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When should I replace, upgrade or retrofit an AC drive?

Many of the AC drives used by the building services community are approaching 20 years old. With careful maintenance throughout this period, the drives should still be giving good service. But there comes a point in any drive’s life cycle where the decision has to be taken: do you replace, upgrade or retrofit? But which is best and when is each relevant?

If you have been maintaining your AC drive well over the past 20 years then it is highly likely you have in place the prerequisite for all AC drive owners, a preventive maintenance program.

For a free on site appraisal of your existing AC drives simply e mail Quantum


Such a program ensures that any components likely to degrade by their very nature, such as the capacitors used within AC drives, are replaced at regular intervals. And here lies our first definition – replacement. It is widely accepted that component parts of an AC drive (such as the capacitors) or a motor (such as the bearings) will need replacement during their lifetime and this is the role of an effective preventive maintenance program.

However, a replacement program can extend beyond the component level. At some stage, the cost of maintaining the old installation, such as hydraulic coupling or throttle control, is out-weighed by the potential energy savings offered by an AC drive. In some cases it is more cost-effective to replace the old drive with a new one that not only is more efficient but uses, among other things, the very latest motor control method, communications and user interfaces. The warranty that comes with the new AC drive will also play a part in this equation, as it ensures low service costs for the first years.

Frequently, AC drives and AC induction motors are installed to replace slip-ring motors, direct-on-line (DOL) starting or soft-starters. There is not much of a price difference between a small drive and soft-start anymore. Replacing with an AC drive means that the benefits of energy savings and improved process control come as part of the package. If an old soft-starter is replaced with an AC drive, the improvement in energy efficiency can quickly pay for the replacement. It is also possible to remove old PLCs and let the logic in the AC drives do the number-crunching.

Applications with 12-pulse drives, used to help mitigate harmonics, can also benefit from being updated with more current AC drive technology. 12-pulse drives use transformers that have losses of about 3 percent. These AC drives can be replaced with new active rectifier drives that will dispense with the need for transformers – and their associated losses – altogether. This will also make the site less prone to disturbances, as a faulty transformer can take weeks to replace, due to its sheer size and weight. A faulty drive, by contrast, can be repaired by a service engineer carrying a case of spares.

For a free on site appraisal of your existing AC drives simply e mail Quantum


The next choice to be considered is whether the AC drive is actually giving you what you want. During 20 years, technology moves on and today’s AC drives offer a whole raft of new functions that were only dreamed about in the early years. In many cases this does not mean you have to throw away your existing drive. Depending on its age, you could decide to upgrade the technology to add functionality, either by downloading the latest software or applying a hardware update.

There are many reasons why this may be a good course of action. It could be that enhanced communications are now needed; or more process intelligence is required including exact energy saving levels measured in kWh, CO2 emissions or in monetary terms. In fact an upgrade can have a major impact on the actual process by bringing new levels of efficiency and control.

So an existing AC drive can often be upgraded by adding the latest software or hardware options to improve the performance of the application. Drive upgrades are designed for improving the performance and extending both the functionality and the lifetime of the drive to provide end-users with the best possible return on their investments.

For a free on site appraisal of your existing AC drives simply e mail Quantum


That then leaves retrofit. It may be that no process changes are required but that the existing drive system, in its entirety, is coming to the end of its life cycle. ABB calls this the classic phase and it is here when the product support and access to spares is being tapered off.

A retrofit will endeavour to salvage as much of the existing drive system infrastructure as possible, while introducing a far more compact, robust and efficient drive. It also brings the possibility to have some new features such as an improved user interface or new functionality such as fault loggers.

Today, manufacturers like ABB offer a well defined life cycle management plan which ensures that any AC drive is maintained to the highest standards, thereby ensuring that the risk of failure is minimised. The life cycle management plan looks after all likely areas of drive failure and makes sure there is a plan in place to combat any risk.

For example, inadequate cooling is a common source of failure. If AC drives are not maintained according to the manufacturer’s maintenance schedules – such as regular replacement of air filters and annual checking and cleaning of heat sink fins – then insufficient air flows through the drive, causing failure.

However, there comes a point in any product’s life cycle when it has to be phased out as newer models with the latest technology just make the support of existing technology counter-productive.

It is at this point that taking out the old drive and fitting a new drive becomes the most economical option. Some manufacturers are developing services in anticipation of their legacy products being retrofitted.

In a retrofit project, existing cabling, motors and cabinets often remain in use, while the drive or drive system is replaced either completely or partly. Retrofitting is typically carried out during planned production shutdowns, without causing extra production downtime.

For a free on site appraisal of your existing AC drives simply e mail Quantum

Don’t forget the motor

The decision to replace, upgrade or retrofit a drive will be usually the result of either: stricter production or process requirements calling for existing drive replacement; a complete failure of the drive, making it irreparable; or the original manufacturer unable to support the product with spares.

Whichever project type is being undertaken, getting payback on drive installations is much easier now than it was when the sites were built, as energy prices have gone up while the prices of AC drives have fallen to about a quarter of what they used to be 20 years ago.

When replacing an AC drive, the motor should also be considered. The typical life of a motor is 15 to 20 years, so if the drive is due for renewal, so is the motor. New motors are more efficient than older ones and are better suited to working with AC drives.

For a free on site appraisal of your existing AC drives and motors simply e mail Quantum


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