Maintenance of Potential Transformer (PT and CVT)

The maintenance of a potential transformer is somewhat similar to the maintenance of a current transformer.

The potential transformer performs a vital role in voltage measurement and distance protection scheme of the system.

There is a limited number of potential transformers in an electrical substation. It is not as much as current transformers.

Also, a capacitive voltage transformer (CVT) is a kind of potential transformer. But it serves for dual purposes. The CVT also performs the PLCC carrier protection of transmission lines. In other sense, it also serves as a coupling capacitor.

We need to act the followings for maintenances of a potential transformer or a capacitor voltage transformer.

maintenance of potential transformer

Steps for maintenances of a potential transformer

  1. We need to check the oil leakage of the electromagnetic unit tank of a PT very often.
  2. For oil-filled PT or CVT, we need to watch the oil level of the equipment often. The oil level is visible on the oil level indicator glass fitted on the upper portion of the PT or CVT.
  3. We also need to measure the tanδ value of PTs, and CVTs to judge the condition of insulation oil inside it. It the value of tanδ comes more than recommended, we need to take necessary steps to rectify it.  Sometimes, depending on the condition of the equipment, we need to simply replace the equipment by a good one.
  4. Like other pieces of equipment like current transformers, circuit breakers, PTs and CTVs need clean insulator to maintain its proper creepage distance. We clean the insulator with clean, dry and fluffy free cloths.
  5. We should visually check the HF point in case of CVTs.
  6. Thermovision scanning is also required. If we find any high temperature in any power connection or in any part of the body of the PT, we need to take proper action.
  7. We also check the PT junction box for the connections of all points including the earthing connections. If there is any loose connection, we need to re-tight it immediately.
  8. We need to keep the box clean. If any point work deteriorates, we need to repaint that portion or entire box immediately.
  9. If any gasket of the junction box cover becomes damaged, we need to replace it without waiting. Because it prevents the moisture entry inside the junction box.

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