Study on microprocessor-based adaptive protective relay for heavy duty electric traction system

In China, 3 or 2 zones´ distance relay and ΔI current increment relay are usually used as main and backup feeder protection of electric traction systems. This approach is successful in conventional electric traction systems. In order to eliminate the restriction caused by railway communication on development of national economy, heavy duty transportation is the main direction planned by the Ministry of Railways. Because of the complexity of power feeding manner, locomotive operating manner and fault type for heavy duty electric traction system (HDETS), conventional protection could not meet the demands for correctly operating. Mochinaga Yoshifumi and Hisamizu Yasuji (1993) found a method which uses the total harmonic distortion (THD) including the major harmonic frequencies of 3rd, 5th and 7th as a criterion. If THD is larger than 15%, the measured impedance of the distance relay is compared with a lower setting value, otherwise, it is compared with a higher value. Chen Xiaochuan et al. (1995) use THD for adjusting the boundary of distance relay. Weller, G.C. et al. (1989) proposed a conventional distance relay with a harmonically restrained overcurrent element used THD also. These papers have not entirely solved the problems of maloperation and rejecting operation. The purpose of this paper is to analyze the behavior of conventional protection used in HDETS and find a new algorithm suited to this system