by:
Mabick A.W.
5/26/2024
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OBJECTIVE
At the end of the presentation we will know the following:
1. Motor installation
2. Motor terminal block connection
3. Power circuit and control circuit
4. Control components and motor control protection
5. Methods of motor control circuit and its advantages.
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Motor Installation
 An Electric motor is a machine which coverts electrical
energy into mechanical energy for various function.
 An Electrical motor can be either DC or AC and single or
three phase supplied.
 The operation of electrical equipment such as electrical
motor involves the use of various devices such as;
Fuses
Switches
Circuit breaker
Relays
Magnetic contactor
Breaking devices
Motor Installation
Types of Electric Motors
D.C motors
 Series motors
 Shunt/mesh/parallel
 Compound (long shunt or short shunt)
 Universal motors
A.C motors
Single phase ac motors
Split phase induction motor
Repulsion type motor
Capacitor-start capacitor-run
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Motor Installation
 Electric motors should be installed in locations of easy
access for inspection and maintenance
 If the surrounding atmosphere contains humid, corrosive
of flammable substances or particles, it is essential to
ensure an adequate degree of protection.
 Under no circumstances, motors can be enclosed in boxes
or reduce the free circulation of cooling air.
 Foundation
 The motor base must be level and free from vibrations,
for this reason, concrete foundation is recommended
Motor`s Foundation Plan
The foundation plan is usually recommended by the
manufacturer, though the Total installation comprises
the following features;
i. Foundation made of cement-concrete
ii. Bed-plates; foundation bolts and nuts
 The machine is bolted to the “bed plates” the bed
plates is fixed on a leveled foundation. The foundation
may be common for motors and the driven machines
or alternatively a separate foundation may be provided
for motor and driven machine.
 The design of the foundation depends on the size and
speed of the motor/machine.
Basic requirements of a good foundation
i. Rigidity (firm/strong)
ii. Freedom from vibration
iii. Horizontal leveling
For concrete foundation the following Depth can be taken as
a general guide;
 Up to 1kW-100mm to 120mm deep
 1kW to 2.5kW -120mm to 200mm deep
 2.5kW to 4.5kW -200mm to 300mm deep
 4.5kW to 9kW -300mm to 450mm deep
The foundation should be carried some 150mm or above
floor level, for better protection and should protect some
200mm to 220mm outside the slide rails or base plate.
Composition of the concrete used for machine
foundation is as follows;
 4 parts- Gravels/small stones/
 2 parts- fine/sharp sand
 1 part- cement
Giving the ratio of
1:2:4
Common shapes of foundation
bolts
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Motor Installation
 Alignment/leveling
 The electrical motor must be accurately aligned with the
driven machine, particularly in case of direct coupling.
 An incorrect alignment can cause bearing defects,
vibrations and even shaft breaking
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Motor Installation
 Supply system
 Proper electric power supply is very important.
 All the wires and protection system must ensure an
excellent quality of electric power supply on the motor
terminals.
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Factors to be considered when selecting motors and
control gears for machine drive before planning for
installation work;
1. Power output required from the motor (KW/Horse
power) 1HP = 0.746KW
2. Operating speed of the motor and speed
characteristics
3. Speed control
4. Methods of starting i.e. DOL etc
5. Starting torque (turning moment of the shaft)
6. Type/method of coupling i.e. direct coupling, belt
drive, flat belt, vee belt, rope drive or gear drive
CONT..
7. Type of frame enclosure i.e. totally enclosed, drip
proof or weather proof
8. Nature of atmosphere and temperature in which its
to operate
9. Duration of running/ duty cycles i.e. continuously,
intermittent or variable
10. Nature of electric power supply i.e. D.C or A.C
11. Class of motor/ machine i.e. essential or non
essential service machine.
Starting Methods of A.C Motors
Due to inrush starting current during motor
starting the following methods are used to limit the
starting current for the safe operation of electric
motors;
a) Direct –on – line starting methods (D.O.L)
b) Star delta starting methods
c) Resistor starting methods
d) Auto transformer starting methods
e) Tyristor starting methods (soft staring using VFD)
ACCEPTING AND INSPECTION OF
ORDED MOTOR
 Before accepting and receiving the ordered motor, Check the
following point;
 Name plate ratings of motor
Power supply
Full load current
Connection style (star or delta)
 Any damage of motor
Fan and winding test
 All accessories and accompanying instruction manuals if are in
good order
 Revolution arrowhead indicator
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MOTOR CONTROL
COMPONENTS AND
PROTECTION
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MOTOR CONTROL COMPONENTS
MAGNETIC CONTACTOR
main contacts
A magnetic contactor is an
electromagnetically
Operated
switch/ devices which operates
when the circuit feeding its
control circuit is completed.
It is controlled by a Push switch
It is not a manually operated
device.
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Supply terminals
Auxiliary
contact(s)
20
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 The basic parts of the contactor are;
 Operating coil
 Magnetic circuit (Armature)
 Pressure springs
 The contacts
 Contactor has main contacts used for power circuit and
auxiliary contact used for control circuit.
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STATIONARY
CONTACTS
MOVABLE
CONTACTS AND
ARMATURE
COIL
CONNECTIONS
HOLDING COIL
STATIONARY
CONTACTS
L1
STATIONARY
CONTACTS
MOVABLE
CONTACTS
SPRINGS
COIL
STATIONARY
ELECTROMAGNET
ARMATURE
T1
L2
T2
L3
T3
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Circuit diagram of a contactor
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Operation of the contactor
 When the control current energizes the operating coil of the
contactor, its magnet core attracts a steel armature, the armature
closes the main contacts in the the power circuits.
 There are compressing springs which causes the movable contacts
to come back when operating coil is off
 The contactor also has auxiliary contacts with normally closed
contacts (NC) or normally open contacts (NO) or both placed in
the control current circuits and intended to perform auxiliary
control.
 A.C contactors are usually employed as part of Magntic Starters.
 Most often, a magnetic contactors, thermal relays and control
buttons.
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Normally Open Contact ( NO )
This is the normal state of the contact when the
electromagnet ( coil ) is de-energised. This contact will
close instantaneously when the electromagnet is
energised. When the coil de-energised, this contact will
return to its normal state i.e. open.
Normally Closed Contact ( NC )
This is the normal state of the contact when the
electromagnet is de-energised. The contact will open
instantaneously when the electromagnet is energised.
When the coil de-energised,the contact will return to its
normal state i.e. closed.
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SWITCHES
SWITCH
Switch is an electrical device that can break and connect an electrical circuit,
as well as interrupting the flow of current or divert it from one conductor to
the other.
Types of switches typically used
in motor control applications:
1.
2.
3.
4.
5.
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Pushbutton switch
Limit switch
Selector switch
Footswitch
Toggle switch
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START BUTTON
A start button consists of a green coloured actuator, which
when pressed operates a normally open contact. On
pressing the green actuator the normally open contact will
close.
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STOP BUTTON
 A stop button consists of a red coloured actuator, which
when pressed operates a normally closed contact. On
pressing the red actuator the normally closed contact will
open.
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 Full Load current rating (FLA) -the nominal current flow to the motor
after motor start and under normal operation conditions. Used to
calculate inrush current and select short circuit protective devices
 Locked Rotor Current (LRA)–occurs when something prevents the
motor from turning, typically 600% of the motor FLA.
 Inrush Current –occurs immediately after starting a motor. Circuit
breakers and fuses must be sized to accommodate this current.
Overload protective relays, provide protection for motor currents from
125% of the motor FLA up to the LRA of 600%.
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 The amount of heat generated is proportional to both the amount of current
flow and the resistance of the conductive path.
 Because conductors can be damaged by excess heat, each conductor has a
continuous current rating, also called its ampacity.
The following are potential causes of overcurrent:
 Short circuit -When two or more bare conductors touch causing the resistance
between the two to drop
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 Overload -When the current exceeds the trip class of the device
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TIMER
Relay timer contains an
auxiliary contacts NO and NC
that can be integrated into
motor control circuits. The
initial state of its contact will
change when activated after
pre-determined value.
The timer unit can be set into
seconds or minutes depending
on the application
requirements.
For longer and iterative tasks,
real time timers are available.
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THERMAL OVERLOAD RELAY
Line terminals
Thermal overload relay is
an electrical component
used in motor control
applications
which
provide protection for
motor against excessive
current.
reset
Set value dial
Auxiliary contact(s)
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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.
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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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THERMAL OVERLOAD RELAY
Typical set-up of contactor and overload relay
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THERMAL OVERLOAD RELAY
Characteristics:
1. Allow harmless temporary overloads (such as
motor starting) without disrupting the circuit.
2. Trip and open a circuit if current is high enough to
cause motor damage over a period of time.
3. Can be reset once the overload is removed.
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OVER/ UNDER VOLTAGE RELAY
This component protects the motor against over voltage and under voltage
situation.
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LIMIT SWITH
Is an electromechanical device that consists of an actuator
that is connected mechanically to the set of contacts.
When the Object travels towards and comes in touch with
the actuator, the limit switch can connect(make) or break
electrical circuit.
A Limit switch is used to convert mechanical motion of the
objects or machines into electrical energy for various
switching operation.
It has two contacts states; NO and NC.
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STAR AND DELTA CONNECTION
STAR CONNECTION
 Two windings are connected in series.
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DELTA CONNECTION
The windings are connected in parallel.
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Circuit representation of motor
winding
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Circuit representation of motor
winding.
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MOTOR STARTING METHODS
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Why motors employ a starting methods?
 To reduce heavy starting currents and prevent motor from
overheating
 To provide overload and low voltage protection
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THE COMMON METHODS OF
STARTING 3-PHASE MOTOR
 The methods used to start induction motor are;
a) Direct –on – line starting methods (D.O.L)
b) Star delta starting methods
c) Resistor starting methods
d) Auto transformer starting methods
e) Tyristor starting methods (soft starting using VFD)
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1. DIRECT ONLINE STARTING METHOD
It directly connects the contacts of the motor
to the full supply voltage.
The starting current is very large, normally 6 to
8 times the rated current. In order to avoid
excessive voltage drops in the supply line due
to high starting currents, The DOL starter is
used only for motors with a rating of less than
1OH.P
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POWER CIRCUIT AND CONTROL CIRCUIT
POWER CIRCUIT- is a circuit used to supply electric energy
to the motor.
CONTROL CIRCUIT- is a circuit used to supply control
components in the motor control circuit.
POWER CIRCUIT + CONTROL CIRCUIT= COMPLETE MOTOR
CONTROL CIRCUIT
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Power/Main circuit
 The main components of Power
circuit are;
i. Disconnectors /Main Isolators
(isolation)
ii. Fused isolator/Circuit breakers
(Short circuit protection)
iii. Contactor
(Switching)
iv. Overload relay
(Running overcurrent) protection
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Control circuit
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ADVANTAGES AND DIS-ADVANTAGES OF DOL
STARTER
ADVANTAGES
 Simple and most economical starter.
 More comfortable to design, operate and control
 It provides nearly full starting torque at starting
 Easy to understand and trouble shoot
 DOL starter connects the supply to the delta winding of
the motor.
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DIS-ADVANTAGES
 It draws high starting current 6 to 8 times the full load
rated current
 It reduces the life span of the machine
 It is mechanically tough
 Unnecessary high starting torque
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FORWARD AND REVERSE DOL
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MOTOR STAR DELTA STARTING
METHODS
 The windings of three phase induction motor are
switched between star and delta connection to start the
motor.
 The phase voltage in star connection is reduced by the
1
factor .
3
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TRY TO
DRAW MANUAL STAR DELTA STARTING CONTROL CIRCUIT FOR
THREE PHASE INDUCTION MOTOR.
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TUTORIAL
QN1. As an engineer, you are asked to design an automatic
control system for an opening and closing of MUST main
gate. The sequence and details of operations are:
a) The MUST main gate is opened or closed using a push
button and limit switches when pressed and depressed
respectively.
b) When switch is depressed, the MUST main gate will be
opened if originally closed or closed if it was originally
open.
c) To open the main gate, the motor should turn counterclockwise direction.
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d)To close the main gate, the motor should turn clockwise
direction.
e) Obviously, the motor cannot be run clock-wise and
counter-clockwise at the same time.
f) There are two limit switches that indicate if the motor is
fully open or fully closed.
g) Excess load on the motor while running is detected.
h) The main gate should reverse its direction when an
overload is detected.
j) The gate light Yellow will go ON and stay ON for 20
seconds after each closing or opening.
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TASK
i. Clearly define all the necessary components of the
control system.
ii. Draw a detailed Power and control circuit according to
above sequence operation
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QN 2
a) Select suitable methods of starting 3Kw three phase,
induction motor and give a reason for your selection
b) Draw a well labelled circuit diagrams for starting a 3Kw
three phase induction motor in forward and reverse
direction to be used for industrial application
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