Calculating Generator Shaft Torque

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Discussion Overview

The discussion revolves around calculating the torque required for a generator shaft in a project involving a Permanent Magnet Generator (PMG) producing 5KW at 840V and 189 RPM. Participants are examining the torque values provided by the manufacturer and exploring the relationship between motor and generator torque, as well as the feasibility of using a motor to drive the generator.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant questions the manufacturer's torque curve, stating that 350Nm of shaft torque at full power extraction seems inconsistent with the generator's output of 5KW.
  • Another participant calculates that 5kW at 189RPM corresponds to approximately 252.6Nm of torque, while 350Nm at the same RPM would yield about 6.93kW.
  • A participant raises the question of whether there is a direct correlation between motor torque and generator torque, expressing confusion over why they would be the same and suggesting it should take less torque to generate power than to consume it.
  • There is a proposal to drive the 5kW generator with a 2.2kW motor at 3600 RPM using an 18:1 gear reduction, questioning if this setup could produce the necessary torque for the generator.
  • Another participant suggests applying the torque equation to the 2.2kW motor to determine the input torque and whether the increased output torque from the gear reduction would meet the generator's torque requirements.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the manufacturer's torque specifications and the relationship between motor and generator torque. The discussion remains unresolved regarding the feasibility of the proposed motor and gear setup.

Contextual Notes

Participants have not reached consensus on the torque values or the implications of using a motor to drive the generator. There are also assumptions regarding efficiency losses in the transmission that have not been quantified.

Who May Find This Useful

Individuals interested in generator design, torque calculations, and the relationship between motor and generator performance may find this discussion relevant.

donbcg
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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 formula 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
 
Engineering news on Phys.org
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)
 
john.phillip said:
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?
 
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 ?
 

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