Electric Braking

Q. What are the requirements of good electric braking?

Answer. The requirements of good electric braking are:

(i) The braking should be quick and reliable in action.

(ii) The braking must be controllable.

(iii) Some suitable means must be provided for dissipation of kinetic energy of the moving parts of the motor and its driven machines. 

(iv) Failure of any part of the braking system must result in the application of brakes. What are various types of electric braking used?

Q. What are various types of electric braking used?

Answer. There are three types of electric braking, all of which are applicable to the usual types of electric motors. viz. plugging (or counter-current braking), dynamic (or rheostatic) braking and regenerative braking.

Q. What are braking systems applicable to a dc shunt motor?

Answer. The braking systems applicable to a shunt motor are plugging, dynamic and regenerative braking.

Q. What is mean by plugging?

Answer. Plugging means stopping of an electric motor by instantaneously reversing its torque till it stops.

Q. How plugging of a dc motor is done?

Answer. Plugging is obtained in a dc motor by reversing the supply terminals to the armature of the motor.

Q. What is dynamic braking?

Answer. In dynamic braking, the motor is disconnected from the supply and operated as a generator driven by the kinetic energy of the motor and its driven machines. The kinetic energy of rotation is converted into electrical energy which is dissipated in the external resistance connected across the motor at the braking instant.

Q. Why rheostatic braking is economical to plugging?

Answer. In rheostatic braking, energy required from the supply to brake the motor is eliminated as compared to the plugging.

Q. What is the most economical method of electric braking?

Answer. Regenerative braking.

Q. What is regenerative braking?

Answer. In regenerative braking, the electric machine operation is changed from motoring to generating, mechanical energy is convened into electrical energy, part of which is returned to the supply and the rest of the energy is lost as heat in the windings and bearings of the electrical machines.

Q. In case of a dc series motor, when it is disconnected from the supply and is connected across a braking resistance, it is essential to change over the field winding connections. Why?

Answer. Otherwise, the current through the field winding will also be reversed, and no braking effect will occur.

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