This document discusses different types of motor starters used for AC and DC motors. It describes the necessity of starters to limit inrush current and protect motors. The main types covered are DOL, star-delta, and autotransformer starters. It provides information on their wiring diagrams, motor starting characteristics, advantages and disadvantages, suitable motor sizes and applications. Current ratings for motors used with different starters are also included.

1. starter
-B. Prasad
Chartered
Engineer

2. Necessity of starter
 At starting ,the speed of motor is zero so
that the back e.m.f. In the armature is
zero.
 Armature resistance is so low, if it is
connected to power supply directly ; huge
current will pass thru armature.
 The huge current may damage the
machine, major heat, very high speed in
case of DC series motor.
 Ia = V/Ra

3. Function of starter
 Start and stop the motor.
 Limit inrush current where necessary.
 Permit automatic control when required
 Protect motor and other connected
equipments from over voltage, no voltage,
under voltage, single phasing etc.

4. Motor Starter Features.
 Rated by current (amperes) or power
(horsepower)
 Remote ON/OFF control
 Motor overload protection
 Starting and stopping (electrical life)
 Plugging and jogging (rapid making and
breaking current)

5. Type of starter
forDC Motor
 Two point starter for DC series motor
 Three point starter for shunt motor
 Four point starter for compound motor
ForAC Motor
 DOL Starter
 Star-Delta
 Auto-transformer
 Variable Frequency drive

6. Wiring Diagram of DOL Starter:

7. MotorStarting Characteristics on DOL
Starter:
 Available starting current: 100%.
 Peak starting current: 6 to 8 Full
Load Current.
 Peak starting torque: 100%

8. Advantages of DOL Starter:
 Most Economical and Cheapest Starter
 Simple to establish, operate and maintain
 Simple Control Circuitry
 Easy to understand and trouble‐shoot.
 It provides 100% torque at the time of starting.
 Only one set of cable is required from starter
to motor.
 Motor is connected in delta at motor terminals.

9. Disadvantages of DOL Starter:
 It does not reduce the starting current of the
motor.
 High Starting Current: Very High Starting
Current (Typically 6 to 8 times the FLC of the
motor).
 Mechanically Harsh: Thermal Stress on the
motor, thereby reducing its life.
 Voltage Dip: There is a big voltage dip in the
electrical installation
 High starting Torque: Unnecessary high
starting torque, even when not required by the

10. Suitability
DOL is Suitable for:
 Small water pumps, compressors, fans and
conveyor belts.
 Motor rating up to 5.5KW
DOL is not suitable for:
 The peak starting current would result in a
serious voltage drop on the supply system
 Motor rating above 5.5KW

11. Star delta starter
 Most induction motors are started directly on
line, but when very large motors are started
that way, they cause a disturbance of voltage
on the supply lines due to large starting
current surges.
 To limit the starting current surge, large
induction motors are started at reduced
voltage and then have full supply voltage
reconnected when they run up to near rotated
speed.

12. Star-Delta Connection in transformer

13. Star-Delta Connection in motor

14. Star delta power circuit

15. Star delta control circuit

16. MotorStarting Characteristics of Star-
Delta Starter:
 Available starting current: 33% Full
Load Current.
 Peak starting current: 1.3 to 2.6 Full
Load Current.
 Peak starting torque: 33% Full Load
Torque.

17. Advantages of Star-Delta
starter:
 The operation of the star-delta method is
simple and rugged
 It is relatively cheap compared to other
reduced voltage methods.
 Good Torque/Current Performance.
 It draws 2 times starting current of the full
load ampere of the motor connected

18. Disadvantages of Star-Delta starter:
 Low Starting Torque, only 33% starting torque
 Break In Supply – Possible Transients
 Six Terminal Motor Required (Delta Connected).
 It requires 2 set of cables from starter to motor.
 The delta of motor is formed in starter and not on motor
terminals.
 Applications with a load torque higher than 50 % of the motor
rated torque will not be able to start using the start-delta
starter.
 Low Starting Torque: reduction of the line voltage by a factor
of 1/√3 (57.7%) to the motor and the current is reduced to 1/3
of the current at full voltage, but the starting torque is also
reduced 1/3 to 1/5 of the DOL starting torque .

19. Reversing of Direction

20. Variablefrequencydrive(VFD)
 A variable -fre q ue ncy drive (VFD), also termed
adjustable-frequency drive, variable speed
drive, AC drive, micro drive or inverter drive is
a type of adjustable-speed drive used in
electro-mechanical drive systems.
 It co ntro ls AC m o to r spe e d and to rq ue by
varying m o to r input fre q ue ncy and vo ltag e .

21. Principle of VFD
 Variable frequency Drive, principle of the
same is by regulating the frequency, we can
regulate the speed of drive
Example - n=120f/p
 Where,
 n - speed
 f - frequency
 p – nos. of poles

22. VFD flow diagram

23. VFD 3-phase power conversion

24. Application
 Cane Carrier Drive,
 Feeder Table Drive,
 Milling Plant Drive,
 Raw juice Pumps,
 Sulphited Juice Pumps,
 Molasses Pumps,
 Injection Pumps,
 Cooling Tower Pumps and
 Centrifugals for a Sugar Curing and Chemical
Dosing pump.

25. Auto transformer

26. Circuit and function
 An auto-transformer starter makes it possible
to start squirrel-cage induction motors with
reduced starting current, as the voltage across
the motor is reduced during starting.
 In contrast to the star-delta connection, only
three motor leads and terminals are required.
On starting, the motor is connected to the
tappings of the auto-transformer.

27. Starting Characteristics:
 Motor terminal voltage less than line voltage
(by transformer ratio).
 Motor current exceeds line current (by inverse
of transformer ratio).
 Starting torque is reduced by the square of the
terminal voltage.
Applications:
 Where complete acceleration at reduced
amperes is needed.
 Where line ampere reduction requirements are
severe, and load torque is not minimal.

28. Difference between DOL/Star delta
/Autotransformer
Sr
.
DOL Starter Stardelta starter Auto transformer
starter
1 Used up to 5 HP Used 5 HP to 20HP Used above 20 HP
2 Does not
decrease the
starting current
Decreases the starting
current by 1/3 times
Decreases the
starting current as
required
3 It is cheap It is costly It is more costly
4 It connects
directly the motor
with supply for
starting as well as
for running
It connects the motor first in
star at the time of starting in
delta for running
It connects the motor
according to the
taping taken out from
the auto transformer

29. Current in Star Delta (380to
415V)
MotorKW Rated phase
current-A
MCB-A Fuse -A MCCB-A
1.1 1.4-1.75 6 6 6
2.2 2.6-3 10 10 6
3.7 4.3-5.2 16 20 16
5.5 5.8-7 20 25 16
7.5 7.5-9.3 25 32 25
11 11-13.2 32 40 32
15 14.5-18 40 50 50
18.5 17.3-21.3 40 63 50
22 21.3-26.6 63 80 80
30 30-36.5 80 100 80
37 36-42 80 125 100

30. Current in DOL (380-415V motor)
MotorKW Rated line
current-A
MCB-A Fuse -A MCCB-A
1.1 2.5-3 16 10 6
2.2 4.5-5 16 20 6
3.7 7.5-9 25 25 16
5.5 10-12 32 32 16
7.5 13-16 40 40 25
11 19-23 50 50 32
15 25-31 63 63 50
18.5 30-37 80 80 50
22 37-46 100 100 80
30 52-63 Not used 125 80

31. WIRE/Cable SIZE
International standard wire sizes (IEC 60228)
 0.5 mm² 0.75 mm² 1 mm² 1.5 mm² 2.5
mm²
4 mm²
 6 mm² 10 mm² 16 mm² 25 mm²
35 mm² 50 mm²
 70 mm² 95 mm² 120 mm² 150 mm²
185 mm² 240 mm²
 300 mm² 400 mm² 500 mm² 630 mm²
800 mm² 1000 mm

32. ACT FAST AND INITIATE
FIRST
 बड़ा सोचो
 तेजी से सोचो व
 सबसे पहले सोचो
 िवचारो पर िकसी का
 एकािधकार नही होता.
---- धीरभाई अमबानी

33. THANK YOU