How to Judge Burned Transformer Windings

It is crucial to accurately judge whether the transformer windings are burned for equipment maintenance and fault troubleshooting. The judgment can be carried out through visual inspection, smell identification, resistance measurement, insulation testing and operational abnormal phenomena.

Smell Judgment

If you smell a strong pungent burning odor of insulating paint and scorched wire near the transformer, it is a typical sign of winding burnout caused by overheating.

Visual Inspection

Observe the appearance of the transformer: check if the winding coil has discoloration, blackening, charring, melting of insulating layer, or bulging and cracking of the coil package; serious burnout will be accompanied by falling off of insulating material and exposed copper wire.

DC Resistance Measurement

Use a multimeter or DC resistance tester to measure the DC resistance of each phase winding. If the resistance value is obviously lower than the standard value, it indicates inter-turn short circuit of the winding; if the resistance is infinite, it means the winding is burned and open-circuited. The resistance difference between three-phase windings exceeding the specified range also proves winding damage.

Insulation Resistance Test

Measure the insulation resistance between windings and between winding and iron core/ground with an insulation megger. If the insulation value is far lower than the qualified standard or approaches zero, the insulation layer of the winding has been broken down and burned down.

Operating Abnormality Judgment

When the transformer is put into operation, phenomena such as abnormal loud buzzing, severe heating, sudden tripping of protection switch, smoke emission or even spark discharge all are comprehensive symptoms of burned windings.