Effect of Series Capacitor Compensation on Distance Protection of Multi-Conductor Transmission Lines

No Thumbnail Available
Farouk Mohamed, Ahmed
Journal Title
Journal ISSN
Volume Title
The performance of standard distance relay schemes when applied on uncompensated long distance high voltage lines has been shown to be unsatisfactory. The urgent need for the change in the philosophy of distance when long uncompensated high voltage lines are evolved has been clearly pointed out. When a series capacitor is used to compensate for part of the line series reactance, in order to improve on the stability of the system and increase its carrying capacity it adds to the difficulties of protecting such lines. In this thesis the theory of Natural Modes has been used to investigate the, distance protection problems of series compensated long distance high voltage lines. A brief description of this theory is given in Chapter II. Digital computers are needed for obtaining numerical solutions. Due to the limited capacity of the digital computer at the Computer Centre at the University of Khartoum a symmetrical line model has been considered in order to obviate the limitations of the digital computer. The Ndal analysis is adopted in the analysis in the systematic building up of the .system model for any number of feeding points, number of series capacitor bank (s), location of series bank (s) and fault locations. A detailed description of the computer programme used to obtain the fault impedence loci for a series compensated line is given. The programme has been checked against results of previous work and these are fully illustrated. A detailed study of the fault impedence loci for a series compensated long distance high voltage line fed from one end has been carried out. The series capacitor has occupied two locations into this study, namely the sending end and centre of the' line. The apparent impedances seen by distance relays when no relay compensation, is being applied and those when different principles of relay compensation are applied have been presented. Also a trial has been made to obtain the multi-conductor effect using the eigen values and eigenvectors obtained for the symmetrical model with the asymmetrical impedance and admittance matrices of the untransposed line. The results obtained using this less accurate model are presented and compared with results presented else where. Then a detailed study for investigating the performance of a more realistic case of a series compensated long distance high voltage transmission 1ine fed from its two ends is presented. In 'this study the apparent impedance loci when the indifferent principles of relay compensation are applied are given. Here series compensation has either been concentrated in one bank or split into two identical banks. In the former case the series capacitor bank has occupied two positions along the line length, viz 1/3 line length from the sending end and centre of the line, in .the latter case the capacitor banks are situated 1/3 line 1ength from each end. The impedance loci seen by relays at the sending and receiving end are presented. Also the effect of varying the load angle on the fault impedance loci seen by relays at the two ends has been investigated and results obtained are also given. In a recent paper, Wedpohl, L.M. and Mohamed, S.E.T, .1970 'Apparent Impedances of Very Long Multi-Conductor Transmission Lines, it has been shown that resonance occurs at nearly one eighth wave-length in case of an unbalanced single line earth fault. In this study it has been shown that using series capacitor compensation results in an increase in the line length for which parallel resonance occurs. The practicability of distance type protective schemes is illustrated for lines with series compensation where the limitations of these schemes are made apparent.
Series ,Capacitor, Compensation, Distance Protection , Multi-Conductor, Transmission Lines