Practical Preventive Maintenance for VSDs

Modern variable speed drives (VSDs) rarely fail and, like your typical motor car, when well-looked after they can provide many years of incident-free service with a lifespan of several decades. However, as with any car, in order to achieve the longevity intended by the manufacturer, you still need to take good care of your drive, keep it maintained, and ensure that it is operating within its design specifications.

The car analogy doesn't end there. Most motorists are capable of checking their oil levels or keeping the windscreen washer fluid topped up, and similarly, there are some basic maintenance tasks that can be carried out in the field. However, it should be pointed out that anything more involved, i.e.' under the hood', or requiring any sort of component replacement, should be carried out by the manufacturer or an accredited service engineer.

BASIC MAINTENANCE TIPS

Fans and filters should be regularly cleaned to prevent the build-up of dust. Heat is a drive's number one enemy, so it is important to ensure that the drive has a constant supply of clean air to prevent overheating. Indeed, for every 10° rise in operating temperature, the lifespan of the drive's capacitors will halve. This can be prevented by periodically spraying air through the heat sink fan. The air must be oil-free and contain no water. Fans and filters may be replaced in accordance with the manufacturer's recommendations, but again this should be carried out by an accredited professional.

Checking and tightening external connections while equipment is dead and isolated is also important, as heat cycling and vibrations can loosen them over time, potentially resulting in nuisance trips, overvoltage faults, clearing of input fuses, or damage to protective components. This should be done at least annually, or more frequently if the drive is situated in an area where vibrations are likely to be an issue.

Beyond keeping the drive clear of debris and checking connections, preventive maintenance in the field is not so much about the inner workings of the drive itself, but about making sure that the conditions around it are conducive to healthy operation. Excessive moisture, dust, heat and corrosive gases can all affect drive operation, and shorten the time needed between maintenance intervals, as well as the drive's expected lifetime. The more you can mitigate this, the better it will be for your drive. The manufacturer's recommendations for maintenance intervals will typically make the assumption that the drive is operating in a clean and dry environment, free from contaminants. These recommendations should therefore be considered a baseline, as the tougher the environment, the more frequently the drive will need checking and maintaining.

WHEN TO GIVE YOUR DRIVE AN MOT

In normal conditions, a drive can operate for many years without incident. However, this doesn't mean that maintenance can be neglected, because on a long enough timeline, a poorly maintained drive will eventually fail, just like a poorly maintained car. Many facilities are reluctant to interrupt production for any length of time, particularly on critical applications. However, this has to be weighed up against the implications of a drive failing unexpectedly, which can result in much longer periods of downtime, and will have serious knock-on effects on the rest of the facility. Emergency repairs, or sourcing a replacement at short notice, can also be very costly, with the clock constantly ticking in terms of lost production for every second that the drive and/or process is out of action. Regular preventive maintenance is essentially an investment in avoiding failures and eliminating production disruption.

While processes may vary from manufacturer to manufacturer, in ABB's case preventive maintenance can be carried out in three-, six- or nine-year intervals – depending on the type and criticality of the drive, and level of service agreement. A dedicated workshop provides comprehensive inspection, maintenance and testing procedures that are not always possible or practicable in the field due to, for instance, a lack of space, harsh environments, or limitations on access to the device's location. The drive will be stripped down and components thoroughly inspected and cleaned, and any components replaced according to the device's maintenance schedule, or if they show signs of premature wear. The drive is then functionally tested before being shipped back to the customer.

Aside from significantly reducing the likelihood of unplanned downtime from unexpected drive failures, regular preventive servicing can also eliminate performance drift over time, ensuring that it is returned to its original efficiency from the day it was first installed. Allowing the manufacturer to service the drive also guarantees that only genuine spare parts are used, along with factory-approved diagnostics, repair and testing procedures.

THE WIDER CONTEXT

Preventive maintenance can be taken a step further through effective lifecycle management of drive assets. This is achieved by taking a strategic whole-life approach to the management of both maintenance and upgrades for all drives in a fleet, considering maintenance requirements within the context of a drive's lifecycle stage. This can be as simple as sending a drive's serial number to the manufacturer and asking them to check its maintenance requirements, or registering it for reminders when it is due to be serviced. This helps facilities to arrange services around planned downtime, ensuring that their drive remains in peak condition while eliminating the risk of unexpected failures.

Ultimately, better preventive maintenance allows drive owners and operators to exploit their assets for longer, and increase their ROI. The reduced likelihood of failures means that drives have to be replaced less often, which not only saves money in avoiding early replacements, but also means fewer drives need to be disposed of prematurely, helping to lessen the impact of the drive on the environment.

IN SUMMARY

Drives are extremely reliable, and, when well taken care of, will often provide many years of service. However, they are not indestructible, particularly when operated in harsh conditions. An effective preventive maintenance programme can help to significantly reduce maintenance costs, and all but eliminate the cost of having to unexpectedly replace an asset, as well as any unplanned drive downtime that may entail as a result. Implementing such a programme requires a strategic approach, taking into account a drive's age, criticality and operating environment, but when done successfully, it can provide significant benefits for the overall resilience and reliability of processes. Just like your car, if you take care of your drive, it will take care of you.