inverter duty motor

[place1234]

I have a Reliance inverter duty motor, on the report , there writes:
duty HP RPM AMPS VOLTS HERTZ
CONT 400 1150 445 575 58
CONT 400 2400 387 575 121

My questions are :
1. why 58herz? This motor is for China market, so the base frequencey should be 60herz?
2. why 121 herz? Any indicates ?

 

[Skogsgurra]

Many motors are specially designed (or tested and marked) for certain applications. Compressors are an example that springs to mind.

Compressors have their operating points specified at different speeds and there used to be gearboxes that took the fixed speed of a 50 or 60 Hz motor to that speed. Today, the motors are run at a frequency that produces the desired speed and the motors is specified for that speed. It is not uncommon to have one set of data for the rated operation point and one set of data for the maximum operating point.

My guess is that your motor is one of those.

Gunnar Englund

http://www.gke.org

 

[petronila]

Hello Place1234,

In The Squirrell cage induction electric motors the shaft speed is labelled at the nameplate. The shaft speed is different like Synchronous speed= 120*F/Poles, Note: Depends of Frecuencie and Number of Poles, the difference in this two speeds is called slip,in your case the nameplate saids the shaft´s speed at some frecuencie,1150 RPM at 58 Hz and 2400 RPM at 121 Hz. This minds the motor is 6 Poles.For a 6 poles motor at 60 Hz The synch RPM will be : 120*60/6 = 1200 so the motor´s design shaft rpm is 1150 * 60/58 = 1190 or 2400 * 60/121 = 1190. You could run this motor at 60 Hz with a Shaft speed of 1190 RPM.

I hope this could help.

Regards

Petronila

 

[DickDV]

A motor designed for inverter duty need not take into consideration the utility frequency at all. The designer can specify whatever basespeed and overspeed limits and profile he chooses and design the motor accordingly.

When programming the VFD, it becomes the drive programmer's duty to set up the drive output characteristics to match the requirements of the motor.

The above assumes that the motor is not intended for any across-the-line duty. There are, of course, inverter duty motors that are labeled for both services and you would expect that they would be designed for the utility grid frequencies since they just might have to run directly on the grid.

 

[HCBFlash]

Remember, this is a device that is used to produce mechanical power, and the electrical characteristics are secondary.

On a motor built for use with an inverter type speed control (variable frequency inter alia) the "synchronous" speed, Hz, are obviously just derived numbers. Volts is a specified value, and Amps are in this case specified (power factor needs to be known, and it will vary).

To drive a load, the primary mechanical constraints (or specified values) are Power and speed. Given those two, select a rated voltage, and calc the amps. Basic design shaft speed (1150rpm)is that of a common 6-pole SCIM with 4% slip. The motor is designed to produce its rated horsepower at that speed. The motor simply needs 58Hz to produce it, because it has less than 4% slip. (4% slip is somewhat high for an ordinary NEMA Design B, but your motor is not an ordinary NEMA - B)

I would deduce from the rated RPMs (as well as experience) that the motor needs to operate at no less than that speed, under full load, to avoid overheating. The motor is not designed to operate at over 2400rpm. Bearings, shaft run-out, rotor balance, eddy currents, and other factors all affect this figure.


don't forget:
-electrical power input and mechanical power output are not equal to each other.
-slip varies slightly
-power factor can vary widely


.

remember: An opinion is only as good as the one who gives it!

 

[MacRae]

"This motor is for China market, so the base frequencey should be 60herz?"

Actually China mains are 50Hz

 

[ozmosis]

place1234
The bottom line is, make sure your Chinese customer does fit a VFD to control this motor otherwise problems will occur if they just connect to the mains supply, and, as already mentioned, the VFD needs commissioning correctly to ensure the correct v/f characteristic. It could get very hot if full volts are applied at 50Hz.