Microprocessor based three step quadrilateral distance relay for the protection of EHV/UHV transmission lines

The development of a three-zone quadrilateral distance relay for the protection of EHV/UHV transmission lines is discussed. The proposed scheme is based on the Fourier transform method of extracting the fundamental components of voltage and current signals from nonsinusoidal post fault signals. The determination of the quadrilateral characteristic is completed through software. The relay is successfully tested for a number of different three-step quadrilateral characteristics. It is shown that any quadrilateral characteristic can be obtained. Recommendations are made on using 16 bit microprocessors to reduce the operating time and for better accuracy