I am trying to do a simulation on the start up speed to a system powered by an AC motor.
As part of this I am trying to find a mathematical torque/speed curve that I can use.
I expect a curve that looks something like this.
I have used the equations HERE as reference for the below calculations.
My general process is
- Determine motor resistance & inductance based on published data for full load conditions
- Use this to plot a curve of the motors torque speed relationship
However the curve I am getting looks nothing like the published curve at low speeds. Have I done anything wrong, or is there a more accurate model I can use.
I am using a WEG motor as a reference with the following published data
- Frame: 315H/G
- Output: 185 kW
- Frequency: 50 Hz
- Poles: 6
- Full load speed: 988
- Slip: 1.20 %
- Voltage: 415 V
- Rated current: 328 A
- Locked rotor current: 2000 A
- Locked rotor current (Il/In): 6.1
- No load current: 119 A
- Full load torque: 1789 Nm
- Locked rotor torque: 190 %
- Breakdown torque: 210 %
The best I can fit based on Charles Cowie's Answer
- Rth = 0.03424
- Xth = 1E-9
- R2 = 0.0020499
- X = 1E-8
This still looks nothing like the published curve I am going to give up and go with just taking samples from number of motor curves. But I would still like to get a solution to this.