Basic Electrical Eng

8/3/2019 Basic Electrical Eng

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1/13/2012Electrical Engineering Fundamentals for Non-EEs; B. Rauf10

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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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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Outputs From Simple

Diode Circuits:


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SpecialTypes of Diodes:

Outputs From Simple Diode Circuits:


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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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1/13/2012Electrical Engineering Fundamentals for Non-EE's; B. Rauf 1

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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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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