TheReason Analysis of Transformer Overheating

I , the cause of the failure of the transformer itself

During the operation of the transformer, when the heat generation and heat dissipation reach a balance state, the temperature of each part tends to be stable. If under the same conditions, the oil temperature is higher than usual by more than 10°C, or the load remains unchanged, but the temperature continues to rise, it can be considered that a fault has occurred inside the transformer.

1. Poor contact of the tap changer

Due to the insufficient pressure of the contact point of the tap changer during operation or the contamination of the contact point, the contact resistance increases. The increase of the contact resistance will cause the temperature of the contact to rise and generate heat. Especially after switching taps and when the transformer is overloaded, it is easier to make the tap changer poor contact and generate heat.

The poor contact of the tap changer can be judged from the frequent action of light gas, and by taking oil samples for testing, it can be found that the poor contact of the tap changer makes the oil flash point drop rapidly; in addition, the tap can be determined by measuring the DC resistance value of the coil. The contact condition of the switch.

2. Turn-to-turn short circuit of winding coil

Due to the insulation damage between several adjacent turns of the coil, a closed short-circuit circulating current will appear. At the same time, the number of turns of the coil of this phase is reduced, and the high heat generated by the short-circuit circulating current will cause the temperature rise of the transformer to be too high, and in serious cases, the transformer will be burned.

There are many reasons for the short circuit between turns of the coil. For example, the rough manufacturing process of the coil causes the insulation to be mechanically damaged; the high temperature causes the insulation to age; The main reasons are overvoltage and overcurrent. Severe turn-to-turn short-circuit makes the oil temperature rise, and the oil at the short-circuited turn seems to be boiling, and the sound of "gurgling" can be heard. When the oil sample was taken for testing, the oil quality deteriorated and developed from light gas action to heavy gas action. At this time, the inter-turn short circuit can also be found by measuring the DC resistance.

3. Short circuit between iron core silicon steel sheets

Due to external force damage or insulation aging and other reasons, the insulation between silicon steel sheets is damaged, the eddy current increases, and local overheating is caused. In addition, the damage to the insulation of the core screw is also the cause of the eddy current. The light one causes local heating, and generally the rise of the transformer oil temperature cannot be observed; Heavy gas action in severe cases.

4. Lack of oil or blockage in the cooling pipe

Transformer oil is the main insulation inside the transformer, which plays the role of insulation, cooling and arc extinguishing. If there is a shortage of oil or the inside of the heat dissipation pipe is blocked, the cooling speed of the oil circulation will decrease, which will cause the temperature of the transformer to rise during operation.

II. the external reasons for the high temperature of the transformer

1. Severe overload

During the operation of the transformer, the hysteresis loss of the iron core, the eddy current loss and the copper loss of the coil are all converted into heat, which makes the temperature rise. Iron loss is a basically constant loss, which is related to the transformer structure, so it cannot be reduced or eliminated during operation, while copper loss changes with the change of load. When the load is severe, the increase of copper loss will cause the temperature of the transformer to rise.

2. The air inlet and outlet of the transformer room are blocked or the dust is serious

The air inlet and outlet of the transformer room are the channels for air convection during the operation of the transformer. Once blocked or heavily dusted, the heating conditions of the transformer remain unchanged but the heat dissipation conditions become worse, and the heat cannot be dissipated to the surroundings in time, resulting in a rise in the temperature of the transformer during operation. Measure the air temperature at a place 1.5m to 2m away from the transformer oil tank and half the height of the oil tank. If the measured temperature is 8-10°C higher than the ambient air temperature, the ventilation of the transformer room should be improved.

3. Transformer cooling cycle system failure

In addition to using cooling pipes for heat dissipation, power transformers also have cooling methods such as forced air cooling, forced oil circulation, and water circulation. Once the cooling system fails or the cooling conditions are poor, the temperature of the transformer in operation will rise.

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