Can A Motor Be Run On Lower/Higher Than Rated Frequency? 2

[abo2eyes]

really i am puzzled when i have my winding motor burned with 60 hz rating
what i have to do to make new winding but with 50 hz rating ???????

 

[MiketheEngineer]

ASK the MFG!!!

 

[jraef]

Look at the V/Hz ratio of a motor, that is what the design is based upon. As long as you maintain a +-10% window of that ratio, the motor should be fine. But the difference between 50Hz and 60Hz is outside of that range, so the motor may burn up if this is not taken into consideration.

So for instance, 60Hz motors are often rated 460V/60Hz, which ia a V/Hz ratio of 7.67:1. If you then apply 50Hz, you must lower the applied voltage appropriately. 400V 50Hz is a ratio of 8:1, that is well within that 10% window. Nice how that works out huh? So the opposite is true as well, if you have a 400V 50Hz motor and you want to run it at 60Hz, you must increase the voltage to 480V and it will be fine.

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— Kilgore Trout (via Kurt Vonnegut)
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[ScusaMe]

In a given rating, a motor designed to run on 60 Hz has less iron in the frame than a 50 Hz motor. Ergo, the Volt-Time Area of the iron is less in the 60 hz motor than in the 50 hz motor of the same rating.

So that would mean that you would have to derate the motor if you wind it for 50 hz ... by the ratio of 5/6.


Ergo, if the 60 Hz motor is rated at 7.5 hp (5 kW).... after rewinding it for 50 Hz, you would have to derate it to 4 kW.

 

[abo2eyes]

so u mean i derate the motor to 4 kw cause the torque is decrease cause of decreasing the voltage ?
secondly i do not know the roles to make new winding but with 50 hz?
really i donot know the difference in manufacturing between the both motors with 50 hz and 60 hz

 

[dpc]

If this is a small 4kW motor, why not just buy a new motor with the proper rating.

Also, you need to practice writing in standard English, not text messages. This is a professional forum so please write in a professional way.

 

[ScottyUK]

"so u mean i derate the motor to 4 kw cause the torque is decrease cause of decreasing the voltage ?"

No, you de-rate it because at 50Hz the available torque remains unchanged but the motor is rotating at 5/6 of the speed at 60Hz.


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

 

[waross]

The current rating of the motor stays the same. If you go below the V/Hz ratio you will be under-utilizing your motor. If you go above the V/Hz ratio the motor iron will saturate and the motor will probably burn out.
At the proper V/Hz ratio the current and the torque will be the same. The speed is frequency dependent so that the HP will change in the ratio of the frequencies, eg: 50/60 or 5/6.


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

 

[7anoter4]

If the supply voltage and windings will remain the same :no. of poles,no.of turns per phase,
the magnetic flux density in the air gap will be 20% more and then the no-load current will be 30-50% more.
If the required torque will be the same the active current drawn from the network will be 10- 20% less.
[but total current will grow 10% at least].
The starting current will be more 15% as the reactance will drop 20%.

 

[petronila]

Hello abo2eyes

Looking for the cause of failure I will add something more, take account if the motor is powered with 230 or 400 Volts (50 Hz).

1. In case of 230 V: 230 V/60 Hz = 3.83 V/Hz * 50 = 191.6 V then the 60 Hz motor is working with 2 problems: over-voltage and power loose by the speed decrease.

2. In case of 400 V: 460 V/60 Hz= 7.66 V/Hz * 50 = 383.3 V the motor will works with proper voltage but will have the same power loose.

New or Rewinding? If the motor is special type or the new one will take a long delivery time, the option could be rewinding with 50 Hz rating.

A good workshop can redesign the windings and the motor will works fine.

Take account If you buy a new motor then the best is increase the power rating at least on 20% (To compensate the output power loose,) but maybe the new motor could be manufactured with different frame and you will need mechanical modifications to proper instalation, also taking account the most 60 Hz motors are imperial.

Maybe the rewinding is not a wrong choise.

Regards,


Carlos

 

[abo2eyes]

really i appreciate that sorry English is not my native
eng carlos i understand now that the diffrence in manufacturing between both 50 hz and 60 hz is the winding way is that true ?
secondly how to re-desgin the motor to operate on 50 hz ?

thanks

 

[waross]

Most of us who have converted motors between 60 and 50 Hz. calculate the optimum voltage at the new frequency and work on supplying the proper voltage.

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

 

[petronila]

Hello abo2eyes,

Usually the two voltages, Low Voltage 60 Hz motors, are designed to work at 230/460 then the winding most be proper connected to works fine, and the 230 V connection is the twice of High voltage connection. (YY -Y) or (DD/D) but in the 50 Hz motors designed to work with two voltages (230/400) or (400/690) the voltage ratio is 1.732 and are designed for D-Y connections, D for low voltage and Y for high voltage.

The 60 Hz motors can work in 50 Hz power sources in the high voltage connection but not in the low voltage connection( YY is very different than Delta connection) and the problems will be the exposed in the last post, so if you have a very sharp motor then will be operate under overload conditions and fail.
Some 60 Hz motors works proper on 50 Hz power sources due to are oversized.

Taking account the above information, if you want to redesign the 60 Hz motor to operate at 50 Hz you have to manipulate the Turns, wire mm2 and winding connections, this can be done by experienced/trained people and with the help of redesign programs that will calculate the right winding.The new parameters depends of the stator sizes and magnetic density in air gap, tooth and back iron.

I think the best is send the motor to one good and reliable workshop.

Regards

Carlos

 

[waross]

The motor doesn't care, but 50 Hz is used in Europe where 6 lead, wye:delta motors are the most common.
60 Hz is used in North America where 9 lead dual voltage motors are the most common.

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