This document discusses starters used for DC motors. It explains that starters are necessary to limit starting current and torque for DC motors. It describes two-point, three-point, and four-point starters. Two-point starters are used for DC series motors, while three-point starters help control current in shunt and compound DC motors. Four-point starters function similarly but add a terminal to allow operation above normal speeds without tripping. In conclusion, the document emphasizes that starters play an important role in protecting DC motors, and motors should not be operated without appropriate starters.

1. FURQAN SADIQ 2012108
HAMZA WAHEED 2012130

2. 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.

3. E = Eb + IaRa
where E is the voltage supplied, Eb is the back emf, Ia is
the armature current and Ra is the armature resistance.
At starting ,the speed of motor is zero so that the back
e.m.f. In the armature is zero.

4.  When Back Emf is zero:
E=0 +IaRa
through which the final equation we get is:
E/Ra=Ia

5. 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 [1]
τ = KϕIa [1]

6.  To prevent this several methods have been adopted, almost all Of which include
adding an external resistor to the armature winding
 Ia =E/Ra + Rext [1]
Final Equation becomes:
Ia =E −Eb /Ra + Rext [1]
 Now to maintain current at the rated value, Rext is gradually decreased till it
reaches a value of zero when the back emf is at its maximum. All of this is
achieved by means of a DC starter

7. 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)

8. For DC Motor
Two point starter for DC series motor
Three point starter for shunt motor
Four point starter for compound motor[3]

9.  A 3 point helps in the starting and running of a shunt wound DC
motor or compound wound DC motor by adding some external
resistance to the armature circuit and decreasing the overall current
to below the rated value
 . These devices are so named because they connect to the motor
using three terminals: the armature (A) terminal connected to the
armature winding; the line (L) connected to the positive supply pole;
and the field (F) terminal linked to the field winding.

11. USED IN SHUNT MOTORS
MAJORLY BUT SOMETIMES IN
COMPOUND AS WELL
[4]

12.  Four-point starters are identical to three-point devices, but they add an additional
terminal (N) that links the supply to the no voltage coil.
 These starters are typically employed in applications where the motor is expected
to operate above normal speed.
 The N terminal is necessary because higher speeds reduce field currents through
the F terminal so that the handle is unable to remain in the RUN position
 By establishing an independent current supply to the NVC, the motor can run
continuously regardless of field current and will not be unnecessarily tripped by
high-speed operation or speed changes.

13. USED IN COMPOUND DC
MOTOS
[5]

14.  This paper is about the starters used in DC Motors. Starters are really important
as this paper shows and are essential to a motor.
 starters play an important role in limiting starting current and torque for a DC
motor and are described in detail under their headings
 Hence,it would be a folly to use a DC motor without starters despite of all abve
mentioned Consequences

15.  [1] Stephen J. Chapman, Electric Machinery Fundamentals, 4th ed. NewYork:
McGraw Hill, 2005
 [2] “Starting of DC Motor,” http://www.electrical4u.com/ starting-methods-to-limit-
starting-current-torque-of-dc-motor, Dec. 8, 2014.
 [3] Rakesh J. Waghmareand Dr. S.BPatil, “Need of Starters in DC Motors”,
International Journal of Science, Engineering and Technology Research, vol. 2, no.
12, Dec. 2013.
 [4] “3 Point Starter — Working Principle and Construction of Three Point Starter”
http://www.electrical4u.com/ 3-point-starter-working-principle-and-construction-
of-three-point-starter/, Dec. 8, 2014.
 [5] “4 Point Starter — Working Principle and Construction of Four Point Starter,”
http://www.electrical4u.com/ 4-point-starter-working-principle-and-construction-
of-four-point-starter/, Dec 8,2014.