Motor rating 2

[Indy]

Hi we have been offered a motor with the following characteristics
22kw 3 phase 50Hz
380V-480V
43.5A-35A
How can we work out the current drawn at 415V 50Hz?

Thanks

 

[xnuke]

Interpolate. It may not be exact, but it'll be close.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Skogsgurra]

That motor has an unusually broad voltage range. Is it really true that current goes down as voltage goes up? In my world, the PF will go down as voltage increases and with it the current. I could buy it if there were two different frequencies - like 50 and 60 Hz. That wouldn't be a perfect fit, either. But close enough.

It may simply be so that a few data are missing from the offer. Like at what frequencies the different data are valid.

The fact that the motor is said to work at 380 up to 480 V may also be a typo. If the motor is a 400 V 50 Hz motor, the 5% limits are 380 - 420 V. So it may be a typo where someone without knowing what it is about wrote 480 instead of 420. You never know ...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Tmoose]

FWIW The FLA for the max and minimum rated voltages work out proportionally OK.

380 X 43.5A = 480 X 35A = 415 X 40A.

I wonder how certain it is that the operating load will be 22kW.

 

[Skogsgurra]

OK. But that is an unusual way of writing a spec. Voltage order: low-high and current order: high-low. That is how confusion is created.

And a motor with that a broad voltage range will not be cheap. If it is possible at all. You will get lots of slip at the low voltage. And heat the rotor a lot. Plus a bad PF at high voltage. I still think that that spec is missing something.

The only possible alternative that I see is that it is an integral motor (with built-in VFD). Then the math works.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Likely he is leaving something out, not understanding it would be important since it wouldn't apply to his situation when using 50Hz.

380V @ 50Hz
460V @ 60Hz

The V/Hz ratio is virtually the same and motors are virtually interchangeable under those circumstances.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[edison123]

If you want a motor at 415 V, 50 Hz, the supplier should offer that motor instead of this nonsense.

Muthu

http://www.edison.co.in

 

[edison123]

Tmoose

It's not that linear. There is flux saturation that comes into play and hence the V/F factor.

Muthu

http://www.edison.co.in

 

[waross]

It may be a 28 kW motor at 480 Volts, but rated as 22 kW. That would allow a full 22 kW from 480 Volts down to 380 Volts.
We something similar with 200/230:460 Volt rated motors. These are basically a 230:460 Volt motor but are the HP is derated 15% to allow safe use on 208 Volt circuits.
eg: a 5 HP motor rated at 200/230:460 Volts is built as a 5.75 HP, 230:460 Volt motor.
It is rated at 5 HP and will safely produce 5 HP at 200 (or 208)volts.
I try to use these for rural applications due to the often poor voltage regulation on long rural circuits.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Indy]

Hi sorry for not being clearer the motor comes with a built in vfd. Hopefully this will clear up some of the confusion.

Thanks

 

[Skogsgurra]

Waiting for input from OP.
Bill's explanation seems to be the most plausible. So far.
But it doesn't explain the reduced current at the higher voltage. An integral motor would.
To some guys, a motor may be a motor and a "black box". So, even a VFD+motor may be called a "motor".

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

To a first approximation that VFD will behave like a constant power load, so the crude V x I calculation will be valid enough for sizing the supply. By my reckoning it will be 40A at 415V, give or take a little.

 

[edison123]

"Hopefully this will clear up some of the confusion."

Nope.

Muthu

http://www.edison.co.in

 

[Skogsgurra]

Thanks Indy!

Nothing is as satisfying as finding an answer to an impossible riddle and that the old Sherlock (Holmes) is live and kicking: "When you have excluded all other possibilities, the only one is the one remaining - how far-fetched it ever seems"

All is clear.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Good call on the VFD Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BlackJackJacques]

Assuming the current given is the kVA current, the power factor is about 0.76 So current at 415 Volts is (22000/(1.73 x 415 x .76)) = 40.3A

 

[7anoter4]

According to ABB IEC Low Voltage Induction Motors 400 V 50 Hz catalogue

http://www.bj-gear.com/fileadmin/filer/dokumenter/combination_20400v_2050hz_gb_2006_2005_1_.pdf

page 5 the motor for 380 V/50 Hz it is wound for 400 V/50 Hz and it can work at 415 V/50 at 98% of rated current.
A motor wound for 400V/ 50 Hz it can work at 480V/60 Hz in the same conditions.

 

[ScottyUK]

7anoter4,

Don't forget that in this case there's a VFD between the motor and the supply. It behaves like a constant power load - more volts = less amps and vice-versa. The motor doesn't see the supply conditions.

 

[rhatcher]

Scotty is correct, the OP stated that the motor includes a built-in VFD so the voltage/current ratings are probably at the VFD terminals, not the motor terminals. I note that both ratings equal about 28kVA which is probably about right for a 22kW motor/VFD combo.

I have employed a similar strategy for customers requiring multiple voltage/frequency ratimgs. The input voltage and frequency to the VFD are irrelevant, within limits, as long as the voltage is high enough to supply the motor. I suspect that the motor itself is rated for 380V/50hz and the internal VFD is hard coded to provide this voltage/frequency irrespective of the input voltage/frequency (within the 380V/50hz-480V/60hz envelope). If this is the case, the current at 415V will be about 40 amps.