Digital distance relays

摘要

In a digital distance relay including sample-hold circuits for sampling the voltage and current of an electric power line system, analog-digital converters for converting the outputs of the sample-hold circuits into digital values, memory devices for memorizing the digital values and a program, and a central processing unit for exercising a relaying operation, there is provided a central processing unit which includes means for determining whether at least one of the digital values is greater than a predetermined value. The relaying operation of the distance relay is initiated only when the one digital value is greater than the predetermined value. A method is disclosed which includes the above determining step.