I need to estimate the torque τ(t) of a three-phase motor during the initial acceleration. I have readings of the instantaneous values of current and voltage (relative to ground) for one of the phases. This means i have the RMS current and voltage as well as the power factor. To summer i have the following quantities as a function of time:
- I(t)
- V(t)
- φ(t)
- cos_φ(t)
- Pin(t)
- If necessary i could also measure the voltage/power of the load.
My question is how to estimate/approximate the torque τ(t)?
Edit: I forgot to mention that the motor powers a generator so i can measure the output power of the electric load.
Dear Boris, for a synchron-motor you can find. For an asynchron-motor you have many nonlinearities in the start-time. You can not find the torque.
Torque in any motor A.C/D.C(universal motor the best example), torque is produced due to force produced on rotor conductor is due to strong field on one side and weak field on other side due to current, and force couple would be produced by the opposite sides of coils/bars on perifery of rotor, would produced the torque to rotates the rotor. Hence stator and rotor magnetic field praporsnal to respective current, with proper optimized phase difference would be of prime importance. The current in stator or rotor depends on voltage applied or induced(by speed/frequency), and the respective impedance offered, which depends on type of motor and size, on the basis of these parameter torque equation could be developed for respective motor....
Thank you all for your answers.
Christian Jacob, that is why i want to approximate it. It doesn't have to be super accurate.
Sudha Balagopalan, it seems i forgot to mention the motor powers a generator so i can measure the output power of the load (electric load).
Bhupendra Desai, i am trying to find a way to approximate the torque by only measuring electric parameters (currents, voltages, cosfi, etc.).
I found this equation for a DC motor from http://simplemotor.com/calculations/
τ = (I * V * E *60) / (rpm * 2π)
where E is the efficiency.
But i am not sure if it is applicable for a three-phase AC motor. Also it would require the rpm but i suppose that is relatively easy measurable (or perhaps approximable).