Motor Overvoltage

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fifty60

fifty60

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I have a motor that is rated at 200V 50Hz. The rated tolerance is plus/minus 10%. If I were to operate the motor at 230V 50Hz, but reduced the load, can I reasonably expect the motor to not fail any sooner than operating at the correct rated load?

I am able to see that the amps are below the FLA of the motor, even at the 230V 50Hz. If I increased the load, the amps would go above FLA and the overload will trip.

To sum up my question, is it ok to overvoltage a motor if I reduce the load and make sure the amps are below FLA?

Would the same answer apply to refrigeration compressors? Overvoltage + reduced load = ok operation and equipment life expectancy?
 
fifty60 said:
I have a motor that is rated at 200V 50Hz. The rated tolerance is plus/minus 10%. If I were to operate the motor at 230V 50Hz, but reduced the load, can I reasonably expect the motor to not fail any sooner than operating at the correct rated load?

I am able to see that the amps are below the FLA of the motor, even at the 230V 50Hz. If I increased the load, the amps would go above FLA and the overload will trip.

To sum up my question, is it ok to overvoltage a motor if I reduce the load and make sure the amps are below FLA?

Would the same answer apply to refrigeration compressors? Overvoltage + reduced load = ok operation and equipment life expectancy?
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Take a look at NEMA MG 1-12.44.1 and it will tell you no.

Plus or minus 10% of rated voltage with rated frequency.(220)
Plus or minus 5% of rated frequency with rated voltage.
 
Gregg Harris said:
Take a look at NEMA MG 1-12.44.1 and it will tell you no.

Plus or minus 10% of rated voltage with rated frequency.(220)
Plus or minus 5% of rated frequency with rated voltage.
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Also keep in mind that a motor designed to operate at 50Hz probably has not been designed to NEMA standards.
 
140227-2106 EST

So long as you do not breakdown the wire insulation and don't overheat the windings or core I don't think it matters what voltage is applied. This includes frequency. You may not get useful motor operation, but that is not the question.

A small old 1/3 HP single phase motor I use for some tests is rated 115 V 60 Hz 5.9 A. Some measurements with no mechanical load except friction are:

Volts .... Current .... Power .... Power ... I^2
........................................... Ratio ... Ratio

115 ........ 4.56 ........ 132 ...... 1.0 ...... 1.0
127 ........ 5.90 ........ 197 ...... 1.5 ...... 1.7 .............. this voltage is about 10% high.
139 ........ 7.51 ........ 285 ...... 2.2 ...... 2.7

Some of the input power is into other factors than I^2 losses, and they don't increase as rapidly as current.

.
 
gar said:
140227-2106 EST

So long as you do not breakdown the wire insulation and don't overheat the windings or core I don't think it matters what voltage is applied. This includes frequency. You may not get useful motor operation, but that is not the question.

A small old 1/3 HP single phase motor I use for some tests is rated 115 V 60 Hz 5.9 A. Some measurements with no mechanical load except friction are:

Volts .... Current .... Power .... Power ... I^2
........................................... Ratio ... Ratio

115 ........ 4.56 ........ 132 ...... 1.0 ...... 1.0
127 ........ 5.90 ........ 197 ...... 1.5 ...... 1.7 .............. this voltage is about 10% high.
139 ........ 7.51 ........ 285 ...... 2.2 ...... 2.7

Some of the input power is into other factors than I^2 losses, and they don't increase as rapidly as current.

.
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Overvoltage + reduced load = ok operation and equipment life expectancy?

I do believe he is asking a question as to whether or not it will function and have a normal life expectancy.
 
It is not a NEMA motor. I am mostly concerned about motor life expectancy. If I have a motor that is operating at 10-20V above its rated voltage plus 10%, but the current is still well below the FLA of the motor because the load on the motor is below its max rated load, should I consider installing a bucking transformer to drop the voltage. Or, should I only be concerned if the voltage is too high and the current drawn is also too high.
 
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Gregg Harris said:
Why is that? There are plenty of NEMA 50 Hz motors produced
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I could be wrong, but am guessing most NEMA motors would be designed for 60 Hz.

The only 50 Hz motors that I can recall seeing were usually European made and probably not made to NEMA standards.

There are dual rated 50/60 Hz motors out there and likely may be some that are NEMA designed.
 
fifty60 said:
It is not a NEMA motor. I am mostly concerned about motor life expectancy. If I have a motor that is operating at 10-20V above its rated voltage plus 10%, but the current is still well below the FLA of the motor because the load on the motor is below its max rated load, should I consider installing a bucking transformer to drop the voltage. Or, should I only be concerned if the voltage is too high and the current drawn is also too high.
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Two main issues here.

1) The simplest way to look at this is to calculate the ratio of voltage and frequency, then look at what happens when you deviate beyond the stated tolerances. NEMA stipulates +-10%, but IEC might be different, and any motor mfr can stipulate a wider range depending on their intended market. 200V 50Hz is used in Japan, but half of Japan uses 60Hz, so motors designed for use there tend to try to cover that spread. So check with your specific supplier. But if you do have to deviate beyond the tolerance, going UNDER the ratio loses torque, going OVER the ratio increases flux heating. If you are under torque, reducing the load may make it OK, but if you are over saturating, reducing the load makes little difference, other than reducing the load contribution to motor heating. In other words over exciting the motor is going to heat it up more regardless of load, so load reduction has much less effect on motor life.

2) Starting torque (locked rotor torque) varies by the square of the voltage change. So having extra high voltage means a significantly higher risk of torque shock to the load. I have seen it twist shafts off.

There are some soft starters available that will allow you to manually adjust the final output voltage it gets to in order to match what your motor needs. That would also solve your torque shock issue as well. The caveat is, in order to do this, the SCRs are in the circuit full time, you CANNOT use a bypass contactor. That then means you must deal with the running current heat, figure 4-1/2 watts per running load amp in your panel. If you can ventilate, no problem. If you cannot, problem.
 
gar said:
140227-2106 EST

So long as you do not breakdown the wire insulation and don't overheat the windings or core I don't think it matters what voltage is applied. This includes frequency.
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absolutely.

I agree. I don't care if it iec or nema, blue, red or gray.

op did not ask effect on nameplate hp rating or speed or any of the other twenty seven things we could tell him about what is happening inside the motor.

simple answer is:

if the current draw is at or below the nameplate amp rating it will suffer no issue with shorter life.
 
mike_kilroy said:
absolutely.

I agree. I don't care if it iec or nema, blue, red or gray.

op did not ask effect on nameplate hp rating or speed or any of the other twenty seven things we could tell him about what is happening inside the motor.

simple answer is:

if the current draw is at or below the nameplate amp rating it will suffer no issue with shorter life.
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And in general you still need to be within same volts/frequency ratio as the nameplate volts/frequency. As Jraef said you could still have over excitation at a lesser load and cause excess heating eventually destroying the insulation of the windings.
 
kwired said:
And in general you still need to be within same volts/frequency ratio as the nameplate volts/frequency. As Jraef said you could still have over excitation at a lesser load and cause excess heating eventually destroying the insulation of the windings.
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My concern would be the heating in the rotor, not stator - in a case of overmagnetizing - ie., supplying HIGHER voltage; I would have to study the effects of large over or under magnetization on rotor currents: I strongly suspect undermag (low voltage like this) would cause LESS rotor heating and over mag would cause more than the design called for. Anyone ever looked at this and can give info?

Since this post is about undervoltage, the issue of heat should all be in the stator windings. Undervoltage means under magnetization (Isd is lower) which means the motor Kt is lower (it produces LESS torque per amp put in, so for the same load, it will simply require more Isq torque producing amps. Lower Isd, higher Isq. Since heat is vector sum of these, it does not matter which is at what level, as long at the vector sum is = or less than the nameplate amps.

a couple times per year I must commission unkown spindle motors knowing only the motor amp and generic (usually fake) base speed voltage rating. I begin, unloaded of course, a typical 460v type motor with about 100v@50hz - it runs fine. I slowly increase voltage watching Isq/Isd . Then we load the motor with simple linear accel/decels and do it again. Pretty easy to find the sweet spot where the motor uses min vector current; but that still does not gaurantee I found the designed /hz rating. But there are a lot of motors running out there making their rated hp cuts all these years without overheating.

In addition, we also sometimes eliminated motor self resonant points by manipulating the v/hz curve on skalar drives by as much as 2x hi or lower than correct at some frequencies.

As previously stated for this undervoltage case (& probably overvoltage within reason - swag guess 2x v/hz curve - but I won't swear to that), if vector sum of both currents (reads = what seen on clamp on ammeter around a leg) is below the nameplate current rating, one will not cause excess heat in the stator windings. Simple math here; can't happen.
 
fifty60 said:
I have a motor that is rated at 200V 50Hz. The rated tolerance is plus/minus 10%. If I were to operate the motor at 230V 50Hz, ...
Click to expand...

mike_kilroy said:
...
Since this post is about undervoltage, the issue of heat should all be in the stator windings. ...
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This issue is about OVER voltage, not under. I think other responses have been based on that misinterpretation as well. Under voltage will affect torque, but can be mitigated by dropping load. OVER voltage affects heat by increasing magnetic flux and saturation, load will be less relevant.
 
RE:over mag would cause more than the design called for. Anyone ever looked at this and can give info

hysterysis losses increase as the cube of the core flux, and that is prior to entering saturation. Once you saturate, then huge overcurrents and harmonics start to come into play.
Volts (net)= number of turns * area of stator poles * core flux * 2pi * frequency; so you can see that core flux proportional to voltage, so stator iron heating goes up by factor of 1.7 if number of turns on poles not increased also.
Motor designers often design so that hysterysis losses are a bit less than IsqR losses; so, to answer original querry, your core losse4s maybe double, you need to run at 70% current or <70% load.
ASSUMING you are not saturating the stator.

Say the core saturates at 1.8T, and design (typical) is for 1.5T. 6/5*1.5 = right at saturation. If you look at the current waveform with a scope and see little sharp bumps or humps at the peaks, you are saturating and generating lots of harmonics.
 
junkhound said:
RE:over mag would cause more than the design called for. Anyone ever looked at this and can give info

hysterysis losses increase as the cube of the core flux, and that is prior to entering saturation. Once you saturate, then huge overcurrents and harmonics start to come into play.
Volts (net)= number of turns * area of stator poles * core flux * 2pi * frequency; so you can see that core flux proportional to voltage, so stator iron heating goes up by factor of 1.7 if number of turns on poles not increased also.
Motor designers often design so that hysterysis losses are a bit less than IsqR losses; so, to answer original querry, your core losse4s maybe double, you need to run at 70% current or <70% load.
ASSUMING you are not saturating the stator.

Say the core saturates at 1.8T, and design (typical) is for 1.5T. 6/5*1.5 = right at saturation. If you look at the current waveform with a scope and see little sharp bumps or humps at the peaks, you are saturating and generating lots of harmonics.
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I don't know where you get the 6/5 factor but yes, saturation would be my concern also.
 
GoldDigger said:
6/5 = 60/50.
Ratio of design frequency to use frequency in some cases.

Tapatalk!
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The OP wants to run the motor at its design frequency of 50Hz.
Running it at 60Hz would reduce the flux, not increase it.
Flux is a volt second integral and the 60Hz has a shorter period.
 
Besoeker said:
The OP wants to run the motor at its design frequency of 50Hz.
Running it at 60Hz would reduce the flux, not increase it.
Flux is a volt second integral and the 60Hz has a shorter period.
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Quite true. I was just trying to explain where junkhound got the factor he mentioned, not trying to say that his analysis was applicable to the OP's question!
Thank you for expanding on that. :)
 
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