Key points for operation and maintenance of current transformers

Daily inspection and regular maintenance of current transformers can not only extend the service life, but also reduce the failure rate and improve customer trust. It can be operated from the following dimensions

1. Regular operation inspection content: simple and meticulous to avoid hidden dangers

1. Check the wiring status
Confirm whether the secondary wiring is firm and whether the terminals are loose or corroded

Check that there are no traces of sparks on the wiring row to avoid poor contact leading to measurement errors or protection failures

Ensure that the secondary circuit is not accidentally opened to avoid the transformer secondary high voltage from injuring people or burning

✅ It is recommended to check once every quarter or during the equipment inspection cycle, especially for CTs used in humid and dusty areas.

2. Check the fastening bolts and brackets
Carefully check whether the fixing bolts are loose

Whether the bracket and the mounting seat are deformed or rusted

Multiple CTs installed side by side should maintain uniform spacing to avoid stress concentration or offset affecting the measurement accuracy

✅ Regular tightening can prevent loosening caused by vibration or thermal expansion and contraction, especially in outdoor or mechanical vibration installation environments.

3. Surface cleaning and appearance inspection
Remove dust, water vapor or oil stains on the shell

Check whether the shell has cracks, leakage traces or foreign objects attached

Observe whether the nameplate information is clear to facilitate subsequent maintenance identification

✅ If the shell is found to be cracked or discolored, it should be replaced in time to prevent the insulation performance from deteriorating.

2. Special maintenance points for high-voltage current transformers
The oil-immersed or epoxy-cast transformers used in high-voltage systems have high working voltages and strict insulation requirements, and more stringent periodic maintenance is required.

1. Insulation resistance test
Use a megohmmeter (usually 2500V or 5000V) to regularly test the insulation of the primary and secondary windings to the ground

Compare historical data. If the value drops significantly, find out the cause and take preventive measures

✅ It is recommended to perform insulation tests 1~2 times a year, especially in the rainy season, cold winter or when the equipment is shut down for maintenance.

2. Check the oil level and oil quality (for oil-immersed CT)
Check whether the oil level is within the normal range of the window to avoid the insulation performance being reduced due to too low oil level

If conditions permit, regularly sample and check the oil quality to see if there is emulsification, discoloration or impurity accumulation

Check whether the oil tank seal is intact to prevent moisture absorption or oil leakage

✅ When the oil level is too low, add oil and find out the cause. If the seal is aged, replace the sealing gasket.

3. Confirmation of open circuit protection device
Check whether the transformer is equipped with secondary open circuit protection (such as shorting piece, automatic shorting device)

Confirm that the protection device is sensitive and reliable to avoid high voltage when the secondary circuit is accidentally disconnected during operation

III. Precautions for use in special environments
For transformers installed in special environments such as high altitude, strong corrosion, extreme cold, sand and dust, it is recommended to take the following additional maintenance measures:

Install a protective cover or insulating box to prevent moisture and particulate matter from intruding

Add a cable sheath to extend the life of the secondary cable

Increase the frequency of inspection, such as visual inspection once a month + comprehensive maintenance once every six months