Before the UL101 ultrasound detector was being used for routine maintenance in their electrical system, an aluminum mill had an issue with this connection on a 2000 kV transformer at one of their facilities. The "former" technician did not buy the correct sized cable, though. They decided to put three cables together in one crimp figuring those 3 together would carry the same rated ampacity as buying the recommended cable. It went by for several years like that but no one knows at what point the cable got as corroded as it did.
The UL101 was purchased and the maintenance technicians were trained as part of the predictive maintenance program. Electrical inspections are now performed quarterly in panels and on the transformers using both ultrasound and infrared.
Once the UL101 was utilized, it was discovered that this connector was producing ultrasound caused by the corrosion. However, infrared did not detect the problem due to no heat being emitted. The transformer was turned off during production off-hours and visually inspected. The corrosion was apparent when looked at closely. The corroded cable was replaced and put back into service at a cost of $200.
There are two other scenarios that could have occurred if the UL101 was not used to discover the partial discharge from this connector.
- Corroded connection shorts tripping breaker, shuts down equipment unexpectedly - estimated $8,400 cost avoidance savings ($3,300 probability weighted benefit)
- Corroded connection shorts tripping breaker, shuts down equipment unexpectedly, transformer gets damaged beyond repair, must be replaced with new - estimated $118,000 cost avoidance savings ($59,000 probability weighted benefit)
The UL101 continues to be utilized for routine inspection for the electrical and mechanical predictive/preventive maintenance programs. And now, InCTRL is being integrated into the program for recording, trending, analysis, and reporting.