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2. Buchholz Relay:

Mechanical Faults:

Serves for the protection of power transformers againstGas accumulation

Loss of insulation liquid

Flow of insulation liquid

caused by flow of high eddy currents, local over heating, Arcing or Partialdischarges occurring within the tank!uchhol" relay consists of

 An #pper Float

 A Lower Float

 A damper

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2. Buchholz Relay (Cont)

!uchhol" relay ⇒ two oil filled chambers with two floats $ relays

arranged vertically over one another

#pper float⇒ alarms operator

lower float ⇒ trips the transformer from e%ternal supply&load

'igh eddy currents $ local overheating $ Leakage of insulation liquid occur

within the tank ⇒ bubbles of resultant gas rise to the top of the tank ⇒ 

gas moves to the pipe between the conservator and the tank, and goes to

the !uchhol" relay chamber ⇒ gas builds up in the chamber ⇒ oil Level

decreases to a level ⇒ produce an alarm

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Upper float ⇒ switch for alarm

Acts when local overheating ⇒ gradual decomposition of liquid $

 solid insulation material $ formation of gasses

Lower float ⇒ switch for tripping

Acts when local overheating ⇒ gradual decomposition of liquid $ solidinsulation material $ formation of gasses or loss of insulation liquid ⇒ crosses alarming float and reach to the tripping float

2. Buchholz Relay: (Cont)

Buchholz Relay Functionality:

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Daper ⇒ mechanical switch which force the lower float to generatetripping

Acts when

high energy discharges ⇒ gases decomposition rapid and vigorous

⇒ high pressure waves generation ⇒ flow of insulation liquid towardse%pansion vessel

)hese pressure waves pushes the damper towards the lower float

which in turn produces tripping

2. Buchholz Relay: (Cont)

Buchholz Relay Functionality:

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Formation of gasses caused by local overheating, or loss

of insulation material (oil) causes decrease in oil level

reach trip level, forcing loer float to generate !"#$

%igh pressure aves are produced due to very high energy

discharges& #t causes the flo of insulation material toards the

e'pansion vessel pushing the damper hich in turns pushes

loer float to generate !"#$&

Formation of gasses caused by local overheating,

reaches a point forcing upper float to generate "*&

+onservator 

      

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a. Buchholz Relay !or"in#:

#pper Float

Lower Float

Buchholz Relay

*amper

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