Optimising protection at the customer´s point of connection

This paper presents some simple guidelines for selecting the settings on the protective equipment at a customer´s point of connection (POC). The scenario considered is a customer on a radial supply from a network where time-current coordinated devices provide overcurrent and earth fault protection in both parties´ networks. A single line diagram of such a connection is shown in Fig. 1. It is assumed that the utility network is grounded is such a way as to provide a reasonable level of earth fault current. A case is made for the more widespread use of extremely inverse overcurrent protection characteristics in power supply networks. In this paper the electricity supply network operator is referred to as the utility.