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
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
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If we learn from our mistakes I'm getting a great education!
RE: Motor
Guardiano
RE: Motor
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
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"Why not the best?"
Jimmy Carter
RE: Motor
Guardiano
RE: Motor
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor
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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RE: Motor
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RE: Motor
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RE: Motor
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
Guardiano
RE: 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
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.
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RE: Motor
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RE: Motor
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
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor
Not uncommon.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor
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
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
I understand the haeting of a motor is subjective but the motor is running excessively hot.
Guardiano
RE: Motor
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
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
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
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
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.
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If we learn from our mistakes I'm getting a great education!
RE: Motor
Rafiq Bulsara
http://www.srengineersct.com
RE: Motor
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Motor
Rafiq Bulsara
http://www.srengineersct.com
RE: Motor
RE: Motor
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
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
Guardiano
RE: 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
Guardiano
RE: Motor
Muthu
www.edison.co.in
RE: Motor
"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