The document discusses induction generators. It explains that an induction generator operates when an induction motor runs above synchronous speed, causing the rotor to spin faster than synchronous speed with negative slip. It operates similarly to an induction motor but delivers power to a load instead of drawing power. Reactive power must be supplied by a capacitor bank to develop the rotating magnetic field since induction generators are not self-excited. Induction generators have advantages of simple and rugged construction but disadvantages of lower efficiency and inability to regulate voltage without external sources. They are well suited for variable speed applications like wind turbines.

1. N R A M POLYTECNIC NITTE
DEPARTMENT OF ELECTRICAL AND
ELECTRONICS ENGG
NAME OF THE STUDENT : PRASHANTH KOTIAN
ROLL NO : 53
REGISTER NUMBER : 309EE17304
SUBJECT NAME : TRANSFORMER & AC MOTOR
SUBJECT CODE : 15EE41T
ACTIVITY : INDUCTION GENERATOR
SUBMITTED TO : VISHWANATHAN K

2.  Induction generator
 Principle of operation
 Induction generator
 Reactive power requirement,
voltage built up & control.
 Advantages & Disadvantages
 Application
CONTENTS

3.  When the induction motor runs above the
synchronous speed then its runs as a generator
called induction generator.
 The negative slip indicate that the rotor of
induction motor is running faster then the
synchronous speed.
INDUCTION GENERATOR

4.  Fig. show the induction generator which is
driven by the prime mover such as a wind
turbine is connected to a load.
 When the speed of induction generator
above synchronous speed the active power
delivered by the 3- phase load.
 The corresponding mode of operation of
induction machine is called generating mode
& the slip of induction machine will be
negative.
 The construction of induction generator is
the same as that of induction motor.

5. TORQUE-SPEED CHARACTERISTICS
 An Induction machine
Can function as a motor, a brake, and synchronous motor. All three
operating modes can be seen from the torque-speed curve

7. Principle of operation
 When the 3-phase induction motor is driven at a
speed greater than synchronous speed(-ve slip) by
an external prime mover with exciting current
provided either from 3- phase line or capacitor bank.
 The emf and current of slip frequency will appear in
the rotor winding.
 In generating mode of operation, an external prime
mover drives the rotor above the synchronous
speed.
 The stator flux induces currents in the rotor, but
since the opposing rotor flux in now cutting the stator
coils & the motor operates as a generator.

8. Reactive power requirement, voltage built-up &
control
 The induction generator is not self excited
machine, therefore develop rotating magnetic
field.
 The reactive power is also required for the
connected inductive load to improve the
power factor on the load.
 The induction generator using the delta
connected capacitor bank for the supply of
reactive power is called self excited or
isolated induction generator.

9.  The reactive power required by the generator
and for the connected inductive load is
supplied by the capacitor bank.
 To achieve a given voltage level in an
induction generator, the capacitor bank must
supply the magnetizing or exciting current
corresponding to that level.
 For a particular value of capacitance, the
curve between the voltage and magnetizing or
capacitive current will be linear.

10.  The fig. indicates that how the voltage is built
up different values of capacitance.
 At a point P the reactive power demanded by
the generator is equal to the reactive power
supplied by the capacitor bank.
 For a lagging power factor load, the voltage
collapses very rapidly.

11. ADVANTAGES
 Mechanically & electrically simpler than
other types of generator.
 Construction: simple, robust & rugged.
 Relatively cheaper.
 Requires no brushes & commutator.
 easy in maintenance.
 They do not have to be synchronized to
the supply lines as does a synchronous
generator

12. DISADVANTAGES
 It is not suitable for separate, isolated
operation
 It consumes rather than supplies
magnetizing KVAR.
 It cannot contribute to the maintenance
of system. voltage levels (this is left
entirely to the synchronous generators
or capacitors).
 In general it has a lower efficiency

13. APPLICATION
 Induction generator are often used in wind
turbines and small station due to their
ability to produce useful power at varying
rotor speed.
 Particularly suitable for wind generating
stations as in this speed is always a
variable factor.
 They are also very useful automatic
dynamic braking such as for braking
purpose in case of railways.
 Induction generator for a fixed wind turbine
system.