance Zc is calculated from the fault loop quantities composed as for the classic distance relays, but with the compensation in case of the fault loop voltage. The compensation is performed for the voltage drop across the capacitor bank. For this purpose the instantaneous voltage drops across SCs&MOVs have to be estimated on the base of the parameters of SCs&MOVs and locally measured phase currents in Bus A. The distance relay algorithm based on differential equation method with rectangular differentiations and orthogonal components (by half-period Fourier filtration). Reconstruction of the waveform of the voltage drop across SC&MOV based on the fast on-line solving the nonlinear differential equation combined with multiplying sampling frequency technique At the final stage all methods realize the first zone logic for fault detection in serial compensated line with is detailed described in [11]. The brief characteristic of the basic idea, is as follows : • the algorithm estimates the voltage drops across series capacitors and MOVs (in all three phases) based on the currents at the relaying point by on-line solving an appropriate non-linear differential equation, • the relay compensates the phase voltages for the estimated voltage drops across SCs&MOVs, • two impedances are next calculated: the first one (Z) results from measured voltages and currents (no compensation), the second one (ZA) results from measured currents and compensated voltages (compensation), • location of the measured impedances is checked with respect to three specially shaped regions on the impedance plane and depending on the checking results and the trip permission from the impedance unit is sent, II. CALCULATION OF THE VOLTAGE DROPS ACROSS SCS&MOVS Let’s consider a parallel connection of series capacitor C and MOV as shown in Fig. 1. The v-i characteristic of the MOV is commonly approximated by the following exponential equation: q REF x MOV V v P i ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = (1) 978-1-4244-8286-3/10/$26.00 ©2010 IEEE 513