Electrical transformer maintenance

Electrical transformer maintenance
Transformers Maintenance

Why transformer maintenance is required?

All equipment, machines, and devices need maintenance to work properly, extend their lifetime, reduce unplanned outages of service, and prevent unexpected faults. Electrical transformers are not an exception.

Transformer maintenance is important. It’s essential to perform an effective preventive maintenance (PM) program for electrical transformers. They are not free of maintenance but are low maintenance.

In my work as an electrical engineer, I realized that the transformer with no PM program is an accident in the location that when happens causes a huge miss for the organization. It can explode.

In this article let’s dive into the maintenance of electrical transformers and learn the expected faults if no maintenance program is followed correctly.

Transformers consist of many parts, Each part needs its PM. Hereunder are Statistics of failure in different parts.

Failure statistics of transformer parts
Failure statistics of transformer – Source IEEE C37.91-2000

Transformer Maintenance regular checks

transformer breather oil cap and silica gel
the transformer breather oil cap and silica gel

The following maintenance checklist should be periodically performed (weekly is fine).

  • The transformer oil level (in oil-immersed transformers) must be checked regularly to prevent dry working if the oil leakage occurs. The main job of oil used in transformers is cooling, No oil no cooling, then the excessive heat could burn the windings. Checking the oil level is done by the oil level gauge.
  • Breather silica gel color. If the color change that would mean it absorbed humidity and must be replaced. When replacing the silica gel always comply with the amount the manufacturer recommends.
  • Cooling fans and oil pumps check. Especially in hot areas and days. A common issue is that plastic bags come to the fans and prevent airflow. Check for damaged fan blades, And also make sure the blades are clean. Check fan rotation direction.
  • Oil leakage on and around the transformer body. If any oil is found, You must check its source and repair it. Usually, oil leakage commonly happens from joints and bolts.
  • Transformer temperature. Check the temperature gauge and record it. Don’t forget to check the maximum temperature red pointer.
  • Check the radiator for any bird’s nests. Its commonly make nests inside the radiator.

The following checklist needs longer intervals to be performed, Annually is fine:

11KV transformer bushings
11KV transformer bushings
  • Bushing cleaning and checking for cracks or broken parts. This can be done remotely with no direct contact and no power isolation is required. Cleaning while the transformer is energized is done using water. But must be done by an authorized and experienced team.
  • Oil sampling for lab tests and analysis. The oil analysis shows us a good picture of the transformer condition, possible faults, and undetected ones.
  • The pressure Release Device and Buchholz relay proper function must be checked annually.
  • CT secondary connections must be checked, and tightened.
  • Check the control panel of the cooling fans and pumps.
You can read my detailed articles about :

What to do if the transformer oil has water content?

The water in the transformer oil reduces its breakdown voltage. But if the oil has content water then oil filtration is the best choice to remove this water.

The filtration unit works while the transformer is in service. Oil filtering is an important process that eliminates dissolved water, dissolved gasses, and solid particles.

When to change transformer oil?

damaged silica gel by bad oil
damaged silica gel by bad oil

Transformer oil has usually long life in service. While in some cases it is recommended to change the transformer oil.

  • If a short circuit occurs inside the transformer i.e winding short circuit, In this case, the oil proprieties may change. Good oil analysis and lab tests tell us if it is still usable or not.
  • If oil is aged or oxidized, An economic assessment would be a good judgment to seize the opportunity to replace the oil.
  • If there is other work, for which the oil must be removed, to be carried out on the transformer, then replacing the oil with a reclaimed one will be a good choice.