The Benefits of Variable Speed Drives

In this industry note, we discuss the economic benefits of implementing Variable Speed Drives (VSDs) on your site.

What is a Variable Speed Drive?

A VSD controls the speed of induction or synchronous motors by adjusting the frequency and voltage supplied to the motor. They are typically installed in the switch room and can be applied to many types of equipment including conveyors, centrifuges, pumps, compressors, and fans.

Electric motors in industry consume about 70% of total electricity demand. VSD technology can provide major energy savings through integrated programming for process control, without the complexity of additional control equipment such as control valves.

The value of a VSD today

Early VSD technology was often unreliable and noisy, however this is no longer the case and guarantees of
1-3 years are now offered as standard. Maintenance requirements are minimal as long as the VSD is in a cool, clean and dry environment.

Using a VSD can significantly reduce maintenance costs for other plant equipment. At lower speeds you will find that bearings run cooler, fan blades and pump impellors last longer, vibration issues are reduced, and belt tensions are maintained for longer.  A VSD can also regulate pump speed to avoid “water hammer” effects and prevent cavitation by monitoring suction pressure.

Additionally, many VSDs now come with built-in logic for multiple pump master/slave constant pressure operation, dry run protection, and minimum flow/runoff protection.

Cost-benefit analysis

The purchase price of an average pump represents only 10% of its lifetime cost, with 32% due to energy consumption and 20% due to maintenance. Power consumption can potentially be halved by operating a pump at 80% of the rated pump speed. Equipment wear is also reduced. The additional cost of a VSD can often be offset by removing the need for minimum flow recirculation lines and control valves. These combined savings can result in a VSD having a payback period of as little as one year.

Guidelines for purchase

Successful manufacturers differentiate themselves by providing off the shelf spares and high levels of technical support. There is value in standardising VSD selection across your plant, as it can allow for simpler integration into the existing control system and reduced spare parts inventory. A VSD can be sold individually or paired with new pumps. Retrofitting is often the most economical choice, but purchasing a combined package can have benefits with the assurance that the motor will be matched to the VSD.

Closing statement

VSD technology could significantly reduce your energy costs. TfA’s team has the capability and experience to advise on the viability of VSD technology for clients looking to take advantage of their benefits.

To learn more about how VSD technology can benefit your operation, please contact Keith Sharp (Engineering Manager) who would be happy to discuss further.