Adaptive distance protection of double-circuit lines based on differential equation fault loop model Marcin Bozek Wroclaw University of Technology Wybrzeze Wyspianskiego 27 50-370 Wroclaw, Poland Jan Izykowski Wroclaw University of Technology Wybrzeze Wyspianskiego 27 50-370 Wroclaw, Poland Abstract – The paper presents an adaptive procedure for digital distance protection device that allows to compensate for the negative influence of the reactance effect, caused by fault resistance and pre-fault power flow. The procedure utilizes locally measured phase currents and voltages and has been designed to operate with double-circuit power lines. The algorithm calculates on-line shift vector components that allow to change the position of relay operating characteristics. As a result, it is possible to avoid mis- or maloperation of the distance relay. Evaluation of the algorithm has been performed with use of voltage and current signals obtained from versatile simulations in ATP-EMTP. I. INTRODUCTION Power system protection has always been and still is a vital topic, due to still increasing demands concerning dependability and reliability of power transfer. Since power system elements are interconnected, a single disturbance that occurs at particular point, may affect other parts of the system and cause equipment damage as well as deprive consumers of electrical energy. Such failures, covering up large areas and known as blackouts, have taken place recently and in most cases have been caused by mis- or maloperation of protection devices. That is why developments in protection devices area are of such importance [2]. Since overhead power lines are most prone to faults and other disturbances that are difficult to predict, it is necessary to provide these lines with protection devices that would operate in a reliable and fast way. It is worth mentioning, that operation of every protection device protecting power line may be interfered by many unpredictable factors. In case of widely used distance protection devices, operation principle of the relay is simple and is based on comparison of the measured impedance with tripping characteristics. The operation of the relay depends strongly on the shape of the relay characteristics, which is in most cases adjusted strictly to the system operation conditions that occur in the place, where the relay is located. Since line load may vary and short overloads are allowed, the characteristics have to take into account all possible conditions that are acknowledged as normal and also distinguish all disturbances. Unfortunately, there are many factors that affect measured impedance, such as mutual coupling in case of parallel lines, power swings and fault resistance. This work presents an algorithm that allows to compensate for the negative influence of the reactance effect. Complete availability of signals (phase currents and voltages from the faulted line and phase currents from the sound line) has been considered in this algorithm (Fig. 1). Rel AB AA BA BB Z LB F SA E SA Z AA V AA I AB I L Z d L Z –d) ( 1 SB Z SB E Fig. 1. Schematic diagram of a double-circuit transmission line with equivalent sources and complete availability of signals. II. REACTANCE EFFECT The reactance effect may be observed in case of non-solid faults, i. e. when there is an additional resistance of unknown value in the fault circuit. In that case one may notice, that both resistance and reactance are measured with an additional error that comes from the combination of fault resistance and power flow [3], [5]. Two examples of negative influence of the reactance effect (depending on power flow direction) are shown in Fig. 2a, b. Fig. 2a, b depicts also the shift vector (ΔZ), which derivation is further presented. Fig. 3 and Fig. 4 present resistance and reactance measured by the relay. One may notice that there is a certain error in measurement (both resistance and reactance). BB F AA X AA_P R AA_P L Z d 1 AA_P Z Z Δ Fig. 2a. Example of reactance effect in case of power flow from station BB to station AA.