I need help from you, electrical guyes.
I am a materials guy and I am working on inductor materials, soft magnetic materials.
I tired to understand how induction motor works. And I found lots of difficulties.
My questions are;
1. Is induction motors a constant power machine or not?
Since the resistance of stator winding is fixed and the applied voltage is constant to the stator, so it looks to me that current flow is fixed regardless of loading. But I found that this is not the case. Why is that?
If the rotor draws current by magnetization, still the resistance of the stator is same. Could you please explain it not by an electrical circuit but by reasoning? Say
No load case
- current in stator winding induce magnetic field,
- stator tooth are magnetized by the magnetic field,
- magnetic field in the stator magnetizes the rotor,
- EMF is induced in a rotor bar,
- magnetic field of opposite direction forms inthe rotor bar,
- rotation of rotor
Load case
- current in stator winding induce magnetic field,
- stator tooth are magnetized by the magnetic field,
- magnetic field in the stator magnetizes the rotor,
- EMF is induced in a rotor bar,
- magnetic field of opposite direction forms inthe rotor bar,
- slip in the rotor due to load
- rotation of rotor
The only difference is slip.
How does slip influence more current at stator winding?
2. No load current vs load current
What is the meaning of efficiency of induction motors?
People mention that the efficiency of induction motors is 75-90%.
And I found that the magnetizing current for inductor is about 20~60% (average 33% of FLC). Magnetizing current means current for no load case. (No mechanical work at all.)
If the magnetizing current is 33%, does this mean that sum of loading current and loss current is 67%? If this is the case, the efficiency of , say, 90% is actually 67%x0.9?
According to www.lmphotonics.com/energy.htm
The current flowing into an induction motor comprises three major components, magnetizing current, loss current and load current. The magnetizing current is essentially constant, being dependent only on the applied voltage....For a large motor, the magnetizing current can be as low as 20% of the rated full load current of the motor.
3. If high permeability materials were developed, how will it affect the efficiency of motor?
For example, to magnetze the stator core to 1.5T, an existing material needs 1000A/m. And the new material needs 500A/m.
Does the above case mean that with the new material, magnetizing current is reduce by half? So we can save lots of energy?
Is there any effect on load current?
Thanks in advance!
I am a materials guy and I am working on inductor materials, soft magnetic materials.
I tired to understand how induction motor works. And I found lots of difficulties.
My questions are;
1. Is induction motors a constant power machine or not?
Since the resistance of stator winding is fixed and the applied voltage is constant to the stator, so it looks to me that current flow is fixed regardless of loading. But I found that this is not the case. Why is that?
If the rotor draws current by magnetization, still the resistance of the stator is same. Could you please explain it not by an electrical circuit but by reasoning? Say
No load case
- current in stator winding induce magnetic field,
- stator tooth are magnetized by the magnetic field,
- magnetic field in the stator magnetizes the rotor,
- EMF is induced in a rotor bar,
- magnetic field of opposite direction forms inthe rotor bar,
- rotation of rotor
Load case
- current in stator winding induce magnetic field,
- stator tooth are magnetized by the magnetic field,
- magnetic field in the stator magnetizes the rotor,
- EMF is induced in a rotor bar,
- magnetic field of opposite direction forms inthe rotor bar,
- slip in the rotor due to load
- rotation of rotor
The only difference is slip.
How does slip influence more current at stator winding?
2. No load current vs load current
What is the meaning of efficiency of induction motors?
People mention that the efficiency of induction motors is 75-90%.
And I found that the magnetizing current for inductor is about 20~60% (average 33% of FLC). Magnetizing current means current for no load case. (No mechanical work at all.)
If the magnetizing current is 33%, does this mean that sum of loading current and loss current is 67%? If this is the case, the efficiency of , say, 90% is actually 67%x0.9?
According to www.lmphotonics.com/energy.htm
The current flowing into an induction motor comprises three major components, magnetizing current, loss current and load current. The magnetizing current is essentially constant, being dependent only on the applied voltage....For a large motor, the magnetizing current can be as low as 20% of the rated full load current of the motor.
3. If high permeability materials were developed, how will it affect the efficiency of motor?
For example, to magnetze the stator core to 1.5T, an existing material needs 1000A/m. And the new material needs 500A/m.
Does the above case mean that with the new material, magnetizing current is reduce by half? So we can save lots of energy?
Is there any effect on load current?
Thanks in advance!