Based on bus differential protection through the device BP-2A theory and practice at the scene, this paper analyses external bus fault caused the actual situation of bus link circuit breaker misoperation.

Research of busbar protection s logic on dead-zone fault of coupler;

The article introduces two arithmetic of partial differential,and analyses the method of using compare the current vector of coupler breaker,and provides sampling arithmetic and vector arithmetic.

Automatic switching malfunction of 2245 coupler due to upper power source loss of Guang an 220 kV substation was discussed.

This paper analyses problems existing in practice and corresponding improvement measures,points out the problem of adopting typical design for bus coupler malfunction protection when bus-bar or bus-coupler dead zone fault exists presently,and also enu.

This paper introduced the configuration of 220kV microprocessor-based bus protection of Hunan power grid,analyzed interrelation among bus differential,bus coupler malfunction and breaker malfunction protections,and enumerated the necessity and feasibility of canceling external starting loop in bus-coupler malfunction and the unattached voltage blocking device RCS-918A.