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12 comments
Power-User

Join Date: Aug 2007
Location: Lahore
Posts: 330

Running a 50 HZ Motor at 60 HZ

12/04/2008 11:34 PM

Dear friends

What happen if we run a 50HZ motor run on 60HZ?

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Join Date: Jun 2007
Location: dubai,UAE
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#1

Re: 50HZ motor run on 60HZ

12/05/2008 1:00 AM

Induction motors use an iron core and require flux in the iron to operate. In order to achieve the commercial goals of smasllest size and lowest price at best efficiency, induction motors are designed to operate at a high level of flux in the iron. The flux is determined by the turns, voltage and frequency. In a modern motor, if the flux is increased by a small amount, the iron losses increase and the iron tends towards saturation. At saturation, the inductance begins to fall and the current increases further. To reduce the flux at a given voltage and frequency, the turns on the stator are increased. This reduces the Iron loss, but a longer length of thinner wire is used and the copper loss increases. Design becomes a balancing act between copper loss and iron loss and so the design is optimised for a given voltage and frequency. If the voltage applied to the motor is held constant and the frequency is increased, the inductive reactance increases and so the flux reduces. This effectively reduces the maximum torque capacity of the motor and so the motor power rating at the higher frequency remains the same. If the voltage applied to the motor is held constant and the frequency is reduced, the current will increase and in theory, the torque will also increase. The motor should be able to deliver the same power also, BUT the flux in the iron is now too high resulting in excessive iron loss, and the motor will fail prematurely. Above a very low frequency, (5 - 10Hz) the impedance of the magentising circuit of the motor is primarily inductive and so in order to keep the flux within limits, it is important to keep a linear V/F ratio (Voltage to Frequency ratio). If the frequency is reduced by 10%, the voltage must also be reduced by 10%. Because the flux in the iron remains the same, the torque capacity remains the same and so the power rating of the motor also drops by 10%.

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Power-User
Engineering Fields - Mechanical Engineering - New Member

Join Date: Apr 2007
Posts: 171
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#3
In reply to #1

Re: 50HZ motor run on 60HZ

12/06/2008 10:25 AM

It this the same principle used in VFD's?

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Power-User

Join Date: May 2011
Location: Chennai, TAMIL NADU, INDIA
Posts: 110
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#9
In reply to #3

Re: 50HZ motor run on 60HZ

08/02/2011 12:32 PM

Dear Mr. pc,

The VFD principle is totally different and cannot be compared to 50 to 60 cycles/sec. operation.

RAJESWARI.

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Participant

Join Date: Dec 2008
Posts: 1
#4
In reply to #1

Re: 50HZ motor run on 60HZ

12/06/2008 2:54 PM

Thank you for the detailed response:)

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Guru

Join Date: May 2007
Location: Budapest, Hungary, HA5YAR
Posts: 612
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#5
In reply to #1

Re: 50HZ motor run on 60HZ

12/08/2008 10:33 AM

You wrote:

This effectively reduces the maximum torque capacity of the motor and so the motor power rating at the higher frequency remains the same.

One small addition: because the higher frequency results higher speed.

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Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
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#7
In reply to #1

Re: 50HZ motor run on 60HZ

06/29/2010 12:35 PM

All that said, there is the ubiquitous issue of voltage to deal with. In many, if not most, countries outside of North America, 50Hz power is at a nominal 400V (380 - 415V). If you are referring to a nominal 400V system, then using a 460V 60Hz rated motor is perfectly acceptable. The V/Hz ratio is effectively the same; 400/50 = 8.0 V/Hz whereas 460 / 60 = 7.7 V/Hz. Motor design specifications allow for a +-10% deviation in voltage, which translates to the same in V/Hz ratio, so being that 7.7/8.0 = approx. a 4% deviation, this is well within acceptable. The output power will change by the ratio of the frequency difference (20%) so you must keep that in mind, but other than that, this is done all the time.

If on the other hand you are referring to 230/50Hz vs 240V/60Hz, then you run into problems.

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Guru
Engineering Fields - Mechanical Engineering - New Member South Africa - Member - New Member

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#2

Re: 50HZ motor run on 60HZ

12/05/2008 3:13 AM

It goes faster and fails sooner.

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#6
In reply to #2

Re: 50HZ motor run on 60HZ

06/29/2010 11:42 AM

Do you seriously think the bearings cant handle the speed?

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Power-User

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#8

Re: Running a 50 HZ Motor at 60 HZ

08/02/2011 12:29 PM

Dear Mr.Signode,

In simple terms,

1. The Synchronous Speed will increase by 20%, as the speed is governed by the equation N X (P/2)/120 and slip is to be duly accounted for actual speed.

2. The Impedence will increase as it is governed by Impedence and it is calculated by 2 x Pi x f x L, where Pi = 3.14, f = frquency, L = inductance in Henry.

3. Bearing damages may freuently occur.

4. Power drawn by the motor will be more.

5. If the motor is driving a centrifugal water pump, Head developed will be 44% more and the load will be 72.8% more and hence motor will trip.

RAJESWARI.

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Member

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Posts: 5
#10

Re: Running a 50 HZ Motor at 60 HZ

08/02/2011 4:12 PM

I think all of the above technical answers do well in explaining what happens if the 50HZ motor is operated at 60HZ. I don't believe the bearings will fail at that minor speed increase. Mostly you will have a de-rated motor with less torque available. Not a wise choice to apply a 50HZ motor to a 60HZ supply.

Many people just use a VFD rated for the FLA (Current) of the motor and set the output to 50HZ. This way they get full speed control and motor protection and can use either the 50HZ or 60HZ motor.

A great resource for VFDs is Technicon

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Power-User

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Location: Chennai, TAMIL NADU, INDIA
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#11
In reply to #10

Re: Running a 50 HZ Motor at 60 HZ

08/03/2011 12:30 PM

Dear Mr. wagado,

You have mentioned that "I don't believe the bearings will fail at that minor speed increase." From your point of view how much will be the speed incease.

The Synchronous speed will increase by 20% if the frequency is 60 CPS from 50 CPS, which is governed by the equation referred by me and 20% increase of speed is not minor increase of speed.

If SLIP is considered, which may be 4%, the actual speed will be 3456 RPM at 60 cycles per second supply as against a speed of 2880 RPM with 50 cycles per second.

Let CR4 Members give their views.

Thanks,

RAJJESWARI.

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Member

Join Date: Aug 2011
Posts: 5
#12
In reply to #11

Re: Running a 50 HZ Motor at 60 HZ

08/03/2011 2:34 PM

Dear Mr. Rajeswari,

You have said "Let CR4 Members give their views." Thank you for putting me in my place. For a moment I thought forums like this were for the purpose of expressing opinion and giving advice. Sorry I will only ask questions in this thread rather than offending the intelligence of others.

Questions for you:

Why do most motor manufacturers test to IEC 34-14 grade N Balancing Standards that require testing from 600 to 3600RPM while holding to the same vibration requirements?

Are motor bearings typically rated for the exact synchronous speed, or a standard RPM rating above the motor nameplate RPM?

Would it be good engineering practice and quality design for a motor manufacturer to supply a bearing that does not meet the RPM required for IEC 34-14 Grade N testing?

Based on the bearing load formula outlined in this article (Bearing Life) would you agree that a 20% increase in speed would be equivalent to a 10% reduction in bearing life?

What is the typical bearing life for an IEC or NEMA motor?

What do you believe the bearing life to be at 60HZ vs 50HZ?

I look forward to your answers.

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Users who posted comments:

Anonymous Poster (1); deggs32 (1); JRaef (1); koshy.dennis (1); pc (1); Qqberci (1); rajeswari (3); The Prof (1); wagado (2)

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