Interest and inquiries about MV drives have increased in recent months. That’s probably due to a number of factors, including improved drive technology, more interest in energy savings, and simply that the vast majority of medium voltage motors are not presently on VFDs.
Research has shown that 70% of medium voltage motors presently operate either fans or pumps. Centrifugal loads are well documented sources of energy savings, given that the power consumed by the load reduces exponentially as the speed goes down. This far exceeds any savings possible with valves, dampers, or vanes, and has been the driving factor in most low voltage VFD applications.
In general, pump and fan applications are easy retrofits, and the paybacks are simple to calculate. Usually, where MV is concerned, the higher the HP, the more cost effective the MV drive will look in terms of initial price.
The market for MV Drives is still very open. Only 3% of medium voltage motors are presently operating on VFDs, and even if you just consider the straight forward pump and fan applications, that’s a large number of very good retrofit opportunities.
Medium Voltage, in general, refers to 2300 and 4160 VAC in the United States. While 480 volts is certainly dangerous, most plant electricians and drive service personnel are familiar with routine safety practices at those voltages. Medium voltage presents a different set of circumstances however, and the number of drive companies that will sell and service equipment at these levels diminishes considerably. Interestingly, arc flash danger on large horsepower drives actually diminishes at medium voltage as compared to a standard 480 volt drive.
The development of medium voltage drives began in the mid 80’s, when GTO s (Gate Turn Off Devices) became available in the 4500 volt range. These were the standard switching device in MV drives until the 90’s, when most notably, the high voltage IGBT (Isolated Gate Bi Polar Device) became available. IGBTs have proven much more reliable. Since they require little in the way of driving current, they’ve permitted MV drives to be more efficient and smaller. Like low voltage drives, newer MV drives are considerably more user friendly than older units.
MV drive applications can present technical challenges. While not unlike that of low voltage drives, the challenges tend to be exacerbated due to higher voltages and power. Harmonic mitigation, along with power factor issues have to be considered. Motor cable lengths can be very important due to dv/dt and reflected waves, and must be considered prior to placing a MV drive on the application. On the positive side, the energy savings can be tremendous. (Toshiba MV Drives allow 1000 feet of cable).
All in all, we expect MV drive applications to become more commonplace. MV Softstarters are also growing. At EMA, we sell the Toshiba MV drives and softstarters, and service all brands. (for a recent service report.. click HERE ). Use the contact form on the right or call 800-848-2504800-848-2504. (see bottom of page for your nearest EMA location)
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