In the past article, we have established that VFDs are useful in applications where the load needs to be driven at various speed. Weve also seen the ease of how VFDs can be integrated into existing control system. But how do you maximize your investment on a VFD in the long run? This article offers useful hints.
Getting The Best Out Of Your VFD
It is pointless to drive a motor that is constantly running at 100% of its operating speed with a VFD. You will only get significant energy savings when the motor is operating at less than its maximum capacity. A VFD can reduce the speed of a pump or fan and opens a valve or damper with a lesser change in pressure.
A VFD does not suffer from hysteresis and outperforms valves and dampers in accuracy and repeatability. Besides that, it also minimizes wear on valves, dampers ducts, and pipes. The lifespan of rotators are increased as using a VFD creates less strain during start. Switchgear also does not suffer from unnecessary burden as the VFD draws minimal current when powered up.
With all considerations in place, it usually takes less than two years to have the savings in cost justifying the purchase of a VFD. A bigger motor usually means larger savings is achieved. Youll typically get great savings when integrating a VFD to a pump, although you need to ensure that the applications that are used do not require them to run at high speed.
Mixers and agitators can also benefit greatly from a VFD. Besides minimizing power consumption, a VFD provides better control in the mixing process. A conveyor system that needs its speed to be varied is also best fitted with a VFD.
Youll also want to take account of the use rate of the system itself. For example, a 50-hp motor that operates without stopping will consume more energy than a 100-HP that only runs for 8 hours on weekdays only. Assuming that both run at a reduced speed, the former one will benefit the most from a VFD.
Durability Of The VFD
As with any electronic product, the VFD is bound to fail eventually. Comparatively, VFDs have shorter shelf lives than soft starters. You may want to factor in the cost of removal, troubleshooting, and installation to reflect a better figure of the total savings in terms of money. If it fails after its warranty period, the repair cost shall be included as well.
The most common cause of VFD failures is the dc bus filtering electrolytic capacitors. This usually happens when the VFD is idling for a couple of years and it affects the electrolytes of the capacitor. To be safe in any situation, keep a VFD as a spare that hasnt be used for years, and get the capacitors replaced.
Its clear that installing a VFD on the right motor greatly increases its energy efficiency. With VFDs coming in different sizes and shapes, it is best to consult an experienced system integrator to know what best fits your application.
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