Like many of you, until recent years I was unaware of the effects of harmonic currents on electronics, motors, and motor drives.
Oftentimes, shop repairs just involve diagnosing the problem, discovering bad parts, and replacing them. But in this global world of short-lived products, replacing the parts can sometimes be a challenge.
Here at EMA, we repair a variety of drives (VFDs and DC Drives) from a variety of manufacturers and customers.
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.
A reactor designed for Variable Frequency Drives (VFD’s) is typically nothing more than a coil of wire wrapped around a laminated steel core. The characteristic of the reactor that we desire is inductance, “the opposition to a rapid change in current flow”.
EMA has been servicing the electric motor drives on large tunnel boring machines for some time now. A Drive Lines newsletter article, Boring Service Call, was published in January of 07 about a specific call here in Georgia.
We were asked by Cornell University to look at replacing the VFD and programmable logic controller (PLC) for their boiler’s induced draft (ID) fan. The PLC was an old Telemechanique unit, and the program resided on a 5.25 inch floppy.
We’ve seen two instances recently of extensively damaged Toshiba VT130P2 800 horsepower VFD s. These particular variable frequency drives are often found in waste water treatment plants.
EMA’s Cortland New York service facility was recently called to look at a 1000 horsepower load commutated Ross Hill Drive (LCI). These drives require a special motor, which has a salient pole or fixed field rotor to operate.
Recently a customer requested a VFD with a bypass option to replace a thirty year old stand-alone VFD for his HVAC application. A bypass option permits the motor to be started across the line in the event the VFD fails.