Abstract：Protection’s misoperation will be caused when line and transformer protection in normal operation cannot collect the bus voltage. It is one of the main reason that the abnormal auxiliary contact of disconnecting links in voltage switching circuit. This essay summarizes what causes the abnormality in voltage switching circuit by analyzing a case of line protection misoperation because the auxiliary contact is adhesive which is normally closed. For these causes, the hidden danger of improvement project now available has been raised. Then there are three improvement projects can effectively avoid the risk of protection’s voltage-loss has been designed and put forward, one of which can eliminate the danger is microcomputer-based voltage switching circuit and its specific realization logics are designed.
2016, Vol. 17 
