We also listened to sound files taken from the B and C Phase bushings. When scanned with Young’s infrared camera, neither revealed any signs of heat. However, both projected signs of tracking when scanned with the SDT ultrasound collector.
Following a diagnosis of the suspicious transformers, the decision was taken to perform simple maintenance during the next scheduled outage. We were convinced that the discharges identified during ultrasound scanning were, in fact, tracking in its early stages because infrared scans revealed no signs of heat.
Because the problem was found early enough, simple maintenance could be performed on human terms rather than those dictated by a failure.
According to Young, their simple maintenance merely included cleaning and tightening all connections on A, B, and C phase.
When we look at the time signal in Figure 5, we can see that simple maintenance improved the situation significantly. Since tracking is a stage of partial discharge that can damage connectors and insulators, Young will need to keep an eye on the transformers with ultrasound scans.
Gerdau’s case study is a great field example of how combining two predictive technologies ensures that critical issues are identified at the earliest potential stage of failure.
Gerdau was able to prevent excessive transformer damage by detecting the presence of early tracking with ultrasound. They were allowed to schedule maintenance and resolve the issue on their own terms. The best part was that all that was necessary in terms of maintenance was a simple cleaning and re-tightening of connections.
Finally, because the problem was discovered early, electrical maintenance technicians are now aware of a possible weak link in the transformer.
To avoid a more catastrophic outage, vigilance will be increased, and infrared and ultrasound scans will be performed more frequently.
On Gerdau’s transformer issue, ultrasonic and infrared inspections worked well together, and there’s no reason why the combination shouldn’t be considered a winner for detecting partial discharge on insulators, MCC panels, and high-voltage transmission and distribution lines.