Categorizing Faults via DGA. GE Grid Solutions M&D

Transcription

1 ategorizing Faults via DGA GE Grid Solutions M&D

2 First, What Is Transformer Dissolved Gas Analysis? Sample Test Doc Diagnosis Doctors extract information about our health from our blood. Technicians extract information about the health of our transformers from the oil via DGA. Substations are more challenging for this sampling process than a doctor s office.

3 Transformer Dissolved Gas Analysis, The Process & Logic Duvall s Triangle Sample Test Tech Diagnosis We prefer a clean sample with no issues detected, just as a blood test in a doctor s office.

4 Transformer onstruction Bushings Tap changer ooling System oils Oil Tank ontrol abinet ore

5 What Are The Relevant Gases? Paper & Oil Gases ot Metal Gases

6 6 Oil degradation Typical oil Molecule

7 Knowing Industry Standards & Their Intended Use Dissolved key gas concentration ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; limits - IEEE O O2 TDG ondition ondition ,5-4, 721-1,92 ondition ,8 41-1, ,4 4,1-1,1,921-4,63 ondition 4 >1,8 >1, >35 >2 >15 >1,4 >1, >4,63 ondition 1 ondition 2 ondition 3 ondition 4 TDG below this level indicates satisfactory operation. Any individual combustible gas exceeding specified levels should prompt additional investigation. TDG within this range indicates greater than normal combustible gas level. Any individual combustible gas exceeding specified levels should prompt additional investigation. Action should be taken to establish a trend. Fault (s) may be present. TDG within this range indicates a high level of decomposition. Any individual combustible gas exceeding specified levels should prompt additional investigation. Immediate action should be taken to establish a trend. Fault (s) are probably present. TDG within this range indicates excessive decomposition. ontinued operation could result in failure of the transformer.

8 Understanding Duval s Triangle, Fault odes.

9 IEEE Key Gases Evaluation Arcing in Oil Partial Discharge in Oil 6% 5% 4% 3% 2% O % 8% 6% 4% O % 22 2% 22 % % Overheated Oil Overheated ellulose 7% 6% 5% 4% 3% 2% 1% O % 8% 6% 4% 2% O % %

10 Ratios for key gases Doernenburg Ratios for key gases Doernenburg Suggested fault diagnosis Ratio 1 (R1) 4/2 Oil Gas space Ratio 2 (R2) 22/24 Oil Gas space Ratio 3 (R3) 22/4 Oil Gas space Ratio 4 (R4) 26/22 Oil Gas space 1. Thermal decomposition >1. >.1 <.75 <1. <.3 <.1 >.4 >.2 2. Partial discharge (low-intensity PD) <.1 <.1 Not significant <.3 <.1 >.4 >.2 3. Arcing (high-intensity PD) >.1 to <1. >.1 to <.1 >.75 >1. >.3 >.1 <.4 <.2

11 Rogers Ratios For Key Gases Rogers ratios for key gases ase R2 22/24 R1 4/2 R5 24/26 Suggested fault diagnosis <.1 >.1 to <1. <1. Unit normal 1 <.1 <.1 <1. Low-energy density arcing Pd a 2.1 to 3..1 to 1. >3. Arcing igh-energy discharge 3 <.1 >.1 to <1. 1. to 3. Low temperature thermal 4 <.1 >1. 1. to 3. Thermal <7 5 <.1 >1. >3. Thermal >7 a There will be a tendency for the ratios R2 and R5 to increase to a ratio above 3 as the discharge develops in intensity.

12 Transformer Operating Temperatures 2 8? First signs of gassing begins around 1 with O2 & O. First signs of hot metal gases begins around 15.

13 Diagnosing Transformer Main Tank Faults

14 Where s The Problem? Nitrogen Sealed #1 36 MVA Nitrogen Sealed #2 3 MVA 4% 4% 3% 3% 2% 2% 1% 1% % % O2/O Ratio 7 6 O2/O Ratio Pre Event Post Event Pre Event Post Event

15 Where s The Problem? ontinued Winding Failure #1 Primary Lead Repairable #2 Transformer Replaced Transformer Repaired

16 O2/O Ratio Experiment O2/O RATIO oil flash paper 2 1 test1 test2 test3 test4 test5 test6 tes 7 test8 test9 test1

17 Where s The Problem? DATE 2 O2 N2 4 O O TDG O2/O 11/4/ ,771 68, , , /8/ ,477 81, , , , /23/ ,893 76, , , , /22/ ,34 71, ,2 32 1, , /6/ ,639 68, , 325 2, , /13/ ,897 59,148 1, , , , /12/ ,613 72,536 1, , , , /25/ ,233 67,438 1, , , , O2/O 2% Decline Overall 3, % Increase Overall O2/O Linear (O2/O) 3, 2,5 2, 1,5 1, DET oked 24 Linear (24 )

18 Descending O2/O Ratios - 75 MVA, N2 Blanketed M DATE 2 O2 4 O O O2/O 3-Jul- 12 ND ND ND ND 7 6-Jul-11 ND ND Jan- 1 ND ND Mar-9 ND 1738 TRAE ND TRAE Mar- 8 ND ND Feb- 7 ND 1667 TRAE ND 3 37 O2/O % Drop in 5 Years O2/O Linear (O2/O)

19 15 MVA, 1 kv Manufactured 1999 Pre-Fault M Date 2 O2 O2 O O2/O 211 < < < < < <1 <1 < < <1 <1 < < <1 < O2/O O2/O Linear (O2/O) O2/O Ratio % Drop

20 1999, 15 MVA, 1 kv, omplete Picture Date 2 O2 O2 O O2/O 211 < < < < < <1 <1 < < <1 <1 < < <1 < post fault O2/O 96% Drop O2/O Ratio O2/O Linear (O2/O)

21 1 MVA Mobile Transformer Test Date ydrogen Methane Ethane Ethylene Acetylene O2 O O2/O Nitrogen Oxygen 9/5/ /19/24 4 o /16/ /14/ /7/ /18/ O2/O DET Failed % Increase Overall O2/O Linear (O2/O)

22 115-4kV, MVA Rating 18/24/33.6 Test Date ydrogen Methane Ethane Ethylene Acetylene O2 O O2/O Nitrogen Oxygen 2/19/ /1/ /31/ /21/ /29/ O2/O O2/O Linear (O2/O) O2/O Ratio % Drop

23 Analyzing Events via O2/O O O O2 O O2/O Ratio ppm 21 ppm Failed the following year, ppm 2 ppm

24 Finding The Problem 2 2 >5 2 4 > >7 4 >293 O 2 <25 O<5 Gassing began in MVA Nitrogen Blanket O2:O Linear (O2:O)

25 Finding The Problem, ontinued Long history of gassing including acetylene and high levels of ethylene. Due to high combustible gas levels and the increasing O 2 :O ratio, problem was narrowed down to overheating occurring on either the DET or primary/secondary leads. Primary lead was found bare against a corona shield. It was re-taped and in subsequent DGA tests there has been no production of combustible gas.

26 Do I ave ealthy Paper? Are There Indicators Within DGA? M Date O2 O O2 O2/O June-12 ND ND Nov-13 ND 3 4 ND ND Sept-14 ND 3 ND ND ND July ND ND O2/O RATIO O2/O RATIO

27 Acetylene Is Problematic, But Is It Fatal? Not always: Is it present due to activity in the winding insulation, or is it bare metal? The problem could be easy to get to and simple to repair. Transformers have been discarded when the problem was a simple fix, but that was unknown at the time. It can mean the difference between a few thousand dollar$ in repairs, versus a few million dollar$ in potential replacement costs.

28 Effects Of Thumping Faults With A Power Transformer Sampled right after main tank fault. Notice the arcing signature in the main tank.

29 Effects Of Thumping Faults With A Power Transformer, ontinued 6% 5% 4% 3% 2% 1% % Main Tank Arcing Effects of Thumping Faults w/power Transformer % Gas Generation hart -Arcing in Oil kkkkkkkkkkkkkkkkkk Reference: IEEE Std kk 6% 5% 4% 3% 2% 1% % O2/O Ratio 15 1 Pre-Fault Ratio Post Fault Ratio 5

30 Summary/onclusion All internal faults are not fatal. Know your fleet. It will be beneficial in solving the diagnostic puzzles as they present themselves. All faults are not as easily identified. Don t give up, as there is an answer. Allow software to help with the data analysis and direct you to the critical assets and information, which are now available. Trending the fluctuations of gas concentration, rate of change and ratios is very important for understanding your transformers vital signs. Know when to reach out for additional support, if needed. We are all in this together.