Maintenance Schedule for Transformers

 
Category
Major
Medium
Minor
  • Watch Operating Conditions, i.e, ambient temperature, oil temperature, current reading and variation of primary voltage. Check position of tap switch and readjust if necessary.
H
D
M
  • Inspect general condition, see if there is any unusual noise. Check oil level in tank and bushing.
D
W
M
  • Check Transformer bushing insulator and examine for fine cracks, if any. Check tightness of external electrical connections.
M
3-M
6-M
  • Check breather and ensure that the passage is clear.
-
-
-
  • Test operation of all protective alarms and relays, batteries and wiring.
3-M
3-M
-
  • Take megger readings and record.
3-M
6-M
Y
  • Check ground connections and record earth resistance.
3-M
6-M
Y
  • Test oil for dielectric strength, acidity, colour etc.Drain out samples of oil from drain plugs at the bottom of the tank. Examine for water, sludge and acidity. Drain out until clean sample is obtained. Replenish with good dry oil. Carry out oil filtration if required.
3-M
Y
2-Y
  • Check tightness of all cover bolts.
3-M
Y
2-Y
  • Check lightning arresters. Check spark gaps.
6-M
6-M
Y
  • Throughly overhaul after lifting up the core. Repaint the tank, if necessary.
10-Y
7-Y
5-Y

Note: H - Hour, D - Daily, M - Monthly, Y - Yearly
  • Major installations at large grid substations which are manned all the time, with unit sizes of 1000 to 10,000 KVA or more. Quite often the transformer loading is quite high.
  • Medium installations in small substations with unit capacities of 250 KVA to 1000 KVA.
  • Minor installations upto 250 KVA unit capacity which are often unattended and often at remote points, such as pole mounted and rural distribution transformers.

The intervals of inspection are indicated as : H for hourly, D for daily, W for weekly, M for Monthly, 3-M and 6-M for every 3 months and 6 months, Y for yearly, 2-Y and 5-Y for two years and five years respectively.

In major anf medium installations a standby transformer should always be available to be switched on at a moment's notice, in place of the large unit installed. It should be maintained to the same standards as the other units, and periodically put to use to keep it in a good and healthy condition.

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