Many of the drives we sell and repair at EMA are large horsepower VFDs. Some of the larger horsepower VFDs are medium voltage, but we also see a fair amount of low voltage VFDs in the 500 to 1000 HP range.
Large Horsepower VFDs have many of the same design architectures as low voltage VFDs. This is especially true in low voltage large horsepower VFDs. Medium Voltage VFDs are significantly different, and design topologies vary significantly between different manufactures. ( We have a number of blogs on our site about this.. Click Here for an example.. )
We also repair a significant number of large horsepower DC drives. (See “We still do DC drive repairs” )
The vast majority of large horsepower medium and low voltage VFD repair is done in the field. Unlike their smaller low HP cousins, these large VFDs are not easily replaced, nor are they easily shipped in for a shop repair.
Most of these, especially in medium voltage VFDs, are compartmentalized, such that power cells and so forth can be sent in for repair. In fact, we stock the Robicon power cells. (Click HERE for info)
The ancillary issues that often accompany VFD problems increase substantially with large horsepower VFDs. For instance, Harmonics or other power line disturbances can present significant problems within the power systems feeding large horsepower VFDs. With low horsepower VFDs you can often resolve these problems inexpensively, but that’s rarely true where high horsepower VFDs are involved.
Large horsepower VFDs, especially medium voltage VFDs are 
usually fed by fairly complex switchgear. Sometimes drive faults damage the switchgear, and this can present a troubleshooting challenge to the drive technician on site.
Large horsepower VFDs, especially medium voltage VFDs, require careful adherence to safety procedures. These necessary safety procedures (we often say at EMA, that there is NO casual contact with medium voltage) do make troubleshooting slower. Working on live circuits is dangerous even in low horsepower units, but much more so when around high horsepower VFDs.
Generally, above 1000 HP, you will find medium voltage VFDs almost exclusively. Between about 500 and 1000 HP, you will find a mix of low and medium voltage.
Almost all low voltage VFDs are voltage source inverters, and generally, voltage source is found in medium voltage below 10,000 HP VFDs. Above 10,000 you will tend to find current source medium voltage VFDs.
Current Source VFDs present special challenges to drive techs, and EMA is one of the few companies that provides field service and repair on current source drives.
If you have large horsepower, critical application, VFDs whether low or medium voltage, voltage source or current source, then you should be using us.
We also stock up to 1000 HP VFDs in the event of an emergency replacement.
No One, Anywhere, is Better at Drives than we are.
To contact us.. use any of the methods on the right of this page, OR, call us at 770-448-4644770-448-4644 between 8 and 5 eastern time. We have the highest customer satisfaction rating in our industry.