electrical system maintenance
TRANSCRIPT
Maintenance Awareness
Electrical System Maintenance• Section 3.1 - Voltage, Current,
Resistance • Section 3.2 - Ohm’s Law• Section 3.3 - Series Circuits• Section 3.4 - Parallel Circuits • Section 3.5 - Alternating Current• Section 3.6 - Transformers• Section 3.7 - Motors• Section 3.8 - Automation
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• Examine electricity to determine current, voltage, resistance by applying Ohm’s Law.
• Describe the differences in series and parallel resistive electrical circuits.
• Explain the differences between AC and DC motors
• Identify the need for voltage transformers
• Describe the role of PLC’s in automation systems
Objectives
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Structure of Matter
• Molecules• Atom• Element
•Nucleus•Proton•Neutrons•Electrons
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What is Electricity?A form of energy produced by the flow of negatively (electrons [-]) charged atomic
particles. A stream of electrons, or an electric current.
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What is Voltage?
Voltage: is the difference of electrical potential between two points of an electrical circuit expressed in volts. It measures the capacity (potential) of an electric field to cause an electric current in an electrical conductor.
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CurrentCurrent refers to electric current, which is the flow of electric charge. An example of an electric current flow from the source through a light bulb and back to the source. Probably the most familiar form of electric current is the flow of electrons in a metallic wire.
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Resistance
Electrical resistance is a measure of the degree to which a body opposes the passage of an electric current. The unit of electrical resistance is the ohm.
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3.2: Ohm’s Law
• Georg Simon Ohm, born in Erlangen, Bavaria, March 16, 1787.
• Ohm's experimentation with voltage and direct current led him to the fundamental relationship that they are exactly proportional in a perfect conductor.
• Ohm's Law (V=IR) is basic to the study of electronics.
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Ohm’s LawIdentifies the relationship between voltage, current, and resistance
• If any two values are known, the other can be calculated
V R X I
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Ohm’s Law Measurements
• To find voltage (V) measured in volts cover up the V, V=IR
• To find current (I) measured in amperes cover up the I, I=V/R
• To find resistance (R) measured in ohmsCover up the R, R=V/I V
R I12/146
Basic Resistive Electrical Circuits
Basic resistive electrical circuits:– Series resistive circuit
– Parallel resistive circuit
– Combination or series-parallel resistive circuit
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3.3: Definition of a Series Resistive Circuit
• Series resistive circuit has one or more resistors and gets its name from only having one path for the charges to move along.
• The following rules apply to a series circuit:• The sum of the potential drops equals the
potential rise of the source.
• The current is the same everywhere in the series circuit.
• The total resistance of the circuit is equal to the sum of the individual resistances.
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Example of a Series Resistive Circuit
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Series Resistive Circuit Formulas1.The total voltage is the sum of the voltage on each
component.
VT = V1 + V2 + V3 +...+ Vn
2.The total resistance is equal to the sum of the resistance of each component.
RT = R1 + R2 + R3 +...+ Rn
3.The total current is the same in every component.
IT = I1 = I2 = I3 = I4 =...= In16/146
Series vs. Parallel
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3.4: Definition of a Parallel Resistive Circuit
• A parallel resistive circuit that must have two or more resistors.
• Has multiple (parallel) paths so that charges can move through any of several paths.
• The following rules apply to a parallel circuit:• The potential drops of each branch equals the potential rise of the
source.
• The total current is equal to the sum of the currents in the branches.
• The inverse of the total resistance of the circuit is equal to the sum of the inverses of the individual resistances.
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Parallel Circuit
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Parallel Resistive Circuit Formulas 1.The total voltage is equal in every component.
VT = V1 = V2 = V3 =...= Vn
2.The resistance is equal to the sum of resistance on each component divided by the product of resistance of each component. 1/RT = 1/R1 + 1/R2 +...+ 1/Rn
3.The total current is equal to the sum of current in each component. IT = I1 + I2 + I3 + I4 +...+ In
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Example of a Series-Parallel Resistive Circuit
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Definition of a Series-Parallel Resistive Circuit
• A series-parallel circuit is the series and the parallel circuit combined. When finding amperes, ohms or voltage in a series-parallel resistive circuit you actually solve separate problems and then combine your findings.
• The following rules apply to a series-parallel resistive circuit:• The total voltage is the voltage of series plus the voltage of
parallel.
• The total resistance is the resistance of series plus the resistance of parallel.
• The total current is equal to the current of series and to the sum of the current of parallel circuit.
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Series-Parallel Resistive Circuit Formulas
1.The total voltage is the voltage of series plus the voltage of parallel. VT = V1 + V2 = V1 + V3
2.The total resistance is the resistance of series plus the resistance of parallel. RT = R1 + [(R2R3)/(R2 + R3)]
3.The total current is equal to the current on series and to the sum of the current of parallel circuit. IT = I1 = I2 + I3
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Measuring ElectricityVoltmeter – measures potential difference (analog/digital)
DMM- digital multimeterUsed to measure:
•Current (Amperes)•Potential (Volts)•Resistance (Ohms)•Can also transmit control
signal- 4-20 mAMegohmmeters- insulation and ground testing (million ohms) 24/146
Circuit Testers
A circuit tester is a device which is used to test a circuit to determine whether or not power is reaching the circuit. Circuit testers are very inexpensive tools which can be obtained at hardware and home suppliers, and they are critical tools for anyone who works with electricity to have. While they do not provide the detailed information available with a multimeter, they are useful for quick checking of electrical circuits, and they take no time at all to learn to use.
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Circuit Testers
Typically, a circuit tester has a light which illuminates when a circuit is getting power. Some may generate buzzing sounds, and the volume of the sound or the intensity of the light may increase with the amount of power available to the circuit. This can be useful for differentiating between circuits which are being supplied with different amounts of power, or for identifying circuits which are getting too much or too little power, which can be a sign of an electrical short or a similar problem.
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Measuring Electricity• Voltage measured ACROSS a
component (difference in potential between 2 points)
• Current Measured as the flow through a wire
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QUESTION
Meter(voltage)
What is being measured in the circuit below?
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QUESTIONS
Meter
(amperage)
What is being measured in the circuit below?
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3.5: Alternating Current
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Introduction to Alternating Current• Alternating Current, and its’ associated voltage, reverses
between Positive & Negative polarities, and varies in amplitude with time.
• One complete waveform, or cycle, includes a complete set of variations, with two alternations in polarity.
• Many sources of voltage change direction with time, and produce a resultant waveform. (square wave, sawtooth, triange)
• The most common AC wave form is the Sine Wave.
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Sine Wave Generation
Basic principles of Magnetism:• An electric current in a conductor creates a
magnetic field that surrounds the conductor• Relative motion between a conductor and a
magnetic field, when at least one component of that relative motion is in a direction that is perpendicular to the direction of the field, creates a voltage in the conductor.
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Sine Wave Generation (Cont’d.) • Factors that affect Magnitude of Voltage:
• Strength of the magnetic field• Length of the conductor• Rate of motion
• Since generators have fixed magnetic strength and length of conductor the Rate of Motion is the determining factor.
• Factors that affect Rate of Motion:• Speed of the generator (rpm)• Angle of Motion
MO
TIO
N
MOTION
Rate: 0 Rate: Changing Rate: Maximum
N S No motion thru Rate of motion thru the Maximum motion thruthe lines of flux lines of flux is increasing the lines of flux
MOTION
θ
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One Cycle of Alternating
Current
Sine Wave Generation (Cont’d.) E = Emax sine θ
E = Voltage Induced
Emax = Maximum Induced Voltage
θ = Angle at which the voltage is induced
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Sine Wave Terminology Frequency
• The frequency of a waveform is the number of times per second an identical pattern repeats itself. Each time the waveform changes from zero to a peak value and back to zero is called an alternation.
• The unit of frequency is hertz (Hz). One hertz equals one cycle per second (cps)
Frequency =CyclesSeconds
F = 5/.5 = 10 Hz
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Sine Wave Terminology (Cont’d.)
Period (t)• The period of a waveform is the time required
to complete one cycle.• The period is the inverse of frequency.• @ 10-Hz, period = .1 sec
Period = 1 _Frequency
.1SEC
f = 1/tt= 1/f
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60Hz Sine Wave
• f(frequency) = 60 cycles per second (hz)• t(time) = 1/60 = 16.6ms time of one cycle
16.6ms
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Voltage Waveforms 90° Out of Phase
Phase AngleVO
LTS
0
TIME
WAVE A
WAVE B
360°270°180°90°90°
VA
VB
Vector display of waveform
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Voltage/Current (Inphase - Resistive)
VOLT
S0
TIME
VA
IA
360°270°180°90°
VAIA
Vectors have magnitude and
direction
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Resistance in AC Circuits
V = I/R
I = V/R
R = V/I
Resistance (same in AC & DC circuits)– The characteristic of an electrical component or circuit that
opposes current flow.– Symbol – R– Unit – ohm (Ω)
• 1 ohm is the amount of resistance that opposes 1 volt across the circuit at a current rate of 1 ampere per second.
– Resistor – An electronic component that opposes an electrical current by producing and electrical drop between its’ terminals through the use of various semiconductor materials. V
R I 40/146
Resistance in AC Circuits (Cont’d.)
120V
I = 12A
RL = 10Ω
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Voltage & Current in a Resistive AC Circuit (in phase)
E
I
Resistance in AC Circuits (Cont’d.)
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Inductance in an AC Circuit
Inductance is the characteristic of an AC electrical circuit that opposes the change of current flow.• Symbol – L• Unit – henry (h)
• 1 henry is the amount of inductance that allows 1 volt to be induced when the current changes at a rate of 1 ampere per second.
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Voltage & Current in anInductive AC Circuit
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Inductive Reactance The opposing force which an Inductor creates in an AC circuit.• Not to be confused with Resistance, which is
physical friction within the circuit.• Symbol – XL
• Unit – ohms (Ω)• XL = (2π)fL
•2π – 6.28 (2 x 3.14)•f – Frequency (hertz)•L – Inductance (henrys)
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Capacitance
The ability of an electrical component or circuit to store a charge in an AC circuit.• Symbol – C• Unit – farad (F)
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Calculating Capacitance -
+
C1
C2
CT=C1+C2C
1
C2
Parallel Circuit(like resistors in
series)
Series Circuit(like resistors in
parallel)
1C2
CT= 1C1
1
+
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Voltage & Current in aCapacitive AC Circuit
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Capacitive Reactance
The opposing force which a Capacitor creates in an AC circuit.• Not to be confused with Resistance, which is physical
friction within the circuit.• Symbol – XC
• Unit – ohms (Ω)• XC =
• 2π – 6.28 (2 x 3.14)• f– Frequency (hertz)• C – Capacitance (farads)
(2π)fC
1
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R Circuits • Purely Resistive Circuit Voltage (E) &
Amperage (I) are in-phase
Resistive Circuit
L Circuits • Purely Inductive Circuit Voltage (E)
leads Amperage (I) by 90 °
Inductive Circuit
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C Circuits • Purely Capacitive Circuit Amperage
(I) leads Voltage (E) by 90 °
Capacitive Circuit
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3.6 Transformers– A device that transfers electrical energy from
one circuit to another by electromagnetic induction. No change in frequency
– Must be used with a source voltage that varies in amplitude. (only works in AC circuits)
– Electricity transmission over long distances has lower loss when sent at higher voltages and is then reduced (step-down) to user levels.
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Transformer Construction Transformers consist of:
– Primary Coil (Source)– Secondary Coil (Load)– Core
SecondaryWinding
PrimaryWinding 60
Hz Load
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Transformer Windings
Leads
PrimaryWindings
SecondaryWindings
PaperInsulation
LaminatedCore
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Turns & Voltage Ratios Turns Ratio - may be a voltage step up (1:2) or step down (2:1)
Turns Ratio =
++
Number of turns in the primary Number of turns in the secondary
Input: 480V
Ratio = ____12___/____1__ . pri / sec
Output: _____V
12 / 1480/12
40
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3.7: AC & DC Motors
• Nameplate Marking• Delta & Wye motors• Overcurrent and disconnects• Safety
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Advantages of Electric Motors
• Low Initial Cost• Long Operating Life• Automated Controls• No Fossil Fuels• Saves on Labor Costs• Occupational Safety• On Average 30,000 Productive Hours
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Electric Motors Operation
Electric motors function on the principle of magnetism; where like poles repel, and unlike poles attract.
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Electric Motor Classification
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Horsepower/Torque/Speed Formula
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DC MotorsDC motors have been used in industry for many decades. When used with DC drives, they provide very precise control. DC motors are used for the following:• Elevators• Conveyors• Extruders
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Electric Motors OperationDirect Current (DC) motors cause rotation by
changing the magnetic poles of the armature
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A BC D
E
F
G H
I
Parts of a Basic DC Motor
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DC Motor Terms
Understanding the following terms will aid in identifying DC motor operation:Armature Current: The current required by a motor to produce torque and drive a load. Armature current is proportional to the amount of torque being produced.Base Speed: The motor shaft speed in revolutions per minute (RPM) that occurs when full armature voltage and full field current are supplied to a motor with a full load attached.Commutation: The switching in polarity between the armature and the brushes in a DC motor that keeps current flowing in the same direction.
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DC Motor Terms (Cont’d.)
Understanding the following terms will aid in identifying DC motor operation:Field Current: The current required to energize the field windings of a DC motor. The interaction between the armature current and field current produces flux in the motorFlux: The magnetic field created around an energized conductor or between opposite poles of a permanent magnet. The more lines of flux present, the stronger the magnetic field
North Pole
South PoleFlux
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DC Motor Armature and Frame
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DC Motor Armature
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DC Motor - Nameplate Markings
Horse Power at Base Speed
Base Speed at Rated Load
Rated Armature Voltage
Winding Type: Shunt, Series, Compound, Permanent Magnet
Armature Rated Load Current
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DC Motor - Nameplate Marking
NEMA Insulation Class
Rated Field Voltage
Maximum Ambient Temperature
Enclosure Type
Manufactures Type and Frame Designation
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Industrial 3 Phase PowerThe sine curves show –5 A for phase A, +10 A for phase B, and –5 A for phase C. The + and – signs indicate the direction of the current and the numbers represent the magnitude of the current.
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12 3
4 5
6
7
8
9
10
Parts of a Basic AC Motor
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Induction motors consist of a stator and a rotor enclosed within a frame, with no physical electrical connections between the stator and the rotor.
AC Induction Motor
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The stator consists of a core and windings, or coils, that convert electrical energy to the energy of a magnetic field.
Stator
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Rotor Construction
Hz 60
AMPS 15
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The stator magnetic field induces current in the rotor. The current creates a magnetic field and poles within the rotor.
Squirrel-Cage Rotor
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360° Rotation
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Rotating Magnet
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3 Phase PowerThe motor nameplate typically has a wiring diagram depicting the proper wiring connections for the desired operation.
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Motors: Wye ConfigurationEach phase coil (A, B, and C) is divided into two equal parts and the coils are connected in a standard wye connection.
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Manufacturers of dual-voltage, 3-phase motors sometimes do not make the internal connections. The connections are made externally by the installer.
Low/High Wiring
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Motors: Delta ConfigurationEach phase coil (A, B, and C ) is divided into two equal parts and the coils are connected in a standard delta connection.
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A nameplate is a metal tag permanently attached to an electric motor frame that gives the required electrical ratings, operating ratings, and mechanical-design codes of the motor.
AC Nameplate
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The voltage rating is the voltage level that a motor can use. All motors are designed for optimum performance at a specific voltage level.
AC Nameplate - Voltage
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The current rating is the amount of current a motor draws when delivering full rated power output.
AC Nameplate - Amps
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The phase rating is the power phase(1f, 3f, or DC) that a motor requires. Some electric motor drives allow the input power to the drive to be of a different type and at a different voltage level than the power required by the motor.
AC Nameplate - Phase
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The power rating is the amount of power a motor can deliver to a load. Motors designed for the U.S. market that are 1/20 HP or greater are typically rated in HP, and motors that are less than 1/20 HP are typically rated in watts (W).
AC Nameplate - Power
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The service factor rating is a multiplier that represents the amount of extra load that can be placed on a motor without causing damage.
AC Nameplate - Service Factor
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Overcurrent Disconnects• This is also known as overload protection. Very
important as a motor and subsequent devices powered by them can be damaged
• Components used to protect them:• Overload relays
• Fuses
• Circuit Breakers
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Safety• Implementation of disconnects on motors in
case of overload or short is of paramount importance.
• Grounding must be done properly to prevent additional voltage generation.
• Motors need to be level to prevent mechanical failures that are serious safety problems.
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1. The switching in polarity between the armature and the brushes in a DC motor that keeps current flowing in the same direction is called ____________. a) Armature Currentb) Base Speedc) Commutationd) Field Currente) Flux
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2. The speed of a rotating object can be expressed as _____.
a) Revolutions per minuteb) Cycles per secondc) Acceleration per miled) Pounds per feete) Feet per minute
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Electric Motor
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3. Part “A” is the ____________a) Bearingb) Fanc) Rotord) Shafte) Stator
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4. Part “B” is the ____________a) Bearingb) Fanc) Rotord) Shafte) Stator
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5. Part “E” is the ____________a) Bearingb) Fanc) Rotord) Shafte) Stator
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Motor Control Protection • The function & purpose of motor controls• Protective functions of motors starters• Sizing of fuses and overloads
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Motor Controls
Depending on the application, things that may need to be controlled could include:
• Speed
• Start/Stop/Reverse
• Shut down breaking
• Voltage/Current
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Across the Line• Simplest Method – Least Expensive• Windings/terminals connected directly to voltage
source
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Manual Motor StarterAdvantage
• Lower cost than magnetic starter• Used for fractional HP motors• Contacts remain closed if power is
removed
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Magnetic StarterFor larger motors or applications in need of higher degree of control
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Relay
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Circuit ProtectionConditions requiring protection
• Direct shorts/short circuit
• Excessive current
• Excessive heat
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Protection Devices
• Fuses • Circuit Breakers• Surge Protection
• Overload Clutch Coupling
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Overcurrent Protection
• Interrupts circuit when there is excessive current either from short circuit or ground fault.
• Typical protection devices• Fuse• Circuit Breaker
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Fuse Ratings• Physical Size• Current Rating• Voltage Rating• Time Delay
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Overload Protection• Protects motor from a mechanical overload• Effects of overload can be high temperature
due to high current from overload• Not the same as start up current
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QUESTION
• If a motor circuit starts blowing fuses/tripping thermals, the most likely cause is _________.overload
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Sizing Fuses & OverloadsProper rated Time Delay Fuses should be 150% to 175% of the motor full-load current
—This is so it can handle initial start up—There are ways to overcome start up issues by a
slow burn fuse. It won’t burn open on start up when loads are very large.
• NEC Table 430-152 Overcurrent Devices
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NEC TABLE
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Time Delay FuseThese are generally dual element fuses with both thermal and instantaneous trip features that allow the motor starting current to flow for a short time without blowing the fuse.
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Circuit BreakersCircuit Breakers are used instead of fuses due to the fact that fuses are a one time use only. A circuit breaker can be reset when it trips. Once a fuse has opened it must be replaced.
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Simple Breaker Operation
Not Tripped Tripped
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Thermal OverloadPreset value opens when temperature is reached
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Sizing Motor Protection• Determine Motor Full Load Amps• Determine size of branch conductors
• NEC 430-22 says conductor ampacity = FLA x 125%
• Determine branch circuit over current device size
• Determine the required size for the motor running overload protection
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Magnetic Motor StartersA magnetic starter is an electromagnetically operated switch which provides a safe method for starting an electric motor with a large load. Magnetic starters also provide under-voltage and overload protection and an automatic cutoff in the event of a power failure.
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Motor Control Circuits
A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.
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Motor Control Center (MCC)
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Motor Control Bucket (MCC)
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Troubleshooting Electric Motors
• Power Supply• Overheating• Contamination• Lubrication• Brush Damage• Unusual Loads
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QUESTIONA technician has unwired a motor from the power source and the circuit breaker still trips.The next logical step is to__________________ .replace the breaker
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Sequencing Motor StartA Power Diagram used with a Ladder Diagram to determine sequence of operationsTime delay circuits may be used to take the place of the manual start (2 PB below)
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3.8 Automated Systems Here are several examples of components of an automated system. Keep in mind that every component does not have to be present to have an automated system.
• Automated machine tools• Transfer lines• Automated assembly systems• Industrial robots • Automated material handling and storage systems• Automatic inspection systems for quality control
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Programmable Automation
Programmable automation has the capability to change the sequence of operations through reprogramming the computer system to accommodate different product configurations. Typical features of programmable automation include:
• High investment in programmable equipment• Lower production rates than fixed automation• Flexibility to deal with variations and changes in
product configuration• Suitability for batch production• Physical setup and part program must be
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Reasons for Automating • To increase labor productivity• To reduce labor cost• To mitigate the effects of labor shortages• To reduce or remove routine manual and
clerical tasks• To improve worker safety• To improve product quality• To reduce manufacturing lead time• To accomplish what cannot be done
manually• To avoid the high cost of not automating
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Programmable Logic Controller• A programmable logic controller (PLC) is a
specialized computer used to control machines and processes.
• It uses a programmable memory to store instructions and specific functions that include On/Off control, timing, counting, sequencing, arithmetic and data handling.
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Programmable Logic Controllers( Definition according to NEMA standard ICS3-1978)
A digitally operating electronic apparatus which uses a programming memory for the internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through digital or analog modules, various types of machines or process.
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Components of a PLC
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Components of a PLC (Cont’d.)
• CPU - Interprets the inputs & outputs and carries out the actions based on the program, communicates the programmed decision as a signal output.
• Power Supply - converts AC to DC for the other modules.
• Memory - where the program and data is stored
• I/O - receives information from switches, sensors, etc. and outputs actions to motors, solenoids, valves, etc.
• Communication Interface - concerned with connection to other devices.
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Input Switches
Input device that gives the operator control to energize and de-energize a circuit
Flexible or rigid protection for I/O wiring is provided to prevent damage
Normally Open (NO)
Normally Closed (NC)
Held Closed (HC)
Held Open (HO)
A light switch is an example of an Input Switch
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In a PLC wiring diagram, each input is wired to a designated input terminal and each output is wired to a designated output terminal.
PLC Wiring Diagram
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I/O Modules• The I/O interface section of a PLC connects the CPU to the external field devices. • The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices. • Input modules converts signals from discrete or analog input devices to logic levels acceptable to PLC’s processor. • Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices.
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OFFLogic 0
IN
PLC
InputModule
24 V dc
OFFLogic 1
IN
PLC
InputModule
24 V dc
Memory
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IN
PLCAnalogInputModule
Tank
Level Transmitter
An analog input is an input signal that has a continuous signal. Typical inputs may vary from 0 to 20mA, 4 to 20mA or 0 to10V. Below, a level transmitter monitors the level of liquid in the tank. Depending on the level, the signal to the PLC can either increase or decrease as the level increases or decreases.
Analog Input
Memory word32 bits
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Output Modules
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Ladder Diagram
Ladder Diagrams were used to describe early relay control logic
Relays served as the brains of machine control
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Basic Ladder InstructionsSymbol Logic
Examine if Closed (XIC) – Instruction is true when input is energized
Examine if Open (XIO) – Instruction is true when input is NOT energized
Output Enabled (OTE) – Mimics the action of a conventional relay coil
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XIC vs XIOXIO
XIC
XIO
XIC
Hardware Software Hardware
ON
ON
OFF
OFF
Closed closed? True
Closed open? False
Open closed? False
Open open? True
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Ladder Diagram Rules
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How PLC Works
01
02
03
04
00
04
03
02
01
000
1
0
1
0
0
1
0
0
0
0001
I:001O:001
O:001/01
01
I:001
0301
O:001O:001
03
01
00
01
03
04
Processor MemoryInputModule
Output Module
120 VAC120 VAC
InputMap
OutputMap
Ladder Logic in
Reads inputsExecutes ProgramSets OutputsRepeats
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Numbers and letters are used to assign (address) inputs, outputs, timers, and other internal and external components.
Tags and Addressing
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Tags• Tags are the method for assigning and
referencing memory locations• Tags are not Variables• A PLC Tag is not a Description
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PLC Input & Output Mapping
00
O:001
I:001
O:001/01
04
I:001
01
O:001
00
03
01
01
03
O:001
01
02
00
01
02
03
04
START
STOP
MOTORRELAYCOIL
ON LIGHTMOTOR
START SW
STOP SW
M
M
L1
L1 N
N
SELF HOLDING FOR "M"
RELAY COIL
CONTROLPOWER
ON LIGHT
INPUT RACK SLOT ADDRESSI: 0 01 / 03
OUTPUT RACK SLOT ADDRESSO: 0 01 / 03
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I/O base tags use the following format:
Location:Slot:Type.Member.Bit
“Local” or Module Name for Remote
I/O Point (Optional)
“Data” (I/O values), “Fault,” etc.
“I” for Input, “O” for Output, “C” for Configuration
Module Slot Number
I/O Module Tag (Allen Bradley)
Examples – Local:2:I.data 4 Local:7:O.ch 0 data
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QUESTION
(2)
Which rung in following diagram is an example of “and” control logic?
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National Electrical Code
• NEC – purpose is to provide rules for protection of persons and property from hazards arising from the use of electricity.
• The code covers the installation of electrical conductors, equipment and raceways, signaling and communications conductors and optical fiber.
• Code Update every 3 years ( 2011, 2014, 2017).
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How it Works!The NEC chapters are:
• General• Wiring and Protection• Wiring Methods and Materials• Equipment for General Use• Special Occupancies• Special Equipment• Special Conditions• Communications Systems• Tables
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Summary• Examine electricity to determine current,
voltage, resistance by applying Ohm’s Law.• Describe the differences in series and parallel
resistive electrical circuits.• Explain the differences between AC and DC
motors• Identify the need for voltage transformers• Describe the role of PLC’s in automation
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