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Fundamentals Of ElectricityFundamentals Of Electricity
Simple DC
Series
Circuit,
Simple DC
ParallelCircuit,
Rt = R1+R2+R3
Rt = (R1.R2.R3 )
/(R2.R1+R3.R2+R1 .R3)
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Simple AC
Series
Circuit,
Simple AC
ParallelCircuit,
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Three Phase(AC)
Transformer
Configurations
Note:
a = Turns Ratio
= Np/Ns
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Impedance : Definition : Impedance is the current
resisting and impeding characteristic ofload or conductor in an AC Circuit.
Symbol for Impedance: Z
Z = R + jXl - jXc
Where,jXl = Zl and, -jXc =Zc
Unit for Impedance: Ohms or;s.
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Ohms Law: Mathematical Statement of the Ohms
Law:
V = I R forDC circuits
V = I Z for AC Circuits
Note: BOLD letters, in general, represent
Vectoral quantities
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ImpedanceImpedanceCalculation:Calculation:
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Fundamentals Of ElectricityFundamentals Of Electricity
Power :
Definition: Power is defined as the capacity of a systemto perform work or Rate of work performed by a system.
Symbols and Types of Power:
Pdc=V.
I , in watts.Note: Pdc= Preal
Papparent = S= Apparent Power (kVA) or Total AC
Power
Preal =P= Real Power Comp. of Apparent Power, in kW
Preactive = Q = Reactive Comp. of App. Power in kVAR Pappent = (Preal)2 + (Preactive)2 orS= (P)2 +(Q)2
Magnitude ofTotal (3 ) Power = S= 3.VL.IL
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Power Factor : Definition: Power Factor is defined as the Ratio
of Real Power (kW) to Apparent Power (kVA). Itis also defined as the quantity cos(U - J).
PF = P/S orPF = cos(U - J),
where U is the angle of voltage V, where V =VRMS U
J is the angle of current i =IRMS JNote:Detailed discussion on the topic of Power
Factor is covered under the Power Factorsegment of this seminar.
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Voltage Regulation:Definition: Real voltage sources are unable
to hold the voltage constant as they assumea significant amount of load (Resistance orImpedance). This results in the differencebetween Vno load and Vfull load.
The formula for Voltage Regulation is as
follows:Voltage Reg. = (Vno load - Vfull load)/ Vfull load x 100%
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Service Factor of a Motor:
Definition: Service factor of a motor is the
ratio of safe to standard (nameplate) loads.Service factor is expressed in decimal. Theformula for Service Factor is as follows:
Service Factor = Safe Load / Nameplate Load
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Classifications ofMotors:Motor categorization by NEMA, National
ElectricalManufacturers Association:
Speed:
Constant Speed
Adjustable SpeedMultispeed
Varying Speed
Service Classification:
General
DefiniteSpecial Purpose
Varying Speed
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Classifications ofMotors, contd.:
Motor Class is determined by the maximumallowable operating temperature of the motor,
which is dependant on the type/grade ofinsulation used in the motor.
Class A: 105r C
Class B: 130r C
Class F: 155r C
Class H: 180r C
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Kirchhoffs Voltage Law (KVL):
Algebraic sum of voltage drops aroundany closed path, within a circuit, isequal to the sum of voltages presentedby all of the voltage sources. Themathematical representation of KVL
is as follows:7 VDrops = 7 VSource
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Kirchhoffs Current Law (KCL):
Total current flowing into a node is
equal to the total current that flowsout of the node. The mathematicalrepresentation of KCL is as follows:
7 iin = 7 iout
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Motor Speed Calculation:
Given:
Number of Poles = P = 4
Frequency of AC Power Supply to the Motor, in Hertz = f = 60
Hz
Speed, in RPM = S = ?
Formula: S x P = 120 x f
S = (120 x f ) / P
S = (120 x 60) / 4 = 1800 RPM
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Motor Slip:Slip is usually expressed in percent and can be computed as follows:
Percent slip = (Synchronous speed - Actual speed ) x 100
Synchronous Speed
Induction motors are made with slip ranging from less than 5% up to
20%. A motor with a slip of 5% or less is known as a normal-slip motor. A
normal-slip motor is sometimes referred to as a 'constant speed'motor because the speed changes very little from no-load to full-loadconditions. A common four-pole motor with a synchronous speed of1,800 rpm may have a no-load speed of 1,795 rpm and a full-loadspeed of 1,750 rpm. The rate-of-change of slip is approximately linear
from 10% to 110% load, when all other factors such as temperatureand voltage are held constant. Motors with slip over 5% are used forhard to start applications.
The direction of rotation of a polyphase ac induction motor depends onthe connection of the stator leads to the power lines. Interchangingany two input leads reverses rotation.
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Motor Torque, Power and Horsepower:
Torque is equivalent to the amount of work performed.Torque can be considered as turning effort. For example,suppose a wheel with a crank arm one-foot long takes aforce of one pound to turn at steady rate. The torquerequired would be one pound times one foot or one foot-
pound.
Horsepower, i .e. Power, is defined as the rate at whichwork is performed or rate at which torque is produced.
In the wheel cranking example above, if one were to crankthe wheel twice as fast, the torque remains the same butthe power and horsepower delivered would double,regardless of how fast the crank is turned, as long as thecrank is turned at a steady speed.
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Motor Torque and Horsepower,contd.:
Power, Horsepower and Torque Relationship:
Torque(ft-lbf) = 5250 x P (horsepower)Speed (rpm)
Torque(N-m) = 9549 x P (kW)
Speed (rpm)
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Fundamentals Of Electricity in Industrial and Commercial EnvironmentFundamentals Of Electricity in Industrial and Commercial Environment
Motor Power Line Current Calculation:
Motor Nameplate Information:
Power rating, in HP (Horse Power) = P = 10 HP
Voltage Rating = 480 VAC
No. of Phases = 3; also stated as 3 Power Factor = PF = 0.8
Efficiency = Eff. = 0.9
Magnitude of Line Current = FLA, Full Load Current = I = I = ?Note: 1 HP = 746 Watts = 746 W = 0.746 kW
Formula: I = Power in Watts / PF / Eff./ (3 x VL) I = 10HP x 746 W/HP/0.8/0.9/(3 x480VAC)
I = 12.46 Amps
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Miscellaneous: Demand: This term means the highest average
power (kW) in a given interval, or demandinterval. Electric utilities charge commercial andindustrial customers for the peak demand set
each month. Peak demand: This is the maximum demand
used in any demand interval for a given month.
Load factor: The load factor is the ratio ofaverage power to peak demand. Utility
customers are sometimes penalized for low loadfactor that can occur when large amounts ofpower are used in short periods of time, insteadof at a steady rate for long periods of time.
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ElectronicsElectronics
Semiconductor
Diode:
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ElectronicsElectronics
Outputs From Simple
Diode Circuits:
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ElectronicsElectronics
SpecialTypes of Diodes:
Outputs From Simple Diode Circuits:
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ElectronicsElectronics
Bipolar Junction Transistor
Operating Regions
Bipolar Junction
Transistors:
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StandardsStandards
NEMA: National Electrical ManufacturersAssociation; www.nema.org NEMA, created in the fall of 1926 by the merger of the Electric Power
Club and the Associated Manufacturers of Electrical Supplies, providesa forum for the standardization of electrical equipment, enablingconsumers to select from a range of safe, effective, and compatibleelectrical products.
ANSI: American National Standards Institute;www.ansi.org The American National Standards Institute (ANSI) is a private,
non-profit organization that administers and coordinates the U.S.voluntary standardization and conformity assessment system
IEC: International Electrotechnical Commission. IEC is the authoritative worldwide body responsible for
developing consensus global standards in the electrotechnicalfield
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StandardsStandards
IEEE: Institute of Electrical and ElectronicEngineers; www.ieee.org The IEEE is a non-profit, technical professional association
for Electrical and Electronics Engineers.
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Power Distribution SystemsPower Distribution Systems
PowerDistribution Systems Consist of: MCC or Motor Control Centers
Loop Switches
Transformers
Voltage Regulators
Capacitor Banks Circuit Breakers
OCBs, Oil Circuit Breakers
Air Circuit Breakers
Disconnect Switches
Fuses
Starters and Combination Starters
PowerMonitoring and Control Systems
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Power Factor CorrectionPower Factor Correction
Bobby Rauf
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TopicsTopics
Power Factor, Definition, Conceptand Formulas
Power Factor Correction /Improvement Example
Additional Comments /Discussion on Power Factor
Power Factor and LossCalculation Example
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Fundamentals Of ElectricityFundamentals Of Electricity
Power Factor, Definition, Concept andFormula:
Definition: Power Factor is defined as the Ratioof Real Power (kW) to Apparent Power (kVA). It
is also defined as the quantity cos(U - J).PF = P/S orPF = cos(U - J),
where U is the angle of voltage V, where V =VRMS U
J is the angle of current i =IRMS J % PF = (PF) x 100
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Power Factor, contd.: Leading Power Factor:
Power factor is said to be leading when, J
the angle of the current, exceeds U, the angleof the voltage.In other words, (U - J) is negative.Impedance, Zc, due to pure capacitance
reactance, Xc, has a negative angle. Or, Zc =
Xc -90
Zc= Xc
-90=-j Xc
I
V U - J
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Power Factor, contd.: Lagging Power Factor:
Power factor is said to be lagging when, J the angleof the current, is less than U, the angle of the voltage.
In other words, (U - J) is positive.Impedance, Zl, due to pure inductive reactance, Xl,
has a positive angle. Or, Zl = Xl 90
In Inductive Circuits, add Capacitance, or
Capacitive Reactance, Xc, to offset the InductiveReactance, Xl, and to Increase the PF.
Zl = Xl +90=+j Xl
90Deg.
UV
I
V
V
I
Pf Angle
= U - J
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Power Factor, contd :
C = ( Q1 - Q2 )
2 T f V2
Where,C = Capacitance (F) required to reduce the
Reactive or Imaginary Power from Q1 to Q2Q1 = Initial, higher Reactive Power, in VARs
Q2 = Improved, lower Reactive Power, in VARsV = Voltage, in Volts
f = Frequency, in Hz
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