Research On A Distrubuted Digital Bus Protection System

This subject presents a new numerical distributed bus protection without the central unit. This protection consists of bay units which has the same hardware and software and is connected with computer communication in a sample circle. The bay units are monogamy with each electrical element connected with busbar in protection zone. The computer communication operates on optical fibre at only 375 bps when there are 18 bay units and the sampling frequency of the relay is 1200Hz . The synchronization sampling time of different bay units is less than 1 microsecond by means of special technology. The bus protection algorithms is based on a stabilised differential current algorithm and implementation of differential protection according to every sampled value . The influence of protection of CT saturation with fully offset fault current and its relation to stabilising factor for distributed bus protection are discussed in this paper. This busbar protection has high redundance. There are two relays using different CT winding with the same function in this protection . This protection can only trip when both two relays detect a fault in protection zone at the same time. One of the relays has two computer communication channels and another has one when this protection operates at dual bus and the relay uses as select element. In this subject , the theory of directional bus protection using for distributed way by means of digital line protection with a normal computer communication is discussed for the first time. In this case , there isn抰 influence of CT saturation for bus relay. It is benefit to distributed integrated substation automation system. The numerical distributed bus protection had been tested will be put into operation in a 220kV substation.