Increased operating efficiencies, decreased energy consumption and lower operating costs are the primary benefits of specifying variable speed drives (VSDs). However, those are just a few of the many advantages they bring to bear. Let’s take a look at some more of the key benefits of these devices in commercial and industrial settings.
Extended Motor Life
Carefully managing the operation of an electric motor extends its useful life. Left to function on their own, motors can demand as much as eight times their normal load at startup. These surges increase the amount of heat the motor must endure, the effect of which accumulates over time. They also place added strain on the motor’s windings. VSDs (also commonly referred to as variable frequency drives, or VFDs) start a motor at zero voltage and ramp it up slowly. This minimizes the power needed to set the mechanism into operation, which in turn reduces the wear and tear on the motor.
Stabilizes Current Flow
When a sudden surge of power is drawn to activate a motor, that excess must flow through the power lines feeding the system. This means they are tasked with handling more load than is absolutely necessary for the efficient functioning of the system. Additionally, when motors draw a huge surge of power, other components in the system get starved, which can cause them to trip offline due to inadequate voltage. This can damage computers, various sensors and proximity switches over time.
Precise Speed Control
We’ve already covered how VSDs ramp motors up to speed gradually. They are also useful for managing the speed of motors once they are in operation. This can be particularly useful in a conveyor system, as it can help keep product in place more readily while being transported.
Let’s take a bottling plant as an example. Ramping up slowly keeps the bottles in place when the line starts moving. The precise speed control afforded by VSDs then allows you to speed up and slow the line smoothly to avoid upsetting the bottles during various aspects of the bottling process. Variable speed drives can also be set to limit the torque output of motors so jams can be addressed without risking overloads.
In some cases, specifying a VFD can eliminate the need for certain drivetrain components. For example, you can use a VFD to slow a driven belt, rather than specifying gearing reductions to accomplish the same task. If your planned system currently relies upon gearing to reduce the speed of a belt driven by a motor, a VFD could replace that gearbox and afford you even more precise control.
To recap, among the key benefits of variable speed drives are:
1. Reduction in power line disturbances.
2. Lower startup power requirements.
3. Precise control over speed, acceleration and torque output.
4. Reduced energy consumption.
5. Cost savings over time.
You’ll note that last benefit was listed with the caveat “over time.” This is because specifying VSDs can make a system more expensive to configure up front. However, the cost savings over time will typically make up for the higher initial cost. Further, the price of VSDs has come down considerably since they were initially introduced, so using them is less costly than ever before.
With all of that said, a soft starter might be a better solution in certain situations, particularly when variable operating speeds aren’t required. Further, VSDs tend to be rather inefficient in no-flow or near-zero-flow conditions. However, if your system can benefit from both soft starting and speed control during operation, a VSD is likely to be the solution you need.