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Elements of Electrical Design –
2150904
Active Learning Assignment
“Topics”
STARTERS
Guided By: Jaimini
Presented by :
Ankit singh-130120109003
Abdul chhipa-130120109005
Raj makda-130120109017
Branch : Electrical Engineering
Div : B
Batch : B1
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

FUCTION 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.
Types of Starter
for DC Motor

Two point starter for DC series motor
Three point starter for shunt motor
 Four point starter for compound motor

THREE POINT STARTER FOR DC
MOTORS:


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.
3 POINT STARTER
4 POINT STARTER




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.
4 POINT STARTER
Types of Starter for
Induction motors









For slip-ring induction motors:
Rotor rheostat starter
For squirrel cage induction motors:
D.O.L starter
Primary resistance starter
Auto transformer starter
Star delta starter
Other starters:
Soft starters
Starting of slip ring induction
motor

In case of slip ring induction motors it is possible to add
external resistance in rotor phases as wound rotor has 3-phase star connected winding to limit the starting high
current.
Rotor resistance starter



In rotor resistance starter the three terminals of the rotor
winding are connected to a variable external resistances
through slip rings.
Full supply voltage is applied across the stator. Resistances are
fully in the circuit at starting , so that the starting current is
reduced. The external variable resistance connected in each
phase of the rotor circuit not only reduce the current at starting
but increases the starting torque also due to improvement in
power factor.
The rotor circuit resistance is gradually cut out , as the motor
speeds up and during normal running condition ,the rotor
circuit resistance is completely cut out and the slip rings are
short circuited.
D.O.L.(direct on line) starter





A Starter Which Connects A Motor Directly Across The
Line Is Called D.O.L. Starter.
In This Method, The Motor Is Connected By Means Of A
Starter Across The Full Supply Voltage.
It Is Very Simple, Inexpensive, Easy To Install And Maintain.
It Consist - START Button
- OFF Button
- Electromagnetic Contector
- Overload Relay
Switching By This Starter Is Directly From Line Without Any
Provision To Control The Starting Current i.e. There Is No
Device To Reduce The Starting Current In This Starter.
WIRING DIAGRAM OF D.O.L STARTER

L1,L2,L3 - LINES

M – MAIN CONTACTS

M(a) – AUXILIARY OR
MAINTAINING CONTACT

S1 – START PUSH BUTTON

S2 – OFF PUSH BUTTON



OLC – OVERLOAD RELAY
COIL
OL – OVERLOAD RELAY
CONTECT
C – MAGNETIC COIL OR
OPERATING COIL
OPERATION OF D.O.L STARTER
1) When START Button Is Pressed

When Start(s1) Button is pressed, Path is
L1 - S2 - S1 – C – OL - L2

Coil C Is Energized ,It Closes Contacts M And Connects The
Motor Across The Line.

Maintaining Contact M(a) Is Used To Keep The Holding Or
Operating Coil Energized After The Finger Is Removed From
START Push Button (S1).
2) When OFF Button Is Pressed

When OFF(s2) Button is pressed, Path is
Disconnected.

Coil C Is De-Energized, The Main Contacts M Are
Opened. Supply To Motor Is Disconnected And
Motor Stops.
.
2) Overload Protection
 The Motor Is Protected Against Overload By A
Thermal Overload Relay Which Open Circuits the
Control Circuit When Overload occure.
 The Normally Closed Contacts O.L Is Opened And The
Contactor Coil C is De-Energized To Disconnect The Motor
From The Supply.
 Rate Of Temperature Is Very High So Motor May Be
Damaged If The Starting Period Is large. Which May Be
Due To Excessive Load Or Excessive Voltage Drop In The
Supply Lines.
 Only Used For Less Than 5 KW Squirrel Cage Induction
Motor
Advantages of d.o.l
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.
disadvantages of d.o.l
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 load.
Auto transformer starter
Circuit and function

An auto-transformer starter makes it possible to start squirrelcage 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 tapping of the auto-transformer.
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.

Difference between d.o.l/ star delta/
autotransformer
Sr. DOL Starter
Star delta 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 It connects the motor
at the time of starting in delta according to the taping
for running
taken out from the auto
transformer
THANK YOU