Motor Generator Inverter layout

[lyen12]

There are two caged induction motors which were given to us in a bad condition and were refurbished to like-new now. I am thinking of doing a demonstration of having one motor driving another motor to generate power.

Motor A is rated to 300kW 4kV 4pole 60Hz,
Motor B is 400kW 6kV 4pole 50Hz.
I have an inverter 900kW 3kV and a 50Hz supply.
All of these are three-phase.

I am planning to connect the inverter to Motor A (300kW 4kV) to drive Motor B to act as a generator, which can then be used to drive load such as a fan/compressor, etc.

Motor A probably need to run at 3kV 225kW to match the inverter input voltage. The generator (motor B) does not need to generate the max power. The purpose is to demonstrate the principle of motoring and generating. Do you think this concept will work? Any comments are welcomed.

 

[davidbeach]

How do you plan on supplying the excitation vars to motor B? An induction motor can be used to generate power, but it doesn't generate voltage on its own.

 

[waross]

Both the induction motor and the induction generator will have an inherent slip frequency. The output frequency will be the supply frequency minus both slip frequencies. The slip frequencies will increase as the load increases.
An induction generator generally derives the magnetizing current from the grid.
I have tried that demonstration a couple of times with a DC motor driving a motor of about 3 HP. With the equipment available in one shop the demonstration worked.
With the equipment available in the second shop, I was unsuccessful.
Connecting a bank of capacitors across the terminals of the induction motor may help.
I would start with the amount of capacity needed to correct the power factor to unity.
Please give us some feedback on the results.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[lyen12]

update. with this amount of investment made, we will be able to build a test bed for future test/experiment.
Looks like we will be getting a 4-quadrant inverter, which will then be able to link it back to the 900kW inverter (via the busbar i suppose). That way the 4-quadrant inverter should act like a 'grid' for kVAr supply. This way I do not have to worry about connecting up bank of capacitors and do not need any load.

Do you think this will work?

 

[LionelHutz]

What is the intended goal now?

You can demonstrate induction generation by connecting the load motor to the grid and then slightly over-speeding the prime mover motor with any old cheap VFD.