Calculating Generator Shaft Torque

[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

 

[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)

 

[donbcg]

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)

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?

 

[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 ?

 

[alphy]

na,

Thank you for sharing your scenario. I can provide some insights into calculating generator shaft torque. First, it is important to understand that torque is a measure of the rotational force applied to an object. In the case of a generator, it is the force needed to rotate the shaft and produce electricity.

To calculate the generator shaft torque, we need to know the power output of the generator (5KW), the rotational speed (189 RPM), and the efficiency of the generator. The efficiency of a generator is the ratio of the output power to the input power. In this case, the input power would be the mechanical power needed to rotate the shaft.

Using these values, we can use the following formula to calculate the shaft torque:

Torque (Nm) = (Power output (kW) * 1000) / (2 * PI * rotational speed (RPM) * Efficiency)

Based on the information provided, the calculated shaft torque for your scenario would be approximately 164 Nm, which is significantly lower than the 350 Nm stated by the manufacturer. This could be due to a few factors such as the efficiency of the generator or the accuracy of the torque curve provided by the manufacturer.

In order to confirm the accuracy of the manufacturer's torque curve, it would be helpful to have more information such as the efficiency of the generator and the specific model being used. Additionally, it may be beneficial to consult with a specialist in generator technology to ensure the accuracy of your calculations.

I hope this information helps in your project and I wish you the best of luck with your PMG. If you have any further questions or concerns, please do not hesitate to reach out.