I. Lead Wire Faults
Detection Method: The three-phase DC resistance unbalance rate greatly exceeds 4%, or a certain phase is completely open.
Handling Method: The core should be lifted for inspection to determine the fault location. For poor contact, re-polish and tighten. For poor welding, re-weld. For insufficient welding area, increase it. For insufficient lead cross-section, replace (enlarge) it to meet requirements.
II. Tap Changer Faults
Detection Method: Measure the DC resistance of different taps. If completely open, it indicates the switch is burnt out. If the DC resistance of a certain tap is unbalanced, it indicates individual contacts are burnt. A strong burnt smell indicates overheating or arcing.
Handling Method: The core should be lifted for inspection. If the switch contacts only have overheating, poor contact, or slight arc marks, they can be disassembled for repair and reused. If severely burnt or there is a discharge between contacts and ground, replace the switch with a new one. When discharge to ground occurs, it may cause deformation of the voltage regulation winding turns in the high-voltage coil. For severe cases, the coil should be repaired or rewound (replaced).
III. Coil Faults
Detection Method: Coil faults usually result in oil conservator oil spillage, tank bulging, and a burnt oil smell. Measure insulation resistance and DC resistance. Insulation resistance is "zero", and DC resistance increases and is unstable.
Handling Method: Lift the core for inspection to determine the fault condition. If the damage is minor, repair and reuse. If the fault is severe, consider replacing the coil. For poor sealing of the oil conservator, technical renovation should be carried out.
IV. Insulation Deterioration
Detection Method: Regularly perform insulation resistance and oil tests on the transformer. If the measured values vary greatly or are lower than the requirements of the "Regulations", it can be determined that the transformer is damp or the oil insulation resistance has decreased.
Handling Method: If the transformer insulation resistance drops, it should be thoroughly dried. If the oil insulation resistance drops, the oil can be replaced or filtered. For poor sealing of the transformer and faults in the moisture absorber, repair should be carried out.
V. Core Faults
Detection Method: Measure the insulation resistance of the core clamping bolts. If it is less than 10 megohms, maintenance should be performed.
Handling Method: After lifting the core, remove the damaged clamping bolts and replace the insulation.
