CONSIDERATIONS ON COORDINATED PROTECTION BY CONNECTING DISTRIBUTED GENERATORS TO POWER SYSTEM

This paper describes considerations to protect substation system in power system by focusing on maintaining existing protection coordination scheme of the distribution system. Due to reverse power flow by increase of distributed generators in a distribution system, there are two important issues related to fault current to protect distribution system. One is to protect distribution system of the secondary side of a main transformer against fault applied to adjacent transmission system. The other is to preferentially trip the secondary side of the distribution system than a distant relay in transmission system against a fault applied to secondary side of the main transformer. The paper deals with those protection coordination issues and present a method to decide allowed penetration capacity of distribution generators in respect of keeping the protection coordination by time domain.