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Electric Predictive and Preventive Maintenance


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OLTC Maintenance and servicing

On-load tap changers (or circuit tap changers) as the name suggests, permit tap changing and hence voltage regulation with the transformer on-load. Tap changing is usually done on the HV winding for two reasons:

  1. Because the currents are lower, the tap changer contacts, leads, etc., can be smaller.
  2. As the HV winding is wound outside the LV winding, it is easier to get the tapping connections out to the tap changer.


Due to this tap changing carbon is formed in the OLTC tank and diverter switch contacts gets worn out. The maintenance primarily consists servicing of

  1. Diverter switch contacts
  2. Checking the oil level in the diverter switch chamber
  3. Replacement of diverter switch oil when the same becomes unsuitable for further service.
  4. Checking motor driving mechanism
  5. Removing carbon & sludge from OLTC tank
  6. Filtration & Dehydration of transformer oil