Reasons to Consider Using Variable Speed Equipment

What is VFD?

Variable Frequency Drives (or VFDs) are becoming almost standard part of aquatics equipment room packages. Most VFDs are fairly simple to install and operate however, they are quite complex with respect to their sophisticated hardware and software impleme ntations. VFD functionality and operation can be greatly improved by understanding basic VFD theory,terminology and interfacing options.

Full-voltage-contact starters have been employed for many years. As can be seen in Figure 1, these starters provide a switch to allow electric current to flow to the motor and start it running full speed. They typically include thermal or electronic overload devices and instantaneous protection devices to keep the motor from drawing too much current and subsequently failing. The reduced-voltage starter is shown in Figure 1-2 and is a more expensive device used to start an electric motor. It employs thyristors only on starting, to limit the voltage and current to the motor. This provides for an acceleration ramp up to the motor’s full speed. The reduced-voltage starter also provides overload protection for the motor.


There are also other means of starting a machine or process that are mechanical in nature. One such means is the fluid coupling. Figure 1-3. A fluid coupling works in conjuction with a prime mover to softly engage or start a shaft. By using hydraulic fluids and centrifugal forces, the fluid coupling softly brings the driven component up to full speed. No variable speed control is attained. Likewise, a process may require perpheral components to be on or off, selectively. These on and off states of motion can be controlled by enaging and disgengaging a mechanical clutch that is connected to a prime mover. Again, no variable speed control is attained with this equipment.

The previously mentioned starter equipment cannot be used to change the speed of a given machine or process. Any time some speed lower than the full, base speed of the systemis requried, variable-speed drives must be considered. Better stated, any time the speed has to change (off of full speed) and conventional gear/speed reduction will not do, then variable speed drives must be employed. Merely slowing the speed of a process or machine down by reducing its speed with gearing still does not allow for speed changes. For example, using a 1750-rpm, full-speed mtor and gear reduction of two to one yields an output speed of 875rpm but no speeds above or below 875. This is when varialbe-speed drives have to be used.

Two other reasons that variable-speed drives are attractive are energy savings and the fact that they can be easily incorporated into the modern-day automated factory. An electronic AC variable-speed drive can operate an electric motor at a reduced speed and at a lower level of power. As for the automated factory conecpt, elecronic variable-speed-drive equipment lends itself well to being interconnected to other electronic factory devices. Microprossors, feedback devices, and communication capabilities make variable speed drives usefull to the automated facility.

Wrapping It Up

Other common names for a Variable Frequency Drive are; Adjustable Speed Drive, Adjustable Frequency Drive, AC Drive, Microdrive, and Inverter. A VFD is a great solution when a flexible fan speed solution is required. The integration of Variable Frequency Drives in HVAC units are becoming required by code. The programming of some VFD’s are complex and can be overwhelming. I suggest you understand its basic functionality, but leave the programming to a skilled electrical worker.

About Fasttobuy

Fasttobuy stocks the drives you need for when you need them. We carry various VFD manufacturers from Mitsubishi to Hitachi to Delta to provide you with a brand you know and trust. Our VFD inventory ranges from 1/4 HP to over 1000 HP, and we supply both single-phase and three-phase drives in various voltages (115 V, 230 V, 460 V, 2300 V, 3300 V, and 4160 V) to help meet the specifications of your current system. We carry new, surplus, factory refurbished, and demo drives to help you find a drive that fits your budget.

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