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Energy Savings using Medium Voltage VFD

The concept of using variable frequency drives to reduce energy costs is well established. Depending on which survey you read, around 80% of VFD s sold are sold, at least in part, for the purposes of saving energy. No serious person questions the fact that AC Drives save energy.

Affinity Laws for Fans and PumpsDespite the fact that using variable frequency drives to reduce electrical costs is common, it’s often overlooked when running medium voltage motors on centrifugal loads, such as fans and pumps. The image on the right is a simple representation of what’s known as the affinity laws for fans and pumps. Keep in mind, that these aren’t electrical laws, they’re mechanical, but the benefits derived from putting VFDs on centrifugal loads are commonly seen as reductions in electrical costs. However, IF you’re generating your own power in a remote location, you would note the savings in terms of fuel consumption.

Historically, medium voltage VFDs were costly, and unreliable. In fact, here at EMA, the rule of thumb we used was that anything under 2500 HP was probably too expensive to apply a medium voltage drive.

Toshiba Medium Voltage VFDHowever, now we sell medium voltage drives in the 300 – 500 Horsepower range on a regular basis, and the cost savings are wonderful. The state of the art in power electronics is now such that the reliability of medium voltage drives compares with the excellent reliability record of low voltage VFDs. Likewise, the cost of a medium voltage VFD has become much more reasonable in recent years.

Here’s a very generic and simplified hypothetical …

If you have a 2000 HP 4160 VAC motor running a centrifugal fan across the line 24/7, and you pay 7 cents per KWH, your yearly electrical costs are roughly $778,105.00 with a 25% average flow restriction via dampers.

However, IF instead of using dampers, you use a medium voltage VFD rated at 2000 HP, and slowed the motor by 25%, your costs would be $384,475 . An increased savings of $393,630.00

Depending upon your installation costs, for most applications, that’s about a one year payback, and after that, you simply reap the benefits. The larger your motor, and the more reduction you use, the greater the energy savings.

Medium Voltage VFDs are fantastic energy savers! EMA can actually measure your energy usage, and do a precise calculation on what savings you can expect on any given application. Just contact us to discuss any medium voltage application you may have.

We also sell medium voltage motors, and do field service on nearly all brands of medium voltage VFDs. Contact your nearest EMA facility on the bottom of this page, or hit the contact icon on the right.

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