What Causes Boiling or Popping in Transformers

Normal operating sound of a transformer. Although a transformer is static equipment, a slight, continuous "humming" sound can be heard during operation. This sound is an inherent characteristic of operating electrical equipment, commonly known as "noise." A uniform and continuous sound is considered normal; an uneven or intermittent noise is abnormal. Tools such as a stethoscope rod can assist in determining whether the transformer's sound is normal. The causes of this noise are as follows:

• Vibration of silicon steel laminations due to the magnetic field from the magnetizing current.

• Vibration caused by electromagnetic forces between core joints and laminations.

• Vibration resulting from electromagnetic forces between winding conductors or coils.

• Vibration caused by loose components attached to the transformer.

If the transformer's sound is louder than usual and uniform, possible reasons include:

• Overvoltage in the power network. When a single-phase-to-ground fault or resonant overvoltage occurs in the grid, the transformer noise increases. In such cases, comprehensive judgment should be made in conjunction with voltage meter readings.

• Transformer overload, which causes the transformer to emit a heavy "humming" sound.

• Abnormal sounds from the transformer. If the sound is louder than normal and contains obvious noise, but current and voltage show no significant abnormalities, it may be due to loose core clamps or tightening bolts, causing increased vibration of the silicon steel laminations.

• Discharge sounds from the transformer. If partial discharge occurs inside or on the surface of the transformer, cracking or "popping" sounds may be heard. In such cases, if blue corona or sparks are visible near the transformer bushings during nighttime or rainy weather, it indicates severe contamination of the porcelain components or poor contact at connection points. Internal discharge may result from electrostatic discharge of ungrounded components or poor contact in the tap changer. Further inspection or de-energization of the transformer is required.

• Boiling water sounds from the transformer. If the sound includes a boiling noise, accompanied by rapid temperature rise and rising oil level, it should be diagnosed as a short-circuit fault in the transformer windings or severe overheating due to poor contact in the tap changer. Immediate de-energization and inspection are necessary.

• Cracking or explosive sounds from the transformer. If the sound includes irregular cracking noises, it indicates insulation breakdown either inside or on the surface of the transformer. The transformer must be immediately de-energized and inspected.

• Impact or friction sounds from the transformer. If the transformer's sound contains continuous, rhythmic impact or friction noises, it could be caused by external component friction or external sources of high-order harmonics. Appropriate measures should be taken based on the specific situation.