IEEE Transformer Committee Atlanta Arturo Núñez MISTRAS Group, Inc. (dba Physical Acoustics Corporation)

Transcription

1 IEEE Transformer Committee Atlanta 2016 Arturo Núñez MISTRAS Group, Inc. (dba Physical Acoustics Corporation)

2 A A A A A A A A A AE Sensor

3 ACOUSTIC EMISSIONS

4 INSTALLATION AE SENSORS HFCT Other info: DGA Winding Temp. LTC motor current Main tank and LTC compartment temperature Load current Pump current

5 CASE STUDY 1 Three phase Transformer Core form 144/13.8 Kv ONAN/ONAF/OFAF 90/120/160 MVA Built in 1996 A slight increase in combustible gases was observed on this unit since February An acoustic emission test was performed on June 2010 to try detect and locate the gassing source.

6 Dissolved Gas Analysis Data prior to AE test DATE H 2 CO CO 2 CH 4 C 2 H 6 C 2 H 4 C 2 H 2 TDCG 02-Feb Ene Dic

7 Dissolved Gas Analysis A sudden increase in the gas concentration was observed on December 2010 (few months after the acoustic test). Acoustic Test performed on June 3-4, 2010

8 FAULT LOCATION Several acoustic emission sensors were placed on the main tank. At the end of the monitoring period in June 2010, an area of acoustic activity was detected on the upper part of Phase U (Cluster 1).

9 Internal inspection The unit remained in operation for 6 more months until the unit was inspected in January On the area where the acoustic activity was located, severe damaged was found on the conductor of Phase U, on the upper part of the coil. After the internal inspection the oil for this transformer tested positive for Corrosive Sulfur

10 Internal Inspection TOP COIL TAP 3 BOTTOM COIL

11 TDCG Case 3 Nuclear plant GSU DGA trend /14/09 1/22/10 5/2/10 8/10/10 11/18/10 2/26/11 6/6/11 9/14/11 12/23/11 4/1/12 Date

12 AE Cluster Location of AE signals and corresponding correlation with DGA

13 Location of AE signals and corresponding overheating inside the transformer

14 Remedial action: Added insulation to flux shields shield spanner

15 2002 OVERHEATED BUS BAR EPRI Substation Equipment Diagnostics Conference Paper, 2004 GSU Transformer

16 CASE STUDY 2 CASE 6 ON IEEE STD. C57.127, 2007 DATE H2 CO CO2 CH4 C2H6 C2H4 C2H2 TDCG 05/31/

17 ON-LINE MONITORING CASE STUDY EPRI Substation Equipment,Maintenance Optimization and Diagnostic Conference Paper, 2009 Ethylene gasser transformer No spare available Next to a River (risk of mineral oil contamination if failed) Monitored acoustically to provide warning if fault increased in severity Two areas of activity found at different times

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19 DGA Sample Date Top Oil Temp C Hydrogen (H2) Methane (CH4) Carbon Monox. (CO) Ethane (C2H6) Carbon Dioxide (CO2) Ethylene (C2H4) Acetylene (C2H2) COMB GAS Comb Gas Rate ppm/day 01/12/ /06/ /29/ /08/ /17/ /10/ /23/ /12/ /27/ /05/

20 ON-LINE MONITORING Highest acoustic activity when unit was loaded for extended periods of time Utility reduced the load on the unit (when possible) and the gassing and acoustic activity decreased Sudden increase in acoustic activity and gassing in December 2008 prompted to remove unit from service

21 Fault gas interpretation results C Thermal-oil fault profile, Condition 2 IEC standard 60599: Thermal fault >700 C (T3)

22 Removed from operation after 8 months of continuous monitoring Electrical tests applied at manufacturer s facility. All tests passed. Tank was opened and an unintentional core ground was found Evidence prior to teardown

23 Transformer tear-down in progress

24 2D HIGH VOLTAGE VIEW Fault location indicated on the pre-teardown unit On dismantling of the frame, the fault was found in the predicted area

25 2D RIGHT SIDE VIEW The predicted location aligned well with the findings Good correlation of the fault with the predicted area

26 2D TOP VIEW The predicted location aligned well with the findings Good correlation of the fault with the predicted area

27 Close-up of the burnt core-steel and tank Direct correlation between the damaged core-steel and the burnt tank where sharp burrs from the core-steel cause an unintentional core-ground and hence overheating

28 Location of the problem Burn marks on deformed core-steel

29 OLM - Summary The application of Acoustic Emission was successful in locating the problem in the unit after tear-down The added information provided by the Acoustic Emission results was an aid in the decision-making on whether to take the unit out of service or not The timely information provided to the customer allowed them to maintain this unit in service for 8 months (while waiting for a new unit)

30 Questions? Arturo Núñez Substation Reliability COE Manager MISTRAS Group, Inc. (609)