FAQ

3-phase Induction Motor Efficiency and other issues?

induction motor, Motor control, Motor testing, Three phase motor
I'm in a motor design. Currently, I'm using JMAG Express to estimate the right sizing requirements for a 3-phase Induction Motor that I want to build among friends. As you can see from the picture, I need to be able to reach 3200 RPMs speed, 440 N*m torque and 120kW of max power. I've played around with some of the values in JMAG to reach a weight of around 20kg as you can see from the picture. The low weight is a very important requirement for the project and it should not exceed 50kg. I'm using 48 slots for the stator and 26 for the rotor which is a Caged type. Winding is concentrated with 32 turns.
Induction Motor Speed vs Efficiency
One of the problems I'm seeing is in the Speed vs Efficiency curve. If I understand correctly, this should be more of an exponential curve like the one I have drawn, and not a linear one like I'm getting from the software. Why I am getting these results?

My second question is regarding the Drive requirements vs Main Requirements Voltage. In the main requirements I specify 410V as the Power Supply Voltage and under Drive I'm setting 410V for the Amplitude. Assuming that the PS Voltage is the DC Voltage that drives the inverter which in turns converts this into AC, is the Amplitude the value from one of the phases of the AC output of the inverter (which would be one of the inputs into the motor phases)? If so, what value should I be using instead of the 410V and what is the equation to get this value? If not, are both values the same thing?

My last and third question is regarding the winding parameters. JMAG just gives you the option of changing the Turns which I have set to 32 and the Phase Resistance. However, I don't understand how to determine the right gauge for the actual wires from these results and JMAG doesn't seem to give you this number or any kind of wire dimension. How can I determine this?

I'm open to any suggestions and appreciate any feedback or resource that you may provide. Thanks!
<- - Make a Comment - ->
First, since you are trying to reach 3200RPM with the drive, I assume you have designed a 2 pole winding. If that is true, a 48/26 slot is a strange slot combo that I never used in my designs. If I had a 2 pole 48 slot stator, you would better be served, from a stray loss and a noise standpoint, going with a 38 or 40 slot rotor. If noise is a big concern, a rotor slot choice of 56 would be warranted, but this choice will definitely drive up your stray losses. As for the wire size, once you establish your TPC, the wire size is primarily driven by the slot opening. We always made sure we could fit three wires across the opening i.e. if you have a slot opening of .15", you would go with a max diameter wire of .05". This is for obviously to make it easier to wind. Then, you just need to look at your slot fill. If I was winding a stator slot and not very experienced at it, you want the slot fill to stay around 75%.
<- - Comment made by: Brian - ->
You will not achieve 20 kg with a 120 kW induction machine at 3200 r/min - at least not without a gearbox. The suggestions apply as well BUT one I did not see is a comment on your concentrated winding. With 48 stator slots - a very good choice for a 2 pole motor matching the speed requirement - the correct winding will be a distributed lap wound winding with short chording / pitching.

Siemens recently developed a 250 kW 2500 r/min motor specifically for aircraft use - weighing little over 50 kg. This is a PERMANENT MAGNET SYNCHRONOUS AXIAL FLUX MACHINE - which can develop this range of power to mass ratio.
You will not achieve the same with a standard radial flux squirrel cage induction motor. I imagine you'll get to somewhere around 50 kg.
If reducing weight is your key criterion - and you can choose your design - use PM axial flux. Look up Siemens' design and you will get ideas. There is no rocket science in theirs - just good engineering optimization. Good luck.
<- - Comment made by: Robert - ->
After the three-phase AC is connected to the three-phase motor, a rotating magnetic field will be generated. The rotating magnetic field cuts the rotor winding to generate induced current in the rotor winding (the rotor winding is a closed path). The current carrying rotor conductor will generate electromagnetic force under the action of the stator rotating magnetic field, so as to form electromagnetic torque on the motor shaft and drive the motor to rotate, And the rotation direction of the motor is the same as that of the rotating magnetic field.
<- - Comment made by: OKmarts.com Online Store - ->
After the three-phase AC is connected to the three-phase motor, a rotating magnetic field will be generated. The rotating magnetic field cuts the rotor winding to generate induced current in the rotor winding (the rotor winding is a closed path). The current carrying rotor conductor will generate electromagnetic force under the action of the stator rotating magnetic field, so as to form electromagnetic torque on the motor shaft and drive the motor to rotate, And the rotation direction of the motor is the same as that of the rotating magnetic field.
<- - Comment made by: OKmarts.com Online Store - ->
Okmarts provide many engineering parts. If you are interested in its websites, you can browse it. Okmarts industrial online store provides various quality industrial products, servo amplifier, servo motor, servo driver, frequency converter, solenoid valve, overhaul kits, Thyristor.Siemens PLC 6AG1214-1BD23-2XB0
<- - Comment made by: okmarts - ->
Okmarts provide many engineering parts. If you are interested in its websites, you can browse it. Okmarts industrial online store provides various quality industrial products, servo amplifier, servo motor, servo driver, frequency converter, solenoid valve, overhaul kits, Thyristor.Siemens PLC 6AG1214-1BD23-2XB0
<- - Comment made by: okmarts - ->
Okmarts provide many engineering parts. If you are interested in its websites, you can browse it. Okmarts industrial online store provides various quality industrial products, servo amplifier, servo motor, servo driver, frequency converter, solenoid valve, overhaul kits, Thyristor.Siemens PLC 6AG1214-1BD23-2XB0
<- - Comment made by: okmarts - ->
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