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parvindar

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Join Date: Sep 2015

Posts: 1

20 MVA Transformer Problem.

09/09/2015 3:29 AM

we have 20 mva(15.75/6.9 kv dyn11) unit transformer.during rolling of turbine our UT draws enormous current on residual voltage of 500v.after isolating it from system same problem exist.But after draining oil from transformer when we applied 415 v on HV side a spark comes from the core side(exactly not know if it is winding or core) 2 times. After that all testing reports come normal.Kindly suggest the problem.......dga report attached

DGA TEST REPORT

S.N.

Tx. NAME

Tx. Make

MVA

S.No.

GAS CONTENT IN PPM

REMARKS

DATE

CH4

CO2

C2H2

C2H4

C2H6

H2O

400-900

35-130

5300-12000

15-50

110-250

50-70

60-150

U # 3 UT.

CGL

MT 7324/02

05.09.2015

175

229

1824

8.5

536

201

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#1 "Re: 20 MVA Transformer Problem." by RAMConsult on 09/09/2015 5:42 AM (score 5)

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#3 "Re: 20 MVA Transformer Problem." by SolarEagle on 09/09/2015 4:31 PM (score 1)

RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#1 Re: 20 MVA Transformer Problem. 09/09/2015 5:42 AM
	You have a number of problems: 1) A severe overheating problem, as indicated by high Ethylene and Ethylene/Ethane ratio, with heating to near 700ºC, 2) Local overheating (hotspot) as indicated by high Ethane levels nearly 5.75 times normal, 3) A sparking problem as indicated by Methane nearly 3 times normal. It's time for someone with an understanding of DGA to help you further understand how to interpret the numbers, or you can learn about it from the competent engineers that you need to contract with to do a complete internal inspection of the transformer. My guess is that the excitation system was put in service long before the unit reached 95% of rated speed or was allowed to coast down without tripping the excitation system, and the unit was subjected to high Volts/Hertz and overexcitation resulting in core and insulation damage. Now pay someone to assess the damage. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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Legolaz Power-User Join Date: Sep 2015 Posts: 482	#2 In reply to #1 Re: 20 MVA Transformer Problem. 09/09/2015 8:49 AM
	GA __________________ The doctor said "just one post or reply aday in CR4, take it or leave it". I said, "what does that mean?"
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SolarEagle

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Location: by the beach in Florida

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Re: 20 MVA Transformer Problem.

09/09/2015 4:31 PM

ANSI/IEEE Std C57.104 [1] provides guidance on concentration limits of the key gases:

Dissolved gas concentration limit (ppm)								Interpretation
Hydrogen (H ₂)	Methane (CH ₄)	Acetylene (C ₂H₂)	Ethylene (C ₂H₄)	Ethane (C ₂H₆)	Carbon monoxide (CO)	Carbon dioxide (CO ₂)	TDCG (*)	Interpretation
100	120	1	50	65	350	2500	720	Satisfactory
101 - 700	121 - 400	2 - 9	51 - 100	66 - 100	351 - 570	2500 - 4000	721 - 1920	Fault may be present
701 - 1800	401 - 1000	10 - 35	101 - 200	101 - 150	571 - 1400	4001 - 10000	1921 - 4630	Fault probably present
>1800	>1000	>35	>200	>150	>1400	>10000	>4630	Continued operation could result in failure

(*) TDCG = Total dissolved combustible gas

http://www.openelectrical.org/wiki/index.php?title=DGA_Testing

http://tdworld.com/archive/power-transformers-rebuilt-field-site-repairs-110-kv-distribution-transformers-and-220-400-k

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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#4 Re: 20 MVA Transformer Problem. 09/10/2015 5:31 PM
	The problem is an unwillingness to discuss the technicalities directly with the transformer manufacturer using the telephone. The solution is simple. Get dialling. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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