Current Transformer Troubleshooting: 6 Common Problems + Solutions

Current transformers (CTs) play a vital role in power systems, but they can experience various faults during operation. Understanding these common faults and their solutions can help you troubleshoot and resolve them promptly, ensuring safe and stable operation of your equipment. Below are six common faults and their solutions.

Fault 1: Secondary side open circuit (most dangerous)

Phenomenon:

• The ammeter and power meter indicate zero, and the energy meter does not rotate.
• The CT makes a “squeaking” discharge sound and even emits sparks.
• The terminal block may be burnt.

reason:

• The secondary circuit wiring is loose, the short-circuit switch is not closed, or the instrument load is too large (exceeding the CT capacity).

deal with:

1. Immediately disconnect the primary side load (e.g., by turning off the power).
2. Short-circuit the secondary side using an insulating tool (be sure to wear gloves!).
3. Check the wiring or replace damaged parts.

Fault 2: CT overheating (most common)

Phenomenon:

• The CT casing is obviously hot to the touch (over 70°C) and the temperature test wax sheet turns red.

reason:

• The coil screws are loose (contact resistance increases, causing heat).
• The secondary side load is too large (too many instruments are connected).
• The ambient temperature is too high (poor ventilation).

deal with:

1. Check if the wiring is loose.
2. Reduce the secondary side load.
3. Improve ventilation (such as installing a cooling fan).

Fault 3: Internal smoke/burning smell (most serious)

Phenomenon:

• If the CT body emits smoke and a pungent burning smell, it may be due to insulation aging or inter-turn short circuit.

reason:

• Long-term overload operation.
• The insulation material is damp (e.g. water seepage during rain).
• Excessive voltage breaks down the insulation.

deal with:

1. Immediately stop using CT.
2. Replace the device with a new one (internal insulation damage cannot be repaired).

Fault 4: Abnormal sound (be vigilant)

Phenomenon:

• The CT makes an abnormal “buzzing” sound (louder than normal operation) or a “crackling” discharge sound.

reason:

• The iron core is loose (vibrating and making sounds).
• The secondary side is open (discharge sound).
• The primary current fluctuates greatly (e.g. when a motor starts).

deal with:

1. Check the core fixing screws.
2. Check whether the secondary side is open circuit.
3. If the current fluctuation is normal, there is no need to worry.

Fault 5: Oil leakage from oil-filled CT (urgent treatment required)

Phenomenon:

• The oil level drops and oil seeps out from the seal. In severe cases, the oil level is below the minimum mark.

reason:

• The sealing rubber ring is aged, the oil pipe is broken, or the CT is hit.

deal with:

1. Immediately stop using CT.
2. Add oil (same type of insulating oil).
3. If the oil leakage is serious, it needs to be returned to the factory for repair.

Daily inspection focus:

• Check: Check whether the porcelain sleeve has any damage or discharge marks.
• Touch: Check whether the shell temperature is normal.
• Check: Check the oil level and whether the secondary side wiring is loose.
• Remember: Regularly calibrate the error (recommended once a year).

By following the above troubleshooting and troubleshooting guide, you can more effectively maintain your current transformer and ensure its safe and stable operation.