An Incremental Quantity Based Protection with Capacitor Voltage Estimation for Mid-Line Series Compensation

Series capacitors are installed in transmission lines to increase power transfer capacity. However, their addition creates challenges for the line protection. Security and speed of phasor based protection schemes that work with local measurements (communication independent) are severely affected in the presence of series capacitors. Therefore, time-domain based protection methods may be considered as a potential solution for communication independent protection of series compensated lines. In this paper, an incremental quantity based protection scheme is presented for series compensated lines with the capacitor in the middle of the line. The method involves estimating the voltage across the capacitor bank, based on the current in the capacitor bank and metal oxide varistor during faults. Then this capacitor voltage estimation is used to implement the incremental quantity protection. The incremental quantity method consists of fault detection, phase selection, directional discrimination and distance estimation. A PSCAD model of a 500 kV, 200 km transmission line is used to simulate fault cases for evaluating the method. The proposed method is tested with different compensation levels, fault types, fault positions, inception angles, fault resistances and source impedance ratios. The results show that the proposed method can meet the dependability and security demands for the protection of series compensated lines.
QC 20220509