This document discusses various electrical machine experiments conducted in an electrical workshop lab, including starting methods, protection, and dismantling/assembling of induction and DC machines. It lists experiments on direct online, forward/reverse, and star-delta starters for induction motors. Other experiments include inching circuits, interlocking groups of drives, and wiring undervoltage relays. Causes of motor failure like overloads and bearing failure are discussed. The document also covers electric shock dangers, precautions in the lab, protection from single phasing and under/over voltage, dielectric testing of transformer oil, and starting methods for slip ring and squirrel cage induction motors.

1. Starting methods and protection of
equipment Electrical machines
K.Sateesh kumar
Snist

2. Electrical Work shop lab
Objectives:
Starting methods of induction machines
Operations on induction machines
Protection of induction machines
Oil testing
Construction of Induction and Dc machines

3. List of Events (Experiments)
1 DIRECT ON-LINE STARTER
2 FORWARD and REVERSE STARTER WIRING AND TESTING
3 STAR-DELTA STARTER WIRING AND TESTING SUITABLE FOR 5 HP MOTOR
4 INCHING (JOGGING )CIRCUIT FOR AC MOTOR
5 INTERLOCKING OF GROUP OF DRIVES
6 STUDY OF PHASE FAILURE RELAY (SINGLE PHASE PREVENTOR)
STARTER FOR TWO SPEED, TWO WINDING (SEPARATE WINDING) MOTOR
7 3-PHASE SQUIRREL CAGE INDUCTION MOTOR DISMANTLING, ASSEMBLING AND TESTING
8 1-PHASE CAPACITOR START CAPACITOR RUN INDUCTION MOTOR DIS-MANTLING,
ASSEMBLING AND TESTING
DC MACHINE DIS-MANTLING AND ASSEMBLING AND TESTING
9 WIRING UNDERVOLTAGE RELAY TO A DOL STARTER
WIRINING OF SLIPRING MOTOR STARTER AND TESTING
10 TESTING OF DIELECTRIC STRENGTH OF TRANSFORMOR OIL

4. Why ?
Cause Percentage
Overloads 30 %
Contaminants 19%
Single – Phasing 14%
Bearing Failure 13%
Old age 10%
Rotor failure 5%
Miscellaneous 9%
44% of motor failure problems are related to HEAT

5. Electric Shock and Human Perception
Current Reaction
1 Milliampere Perception level
5 Milliamperes Slight shock felt; not painful but disturbing
6-30 Milliamperes Painful shock; “Let go” range
50-150 Milliamperes Extreme pain, respiratory arrest, severe
muscular contraction
1000-4300 Milliamperes Ventricular fibrillation-a cause of cardiac
arrest and sudden cardiac death
10,000 + Milliamperes Cardiac arrest, severe burns and death

6. Paying attention !!?

7. PRE-CAUTIONS
Wearing of shoes and apron is
ESSENTIAL
Never work alone in the lab/workshop
Keep away from all moving parts
Stay away from the open terminals & do
not allow any loose connections
Never touch any live terminals, while
experiment is being conducted.
Switch on the supply, only after getting
the circuit checked by the guide.
Maintain discipline ALWAYS.

8. Importance of Protection from Single
Phasing
To maintain the same power input to the motor during single phasing the current in the
remaining two phases will increase by1.73 times.
Single phasing of the motor results in superposition of negative sequence of current flow
over the positive sequence through the motor windings.
These negative sequence currents are of double frequency as compared to positive
sequence currents.
As the iron losses are proportional to frequency, the negative sequence currents cause
higher iron losses and therefore greater heating of the rotor. Rotor heating is further
increased due to skin effect (due to higher frequency).
This undetectedheated. This excessive heat can finally cause burnout of the motor
To avoid failure of the motor due to single phasing, phase failure relay or commercially
known as single phase preventer is used.
heating can damage the rotor and due to convection, the stator winding also gets

9. Importance of Protection from
Under-Voltage and Over-Voltage
Power systems loads are MVA loads (motors, uninterrupted
power supplies, etc.). As the voltage decreases, the load
current increases while the power system transfer capability
decreases.
An overvoltage is a sustained system voltage in excess of
transformer capacity, motor, generator, or reactor voltage
rating. Dielectric breaks down.

10. Dielectric Testing of Oil
Transformer oil or insulating oil is usually a highly-refined mineral oil that is stable at high
temperatures and has excellent electrical insulating properties.
It is used in oil-filled transformers, some types of high voltage capacitors,
fluorescent lamp ballasts, and some types of high voltage switches and circuit breakers.
Its functions are to insulate, suppress corona and arcing, and to serve as a coolant
Transformer oils are subject to electrical and mechanical stresses while a transformer is
in operation. In addition there is contamination caused by chemical interactions with
windings and other solid insulation, catalyzed by high operating temperature.
The original chemical properties of transformer oil change gradually, rendering it
ineffective for its intended purpose after many years. Oil in large transformers and
electrical apparatus is periodically tested for its electrical and chemical properties, to
make sure it is suitable for further use

11. Starting of Induction Motor
 For induction motors, the starting torque is approximately proportional to
the square of the starting current drawn from the line. ∝ I2
 This starting current is proportional to the applied voltage (V)
 Torque can also be considered to be approximately proportional to the
applied voltage. ∝ V2
 An induction motor will develop far too much torque when connected
directly to the supply.
At the instant of start-up, there are some un-necessary effect on
electrical and the mechanical components.
11

12. Un-Necessary Electrical Effects
12
 A heavy current surge on the electrical supply which can
be severe enough to cause voltage dips and flickering
lights.
 Burning of contacts due to high currents which are many
times the motor full-load current.

13. Problems Arises by these Effects
 Greater chance of unscheduled shutdowns
 Oversized mechanical and electrical components to
cater for the power surge on start up.
 Short component life.
13

14. Solution of the problems…..
Starter
By Adjusting voltage during starting, the current drawn by the motor and the
torque produced by the motor can be reduced and controlled.
14

15. 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.
 Motor overload protection

16. Types of Starter for 3-Ph 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

17. 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.

18. D.O.L.(direct on line) starter

19. Components of D.O.L. starter :Components of a DOL Starter
Overload Unit (Thermal type)
Main pole terminals 1, 3 & 5
When motor overheats due to overload
conditions, main poles latch open
Auxiliary contacts also latch open and
when interlocked within control
circuit prevents motor restarting by
itself when cool.
Main pole terminals 2, 4 & 6
N/O
Auxiliary
contacts
97 & 98
N/C
Auxiliary
contacts
95 & 96
Reset
button
Red pushbutton can be used to reset

20. Components of a DOL Starter:
Start and Stop pushbuttons
Start button is green and
flush mounted
Stop button is red and
protruding
N/O contact N/C contact
Emergency Stop button has a
red mushroom head which
latches in and must be turned
to release
Contacts at the
back of
switches can
be either N/O
or N/C

21. THERMAL OVERLOAD RELAY
Thermal overload relay is
an electrical component
used in motor control
applications which
provide protection for
motor against excessive
current.
Line
terminals
reset
Set value dial
Auxiliary contact(s)
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22. THERMAL OVERLOAD RELAY
Principles of operation:
This component has a bimetal
strip that is made of two
dissimilar metals bonded
together. The two metals have
different thermal expansion
characteristics, so the bimetal
strip bends at a given rate when
heated.
As current rises, heat also rises.
The hotter the bimetal strip
becomes, the more it bends. In
an overload condition, the heat
generated from the heater will
cause the bimetal strip to bend
until the mechanism is tripped,
stopping the motor.
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23. OVER/ UNDER VOLTAGE RELAY
This component protects
the motor against over
voltage and under voltage
situation.
Typical installation diagram for
over/under voltage protection
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24. OVER/ UNDER VOLTAGE RELAY OPERATION
11 12 21 22
21 24
1411
Motor contactor
Over-voltage
alarm
Under-voltage alarm
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25. PHASE LOSS/ PHASE SEQUENCE RELAY
Phase control relays monitor:
■ Phase sequence
■ Loss of one or more phases
■ Unbalance level
In 3-phase system, phase
loss
Is the event when one or two
phases is/are disconnected in
the main supply. Phase
sequence on the other hand is
when two of the phases are
interchanged resulting to a
reverse rotation of a 3-phase
motor.
Phase loss is mandatory
protection to every motor
operation. Phase sequence is
for selective purposes only
such as pumps that reversing
the motor direction may cause
serious damage to the
equipment.

26. PHASE LOSS/ PHASE SEQUENCE
WIRING DIAGRAMMotor contactor
PL/PS NC contacts
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PHASE
PROTECTION
RELAY

27. Star-delta starter

28. Star-delta starter

29. 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

30. Disadvantages of Star-Delta starter:
Low Starting Torque, only 33% starting torque
Six Terminal Motor Required (Delta Connected).
It requires 2 set of cables from starter to motor.

31. Difference between DOL/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 at the time of starting in
delta for running
It connects the motor
according to the taping
taken out from the auto
transformer

33. THANK YOU