Transformers are static devices, totally enclosed and generally oil immersed. Therefore, chances of faults occurring on them are very rare. But when fault occurring , It is very harmful for power system and our environment. So there are many protection system keep in back-up protection of power system safety.

1. Re-presented by
EEE-15D
ID:201213515041,17,30,36,49
Bangladesh University

2. Transformers are static devices, totally enclosed
and generally oil immersed. Therefore, chances
of faults occurring on them are very rare. But
when fault occurring , It is very harmful for power
system and our environment. So there are many
protection system keep in back-up protection of
power system safety.

3. Differential
Protection
Over Current
Protection
Buchholz Relay
Protection
Earth-fault Relay
Protection

4. Buchholz Relay Protection Fault:
Earth Fault
Winding Short Circuit
Phase to Phase Fault

5. Important Parts:
Alarm Circuit
Trip Circuit
Mercury Switch

6. The Buchholz relay operation may be actuated without
any fault in the transformer. When a fault occurs, some
transformer oil goes up in the main tank with decomposition.
The products of de-composition contain more than 70% of
hydrogen gas. When a predetermined amount of gas gets
accumulated, the contacts of mercury switch attached to it. This
completes the alarm circuit to sound an *alarm. The oil in the
main tank rushes towards the conservator via the Buchholz
relay and in doing so tilts the flap to close the contacts of
mercury switch. This completes the trip circuit to open the
circuit breaker controlling the transformer.

7. Main application are:
Leakage current fault protection of transformer
Phase to phase fault protection of transformer
Insulation failure of windings
Fall of oil level of transformer etc.

8. It is the simplest form of transformer protection.
It can be used high power application( up to 500Kva)
It is the best protection system than any others.

9. It can only be used with oil immersed transformers
equipped with conservator.
The device can detect only faults below oil level in the
transformer. Therefore, separate protection is needed for
connecting cables.