575/600 or 480/460 V

[SilverArc]

Hi
I am seeking a basic advise in regards to rating for motors.

For example I have a 200 HP motor rated at 575 V but the supply is 600 V. Now, normally at the panel where the motor is hooked might have 600 or 590 v. So, if I have to plug this information in a software package for a 600 v system. Should I plug the info for motor as 575 V or 600 V ?
As the value of current will be different for both voltages.

And I beleive the same reply will work for 460 or 480 v systems.

I would appreciate a word.

Thanks

 

[jraef]

The difference is semantics really.600V, 480V, 240V etc. are called the "distribution" voltages, reflecting the measurable levels coming from the utility and/or transformer secondaries. 575V, 460V, 230V etc. are called the "utilization" voltages and reflect the design of the machines or systems connected to use that power.

575V is the "nominal" design voltage for the motor, taking into account the likely voltage drop over distance etc. Motor design voltages are +-10% per NEMA standards, so by saying a motor is 575V, it really means it can be technically used on a system with anywhere from 517.5V to 639V, although in reality is was selected to accommodate 550V and 600V systems in existence in N. America. The same holds true for 460 vs 480V, the nominal motor design voltage is 460 because we have power systems that range from 440 to 480V and 460 was a good compromise.

For your purposes, use your distribution voltage if you are doing a system study, but remember to factor in voltage drop if you are working on studying something at the motor terminals. The motor design voltage is relevant only when looking at motor heating, torque ratings etc.



JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

As jraef said, it's the difference between nominal system voltage and the utilization voltage to allow for the inevitable voltage drop.

The software I use for analysis (EasyPower) uses the equipment nameplate voltage in its database. If the bus voltage differs too much from the equipment voltage, you get a warning when entering the data.

It will depend on the software to some extent, I think.

 

[waross]

I believe that using the system voltage and the motor rated current will give good results. You have an allowance for voltage drop and the motor will draw slightly less current at a higher voltage. Any errors will be conservative.
respectfully