This is a detailed PPT of Starting Methods of Three Phase Induction Motors and Introduction to Starters.

1. Starting Methods of Three Phase
Induction Motors
Udit J. Modi
Department of Mechanical Engineering
Institute of Technology
Nirma University, Ahmedabad

2. Starting of Induction Motors
• When the supply is connected to the stator of a three phase
IM, a rotating magnetic field is produced and the rotor starts
running. Thus, a 3-ϕ IM is self starting. At the time of
starting the motor slip is unity and the starting current is
very large.
• IM when direct switched, take five to seven times their full
load current and develop 1.5 to 2.5 times line voltage drop
which will affect the operation of other electrical equipment
connected to the same line.
• The purpose of starter is not to start the motor as the name
implies. The starter of the motor performs two functions:
• To reduce the heavy starting current.
• To provide overload and under voltage protection.

3. • 3-ϕ IM may be started by applying reduced voltage to
the motor during starting period. The torque of an IM
is proportional to the square of the applied voltage.
Thus, a greater torque is exerted by a motor when it
is started on full voltage than when it is started on
reduced voltage.
• STARTING OF CAGE MOTORS
• The following are the commonly used starters for
squirrel cage motors:
1. Direct on-line starter (DOL starter)
2. Primary resistor starter
3. Auto-transformer starter
4. Star-Delta starter

4. Direct-on-line Starter
Three phase supply
L1 L2 L3
Fuses
MMMAa
b
C
Start
N.O.
S1
D1
N.C.
S3
Remote
stop
S2
N.C. Stop
OLC
MOTOR

5. Primary Resistor
Starter
L1
L2
L3
Stator
Rotor
Starter
xV1
V1

6. Auto-transformer Starter
MOTOR
Auto
transformer
Start
Run
3-phase
supply

7. Star-Delta Starter
Stator
Rotor
Star
Delta
L1
L2
L3

8. Starting of Slip-ring Motors:
Rotor Rheostat Starter