Simple phase-detection relay for distribution networks

For the detection of reverse power flow in medium-voltage networks, induction-disc-type relays are usually employed. This paper describes a simple phase-detection relay which is capable of indicating revers power flow in certain types of network. The relay described uses the characteristics of Zener diodes and is simple in design, cheap in cost and is capable of extensive application. The performance of a laboratory-prototype relay under steady-state and transient conditions is described. It is shown that the relay operates irrespective of the phases on which the fault occurs. A linear coupler from which the current signal can be derived helps to reduce unwanted transient effects.