Does a grid-connected induction generator create phase difference between the grid voltage and generated current?

Question

I saw an answer to another question that stated:

"An ordinary induction generator connected to a power grid will draw lagging reactive volt-amperes from the grid and supply real power to the grid. It is simultaneously a lagging power-factor load and a unity power factor supply."

I believe they are saying that a grid-connected induction generator takes a -90 degree phase shifted magnetization current from the grid and produces an output current through a load in phase with the grid voltage. Is this correct?

If this is correct, I am a little confused.

I thought an induction motor ran above synchronous speed worked as a generator because above synchronous speed the rotor cuts the stator flux in the opposite direction as below synchronous speed, therefore inducing currents in an opposite direction and a magnetic field of opposite polarity as before in the rotor.

I assumed the rotor field would align with the stator field and would therefore induce currents in those stator windings with the most current and therefore the strongest magnetic field. This may be an invalid assumption.

But the current producing the stator magnetic field is the magnetizing current, -90 degrees out of phase with the grid voltage. So this means that the current induced by the rotor field is in phase with the stator magnetizing current. Yet this cannot be true if this current is supposed to be in phase with the source voltage, as the above answer suggested.

I suspect I am fundamentally misunderstanding the working principles of induction generators. Please correct my errors in thinking. Thanks.

Answer 1

I believe they are saying that a grid-connected induction generator takes a -90 degree phase shifted magnetization current from the grid and produces an output current through a load in phase with the grid voltage. Is this correct?

Yes, that is what I said.

I thought an induction motor ran above synchronous speed worked as a generator because above synchronous speed the rotor cuts the stator flux in the opposite direction as below synchronous speed, therefore inducing currents in an opposite direction and a magnetic field of opposite polarity as before in the rotor.

I am not sure what that means.

I assumed the rotor field would align with the stator field and would therefore induce currents in those stator windings with the most current and therefore the strongest magnetic field. This may be an invalid assumption.

Yes, the rotor field is aligned with the stator field. However as the two fields rotate, they not directly aligned, there is an angle between them called the torque angle. The torque is proportional to the sine of the angle. If the stator field leads the rotor field, the angle and the torque are positive. If the rotor field leads the stator field, the angle and the sine are negative. Positive torque means the machine is acting as a motor and negative torque means it is operating as a generator.

The current that the motor produces as a generator is produced in the rotor and passed to the stator by transformer action. It he equivalent circuit, the current is produced by a negative resistance in the rotor circuit.

Look at my answer to Can someone verify my understanding of induction motors? and the three links in that answer. Note that the motor slip "s" is negative when the motor is acting as a generator.