Servomotor driven by another, and not powered

What happens when a servomotor is driven by another by another motor at high speed, but the servomotor itself is not power, but indeed connected to a drive?
Because the servomotor has permanent magnets I suppose voltage will be induced in the windings and thus the connection leads.
I suppose the freewheeling diodes at the power stage of the drive will conduct the generated current.
Will this harm the drive, or is there no risk at all?

Damage to VSD's can be caused by Back EMF
The servo is different but always connected to it's controller.
It may be possible but is it worth the risk -
I would say no.

Yes there is a big risk as the energy needs to flow out of the controller and that is impossible as the power can only supply.
you will need a real four quadrant controller.

It depends on what you mean by high speed. I have personally never seen a drive damaged by doing this as long as the servomotor peak back EMF does not exceed the drives rated bus voltage. If you go fast enough to exceed the drives rated voltage drive power circuit components will start to blow up.

Keith

Important remark : the servomotor that will be driven by another will not be powered, the respective drive will be in OFF2 or inhibit status, off course there is no brake on the motor.
It's for a demo configuration where I want two drive to be mechanically coupled. If I activate both I can put one in torque mode to act as load on the other one. But my question was for the case I only wanted to work with one motor and I disabled the second motor. I wanted to be sure if the driven motor would not dammage the drive if turning in an electrically disabled state at high speed becauase of the voltage generated by the rotating permanent magnets of the servomotor.

I think it is going to depend on the voltage level that is developed at the output terminals of the disabled drive. Can you open the circuit with a contactor?

Plc_User said:

Because the servomotor has permanent magnets ...

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Are you sure of this?
Most servomotor today are AC.

Even in a normal AC-motor, the current flowing through the rotor is always DC.

Plc_User said:

What happens when a servomotor is driven by another by another motor at high speed, but the servomotor itself is not power, but indeed connected to a drive?
Because the servomotor has permanent magnets I suppose voltage will be induced in the windings and thus the connection leads.
I suppose the freewheeling diodes at the power stage of the drive will conduct the generated current.
Will this harm the drive, or is there no risk at all?

Click to expand...

Here is what I understand to be the setup
Two motor and drive setups
Motors are matched either perm mag DC or 3 phase AC brushless DC aka Perm Mag Synch Motor (pmsm). He did not specify which.
Motors are mechanically coupled
Wants to drive one in motor mode and other as generator ie motor being overhauled ie driven by other unit.

If as suggested he put a contactor on one to disconnect it from its controller all he would have is a generator with no connected load. He will not be able to vary load on the "generator".

With two 4 quad drives he should be able to have one as a motor driving the other as overhauling ie generate. Will have to have some kind of dummy load ie resistors to dump excess power to avoid raising DC bus voltage too high (assuming VFD are used).

Dan Bentler