Transformers sometimes show signs of abnormal operation. The most common indicators are unusual sounds and high oil temperature. Recognizing these signs early helps prevent major failures. This guide explains different abnormal sounds, their possible causes, and what to do when the top oil temperature rises.

1. Normal vs. Abnormal Transformer Sound

When you energize a transformer, it produces a steady buzzing sound. This sound comes from the effect of high‑voltage magnetic flux. Under normal operation, the sound is uniform and consistent.

However, when you hear other noises, you must investigate the cause immediately.

2. Common Abnormal Sounds and Their Causes

2.1 Louder but Still Uniform Sound

If the transformer sound is louder than usual but remains uniform, consider these possible causes:

Cause	Explanation
Overvoltage in the grid	Single‑phase grounding or resonance overvoltage increases the sound level
Transformer overload	Heavy “hum” sound indicates load exceeding normal rating

Solution:

• Analyze the cause and make a record.
• Strengthen monitoring.
• If overload is the cause, reduce the load according to site regulations.
• Restore the transformer to normal operation as soon as possible.

2.2 Noise (Irregular Vibration Sound)

A noise that is not the usual hum often comes from loose parts inside the transformer. For example, an internal clamp or a screw pressing the iron core may have loosened. This increases vibration of the silicon steel sheets.

What to do:

• If the sound increases significantly but current and voltage remain normal, the issue is likely mechanical.
• Temporary action: If it does not affect operation, make a record, strengthen monitoring, and report to dispatch.
• Then, apply for a power outage to inspect and tighten the loose parts.

2.3 Discharge Sound (“Crackling”)

A crackling discharge sound is a serious warning. Observe where it comes from:

• Near bushings (visible blue corona or sparks at night/in rain) → Heavy dirt on porcelain parts or poor contact of equipment line cards.
• Inside the transformer → Electrostatic discharge of ungrounded components, inter‑turn discharge of the coil, or poor contact of the tap changer.

Solution:
Report immediately to the dispatcher and relevant leaders. Apply for a power outage to inspect the transformer.

2.4 Popping Sound

A popping sound often indicates internal or surface insulation breakdown. Therefore, you must stop the transformer immediately for inspection.

2.5 Water‑Boiling Sound

If you hear a sound like water boiling, and at the same time:

• The temperature changes sharply
• The oil level rises

Then, you should judge that the transformer winding is short‑circuited or the tap changer has poor contact causing severe overheating. Stop the transformer immediately and inspect it.

3. High Top Oil Temperature

During normal operation, you should regularly measure the top oil temperature. This temperature helps you control the winding temperature and prevents insulation aging.

When to Worry

Under normal load and normal cooling conditions, pay attention if:

• The top oil temperature is more than 10°C higher than usual
• The load remains unchanged but the oil temperature continues to rise

These signs point to internal faults such as:

• Core fire (local overheating)
• Short circuit between winding turns

⚠️ Action: Stop the transformer immediately to prevent the accident from expanding.

Why High Oil Temperature Matters

High oil temperature accelerates insulation aging. Once the insulation level drops, the transformer becomes vulnerable to further failures. Consequently, early detection and shutdown are critical.

4. Summary Table: Abnormal Sounds & Actions

Sound Type	Possible Cause	Immediate Action
Louder, uniform	Overvoltage or overload	Reduce load or monitor
Noise (vibration)	Loose internal parts	Record, monitor, then schedule outage
Crackling (discharge)	Dirty bushings or internal discharge	Report, apply for outage
Popping	Insulation breakdown	Stop immediately
Water boiling	Winding short or tap changer fault	Stop immediately

5. Preventive Measures

• Perform regular sound and temperature monitoring.
• Keep transformer bushings clean.
• Avoid prolonged overloads.
• Test transformer oil periodically.
• Schedule routine internal inspections.