Small description of starting and cooling methods of induction motors. 3 phase motor starting is included in it.

1. STARTING AND COOLING METHODS
OF MOTOR
Prepared by
Jyothis Prasad T

2. Starting methods
Why we need a starter
• At starting there is no back emf in armature
• So when connects directly to the supply huge
current may flow through the armature.
• A high current may damage the armature
winding.
• Starters used in order to limit the starting current
and protect the motor.

3. Starting methods selected on the basis of
• Capacity of the power lines
• Design of motor
• Type of load

4. For squirrel cage induction motor
1. Full voltage starting
• Direct online starting (DOL)
2. Reduced voltage starting
• Stator resistor starting method
• Auto transformer starting method
• Star delta starting method
• Soft starter
For slip ring induction motor
• Rotor resistance starting method
3. Other
• Variable Frequency Drive(VFD)

5. Full voltage starting
Direct online starting (DOL)

7. • Direct switching of stator to the power lines.
• Motor will draws high supply of power. 5-7
times of full load current.
• There is no provisions in this method to limit
the starting current.

8. Advantages Of DOL
• Most economical and cheapest
• Easy to establish, operate and maintain
• Provides 100% torque at starting
Disadvantages
• High starting current
• Voltage dip in power lines
• Thermal stress on motor, there by reducing the life.
Suitable for motor rating up to 5.5kW

9. Reduced voltage starting
1. Stator resistor starting method

10. • Smooth starting of small induction motors.
• Resistors are connected between the supply and
motor
• Resistors are positioned so as the supply voltage
across the motor will be a fraction of the supply
voltage.
• So the starting torque also reduced, since 𝑇 ∝
𝑉^2
• It is not recommended to use primary resistors
type of starting method for motors with high
starting torque requirements.

11. Advantages
• Smooth acceleration
• Less expensive than auto transformer starter for
lower output ratings
Disadvantages
• Heat is given by the resistors
• Expensive resistors are required since starting
time exceeds 5 seconds
This method is only used for small motors

12. 2. Auto transformer starting

13. • An autotransformer between motor and the
supply lines
• Autotransformer is a step down transformer
• At first a reduced voltage applied across the
motor
• After gaining appropriate speed, say 80%, then
the autotransformer changes to run position
Suitable for motor rating above 20kW

14. 3. Star Delta starting

15. • Its used in the motor which designed to run
on delta connected stator.
• A two way switch to connect star connected
winding while starting.
• Only 58% of supply voltage came across the
motor while starting.

16. Advantages
• Operation of star delta method is simple and rugged.
• Relatively cheap compared to the other reduced voltage
methods.
• Good torque/current performances.
Disadvantages
• Low starting torque, only 33% of starting torque compared
to DOL starter.
• Requires two sets of cable from starter to motor.
Suitable for motor ratings 4-20kW

17. 4. Soft starter
Soft starter is an electronic starter used to
control the voltage applied on the motor during
start and stop, and to accelerate and decelerate
the speed of induction motor.

18. • The voltage control is achieved by using solid
state AC switches
• These switches can be either triac,SCR,or SCR
and Diode
• In this there are open loop control and closed
loop control

19. Advantages of soft starters
• Smooth acceleration to full speed
• Extended life of motor and mechanical components
• Easy operation
• Suitable for all types of induction motors
Soft starters can applied to slip ring induction motors,
however if the motor is employed to give high starting
torque on its entire working, soft starter not going to give
satisfactory solution.

20. • Rotor resistance starter.

21. • This starting method applicable for SLIP RING
Induction motor only.
• At starting an external resistance is added to
the rotor, so the starting current can be
reduced.
• As the speed of motor increases, rotor
resistance removed.

22. Variable frequency drive (VFD)
A VFD can control the speed of the motor during
its start, stop as well as through out the running.
The frequency of the power applied to an AC
motor determines the motor speed, based on
the following equation:
N = (120 x f)/p
N = speed (rpm) f = frequency (Hz) p = number
of poles

23. Benefits
• Controls starting, stopping and acceleration
• Provides smooth motion for applications like
elevators, escalators, etc
• Fully adjustable speed, reduces power when
not required.

24. Comparison of Soft starter and VFD
Soft Starter VFD
Less expensive More expensive
Less space needed More space needed
Can save less energy through out its
life
Can save more energy though out its
life
More speed control on starting and
stopping only
Speed control over starting, stopping
and throughout the entire operation
VFD can initially cost 2-3 times more than soft starters. If the application
needs control over start and stop only, its better to go for soft starter, and if
speed control needed through out the working, must choose VFD.

25. Cooling of Motors
Why cooling needed ?
• Energy conversion in electrical machine
associated with losses.
• These losses appears as temperature rise
beyond its optimum level.
• Heat is dissipated to the surroundings by
conduction and convection.

26. Cooling methods
1. Self ventilated with integral fan cooling (IC 01)
2. Separate ventilation with radial fitted fan unit (IC
06)
3. Single pipe ventilated (IC 17)
4. Double pipe ventilated (IC 37)
5. Totally enclosed non ventilated (IC 410)
6. Totally enclosed fan cooled (IC 411)
7. External surface cooling (IC 416)

27. 1.Self ventilated with integral fan
cooling
The cooling air is blown through the motor by a
fan mounted on the shaft.

28. 2. Separate ventilation with radial
fitted fan unit
The cooling air is blown through the motor by a
separately excited fan motor . The inlet side of the
fan may equipped with an air filter.

29. 3. Single pipe ventilated
The cooling air is blown across the motor through the pipe
connection with a separate customer provided separate
blower fan and discharges on the other side to open space
4. Double pipe ventilated
The cooling air is blown across the motor through the pipe
connection with a separate customer provided separate
blower fan and discharges on the other sides pipe
connection

30. 5. Totally enclosed non ventilated
Cooling without using fan , only by natural
ventilation and radiation on the totally enclosed
motor surface.

31. 6. Totally enclosed fan cooled
Cooling air blown over the totally enclosed
motor surface by a fan mounted on the shaft

32. 7. External surface cooling
Cooling air is blown over the totally enclosed
motor surface by a separately excited fan motor

33. Thank you