# Calculating Generator Shaft Torque

1. Aug 11, 2010

### donbcg

Gentlemen,

Here is my scenario. I am building a new project utilizing a PMG that produces 5KW at 840V at 189 RPM. The manufacturer is supplying me with a torque curve that does not appear to be correct. They say, at full power extraction it has 350Nm of shaft torque. Is this correct? If so, why? That equates to roughly 20HP or 18KW.

This is either a wasteful course to generate electricity, or the math is being lost in translation.

I am in the PLC/Autmation Integrator arena and haven't the correct forumla to calculate. Nor do I now what information is required to build the equation. Motor torque, easy. Generator torque, not so much.

I appreciate all the assistance in advance.

Don

2. Aug 11, 2010

### john.phillip

5kW@189RPM = 252.6N.m

350N.m@189RPM = 6.93kW

Using Power [W] and Rot [RPM] to get Torque [N.m], the equation will be:

Torque = Power x 60 / (2 x PI x Rot)

3. Aug 12, 2010

### donbcg

Is it true then that there is a direct corelation between motor torque and generator torque? Why is this the same? Shouldn't it take less torque to make rather than use?

Let's say I drive the 5K @189RPM generator with a 2.2K@3600 motor geared appr. 18:1. Is it possible to do this?

4. Aug 12, 2010

### john.phillip

Apply the equation to 2.2kW@3600 to get the input torque.

Using the 18:1 reduction, the output torque will be greatly increased. Will this increased output torque supply the required torque of 252.6N.m for the generator ?

If not, what would be the generated power, disregarding transmission efficiency losses ?