Improved quality of supply in MV distribution networks using directional blocking scheme

Electricity distribution companies serving modern metropolitan areas and automated industries will come under increasing pressure to reduce the impact of short interruptions and voltage dips. This can only be achieved by using sectionalising circuit breakers and unit protected feeders. The present paper describes a trial scheme in Hong Kong which showed that directional blocking unit protection can deliver improved quality of supply. In the case of the Hon Kong Electric Company, it was possible to use available VF channels for signalling. However, the scheme could have universal application if the blocking signals are transmitted on the MV power line.