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ajaz ahed
09-11-2014 08:27 PM

will Buchholz relay operate if fault occur in transformer bushing?

any one tell me about Buchhloz relay operation and also clear me if fault comes in transformer bushing the relay will also the sense the fault or not.
09-11-2014 10:52 PM
Top #2
09-11-2014 10:52 PM
No. Buchhloz Relay would remain unaffected by occurrence of fault in Transformer Bushing. The reason is that construction of Transformer Bushing is such that its internal atmosphere is physically totally isolated from the internal atmosphere of transformer. Right practice is to get Bushings factory tested for “Tan δ” (or Tan Delta). Thereafter, Tan δ for Bushings should be repeated after judicious intervals for predicting possibility of deterioration and resultant fault. Test for Tan δ of Transformer windings should also be similarly undertaken.
09-12-2014 01:41 AM
Top #3
09-12-2014 01:41 AM
Dear Mr. Ajaz Ahed, you have privately asked me to respond to your further query as below.
"What kind of protection will operate while fault occur on bushing."
I thought that it would be better to respond through the Forum so that what we discuss remains in public domain.
If a fault occurs in Bushing, in effect it would be a Phase-Ground Fault and Protective Relays would respond depending upon how they have engineered to behave in this case and also depending upon where CTs are located.
If the transformer concerned is equipped with Bushing CTs, the Phase-Ground Fault resulting from Bushing Fault would most likely fall outside transformer Differential Protection Zone (over all behaviour would depending upon whether or not the CTs saturate).
For more details I would prefer to recommend the following websites.

http://www.dbc.wroc.pl/Content/3458/high_voltage_engineering.pdfhttp://www.sandc.com/edocs_pdfs/EDOC_027579.pdfhttp://www05.abb.com/global/scot/scot252.nsf/veritydisplay/742ebb4cde015790c1257b44003695c3/$file/1ZDE000011 en_flyer TMU 100.pdf
09-12-2014 04:13 AM
Top #4
Senthil Kumar
09-12-2014 04:13 AM
anyone response to explain? pole slipping protection settings?and why we used blinders line,mean of locus line?
09-12-2014 07:04 AM
Top #5
09-12-2014 07:04 AM
Bucholz relay operates based on the accumulation of gases that occur due to decomposition of transformer insulation, arcing which breaks down the transformer oil and results in the creation of gases. These gases rise up to the top of the power transformer and gets accumulated in the Bucholz relay.
Faults on Bushing will be sensed by the transformer differential relay if you have a unit differential relay, then by phase to ground relays.
09-12-2014 09:57 AM
Top #6
Gary Fox
09-12-2014 09:57 AM
Bushing mounted CTs are typically mouned just inside the top of the tank on top mounted bushings. If the uppern part of the porcelain fails, the differential relay will not see the fault. It is preferred for the differenctial relay zone to incorporate the breakers that isolate the transformer on primary and secondary. If the CTs are mounte on the breakers the differenctila relay will operate for in-tank faults, bushing faults anywhere on the bushing and faults on the cables connecting the breakers to the transformer. The most complete solution. But also could be more difficult to apply due to the increased secondary wire length requiring higher CT excitation voltage.
09-12-2014 12:01 PM
Top #7
kashif aziz
09-12-2014 12:01 PM
09-12-2014 02:16 PM
Top #8
Manoj Badave
09-12-2014 02:16 PM
Dear Ajaz,
as Anand Kumar sir, nicely explained, Buchholz's relay is for faults inside the transformer tank, and it operates on the gas pressure or rush of oil, depending on the type of fault.
For bushing faults other fast operating protections, such as earth fault, differential protections are implied in the system.
in your question you have not mentioned about type of transformer, if it is a small distribution transformer, unit protections like differential protection may not be there, as the cost of protection is greater than the transformer cost. in such case, over current protections, even like fuses can give adequate protection.
For large transformers, yes all these advanced protection techniques are used.
as far as transformer bushing is concerned, there are chances of internal failure due to partial discharge which is due to manufacturing defect in the porcelain insulator. to carry out tan delta testing periodically will give you estimate of the condition of bushing.
You can maintain the bushings by keeping them clean externally, monitor and arrest leakages regularly.
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