Transformers form an indispensable part of electric power supply throughout industrial, commercial, and residential settings. They are used to convert electric power to an appropriate voltage and current value as is necessary for a particular setting.
In a transformer, the function of providing insulation is catered to by a transformer’s oil filtration and paper insulation. Since the oil also works as a coolant, it has to be stable at very high temperatures in both electrical and chemical conditions.
Therefore, the transformer oil must have a high flashpoint of about 140° Celsius or higher, a low pour point of about -30° Celsius or less, and a dielectric breakdown voltage of about 28 to 30 kilovolts or higher.
Advantages of Transformers Oil Filtration
The filtration or purification of the transformer oil is essential as, with time and usage, the oil gets contaminated with dirt, sludge, and other dissolved impurities like moisture and gases.
Regular filtration of the transformer oil ensures longer life of the transformer.
- Filtration of the transformer oil increases its insulating properties. When the insulating oil gets contaminated with impurities like dirt and sludge, it reduces the insulating capacity of the oil. A filtering device has to be used to remove these impurities. If the dirt is below 10 microns, then a simple filter may not be able to remove the dirt, and an electrostatic filter will need to be used.
- With improved insulation, the transformer will have a longer lifespan than a neglected transformer.
- The breakdown voltage of the transformer oil can be restored to its original value with regular purification.
If the insulating oil is not purified, then the following processes can occur, reducing the working capacity of the transformer:
- Arcing; is the formation of an electric arc that can lead to the breakdown of the system.
- The oil will overheat and, in turn, overheat the whole system.
- The ionization of the fluid through electric discharge will occur through a process known as corona discharge.
- The insulating strength of the transformer oil will decrease considerably.
Therefore, when timely tests are conducted and the purification of the oil is done properly, the transformer will continue to function well.
Some Tests and Their Values for the Oil
- Appearance: Unused oil in a new Power Transformers Manufacturers India should be clear and free from suspended matter and sediments. The appearance of insulating oil that is in service should be clear with no visible impurities. Any sediments or sludge below 0.02% by mass can be overlooked.
- Water Content: There should be no free water in the oil. If there is, it is an indication that the already dissolved water has reached its saturation point. The value of water in the new oil should not exceed 20 ppm. This can go up to 30 ppm in service, but a value greater than that indicates that the paper insulation is loaded with too much moisture.
- Breakdown Voltage: The breakdown voltage of the oil should be 30 kV or more but can reduce slightly with in-service oils.
- Acidity: The maximum value for new oils is 0.03mg KOH/gm. This value can go up to 0.05 mg KOH/gm with usage.
- Viscosity: The viscosity of the oil should be 27 cSt maximum.
- Flashpoint: The minimum accepted value of the flashpoint is 140° Celsius. This value, with use, should not decrease more than 15 degrees from the initial value.
- Pour point: the maximum value for this should be -6° Celsius.
Tests for resistivity, dissolved gases, oxidation stability, and interfacial tension should also be conducted periodically.