 Myself, Mrs. Veena Sunil Patki, Assistant Professor, Department of Electronics Engineering, Valkan Institute of Technology, Sallapur, welcome you for this session. At the end of this session, students can describe types of electric braking. Brake is an equipment used to reduce the speed of any moving or rotating equipment like vehicles, locomotives. The process of applying brakes is called as braking. We can classify braking into two parts, mechanical braking and electrical braking. In mechanical braking, speed of motor is reduced by mechanical process, power is wasted in the form of heat and it requires frequent maintenance. Mechanical braking is used to hold the drive at standstill. In electrical braking, the whole process depends on the flux and torque direction. Mechanical braking allows smooth stop. It is used where frequent, quick, accurate and emergency stops are required. It keeps the speed within safe limit or hoist. Speed of the driven unit is suitably controlled during its deceleration. Types of electric braking, there are various types of motors having different properties. Hence, these braking methods also differs for each motor. We can divide braking into three parts, dynamic or rheostatic braking, plugging or reverse current braking and regenerative braking. So let us discuss about all these types one by one. For shunt motor, supply voltage is replaced by resistance across armature for dynamic or rheostatic braking. So you can see here the current direction for the shunt motor is downward. So here the armature current direction is downward and the motor rotates in clockwise direction. For dynamic braking, this armature supply is disconnected and the variable resistance is connected across the armature. The back AMF is there across armature and due to that back AMF current through this armature is reversed. So current direction is now upward. So the torque which is created on the motor is now reversed and due to that the braking will be applied. So we can calculate the braking torque. So armature current is given by Eb by R plus Ra where Eb equal to k1 and phi. So here we can calculate the braking torque equal to k2 Ia phi. If we put Ia in this equation here the braking torque is equal to k3n phi square. If flux is constant, braking torque is directly proportional to speed and when speed decreases to zero that braking torque becomes zero. For this shunt motor armature or field winding current is reversed for plugging or reverse current braking. So here you can see here in this diagram again the current direction is downward and here in this diagram armature connections are reversed. So A1 is connected to here and A2 is connected to positive of the terminal. So current direction will be reversed that is upward in this diagram you can see. So here the torque which is created due to this connection will be reversed and that will create the brake on the motor that will reduce the speed of the motor. But here due to this connection the back EMF and the supply voltage both are in series. So we can calculate the armature current equal to V plus Eb divided by R plus Ra. So braking torque is given by k2 Ia phi. So Ia is equal to V by Ra R plus Ra plus k1n phi by R plus Ra. If I put this Ia in this equation so we will get the equation like this and if we find out that in braking torque that braking torque equal to k3 plus k4n phi square. So if flux is constant and when speed decreases to 0 braking torque equal to k3 means some braking torque is there at standstill position. So here we can use this reverse current braking or plugging in controlling elevators, rolling wheels, printing press, machine tools etc. But in this method motor tries to accelerate in other direction after coming to rest. So some auxiliary device is required to cut off the supply as soon as the motor comes to rest in case of failure of supply this method is ineffective. So regenerative braking motor run at a speed higher than no load speed with a constant excitation. Due to this back EMF becomes greater than supply voltage and machine acts as a generator. That power is delivered to the line from the motor means that machine acts as a generator and current direction through armature is also reversed the same effect can be obtained by if we increase the shunt current or the field current which increases the flux in the motor and the speed decreases because the speed is inversely proportional to flux. So for shunt motor if back EMF is greater than supply voltage armature current reverses. So the direction of torque reverses and speed falls until back EMF becomes equal to supply voltage. So you can see here the direction of the current through the armature is downward but if we make the speed of the motor above the rated speed above the no load speed that motor acts as a generator and the direction of the armature current is reversed that is upward and that will create the opposite direction torque. So we can apply regenerative braking where frequent braking and slowing of drives is required. It is useful in holding a descending load of high potential energy at a constant speed it is also used to control the speed of motors driving loads such as in electric locomotives elevators cranes and hoist but this method cannot be used for stopping the motor but used for controlling the speed above the no load speed. Now pause the video and think about this question so polarity of supply voltage is reversed in which type of braking regenerative braking dynamic braking plugging none of these. So what is the answer plugging now let us discuss about the dynamic or rheostatic braking for series motor. So here in this series motor the current direction is downward and if we disconnect the supply voltage and if we connect the resistance but here we have to reverse connections of the armature winding or field winding for this rheostatic braking or dynamic braking. So that we can make the direction of the current through this series motor opposite and the torque which is created on the motor will be reversed. So here the A1 is connected to negative and A2 is connected to the positive through this variable resistance so that the opposite torque is created on the motor and motor tries to stop. So plugging or reverse current braking for this series motor so current direction is downward you can see here for the plugging series motor this armature the connections is reversed and one resistance is connected in series with the armature. So the opposite torque is created and braking will be applied. For regenerative braking for series motor increase in excitation results decrease in speed as such it is not possible to get EMF more than voltage it is not possible to make field current more than the armature current hence regeneration braking with series motor is not possible but can be used with traction motors with some special arrangements. So you can refer the books Electrical Engineering by B. L. Thareja, Principles of Electrical Machines by V. K. Mehta and Rohit Mehta. Thank you.