Motor run

[ntnu10]

If would like to run the 480V, 60Hz, 780kw, 1137A, 1791r/min motor to 400V, 50hz.
How will it affect the speed, out-power delivered by motor, current drawn by the motor and torque.
Can anybody please help with that?

 

[micalbrch]

See here:

http://www.eng-tips.com/viewthread.cfm?qid=368916

 

[flexoprinting]

Your question is very basic. Don't do it! you will let out the magic smoke. Is it a dual voltage motor? Give all the data plate details, is it driven by VFD?

Chuck

 

[jraef]

Torque and current will remain roughly the same, speed will drop to 5/6 of rated, which will affect the kW rating at the shaft, if that's important. But more often than not it is torque that is paramount in a machine design. If speed is critical, you may need to change belt or gear ratios.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[flexoprinting]

Dang Jeff! I was under the assumption to not increase or decrease the voltage no more than 10%. Well I stand corrected now and need to dig into some books to understand better. I am not doubting you! Just need more education on this side of the key board. The lower voltage coupled with lower frequency I was thinking less cooling and more current. Time to read some when I get off work.

Chuck

 

[waross]

The important parameter is the Volts per Hertz ratio.
480 Volts at 60 Hertz is an 8:1 Volts per Hertz ratio.
400 Volts at 50 Hertz is an 8:1 Volts per Hertz ratio.
As jraef said;
"Torque and current will remain roughly the same, speed will drop to 5/6 of rated, speed will drop to 5/6 of rated, which will affect the kW rating at the shaft,"
I would add that 400V is 5/6 of 480V and the electrical kW consumption will drop by about the same ratio as the mechanical kW.

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

 

[flexoprinting]

Thanks Bill and Jeff! I knew that, it was located behind other dead brain cells in there. So the OP will see..

A decrease of 299 rpm, 5% less locked rotor current, and 650 Kw instead of 780 Kw, and since current drop is negligible replacement of overloads is unnecessary.

Chuck

 

[jraef]

Where it can get tricky is going the other way, when the load is a centrifugal machine. The Affinity Law regarding speed and power (Power required by the machine varies at the cube of the speed change) works both ways. So when you increase the speed by 20% by running a 50Hz pump at 60Hz, the pump will require 173% of the power it did at 50Hz. If you have a throttling valve you can correct it by reducing flow, it's just a gottcha that catches people off guard now and then.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington