the reasons for
transformer backup protection are：
（1） Short-circuit of high-voltage side of the
transformer（2） short circuit of low-voltage busbar of the
transformer （3） differential protection fails for there are fault in the differential protection range.
（4） Backup protection malfunction。
（5） the faults in the LV linesand the move of output protection cabinet cause the tripping operation for the
transformer is overloaded.
Treatment principle is：
（1） if the overload protection device find the phenomenons of voltage drop, shock, arc light, sound and son on, it should check the outside of the
transformer, and if the problem resolved at once, then it can commissionging operate, otherwise, it should be prepare to take security measurements: if there is no problem, it can also do the commissiong operate; to those
transformer without differential protection, it should also do the insulation test besides the outside inspection.
（2） If it is the LV outputting lines happen faults, and the line protection moves, it can manually remove the falut line switch, and then tranmiss the power to the
transformer.
（3） If the differential protection range happens fault and the differential protection failure, it should deal with according to the differential protection action.
（4） If it is the secondary circuit happens fault which belongs to the false function or mistouch, the person on duty should commissioning tranmiss the power.
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