Acoustic Emission in power transformers. Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P , México, D.F.

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1 Acoustic Emission in power transformers 1

2 More expensive equipment in the substation Many years of operation First indication of a problem: Dissolved Gases Begin investigation to determine the origin of the gases Remove the operating unit for testing online is becoming more difficult. The more information you get with the processor online, the better plan future actions. a) Analysis of Dissolved Gases b) Thermography c) Vibration d) AE If there is a failure: a) On-Site Repair b) Send him manufacturer In both cases it would be very convenient to know the position of the fault POWER TRANSFORMERS 2

3 CASE 1. Overheating of a bar in a transformer machine 25/500 kv, three-phase, 784 MVA Westinghouse, ironclad. Transformer in operation for 20 years without problems. Began to generate gases (methane, ethane, ethylene and hydrogen). Total Gases = 9000 ppm. AGD indicated a thermal fault. Tested with AE for 68 hours in May areas (clusters) of acoustic activity were detected. 3

4 CASE 1. Overheating of a bar in a transformer machine 4

5 ADVANTAGES In-line Non-invasive Detects real-time activity Early Detection LOCATION OF THE FAULT IN 3D Internal inspection is oriented to specific areas on the transformer. Quick Evaluation Highly sensitive Permanent record of the test Global Monitoring 5

6 Flaw Sensor LOW VOLTAJE Acoustic Emission Vertical Depth (0,0,0) Horizontal Event Note: The origin (0,0,0) corresponds to the lower left corner High Voltage side. 6

7 Acoustic Emission SEVERITY A. Normal: No acoustic activity was detected. Continue normal operation. B. Low intensity activity detected: No monitoring is required, keep the area as a reference for future tests or internal inspections. Continue normal operation C. Middle intensity: monitoring is recommended, using other nondestructive tests such as vibration analysis to confirm and monitor the gases dissolved in greater detail. D. Intensive: Scouting is highly recommended. Use other non-destructive tests such as vibration analysis to confirm, increase the oil sampling periods, plan the operation output and consider making an internal inspection or major maintenance 7

8 CASE 2. TR74 transformer Channel 12 Tested in October No events were detected Continuous Activity in channel 12 Fault in January 2003 (15 months after AE test) Area fails: high voltage winding, part down coil phase C 8

9 CASE 2. TR74 transformer Tested in October 2001: Two areas of activity, both in phase C. "Cluster" 1 in the high part of the coil and cluster 2 in the middle. Also, continuous activity was detected at the bottom of the coil. Tested again in February Increase in activity with respect to the test in 2001, the same area where the unit TR74 failed. 9

10 CASE 2. TR73 transformer Tested for the first time in February Acoustic activity source located at the bottom of the coil Phase A. "Cluster" 1 Possible origins: a) Regulating transformer b) Bottom Coil Phase A. (same position - different phase - that units TR72 & TR74) Still operating 10

11 CASE 3. Autotransformer, originally a Westinghouse but repaired by GE in 1989, 138/69 kv, OA / FA / FOA, 50/66/83/93 MVA, core type Oil on top of the high tension nozzle H2 was darkening... 11

12 CASE 3 Do not was expected to find acoustic activity in the main tank because the values of dissolved gases showed normal operation of the transformer. Date H2 CO CO2 CH4 C2H6 C2H4 C2H2 TDCG 7/23/ "Cluster" 1 located a few inches from the wall of high voltage (HV), opposite the area where is located the bottom of this nozzle (H2). 12

13 CASE 4 Detection of partial discharges during the voltage induced test Repair Workshop 230/13.8 kv, three-phase AE was used during the voltage induced test RIV indicated up to 2000 µv and a level of 400 pc in phase A Sensors were repositioned on based on the acoustic activity detected 13

14 CASE 4 Two areas of activity were detected AE detected at 50% of rated voltage AE registered with a levels of 100 µv of RIV Internal Inspection: Discoloration in the insulating paper of phase B Low voltage terminals and changer under load were not separated properly and well insulated. Unit tested after being repaired and obtained a value of 200 µv 14

15 Location of sensors For a transformer of core three phases, install 1 sensor in the general area of the connection of the bottom of each spile. Place additional sensors about the center of each member of the winding on the sides of high and low voltage of tank If additional sensors are available, placing on the ends of the tank. For a transformation of 1 core of one phase, install 1 sensor in the general area of each spile in the bottom connection. Place additional sensors approximately at center in each member of the windings on four sides of the tank. 15

16 Location of sensors If the transformer has a preventive autotransformer inside, you should consider placing 1 or 2 transducers near this location. Using the same sensor locations and settings of the software with the test identical transformers, is allowed to establish environmental reference data for that particular design. The sensors can move to improve the signal reception from a specific source Sufficient coupling gel should be applied to the transducer face to ensure efficient transmission of AE signals from the tank wall to the crystal detection. Blocks of magnetic protection of sensors signal: The place where protection is installed is generally obtained by reference to the images or notes from past experience with the transformer. 16

17 Location of sensors AE sensors are installed in proximity to the high voltage spile. An additional sensor was installed on the opposite side. 17

18 Location of sensors EA sensors on side-wall of the transformer is placed to monitor the inner core. An AE sensor was placed on the opposite side-wall of the transformer. 18

19 Cooling System Efficiency Connects Oil level Accessories (pumps, changer) Termography 19

20 Dissolved gases analysis in field Portable chromatograph Detects all fault gases Results in 20 minutes Can be used in transformers, switches and load derivation changers 20

21 Vibration Loosening of internal components Periodic measurements to detect tendencies in the behavior of the equipment 21