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Motor

Motor

(OP)
Hello forum memebers,

I have a motor on site which I presume is rated for 60 Hz operation. My network is 400 V 50 Hz. The motor is heating anormally and my belief is that the iron core is overfluxing.. The motor came from brasil and the supplier is claiming that it is designed for both 50 and 60 Hz.
I find this hard to believe.
Your views, please.

Guardiano

RE: Motor

Have a read of FAQ237-1224: Motors: Changing between a 50 and 60Hz supply. which explains most of the problems with changing between supply frequencies. It might well be suitable for operation at either 50 or 60Hz but only if the supply voltage changed in proportion.
 
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Motor

(OP)
Agree ScottyUK. The motor nameplate reads 380 V 50/60 Hz.

Guardiano

RE: Motor

380V @ 50 Hz x 5/6 = 456V. At 400V you are about 12% low on the voltage. If the motor is loaded 100% it will overheat. You may consider an auto transformer set to boost the motor voltage up to 456V.
Wye connected auto transformers need a neutral connection. I have seen issues with ground fault protection when the wye point was connected to ground rather than to a true neutral.
With two auto transformers connected in open delta, the line currents will no longer be equal. This is usually not an issue. If you are running a large number of motor/auto transformer sets on a small generator, you should transpose the connections so as to present a better current balance to the generator.
Issues are possible with either connection.
I have experienced issues with the three transformer wye connected scheme.
I have not experienced issues with two auto transformers  connected in open delta.
I like symmetry, but in the case of voltage adjusting with auto transformers, I prefer the unsymmetrical open delta connection.

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

RE: Motor

(OP)
Thanks Waross for your comments. Based on voltage and frequency considerations,a motor is designed for either 50 or 60 Hz operation. Dual operations at both frequencies and same voltage defeat motor theory.Correct !

Guardiano

RE: Motor

Correct. The 5:6 factor is always there. A motor may be over sized so as to be usable at either frequency. This will obscure the 5:6 factor but the factor will still be there by virtue of the fact that the motor is over sized by 6:5 on the most favorable voltage/frequency.

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

RE: Motor

One thing that seems clear is you are not likely overfluxing.
The nameplate says "380 V 50/60 Hz"
We're not sure if this really is supposed to mean
380V/50hz = 456V/60hz
OR
380V/60hz = 316V/50hz

In the first case you should be  doing pretty well, with normal tolerances on supply voltage and voltage drop.
In the 2nd case you have undervoltage which leads to the scenario waross mentioned.

Either way  you shouldn't be overfluxing the motor.

Have you measured the current?   Where are you measuring temperature and how hot is it and what is the insulation rating and what is the motor rate temperature rise?
 

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Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor

Also for current measurement - should check all 3 phases to check for unbalance.

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Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor

And needless to say if you report current measurements back here, we'll also want to know more nameplate info to judge the full load current.

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Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor

Bill - you might to want to recheck your calculations.

I think the motor is rated for 380 V for 50 Hz and not for 60 Hz since as pete says, the latter Hz would mean 316 V at 50 Hz, which is non-standard voltage in any part of the world as far as I know.

So, if you run a 380 V, 50 Hz motor at 400 V, 50 Hz, you're over-fluxing the motor by about 5% which should not be really a problem.

But overheating could also be due to overloading, inefficient fan, higher ambient etc.

You need to post the complete motor nameplate details along with the actual load current and the ambient temperature and the motor temperature.

Muthu
www.edison.co.in

RE: Motor

(OP)
Edison123,Please correct me if I`m wrong. Running a 380 V 60 Hz motor at 380 V 50 Hz means overfluxing the motor by 20 %. The full load current of the motor is 4.6 A and the motor is running at 4.0 A but is extrememly hot.My assumption is that the motor is rated at 380 V 60 Hz.

Guardiano

RE: Motor

You're right if the motor is rated at 380 V, 60 Hz, which I doubt. And in your case, you worsening it by running at 400 V by adding 5% more (if indeed it is a 60 Hz motor).

Overload doesn't seem to be a problem. How about actual measured motor temp ? Running extermely hot is a bit subjective. And how is the ambient near the motor ?

Muthu
www.edison.co.in

RE: Motor

Sorry, my post was incorrect where I said you're not overfluxing. Could be depending on interpretation of nameplate as you'all have figured out.

I agree. "Running hot" means nothing to me.  We just had what I assume is common occurence for other folks. Replaced an old 60hp 460vac motor with new high efficient 60hp 460vac motor from the same OEM that "looks" identical to the old one.  The operators say the new one "runs hot".  The temperature tapers from cool to hot going from outboard to inboard as expected and it's around 200F on the inboard endbell.  Don't know what the winding temps are but I have no evidence they are aproaching thermal limits.  Talked to the OEM and he confirmed they have smaller fans in that new high efficient motor that "looks the same". It's hotter than they're used to, but that doesn't mean it's a problem.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor

Sorry, it was 180F on the endbell. 200F is what I estimated the bearing temperature to be using thumbrule that bearing runs 10-20F hotter than housing.

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Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor

Thanks for the heads up edison123.
I apologize. I misread the supply as 400V 60Hz rather than 400V 50 Hz.
I agree with edison123, 5% over voltage should not be a problem. What current does the motor draw?
How are you determining that the motor is overheating? Many motors normally run much hotter than many people realize.  

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

RE: Motor

Thanks Itsmoked. I suspect that the motor may be running normally, but the normal temperature is higher than expected.
Not uncommon.

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

RE: Motor

Guardiano,

Note the number of leads, some motors are manufactured for 4  voltages  but the key is in the leads connections for 60 Hz   you can have Double Delta for 230 V, Delta for 460 V and two stars for 380 Volts.I suggest Check connections.

In Delta 460/60 = 7.6 in the same delta 7.6 x 50= 380 so the motor could run proper  at both frecuencies and too at 660 Volts in star(50 Hz)

In Two stars 380/60= 6.33 x 50= 316 don`t work proper  

Then the motor is designed for 4 Voltages two frecuencies

60 Hz: 230/460  and  50 Hz: 380/660

Regards

Carlos   

RE: Motor

No motor is rated for 380V 50/60Hz. No motor is technically rated for any specific frequency, other than how the V/Hz ratio works out.

A motor rated 380V 50Hz has a V/Hz ratio of 7.6:1
A motor rated 460V 60Hz has a V/Hz ratio of 7.7:1, close enough
This can be the same motor, hence a statement saying "It is rated for 50 or 60Hz" would be technically correct, albeit inaccurate by omission of other pertinent facts. So basically that statement of the motor being rated for 50/60Hz is effectively meaningless without a context of voltage(s).

Motor voltage ratings are also designed around a +-10% variance, so 380/400 is statistically irrelevant.

So assuming you have properly determined that the motor is "over heating" (because as others have said, that is a subjective term), then the next step is to determine why. Here is my experiences with Brazilian made motors:

1) Some, especially larger sizes, are often used in mining applications in Brazil where they use higher than "expected" voltages. They often use dual voltage motors that are designed as 380/660V, where they are 380V if connected in Delta, 660V if connected in Wye (Star). Unfortunately, most people who encounter dual voltage motors expect to see the low voltage as 220V, and the high voltage as 380V. So if by chance you have one of those Brazilian motors and you did not pay close attention to the nameplate connection patterns or they are gone), then you have the motor connected in Star thinking it was the "high" voltage connection. This means that although the motor is trying to spin the correct speed, it is producing 1/3 of it's rated torque and is falling deeply behind the slip curve into a near stall condition. This will definitely cause overheating.

2) The major Brazilian motor mfr that I have dealt with in the past, Weg, had a serious QC problem years ago and a lot of their motors had bad bearings and soft shafts, so the shafts would actually flex under the weight of the rotor and rub against the stator. If your motor is over 20 years old, I would be suspicious of that. That situation no longer exists with their motors, but I am not completely sure of when they fixed it. Some people tell me 10 years ago, others have said 15+ years ago. But suffice to say there are still a lot of those old motors out there.


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RE: Motor

(OP)
Thanks all for the comments. The nameplate reads 220 V 8 A, 380 v 4,7 A and 440 V 4 A.It also mentions four voltages, 220 V double delta, 380 V double star, 440 V the two windings in series and delta connected and 760 V the two windings in series and star connected.
I understand the haeting of a motor is subjective but the motor is running excessively hot.

Guardiano

RE: Motor

Guardiano; You keep saying HOT but a happy motor can normally be much hotter than you can touch!

Run a temp gun all over it and tell us what the maximum temperature is.   Also point the temp gun at a static piece of metal in the immediate area that can NOT be heated by the sun or any other heat source, so we can see the immediate ambient that the motor is operating in.

 

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor

So, it's motor for 4 different voltages and two different frequencies (which was not clearly told by OP upfront).

Looks like 380 V is for 50 Hz and 440 V is for 60 Hz. So, running at 400 V, 50 Hz is not a big issue.

Again, post measured temps, otherwise this thread is useless.

Muthu
www.edison.co.in

RE: Motor

Quote:

Again, post measured temps, otherwise this thread is useless.

I couldn't agree more!

You could also measure the rpm of the motor to determine what the slip is.

4A on a motor rated 4.8A while running at what appears to be rated voltage and frequency indicates there is no problem.

 

RE: Motor

A correction after looking at the voltages and their connections.

Each phase winding has two sets of winding. These windings are connected in the permutation of series/parallel and wye/delta depending on the applied voltage. In all four voltage ratings, the voltage across each set of winding remains the same meaning the flux density remains the same.

So this motor is designed for one frequency only, either 50 or 60 Hz. If supplier claims both 50 & 60 Hz, it's nonsense.

Given the voltage ratings, it's more likely 50 Hz (members living in 60 Hz world can correct me if I'm wrong).

To the OP - What's the open shaft (i.e. uncoupled) current ? That could indicate if the motor is over-fluxing at 400 V.

Muthu
www.edison.co.in

RE: Motor

"So this motor is designed for one frequency only..."

I do agree that the voltages listed on the nameplate are likely all quoted at one frequency but that doesn't preclude operation at another frequency: I disagree that the motor is designed for only one frequency - it is designed for four volt/Hz ratios which depend on the winding connections. The only question is whether those ratios happen to coincide reasonably well with a standard frequency / voltage combination in the 60Hz world.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Motor

All this while if the motor has not smoked, all is well. Too much discussion for a 4 amp motor!

Rafiq Bulsara
http://www.srengineersct.com

RE: Motor

Just think if we were charging consultant rates... the OP could have bought the motor ten times over by now! smile
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Motor

I don't know if this helps or not, but we send machines to Brazil all of the time.  They are indeed 380V 60Hz.  The ironic part is that we use Weg motors.  The NEMA motors do not come in that voltage/HZ even though they are made in Brazil.  Apparently, IEC motors do.

RE: Motor

Scotty

AFAIK, the US voltages are 575, 480, 220 & 208 V and none of them are close to this motor's voltage ratings.

Muthu
www.edison.co.in

RE: Motor

System voltages are multiples of 120V:
120V, 240V, 480V, and 600V.  120V x 1.73 = 208V (other line to neutral voltages are 277V and 347V) Lighting equipment is available for these voltages.
Motor voltages are multiples of 115 volts:
115V, 230V, 460V and 575v. 115V x 1.73 = 200V.

A motor which draws 10A on a  240V system will be expected to draw 11.5A with the same load on a 208V system. If the motor is wound with over sized wire that will pass 11.5A without overheating, the motor may be rated 200/230/460V.
The current ratings will be 11.5/10/5A.
This is common for commercial refrigeration equipment in Canada.

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

RE: Motor

(OP)
The temperature of the motor casing measured with a laser gun is 122 Deg C. The insulation class of the motor is F.

Guardiano

RE: Motor

Class F means the internal windings can be at 155C and you would get 10,000hrs life from the motor.

That said it does sound too hot to me.

Is this a TEFC motor?

Please tell us the make and model number.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor

(OP)
It`a a 2 HP motovibrator manufactured by Pricemaq in Brasil.

Guardiano

RE: Motor

120 deg C on the casing is hot. Try the 440 V connection instead of 380 V.

Muthu
www.edison.co.in

RE: Motor

Jraef,

"No motor is rated for 380V 50/60Hz" I not agree, this is true if you have the same  conditions in the motor´s winding and the turns and  connection no change.

When the connections are switched the turns change and the motor´s perfomance is not the same.

For an Induction Motor,the Torque is proportional to Current times Flux.When you perform changes in the winding This parameter change.
  
The Back emf is in opposition to the applied voltage in each phase of the motor and is given by:  E= 4,44ØFNCfDf  where E is back emf, F=frecuency, N= Turns in serie per phase, Ø= Flux per Pole,Cf= Chord Factor and Df= Distribution factor.

To maintain the motor performance (Eficiency and Torque) is necessary to control the flux per pole
For  (380V/50-60 Hz) the designer will have  two variables to control F and N and the product of this ones most remain constant in order to satisfy the above Back emf per phase.

In Delta connection the turns per phase are different than two star connection this will balance the frecuency change.

Regards

Carlos

 

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