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Service Report: Ross Hill Load Commutated Inverter

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.

The drive cabinet showed extensive arc-flash damage, evidently from a loose bolt, which had actually

Jon Blakeslee repairing the unit

exploded from the heat, melted the bus bars, and spread molten metal and components throughout the cabinet. The circuit boards and relays were badly damaged, as were the thyristors (SCR) in the power section. The manufacturer had been sold to another company, and they in essence told the customer that nothing could be done to repair this unit.

If this had been a smaller horsepower, or a less sophisticated application, we would have simply suggested replacing the drive, but due to the special motor and application requirements, that wasn’t a viable alternative.

So the decision was made to repair the unit. This required the tedious task of rebuilding a number of circuit boards in addition to repairing the power sections and the relay logic sections. Technicians from EMA New York spent long hours working on this, and finally had it ready for site testing. Once testing began, they discovered that the motor shaft encoder was faulty as well. The encoder was an obsolete model, no longer available. EMA researched and eventually contracted with an encoder manufacturer to supply a modified encoder that would work on this application. (In LCI drives, the exact rotor position must be known at all times in order to facilitate the commutation of the power section.)

Once this was done, the 1000 Horsepower machine once again ran well.

These are the kinds of calls that really set EMA apart from many of our competitors. EMA technicians can rebuild large high capacity power sections, and at the same time, do the intricate troubleshooting and solder work necessary to repair damaged circuit boards.

But perhaps even more importantly, EMA doesn’t abandon customers when the equipment manufacturer tells them there’s nothing that can be done. We can’t promise to deliver miracles, but our company culture really leans away from telling anyone that “there’s nothing that can be done.” We’ll figure out some way to get that machine running again. It’s one of the primary reasons we enjoy such a high customer satisfaction rating; the highest in our industry.

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5 Responses

  1. I didn’t have any idea that you guys could work on that sort of equipment. Thanks for the post.

  2. This was a very difficult repair that involved weeks of research, emails around the world, and much “out of the box” thinking. There were numerous questions regarding how the different circuits worked, the process for calibration and especially alignment of the encoder to the motor poles. EMA had to figure out for ourselves….the original people involved with this drive were long gone. The entire EMA Service Department dedicated themselves to seeing this application run again.
    I was extremely proud when this pump was back online, and consider this one of our most challenging, and satisfying repairs to date.
    Dean Williams
    Vice President of Technical Services
    EMA of NY Inc.

  3. I worked for Ross Hill in the early 90s, first as a test engineer and then as a field service engineer. First job out of college. Sounds like this was a synchronous motor or DC drive. I did some work on the synchronous drives, including some “back to back” testing, and I worked on a few DC drives, but I mainly worked on the medium voltage induction motor drives. I have extensive schematics and documentation for these drives.

  4. For the time it was outstanding .
    It was one of the first to use optoelectronics to fore the SCR with fiber optics .
    That isolated voltage .

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