Winding Temperature (WT) and Oil Temperature (OT) of a transformer

Winding temperature is the temperature of the transformer windings, which are the coils of copper or aluminum wire that carry the electric current. Oil temperature is the temperature of the transformer oil, which is a liquid that insulates and cools the windings.

The winding temperature is always higher than the oil temperature because the windings generate heat as electricity flows through them. The difference between the winding temperature and the oil temperature is known as the hot spot temperature.

The winding temperature is the most important temperature to monitor in a transformer because excessive heat can damage the insulation and lead to transformer failure. The maximum allowable winding temperature will vary depending on the type of transformer and the insulation materials used. However, a general guideline is that the winding temperature should not exceed 115 °C (239 °F).

The oil temperature is also important to monitor because excessive heat can degrade the oil and reduce its insulating and cooling properties. The maximum allowable oil temperature will also vary depending on the type of transformer and the oil used. However, a general guideline is that the oil temperature should not exceed 90 °C (194 °F).

Factors that affect winding and oil temperature

The winding and oil temperature of a transformer can be affected by a number of factors, including:

• Load: The load on the transformer is the biggest factor affecting its temperature. A higher load will generate more heat in the windings, which will increase the winding and oil temperature.
• Ambient temperature: The ambient temperature, or the temperature of the air surrounding the transformer, will also affect its temperature. A higher ambient temperature will cause the transformer to run hotter.
• Ventilation: The ventilation of the transformer is also important. If the transformer is not properly ventilated, the heat generated by the windings will not be able to escape, which will cause the transformer to overheat.
• Age and condition of the transformer: Older transformers and transformers that are in poor condition may be more likely to overheat.

Monitoring winding and oil temperature

It is important to monitor the winding and oil temperature of transformers to prevent overheating. This can be done using a variety of methods, including:

• Temperature sensors: Temperature sensors can be installed in the windings and oil to measure the temperature directly.
• Infrared thermography: Infrared thermography can be used to measure the temperature of the transformer windings and other components without contact.
• Oil analysis: Oil analysis can be used to monitor the condition of the transformer oil and identify any potential problems that could lead to overheating.

If the winding or oil temperature of a transformer is found to be high, it is important to identify and address the cause of the problem. This may involve reducing the load on the transformer, improving the ventilation, or repairing or replacing the transformer.