I. Lead Wire Faults
Detection method: The three-phase DC resistance unbalance rate greatly exceeds 4% or one phase is completely open.
Troubleshooting: Lift the core for inspection, determine the fault location, and re-polish and tighten any poor contacts. Re-weld any poor welds. Increase the welding area if insufficient. Replace (enlarge) the lead wire if the cross-section is insufficient to meet requirements.
II. Tap Changer Faults
Detection method: Measure the DC resistance at different tap positions. If completely open, the switch is burnt out. If the DC resistance at a certain tap is unbalanced, individual contacts are burnt. A strong burnt odor indicates overheating or arcing.
Troubleshooting: Lift the core for inspection. If the switch contacts only show overheating, poor contact, or slight arcing marks, they can be disassembled for repair and reused. If severely burnt or if there is a discharge to ground between contacts, replace the switch. When discharge to ground occurs, it may cause deformation of the voltage regulation winding turns in the high-voltage coil. For severe cases, repair the coil or rewind (replace) it.
III. Coil Faults
Detection method: Coil faults often result in oil spillage from the conservator, tank bulging, and a burnt oil odor. Measure insulation resistance and DC resistance; insulation resistance may be "zero," and DC resistance increases and is unstable.
Troubleshooting: Lift the core for inspection to determine the fault condition. If damage is minor, repair and reuse. If severely damaged, consider replacing the coil. For poor sealing of the conservator, carry out technical improvements.
IV. Insulation Deterioration
Detection method: Regularly perform insulation resistance and oil tests on the transformer. If measured values vary significantly or fall below the requirements of the "Regulations," it can be determined that the transformer is damp or the oil insulation resistance has decreased.
Troubleshooting: If the transformer insulation resistance drops, thoroughly dry it. If oil insulation drops, replace or filter the oil. Repair any poor sealing of the transformer and faults in the moisture absorber.
V. Core Faults
Detection method: Measure the insulation resistance of the core bolts. If it is less than 10 megohms, repair is needed.
Troubleshooting: After lifting the core, remove the damaged core bolts and replace the insulation.
