Turn it off to save money

Edited by the Engineeringtalk editorial team Nov 18, 2003

UK industry is missing out on opportunities for energy saving in its largest area of motor operations, says James Bowler of Fairford Electronics.

UK industry is missing out on opportunities for energy saving in its largest area of motor operations, says James Bowler of Fairford Electronics.

Much has been written about the energy saving role of inverter drives in variable speed applications.

However, by far by far the largest number of AC induction motors used by UK industry are operated at fixed speeds, and although the potential for saving energy with these units has been largely ignored, worthwhile savings can be achieved using energy optimising soft starters.

The "optimising soft starter" offers the advantage of improving motor efficiency at part loads, which reduces energy consumption during the run phase of motor operation.

Although induction motors are relatively efficient machines - motors larger than 11kW, are rarely less than 90% efficient at full load - it is well known that a motor connected to the normal fixed-voltage supply network will experience a worsening power-factor and efficiency as the motor load reduces.

In theory, the potential for energy savings can arise in all aspects of a motor's operation, in practice however it is during the motor run phase that the soft starter's optimising function will act to improve the overall efficiency of a motor, giving rise to an opportunity for energy cost reduction.

Nevertheless, it is important to keep in perspective the extent to which reductions in energy consumption are possible in fixed-speed applications since it is an area where many unsubstantiated claims are made.

Much depends on the efficiency of the motor being controlled.

As a rule of thumb, larger motors tend to be better designed with more copper and iron, relatively smaller air-gaps etc., making for higher efficiency machines, whereas their mass-produced low kilowatt counterparts can exhibit quite low efficiencies.

In addition to energy optimisation there is a method whereby substantial savings can achieved in fixed-speed applications, simply by acknowledging the less savage effects of motor starting when using the Fairford QFE and Startmaster soft starters.

The more gentle start allows a much higher frequency of starting, which means that idling machinery can be switched on and off more frequently.

Simple, automatic detectors are available which, when combined with a Fairford QFE controller can convert conveyors, for example, to a quiescent mode whenever material is not being processed, during lunch breaks etc.

Depending on the operational conditions, hours run etc, very acceptable payback periods can be assured from controlling fixed-speed motor applications in this way.

With the relatively high no-load power requirements of much of the industry's machinery, 20-40kWh or more can easily be saved each hour by the simple act of switching off when no material is being processed.