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The Buchholz relay functions by making use of the liberated
gas inside the transformer due to an internal fault, to
actuate an alarm or trip the circuit breaker depending on
the seriousness of the fault. The virtue of buchholz relay
is that it detects an incipient fault i.e in the very early
stage itself before serious damage is done, whereas others
relays operate after the fault has occurred. Therefore
repair measures are simpler. Example of incipient faults are
short circuited core laminations, broken down core bolt
insulation, failure of inter turn insulation and consequent
local over heating , bad switch contacts and faulty joints etc..
The relay comprises a cast iron housing inserted in the pipe
connecting the transformer tank with the conservator tank.
It consists of two bucket mechanisms each connected to a
tilting head on which a mercury switch is mounted. The upper
assembly , traps small gas bubbles generated by an incipient
fault and if sufficient gas has been collected, it closes a
contact and sounds a hooter in the control panel in the
SUBSTATION. The lower assembly which is directly in the path
of the connecting pipe operates when there is a serious
internal fault like a short circuit between phases , coils
or turns, earth fault, arcing or puncturing of bushing
insulator inside the tank. This liberates a considerable
amount of gas, and the displaced oil and gas surge through
the connecting pipe, and impinge upon a deflection plate
fixed on the lower assembly in line with pipe. This tilts
the Mercury switch which in line with the pipe. This tilts
the Mercury switch which in turn trips the circuit breakers.
The buchholz relay also detects accumulation of air on
account of low oil level, or faulty oil pumps. A per cock is
provided on the top of the housing to draw samples of
accumulated gas for analysis. An inspection window shows the
amount of gas which has accumulated. Provision is made for
manual operation on the alarm and tripping mechanisms to
facilities testing. A better method is to pump air through
the pet cock
Ref- Dr G.V Rao Phd
If any other result please send to my id -
mastalinprabu@gmail.com
With thanks
M.STALIN
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