the physical difference between the 50Hz and 60Hz motor

[Wedoca]

guys, is there really a phsical difference in the 50Hz and 60Hz Motor ??? I always though that they are just rated differently, and what I meant by that is since they are made to be used in a country thats either 50 or 60 hz therefore they are factory test and rated at that frequency. thus if they are ever use on a different electrial system with different frequency, and thats when the motor perfermance doesn't match the spec. I am correct???

 

[dpc]

The nominal speed of the motor is a function of the number of poles in the motor and the system frequency. An 1800 rpm motor designed for 60 Hz will run at 1500 rpm at 50 Hz.

There are design differences due to the difference in inductive reactances and flux as a function of frequency.



David Castor

http://www.cvoes.com

 

[itsmoked]

Same hp rating would give you a 50Hz motor 1/5th (20%) larger than the equivalent 60Hz motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

I agree with Keith if you spec'd two custom motors and changed only frequency (speed) and left all other things equal, you'd expect approx 20% increase in size for the 50hz motor. Because as a first approximation the size of a motor varies with rated torque. It's the same reasons a 4-pole can be almost twice the size of 2-pole of same horsepower rating.

The all other things being equal seems like something to watch our for, and I doubt there are many situations where all other things are exactly equal.

A related FAQ

http://www.eng-tips.com/faqs.cfm?fid=1224

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[ozmosis]

Another way to look at this question would be to see the difference between motors that are only designed to run on a VFD. These motors would typically have a base frequency of anything between 60-90Hz (although the operating frequency would be anything up to 3 times that and down to zero).The physical sizes of these motors compared to the equivalent power rating at 50 or 60Hz are considerably smaller. Siemens, ABB, Baumuller etc manufacture such motors and, as long as you will not operate at mains supply frequency, then the size/power rating is quite dramatic.

 

[edison123]

I don't see any reason for much physical difference between 50 & 60 Hz motors except that the 60 Hz motors are more likely to be dimensioned in FPS system while 50 Hz ones will be in metric system.

Muthu

http://www.edison.co.in

 

[electricpete]

Depends on what you're assuming. Like Keith, I assumed number of poles constant and horsepower constant, so speed must change (for non-vfd motors). But there are a number of ways to interpet the question.

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[itsmoked]

Try this edison. A motor is like a transformer. Because the frequency is 1/5 lower the magnetic structure will have to 1/5 bigger.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith -I know the motor HP is proportional to speed. I am saying there won't be any special constructional difference between the 50 & 60 Hz motors built on a nearly identical frame except for difference in HP ratings and the inch/metric system.

Muthu

http://www.edison.co.in

 

[rmw]

Well, I am not so much of a motor person, but I sit near someone who is. Recently I needed a 200 HP motor for a pump drive application that will need to operate in 50 and 60 HZ locations (with different size impellers, naturally,) and with their help I was able to pick a frame that would supply the needed HP in both frequencies. Was that an anomaly or is that common?

Since the 60 Hz application called for that very same frame size anyway, is that a good solution or not? Or was it just coincidence?

Is this the same as a dual rated motor or is it just a pick where both frequencies happened to fall into a common frame whether that frame would have been picked for either of the individual 50 or 60 Hz applications?

rmw

 

[electricpete]

I said 20% increase in size but I should have been more specific. It is not 20% increase in dimension. It is not 20% increase in weight which would be roughly be cubed-root of dimension. A better way to view it would be 20% increase in airgap area (2*pi*R*L) which would correspond to assumption that flux density (B) remains the same and rated current density (Amps per meter circumferentially along airgap) remains the same, so torque-per-airgap-area remains the same so rated torque goes up by 20%.

If R and L scale proportionately, it would correspond then the product of R*L has to increase by 20% so each one increases by sqrt(1.2) ~ 1.1.

But there are a lot of things that can change (flux density, current density. Also frame can be oversized.

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[waross]

rmw;
I think that you got lucky and by coincidence, either rating would use the same frame size.

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

 

[electricpete]

It may have been a tangent, but I made an error in my discussion of variation of size of motor with torque (sorry). It should be torque proportional to dimension^3 rather than torque proportional to dimension^2. (where dimension is a unit of lenght like D or L and both D and L are assumed to change proportionately). Here is explanation:

If we assume (as I did before) that the flux density and current density (amps per meter of circumference) are constant, then the total force is proportional to D*L, but the total torque is proportional to D^2 * L, which is roughly proportional to the volume or weight of the motor..

So if motor rated torque goes up by 20%, we may roughly expect the weight goes up by 20%, and the dimensions go up by (1.2)^0.333 ~ 1.063 (6% increase in dimensions).

Here is a link that provides a far better discussion than I could ever provide:

http://books.google.com/books?id=_y...main dimensions of a rotating machine&f=false

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[zlatkodo]

We'll get approximately 20% more power from same core at 60 Hz than at 50 Hz.
This means that , for same power, the core at 50 Hz must be "greater" then at 60 Hz.
It's hard to say what it means "greater". Motor power depends on the internal diameter but also on the core-length. Manufacturer can modify one of these measures or both. Also, it is often the case that the manufacturer uses the same core and frame (due to practical reasons) for the two motors, whose power does not differ too much.
Zlatkodo

 

[Wedoca]

Guys, What I meant in the oringinal question was that is there a wiring difference?? when constructing a motor, does the engineer choice from a pool of 50Hz & 60Hz stators & rotors???? or just choice a stators or rotors with diffenent dimesions and construct the motor according to the needs??? I guess what I am asking is ....are stator and rotors made specificly for 50hz or 60 hz??? so such thing like 50hz stator , 60hz rotor .....know what I am saying ?>>?

 

[electricpete]

Physically there should be very little difference between a
460vac 60hz 100hp motor
... and a
380vac 50hz 80hp motor

wiring differences?

I guess if you were trying to hook up the 460vac 60hz motor to 460vac 50hz power supply, there might be some wiring changes you could make to keep volts/hz roughly constant such as changing to wye for 460v 50hz if original 460v 60hz connection was delta. In that case I think the 50hz rating of the motor might be around 58hp (100hp/sqrt3).

Sorry if I’m not addressing the question. I don’t know how OEM’s approach it... most of the catalogues I look at only mention 60hz. I’m sure others can add more insight.


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[LionelHutz]

are stator and rotors made specificly for 50hz or 60 hz??? so such thing like 50hz stator , 60hz rotor

No, generally there is not.

Peter