Research on ´transient saturation´ of opto-couplers for microprocessor based protective relays

A particular problem with opto-couplers is found that high level, but short transients can couple into the base of the receiving phototransistor and cause its saturation. This transient saturation will effect the opto-coupler isolation and digital inputs´ validity. The solutions for opto-coupler transient saturation are put forward in this paper, which referred to hardware and software ways. These methods are effective and have practical application for microprocessor based protective relays.