Plant & Works Engineering
Why do drives fail?
Published:  06 November, 2015

A drive could theoretically last for a lifetime, but only if properly taken care of. Modern variable-speed drives (VSDs) are exceptionally reliable these days, but they’re not indestructible. That said, if you notice similar persistent or repeated trips in a VSD, then chances are that the drive isn’t actually the problem. If such trips are ignored (e.g. over-temperature), they can sometimes result in the failure of the drive. ABB outlines some of the primary factors that can contribute to why variable-speed drives trip and/or fail.

Incorrect installation

This is the single most important contributory factor to drives tripping or failing, and yet the one that should in theory be the easiest to avoid. For starters, the ambient temperature around the drive shouldn’t exceed 40°C. If the location of the drive makes this impossible then there are ways around it, for instance by cooling the drive externally, but this isn’t an ideal solution and will of course increase energy usage. It’s also important to keep the drive dust-free, as dust can impede the air-flow and lead to overheating.

The drive must be kept dry, as moisture will corrode the circuit boards over time. This can be difficult in, for instance, the food industry where equipment has to be regularly washed down, but again there are ways around it such as mounting the drive in an enclosure with the appropriate ingress protection (IP) rating.

It’s up to the customer to ensure that the authorised value provider (AVP) is briefed properly on exactly where and how the drive will be used.

Poor maintenance

Planned maintenance is far more cost-effective than unplanned breakdown repair, so to prolong the life of your drive as well as saving time and money, it is vital to have in place a programme of preventive maintenance such as annual inspections all the way up to remote monitoring services.

While these things are generally best left to the pros, there are some maintenance activities you can carry out yourself. Spraying compressed air (make sure it’s dry and oil-free) through the heat sink fan will help to keep it clear of dust, and checking connections can prevent arcing from heat cycles and mechanical vibrations. The capacitors in a drive will also wear out over time (usually 5-10 years) and require replacing, so this is something that needs to be checked. Capacitors work much like batteries, and so if the drive is rarely run at full output it’s a good idea to power it up every six months or so to ensure that the capacitors remain at peak performance capability.

Excessive loads

When an operator gets to know their machine it’s natural to want to push the boundaries and see what it can do. This is all well and good if you’re Scotty from Star Trek, and can rig up an inverse tachyon pulse to save the day, but in the real world your drive won’t thank you for running it over its rated level. Often drives are run over capacity due to a lack of experience and/or training, so it’s important to ensure that all operators are aware that running a drive beyond its capabilities can and will damage it, and I doubt they’ll be keen on picking up the repair bill.

For further information please visit ABB’s videos in its “Ask the experts” series on the ABB Authorised Value Provider UK YouTube channel.