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How to know if a variable-speed drive is suitable for your application

Variable-speed drives allow users of electric motor-powered processes to improve control, lower energy consumption and extend equipment life. Selection may not always be straightforward, so here are five issues to consider when deciding on a variable-speed drive.

What are your reasons for ordering a VSD?

Reasons for using a drive in applications such as pumps, fans and conveyors include energy-efficiency improvements, controlling starting current, adjusting operating speed and controlled braking. There are models of drives designed to suit almost any sector, from HVAC to wastewater, so matching the application to the reason for use is a good start.

Get the sizing right

Think about the nature of the motor’s load – will it be constant or variable? Also consider whether your process will require frequent starting and stopping or whether it will be continuous. A drive must be able to satisfy maximum motor demand and so should be sized to meet its highest current requirements at peak torque.

What about braking?

Braking requirements will differ between loads – for example, large inertia loads require fast deceleration – and so must be considered in order to reduce stresses on equipment and subsequent maintenance costs.

I/O requirements

Input/output (I/O) terminals are fitted to most drives to allow for the connection of push buttons, switches and other interactive devices. These allow the drive to integrate into control systems and processes. There are both analogue and digital variants, while more complex systems will require multiple I/Os.

Control mode

AC variable-speed drives use one or more control platforms, which include volts-per-Hertz (V/Hz), sensorless vector (open-loop) and closed-loop. The control mode will depend on the level of speed regulation required. For example, while low-voltage applications such as fans and pumps usually require only V/Hz control, closed-loop is normally used in paper mills and printing presses which demand additional speed control.

Gibbons is a founder member of the Authorized Value Provider network, meaning we’re fully approved to offer sales, installation and associated services for ABB drives. So for all technical queries regarding VSD selection, contact Drives Manager Alan Roberts on 07966 468430 or email

Variable-Speed Drives, Electric Motors

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