ROUTINE OIL TRANSFORMER MAINTENANCE

We regularly get questions about transformer maintenance from our customers.

Do I need to regularly inspect my transformer?
How often should I perform maintenance?
Does maintenance look different for liquid-filled vs dry-type transformers?
Overall, transformers are incredibly reliable. Many customers hook up their transformers and leave them for decades without service. While technically possible, this is not recommended. It’s a good idea to develop a routine maintenance plan for your unit. If issues arise, this plan will help you find them before they become major problems.

A good maintenance program is like your yearly visit to the doctor. You may feel healthy, but it’s still a good idea. Some problems can be solved long before they become serious issues. If you wait till you’re sick and your symptoms are unbearable, it may be too late. It’s the same way with transformers. Some problems start small, and can easily be dealt with early on. If those problems persist, they may grow into something that ultimately fails the transformer.

Leading Causes of Transformer Failure

According to a study by Hartford Steam Boiler Inspection & Insurance Co., the two leading causes of transformer failure are insulation failure and design / manufacture errors. Insulation failures are usually caused by overloading/overheating, transformer aging, or catastrophic events. Both overheating and aging can be identified with a regular maintenance program. Design / manufacturing errors may be identified with initial testing. A maintenance plan can also catch some less obvious design issues before they cause bigger problems.

In this article, we will provide some routine maintenance tips.

Note: This article is not a replacement for a manufacturer’s instructions. Only use this article as a resource for general transformer maintenance.

Routine Oil-filled Transformer Maintenance

Perform annual inspections of oil-filled units. Some circumstances may require more frequent inspections. You will need to de-energize your transformer for certain sections of your maintenance plan. If you have site wide shut downs, try to schedule this maintenance at that time. Never perform maintenance on a transformer without the proper protective equipment. Ensure you follow all local and national safety standards such as OSHA and NFPA 70E.

After taking the proper safety precautions, check the following list during annual maintenance:

External visual inspection

Inspection comes before maintenance. From a safe distance, ensure the unit is operating properly while energized. Listen for loud or strange noises. Unusually loud humming may indicate overloading or overvoltage issues. Review the NEMA TR-1 standard sound levels. Sounds like electrical buzzing, zapping, or the sound of a weed wacker inside the transformer can indicate significant internal arcing. Look for any signs of external tampering, wear, or leaks. Minor weathering and wear is normal. If you do find an oil leak, de-energize the unit and address it. Prolonging repairs on a leak could lead to bigger problems later on.

Internal Inspection

After checking the outside of the unit, inspect the inside of the cabinet. This is especially important if you are energizing a transformer from storage. Before opening the cabinet, de-energize the transformer, and any connected cables or components. With the transformer off, visually inspect the high and low voltage bushings.

Inspect the seal around each gasketed component for leaks. Make sure all valves and devices are operating properly. Finally, make sure the enclosure’s hinges and locking system are free of corrosion and work well. This will help protect your cabinet from the elements, tampering, and other hazards.

Oil Sampling

Oil insulates and cools liquid-filled transformers. It works together with the paper in the windings to provide a transformer’s overall dielectric strength. Over time, both the paper and oil will break down and lose some of their insulating ability (dielectric strength). This breakdown can be witnessed through the generation of certain gasses in the oil. A Dissolved Gas Analysis (DGA) test measures the breakdown of such gasses. It is one of the most reliable ways to check the overall health of your transformer. A DGA can also indicate problems like overloading, catastrophic faults, loose internal connections, and moisture ingress. You should test your transformer’s oil every year by taking an oil sample.

DGA tests will show minimal gassing if the transformer is within its limits. For transformers with a high load, consider performing a DGA test every six months. Otherwise, an annual test is typical.

Gauge Readings

The temperature, pressure, and oil level gauges monitor internal pressure and fluid levels / temperature. Record the unit’s gauge readings. Take careful note of any abnormal values.

Check Liquid Level Gauge

Transformer oil, like all liquids, expands and contracts with temperature changes. Most liquid level gauges use a 25°C reference for standard conditions. It is normal for the gauge to read below the 25°C mark in colder climates. Under warmer temperatures, the gauge may read higher.

Check Pressure Vacuum Gauge

As the oil expands and contracts, the unit’s pressure will also fluctuate. With this in mind, compare the pressure gauge with the oil level and temperature gauge readings. The readings between all three should make sense. The ideal pressure reading under normal operation is between 2 and 5 psi.

Oil Temperature Gauge

The liquid temperature gauge displays the temperature of the fluid inside the tank. Ambient outside temperature and transformer loading influence the oil temperature. The red pointer on the temperature gauge is the maximum level indicator. It shows the historical high point of the gauge’s day-to-day movement.

Record what you observe on all three gauges and save the information. Over time you can prepare a trend analysis to better understand your transformer. If your transformer has abnormal gauge readings, consider all the factors at play. Check out our article for more information on how to read a transformer’s gauges.

The transformer manufacturing plant of CTC in Vietnam

CTC specializes in providing products such as Oil Transformer, Amorphous Transformer, Dry Transformer, Reactor Coil, and other electrical equipment. With 15 years of experience in the field of electricity and transformer manufacturing, we are confident that we can provide you with the optimal solution

– Information source: Maddox Transformer