Method of synchronizing line differential protection device, and line differential protection device

摘要

A method of synchronizing a line differential protection device, the line differential protection device comprising a reference relay (2) and an adaptive relay (1). The method comprises the steps of continuously sampling the currents of all phases to obtain current samples; defining current indicators for all phases of an alternating current system (10) or indicators of a combined quantity formed from the phase currents in the reference relay (2) and the adaptive relay (1) based on each new current sample and the preceding M-1 or M/2-1 samples, M being the number of samples in a sequence at a nominal network frequency; monitoring the amplitude of a phase current of the alternating current system (10) or the amplitude of a combined quantity formed from the phase currents; storing the current indicators in both relays when said amplitude exceeds a predefined limit (I_st). The method further comprises the recurrent steps of transmitting the current indicators defined and stored by the reference relay (2) to the adaptive relay (1) and the current indicators defined and stored by the adaptive relay (1) to the reference relay (2); receiving and storing the received current indicators in both said relays (1, 2); defining a correction parameter (Δn) on the basis of the phase angle of the current indicators of the reference relay (2) and the adaptive relay (1) in the adaptive relay (1); storing indicators in the reference relay (2) at predefined intervals, counting forward a predefined number (N) of sampling intervals before storing new indicators; and storing indicators in the adaptive relay (1) at adaptive intervals, counting forward a number of sampling intervals corresponding to a sum of the predefined number (N) and the correction parameter (Δn) before storing new indicators.