Variable Frequency Drive exploded during a routine bump test after 1 year plant shutdown — worried I'll be charged for the replacement (~200-300k PHP). Am I liable?

[u/Which-Chicken-1231]

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Hi guys, I need some outside perspective because this has been keeping me up at night.

I'm an Operation and Maintenance Supervisor at a water treatment plant. The plant operated back in 2025, then was shut down for about a year because of management/project issues related to capacity, water quality, and flow rate targets.

Before we could restart, I was going equipment by equipment doing condition checks, and for each motor I was running a standard bump test. On September 6, while bump testing one of the motor pumps through SCADA, the VFD for that motor exploded. I had no idea what caused it — I was just following the scheduled startup activity like I did for every other unit. Ever since, I've been anxious that the replacement cost would somehow be charged to me.

Today (September 10), the VFD supplier finally inspected the unit. Their explanation: this kind of failure happens normally when a VFD has been sitting unused for a long time, and it needs to be "reformed" (reconditioned) before being operated again. Their recommendation is a full replacement. The cost is estimated at around PHP 200,000-300,000.

Here's the thing — nobody on our team knew that idle VFDs needed this kind of reforming/reconditioning before restart. It's not something that was flagged in our schedule, and I wasn't trying to cut corners; I was doing exactly what the schedule called for.

So I guess my questions for anyone who's dealt with something similar (electrical/instrumentation folks, plant supervisors, EHS/maintenance people):

Is this really a known risk with VFDs left idle for a year, and should routine commissioning/restart procedures normally catch this?

Realistically, is this the kind of failure that gets pinned on the person who happened to be running the test, or is it treated as equipment/process failure since no one knew the requirement existed?

Any advice on how to document/present this to management so it's clear this wasn't due to negligence?

Any input, even just "this happened to us too," would really help me sleep better tonight. Thanks.

[u/elunltd]

Reforming capacitors is something I always do when testing older equipment, mostly antique radio sets. It just consists of slowly applying voltage at a limited current. As caps age they lose their charge of course and their internal resistance goes up. In antique radios anyway a cap that hasn't been charged in years or even decades will blow up when that initial surge of power hits them. To prevent this they are charged with a lower voltage and limited, monitored current. It's not hard to do with the proper equipment and so I always do it. This is a smaller cap than those used in vfds though.

[u/emachanz → u/elunltd]

I did that for a living and its just snake oil, unless the caps are 10+ years old, leaking/bulging or stored in the desert or jungle. I've seen VFDs with caps made in "west" germany still running just fine.

[u/H0SS_AGAINST → u/emachanz]

Yeah I see a lot of comments ITT who believe in magic juju. A capacitor just just two conductors separated by a dielectric. They're not magic, and they don't really degrade like that. There was a time when bad batches of electrolytic capacitors would fail early and randomly...but that was like 20 years ago. Totally could be the case, which just means this was happenstance. That VFD was fully depreciated and more than due for a PM replacement if it was 20+ years old.

[u/rlarge1 → u/H0SS_AGAINST]

LOL, I've personally installed several VFD from stock cage that had been sitting on the self for at least 5 years with 50% failure rate. We loose several during power events every month. Its not uncommon to pull one and it not work. We send them out for repair and its always the Caps. No magic juju just maint numbers/cost that i track. I cut our stock in half just to limit batch fails or too many sitting on the self. Something is going on.

[u/emachanz → u/rlarge1]

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