Hello,

I need to run a 400Vac 3 phase induction motor at a reduced speed from a 42Vac supply:


Working system now:

0.55kw 3 phase 400Vac motor rewired to work with 42Vac 3 phase. at 1400 rpm:

42Vac supply.


I do not want to change the coils and What I would suggest

replace 0.55Kw with a 2.2 kW
change 1400 rpm to 140 rpm
construct a simple inverter (with an IPM modul to achieve the same torque with 2.2 KW 400Vac (without changing the coils) motor with 42Vac an 140 rpm as the 0.55KW motor (with changed coils) at 1400 rpm )


Is it possible?

I can use extra air cooling on motor. It is not a problem.

I should use 42Vac according to safety regulations and I can also save the mechanical gearbox when I can increase the torque 10x eventhough I decrease the supply to 42Vac without changing the coils.

Is it a dream or is it theoretically possible


thanks:


Ferhat

Hello Incal


If you connect a 400 volt 50Hz motor to a supply of 42 Volt at 50Hz, there will be almost no torque available to do any work. The torque reduces by the square of the voltage, so in theory, you will have 1% of the normal starting torque.

You could reduce the frequency down to 5 Hz to increase the flux in the iron, but the motor speed will be 10% of the rated speed. In practice, the flux will still be low due to the resistance of the winding, so you would probably find that you would need to reduce the frequency down further to get the motor fully fluxed at 42 volts.
You could use a transformer to step the voltage up, or you may be able to alter the connection of the motor from star connection to delta connection. This will help a little, raising the torque by a factor of 3.


I believe that if you really want to run the motor at 42 Volts, then you need to get the motor specially wound for such operation.
Best regards,

Thanks for your Opinion.

I use as a default configuration a 400Vac/42Vac trafo and a special wound motor. But to get all the motors wound each time is too time consuming. (each time 20-25 motor)

I buy brand new 400Vac motors and get them wound each time. (I change the stator coil windings)


a little question to your comment:

>the flux will still be low due to the >resistance of the winding, so you would >probably find that you would need to >reduce the frequency down further to >get the motor fully fluxed at 42 volts.

when I reduce the stator coil resistance (for example I can buy 2.2kW motors not 0.55kW (I need only 0.37Kw power in system)
and at the same time reduce the frequency to 5Hz and connect as a detla connection

Can I get 10x the torque of a 0.37Kw at *1400rpm*!

Again thnaks for your detailed explanations.

incal

NOTE: I can not programm field oriented control. I have the capability to use IPMs and a microcontroller to use only (V/F). Field oriented control may also help further but it is also too time consuming and expensive to program.

Hello incal


The torque that you can get is dependant on the flux in the iron. If you oversize the frame, then you can have more flux and therefore you can get more torque. If you wish to operate at a fixed frequency of 5Hz only, then you can optimise the windings (turns and resistance) to give you the maximum flux that can be operated in a given frame and therefore get maximum torque.
Best regards,

Just as an Amateur and a beginner at motor mechanics I search also a good guide that describes how to wire an 8 Pole induction motor. (Guidelines, practice how to divide wireslots etc.)

Is there a tutorial in Internet. I know that in order to learn it detailed One must work practically in the business. But I do not have the possibility to interact with those who wire motors. What I can become is a used motor cage and rotor and wires. I think I can try it by myself. I now have a 110KW cage and rotor (without wires on it) . And I wish to make small torque experiments. I want to try to wind the 110KW motor as 8 pole and drive it with an IPM Module. The IPM Module has 1200V 150A pro phase and is good snubbered and gives again 5Hz -3 phase sinus. I tried it on inductive load but not with a motor. this time I wish to make it as a Hobby. (400V/42V is an commercial project and I think I should not use too much fantasy there). But I love motors and wish to reach very high torques on induction motors without using gearboxes.

I then wish to connect the old plastic extruder that requires 2500 Nm and will try to drive it without gearboxes. But I must learn how to wire an 8 Pole motor. I can do power electronics but I am very weak at motor winding and motormechanics.


Thanks for the answers to my party fantasy guided questions.
Incal.