Variable Speed Drives

What are variable speed drives?

Variable Speed Drives or VSD’s allow the user to increase or decrease the amount of power being supplied to the motor, which in turn effects the speed. This results in only the energy required being consumed, rather than motors running at a constant speed and using a maximum amount of energy. Through the use of motor controllers, users can expect to see between a 25 and 75% saving in energy – a considerable saving in both cost and with regard to sustainability.

Why use variable speed drives

Generally, any process or application that utilises mechanical equipment are powered by a motor, if not many. Across the hundreds of industries that rely on mechanised production, motors are generally powered ‘across the line’ or single speed and are incapable of acceleration or retardation. This results in motors that are unnecessarily running at full capacity, consuming a lot of energy. If you couple this with the fact that around 95% of those motors are grossly oversized, it isn’t difficult to appreciate the benefits that using variable speed drives would bring.

The benefits of variable speed drives

  • Progressive application of starting current – Variable speed drives allow motors to start at zero frequency and voltage. As the power is increased progressively the voltage builds and the motor windings are magnetised. This process typically utilises 50-70% of the motors full-load capacity whereas – in the absence of a VSD – the starting current required across the line can be up to eight times the full-load current. By controlling the starting current motor windings are under far less stress and as a result, the service-life of the motor is significantly increased.
  • Progressive acceleration – When motors are started across the line, power is applied instantly which puts the motor under a tremendous amount of strain. This unnecessary wear on the internal components of the motor will have a dramatic impact on the motors longevity. Where a variable speed drive is in effect, motors are started at zero and accelerated progressively via the control panel, reducing wear-related breakages and increasing service-life.
  • Adjustable speed during operation – Whilst this doesn’t dramatically improve the longevity of motors, it does massively improve the flexibility within a process. Allowing for changes in that process, reduced starting and finishing speeds and convenient adjustment remotely from the control panel.
  • Progressive deceleration and stopping – Equally important and similarly to controlling acceleration, sudden stopping puts the motor under an increased amount of shock. As well as reducing wear and tear, controlled stopping limit interruptions in the production process and reduce the risk of breakages.

European directive on variable speed drives

As of 2011, the EU legislated a mandatory directive for efficiency in LV motors. The efficiency classes were implemented in incremental phases. The first was in 2011, then 2015 and then most recently 2017. The classes are defined as:

  • IE1 – Standard Efficiency
  • IE2 – High Efficiency
  • IE3 – Premium Efficiency
  • IE4 – Not yet defined

We’re now in phase three of the directive, meaning that motors with a rated output of 0.75-375kW must meet either the IE3 efficiency level OR the IE2 level if fitted with a variable speed drive.

Optimise production through using variable speed drives – contact Dualtec

If you would like more information on how VSD’s could optimise your production process and extend the lifespan of your operating devices – get in touch with one of our helpful team on 0153 5609 314.