Case Study by: Joseph D. Gierlach Jr., TEGG Corporation ~ Pittsburgh, PA
During a scheduled inspection of a facility for a major food processor a number of deficiencies were identified and documented including one ultrasonic class problem within a 12,470 VAC safety disconnect switch (similar to Figure #1 below) feeding a primary side of a main service, oil-filled transformer with a 480 VAC secondary. This was one of two major components that did not make the inventory list for the original inspection program.
Being the conscientious technicians, the contractors decided to listen to the switches with their ultrasonic probe using both the airborne scanning module and the contact attachment. Up on the mezzanine servicing the Main Distribution Panel, there were the two switches, one fed by the 12,470 VAC coming in from the utility, and the other tapped from the line side of switch number one. The vented bottoms of the enclosures made the use of the airborne scanning module elementary. The first switch appeared normal while the second switch had a different tonal quality and also intensity. They made several recordings of each switch.
The red trace illustrates the first switch in which there were no ultrasonic emissions present. The white trace is the recording of the second that clearly has an anomaly indicating tracking. This spectra view disclosed that something was taking place in the second switch that could be nothing short of imminent failure. Action had to be taken as soon as possible with this discovery.
After the switches were secured and opened, a visual inspection quickly uncovered two major deficiencies that could have never been identified while in operation and undoubtedly would have failed at some point. White, powdery residue that is typical of nitric acid was clearly present on conductors and a mica board indicating a potential for an explosion which could disrupt a production and become very costly.
Repair work was initiated. New conductors were cut to length, a mica board was cleaned of all residue that could contribute to a path for current flow to ground, all connections were tightened and torqued to specifications, and the entire service completed with the customer close by to witness the efforts. Once the repair and replacement of the conductors was completed, the final checks with a ductor were performed to ensure that good, solid electrical connections were present to minimize the heating effects of the passive points. Upon completion of this final task, the procedure to restore the utility supply was initiated. Although the units were not part of the preliminary inventory, the discovery of the ultrasonic emission and subsequent analysis with the UE Spectralyzer software indicated a major problem that needed attention. These contractors went beyond their “call of duty” and prevented a major incident for their client in the process.