Transformer operating abnormality can manifest in many ways: unusual sounds, high oil temperature, abnormal oil color, improper oil level, overload, cooling system failure, gas protection action, and local overheating. Recognizing these signs of transformer operating abnormality early helps you prevent major failures. This guide explains each abnormal condition, its possible causes, and the actions you must take.

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1. Abnormal Transformer Sounds

When you energize a transformer, you hear a steady buzzing sound. This sound comes from the effect of high‑voltage magnetic flux. Under normal operation, the sound is uniform. However, when you hear other noises, you should suspect a transformer operating abnormality.

1.1 Noise (Irregular Vibration)

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.

1.2 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.

1.3 Popping Sound

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

1.4 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.

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2. 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. A persistent high top oil temperature is another classic transformer operating abnormality.

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.

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3. Abnormal Oil Color

Normally, transformer oil should be bright yellow and transparent. If you notice a color change in the oil level gauge during operation, contact a lab to take oil samples for analysis.

Critical situation: If the oil color suddenly deteriorates and you see carbon particles or other abnormal phenomena, cut off the power immediately for inspection and treatment.

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4. Abnormal Oil Level

The transformer oil pillow (conservator) has an oil level gauge. It typically shows three marking lines for temperatures of -30°C, +20°C, and +40°C. Use these lines to decide whether to add or drain oil.

4.1 High Oil Level

If the oil level is too high or oil overflows from the oil pillow:

• First, check whether the load and temperature are normal.
• Check for false oil level caused by a clogged breather pipe.
• Action: With the dispatcher‘s consent, change gas (heavy gas) protection to signal mode. Then, clear the breather. If overflow is due to high ambient temperature, drain some oil.

4.2 Low Oil Level

If the oil level is too low:

• Light gas protection may activate.
• When the oil level drops severely, the core and windings become exposed to air. This risks moisture absorption and insulation breakdown.

Action: Use vacuum oil injection to refill the transformer while it is in operation. If the oil level drops rapidly due to a large leak (below the gas relay or continuing to drop), stop the transformer immediately.

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5. Overload Operation

When a transformer operates in overload, you may see:

• Ammeter indication exceeding the stable value
• Signals or alarm bells activating

Handling Principles

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Step	Action
1	Check whether current on each side exceeds the specified value. Report to the duty officer.
2	Check oil level and oil temperature. Put all coolers into operation.
3	Adjust operation mode. If a spare transformer exists, put it online.
4	Contact dispatch to adjust load distribution.
5	For normal overload, determine allowable time based on overload multiple. Monitor oil level and temperature closely. Do not exceed limits. If time exceeded, reduce load immediately.
6	For emergency overload, follow manufacturer‘s allowable multiple and time. If exceeded, reduce load accordingly.
7	Conduct a comprehensive inspection of the transformer and related systems. Report any abnormality.

6. Cooling System Failure

When the cooling system (submersible oil pump, cooling water system, etc.) fails and the transformer sends a standby switch or cooler full stop signal:

1. Immediately check whether the standby cooler has started.
2. Identify the cause of power outage and restore cooling as soon as possible.
3. Strengthen monitoring of top oil temperature and oil level, especially during the full stop period.
4. If the cooling system cannot be restored quickly, apply to reduce load or withdraw the transformer from operation. This prevents overheating damage beyond the specified no‑cooling time.

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7. Gas Protection Action

The gas (Buchholz) relay may act for several reasons:

• A minor internal fault producing weak gas
• Air intruding into the transformer
• Oil level drop
• Other internal faults

Immediate Actions

After a gas protection signal appears:

1. Perform an external inspection of the transformer.
2. Check oil level and oil color in the oil pillow.
3. Check for gas in the gas relay (volume and color).
4. Inspect for oil leakage in the transformer body and forced oil circulation system.
5. Observe load, temperature, and sound changes.

If external inspection reveals no abnormality, take a gas sample from the relay and analyze its nature. Also, take an oil sample for testing to determine the fault type.

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8. Parts Prone to Overheating During Operation

8.1 Poor Contact of Tap Changer

Poor contact increases contact resistance, raises consumption, and causes severe heating. This is especially likely after a tap change or during overload.

8.2 Winding Inter‑Turn Short Circuit

Inter‑turn short circuit means insulation damage between adjacent turns. This creates a closed short‑circuit loop and reduces the number of turns for that phase. The induced short‑circuit current generates high heat and may burn the transformer.

8.3 Short Circuit Between Core Silicon Steel Sheets

Due to external damage or insulation aging, the paint insulation between silicon steel sheets may break down. This increases eddy currents, causes local overheating, and can even melt the core – known as core fire.

8.4 Poor Contact of Other Parts

Loose connections anywhere in the circuit can cause local overheating.

Handling Advice

• Closely monitor temperature changes of overheated parts to ensure safe operation.
• Analyze the cause of overheating.
• Contact dispatch and arrange a power outage for repair.

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9. Summary Table of Abnormal Conditions

Condition	Key Signs	Immediate Action
Noise (vibration)	Irregular sound, current/voltage normal	Record, monitor, schedule outage
Discharge sound	Crackling, corona/sparks	Report, apply for outage
Popping sound	Sharp pop	Stop transformer immediately
Water‑boiling sound	Sound + temperature rise + oil level up	Stop transformer immediately
High oil temperature	>10°C above normal, continues rising	Stop transformer
Abnormal oil color	Dark or carbon particles	Cut power, inspect
High oil level	Overflow	Drain or clear breather
Low oil level	Level below gauge	Vacuum refill or stop if rapid drop
Overload	Current exceeding rating	Reduce load, monitor
Cooling failure	Chiller stop signal	Restore cooling, reduce load
Gas protection	Signal alarm	Inspect, analyze gas/oil
Local overheating	Hot spots	Monitor, analyze, schedule outage