High Speed Protection Scheme for Traction OHE of 25 kV AC Indian Railway System

This paper deals with study of thyristorized electric locomotives and its effect on conventional distance relays used for the protection of traction overhead equipment (OHE). In order to evaluate the impact of thyristorized locomotives on the performance of protective relays, the traction system is modeled using dynamic simulating software (PSCAD/EMTDC). Based on extensive simulations, it has been observed that thyristorized locomotives inject significant amount of current harmonics in the primary side. Moreover, change in drive frequency and steady state/dynamic conditions of motor significantly affect the performance of the conventional distance relays. Hence, an earth fault distance relay having quadrilateral characteristic can not ensure the desired selectivity due to various operating conditions of the traction system. In this paper, using powerful analyzing and decomposing feature of wavelet transform, a new high speed protection scheme which can overcome this disadvantage is proposed. Numerous computer simulation have been carried out on realistic data of Indian railways traction system and the results show that there is a high potential for developing high speed protection scheme for traction OHE.