The long-term normal operation of the transformer under rated voltage and rated load is called the service life of the transformer. The materials for manufacturing transformers are metal materials and insulating materials.
Metal materials are generally resistant to higher temperatures without damage, but insulating materials can quickly age and damage after the temperature exceeds a certain value, so temperature is one of the main factors affecting the service life of the transformer. The life of a transformer can be said to be the life of an insulating material in a certain sense.
3. For oil-immersed transformers, also consider the dissolved oxygen in the oil.
The above three factors determine the service life of the transformer. Practice and research have shown that if the winding can maintain a temperature of 95 ° C continuously, it can guarantee a 20-year service life for the transformer.
According to the relationship between temperature and life, an 8 °C rule can be drawn: based on the life at the above temperature, the service life of the transformer is shortened by 1/2 for every 8 °C increase in winding temperature.
Most of China's power transformers use oil-paper insulation, that is, Class A insulation. For Class A insulated transformers, the normal operating temperature of the transformer winding is 105 °C when the ambient air temperature is 40 °C during normal operation.
Practice and research have shown that if the winding can maintain a continuous temperature of 95 ° C, the transformer can have a 20-year service life.
When the transformer insulation working temperature is 120 °C, the transformer service life is 2 years.
The insulation temperature inside the transformer is mainly related to the magnitude of the load current under the premise that the voltage is basically constant, that is, the load current is large, the insulation temperature is high, and the load current is small, and the insulation temperature is low.
When the transformer is overloaded during operation or running at rated load in summer, the internal insulation is operated at high temperature, and the life loss of the transformer will be accelerated.
If the transformer is under light load or in winter with rated load operation, its internal insulation operates at low temperatures and the transformer life loss can be slowed down. Therefore, in order to make the transformer load capacity fully utilized throughout the year without affecting the normal service life of the transformer, the monthly load can be adjusted appropriately.
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