The Reliability in Action department features case studies submitted by our readers. To have your case study considered for inclusion in an upcoming issue, e-mail it to firstname.lastname@example.org or mail it to Reliable Plant, P.O. Box 87, Fort Atkinson, WI 53538. If we publish your case study, we'll send you an official Reliable Plant T-shirt. Here is this issue's highlighted contribution:
On a routine quarterly infrared inspection of plant electrical power distribution equipment, a high-voltage switch for a transformer was found arcing to the insulation board. A quick and effective response to the dangerous condition avoided a catastrophe at the plant.
The environment at the plant is very humid and the physical assets are 30 years old. The quarterly infrared inspections of electrical distribution equipment routinely reveal significant problems that were not present in the previous inspection.
During one such infrared inspection over the summer, a 12,500-volt disconnect switch for a transformer on the plant roof was found arcing from the switch to an insulation board. Even with a low temperature difference between the fault and the reference temperature - 7 degrees Fahrenheit in this case - this condition had the potential to start a fire in the transformer and cause an explosion if the arcing burned through the insulation board and arced to ground.
The thermographer understood the seriousness of the fault and immediately reported the condition to the plant maintenance manager. After consultation with high-voltage experts, a controlled shutdown was planned to repair the arcing condition and minimize process losses.
The repair was completed within 48 hours of detection without incident and the plant was brought back on line with only about six hours at a reduced rate.
This is a great example of a serious fault with a small temperature difference across components. It also shows the importance of the thermographer understanding the system being inspected and the potential consequences of failure.
In this case, the effective infrared inspection program undoubtedly avoided a catastrophic situation.
Figure 1 shows digital and thermographic images of the back of the disconnect switch before repair.
Figure 2 is the digital image of the insulation board where the arcing situation was occurring.