plugging braking is the technique by which we brakes the electric motors. Plugging is the very fast technique of braking in which supply voltage get reverse. Plugging braking is also known as reverse braking , this technique is used in emergency situation for rapid deceleration .
here it is armature of DC motor and it is field winding this circuit diagram is showing motoring mode , during motoring condition of DC motor back EMF (Eb) remain opposite to the supply voltage (v) as you can see in the diagram back EMF and supply voltage both the direction are opposite.
to perform braking operation we interchange the armature terminal and due to interchange the armature terminal , supply voltage and back EMF, now both are flow in the same direction
a resistance (Rb) is connected to the armature terminal that is known as braking resistance. Now we will understand what is the effect of interchanging armature terminal.
during normal condition of DC motor rotor rotates in clockwise direction but after interchanging the armature terminal , torque acts on armature in anticlockwise direction because the direction of supply voltage has reversed. When reverse torque apply on the armature rotor speed becomes zero when rotor speed become zero we disconnect the supply voltage from circuit.
if we will not remove supply voltage from the circuit then armature will start to rotate in reverse direction that’s why when reverse torque apply on the armature and armature speed becomes zero then we remove supply voltage from the circuit.
How does plugging braking work in three phase induction motor
To apply plugging braking in 3 phase induction motor we reverse the phase sequence , to reverse the phase sequence we interchange the any two terminal of three phase induction motor , due to this rotating magnetic field of three phase induction motor get reverse in air gap of stator and rotor.
In working principle of three phase induction motor we have already study that when three phase AC supply provided in field winding that placed on stator at an angle of 120° , rotating magnetic field produces in the air gap of rotor and stator and in case of plugging braking we interchange any two input terminal of 3 phase induction motor as a result produced rotating magnetic field get reverse and due to reverse rotating magnetic field applied torque on rotor also get reverse so rotor quickly stops. Thus we apply plugging braking in 3 phase induction motor.
Normal slip : (Sn = Ns – Nr/Ns )
Braking slip : ( Sb = Ns + Nr/Ns )
Conclusion
plugging braking operates due to the supply terminal of the motor are reversed either through contactor or solid state switch , due to reversal of supply applied torque on motor also get reverse, reverse torque opposes the speed of motor and finally stops the speed of motor
Applications of plugging braking
- plugging braking is used at that place where rapid deceleration is required such as emergency stops in Elevators , rolling mills and machine tools, mean we can say plugging braking is used for the emergency stop.
- in elevators commonly plugging braking is installed to stop the Elevators
- in rolling mills we have to need of precise control movement that is possible by the help of plugging braking so to control the movement of Rolling Mills generally we use plugging braking.
- Plugging braking is used in the printing process where it quickly stopped the printing Presses .
- in different machine tools we use plugging braking where it allowed for rapid deceleration of the spindle
- Plugging braking is used in the electric vehicles for braking purpose.
- this type of braking technique is used for reverse the direction of torque
- this type of braking system is used in the weight feeders.
Advantages
- since plugging is the type of electric braking so no any type of wear and tear occurs in the system that is main advantage of plugging braking.
- if you have to control the armature voltage at safe value then it can be possible by applying plugging braking you can control the armature voltage at safe value.
- we connect a resistor in series with armature winding that limits the high current so armature winding get protected from the high current or any type of damage.
- this is best technique to apply Brake on DC motor as well as induction motor both types of motor can be adapt this technique for braking purpose.
- generally with paper plugging braking due to less maintenance is required because this is type of electric braking and no any mechanical friction and arc generate that’s why we need of less maintenance.
- this type of braking is reliable braking system.
- there are no any friction part in the plugging braking so it will not produce due to friction
Limitations
- Plugging braking causes high energy consumption and heat generation because plugging converts kinetic energy into heat as a result motor controller and important component of machine get heated.
- due to frequent plugging reverse stock suddenly apply that make cause wear and tear in the motor , in case of plugging braking torque suddenly applies so internal component of the motor can be damage.
- when we apply plugging braking in the machine or different motors then large inrush current draws.
- The abrupt stopping action of plugging braking causes vibrations and stress on mechanical component like shafts & gears .
Important points
Braking definition : braking is the process by which reduce the speed of rotating machine it can be either mechanically or electrically we arrange the system like when we need of brake the rotating machine then quickly we can stop the machine by the help of braking system.
Electrical braking : electrical braking operates by using direction of torque and change in flux to Slow Down The rotating machine that make its different from mechanical braking.
Regenerative braking : regenerative braking is a type of electrical braking that occurs when motor or rotating machine exceeds the synchronous speed NS at the time motor behave like generator and reversing current and torque. : VIDEO
Other topics
- Dynamic braking
- 3 phase induction motor
- Capacitor start capacitor run motor
- Shaded pole induction motor
- Split phase induction motor