Today the VFD is perhaps the most common type of output or load for a control system. As applications are more complicated the VFD has the capacity to control the acceleration of the electric motor, the direction the engine shaft is certainly turning, the torque the motor provides to lots and any other motor parameter that can be sensed. These VFDs are also available in smaller sizes that are cost-effective and take up much less space.
The arrival of advanced microprocessors has allowed the VFD works as an exceptionally versatile device that not only controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs provide ways of braking, power increase during ramp-up, and a number of settings during ramp-down. The biggest financial savings that the VFD provides is certainly that it can make sure that the engine doesn’t pull excessive current when it starts, therefore the overall demand factor for the entire factory can be managed to keep the utility bill only possible. This feature alone can provide payback in excess of 
the cost of the VFD in under one year after buy. It is important to keep in mind that with a normal motor starter, they will draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage occurs across many motors in a manufacturing plant, it pushes the electrical demand too high which often outcomes in the plant paying a penalty for all of the electricity consumed during the billing period. Because the penalty may become just as much as 15% to 25%, the savings on a $30,000/month electric expenses can be used to justify the purchase VFDs for virtually every motor in the plant also if the application might not require functioning at variable speed.
This usually limited the size of the motor that may be managed by a frequency and they were not commonly used. The earliest VFDs used linear amplifiers to regulate all aspects of the VFD. Jumpers and dip switches were used provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller resistors into circuits with capacitors to develop different slopes.
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