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 ability to control the speed of the motor, the direction the electric motor shaft is usually turning, the torque the electric motor provides to a load and any other electric motor parameter which can be sensed. These VFDs are also available in smaller sized sizes that are cost-efficient and take up much less space.
The arrival of advanced microprocessors has allowed the VFD works as an exceptionally versatile device that not merely controls the speed of the engine, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs also provide ways of braking, power increase during ramp-up, and a number of handles during ramp-down. The biggest financial savings that the VFD provides is definitely that it can make sure that the motor doesn’t pull extreme current when it begins, therefore the overall demand factor for the entire 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 under one year after purchase. It is important to remember that with a normal motor starter, they’ll draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage happens across many motors in a manufacturing facility, it pushes the electrical demand too high which frequently outcomes in the plant spending a penalty for every one of the electricity consumed during the billing period. Since the penalty may be as much as 15% to 25%, the financial savings on a $30,000/month electric costs can be utilized to justify the buy VFDs for practically every electric motor in the plant even if the application may not require working 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 initial 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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