Buchholz relay is a gas- actuated relay installed in oil-immersed transformers for protection against all kind of faults. It is used to gives an alarm in case of slow developing faults or incipient faults in the transformer and to disconnect the transformer from the supply in the event of severe internal faults. It is installed in the pipe between the conservator and main tank as shown in fig11 below. This relay is used in oil-immersed transformers of rating above 750 kVA.
CONSTRUCTION
Fig 12 shows the constructional details of buchholz relay. It consists of a domed vessel placed in the pipe between the conservator and main tank of the transformer. The device has two elements. The upper element consists of a mercury type switch attached to a float. The lower element contains a mercury switch mounted on a hinged type flap located on the direct path of flow of oil from the transformer to the conservator. The upper element closes an alarm circuit during slow developing faults whereas the lower element is arranged to trip the circuit breaker in case of severe internal faults.
OPERATION
The operation of buchholz relay is as follows:
i. In case of slow developing faults within the transformer, the heat due to the fault
causes decomposition of some transformer oil in the main tank. The products of decomposition mainly contain 70 % of hydrogen gas. The hydrogen gas being light tries to go into the conservator and in the process gets trapped in the upper part of the relay chamber. When a predetermined amount of gas gets accumulated, it exerts sufficient pressure on the float to cause it to tilt and close the contacts of mercury switch attached to it. This completes the alarm circuit to sound an alarm.
ii. If serious fault occur in the transformer, an enormous amount of gas is generated in
the main tank. The oil in the main tank rushes towards the conservator via the buchholz relay and in doing so it tilts the flap to close the contacts of mercury switch. This completes the trip circuit to open the circuit breaker controlling the transformer.
ADVANTAGES:
- It is the simplest form of transformer protection
- It detects the slow developing faults at a stage much earlier than other forms of
protection.
DISADVANTAGES:
1. It can only be used with oil immersed transformers equipped with conservators
2. The device can detect only faults below oil leveling the transformer. Therefore
separate protection is needed for connecting cables.
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May 21st, 2009 at 8:08 am
I’ll like to know more about transformer protection
August 25th, 2009 at 3:11 am
I real enjoyed your article and I think your lunguage is listener freindly try to get to link your gadjets so that one can follow from one link to the next on items that functionaly work together in a system. keep it up.
September 24th, 2009 at 9:28 am
very good article..
thanks..
November 14th, 2009 at 7:52 am
your language is easily understandable.i would like to know who invented this relay
November 25th, 2009 at 5:27 am
Request for Quotation
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Material Description
1) 1 off Buchholz Relay
Part N°: SPDT
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Quotation Deadline: 26-11-2009
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Kind regards
Andrea Lesar
Tel: +27 21 551 3708
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January 11th, 2010 at 10:49 am
its superb..but cud n e tell its exact location in protection scheme..coz dat ws d question in my semesters n i cudnt answer[:-(]
February 9th, 2010 at 8:04 pm
thak u soo much really very good articcle… would like to know about :
# in protection of electric power circuits. Choose any type of those relays and describe the following:
(i) Constructional details
(ii) Principle of operation
(iii) Latest development in the applications
thank and i am waiting for ur e-mail
March 5th, 2010 at 3:44 am
Quite instructive and understandable. Thanks a lot.
March 16th, 2010 at 10:54 pm
its is a very gud answer n also in simple language
March 23rd, 2010 at 12:43 am
Good insight about the subject.
April 21st, 2010 at 1:18 am
The article is very good and informative.
I would like to ask, what will happen if the Buchholz is installed reverese i.e. arrow pointing towards the Trafo Tank ?
Will it work or not and why ?
May 27th, 2010 at 9:24 pm
Interested in knowing more about Buccholz relay with reed switches having switching capacity 5AMPS 240V AC 5Amps 220Volts DC.Pl inform manufacturers namesof such manufacturers.
June 14th, 2010 at 2:33 am
Good explanation.