Regenerative Braking

Regenerative braking takes place whenever the speed of the motor exceeds the synchronous speed. This baking method is called regenerative baking because here the motor works as generator and supply itself is given power from the load, i.e. motors.

The motor is not disconnected from the supply but remains connected to it and it feed back the braking energy or its KE to the supply system . This method is better than other braking system. This method is used when the load on the motor has overhauling characteristics as in the lowering of the cage of a hoist or the downgrade motion of an electric train. Regeneration takes place when Eb becomes greater than V. This happens when the overhauling load acts as a prime mover and so drives the machines as a generator. Consequently, the direction of armature current and the torque is reversed, hence speed falls until Eb = V. then mechanical brake applied

DC Shunt motor:

As the speed of the motor increases due to overhauling loads, the induced emf exceeds (Eb > V) the supply voltage and the energy will be fed into the supply system. This will quickly decrease the speed of the motor and can be brought to the rest. This constitutes regenerative braking.

DC Series motor:

In dc series motor, complications arise due to the fact that if the motor act as generator, the reversal of current in the armature would cause a reversal of polarity of the series field and hence the field flux will be neutralized. In order to avoid the neutralization of field flux, Special arrangements are then made to obtain the working of motors.

            So it use auxillary field windings which are bunched together in parallel and whole bunch is connected in parallel to the main field. So the machine behaves differentially compound generator when regenerate braking takesplace. If there is slight change in the line voltage the shunt Field will immediately cause the increase in the generated emf. This method is also known as French method.

Regenerative Braking of Three Phase Induction Motors

            Induction motor act as a generator when running at speed higher than the synchronous speed and it feeds power back to the ac mains ie, Regenerating. The machine will work as an induction generator. The value of slip  becomes negative.

 Speed below synchronous, Pole changing method is used for this purpose, If the number of stator poles is increased, synchronous speed will be less than the actual running speed. Machine will work as an induction generator.