75HP 380v 60Hz motor
75HP 380v 60Hz motor
(OP)
OK, we have an order for two machines going to Brazil. The voltage there is 380V/3PH/60Hz. We use Weg motors that just happen to be built in Brazil. For some strange reason, they are telling us this is a long lead custom item that will take months to get. IT'S BRAZIL'S STANDARD VOLTAGE AND THE MOTORS ARE MADE THERE!!
Anyway, my question: Is it possible to use 460V/3/60Hz motors and re-nameplate them to 380V/3/60Hz? Would you use the high or low voltage taps (208-230v or 460v). There has been a mixup with our purchasing department and we may need to get these motors ASAP.
I'm thinking that the widings should be large enough on the 230V taps because 380V will draw less amps. I'm sure there are V/Hz ratio considerations and such, but the only information I could find was going between 50Hz and 60Hz, not 60Hz to 60Hz.
Anyway, my question: Is it possible to use 460V/3/60Hz motors and re-nameplate them to 380V/3/60Hz? Would you use the high or low voltage taps (208-230v or 460v). There has been a mixup with our purchasing department and we may need to get these motors ASAP.
I'm thinking that the widings should be large enough on the 230V taps because 380V will draw less amps. I'm sure there are V/Hz ratio considerations and such, but the only information I could find was going between 50Hz and 60Hz, not 60Hz to 60Hz.





RE: 75HP 380v 60Hz motor
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RE: 75HP 380v 60Hz motor
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RE: 75HP 380v 60Hz motor
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: 75HP 380v 60Hz motor
You'll have a size problem too?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 75HP 380v 60Hz motor
We are waiting to hear from our motor supplier as to what they plan on doing. We knew that they could be long lead custom motors, but the PO's got "lost in the mail".
RE: 75HP 380v 60Hz motor
Assuming original full load nameplate torque is Tnp and the associated slip is Snp. Original slope is Snp/Tnp
Reduce the voltage and the torque at original Snp is Tnp * (380/460)^2 = Tnp*0.83^2.
The new slope is [Snp/Tnp * (1/0.83)^2]
Apply the derating -> We will limit the applied torque to the new torque [T*0.83]
The slip at the rated torque is new torque times new slope = [T*0.83] * [Snp/Tnp * (1/0.83)^2] = (Snp/Tnp)/0.83
About 17% more than the original slip.
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RE: 75HP 380v 60Hz motor
This is probably your fastest and cheapest solution. I'm short of time just now and can't do the calcs. but if you're interested I will probably have time on the weekend to give you transformer sizes and voltages.
respectfully
RE: 75HP 380v 60Hz motor
I said "If you apply rated torque to the motor shaft"
That will give you 46.537.... percent more slip.
I took the liberty to express that as 50 percent. Sorry.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: 75HP 380v 60Hz motor
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 75HP 380v 60Hz motor
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Eng-tips forums: The best place on the web for engineering discussions.
RE: 75HP 380v 60Hz motor
Use a VFD instead and then you can use a 240V motor with the proper setup of the VFD.
RE: 75HP 380v 60Hz motor
Gunnar - going back to your comment. I believe the iron losses in a rotor are insignificant. If we assumed they go as frequency squared, then at 1% slip the watts per pound loss in rotor would be 0.01% of that in the stator.
So the bottom line, I think the motor can be derated by a factor of 380/460 without any further derating associated with concerns about slip. Agree/disagree?
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RE: 75HP 380v 60Hz motor
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RE: 75HP 380v 60Hz motor
I think the motor can be derated by a factor of 380/460 without any further derating associated with concerns about slip. Agree/disagree?
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RE: 75HP 380v 60Hz motor
I believe derating as you suggested is correct. I've never done this practically though to really know the effect. The starting torque reduction could be a problem on a hydraulic pump.
RE: 75HP 380v 60Hz motor
In all reality, it's the purchasing department's problem since the motors were not ordered in time. I'm thinking the solution from the motor manufacturer is going to be re-nameplate a 460/3/60 motor.
I still can't figure out why a Brazilian motor company has trouble supplying motors for their own voltage.
RE: 75HP 380v 60Hz motor
RE: 75HP 380v 60Hz motor
Or maybe not.
respectfully
RE: 75HP 380v 60Hz motor
Better doublecheck to see if a mistake wasn't made with that 60Hz. Good chance they meant 50hz.
RE: 75HP 380v 60Hz motor
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 75HP 380v 60Hz motor
RE: 75HP 380v 60Hz motor
As expected, they plan on re-nameplating standard 460V motors and then running them on the wye configuration. So, it sounds to me that they will use the 230V taps in a paralell wye config because 380V / 1.73 = 230V.
RE: 75HP 380v 60Hz motor
RE: 75HP 380v 60Hz motor
There is a factor increase in voltage per winding going from series to parallel. The 230 must have been series and the 460 must have been parallel per original nameplate.
There is a factor sqrt(3) increase in voltage per winding going from wye to delta.
So for your explanation to work, it must be that the original winding was series wye and you are reconfiguring to series delta. That's a little different than parallel wye. Or maybe I'm confused (has happened before).
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RE: 75HP 380v 60Hz motor
Just thinking this through:
There is a factor of 2 increase in voltage per winding going from series to parallel. The 230 must have been series and the 460 must have been parallel per original nameplate.
There is a factor sqrt(3) increase in voltage per winding going from wye to delta.
So for your explanation to work, it must be that the original 230 volt winding connection was series wye and you are reconfiguring to series delta. That's a little different than parallel wye. Or maybe I'm confused (has happened before).
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RE: 75HP 380v 60Hz motor
I believe using the motor on 460V requires the series delta connection and the 230V configuration requires parallel delta.
This site I found somewhat answers my question.
htt
RE: 75HP 380v 60Hz motor
RE: 75HP 380v 60Hz motor
There is a factor of 2 increase in voltage per winding going from series to parallel. The 230 must have been parallel and the 460 must have been series per original nameplate.
There is a factor sqrt(3) increase in voltage per winding going from wye to delta. If the original winding was suited for 230 in parallel/delta, then could be supplied from sqrt(3)*230 in parallel/wye.
Which is what you said. I had things backwards in my last two messages. Sorry.
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RE: 75HP 380v 60Hz motor
The new operating voltage 230x1.732 = 398.36into 95.4% of the design voltage while operated with 380 Volts, 60 HZ. That is not the best motor but it will work.
If the frequency should be 50 HZ then the connection will be 1 delta good for 5/6x460= 383.3 Volts, 50 HZ into 99.13% of the optimum voltage when powered with 380 Volts, 50 HZ. The motor power will drop to 5/6x75 = 62.5 HP but a pump will drop the power demand with the cubic power of the speeds ratio (5/6)^3x75 = 43.4 HP
If the motors are already wye connected you need a new winding to make them work at 380 V, 60 HZ.
Check carefully the exact voltage and frequency required.