Abstract:Aiming at an abnormal event of protection device caused by poor contact of isolation switch under 3/2 connection mode, the characteristics of contact temperature rise caused by the equal circuit under 3/2 connection mode, current distribution, the increase of contact resistance and line load are analyzed. The characteristics are compared with that of temperature rise caused by poor contact of isolation switch under double bus connection mode. The relationship and differences between contact temperature rise caused by poor contact of isolation switch and the change of load and preferred circuit resistance under 3/2 connection mode are obtained.