Impact of abnormality of bus coupler TWJ on dead-zone protection of bus coupler

In the testing of bus protection,it is found that the dead-zone protection of coupler will fail to operate when bus coupler TWJ cannot act correctly for the reason of contact adherence or jam. By analyzing of the theory and logic diagram of dead-zone protection of coupler, it is presented that the cause of incorrect action of dead-zone protection of coupler is that the bus coupler current is not excluded from the differential bus protection correctly. A new method is proposed to avoid this defect by the leading-in of bus coupler HWJ, then the improved logic diagram is given and analyzed. The analysis results show that the practical engineering value of this method is great because the rejecting operation of dead-zone protection can be avoided and the operation time of protection can be shortened by using it.