1. M. Nageswar Rao,
Sr.Mgr.(EMD)
Date: 01.10.2015

2. Presentation Layout
 Motor applications
 Induction Motors
 Starting methods
 Speed control methods
 Synchronous Motors
 Starting methods
 Speed control methods
 DC Motors
 Starting methods
 Speed control methods
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3. Motor Application
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 Induction motors
 Low cost
 Reliable
 Smaller power ratings
 Synchronous motors
 Constant speed motors
 Low speed <300rpm
 High power ratings in MW range.
 DC motors
 Emergency standby
 Smaller ratings
 Constant speed applications

4. Induction Motor
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5. Induction Motor
 The electromechanical
power per stator phase is
equal to the power
delivered to the
resistance R2(1 - s)/s.
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6. Induction Motor
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7. Induction Motor
-Starting methods
 DOL starter
 Applies full supply voltage
 Draws low p.f. starting current of 600%, causing dip in
supply voltage
 Used for low-inertia loads
 Simple design, low cost, high starting torque.
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8. Induction Motor
-Starting methods
 Star/ Delta starter
 Motor should be brought with all 6 leads.
 Initially motor winding is arranged in STAR and when
the motor attains a speed of 70-80% of rated speed,
winding is re-arranged in DELTA.
 Compared to DOL
 Starting Current is reduced by 1/√3 (i.e. 57%) and
 Starting Torque & Power is reduced by 1/3 (i.e. 33%)
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9. Induction Motor
-Starting methods
DOL Star/Delta
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10. Induction Motor
-Speed control methods
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 Pole changing
 Supply voltage control
 Supply freq. control
 V/f control

11. Induction Motor
-Speed control methods
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 Pole changing method
 Synchronous speed can be changed by changing the
number of stator poles.
 This method is generally used for SCIM, as squirrel cage
rotor adapts itself for any number of stator poles.
 Change in stator poles is achieved by two or more
independent stator windings wound for different
number of poles in same slots.

12. Induction Motor
-Speed control methods
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 Supply Voltage control

13. Induction Motor
-Speed control methods
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 Supply Freq. control

14. Induction Motor
-Speed control methods
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 V/f control

15. Synchronous motor
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16. Synchronous motor
- Starting methods
 DC motor starting
 Asynchronous starting
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17. Synchronous motor
- Starting methods
 DC motor starting
 DC motor on a common shaft.
 When the motor is brought to synchronous speed, AC
current is applied to the stator windings.
 The DC motor now acts as a DC generator and supplies
DC field excitation to the rotor of the synchronous
motor.
 The load may now be placed on the synchronous motor
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18. Synchronous motor
- Starting methods
 Asynchronous starting
 Damper winding (or) squirrel cage winding is embedded
in rotor.
 The rotor accelerates at a speeds upto 95% of
synchronous speed, with a slight slip in reference to the
rotating field.
 On this point, a direct current is applied to the rotor
winding and then taking the motor to synchronism.
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19. Synchronous motor
- Starting methods
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20. Synchronous motor
- Starting method
 Low speed (upto 95% of synch.speed)
 Field ckt. Is short circuited with SCR-2 ON.
 Induced emf in SM field winding is dissipated in FDR
 Pull-in / synchronization
 Control ckt. Fires SCR-1 at proper pull-in speed for
successful synchronizing and at the proper polarity to give
maximum pull-in torque with minimum line disturbance.
 Applies excitation to the synchronous motor field.
 SCR-2 is OFF and FDR is removed from ckt.
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21. Synchronous motor
- Starting method
 Pull-out/ pole-slip
 The control circuit operates to remove excitation should the
motor pull out of step due to a voltage step or excessive
mechanical load.
 On the first half cycle after pull-out, the induced field
voltage will oppose the exciter voltage , causing the net field
current to pass through zero, turning SCR-1 off,
automatically removing excitation.
 SCR-2 operates to connect the FDR back in to the circuit.
 During this time, the motor operates as an induction motor.
 When conditions permit, field is then reapplied as during
starting. 21

22. Synchronous motor
- Starting method
 SCR-2 is turned on only at a voltage higher than the
exciter voltage so it will not be ON when SCR-1 is ON.
 Occasionally, a lightly loaded motor will synchronize
without excitation being applied. This is due to the
reluctance torque. Reluctance torque results from the
magnetic circuit having less reluctance when the
poles line up with the stator flux.
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23. DC Motors
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24. DC Motors
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25. DC Motors
- Starting methods
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 Armature series resistance

26. DC Motors
- Speed control methods
 Field current weakening
 For higher speeds
 Armature resistance control
 For lower speeds
 Armature Supply voltage control
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27. Thank you all
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