Plugging braking

Braking of induction motor by PLUGGING METHOD ,connection, operation, characteristics, pros and cons.

1. Braking of induction motor by PLUGGING METHOD Done by, S.PRAVEENKUMAR, BE-EEE, PSG TECH.

2. In this method braking is done by, supplying additional energy to the motor in to develop a braking torque in a direction opposite to the direction of rotation of shaft thus arresting the movement. PLUGGING/Counter current braking

3. Connection diagram

4. To develop braking torque, the TPDT switch is closed to auto transformer side with a reverse phase sequence RBY. This causes the direction of rotating magnetic field to get reversed immediately in anticlockwise direction. Due to this the direction of torque developed in the rotor becomes opposite to direction of rotation of the shaft. This braking torque causes a rapid reduction in speed. Operation

5. The rate of reduction of speed depends, on magnitude of reverse voltage. This can be controlled by using an auto transformer. Also torque is not zero at zero speed. Thus the motor tends to accelerate and rotate in reverse direction. Characteristics

6. Slip (1<S<2) The value of S can become more than 1 when Ns is made negative. The value of slip Sb becomes, Upon solving,we get S b =2-s

7. Speed reduction is rapid. disadvantages Rotation in opposite direction if the supply is not cut off. During the plugging operation very high losses occur in the form of heat. This heat is more than produced when rotor is normally locked. So it cannot be applied frequently as due to high heat produced rotor which can damage the rotor bars and insulation. Advantages