Setting Method of Overcurrent Protection for Extra-high Transmission Line with Opened Potential Transformer

Potential circuit open has very serious impact on line protection equipments.When a full or partial loss of AC potential circuits happens,most functions,like distance and directional function will be blocked.In order to operate reliably,for micro-processor based protection equipments,the overcurrent protection which is usually composed of phase current elements and zero-sequence current element,is put into service during AC potential circuit loss condition.Considering the practical protection scheme for 220 kV ～ 500 kV networks of Northwest China,with the analysis of all kinds of fault types,the paper draws the conclusion that overcurrent protection with opened TV is highly desirable to cooperate with pilot protection,and phase overcurrent element should be set less than the maximum load while zero-sequence current element should protect the whole line.