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75HP 380v 60Hz motor

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.

RE: 75HP 380v 60Hz motor

There are no problems if you use them on the 460v tap and derate them by 380/460.

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RE: 75HP 380v 60Hz motor

There is also an effect on the torque curve which will decrease by approx (380460)^2.   Affects starting and momentary overload capability.  We don't know much about your application,  and what kind of requirements have been specified for the 460 motor, but I'm guessing that's not a problem if you're driving a centrifugal pump.

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RE: 75HP 380v 60Hz motor

There is one potential trap to fall into. If you apply rated torque to the motor shaft, you will have almost fifty percent more slip - that is 50 percent higher rotor losses. And heat.

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

So what, he'll need 100HP motors to get 75HP out of them?

You'll have a size problem too?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 75HP 380v 60Hz motor

(OP)
  Unfortunately, because our hydraulic tank design, we need to keep the same NEMA frame size as the 75HP motors.  These motors are driving hydraulic pumps.  It's and industrial baler and load is variable, but starting torque is fairly low. We are using soft starters as well.
  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

Gunnar - I don't see where you got the 50% more slip.

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

You have 480 volt rated motors and you have 380 volts available. give each motor two small transformers connected in open delta auto-transformer boost configuration. 380 volts in, 480 volts out.
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

Pete,

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

Gunnar - ok I understand what you were saying. But I think it's a little misleading in that you said there is one more trap directly after my comments.  But my comments already suggested to derate the motor.

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RE: 75HP 380v 60Hz motor

The voltage change on a 240/480V motor puts coils in parallel or series so, each coil sees the same voltage and current on both supply voltages. If you put a 240V motor on 380V it's very likely you will saturate the magnetics and cause high currents.

Use a VFD instead and then you can use a 240V motor with the proper setup of the VFD.

RE: 75HP 380v 60Hz motor

Lionel - I agree it's a problem to hook up on the 230v connection. But you're not objecting to using the 460v connection with 380v system are you?

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

I will mention also that high efficiency motors typically have low slip, but the reason has nothing to do with rotor iron losses.  It has everything to do with rotor resistive losses.  The lower efficiency associated with the old motors is not created by the high slip... it's created by the high rotor resistance (the high slip just comes along for the ride)

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RE: 75HP 380v 60Hz motor

And the bototm line remains as before:

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

Well, if the application requires 75hp and there is no way to install derated motor to still get 75hp then I just didn't see it as a solution.

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

(OP)
  Thanks guys for the info.  Unfortunately, the machines are sold and there is no margin to add transformers or drives.  The two balers each have two 75HP motors driving two pumps.  Often our hydraulic expert sizes the pumps to use into the service factor.  I'm not at work today, so I can't check the exact HP requirements.  This power unit may be sized under 75HP.  Due to nature of the application, the full load is not required constantly and a slight de-rating probably won't hurt.
  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

(OP)
Oh, by the way, the starting torque will be low and we are using soft starts.  That probably won't be a problem.

RE: 75HP 380v 60Hz motor

Re-nameplateing motors for the wrong voltage will certainly be the fastest and cheapest solution in the short term. Let us know how it works in the long term. This may be one of those times when we regulars on the forum learn something new, to our chagrin.
Or maybe not.
respectfully

RE: 75HP 380v 60Hz motor

I suspect the reason Weg is balking at building 380/60 motors is that the real service is 380/50.  That would be a standard motor and a common South American service.

Better doublecheck to see if a mistake wasn't made with that 60Hz.  Good chance they meant 50hz.

RE: 75HP 380v 60Hz motor

Dick; Brazil is 60Hz.  Although it is interesting - there are 4 standards in South America including both frequencies.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 75HP 380v 60Hz motor

(OP)
We have done machines for Saudi-Arabia which are also 380/3/60.  The strangest was Namibia with 550V 50Hz.  We had to get those custom wound.

RE: 75HP 380v 60Hz motor

(OP)
Thanks again for the information!  Here is Weg's solution:
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

(OP)
Sorry, 230V (219.39)

RE: 75HP 380v 60Hz motor

Just thinking this through:

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

Left out a few key words. Let me try again

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

(OP)
  The 12 lead motors we use are either wired in series delta or paralell delta. We only use wye connection if reduced voltage wye-delta starting is required.
  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.

http://www.usmotors.com/products/ProFacts/1-120-7.htm

RE: 75HP 380v 60Hz motor

230 would have been the parallel connection and 460 the series connection.  Each winding would be rated for 230 and two windings in series would give 460.

RE: 75HP 380v 60Hz motor

Yes, you guys are right.  Let me try again:

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

Only when the 60 HZ motors have 12 leads and connected  460 Volts 1 delta / 230V 2 delta, they could be re-connected in wye 2 circuits.
   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.

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