The development of an integrated protection and reclosing relay for rural feeders

The problems encountered in South African 11 kV rural power lines due to the nature of African electric storms is discussed by the author. The relay developed to overcome the problems (type GAD) offers two overcurrent inputs each of which incorporates low set and high set instantaneous elements for instantaneous tripping as well as IDMTL tripping, switch selectable to normal inverse, very inverse, extremely inverse and definite time lag. A separate earth fault input offers similar features to the overcurrent inputs. In addition, a sensitive earth fault element is provided. The author describes the features of this reclosing relay including: definite time on instantaneous elements; line check, status input sensitive earth fault, and busbar zone protection