# Torque and Flux Current

It is said that vector sum of flux and torque current equal to total current drawn by the motor but there are also some currents flowing due to copper losses and rotor leakage inductance. In my opinion, the total current must equal to vector sum of core losses current + torque current and rotor leakage inductance current + flux current ? Is my opinion correct ?

One more question, if we control the motor via contactor , can we say that vector sum of flux and torque current equal to total current drawn by the motor ? I mean if I want to learn how much percent torque I use for a load and I know the flux current of motor which is controlled by contactor. Can I use the formula above to first calculate torque current and then torque percent ?

## 2 Answers

The current that is responsible for producing torque, sometimes called "torque current" is "real current" in AC circuit analysis terminology. The total real current drawn by the motor is the sum of the "torque current" and the current due to core losses. Copper losses don't add to the current, they result in a voltage drop inside the motor.

The magnetizing current or "flux current" is "imaginary current" in AC circuit analysis terminology. The rotor and stator leakage inductance cause voltage drops rather than additional current.

To see how the current and voltages inside the motor are related to the total current and the power losses and the power delivered as mechanical power to the load, you need to analyze the motor's equivalent circuit. It is somewhat as you have imagined that it is, but a bit more complex.

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• I will look for some other questions here that may be of help and post links later. – Charles Cowie Jul 11 '20 at 19:39
• Thanks for appreciated information. the answer was very helpful. I checked the links that you shared. what I meant by rotor leakage inductance current in my question above was that in rotor side the rotor leakage reactance makes rotor current a bit imaginary. not %100 real right ? and my understanding is that torque current is real part of rotor current. so what happens to imaginary part of rotor current ? do we consider it as a part of flux current or just loss current ? – d.alex Jul 11 '20 at 20:35
• Since L2 and R2 are in series with each other, the effect of L2 is to slightly reduce the portion of the rotor voltage that is applied to R2. That does not cause a power loss, but it lightly reduces the power factor as measured at the motor terminals. – Charles Cowie Jul 11 '20 at 20:49

Motor current is the sum of the lossy reactive magnetizing current and the lossy resistive torque producing current.

Both change with commutation frequency and mechanical load and include all the above variables and losses.