For a successfully working transformer, the need for proper installation, loading, and maintenance is just as imperative as is the viability of its design and manufacture. Transformer manufacturers India are aware of this when they build transformers. However, the need for preventive maintenance of transformers is still important for the long lifespan of a working transformer. The tasks performed under preventive maintenance is not exactly the same as those that are done as part of major overhaul repairs. However, some of these tasks may be the same in terms of how it is done.
Preventive Maintenance of Transformers
The general principles behind preventive maintenance are similar in the case of almost all transformers. However, for detailed explanations for specific transformers of a particular manufacturer, consulting the user manual provided by the manufacturer may be necessary.
Protective maintenance is of three types: preventive maintenance that involves scheduling and testing on a regular basis; predictive maintenance that involves additional testing and corrective maintenance which involves repairing or restoring the transformer to its original standards.
1. Insulation: Under preventive maintenance, the insulation of the transformer should be thoroughly checked. Mineral and paper insulation is constantly affected by moisture, air, heat and other elements that are corrosive to its functioning.
2. Inspection: New transformers, when purchased, should be inspected thoroughly before installation to check if they are damaged in any way during the shipping process. This inspection can save a lot of time, energy and money in the present by rejecting damaged goods rather than do continued repairs on the transformers which will only increase the maintenance cost.
3. Testing: After the transformer has been installed, a number of tests should be conducted on it to see if it is working well.
- The insulation resistance of the new transformer should be tested and recorded for comparison purposes in the future when the transformer may require any repairs.
- The AC dielectric test is conducted immediately after the insulation resistance is conducted. This is an important one because the dielectric voltage is much higher than the normal voltage and induces high stress on the transformer.
- The transformer turns ratio is tested to determine the number of turns of the primary coil in comparison to the number of turns in the secondary coil. The accepted values of this ratio should not be more than 0.5% of the calculated value.
- The insulation power factor test measures the watt loss experienced during the working of the transformer.
4. Cleaning: During an inspection or otherwise, if any dirt is found accumulating on the transformer coils or insulator, then it should be immediately removed. The coils can be cleaned by the use of a vacuum cleaner, a blower or compressed air that is clean and free of dirt and impurities. The remaining surfaces like the insulation should be brushed or wiped down with a dry cloth regularly. The use of liquid cleaners is highly inadvisable as these may contain solvents that can corrode the insulating material.
5. Routine Maintenance: For the purpose of routine maintenance, there are a few tests that must be conducted.
- The insulation resistance test of winding to winding and winding to earth.
- Dielectric absorption test of winding to winding and winding to earth for ten minutes.
- The turns ratio test that is similar to the test mentioned earlier.
- AC overpotential test for high and low voltages of winding to earth.
- Insulation PF test of winding to winding and winding to earth. The values of this should be less than 3%.
While drying out a transformer before it is installed or after a major shut down, either external heat, internal heat or both external and internal heat may have to be used but only after any free moisture should is blown off or wiped away.