What Benefits can Variable Speed Drives Bring?

1st July 2013 | Posted by Charlotte Miskell

When AC motors start ‘across the line’ it takes around seven to eight times the motor full-load to start up the motor.  This current generates heat which is responsible for reducing the longevity of the motor over time.  Using a variable speed drives to start the motor instead, ensures that the motor starts at zero frequency and voltage.  As both of these build it magnetises the motor windings, reducing the motor full load current by as much as 70%.  This substantially reduced starting current extends the life of the AC motor as opposed to across the line starting.  Customers can expect to see less wear and tear on the motor and are rewarded with an extended motor life.


Starting an AC motor across the line places an enormous drain on the power distribution system which is connected to the motor.  As this happens the supply voltage tends to sag, dependent on the size of the motor and capacity of the distribution.  These sags can sometimes cause sensitive equipment to tip offline because of the low voltages involved.  Components such as computers, sensors, proximity switches and contactors can all be affected by dips in voltage.  Using a variable frequency drive can eliminate this voltage sag and thus saving the components from dropping out.


As power is proportional to the current multiplied by the voltage, the power needed to start an AC motor across the line is much higher than with a variable frequency drive.  Starting across the line can have a number of issues, especially if industrial customers are charged for surges in power – as this is inherent in starting across the line.  Variable speed drives offer much more of a gradual impact on components, as well as having a number of energy saving benefits to customers.



See what benefits variable frequency drives can bring your business


If you are keen to find out how variable frequency drives can benefit your business, then feel free to contact one of our engineers today.  Variable speed drives are a great way to reduce energy and costs as well as stress on your existing machinery.  To speak to our engineers call 01282 872 450 today.

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