An electrical transformer is the most expensive and necessary equipment of an electrical substation. Therefore, long-term maintenance of transformer is very essential for its long-term high performance and functional life.
A transformer requires various routine maintenance tasks, including the measurement and testing of various parameters of the transformer. There are two main types of transformer maintenance. We do one of them on a regular basis and do the other in emergency as required.
This means that we must perform some maintenance actions regularly to keep a transformer from working smoothly.
Some other types of maintenance for transformers we perform only under the same conditions as they are required are known as emergency or breakdown transformer maintenance. If we do regular maintenance in the right manner and time, then we will need a lot of work for emergency maintenance.
Therefore, periodic maintenance can avoid emergencies and sudden breakdowns. That is why we should focus mainly on status maintenance. This leads to a 0% breakdown of the equipment due to 100% correct maintenance.
Some other types of maintenance for transformers we perform only as they are necessary - known as emergency or breakdown transformer maintenance. But if one performs routine maintenance properly, it reduces the need to perform such emergency maintenance. Regular checking and maintenance of transformers is also known as condition maintenance.
Therefore by maintenance of proper condition, emergency and breakdown maintenance can be avoided. That is why technical personnel should mainly focus on status maintenance. 100% condition maintenance causes 0% breakdown of equipment.
Many different preventive maintenance actions are performed on the transformer. They can be on a daily, monthly, yearly, quarterly, half-yearly or yearly basis. Some transformer maintenance activities only need to be done once in 3 to 4 year intervals.
Daily checking and maintenance
There are three main things which are checked on daily basis.
- Level check of main gauge and protector tank coal gauges.
- Checking the color of silica gel in the breather.
- Checking the leakage of oil from any point of the transformer.
In case of unsatisfactory oil level in the man tank, the oil in the transformer needs to be filled and the transformer tank also needs to be checked for oil leakage. If oil leakage is found then necessary action should be taken to close the leak. If the silica gel turns pink, it should be replaced.
Monthly maintenance of transformer
- The oil level in the oil cup should be checked at intervals of one month under the silica gel breather. If it is found that the oil of the transformer inside the cup falls below the specified level, the oil should be replenished according to the specified level.
- The holes in the breather of silica gel should be checked monthly for breathing and should be cleaned properly if necessary.
- If your electrical transformer has oil filling bushings, make sure that the oil is filled to the right level. If the transformer oil level is low then fill it to the correct level.
Maintenance of transformer on half yearly basis
The oil of the transformer should be checked on a half-yearly basis, ie the transformer oil should be checked once in 6 months, in which the following should be checked
- Dielectric strength,
- Amount of water,
- Amount of acidity,
- Quantity of sludge content in oil
- Flash point, DDA, IFT, resistivity for transformer oil etc. must be checked once in a six month.
In the case of a distribution transformer, since they are operating in the state of light load at all times in the remaining peak hours of the day, maintenance is not required.
Maintenance of transformer on an annual basis
- The auto remote of the cooling system, manual function ie oil pump, air fan and other accessories fitted in the cooling system of the transformer, as well as their control circuit should be checked at one year intervals.
- In the case of treble, the control circuit and the physical condition of the pumps and fans must be checked.
- All the bushings of the transformer should be cleaned with a soft cotton cloth and check for cracking of the bushings during cleaning.
- The OLTC's oil status should be checked every year. For that, oil is sampled from the drain valve of the diverter tank, and this oil sample must be tested for dielectric strength (BDV) and moisture content (PPM).
- If the BDV is lower than the recommended values and PPM is found to be high for moisture, the oil inside the OLTC must be replaced or filtered.
- The mechanical inspection of the Buchholz relay has to be done on an annual basis.
- All Marsling Boxes should be cleaned from the inside at least once a year.
- All illumination, space heaters etc. should be checked whether they are working properly or not. If not, necessary maintenance action should be taken.
- All terminal connections of control and relay wires must be checked for tightness at least once a year.
- All the relays, alarms and control switches etc. along with their circuits in R&C panel (relay and control panel) and RTCC (remote tap changer control panel) panel should also be checked once a year.
- Oil should be checked with OTI, WTI (Oil Temperature Indicator & Winding Temperature Indicator) on the transformer top cover and refill the oil if necessary.
- The proper release of the pressure release device and the Buchholz relay must be checked annually. For that, one should do a short shortening of the wire of trip contacts and alarm contacts of the above devices to see if the related relays in the remote panel are working properly or not.
- Insulation resistance and polarization index of the transformer should be tested with battery powered megger of 5KV range.
- The resistive value of the earth connection should be measured annually with a clamp on earth resistance meter.
Action to be taken once in 2 years
- Calibration of OTI and WTI should be done once in two years.
- The bushing of the transformer should also be checked once in two years.