Common Fault Handling for Current and Voltage Transformers

2025-03-29

Common Fault Handling for Voltage Transformers

Voltage Transformer Primary Fuse Blown

Symptoms:

Phase-to-phase voltage decreases or drops to nearly zero, while unaffected phases remain unchanged or slightly decrease. Line voltage may drop when switching faulty phases.
Power meters and reactive power meters show reduced readings, and energy meters slow down.
A “Voltage Circuit Break” signal is triggered, and fault recorders may activate.

Handling:

Shut down the voltage transformer.
Measure and replace the blown fuse with a spare. If the new fuse blows twice in succession, further replacement is prohibited.
Check whether the fuse holder’s spring clip has loosened after installing the high-voltage fuse.

Symptoms:

Overheating of the transformer body.
Discharge sounds or unusual noises from the interior.
Secondary switches cannot be turned on.
Secondary voltage may increase or decrease, and grounding signals may be triggered.
Frequent fuse blowing due to internal insulation damage or inter-turn faults.

Handling:

Report to the shift supervisor and power down for repair.
If the transformer catches fire, disconnect the bus power supply immediately and extinguish the fire using a dry extinguisher or sand.

Symptoms:

Buzzing sounds from the CT body; in severe cases, it may emit smoke or catch fire.
Sparking discharge at the open circuit point.
Inconsistent readings on three-phase current meters, power meters showing reduced readings, or slow/non-rotating energy meters.
Differential disconnect warning lights activate.

Handling:

Identify the faulty circuit and its impact on protection. Report to the dispatcher and disable affected protections.
Minimize primary current load to reduce secondary circuit voltage. Operate on an insulating mat with insulated gloves and tools.
Short-circuit the secondary terminals near the CT using a high-quality jumper, then locate and fix the open circuit point.
For internal open circuits, power down the system for repairs.

If the cable shield grounding point is behind the zero-sequence CT, reverse the shield line through the CT and ground it.

Measure the DC resistance of primary and secondary windings to detect defects like conductor breakage, poor connections, or short circuits.
Perform ratio testing to ensure accurate primary-to-secondary relationships and relay protection settings.
Conduct polarity tests to avoid wiring errors, along with excitation characteristic tests for safety factor verification.
Measure insulation resistance and perform AC withstand voltage tests to identify and address issues like moisture, contamination, and insulation aging.