Electrical transformer 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 regularly 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 changes that would mean it absorbs 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. It commonly makes 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 without direct contact and no required power isolation. 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.

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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, and dissolved gases.

If the transformer oil has water content, it can be a concerning issue as the presence of water can affect the performance and longevity of the transformer. Here are the steps you can take if the transformer oil has water content:

  1. Identify the source of water: Before taking any corrective measures, it’s crucial to identify the source of the water. The water can enter the transformer due to various reasons such as leakage, condensation, or improper sealing.

  2. Oil sampling and testing: Take a sample of the transformer oil to assess the extent of water content and to check for any other contaminants. Laboratory testing will help in determining the level of water content and its impact on the oil and the transformer.

  3. Drying the transformer: If the water content is not too high, you can consider using heating methods to remove the water. This process involves heating the transformer oil to a specific temperature to vaporize the water, followed by filtering the oil to remove any remaining impurities. This process should be performed cautiously to avoid any damage to the transformer.

  4. Identify and repair any leaks: If the water is entering due to a leak, it’s crucial to identify the location and repair it immediately. This might involve repairing gaskets, seals, or any other damaged components to prevent further water ingress.

  5. Replace the oil if necessary: In cases where the water content is too high or the oil has deteriorated significantly, it might be necessary to replace the transformer oil entirely. This should be done according to the manufacturer’s recommendations and using oil that meets the required specifications for the transformer.

  6. Regular maintenance and monitoring: Implement a regular maintenance and monitoring schedule to check the transformer oil for water content and other contaminants. Regular testing and preventive maintenance can help identify issues before they become severe and can extend the transformer’s life.

  7. Consult experts: If you’re unsure about the best course of action, it’s advisable to consult with experienced professionals or specialists in transformer maintenance and repair. They can provide guidance tailored to the specific circumstances of your transformer.

It’s essential to address the issue of water content in transformer oil promptly to prevent any potential damage to the transformer and to ensure its optimal performance and longevity.

s, and solid particles.

When to change transformer oil?

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

Transformer oil has usually a long life in service. 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.

Maintenance of transformer oil

Maintaining transformer oil is critical for ensuring the proper functioning and longevity of a transformer. Here are some essential steps for the maintenance of transformer oil:

  1. Regular sampling and testing: Regularly sample the transformer oil and conduct tests to analyze its quality. Key tests include dissolved gas analysis (DGA), acidity testing, interfacial tension testing, and dielectric strength testing. These tests help in identifying any potential issues and monitoring the condition of the oil.

  2. Filtration and dehydration: Implement regular filtration and dehydration processes to remove moisture, solid particles, and other contaminants from the transformer oil. This helps in maintaining the dielectric strength and overall quality of the oil.

  3. Temperature control: Ensure that the transformer operates within its specified temperature range. Excessive heat can degrade the quality of the oil and reduce its effectiveness, while very low temperatures can lead to moisture condensation. Maintaining the appropriate temperature range is essential for the longevity of the transformer oil.

  4. Preventive maintenance: Regularly inspect the transformer for any signs of leaks, corrosion, or other issues that may affect the oil. Implement a preventive maintenance schedule to address any potential problems before they escalate.

  5. Reclamation and regeneration: Consider reclamation or regeneration of the transformer oil to extend its lifespan. Reclamation involves removing impurities and restoring the oil to its original condition, while regeneration involves restoring the chemical properties of the oil through various processes.

  6. Use of suitable additives: Utilize appropriate additives to enhance the performance and longevity of the transformer oil. Additives such as antioxidants, inhibitors, and stabilizers can help in improving the oil’s resistance to oxidation and degradation.

  7. Storage and handling: Store and handle the transformer oil properly to prevent contamination and degradation. Ensure that the storage containers are clean, dry, and sealed tightly to avoid the entry of moisture and foreign particles.

  8. Compliance with standards and guidelines: Follow the guidelines and standards provided by relevant authorities and organizations for the maintenance and handling of transformer oil. Adhering to these standards ensures the safety and optimal performance of the transformer.

Regular and thorough maintenance of transformer oil is essential for preventing potential issues and ensuring the reliable operation of the transformer over its operational lifespan. Regular monitoring, timely testing, and adherence to best practices can significantly contribute to the longevity and efficiency of the transformer oil.

Transformer maintenance checklist

Certainly! Below is an example of a simple maintenance checklist table for a transformer:

Maintenance Checklist for Transformer
Item to Check Maintenance Task
Visual Inspection Check for physical damage, leaks, and overheating signs.
Electrical Testing Perform insulation resistance, turns ratio, power factor, and winding resistance tests.
Oil Analysis Conduct DGA, moisture content, acidity, and dielectric strength tests.
Cooling System Inspect and clean radiators, and fans, and check oil levels.
Mechanical Checks Verify connection tightness, inspect gaskets, and lubricate moving parts.
Conservator and Breather Inspect and replace silica gel if necessary.
Tap Changer Inspect for proper operation and perform necessary cleaning and adjustments.
Safety Measures Check safety devices, alarms, and grounding systems.
Documentation Maintain detailed records of all maintenance activities.
Compliance Ensure maintenance complies with relevant standards and regulations.

Feel free to customize this table according to the specific requirements and details of your transformer maintenance checklist.

dry type transformer maintenance checklist

For dry-type transformers, regular maintenance is essential to ensure optimal performance and longevity. Here’s a maintenance checklist tailored for dry-type transformers:

Dry-Type Transformer Maintenance Checklist
Item to Check Maintenance Task
Visual Inspection Check for any physical damage, corrosion, or contamination on the enclosure and components.
Cooling System Verify the proper functioning of fans, vents, or ducts. Clean or replace air filters if necessary.
Insulation Inspect insulation for signs of deterioration, cracking, or hot spots.
Connections Check and tighten all electrical connections, including terminals and bus bars.
Temperature Monitor temperature levels to ensure they are within acceptable operating ranges.
Airflow Ensure unrestricted airflow around the transformer to prevent overheating.
Environmental Conditions Evaluate the transformer’s location for factors like humidity, dust, and corrosive gases.
Dielectric Testing Perform regular insulation resistance and dielectric withstand tests.
Overload Capacity Verify that the transformer’s capacity matches the load requirements.
Sound Listen for any unusual or excessive noise during the operation.
Documentation Maintain detailed records of all maintenance activities and test results.
Compliance Ensure maintenance adheres to relevant industry standards and regulations.

This checklist provides a comprehensive guide for the maintenance of dry-type transformers. Adjustments may be necessary depending on specific transformer models, environmental conditions, and the manufacturer’s recommendations.

Regular inspections and adherence to maintenance schedules can help prevent potential issues and extend the transformer’s lifespan.