The existing problems in wiring schemes of current transformer（TA） used in microcomputer-based differential protection for main transformer in 110kV substation with internal bridge connection operated by Chengdu Power Supply Bureau are analyzed.According to the analysis

suggestions are proposed that connection of secondary current circuits of TA installed in the circuit breakers on each voltage side of transformers should be made separately to the corresponding terminals of the small TA installed in the transformer protection screen

unlike the connection where current addition is made by joining the lines at the terminals before connected with the small TA.The reason for such a change is that incorrect protection actuation may occur if TA saturates at the time of external fault.