Table of Contents

1		Introduction
Replacing old motors
2		Is it for me?
3		How much does it cost?
4		What are the benefits?
Soft starters
5		Is it for me?
6		How much does it cost?
7		What are the benefits?
Variable speed motors
8		Is it for me?
9		How much does it cost?
10		What are the benefits?
11		Step by step guide
12		Case studies
13		Where can I find out more?

Variable speed motors: Is it for me?

For motors operating under varying loads, the motor speed needs to be varied to achieve the best performance. If not, there would be an excesss power supply, which is wasted energy.

Variable speed drives (VSD) are devices that allow shafts speed to be varied according to the driven load, thus reducing the energy consumption. Additionally, they provide soft starting, giving them the advantages of soft starters. See in the next figure, how VSD can decrease the energy consumptions in pumps.

Variable speed motors are available for all power levels. However it is necessary to take into account the following:

The cost-effectiveness of a VSD increases with the variation of the load and the operating hours.

• There is no mass production of VSD for high power motors, so in these cases, they must be custom-made, which increases the price.
• VSD are not usually cost-effective for motors less than 10-15 kWpower.
• VSD could be used to overcome problems associated with the starting. However, this is not the case because of the large price difference between a VSD and a soft starter.