Transformer Fuse Blown | Step-by-Step Fault Diagnosis Guide

If the fuse element on the high-voltage side of the transformer blows or the circuit trips, the first step is to determine whether one phase, two phases, or all three phases are interrupted. This can be determined according to the fault symptoms as shown in the following table:

When a fuse element blows, first check whether the high-voltage side fuse or the lightning arrester gap has short-circuited to ground. If no abnormalities are found during external inspection, it can be concluded that an internal fault has occurred in the transformer. Carefully inspect the transformer for signs of smoke, oil leakage, or abnormal temperature.

Then, use a megohmmeter to test the insulation resistance between the high-voltage and low-voltage windings, as well as the insulation resistance of both the high-voltage and low-voltage windings to ground. Sometimes, an interlayer or turn-to-turn short circuit within the transformer windings can also cause the high-voltage side fuse to blow. If no defects are found when testing the turn-to-turn insulation resistance with a megohmmeter, use a bridge to measure the DC resistance of the windings for further diagnosis. After a comprehensive inspection, identify and rectify the fault, replace the fuse element with one of the same original specifications, and the transformer may then be returned to service.