Research on Testing Method for Photoelectric-Isolated Digital Input in Protective Relayings
Zhi Quan-zhong · Power System Technology · 2010
At present the acquisition of digital input signal and isolation of input signal from external electromagnetic interference for protective relayings are generally implemented by photoelectric coupling.On the basis of analyzing the principle of photoelectric coupling devices and the digital input acquisition circuit for protective relayings,which is designed according to this principle,it is pointed out that the error of digital input signal is mainly caused by DC system grounding in secondary system as well as the charging and discharging of distributed capacity of long cable.Qualitative analysis on acquisition error of digital input signal caused by insulation level decline under special condition is performed.Finally,according to the differences of consequence,it is suggested to divide digital input signals into such categories as direct-trip of protection,logic start-up,position indication,signal and so on.An idea of classification and testing of digital input signals is proposed,in addition,corresponding testing scheme and quoted standards are given.