High PD activity ...
... lead to uncovering a critical problem - the incorrectly installed wedges
Company: Midwest US Utility
Ratings: 173 MW, 18 kV, Hydrogen Cooled Turbine Generator, 3 years in operation
Manufacturer: Confidential
Related Info: 25 years old
PD Sensors: Two bus couplers per phase
Case Study Details:"... With the high H2 pressure (30-35 psig) the [PD] levels were expected to be very low but instead were very high after only a year of operation. We initially expected to find problems with the couplers as we did not believe the results..."
High PD activity (slot discharge)...
...was a foresign of an upcoming failure
Company: Western Canadian Utility
Ratings: 184 MVA, 13.8 kV, Air Cooled Hydro Generator
Manufacturer: Confidential
Related Info: 25 years old
PD Sensors: Four PDA Couplers per phase
Case Study Details: The PD data for this unit has been trended for over ten years. In 1995, semi-conducting paint and CRTV were injected into selected bars ...
Intelligent on-line signature analysis...
...revealed broken rotor bars
Company: A large utility in the US northeast
Ratings: 3000hp, 6.6kV 1785rpm Motor
Manufacturer: Confidential
Case Study Details: The suspicion arose from a constant hum during motor operation and abnormal vibration levels during start-up and running. The plant vibration monitoring system did not have the ability to zoom...
High level system PD noise...
...uncovered a well-developed tracking
Company: Italian utility
Ratings: 390 MW, 20kV, Hydrogen Cooled Turbine Generator
Manufacturer: Confidential
Related Info: Installed in 1970
PD Sensors: Two Bus Couplers per phase
Case Study Details: During a partial discharge measurement using the TGA-B portable instrument, high levels of PD activity (over 3000mV position, well above the highest range, see Figure 1) were detected on the C phase outside...
Reading Instability...
...uncovered internal bad connection on a new transformer
Company: US North-West utility
Ratings: 45 MVA power transformer
Manufacturer: Confidential
A customer was commissioning a new 45 MVA power transformer delivered by an overseas manufacturer. During the test, ADWEL's Digital Winding Resistance ReporteR, DWR-10, was consistently issuing a warning of current interruptions, and did not complete the test. Another DWR-10 instrument was used with similar outcome. All other standard measurements, including TTR, Tan-Delta and insulation resistance indicated acceptable resistance value.
Nevertheless, the customer drained the oil and inspected the transformer to detect that the windings on all 3 phases were not properly secured to the bushings. Had the transformer been energized, a catastrophic failure could have occurred.
Authors
Mark Fenger & Steven R.
Campbell, Iris Power Engineering
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