What Are Common Issues With Transformer Windings and How Can They Be Fixed?

Transformer windings do a lot of the heavy lifting inside a transformer. They carry current, transfer electrical energy, and work with the insulation system to keep the transformer operating safely. Because of that, when something goes wrong with a transformer winding, the problem can become serious pretty quickly.

Winding problems may come from short-circuit forces, overheating, insulation aging, moisture, manufacturing defects, or even rough handling during transportation. Some faults appear suddenly, while others develop slowly over years of operation.

The good news is that many winding problems can be detected before they turn into a major failure. Regular testing and practical transformer maintenance tips can make a big difference.

Common Transformer Winding Issues

A winding is exposed to electrical and mechanical stress every day. During a short circuit, however, the forces can become several times higher than under normal operating conditions. This is when existing weaknesses often show up.

Transformer Winding Deformation

Winding deformation is one of the more serious transformer issues, especially after a high-current short circuit.

Under normal conditions, electromagnetic forces inside a transformer are well controlled. During a fault, though, current can rise dramatically, and the resulting forces can push or pull the windings out of their original position.

A winding may move radially, shift axially, buckle, tilt, or become compressed. Sometimes the damage is obvious during an internal inspection. Other times, the transformer continues running and the problem only becomes apparent during electrical testing.

This is where things can get tricky.

A deformed winding may have smaller insulation clearances than originally designed. Conductors can move closer together, putting extra stress on the turn insulation and main insulation. Eventually, this can lead to an inter-turn short circuit or even a winding-to-ground fault.

After a major short-circuit event, it is therefore a good idea to check the transformer instead of simply assuming everything is fine.

Common diagnostic methods include winding resistance testing, turns ratio testing, frequency response analysis (FRA), and insulation testing.

Turn Insulation Failure and Inter-Turn Short Circuits

The insulation between individual turns is thin, but it has a very important job. If that insulation breaks down, two or more turns can become electrically connected when they should not be.

This is known as an inter-turn short circuit.

At first, the fault might involve only a small section of the winding. The transformer may still appear to operate normally, which can make the problem easy to overlook. But the shorted turns can carry a high circulating current and generate significant local heat.

That heat damages more insulation, which can make the original problem grow rapidly.

Winding insulation failure can be caused by long-term overheating, insulation aging, moisture, mechanical movement, partial discharge, excessive electrical stress, or physical damage.

The repair depends on what engineers find. If the damage is very localized, insulation or winding components may sometimes be repaired. If the conductor or insulation system has been badly damaged, rewinding is usually the safer option.

And there is one important rule here: fix the cause, not just the symptom. If overheating caused the insulation failure, the cooling or loading problem also needs to be addressed.

Main Insulation Breakdown

Transformer windings also rely on main insulation to separate the winding from the core, tank, other windings, and grounded components.

As insulation ages, its electrical and mechanical strength can decrease. Moisture makes matters worse, particularly in oil-immersed transformers. Contaminated or degraded insulating oil can also reduce the overall dielectric performance.

Winding deformation is another potential cause. If the winding moves after a short circuit, insulation distances may become smaller than intended. That creates additional electrical stress and increases the possibility of insulation breakdown.

Depending on the condition, repairs may involve transformer oil treatment, vacuum drying, replacing insulation components, repairing the winding, or completely rewinding the damaged section.

A severely damaged transformer winding should normally be handled by qualified transformer repair personnel rather than through a quick field fix.

Radial Instability of Transformer Windings

Radial instability describes unwanted movement of a winding toward the center or away from the center of the transformer.

This is closely related to short-circuit forces. When a large fault current flows through the windings, strong electromagnetic forces act on the conductors. If the mechanical structure is not strong enough, the winding can buckle or deform.

For example, an inner winding may be pushed inward, while an outer winding can be forced outward. Once the winding loses its original shape, its mechanical strength may also be reduced.

A second fault could then cause even more damage.

Repairing radial deformation depends on its severity. Minor movement may require detailed testing and inspection. More serious deformation can require internal disassembly, mechanical restoration, or winding repair. If the conductors are badly damaged, rewinding may be necessary.

From a design perspective, proper conductor support, spacers, clamping structures, and short-circuit calculations are essential.

Axial Instability of Transformer Windings

Axial instability is another common mechanical problem.

Instead of moving inward or outward, the winding moves along its vertical axis. During a short circuit, electromagnetic forces can push winding sections upward or downward. In some cases, winding sections may become compressed, stretched, tilted, or displaced.

Weak mechanical support, insufficient clamping, or loss of clamping pressure over time can increase the risk.

Axial movement is not just a mechanical issue. Once winding sections move, insulation barriers and clearances can also change. That can eventually contribute to winding insulation failure.

During an inspection, technicians may check winding height, end blocks, spacers, clamping pressure, and the position of the winding relative to other internal components.

The goal is not simply to tighten everything as much as possible. Too much clamping pressure can damage insulation too. The mechanical structure needs to be restored according to the transformer's original design requirements.

Winding Overheating: A Problem You Shouldn't Ignore

Not every winding problem starts with a dramatic short circuit.

Overheating is another common cause of winding deterioration. Transformers operating under heavy loads naturally produce more heat, but excessive temperature can also result from poor cooling, blocked radiators, fan or pump failures, high ambient temperatures, or harmonic currents.

Long-term overheating speeds up insulation aging. In oil-filled transformers, it can also accelerate oil deterioration and produce gases that may be detected through dissolved gas analysis (DGA).

When a transformer is running hotter than expected, check the load, cooling system, oil condition, ventilation, and temperature measurements. Reducing the load may help in the short term, but it is not a permanent solution if the underlying cooling problem remains.

How to Diagnose Transformer Winding Problems

Good maintenance is about finding problems early, not waiting for a transformer to fail.

Winding resistance testing can reveal differences between phases and may identify damaged conductors, loose connections, or other winding abnormalities.

Transformer turns ratio testing checks whether the actual turns ratio matches the expected value. Unexpected changes can indicate winding damage or tap changer problems.

Frequency response analysis (FRA) is particularly useful after a transformer has experienced a short circuit. Changes in the FRA signature can indicate movement or deformation of the winding and core assembly.

Insulation resistance and power factor tests can provide additional information about insulation condition. For oil-immersed transformers, DGA can also help identify overheating, arcing, and other internal problems.

No single test tells the whole story. In practice, engineers usually compare current results with factory test data, previous maintenance records, and other diagnostic results.

Practical Transformer Maintenance Tips

A few straightforward maintenance habits can prevent many winding problems.

First, keep transformer temperatures under control. Avoid unnecessary overloads and make sure fans, pumps, radiators, and ventilation systems are working properly.

Second, pay attention to insulation. For oil-immersed transformers, good oil quality and moisture control are especially important. Regular oil testing can reveal deterioration before it becomes a major problem.

Short-circuit protection also matters. Properly coordinated protection should clear external faults quickly. The longer a transformer is exposed to a high fault current, the greater the mechanical stress on its windings.

And after a major fault, don't skip the inspection just because the transformer is still operating. A winding can be mechanically damaged without showing an obvious external symptom.

Transportation and installation should not be overlooked either. Strong impacts during transportation can shift internal components, while improper installation can introduce additional mechanical stress.

When Should a Transformer Winding Be Repaired or Replaced?

There is no one-size-fits-all answer. The repair decision depends on the type and extent of damage.

The key is to understand why the winding failed in the first place. Replacing a damaged winding without correcting the original problem is asking for trouble.

For example, if repeated overload caused overheating, a new winding will eventually face the same conditions.

Final Thoughts

Transformer winding failures can range from minor insulation deterioration to serious mechanical deformation requiring a complete winding replacement. The main failure modes include turn insulation failure, main insulation breakdown, radial instability, and axial instability.

Short-circuit faults deserve particular attention because they can produce enormous mechanical forces inside the transformer. Even when the transformer keeps running afterward, hidden winding deformation may still be present.

That is why regular testing, proper cooling, insulation management, short-circuit protection, and timely inspections are so important.

In the real world, a little preventive maintenance goes a long way. By monitoring the transformer winding, checking unusual test results, and inspecting equipment after major faults, operators can often catch transformer issues before they become expensive failures.

For transformer owners, EPC contractors, and maintenance teams, the basic approach is simple: monitor, test, investigate, and repair the root cause. It is usually much cheaper-and much less stressful-than dealing with a failed transformer after the fact.

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