This document discusses starters and their significance for DC motors. It describes how starters are used to limit high inrush currents when motors start, preventing issues like blown fuses or damaged windings. The document outlines two common starter types: three-point starters, which insert starting resistance and use a no-volt coil to hold the handle position; and four-point starters, which separately connect the holding coil to avoid unnecessary tripping. While four-point starters avoid some issues, they do not provide high-speed protection if the field fails while the motor is running.

1. Gandhinagar institute of technology
 Sub – DCMT (2130904)
 Topic – Starters & its Significance
 Guided by – Prof. Hitesh Manani
 Sem – 3rd
 Branch – Electrical (b3)
 Academic year – 2015&2016

2. Prepared by
 Manthan Sodha (140120109057)

3. Starters & its Significance

4. Index
 Introduction to starter
 Its Importance
 Types of Starter
 Three Point Starter
 Merits & Demerits
 Four point Starter
 Merits & Demerits

5. Starter
 Before ,we deal with starter we should know some
fundamental.
 Every D.c motors basically are self starting motors.
 As armature & field winding recieves supply
motoring action take place.
 Device which is used as starter conveys wrong
meaning

6.  So we can conclude that “Starter is not required to
start a dc motor , but it enables us to start the motor
in a desired safe way”
 Now at starting instant the speed of motor is zero,
as due to this back emf is also zero .
 As Eb is proportional to N.
 Voltage Eq. is
 V= Eb + IaRa
EbEb

7.  At start,
 V = Ia Ra (as Eb =0)
 So ,generally motor start at normal voltage and as
armature resistance is very small , armature current
start at very high.

8.  As armature current is 15 to 20 times more than the
load current at starting , which we will understand
by 1 eg.
 Consider a motor having full load input power
as 8000 watts,motor rated with 250 v & armature
resistance is 0.5
WW
W

9. High current drawn by armature
causes
 As in constant voltage system, such high inrush of
current may cause line voltage fluctuations , which also
effect the performance of other equipment connected to
same line.
 Such high Ia blows out the fuses.
 Suppose motor start to failed due to problem in field
winding,such high Ia flowing for a longer time may
burn the insulation of armature winding.

10.  Assume that ,we are dealing with shunt motor
operation then
 As armature current is 15 to 20 times more than the
full load current ,the torque developed which is
proportional to Ia is also 15 to 20 times.
 Due to such high torque , the shaft & other
accessories subject to high mechanical stresses.
 This stress causes permanent mechanical damage to
the motor

11.  So to reduce this armature current a variable
resistance is connected in series with the armature
at start.
 This resistance is called starter or starting device.
 So ,basically starter is a current limiting device.
 In beginning the entire resistance is in the series
with armature and then gradually cut-off as motor
gather speed ,producing back e.m.f.

12. Types of Starter
 Three Point Starter
 Four Point Starter

13. Three point Starter

14. overview
 figure shows the schematic diagram of a three point
starter for a shunt motor
 It is so called because it has three terminals L, F and A.
the starter consist of starting resistance divided into
several sections and connected in series with the
armature.
 The tapping points of the starting resistance are known
as number of studs
 . The three terminal L, F and A of the starter are
connected respectively to the positive line terminal,
shunt field terminal and armature terminal.

15.  The other terminal of the armature and shunt field
windings are connected to the negative terminal of
the supply .the no volt coil is connected in the
shunt field circuit.
 One end of the handle is connected to the terminal
L through the over load release coil. The other end
of the handle moves against a spiral spring and
make contact with each stud during starting
operation cutting out more and more starting
resistance as it passes over each stud in clockwise
direction.

16. Working
 1) Initially when a DC supply is switched ON with
handle in the OFF position.
 2) The handle is now moved clockwise to the first stud,
the shunt field winding is directly connected across the
supply while the whole starting resistance is inserted in
series with the armature circuit.
 3) As the handle is gradually moved over to the final
stud, the starting resistance is cut out of the armature
circuit in steps. The handle is now held magnetically by
the no volt release coil which is energized by shunt field
current

17. 4) If the supply voltage is suddenly interrupted or if the
field excitation is accidently cut, the no volt release coil is
demagnetized and the handle goes back to the OFF position
under the pull of the spring.
5)If no volt coil were not used, then in case of failure of
supply. The handle would remain on the final stud.
6)If then supply is restored, the motor will be directly
connected across the supply, resulting in an excessive
armature current.

18. 7) If the motor is overloaded (or any fault occurs) it
will draw excessive current from the supply. This
current will increase the ampere turns of the overload
release coil and pull the armature, thus short circuited
the no volt release coil.
8) The no volt coil is demagnetized and the handle is
pulled to the OFF position by the spring .thus the
motor is automatically disconnected from the supply

19. Limitations Of The Three
Point Starter:
 Unnecessary tripping of starter if a field regulator is
connected in series with the field windings for
speed control operation.
 This combination and magnetizing coil will carry
same current if more and more resistance is added
in field regulator then current in magnetizing coil is
unable to hold the arm in attracted position and
unnecessarily the arm will be released even if there
is no over loading .this is avoided in four point
starter.

20. Four point Starter

21. Overview
 In four point starters, the hold on coil is connected
directly across the supply line through a protective
resistance R. when the armature touches stud no
1.the line current divides into three parts
 i) armature starting resistance and overload release.
 ii) a variable resistance and shunt field winding.
 Iii) Holding coil and current limiting resistance.

22. The basic difference between
three point and four point
starters
 It is the manner in which the hold on coil is
connected.
 The unnecessary tripping of starter can be stopped
by connecting separately or parallel both
magnetizing and field coil.
 They are connected in such a way that both should
carry their individual current. Thus voltage drop in
one coil will not affect the voltage in other coil.

23. Disadvantages of four coil
starter:
 The only limitation of the four point starter is that it
does not provide high speed protection to the
motor.
 If under running condition field gets opened; the
field current reduces to zero.
 As there is some residual flux present and speed
(N) is directly proportional to flux (ø) the motor will
tries to run with dangerously high speed .this is
called high speed action of motor.

24.  In three point starter as no volt coil is directly
connected to across the supply; its current is
maintained irrespective of the current through the
field winding
 Hence it always maintain the handle in run position
as long as supply is there .and thus it doesn’t protect
the motor from field failure conditions which
returns into high speeding of the motor.

25. THANK YOU