Dry Type Transformer Repair and Maintenance: A Guide

May 31, 2024

Prompt: Generate a landscape image of a dry-type transformer

Image generated by DALL-E

Transformers are crucial for regulating the voltage in electrical appliances. They adjust it up or down as needed. They are available in different shapes and sizes and are suitable for residential and commercial use. Dry-type transformers are among the most popular in the commercial and industrial sectors.

Any business using heavy equipment and machinery depends on transformer manufacturers to deliver goods at a steady pace. Transformers help regulate voltage fluctuations and handle the massive energy load.

But why dry-type transformers, and how much maintenance do they require? This guide will walk you through basic information on dry transformers and how to maintain them for optimal performance.

What is a dry-type transformer?

Unlike a traditional transformer, a dry transformer does not contain any liquid like oil for insulation. It is a stationary solid device that works independently and uses resin or air to insulate its windings (wire coils) rather than a liquid.

Dry transformers are typically encased in a ventilated enclosure to allow air to flow freely. This keeps the entire transformer air-cooled, reducing any chance of overheating or causing fire damage.

This design makes them lighter, safer for indoor use, and less susceptible to fire hazards. Dry-type transformers are environmentally friendly and use high-temperature insulation systems for operations.

Moreover, they provide consistent power without the need for fire-resistant vaults. Therefore, they are ideal for use in buildings where fire safety is necessary, such as chemical industries, schools, hospitals, and factories.

Why is maintenance necessary?

Regular maintenance extends the lifespan of your dry-type transformer, minimizing the risk of breakdowns and ensuring consistent power delivery. By implementing the following maintenance measures, you can effectively achieve these objectives:

  • Prevent overheating: Dust buildup on windings and blocked ventilation can inhibit heat dissipation over time, causing the transformer to overheat and sustain significant damage. Therefore, regular cleaning and inspection of these components are essential to prevent heat-related issues.
  • Insulation integrity maintenance: Environmental elements such as moisture and dust can gradually degrade the transformer's insulating materials, increasing the risk of electrical faults. To maintain insulation integrity, it is important to regularly assess the condition of insulation and take necessary measures to protect it from external factors.
  • Early issue detection: Regular inspections and testing can uncover minor problems, such as loose connections, worn-out components, or abnormal heating before they escalate into costly repairs or replacements. By identifying these issues early on, you can address them proactively, ensuring your transformer's optimal performance and longevity.

Safe Maintenance Practices

Remember to keep your dry-type transformer in good shape with regular service and inspections. Use this handy checklist to save time and money on unnecessary repairs while ensuring your equipment runs smoothly. By staying on top of maintenance, you'll be able to catch any issues before they become big problems.

To keep yourself safe, always make sure the transformer is completely turned off and disconnected before doing any maintenance. You should also wear special protective gear when turning off the transformer, but you can take it off once everything is safely turned off and grounded.

Ensure there's enough airflow around the transformer and remove anything blocking it. Also, check for dust or dirt on the transformer and clean it off when the unit is de-energized. If your transformer is in a dusty area, you'll need to inspect it every three to six months, but if it's in a clean space, once a year should be enough.

To learn more about maintaining and testing dry-type transformers, check out the standards and requirements in the National Electric Code (Article 450) and the IEEE Standard Test Code (C57.12.91-2020).

Maintain a temperature log

You must regularly check and note down the temperature of the transformer when it's working at its usual capacity. Then, compare this reading with previous records. Ideally, all three coils for a three-phase dry type of transformer should be around the same temperature when working at full capacity.

Suppose there's a big difference in temperature between the different parts, or the temperature keeps going up even when the transformer is working at the same level. It could mean there's a problem with how the transformer is being cooled, or there might be an issue with the transformer itself.

Inspect visually

An air-cooled transformer needs regular visual inspections. How often depends on how frequently the transformer is used. If used 24 hours a day, seven days a week, it will require more frequent inspections than one that operates only for eight hours daily.

Maintenance should be scheduled during an average shut-down period since the transformer needs to be de-energized for inspection and cleaning. Keep a log of everything you observe and any maintenance done on the machine. It is unnecessary to touch any part of the transformer during the inspection.

Check if there is enough space around the transformer for proper ventilation. Remove anything around it that might block airflow. Do not use the transformer room to store anything else.

Open the enclosure and look for the dust or dirt accumulating on the transformer's surfaces. Suppose you see a significant amount of either. In that case, you will likely need to inspect the transformer more frequently, say, every three months. At any rate, clean the dust and dirt off once you have disconnected the unit from any power source.

Finally, note any noticeable discoloration of the windings or other signs that the unit had overheated at some point. Document it with a photo and show it to the plant engineer.

Clean the unit

When cleaning the transformer, minimize physical contact even if the unit has been de-energized, locked out, and grounded for safety reasons. Use a vacuum or compressed air to remove dirt or dust from the windings and cooling fans.

Avoid directly touching the components. Start by vacuuming the parts, then spray them with dry compressed air at no more than 20 to 25 psi. Do not use chemical cleaners on the unit's surfaces.

Inspect all de-energized electrical connections, tighten accessible hardware, and replace loose insulation or parts. That keeps screws and nuts from working loose during regular operation.

Inspection Checklist

When cleaning the transformer, look for rust on the core steel and clamps. Also, note any carbonization or tracking on the insulation and windings. Examine the windings and surfaces closely for discoloration, which could indicate overheating or a loose connection.

Inspect insulators and electrical connections for cracks, discoloration, corrosion, pits, or looseness. Tighten or replace any hardware components. Contacting a professional to evaluate and repair the transformer may be necessary.

Finally, inspect fans, motors, and other auxiliary devices for proper operation. Document and report all abnormal or suspicious conditions to the plant engineer or facilities manager. They will determine if additional testing or service is needed before re-energizing the unit.

Tests During Routine Maintenance

Remember to regularly check, clean, and test the transformer as part of its upkeep. These tests are essential if you notice any discoloration, burnt marks, or other signs of overheating or electrical issues. They help ensure that the transformer is working well and can catch any problems that might not be obvious. Any test that shows an issue means your transformer needs to be checked and fixed before being used again.

It's crucial to do these tests when the transformer is not connected to power. For safety and accuracy, only a qualified engineer wearing protective gear and using the right testing equipment should perform these tests.

Transformer Turns Ratio (TTR)

A Transformer Turns Ratio (TTR) test checks if a transformer's primary and secondary voltage ratios match the expected values. This helps ensure the transformer's windings and core are in good condition. The test aims for the ratios to be within 0.5 percent of the specified values.

Insulation Resistance (IR)

The Insulation Resistance test checks how well the insulation between the wires wrapped around the transformer holds up. Each transformer has a minimum resistance level that needs to be met. If the test shows lower resistance, it could mean the insulation is wearing out, which indicates that the transformer might fail soon.

Winding Resistance (WR)

When checking the coil windings for each voltage setting, ensure the resistance is close to the value tested at the factory or during the most recent test, within about one percent. The typical insulation and winding resistance levels are in the documentation that came with your transformer.

Other tests

Some diagnostic tests require special equipment and facilities and should be performed by experienced professional engineers.

A reputable manufacturer typically includes a certificate detailing the results of the tests they perform on every new dry-type transformer with the unit. Contact the manufacturer if you need advice on diagnostic testing or have questions about your dry-type transformer's test performance.

Maintenance Keeps the Juice Flowing

Ensuring the reliability and safety of your dry-type transformer is crucial. To maintain the integrity of your equipment, have experienced engineers carry out specialized diagnostic tests. Relying on reputable dry-type transformer manufacturers for certification and guidance is also an excellent idea.

If ever in doubt or need further assistance, do not hesitate to contact the manufacturer. They are equipped to provide the necessary support and advice to guarantee the optimal performance of your unit. Remember, maintaining open communication with your manufacturer is critical to addressing any concerns and securing the longevity of your transformer.


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