Improving supply security on 11-kV overhead network. The development of interconnected operation

The development of more intelligent relay equipment is being actively pursued. This, coupled with automated sectionalising and reclosing facilities, will permit normal interconnection of circuits with the ability to disconnect faulty sections and operate sound sections in a radial mode temporarily. Distance measuring protection relays, which have traditionally been applied to 132 kV and above networks, are becoming a reality at 33 kV and before long possibly at 11 kV. This would ensure clearance of faults within the accepted criteria for high speed protection, generally within 200 ms and certainly within 500 ms. Voltage restrain overcurrent relays which effectively grade on voltage as well as current are being examined. The author describes the development of such state of the art power network protection systems