VFD Accessories
Motors require a great amount of energy when rapidly accelerating to full speed. Variable frequency drives (VFDs) and soft starters can be used to reduce inrush currents and limit torque. This reduces wear and tear caused by frequent starts and stops extending the life of the motor.
Variable frequency drives (VFDs) are electromechanical devices that are used to control the torque and speed of three phase AC motors. This is accomplished by varying the voltage and frequency of the electrical current being sent to the motor. When the motor receives less voltage at a lower frequency, it will run at a fraction of its full speed, thus reducing the wear and tear on the motor while using less energy. VFDs are different from soft starters in that they can control the speed of the motor during both the start and stop cycles, as well as throughout the run cycle. Soft starters can only control the speed during the start cycle.
Using VFDs in industrial applications provide many advantages, such as, easier machine operation and process control, reduction of wear on equipment and ultimately the cost-savings of lower power consumption. VFDs can be used in conveyor systems to provide accurate torque and speed control, reducing the stress on mechanical equipment especially during start and stop functions. Speed control is also possible during run time by installing a remote potentiometer that operators can adjust manually to set the speed for the conveyor. This allows the speed to match the production capacity and ultimately results in cost-savings. Similar process control and savings can be accomplished using VFDs in aquatic applications for pumps that control water flow.
Motor Starters, Soft Starters and VFDs
Motor Starters
Motor starters safely start and stop a motor in industrial applications. They are designed with a contactor, overload and circuit protection. They are used when basic motor control is required, where torque on the motor is not a concern and speed control is not needed. The advantages of motor starters include: lower cost, allows for remote operation, allows for monitoring of motor state (with the use of auxiliary contacts) and they are safe and efficient. The disadvantages include: high inrush current that can cause fuses to blow and breakers to trip if the inrush is too high, and the starter will allow a full torque to start the motor which can cause the motor to ramp up to full speed very quickly potentially causing the motor to wear and degrade prematurely.
Soft Starters
Soft starters protect motors from inrush current by gently ramping up the motor to full speed. They provide all of the same functions as a traditional motor starter. The advantages of soft starters include: they are less expensive than a VFD when only startup control is needed, they are a smaller system than a VFD where space is a concern and they prevent unwanted torque upon startup, prolonging the life of the motor. The disadvantages include: they are more expensive than a traditional motor starter and they do not allow for full speed control.
VFDs
Variable Frequency Drives (VFDs) allow for the slow ramp up of a motor during startup and the slowing down of the motor during shutdown. They also allow for full speed control during the entire run cycle of the motor. VFDs provide the same functions as both the traditional motor starters and soft starters. The advantages of VFDs include: full speed control (start, stop and in-between), more custom control and monitoring, energy savings due to efficient motor usage and less wear and tear on the motors. The disadvantages include: they are more expensive and larger than other motor control options and they generate heat that may require fans or AC units.