8. Braking of Electric Machines

Why BrakingTo stop the electric motor. To sustain the speed of the drive system at the desired value. To prevent the motor from over-speeding.To hold the motor shaft at a certain position regardless of the applied load torque.

1. Regenerative BrakingWhen the load torque causes the machine to run at a speed > no-load speed, but without changing its direction of rotation, the motor is in regenerative braking.

Fl

Fl

Fm

Fm

F

F

(

(

2. Dynamic BrakingWhen the motor is running, kinetic energy is stored in its rotating mass. If the kinetic energy of the motor is dissipated in a resistive element, the motor stops.

3. Counter Current BrakingIf the the airgap field reverses its rotation, the rotor shaft must also reverse its rotation.

Field

Field

A

C

B

A

B

C

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