There are generally three types of electrical braking for motors: regenerative braking, dynamic braking, and plugging. Of the three methods, plugging provides the fastest stop, but it can be harsh on both the electrical and mechanical components.

1. Methods of Electrical
Braking of AC Motors
ELECTRICAL MACHINE II (EE-353)
ANEEQUE AHMAD ********-012
Group No.04 AHMAD FARAZ ********-019
ALI HAMZA ********-020
ARBAB HASSAN ********-035

2. What is Braking?
● The term braking comes from the term brake. A brake is
a mechanical device that inhibits motion by absorbing energy from a
moving system, like vehicles, locomotives.
● Two types of Braking
1. Mechanical Braking
2. Electrical Braking

3. Continue…
Mechanical braking
● In this process of braking, the kinetic energy of the rotating parts is
dissipated in the form of heat by the brake shoes of the brake lining
that rubs on a wheel of vehicle or brake drum.
Electric braking
● In this process of braking, the kinetic energy of the rotating parts of the
motor is converted into electrical energy which in turn is dissipated as
heat energy in resistance or in sometimes, electrical energy is
returned to the supply. Here, no energy is dissipated in brake shoes

4. ADVANTAGES
● Small maintenance cost
● Energy saving
● Reliability
● Smooth operation
● System Capacity

5. METHODS OF ELECTRICAL BRAKING
Electrical braking of AC motors can be done by different methods, which are-
○ Regenerative Braking
○ Dynamic Braking
○ Plugging Braking
○ DC injection Braking

6. REGENERATIVE BRAKING
● In the Regenerative braking method the motor is not disconnected
from the supply.
● It remains connected to it and feeds back the braking energy or it
kinetic energy to the system.
● As no energy is wasted in this method and it is supplied back to the
system, thus overall energy is saved.

7. REGENERATIVE BRAKING
● Thus the regenerative braking is better than Plugging and
Dynamic braking.
● This type of braking is used in traction whenever the train runs
on down.
● The regenerative braking is applied to DC shunt motor, series
motor and 3-phase induction motors

8. Explanation
● We know the power (input) of an induction
motor is given as.
Pin = 3VIscosφs
● Here, φs the phase angle between stator phase
voltage V and the stator phase current Is. Now, for
motoring operation φs < 90o and for braking
operation φs > 90o.

9. Explanation
● When the speed of the motor is more than the synchronous
speed, the relative speed between the motor conductors and
air gap rotating field reverses, as a result the phase angle
because greater than 90, and the power flow reverse and thus
regenerative braking takes place.

10. Explanation
● If the source frequency is fixed then the regenerative
braking of induction motor can only take place if the
speed of the motor is greater than synchronous speed,
● But with a variable frequency source regenerative
braking of induction motor can occur for speeds lower
than synchronous speed

11. Advantage & Disadvantage
● The main advantage of this kind of braking can be said that
the generated power is use fully employed and
● The main disadvantage of this type of braking is that for
fixed frequency sources, braking cannot happen below
synchronous speeds.

12. DYNAMIC BRAKING
ANEEQUE AHMED
18143122-012

13. TYPES
● AC dynamic braking
● Self-dynamic braking
● DC dynamic braking

14. AC DYNAMIC BRAKING
● This type of induction motor braking is obtained when the
motor is made to run on a single phase supply by
disconnecting any one of the three phase from the source.
● It is either left open or it is connected with another phase.
● When the disconnected phase is left open, it is called two
lead connection and when the disconnected phase is
connected to another machine phase it is known as three
load connection.

15. AC DYNAMIC BRAKING

16. Explanation
● When the motor is running on 1-phase supply, the motor is
fed by positive and negative sequence, net torque produced
by the machine at that point of time is sum of torques due to
positive and negative sequence voltage.
● At high resistance the net torque is found to be negative and
braking occurs. From the previous figure the two and three
load connections can be understood.

17. SELF DYNAMIC BRAKING
● In this method there capacitors are kept permanently
connected across the source terminals of the motor. The
value of the capacitors are chosen depending upon their
capability to deliver enough reactive current to excite the
motor and make it work as a generator.
● The braking connection and self-excitation process is shown
in the figure.

18. SELF DYNAMIC BRAKING

19. DC DYNAMIC BRAKING
● To obtain this type of braking the stator of a running
induction motor is connected to a DC supply. Two and three
load connections are the two common type of connections
for star and delta connected stators.

20. DC DYNAMIC BRAKING

21. Explanation
● Now coming to the method of operation, the moment when
AC supply is disconnected and DC supply is introduced
across the terminals of the induction motor, there is a
stationery magnetic field generated due to the DC current
flow and as the rotor of the motor rotates in that field, there is
a field induces in the rotor winding.
● As a result the machine works as a generator and the
generated energy dissipates in the rotor circuit resistance
and dynamic braking of induction motor occur

22. PLUGGING BRAKING
AHMAD FARAZ KASHIF
18143122-019

23. What is Plugging
● Plugging is the method of inducing negative torque in the
rotor of an induction motor to rapidly bring its speed of
rotation to zero. This is done by reversing the supply
connection at the stator terminals.

24. PLUGGING
● Plugging is the most powerful method of braking an electric
motor, consisting of actively applying power to the motor in
the opposite direction of its rotation.
● This is analogous to reversing the engine thrust of a power
boat or an airplane in order to quickly bring it to a halt. For a
VFD, this means a reversal of phase rotation while carefully
applying power to the AC induction motor.

25. What is DC injection
● DC Injection Braking is a braking system used with 3-phase
motors. The VFD outputs a DC current that gets applied to
two of the windings of the motor, which causes the motor to
quickly brake.

26. Continue…
● Like DC injection braking, plugging requires power be
applied to the motor in order to make it stop, and it also
results in all the kinetic energy being dissipated in the rotor.
The advantage held by plugging over DC injection braking is
that the braking torque may be maintained and precisely
controlled all the way to zero speed

27. PLUGGING BRAKING OF INDUCTION MOTOR
● Plugging induction motor braking is done by reversing the
phase sequence of the motor. Plugging braking of induction
motor is done by interchanging connections of any two phases
of stator with respect of supply terminals. And with that the
operation of motoring shifts to plugging braking.
● During plugging the slip is (2 – s), if the original slip of the
running motor is s, then it can be shown in the following way.

28. PLUGGING BRAKING OF INDUCTION MOTOR

29. DC INJECTION BRAKING
ARBAB HASSAN
18143122-035

30. DC INJECTION BRAKING
● DC Injection braking is a method of braking in which direct
current (DC) is applied to the stationary windings of an AC
motor after the AC voltage is removed. This is an efficient
and effective method of braking most AC motors.
● DC injection braking provides a quick and smooth braking
action on all types of loads, including high- speed and high-
inertia loads.

31. DC INJECTION BRAKING
● DC injection braking works just as its name implies by injecting
DC voltage into the motor windings. Before DC injection
braking can begin, the AC power to the motor stator must be
disconnected typically by the opening of a relay.
● In turn, a relay controlling motor braking closes, DC bus
allowing DC voltage sourced by the to be applied to the
windings.

32. DC INJECTION BRAKING
● To prevent the braking current from
exceeding the drive and motor
ratings, circuitry in the VFD(variable
frequency drive) or in an external
braking module controls the amount
of voltage applied.

33. Explanation
● When DC current is applied to the motor windings, it creates a fixed
(rather than rotating) magnetic field. Braking action is produced by
the rotor working to align to this stationary field. The higher the DC
current, the stronger the braking force.
● The only thing that can keep the rotor from stopping with the first
alignment is the rotational inertia of the load connected to the motor
shaft. However, since the braking action of the stator is present at all
times, the motor is braked quickly and smoothly to a standstill.

34. APPLICATION
Industrial AC motors run at high speeds so they can power heavy duty
equipment and machinery. Using high power motors is crucial to any
operation that requires a reliable motor for speed and quality. AC motors
are used in a variety of applications.
They can power fans, planers, conveyors, rolling mills, cut-off saws, wood
hogs, rubber mills, presses, rock crushers, shredders, chippers,
centrifuges, grinders, and other machines or equipment.

35. Limitations
● The energy generated during braking is dissipated as heat by the
motor (particularly the rotor) and the controller, so thermal limitations
of these components dictate how much braking current can be
applied and the amount of time for which it can be applied before
overheating occurs.
● If DC injection braking is used frequently, the additional heating
created during braking must be taken into account when sizing the
motor.

36. Limitations
● Although DC injection braking can
be used to hold a load stationary,
it’s not generally recommended
due to heat generated in the motor.
And because DC injection brakes
require a constant power supply,
they’re not considered fail-safe
devices.

37. ANY QUESTIONS ?!