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Advanced Engineering 2021

NEC Birmingham(B40 1NT)

03/11/2021 - 04/11/2021

Join us in our 12th and most important edition to date, as we invite engineers and management from all (more)

Maximise your drives

Maximise your drives
There's a lot of life in well-protected drives and, what's more, repairs can double their lifespan, says Vic Harris of ERIKS.

There is no reason why a modern DC, AC or servo drive shouldn't operate for around 40,000 hours, or five years, even when used continuously in industrial applications. With appropriate ventilation, some protection from ambient temperatures and airborne contamination, plus some routine maintenance, there's every chance that the drive will live the entire predicted lifespan. Unfortunately, those considerations are not always made, reducing the reliability of drives and, consequently, the systems that the drive units serve.  

However, if engineers do make the right decisions during installation, and implement an appropriate maintenance schedule, the unit will not only function for the full five years but will also be fit to undergo a repair that will double its lifespan. What's more, the repair of a drive can offer more information about overall system health than an outright replacement, so it pays to spend a little time considering the options before splashing out on new equipment.

As mentioned, the factors that can adversely affect drives more than any other are contamination and overheating and there is often a correlation between the two. The accumulation of dust acts as a layer of insulation, confining the heat generated by the components within the drive unit. Dust also obstructs ventilation paths, thus restricting the normal dissipation of heat via the designed cooling system, and absorbs moisture, which can corrode circuits and further contribute to drive failure. The graphs below represent the temperature changes inside two drive cabinets, as measured by ERIKS to help prevent future failure.

A periodic spraying of air through the heat sink fan offers a simple and effective method of preventative maintenance measure, though it must be oil-free, dry air; plant air typically contains oil and water so it is advisable to use compressed air (preferably non-static) to blow away contamination. However, if there is any danger that the air being blown into the drive is itself contaminated with dust, metal or moisture content, it is safer to employ some method of suction cleaning. If dust and other airborne pollutants enter the drive casing and are not removed during regular maintenance, they can cause the fan to fail by damaging the bearings. Once inside bearings, dust can be as harmful as sandpaper to the highly polished surfaces. Fan failure can hasten the decline of a system, causing other drive components, such as electrolytic capacitors, to overheat and eventually fail. 

It pays to prevent these problems by carrying out regular inspections during planned shutdowns for routine maintenance work. Basic drive servicing - including cleaning the cards and fan units, replacing capacitors and checking PCB integrity - can then be carried out, extending drive life and optimising performance without causing downtime.

Having protected your drive as best you can, it will, nevertheless, eventually fail as it does have a finite lifespan. Though you have gained the maximum return or your investment in the unit, you will still be faced with the question of whether to repair or replace a failing unit. However, as with maintenance, a little time and thought applied to the repair-or-replace question can save a lot of trouble and expense further down the line. Drive replacement can be costly in both time and money, especially as the integration of new technology into an older production system can often pose problems. However, a cost-effective alternative to replacement exists, which is to upgrade or retrofit existing units.

Owing to their low cost, units below 4kW are generally not worth repairing, whereas drives of 75kW and above, which tend to be modular and protected by maintenance contracts, do not need to be repaired by plant engineers.  However, there are many units in operation that fall in between those ratings that may be more economically, and conveniently, repaired than replaced.

Though it may seem to be the most effective solution, installing a new drive unit may not necessarily be the best option. Integrating a new drive within your existing system may not be a straightforward operation and, even if it is, a drive replacement may not solve all of your problems. If an exterior fault was responsible for damaging the previous drive, replacement may not reveal the fact and the persisting fault may reduce the effectiveness of the new unit. However, an effective repair is far more likely to identify the root cause of drive failure and could come with a new guarantee equivalent to that of a new unit, without the potential problems of integration. 

ERIKS' drive repairs are supported by a twelve month in-service guarantee (which is the same guarantee that would typically apply to a new unit) and, in addition to gaining information on the root cause of failure, the operator will benefit from an engineer's advice on how to avoid a recurrence of similar problems in the future. When the cost of drive repair can be as little as 50% of that required to purchase a new unit and comes accompanied by the same guarantee plus feedback on the system, it is difficult to argue that repair is not, at least potentially, the best option. 

Even large scale businesses can make savings by repairing rather than replacing. An investment in a drives management programme, during which a detailed survey is conducted to reveal such dangers as failing components and faulty connections, can be more economical than allowing drives to fail and be replaced. So, to maximise the life of your drives it's well worth considering that drive maintenance and repair offers real economic and operational benefits that can not only match but often outweigh the advantages of fitting new drive units.
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