# induction generator

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Hi,

I have conected an induction motor/generator to the UK mains (230v 50hz) and my waterwheel.

THe motor is 4hp 3phase 400v delta. I have connected one winding only to mains so I expect maximum output =4hp/3/(230/400).

When there is no water flowing over the wheel (ie the motor is totally a motor, powering the wheel) the current drawn is 2.5amps.

On increasing the flow over the wheel the current drops to 1.6 amps and then starts to increase.

I have taken it up to 7 amps (for a short time only)

The indicator on the electric meter which shows reverse current is lit, showing that power has been fed into the grid.

Questions:

Does the 1.6 amps represent the amount of excitation that has to be drawn in? (seems like a lot)

How much is the generator generating, 7 amps, 5.4 amps orsome different amount?

How do you measure the power produced (poss by having two meters,each measuring in only a single direction?)

Am I right in thinking that the maximum power will be produced at the maximum (positive) slip so that a full load speed of 1415 should run at 1585?

In this case is it a good idea to look for a motor with the smallest amount of slip (and are purpose made ig`s designed with smaller slip value?)

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• 4 weeks later...

Hello waterman

First, if you have connected one winding only, I assume that you are connecting a single winding to a single phase supply, i.e. phase to neutral 230V.

This will reduce the flux in the iron and therefore the effectiveness of the generator to generate. Additionally, you will need to be carefull not to satll the motor with power applied as t will not develop torque to take it up to synchronous speed.

The motor will draw a magnetising curent, typically, for a motor of this size on the correct voltage, I would expect that the magnetising current would be in the order of 30 - 40% of the rated current of the motor, but can be higher. With a reduced voltage across the windings, the magnetising current will fall.

As you increase the shaft torque driven into the motor from zero, you will go through a minimum current which is the magnetising current and then the current will begin to rise again. When the torque produed by the water wheel is below this minimum current, you are actually drawing power from the grid, and when it is above, you are feeding power back into the grid.

Normally, you would try to keep the current below the rated curent of the motor, but in your case,you are only using two terminals and there could be all sorts of effects that I would not be sure what you should do in terms of maximums. At the end of the day, the loading will just elevate the temperature. I would slowly increase the output current over a long period of time and monitor the temperature rise of the stator and if possible, the rotor. Keep these at reasonable limits and you should be OK.

Best regards,

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• 2 months later...

Hello waterman

First, if you have connected one winding only, I assume that you are connecting a single winding to a single phase supply, i.e. phase to neutral 230V.

This will reduce the flux in the iron and therefore the effectiveness of the generator to generate. Additionally, you will need to be carefull not to satll the motor with power applied as t will not develop torque to take it up to synchronous speed.

The motor will draw a magnetising curent, typically, for a motor of this size on the correct voltage, I would expect that the magnetising current would be in the order of 30 - 40% of the rated current of the motor, but can be higher. With a reduced voltage across the windings, the magnetising current will fall.

As you increase the shaft torque driven into the motor from zero, you will go through a minimum current which is the magnetising current and then the current will begin to rise again. When the torque produed by the water wheel is below this minimum current, you are actually drawing power from the grid, and when it is above, you are feeding power back into the grid.

Normally, you would try to keep the current below the rated curent of the motor, but in your case,you are only using two terminals and there could be all sorts of effects that I would not be sure what you should do in terms of maximums. At the end of the day, the loading will just elevate the temperature. I would slowly increase the output current over a long period of time and monitor the temperature rise of the stator and if possible, the rotor. Keep these at reasonable limits and you should be OK.

Best regards,

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