What a variable speed drive does
A variable speed drive changes the electrical supply to a motor so speed and torque can follow the needs of the process. Drives vary greatly in type and size and need to be selected and programmed for the particular motor and application.
- Pumps
- Conveyors
- Crushers
- Feeders and augers
- Fans
- Compressors
Where the energy saving comes from
Many motors do not need to run at full output all the time. A pump required at full flow during a peak period may be able to run more slowly for the remainder of the day.
For suitable loads, the reduction in energy demand can be much greater than the reduction in motor speed. The source gives an example where a 20 percent speed reduction can produce energy savings approaching 50 percent, depending on the application.
A controlled ramp also reduces the current and mechanical shock associated with frequent starts.
Benefits beyond energy use
- Less mechanical stress on motors, bearings and driven equipment
- More precise conveyor and process control
- Potential reductions in heat and noise
- Integration with existing PLC or building-management controls
Decide from the operating profile
Measure how long the motor operates at each load point, then compare that duty cycle with the proposed drive’s performance. Also consider the remaining life of the plant, installation work, control integration and commissioning.
The right question is whether the expected operating saving and process benefit justify the installed cost over the life of the application.