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A Variable Frequency Drive (VFD) regulates the speed of a 3-phase AC electric motor by controlling the frequency and voltage of the power it delivers to the motor. Today, these devices (also known as Adjustable Speed Drives or Variable Speed Drives) are becoming prevalent in a wide range of applications throughout industry, from motion control applications to ventilation systems, from wastewater processing facilities to machining areas, and many others.VFDs offer many benefits; principle among them the ability to save a substantial amount of energy during motor operation. In that sense, these devices represent both an attractive, “green” engineering solution, and an economical choice. Other benefits worth mentioning include the following: they can maintain torque at levels to match the needs of the load, improve process control, reduce mechanical stress on 3-phase induction motors by providing a “soft start,” and improve an electrical system’s power factor. What’s more, legacy systems that now use throttling devices to regulate motor speed can be retrofitted with VFDs to make speed regulation much more efficient and precise.
Special consideration must be given to the proper installation and operation of the overall system that comprises the VFD, the motor it controls, and the cable that connects them. The way in which VFD-based systems are constructed and operated will have an impact on both the longevity and reliability of all the components of the system, as well as nearby or adjacent systems.
The most significant benefit to using a VFD is energy savings. By matching system capacity to the actual load throughout the entire year, major savings in system motor energy use are achieved.
Another benefit of the units is reduced wear and tear on the motors. When an induction motor is started, it draws a much higher current than during normal operation. This inrush current can be three to ten times the full-load operating current for the motor, generating both heat and stress in the motor's windings and other components. In motors that start and stop frequently, this contributes to early motor failures.
In contrast, when a motor connected to a VFD is started, the VFD applies a very low frequency and low voltage to the motor. Both are gradually ramped up at
a controlled rate to normal operating conditions, extending motor life.
VFDs also provide more precise levels of control of applications. For example, high-rise buildings use a booster pump system on the domestic water supply to maintain adequate water pressure at all levels within the building. Conventional pump controls in this type of application can maintain the pressure within a certain range, but a VFD-based system can maintain more precise control over a wider range of flow rates, while reducing energy requirements and pump wear.
Medium and large industrial sites: Mining, Oil & Gas, Pulp & Paper, manufacturing industry, Metal processing. Medium / large commercial and building areas: Shopping malls, Hotels, Infrastructures: Water treatment, Airport/Harbours, local electrical distribution.