Transformer Vibration Analysis

1. Transformer Vibration Analysis By George Spencer

2. VIBRATION ANALYSIS on TRANSFORMERS • How we got started. • Where we are today. • What we need to do to advance.

3. M&D Center Substation Project • Started in 1990 at PECO Energy. • All successful diagnostic technology from Power Plant programs was applied to Transformers and Support Equipment. • Vibration, Acoustic Emission and Sound Level were considered Special Tests by most Utilities.

4. 1990 • Lot’s of Transformers were failing, everywhere in the world.(1980-95) • Some Utilities were losing better than one percent of their system. • The average life was and still is 25 to 30 years. • Why? They were built to last a minimum of 40 years at full load. • Could it be that the equipment bolted to the transformer was causing them to fail? • Would better “At the factory” and “On the pad” acceptance testing have identified problem Transformers?

5. Vibration Analysis • An ideal machine would not produce any vibration at all because all energy would be channeled into the work being done. • A transformer is a device, having no moving parts. Although this is basically true, there is some movement in the core steel as the AC magnetic field reverses its direction. • Transformer coils must be rigidly blocked to prevent distortion under the stresses caused by heavy currents. • A good design will produce low levels of inherent vibration. • As equipment parts wear/age, the vibration will increase.

6. 120Hz~0.15ips 240 360

7. Vibration Analysis • Properly applied, vibration analysis can detect mechanical problems before they become a threat to the integrity of the equipment. • This early detection can provide valuable lead time to resolve warranty issues with the manufacturer. • Equipment reliability, availability and useful life are also greatly improved.

8. Causes of Transformer Failures • Loose Windings • Deformed Windings • Load Tap Changers • Cooling Systems • Ownership • Technology Application • Factory Issues • Database and Communication

9. Where we are Today

10. VIBRATION ANALYSIS A “STATE OF THE ART” TECHNOLOGY (As applied to rotating power plant equipment) • Early years were tough 1975-1990 • Customers demanded “Time to failure”, now it’s “how much remaining life?” • Analysts were just getting feet wet • User groups were forming (Things got better fast)

11. Vibration Severity Criteria for Transformers • Started with the following overall levels. • 0.25-.50 ips-…Minor • 0.50-.75 ips-… Intermediate Watch list (further investigate) • 0.75-1.0 ips-… Serious Look for oil leaks, hot metal gasses and increasing sound levels. • 1.00 ips or greater-…Critical Oil leaks, gas generation rates and hot spots.

12. Vibration Severity Criteria

13. X X X X Shell Form Eight readings ~ Approx 5 ft from “bottom of core” – 18 in. from corner 9

14. 0.15@240 0.09@360 0.22ips Side 3R Side 3L 0.9ips Side 4L Overhead View of Transformer Side 2R Snd=78db AE=30Cts Snd=80db AE=35Cts 0.05ips Side 4R High Voltage Side Side 2L Side1R Side 1L NOTE: In addition… IR, Functional Tests and a close examination of Transformer Oil is performed.

15. ComparingLike Transformers • The following two transformers are in the same yard. • They are both the same age and MFG.

16. Average Sound level 68 dbc 12

17. Average Sound level 92 dbc

18. Sound Level

19. Vibration Analysis on Pumps Pump Data Points • Axial (Most Important) • 0.1ips or greater is recognized as a serious condition. (User group issue)

20. Comparing 4 normal Pumps Transformer 1A 120 Hz

21. What is wrong here? Transformer 1B 120 Hz

22. Vibration Severity Criteria

23. Vibration Analysis • New Concept in Recognizing Internal Condition of Transformers • Baseline when new (Trend Changes) • Document Current Condition at Load.(50% or greater) • Assess Pump Condition • High Vibration = Oil Leaks

24. Vibration Data • 120 Hz is the dominate frequency • Acquire baseline spectrum, document 120Hz level. Watch for increases/decreases. • Issues for user group • 120Hz goes to high level…Do we have Deformed Windings? • 120hz goes to low level and sound level increases…Loss of Blocking? • Presence of 60Hz in spectrum (Rare)…What is the cause?

25. What we need to do to advance. Form user group • Determine severity criteria. • Decide on Data Point Locations. (Core and Shell Form) • Agree on “C” weighted sound level data instead of the “A” weighted now used by most MFG. • Evaluate DGA data for relationship between “Hot Metal Gas” generation and vibration levels. • Recommend vibration data be acquired as part of factory acceptance testing.

26. What we need to do to advance. (Cont) • Communicate to the Manufacturer what the acceptable levels for Vibration and Sound Level are. • Perform SFRA analysis on various Transformers with abnormal spectrums.