Two maintenance crews performed predictive PM testing a month apart, and got very different results. The testing consisted of voltage measurements and thermography on a section of switchgear that feeds a critical process. A maintenance manager who was standing in for the plant engineer reported the anomaly at the weekly staff meeting.
Alarmed, the plant manager wants a plan for “nipping this in the bud before it bites us in the butt.” Operations has agreed to a half-shift shutdown two weeks hence. The plant engineer doesn’t want the shutdown, and asked you to figure out why the disparity exists.
How qualified are the people who did the thermography?
Mistakes such as poor camera focus produce erroneous results. Hire an outside, Level II thermographer to re-do the thermography. Have this person also review the original images from the other two, and identify technique errors.
Human error can also cause voltage measurement disparities. If you don’t have test ports, people often decide their own test measurement points. They may measure across different impedances and get different readings. Decide on correct measurement points, and use only those.
If the new results show no problems, explain the disparities why they won’t happen again.
