What happens when the problem goes beyond the drive application?

Last month we had a callout to a utility customer who had an ABB low harmonic 315kw VSD fail on short circuit failure, this was in the early hours of a Sunday morning and the failure was beyond an onsite repair due to the extent of the damage.

So we were on site and installing a hire drive within 3 hours of the initial call. The installation went smoothly and our engineer was on his way back to our repair centre to deliver the damaged modules to our internal repairs team, ready to begin the testing and repairing on Monday morning. However an hour into the journey he had a call from site indicating that the hire drive was tripping, the engineer returned to site and found the hire drive was tripping on overcurrent even before the drive was fully powered on, showing us the CT readings from within the drive were being corrupted.

We suspected that this was down to sever harmonics on site, and that the low harmonic drives were not suffering from this as they are protected by the ALCL filters. In order to ensure this was the issue we called in one of our other on call engineers to bring the harmonics analyser so we could monitor the sites network.

Whilst this was happening another of the client’s engineers came to site, and remembered that they had spare modules in another location, however these hadn’t been maintained in anyway or ran for over 18 months. So we collected the spare modules and brought them back to site, we reformed the capacitors on site, whilst our second engineer was logging the harmonics.

The reforming complete, we tested the modules and they passed, so we installed and ran them without issue. By now the logging had been on for a couple of hours so we reviewed the results, which showed cyclic distortion and quite a bit of movement in the harmonics, so we decided to run the harmonics test for a long period and get a bigger sample. We later managed to get a profile for the harmonics and have quoted for the supply of an active power quality filter that will resolve the issue.

When dealing with larger VSDs you need a depth of services available in order to resolve issues like these quickly and efficiently, and also that even when you are holding spares they should be maintained to be of use in a breakdown situation.

If you think you may have a potential harmonics issue on your site then contact us at [email protected] and we can arrange a free harmonics spot check at a time that suits you.

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