Maintenance: Preventive vs. Corrective

By Joe Sarver

You do the math—you make the call

In the midst of one of the rainiest falls on record, a Delta field service engineering team was called in to a municipal waste water treatment pumping station to troubleshoot a 10+ year old 200HP sewage pump drive that was down. The symptom was that the drive was blowing fuses. The conditions at the station were such that the flow thru the plant was normal and being handled by the redundant pump. However, given the weather forecast for heavy rain, the pressing concern was not having the downed pump available should flow through the station approach the design flow rate. This could easily occur with the impending rain and result in serious wastewater flow problems.
Upon arrival Delta engineers inspected the drive and, as expected, found a blown fuse. We replaced the fuse hoping that the drive would stay on line long enough before the fuse would blow to make some electrical measurements and physical observations. Luckily, the drive did stay on just long enough for us to notice an internal arc that was occurring near a bus lead lug on the VFD driver board. As the troubleshooting process continued it became evident that the arcing we observed had damaged components on the driver board. The arcing had occurred from a simple loose connection. In fact, all bus lead terminal screws were less than finger tight. We cleaned up the damaged terminal and checked and tightened all connections. We were lucky enough, and believe me, this is not often the case, that even though the drive and its parts are long since obsolete, a spare driver board was available from the parts kit that came with the original installation. We replaced the damaged board with the spare. Upon power up, the drive ran without any further problems. We had successfully restarted the drive within an hour of our arrival on site.
Given the obsolete nature of this drive, Delta engineers decided to take the failed power board back to the repair bench at our shop and fix it. After a couple of hours of troubleshooting, the Delta drive technician traced the problem to two shorted board components a transistor and diode.
The total cost for this emergency repair was $954.10. A field preventive maintenance (PM) procedure on this drive costs $150. You can do the math. This failure occurred because of a loose connection. This is a condition that is easily corrected during the Delta VFD PM process. In addition to the hard cost, is the value of knowing that your equipment has been properly PM’d. Additionally, and perhaps equally as important for one’s career, is  that potential failure (and thus the criticism for neglecting your equipment) has been minimized. Knowing the facts as described above, what is the call you would have made – preventive maintenance or corrective maintenance?
Delta Automation can help you avoid problems before they start. Our PM program conserves budget dollars and potentially catastrophic failures. As in this case, failure-induced downtime could have created a critical situation that could not be tolerated. Take that proactive next step and ask Delta for a no-obligation, no-cost, VFD PM price quote today.

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About deltaautomation

President of Delta Automation, Inc. Working in industrial automation in excess of 30 years
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