How variable speed drives save energy

Most standard motors on the market are made to run consistently at the same speed, that speed being determined by the supply voltage, the frequency and the number of magnetic poles within the device. They are sometimes referred to as fixed speed systems, due to the fact that they cannot change their speed without additional components being added to them.

One problem that many users find with fixed speed motors is that it’s very difficult to find one that provides the perfect speed for what they plan to use it for. What’s more, you’re likely to come across one that is close enough, but this means using unnecessary amounts of energy and paying for it, too.

That’s where variable speed drives come in handy. These useful pieces of technology have been known to save some users around 50% of the energy they were previously using when running their standard motors.

What are variable speed drives?

Variable speed drives, sometimes referred to as adjustable speed drives, are mechanisms that allow users to vary the speed of their standard motors.

By manipulating both the voltage and the frequency of the motor, users are able to choose what speed the device runs at, as well as finding the perfect speed for your own specific applications. Doing so can reduce energy consumption massively – in fact, some users have benefitted from savings of over £9,000 per year.

With variable speed drives, not only will you make impressive energy savings, you will also reduce the amount of wear on machines as well.

The method behind these energy savings

Variable torque loads

Research has found that variable torque load applications, such as with fans and pumps, can achieve the most significant energy savings using variable speed drives. If these pumps or fans run at as little as half the speed they originally were, the user is able to cut energy usage down to one-eighth of the original usage.

The amount of torque required to operate a fan or pump is around a square of the volume. In order to reduce the fan’s speed to 80%, for example, requires just 65% of the torque and to create that amount of torque requires 51% of the power.

Energy can be reduced even further by introducing what’s known as motor flux optimisation. Again, this comes especially in handy for fan and pump applications under light load conditions.

Pressure, level and temperature control

As mentioned earlier, variable speed drives work by altering the speed of the motor to match the amount of effort that is needed for a specific application. To be able to vary the speed of the motor precisely and effectively, a closed-loop regulator is required, something which measures the amount of output needed for a specific process.

This method is often applied to pressure, level and temperature control, using what’s known as a Proportional-Integral-Derivative control loop.

Load level dependant

Variable speed drives can be used to prevent power loss in a motor under low load conditions. The drive will work to alter the voltage to frequency application depending on the specific load levels. All of this helps to reduce the magnetizing current and the power loss within the motor.

Circulating energy

Some specific variable speed drives work to circulate the energy between motoring and braking drives, thus reducing the energy costs associated with running the motors.

This is particularly useful when machines are used to wind, unwind and rewind materials. In order to do this effectively, the material has to have a good level of tension, so one mechanism is braking to unwind the material, whilst another mechanism is motoring to wind it back. By using a device to circulate the same energy throughout the entire process, you’re able to significantly reduce running costs.

Returning energy to the AC supply

It isn’t possible to feed power back into the AC main supply, which means that any leftover energy is typically converted into heat. Certain variable speed drives are able to allow energy to flow between mechanism and the AC supply, making greater use out of the energy provided and lessening the amount of wasted energy too.

These are just a few of the ways in which variable speed drives can work to save users energy, when running a standard motor. Head over to our collection of variable speed drives, for further information about each of the drives, their specific uses and the benefits they can deliver.