Torque to turn a generator

In summary, Sean is looking for an equation to determine the starting torque for his project involving a Pelton wheel and a motor used as a generator. He is aware that the torque may depend on load resistance and/or current, but is unsure of the exact equation. He is open to measuring other variables and is seeking help from the community. A suggested method for measuring the starting torque of a DC motor/generator is also provided.
  • #1
sc298
10
0
Hi everyone, I'm new here.

I'm taking electronics engineering at exeter uni and I can't find an equation for my current project.

Its to do with max efficiency from a Pelton wheel.

I need to know how much torque it will take to turn a motor (used as a generator) from stationary (zero rpm).

I think it depends on the load resistance and/or current, but I am not too sure.
I should be able to measure any other variables you state.

Any help would be greatly appreciated.

Thank you,
Sean Coleman
 
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  • #2
sc298 said:
I need to know how much torque it will take to turn a motor (used as a generator) from stationary (zero rpm).

The starting torque of a three phase induction motor is given by,

Tstart = Tlr ∙ (Vline,rated / Vline,lr)^2

where,

Tstart = starting torque
Tlr = locked roter torque
Vline,rated = rated line voltage
Vline,lr = locked rotor voltage

Don't forget that the line voltage will depend on whether the motor stator windings are configured as delta or wye.
 
  • #3
For a DC motor/generator, you can measure the torque required to start turning the motor. This torque has to overcome the static friction and other nonlinear frictions like the Stribeck effect.

Put a 1 Ohm high power rated resitor in series with the + terminal of the motor and the + terminal of the power supply. Apply your voltage to the other end of the resistor and - terminal of the supply to the - terminal of the motor, and measure the voltage across this resistor. Slowly increase this voltage just to the point before the motor starts turning. The voltage across the resistor is also the current going into the motor at this point. This is the maximum current draw right before the motor begins turning. Once you see the motor turning, the current will drop down to a lower level. Your motor should have a datasheet telling you its Kt value (torque constant) and it is expressed in terms of Torque/Current.

Multiply the maximum current you measured by this Kt value, and it will tell you the Maximum torque you had to overcome to start the motor. Although you used the generator as a motor to measure that torque, the value still applies for when it is used as a generator also, since it is just the static friction of the motor. Also you will notice that it varies depending on the position of the shaft, and this is just because of inconsistencies in physical part (bumps and grooves, distorted shaft shape, brush contact, etc.) and so at different locations the static friction will vary slightly.
 
Last edited:

1. What is torque to turn a generator?

Torque to turn a generator is the force required to rotate the rotor of a generator, which in turn creates electricity.

2. How is torque to turn a generator calculated?

Torque to turn a generator is calculated by multiplying the force applied to the rotor by the distance from the center of rotation to the point of application of the force.

3. What factors affect the torque required to turn a generator?

The torque required to turn a generator is affected by the size and weight of the rotor, the strength of the magnetic field, and the amount of resistance in the system.

4. How does torque to turn a generator relate to power output?

The torque required to turn a generator is directly proportional to the power output of the generator. This means that as torque increases, so does power output.

5. How can torque to turn a generator be increased?

Torque to turn a generator can be increased by increasing the strength of the magnetic field, increasing the size or weight of the rotor, or reducing resistance in the system.

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