Journal of ELECTRICAL ENGINEERING, VOL. 56, NO. 11-12, 2005, 313–321 RIPPLE CONTROL SIGNAL USING FOR EARTH FAULT LOCATION IN MV NETWORKS Petr Toman — Jaroslava Ors´ agov´ a * At present, digital protections using the admittance principle are able to identify quite reliably a single phase-to-ground connection and to determine the affected feeder. Still, the location of the fault presents a task yet to be solved. The main problem of a fault location consists is a low value of the fault current during a single phase-to-ground fault in compensated networks. This work started of an experiment performed in the second half of 2001. The experiment explored the possibility of identifying the fault location in a circular network by means of ripple-control signal. The work deals with a novel method for fault location that is able to determine the distance of a fault in a radial network (without possibility of circular interconnection) using only values measured in a switching station. The principle of this method was published in 2000 [1]. It presents the application of the method in a real distribution network and the evaluation of the results of this experiment. Keywords: single phase-to-earth faults, compensated network, location of faults, ripple-control signal 1 EARTH FAULT LOCATION IN CIRCLE NETWORK A connection between a phase conductor and the ground in MV networks is called an earth fault. Since the fault current in this case does not depend on the point of the fault, but only on the total capacity (size) of a network, the earth fault location keeps being a problem for MV network operators. This paper describes an ex- periment carried out in a MV network in order to verify the functionality of a method for earth fault location in a ringed network. 1.1 Introduction The experiment was based on the theory worked out by the Haefely-Trench company that was modified by using ripple control signal injection. Sections of the line (Fig. 1.1) marked a and b represent a MV line with an earth fault, section c represents a line that is ringed with the affected line and section d represents the rest of the non-affected part of the network. According to the calculations performed in the Matlab 5.2 program, the point of earth fault in a ringed network depends on the zero-sequence current ratio according to Fig. 1.2 (a line with AlFe 95 mm 2 conductors was used). Fig. 1.1. Elementary diagram of the method. Fig. 1.2. Zero-sequence current ratio I 01 /I 02 , ringed lines im- pedance Za/(Z b + Zc)=0.5 , ringed lines length 30 km; la = 10 km, l b = 10 km, lc = 10 km. Fig. 1.3. Simplified network scheme during measuring. 1.2 Measuring Measuring was performed during normal operation, with a fault simulated on a loaded line. Measuring was made in two steps. First, after earth fault, the affected and non- affected lines were ringed. Then a ripple control signal was injected into 110 kV network. ∗ Department of Electrical Power Engineering, Faculty of Electrical Engineering and Communication of Brno University of Technology, Technick´ a 2848/8, 616 00 Brno, Czech Republic, E-mail: toman@feec.vutbr.cz ISSN 1335-3632 c  2005 FEI STU