Replace, upgrade or retrofit - a designer's AC drive dilemma

Paul Boughton

When redesigning a motor-driven application, a vital decision has to be taken: do you replace, upgrade or retrofit the application's drives? Heikki Kervinen looks at the choices.

When redesigning an industrial application, design engineers are faced with the dilemma of what to do about its AC drives. Should the drives be replaced, upgraded or retrofitted to get the best out of the application and make it more efficient and capable?

- Replacement: For systems using mechanical controls, such as hydraulic couplings or throttles, there comes a time when the cost of maintaining the old installation is out-weighed by the potential energy savings offered by an AC drive. As well as offering more efficiency, replacing these mechanical controls with new AC drives can bring the very latest motor control methods, communications and user interfaces to the application.

Frequently, AC drives and AC induction motors replace slip-ring motors and direct-on-line (DOL) starting. AC drives can also be used to replace soft-starters, bringing improved process control as well as energy savings and improved reliability. This type of replacement is also attractive because the price differences between small drives and soft-starters are no longer as great as they were.

Applications using 12-pulse drives can have these replaced by new active rectifier drives that do not need transformers, which can have losses of around three percent and be difficult to repair. [Page Break]

Whenever there is a need to replace an entire AC drive - from ABB or any other drive manufacturer - or to replace another technology such as mechanical valves or dampers, suppliers like ABB, offer a wide choice of drives of all shapes and sizes, along with invaluable engineering expertise.

- Upgrade: Another fundamental question is whether the AC drive is still providing the correct functionality for the application. Over the past 20 years, AC drives have added a raft of new functions, allowing them to capture data, analyse it using on board software and use the results to control motors via widely used communications protocols such as BACNet. Taking advantage of these functions could be as easy as downloading the latest software or installing some updated hardware.

This could bring many benefits to the process, including faster production times or more data that gives a better, more accurate picture of how the process is performing. An upgrade can have a major impact on the actual process by bringing new levels of efficiency, for example, more accurate positioning that leads to less wastage of materials, while also improving end-product quality. It can also improve the performance and extend both the functionality and the lifetime of the drive to provide the best possible return on investment. [Page Break]

Many ABB drives, for example, only need a simple upgrade of firmware to benefit from new software such as ABB's pump control program. With all the functions generally required by pump users, the pump control program can make it easy to alter a plant's pumping systems or the way its pumps operate.

- Retrofit: In contrast to replacement, a retrofit will look to reuse as much of the existing drive system as possible, while making it more compact, robust and efficient. It also brings the possibility of adding some features new to the application, such as an improved user interface or fault loggers.

In a retrofit project, existing cabling, motors and cabinets are often retained, while the drive or drive system is replaced either completely or partly. A retrofit is typically carried out during planned production shutdowns to avoid unnecessary disruption.

ABB has developed a specific retrofit service for its drives where ABB engineers assess the current drive installation and recommend the appropriate retrofit kit. By reusing as much of the existing electrical and mechanical components as possible, a typical retrofit kit can cost less than replacing the complete drive and cabinet. Benefits include lower capital expenses, reduced engineering costs, lower labour costs, no production losses and quick project execution.v [Page Break]

Quicker payback much easier

A replacement, an upgrade or a retrofit of a drive will usually be undertaken because the process requires new functionality, a serious drive failure has occurred or the original manufacturer is unable to support the product with spares. Whatever the reason for changing the drive set up, a good drive manufacturer will be able to advise on the best route.

Also, it is now easier than ever before to get a quick payback on a drive project - with energy prices rising and drive purchase costs falling to about a quarter of what they were 20 years ago, there has never been a better time to invest in a drive based application. Many countries also offer financial incentives to support the installation of AC drives intended for use in energy-saving projects.

When looking to redesign an application, the motors should not be overlooked. The latest motor designs are more efficient than older ones and are better suited to working with AC drives, leading to even more cost savings.

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Heikki Kervinen is Market Manager, Energy efficiency, ABB Oy, Helsinki, Finland.

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