Answer Posted / s naved masood

For Transformers lesser than 1000KVA
1. Overcurrent protection at HT(fuses or overcurrent relays)
2. Overcurrent protection at LT (LT Air circuit breaker)
3. Moisture protection (Breather with silica gel)
4. Overburden protection (Temperature gauge)
5. surge protection (surge arrestors)
6. Pressure relieve valves
For transformers equal to or above 1 MVA
1. Overcurrent (IDMT and High set char relays)
2. surge protection (surge arrestors)
3. Oil temperature indicators (alarm + trip)
4. Winding temp indicators (alarm + trip)
5. Oil surge relay
6. Pressure relieve valves
7. sudden pressure relays
8. differential Protection
9. Restricted earth fault protection
10. Overfluxing protection
11. Buchholz relay (alarm + trip)
Also there are various tests that are done as a part of preventive maintenence.
1. winding resistance
2. turns ratio
3. Tan delta
4. Dissolved gas analysis
5. Furon analysis
6. Sweep frequency responce analysis
7. Partial discharge
8. Magnetic balance
10. Megger testing

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