480 VFD feeding a 480\4160 stepup transformer

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I share Besoeker's concern.

_If_ the motor is designed to operate at 4160V and 60Hz, and is fed with a 480V to 4160V 60 Hz transformer...and then the VFD is being operated at 48Hz with an appropriately reduced output voltage, then the transformer is probably fine. Perhaps a suitable filter on the output of the VFD to remove some of the pwm noise would make sense, but I don't know that such is really necessary.

But this is exactly the sort of thing (voltage adjusted to match frequency) that one should not assume is actually what is going on.

-Jon
 
winnie said:
I share Besoeker's concern.

_If_ the motor is designed to operate at 4160V and 60Hz, and is fed with a 480V to 4160V 60 Hz transformer...and then the VFD is being operated at 48Hz with an appropriately reduced output voltage, then the transformer is probably fine. Perhaps a suitable filter on the output of the VFD to remove some of the pwm noise would make sense, but I don't know that such is really necessary.

But this is exactly the sort of thing (voltage adjusted to match frequency) that one should not assume is actually what is going on.

-Jon
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Thank you sir.
Assumptions.
 
Besoeker said:
Quite a lot less if it's a centrifugal pump. But let's not wander off topic.
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I don’t know.. as many can see from my responses I am sorta not bright... but... my drill press runs ok, my saws all cut what they need to cut, and my water pump gets the water from the lower tanks to the upper tank within the day... all of which are from the USA and are doing fine with not just the lower Hz but many times a lower voltage... sometimes we only get 104 volts from the electric company...
 
Adamjamma said:
I don’t know.. as many can see from my responses I am sorta not bright... but... my drill press runs ok, my saws all cut what they need to cut, and my water pump gets the water from the lower tanks to the upper tank within the day... all of which are from the USA and are doing fine with not just the lower Hz but many times a lower voltage... sometimes we only get 104 volts from the electric company...
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No dispute with that but, not particularly relevant to the initial topic.
 
Adamjamma said:
But what if it is a 50 Hz system rather than. A60 Hz system? ....
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Adam - give this some thought, 480V generator, 4160V motor, Las Vegas, and you think it is possibly 50HZ? Better work on that one some more.

GoldDigger said:
I would not make it quite that strong.
There just isn't any evidence that the scenario is anything other than what I lined out. I am well aware you can and likely will point out a plethora of possible facts - but that won't change anything. They are still wrong headed.

They can be programmed to keep constant V/f, and that may be the default, but it is not the only VFD operating mode.
True. And the last time you saw one that wasn't constant V/F in a pump application?

Is the VFD set up to control the motor speed?
Huh? As opposed to what else?

Or is there a steady (adjustable?) speed signal being provided to it? Or is it programmed for a fixed output frequency?
Tell me again - Why would that matter? What would that have to do with the OP

I would also want to be sure that the pulse voltage waveform applied will not damage the transformer insulation, particularly if standing waves are present in the transformer feeder.
Great idea if you are designing one. This one is designed and installed.
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winnie said:
I share Besoeker's concern.

_If_ the motor is designed to operate at 4160V and 60Hz, and is fed with a 480V to 4160V 60 Hz transformer...and then the VFD is being operated at 48Hz with an appropriately reduced output voltage, then the transformer is probably fine. Perhaps a suitable filter on the output of the VFD to remove some of the pwm noise would make sense, but I don't know that such is really necessary.

But this is exactly the sort of thing (voltage adjusted to match frequency) that one should not assume is actually what is going on.

-Jon
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Jon -
It is possible the system is running with Flux Capacitors. But I tend to not go that route.

I'm okay assuming the base system is 60 HZ, the motor is 60HZ, 4160V base, the VFD is operating in the normal programming used for pumps, I'm even going to assume the motor is 3 phase.

Note to all:
They are using a generator to feed a VFD which then feeds into the 480 volt side of a transformer with the pump motor being fed from the 4160 volt side
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This is an operating system.
 
Steve -
If you come back after the big dogs get done with the infighting, go back and read my posts. I'll still be correct.

Of course, if after seeing this display, you choose to not return , that would be understandable.
 
Iceworm

Can you explain the need for a VFD?
Why not just feed the transformer directly from the genny?
 
Besoeker said:
...Can you explain the need for a VFD?
Why not just feed the transformer directly from the genny?
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okay - but my answer is a bit frivolous. I'm not making fun of anybody. I'm making fun of the subject.

For a 2 pole motor, base speed = 3600rpm. (Yes, I know there is slip - no, I don't know the pump is 3600rpm )
At 48HZ, motor is turning (48/60) x 3600 = 2880rpm.

Inexplicably, under threat of severe economic thugery, we must drop the flow rate to 80%, and drop the pressure 64% **

So, two alternatives:
1. Wind a 2.5 pole motor. Operate at 60 HZ. Base speed is (60 x 60) x (2/2.5) = 2880 rpm. However, the stator magnetics for this one are tricky. (Probably have to invoke magnetic monopoles.)

2. Apply a co-linear planetary gear train to the 350hp downhole submersible, ratio 1.25:1. This will leave the motor at 3600 and turn the pump impellor at 2880rpm. However, fitting a reverse coupled, oil tight, .8:1, Fuller overdrive into the diameter of a 350HP submersible is again - tricky. (Picture a semi-truck gearshift knob sticking out of the top of the wellhead)

Oh, new though - Let's put the pump on a VFD and drop the frequency to 48 HZ. That will drop the pump to 2880rpm

Translation: I have no clue why they want to turn the pump at .8 x base rpm. And yes, depending on the pump curve, the flow drops 80%, the head drops (.8)^2 = 64%. Although, not exactly, cause it still has to be on the pump curve.

** pump affinity laws: For D1 = D2, n1/n2 = Q1/Q2 = (h1^.5)/(h2^.5)
For those that could afford to pay attention, yes, it is "head" not "pressure". But that's okay, just divide by the specific gravity.
 
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Whoops another thought:
Can you explain the need for a VFD?
Why not just feed the transformer directly from the genny?
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Maybe you meant, "and use a 4160V drive"
Money, as in at 480V drive and 480/4160 transformer was less than a 4160V drive.
Could be that the transformer is 4160D/480Y, which would be the most common and maybe one they had hanging out back,
as opposed to buying a new 480D/4160Y xfm.

All wild guesses.

the worm
 
And another
How about connect the 480V gen to the 480/4160 xfm, connect the xfm direct to the motor,

Turn down the gen throttle to 1440rpm, turn the voltage regulator to 384V. Probably have to trick the UF and UV trips a bit.

Close all the breakers, start the gen. Voltage and frequency come up together. Built in soft start. I like this one.

But it is hard to accomplish running off the utility.

worm
 
The concept of using a transformer on the output of a LV drive to run an MV motor is old, tried and true, it's done that way QUITE a lot in the oilfield industry for ESPs (Electric Submersible Pumps) and in the deep well water pumping industry. They will use 4000V motors because of the long distance from drive to motor, but they don't have 4160V power available, nor does anyone want to spend $250k for a 4160V VFD when they can use a $100k 480V drive and a $50k transformer. In addition, if they don't have anyone qualified to work on 4160V drives, that can be another factor to sticking with 480V.

Yes, there CAN be issues with the transformer operating at variable frequencies, even if the V/Hz ratio is correct. That's mostly due to eddy current heating of the transformer core and harmonic heating in general (remember, this is the OUTPUT side of the VFD where harmonics are not normally mitigated). In the past I used to have custom transformers made that were designed to minimize the eddy current heating effects (better quality grain oriented steel, formed windings etc.), but after observing several competitors using standard off-the-shelf transformers and consulting with some of my internal engineers, I discovered that what most people do is just over size it to compensate, using a high "K-Factor" transformer, designed specifically for handling higher harmonics. In addition, it's best to operate the VFD output at as high of a carrier frequency as possible, that helps with the heating issues. But that then can ALSO cause added heating in the VFD output transistors (more switching = more switching losses), so you have to de-rate the VFD in some cases.

Still, if I have my druthers, I prefer to use a 4160V drive for a 4160V motor, but that's just me. What most people leave out of this equation is the issue of protection for that transformer. Yes, the VFD can be programmed to current limit and if set at the VFD output rating, that can be indefinite. But current limiting indefinitely into a shorted transformer winding is the sort of thing that causes fires. However if you put fuses on that transformer, the act of a fuse clearing on the output of a VFD is something that can take out the transistors. So yes, this scheme saves initial money in most cases, but at the risk of catastrophic failure if anything happens. Factor in the added operating losses through that down-stream transformer that are PERMANENT losses, and the overall long term cost of ownership doesn't look so good. In the oil-well business that's often irrelevant, because the well may not produce long enough to make that matter. In water wells, it's a real economic consideration. In this case, 350HP is roughly 260kW, but running at 48Hz, lets call it 170kW. If the transformer adds just 2% additional losses, that's 3.4kW in losses every hour so assuming 24hr 365 days running, that's almost 30,000 kWh per year, at .11/kWh the long term ADDED costs to do this are over $3k per year. It adds up...
 
GT6Steve...

Don't believe anyone as asked the following questions:

1) How long has the system been in operation?

2) Have any problems been uncovered/revealed?

3) Is the application that of a very deep down-hole pump? If so, what is the water temperature?

Regards, Phil Corso
 
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Adamjamma said:
But what if it is a 50 Hz system rather than. A60 Hz system? Is there a problem then? Items often designed for 60 Hz USA market get used on 50 Hz systems in Caribbean and other parts of the world without problems... in fact, most problems are minor, such as a pump turning slightly slower.. thus moving slightly less water... possibly two gallons a day less... but the water still gets moved... or a turntable runs slightly slower.. most other problems are not really noticed, unless the Hz is used for timing.
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Adamjamma said:
I don’t know.. as many can see from my responses I am sorta not bright... but... my drill press runs ok, my saws all cut what they need to cut, and my water pump gets the water from the lower tanks to the upper tank within the day... all of which are from the USA and are doing fine with not just the lower Hz but many times a lower voltage... sometimes we only get 104 volts from the electric company...
Click to expand...
Some applications, might not matter, but actual output will be different than if ran at original input specifications. That pump that was supposed to deliver X gallons in an hour may not deliver what your process demands if you don't pay attention to details in some situations. Other times it may have been oversized enough it won't really matter.

The fact there is a VFD involved there may be room for compensation, especially if the load never sees 60 Hz.
 
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