Voltage Systems

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Gustav

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Currently I am working in Germany assisting OEMs to built their machinery for the use in the US.
In a lot of cases the question which voltage is the nominal voltage and why do Motors have a different voltage rating as Circuit Breakers leads to a almost never ending discussion.
My opinion, e.g. 480V is the nominal voltage of the power transformer system. 460V on the motors specifies, that this motor can be used with 100% load at 480V minus 4% defined voltage drop, without the risk of overtemperature.
But the question than will be - what happens if the motor is used directly at the transformer terminals including the plus tolerance - this would be 480+10% = 528V. Will the motor than have troubles, like isolation, overvoltage, ...?
How does the UL standard for motors address this?

Many thanks for your reply
Best regards
Gustav
 
Motors are built in accordance with NEMA Standard MG-1.

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12.44 VARIATION FROM RATED VOLTAGE AND RATED FREQUENCY
12.44.1 Running​
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Alternating-current motors shall operate successfully under running conditions at rated load with a
variation in the voltage or the frequency up to the following:
a. Plus or minus 10 percent of rated voltage, with rated frequency for induction motors.
b. Plus or minus 6 percent of rated voltage, with rated frequency for universal motors.
c. Plus or minus 5 percent of rated frequency, with rated voltage.
d. A combined variation in voltage and frequency of 10 percent (sum of absolute values) of the rated
values, provided the frequency variation does not exceed plus or minus 5 percent of rated
frequency, and the voltage variation of universal motors (except fan motors) does not exceed plus
or minus 6 percent of rated voltage.​
 

Gustav

Member
Nominal Voltage 460 or 480

Nominal Voltage 460 or 480

Understood, but which is the rated voltage?
either e.g. 480V or 460V?
and where is it stated

Thanks
Gustav
 

brian john

Senior Member
Location
Leesburg, VA
Depends where you live, in Washington DC the distribution voltage is 480/277 and is normally close to right on. 20 miles away in Rockville, Maryland the voltage is 460/265 and drops to 432/249 at the end of the line. Even lower in the peak summer time demand periods.
 
Gustav said:
Understood, but which is the rated voltage?
either e.g. 480V or 460V?
and where is it stated

Thanks
Gustav

ANSI voltage is listed as 480/277V nominal (system voltage at point of origin) and the motors are rated by NEMA MG-1(ANSI approval date 09.03.2004):

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21.5 VOLTAGE RATINGS​
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Voltages shall be 460, 575, 2300, 4000, 4600, 6600, and 13200 volts. These voltage ratings apply to 60-Hertz circuits.​
 

Gustav

Member
This means, that a motor wiht 460V on its nameplate must be able to operate permanently with 100% load on an 480V system plus 10% tolerance, which is 528V.

Thanks
Gustav
 

Gustav

Member
Thanks for this advice.

I guess I did get a very clear picture now of the "distribution voltage" , "utilization voltage" and tolerances in both "voltages"

Example (range A) at 480V and Motor with 460V rated voltage
distribution voltage = 480V plus/minus 5% = 456V .... 504V
utilzation voltage = 460V plus 10% = 506V, but limited to 504V (ANSI c84.1)
Minimum utilization voltage limited to 440V.

This shows me that motors rated with 460V are perfect to use on an 480V system.

Sorry for doing such long thread for an topic which will be very clear for you working most of your life in the USA. But I need to understand this system in order to give good recommendation to our customers.

Thanks
Best regards
Gustav
 
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