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matthewm1965 (Electrical) (OP)
30 Oct 08 6:32
A question for our American friends. I'm in the UK and working on a US project.

When working with 4.16kV to 480V transformers.  Is that the open circuit voltage or the full load voltage?

What should the motor nameplate voltage be when connected to the "480V" system?

Thanks
Matt
magoo2 (Electrical)
30 Oct 08 7:28
ANSI Std C84.1 is normally used by the North American utilities and will help with your questions.  This covers voltage ratings (60 Hz) for electric power systems and equipment.

The nominal voltage of a system is near the voltage level at which the system normally operates.  Most of these operate within a window of +/- 5%.

On a 480 V system, the motor nameplate applied most often is 460 V.  The NEMA MG 1 standard for motors specifies a +/- 10 % tolerance for motor operating voltage around the nameplate value.

If you do the math, you'll find that the operating of a 460 V motor on a 480 V system works quite well.

The nominal voltage is not really the open circuit voltage or the full load voltage.  I'd expect the open circuit voltage to be between the nominal and the 1.05 X 480 V value and the full load voltage to be between the nominal and 0.95 X 480 V value.
tem1234 (Electrical)
30 Oct 08 7:30

It is the full load voltage.

Motor are usually rated 460 Volts.   
Kiribanda (Electrical)
30 Oct 08 9:10
Matthewm1965,

Nominal voltage is the designated voltage for an electrical  system. Based on the nominal voltage , all the other parameters are defined. (It is like your name. Everything is based on your name) But if you measure the voltage on a system where the nominal voltage is 480 V or 4.16 kV you will not find that value. It may vary +/- (x) percent. Therefore, in ANSI world, that variation is defined in ANSI C84.1. Similarly, Based on above, in ANSI world, the motor "Rated Voltage (Name plate voltage)" is listed for various nominal voltages.

So you have to select the motor name plate voltage accordingly.

Therefore, 460V should be the name plate voltage for motors operating on a nominal system voltage 480V.

In ANSI world. ANSI C57.12.10 lists the standard nominal voltages of the high voltage side of transformers. Accordingly, a 4.16 kV-480 V transformer shall be connected to a network where primary nominal system voltage is 4.16 kV. Then 480V will be the voltage at transformer secondary terminals at full load.

But in IEC world this ratio is different. IEC 60076 doesnot list any secondary voltages.

Hope the above answers your question.

 
matthewm1965 (Electrical) (OP)
30 Oct 08 9:18
Thanks for the quick and helpful answers.
Matt
Helpful Member!  jghrist (Electrical)
30 Oct 08 10:05
The secondary nominal voltage on an ANSI design transformer is the open circuit voltage when nominal primary voltage is applied to the primary.  No voltage drop through the transformer is included.  The regulation value indicates what the loaded secondary voltage would be.
 
Kiribanda (Electrical)
30 Oct 08 13:03
matthewm1965,

Sorry. Made a mistake.

Then 480V will be the voltage at transformer secondary terminals at full load.

Wrong. It should read as "at NO LOAD".




 
Helpful Member!  waross (Electrical)
31 Oct 08 0:36
Supply voltages up to 480V in the US and up to 600V in Canada are multiples of 120V.
120V, 240V, 480V, 600V.
Standard motor ratings are multiples of 115V. 115V, 230V, 460V, 600V.
A relatively new motor voltage is 200V for use on 208V systems.
Common star voltages, 120/208V, 277/480V, 347/600V.
In Canada 347V lighting is used in office buildings.

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

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