When the third main transformer of 110 kV substation designed for three main transformers has not yet been put into operation

the low-voltage side of one main transformer often uses double branch connection to offer power. With the increase of load

the load current on 902 circuit-breaker on the double branch will reach a very high value

which will seriously threaten the safe and stable operation of 902 circuit-breaker. On the basis of choosing the best reconstruction scheme for the primary high voltage part

he reconstruction and setting schemes for the secondary relay protection is provided. The practical operation experience shows that the proposed scheme can be used as an effective solution before No. 3 main transformer being put into operation.