Buchholz relay is a gas-actuated protective relay installed in oil-immersed transformers between the main tank and conservator tank. It contains a float and mercury switch that energizes alarm or trip circuits during faults to indicate issues like oil and gas accumulation, surge, or leakage. The relay prevents accidents during major faults by isolating the transformer.

1. Subject:- Switchgear and Protection
Topic:- Buchholz Relay on Transformer
Prepared By :
Yash kothadia (150110109019)
Abhishek lalkiya (150110109020)
keyur nimavat (150110109027)

2. • Buchholz relay in transformer is an oil container housed
the connecting pipe from the main tank to the
conservator tank.
• Buchholz relay is a type of oil and gas actuated
protection relay mainly used on all oil immersed
insulation transformer more than 500KVA.
• Buchholz relay is a gas-actuated relay installed in oil
immersed transformers for protection
against all kinds of fault.
• Buchholz relay is an oil immersed protective relay
located between the connecting pipe of the conservator
tank to the main tank, which energized an alarm circuit
or trip circuit during transformer faulty conditions.
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3. JULIUSALOWONLE

4. • UPPER ELEMENT-A hinged float i.e. moving up
and down depending upon the oil level in the Buchholz
relay container.
• LOWER ELEMENT-A hinged float or A baffle plate
i.e. in front of inlet (main tank side) of the transformer.
Movement by oil pressure.
• MAIN ELEMENT-Gas release pockets or cocks (on
top).
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5. • MERCURY SWITCH-Depends on the position of
the float(attached to the float).
• OIL SURGE DETECTOR OR FLAP -Detect an oil surge
from the main tank to the conservator tank.
• ALARM-Initiate sound for fault attention.
• TRIP CIRCUIT-Actuate Circuit breaker isolation.
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9. BUCHHOLZ RELAY
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10. JULIUSALOWONLE

11. • Based on Mechanical phenomenon(Mechanically
actuated).
• Minor Internal Fault.
• Severe or Major types of Fault.
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12. • Insulation fault between turns.
• Breakdown of core of transformer.
• Core heating.
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13. • Short-circuit between phases.
• Short-circuit between phases to earth.
• Fault in tap changing equipment.
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14. Gas Float
• Minor
• fault
•
Mercury
switch
Alarm
energized
• Decomposition Lower the Tilting the Alarm
• of transformer float switch contact
• oil (hydrocarbon) closed
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15. • Major
• fault
Baffle
plate
Mercury
switch
Trip
circuit
Circuit
breaker
EnergizedOil
pressure
Tilting
the
switch
• Surge of
• the oil
•
Opened LV
& HV
side
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16. • Oil
• leakage
Air Float
bubbles
Mercury
switch
Alarm
energized
Lower
the float
Tilting
the
switch
•
•
•
Alarm
contact
closed
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17. • Buchholz relay operation may be actuated
without any fault in the transformer.
• OIL TOPPAGE-When oil is added to a transformer, air
may get in together with oil, accumulate under the relay
cover and thus cause false buchholz relay operation.
• MECHANICAL LOCK-is provided in the relay so that
one can lock the movement of mercury switch when oil
is topping up in the transformer and also during
transportation of transformer.
• EXTERNAL FAULT-Over currents flowing through the
winding cause over heated the copper and causes oil to
expand. It increase the oil velocity which is sufficient to
trip over the lower float.
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18. • Buchholz relay prevent accidents during major
fault (isolate the transformer).
• Severity of the fault can be determined without
dismantling the transformer (DGA).
• It trapped gases for bleeding.
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19. • It can sense the fault occurring below oil level only.
Therefore separate protection is needed for connecting
cables.
• it is a time delay operating device (0.1 seconds and average
of 0.2 operating range).
• it can only be used with oil immersed transformers
equipped with conservator tanks
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