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Common Faults in Distribution Transformers During Operation and Simple Repair Methods. Some of these issues are common to all transformers, while others occur only in high-capacity power transformers. This guide covers repairs for minor faults and the eight most common major faults. For more serious faults, professional repair companies with specialized tools and equipment are required. Be sure to identify the issue based on the actual circumstances.

Common Fault Symptoms and Causes in Distribution Transformer

1. Unusual Noises

(1) If the sound is loud and distorted, it may be a problem with the transformer core. For example, the clamps or screws securing the core may be loose.

(2) If the noise includes the sound of boiling water or a “gurgling” sound of escaping bubbles, it may indicate a serious fault in the windings, causing nearby components to overheat severely and resulting in the vaporization of oil. This sound can be caused by poor contact in the tap changer leading to severe localized overheating or an inter-turn short circuit in the transformer. In this case, the transformer should be shut down immediately for inspection and repair.

(3) If continuous, rhythmic knocking or grinding noises are heard, it may be caused by mechanical contact between certain transformer components due to core vibration, or by abnormal noises resulting from electrostatic discharge. Although these noises are unusual, they do not pose a significant risk to operation; therefore, it is not necessary to immediately shut down the transformer. They can be addressed during scheduled maintenance.

2. Abnormal Temperature

Under constant load, heat dissipation conditions, and ambient temperature, the dsitribution transformer’s temperature is higher than it was under the same conditions previously and shows a trend of continuing to rise. The causes of this abnormal temperature rise include:

① Short circuits between turns, between layers, or between strands in the transformer;

② Localized short circuits in the transformer core;

③ Heating of the oil tank, tank cover, and other components due to leakage flux or eddy currents;

④ Prolonged operation under overload conditions or accidental overloads;

⑤ Deterioration of cooling conditions, etc.

3. Line Surge Current

Line transients (also known as line disturbances) rank first among all factors that cause transformer failures. This category includes abnormal phenomena such as closing overvoltages, voltage spikes, and line faults.

4. Poor manufacturing processes

Loose or unsupported wire terminals, loose spacers, poor welds, poor core insulation, and insufficient short-circuit withstand strength.

5. Insulation Aging

A dsitribution transformer that has been operating for an extended period at a power level exceeding its rated capacity. This ultimately causes the transformer to operate under overload conditions, and the excessive heat leads to premature aging of the insulation. As the transformer’s insulating paper ages, its strength decreases. Consequently, the impact of an external fault may cause the insulation to break down, leading to a failure.