This document discusses different starting methods for synchronous motors. It describes using an auxiliary induction motor or DC motor to bring the synchronous motor rotor up to synchronous speed before excitation. It also covers on-load starting methods like using damper windings to start the motor as an induction motor initially or using a variable frequency drive to gradually increase frequency and avoid high starting torque.

1. SYNCHRONOUS MACHINEसरल भाषा में समझे
STARTING METHODS OF
SYNCHRONOUS MOTOR

2. ELECTRICAL MACHINE
Syllabus
 Introduction of Machine
 Classification of Machine
 Construction of DC, Induction & Synchronous machine
 Working Principle of
 DC Machine
 Synchronous machine
 Induction machine
 EMF Equation of
 DC Machine
 Synchronous Machine
 Comparison Between Salient And Cylindrical Poles
 Why synchronous motor is not self start?
 Starting methods of synchronous motor

3. STATOR RORATING
FIELD
STATIONARY
ROTOR
STATIONARY
ROTOR
STATOR
RORATING
FIELD
STATOR
RORATING FIELD
STATOR
RORATING FIELD
STATIONARY
ROTOR
STATIONARY
ROTOR
MAGNETIC
LOCKING

4. SYNCHRONOUS MOTOR STARTING METHODS
STARTING OF
SYNCHRONOUS
MOTOR
BY AUXILIARY
MOTOR
AUXILIARY
INDUCTION
MOTOR
AUXILIARY DC
MOTOR
ON LOAD
STARTING/WITHOUT
AUXILIARY MOTOR
VARIABLE
FREQUENCY
STARTER
DAMPER
WINDING
STARTER

5. SYNCHRONOUS MOTOR STARTING METHODS
BY
AUXILIARY
MOTOR
AUXILIARY
INDUCTION
(PONY) MOTOR
AUXILIARY DC
MOTOR

6. STARTING A SYNCHRONOUS MOTOR USING AUXILIARY INDUCTION MOTOR
 we directly couple a small induction motor (pony motor) with the synchronous motor by shaft.
 We need to bring the rotor of the synchronous motor to synchronous speed before we switch on the
motor.
 Note here, that the number of poles of the induction motor should be less than the
synchronous motor else it will never be able to achieve the synchronous speed of the
synchronous motor.
 After the rotor of
the synchronous
motor is brought to
the synchronous
speed, we switch
on the DC supply
to the rotor.
P=4 F=50
Ns=(120*5)/4
Ns=1500

7. STARTING A SYNCHRONOUS MOTOR USING AUXILIARY DC MACHINE
 A DC machine is coupled to the
synchronous motor.
 The DC machine works like a DC
motor initially and brings the
synchronous motor to synchronous
speed.
 Once it achieves the synchronous
speed, the DC machine works
like a DC generator and supplies
DC to the rotor of the synchronous
motor.
 This method offers easy starting
and better efficiency than the
earlier method.

8. SYNCHRONOUS MOTOR ON LOAD STARTING METHODS
ON LOAD
STARTING
VARIABLE
FREQUENCY
STARTER
DAMPER
WINDING
STARTER

9. STARTING A SYNCHRONOUS MOTOR USING DAMPER WINDINGS
 In this method, the motor is
first started as an induction
motor and then starts running
as a synchronous motor after
achieving synchronous speed.
 For this, damper windings
are used. Damper windings
are additional windings
consisting of copper bars
placed in the slots in the pole
faces.
 The ends of the copper bars
are short-circuited.
 These windings behave as the
rotor of an induction motor.

10. SYNCHRONOUS MOTOR START AS INDUCTION MOTOR
 The stator of synchronous motor is
excited by 3 phase voltage.
 The rotor is connected to slip rings
and further to a TPDT switch.
 Initially, this switch is connected to
‘start’ position which has external
resistance.
 This way of starting is similar to rotor
resistance starting in Induction
Motor.
 As soon as the motor starts rotating
and attains a certain pre-determined
speed, the switch position is
changed to ‘run’.
 The Run position has external
battery supply, which when
connected excites the rotor with DC
Current and poles are formed, and on
the rotor and based on the principle
of magnetic locking.
Start as induction motor

11. VARIABLE FREQUENCY STARTING OF SYNCHRNOUS MOTOR
 In starting a motor,
a VFD initially applies a low
frequency and voltage, thus
avoiding high speed of
rotating magnetic field of
stator winding.
 After the magnetic locking
between rotor magnet poles
and rotating field poles of
the synchronous motor, the
applied frequency increased
to rated frequency to operate
synchronous motor at rated

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