MV 400 HP VFd alternatives
MV 400 HP VFd alternatives
(OP)
We need to speed up a mill for some testing for a few weeks. Contemplating we may wish to try speed increased up to 20 or even 30%. It's a "medium voltage" 4000 V 350 HP induction motor. The manufacturer says it is suitable for VFD use electrically, with modest speed increases being OK but limited because mechanical rotor characteristics are unknown. 350 or 400 HP 460 Volt VFDs are readily available. 4000 V are not, and expensive too. Some 460 VFD manufacturers publish info about installing a step down transformer before the 460 drive, then a step up transformer between the drive and motor.
We are looking at any and all options to be able to speed up the motor and thus the mill for testing. Are there outfits that rent or lease transformers, or VFD/transformer combos? My internet searches have come up empty so far.
thanks,
Dan T
We are looking at any and all options to be able to speed up the motor and thus the mill for testing. Are there outfits that rent or lease transformers, or VFD/transformer combos? My internet searches have come up empty so far.
thanks,
Dan T





RE: MV 400 HP VFd alternatives
RE: MV 400 HP VFd alternatives
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If we learn from our mistakes I'm getting a great education!
RE: MV 400 HP VFd alternatives
The step-down-step-up arrangement was used a lot in large down-hole submersible pump systems, especially around Texas and Oklahoma. There were / are pump suppliers, Reda and Centrilift come to mind, who used to offer a skid mounted system that was this exact arrangement; a step down transformer, 480V VFD and a custom designed step up transformer all in one package. Most likely there are a few of those floating around the surplus market now.
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RE: MV 400 HP VFd alternatives
http://www.espdrives.com/
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RE: MV 400 HP VFd alternatives
I though a lot of the down-hole applications increased the voltage to say the 700-1000V range to compensate for the voltage drop in the motor leads...
RE: MV 400 HP VFd alternatives
I suspect that as well as reducing the voltage drop and the line loss the transformer mitigated a lot of harmonics. I wondered if the transformer was a standard transformer or one specifically designed to reduce harmonics. Does anyone out there have first hand experience with these installations? Comments welcome.
Bill
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"Why not the best?"
Jimmy Carter
RE: MV 400 HP VFd alternatives
So what they tend to do it design the transformer as if it were being used in high frequencies, i.e. more laminations, low hysteresis higher quality steel (in addition to more mass). The winding insulation is also subject to the same issues as the motor windings as well, and although most motor manufacturers have addressed this, most transformer manufacturers see no need to on standard designs. So transformers designed up front for use on the output of the VFD will have higher voltage insulation material as well.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: MV 400 HP VFd alternatives
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: MV 400 HP VFd alternatives
Bill
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"Why not the best?"
Jimmy Carter
RE: MV 400 HP VFd alternatives
I work for this company (so please note), but the application was carried out at a site I visited recently in S.Korea. This is just for info:
h
However, I am quite sure these systems are not rented out due to the case-case engineering work required.
RE: MV 400 HP VFd alternatives
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RE: MV 400 HP VFd alternatives
I know is some cases the feed transformers are phase shift to reduce the harmonic distortion and this is quite an effective (cost effective) solution due to the fact you would need a phase shift transformer anyway on a LV supply for 12/18 pulse systems and this will incur nearly the same cost. Where we have supplied hi-lo-hi solutions it is usually typical where the end user has been 'burnt' with MV Drives (lack of support) and wants the standard LV VFD offer to minimise risk of downtime awaiting for spares/service etc on MV drives where LV drives are a little more common.
RE: MV 400 HP VFd alternatives
There was an old system with transformers from around 1980 which needed to be run from Siemens standard VFDs fed from a 500 V grid and stepping the voltage up with a transformer. The modernization was needed for several reasons - lack of spare parts for the old system was one.
We used the old, existing transformers, no filters whatsoever and were quite lucky with that. Only problem was that we had difficulties going through the full speed range without getting heavy oscillations in the sensorless inverter/motor system. It was solved by going from frequency mode to torque mode and limiting the braking torque. This system has been running for around two years now.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: MV 400 HP VFd alternatives
With a simple V/Hz drive, it would be relatively easy to limit the voltage boost adjustment to avoid saturating the transformer. With a sensorless vector drive which should be used for a constant torque application, it may be more difficult to figure out whay it takes to avoid saturating the transformer.
CJC
http://www.vfdriveinfo.com
RE: MV 400 HP VFd alternatives
Waross - The transformer should make a very good output filter. I'd expect to see close to a sinewave voltage out of the transformer - better than any other filter besides a sinewave filter.
RE: MV 400 HP VFd alternatives
http://www.espdrives.com/ ........"
The espdrives moderator has still not approved my registration.
Got a few eager calls from salefolks offering a new MV drive for 150 to 200 K$ . They also insist that (their!) modern MV drives are more economical than hi-lo-hi method
$150 K will be a hard sell for this R and D project.
First cut at a 400 hp 460 volt motor and VFD is more like 60,000 bucks
I still expect there are some lease, rental, or good used ones for sale out there somewhere.