how to troubleshoot 3 phase transformer?

To troubleshoot a three-phase transformer, start by checking for visible signs of damage or overheating. Use a multimeter to measure voltage across each phase and ensure they are balanced. Inspect connections for tightness and corrosion. Test insulation resistance with a megohmmeter to identify potential shorts. If the transformer is under load, monitor for unusual sounds or vibrations. Finally, analyze any protective relay settings and operation for faults.