Implementation of a digital distance relay using an interpolated integral solution of a differential equation

Low-frequency transient oscillatory voltages and currents have prompted the development of new distance protection schemes for UHV and EHV power lines with large stray capacitances. The authors describe a scheme that is based on a differential equation for the transmission lines. An integral method with an interpolation technique is applied using a very limited number of data at a sampling rate of 600 Hz. A prototype digital distance relay composed of two 16-bit microprocessors is developed. The characteristic test results correspond well to the results of fault simulations. The method is verified to have an accuracy of ±5% and require an operating time of less than 50 ms