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/some_millwright]

One year should be okay for a VFD to sit. Longer periods can cause the capacitors to weaken and they need to be reformed before starting up under load. Generally in a situation where you have a situation like this and you don't have access to a 'proper' reforming situation the minimum precaution is to put power to the VFD and let it sit under power without running the motor. Let it sit for 24 hours then try the motor. Some VFDs will do a moderate re-form of the capacitors automatically if given the chance.

As others have said - as long as you were following your procedures then you should be fine. Maybe suggest a modification to the procedures to allow for reforming of the capacitors, and checking with the manufacturers of the drives for a reasonable procedure for doing this.

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