Today the VFD could very well be the most common type of output or load for a control system. As applications become more complicated the VFD has the capacity to control the velocity of the motor, the direction the electric motor shaft is turning, the torque the engine provides to lots and any other engine parameter that can be sensed. These VFDs are also obtainable in smaller sized sizes that are cost-effective and take up much less space.
The arrival of advanced microprocessors has allowed the VFD works as an extremely versatile device that not only controls the speed of the electric motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of braking, power boost during ramp-up, and a number of handles during ramp-down. The biggest financial savings that the VFD provides is certainly that it can make sure that the motor doesn’t pull excessive current when it begins, so the overall demand element for the whole factory can be controlled to keep carefully the utility bill as low as possible. This feature only can provide payback more than the cost of the VFD in less than one year after buy. It is important to remember that with a normal motor starter, they will draw locked-rotor amperage (LRA) when they are beginning. When the locked-rotor amperage takes place across many motors in a manufacturing facility, it pushes the electrical demand too high which often results in the plant paying a penalty for all of the electricity consumed during the billing period. Because the penalty may be just as much as 15% to 25%, the savings on a $30,000/month electric costs can be used to justify the purchase VFDs for virtually every motor in the plant actually if the application may not require functioning at variable speed.
This usually limited the size of the motor that may be controlled by a frequency and they were not commonly used. The initial VFDs used linear amplifiers to control all aspects of the VFD. Jumpers and dip switches were utilized provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller resistors into circuits with capacitors to generate different slopes.
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