Fundamentals Of Electricity For Non-EE - Part 2.pdf · Fundamentals Of Electricity Power Factor : zDefinition: Power Factor is defined as the Ratio of Real Power (kW) to Apparent

Fundamentals Of ElectricityFundamentals Of Electricity

Simple DC Series Circuit,

Rt = R1+R2+R3

Simple DC Parallel Circuit,

Rt = (R1.R2.R3 ) /(R2.R1+R3.R2+R1 .R3)

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Electrical Engineering Fundamentals for Non-EEs; © B. Rauf


Simple AC Series Circuit,

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Simple AC Parallel Circuit,



Three Phase (AC) Transformer Configurations

Note:

a = Turns Ratio = Np/Ns


Impedance :Definition : Impedance is the current resisting and impeding characteristic of load or conductor in an AC Circuit.

Symbol for Impedance: Z Z = R + jXl - jXcWhere, jXl = Zl and, -jXc = Zc

Unit for Impedance: Ohms or Ωs.

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Ohms Law:Mathematical Statement of the Ohm’s Law:V = I R for DC circuitsV = I Z for AC CircuitsNote: BOLD letters, in general, represent

Vectoral quantities

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Impedance Impedance Calculation:Calculation:


Power :Definition: Power is defined as the capacity of a system to perform work or Rate of work performed by a system.Symbols and Types of Power:Pdc= V.I , in watts. Note: Pdc= PrealPapparent = S = Apparent Power (kVA) or Total AC

PowerPreal = P = Real Power Comp. of Apparent Power, in kWPreactive = Q = Reactive Comp. of App. Power in kVAR Pappent = (Preal)2 + (Preactive)2 orS= (P)2 +(Q)2

Magnitude of Total (3 ∅ ) Power = S= √3. VL.IL



Power Factor :Definition: Power Factor is defined as the Ratio of Real Power (kW) to Apparent Power (kVA). It is also defined as the quantity cos(θ - φ).

PF = P/S orPF = cos(θ - φ),

where θ is the angle of voltage V, where V = VRMS ∠ θφ is the angle of current i = I RMS ∠ φ

Note: Detailed discussion on the topic of Power Factor is covered under the Power Factor segment of this seminar.

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Voltage Regulation:Definition: Real voltage sources are unable

to hold the voltage constant as they assume a significant amount of load (Resistance or Impedance). This results in the difference between 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. The formula for Service Factor is as follows:Service Factor = Safe Load / Nameplate Load

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Classifications of Motors:Motor categorization by NEMA, National Electrical Manufacturers Association:

Speed:Constant SpeedAdjustable SpeedMultispeedVarying Speed

Service Classification: General DefiniteSpecial PurposeVarying Speed

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Classifications of Motors, contd.:

Motor Class is determined by the maximum allowable operating temperature of the motor, which is dependant on the type/grade of insulation used in the motor.

Class A: 105° CClass B: 130° CClass F: 155° CClass H: 180° C

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Kirchhoff’s Voltage Law (KVL):Algebraic sum of voltage drops around

any closed path, within a circuit, is equal to the sum of voltages presented by all of the voltage sources. The mathematical representation of KVL is as follows:Σ VDrops = Σ VSource

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Kirchhoff’s Current Law (KCL):

Total current flowing into a node is equal to the total current that flows out of the node. The mathematical representation of KCL is as follows:

Σ iin = Σ iout

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Motor Speed Calculation:

Given: Number of Poles = P = 4Frequency of AC Power Supply to the Motor, in Hertz = f = 60

HzSpeed, 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 100Synchronous 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-load conditions. A common four-pole motor with a synchronous speed of 1,800 rpm may have a no-load speed of 1,795 rpm and a full-load speed of 1,750 rpm. The rate-of-change of slip is approximately linear from 10% to 110% load, when all other factors such as temperature and voltage are held constant. Motors with slip over 5% are used for hard to start applications.

The direction of rotation of a polyphase ac induction motor depends on the connection of the stator leads to the power lines. Interchanging any two input leads reverses rotation.



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 a force of one pound to turn at steady rate. The torque required would be one pound times one foot or one foot-pound.

Horsepower, i .e. Power, is defined as the rate at which work is performed or rate at which torque is produced.

In the wheel cranking example above, if one were to crank the wheel twice as fast, the torque remains the same but the power and horsepower delivered would double, regardless of how fast the crank is turned, as long as the crank 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 EnvironFundamentals Of Electricity in Industrial and Commercial Environmentment

Motor Power – Line Current Calculation:

Motor Nameplate Information:Power rating, in HP (Horse Power) = P = 10 HPVoltage Rating = 480 VACNo. of Phases = 3; also stated as 3 ∅Power Factor = PF = 0.8Efficiency = Eff. = 0.9Magnitude 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 demand interval. Electric utilities charge commercial and industrial 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 of average power to peak demand. Utility customers are sometimes penalized for low load factor that can occur when large amounts of power are used in short periods of time, instead of 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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Special Types of Diodes:

Outputs From Simple Diode Circuits:


Bipolar Junction Transistor Operating Regions

Bipolar Junction Transistors:

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StandardsStandards

NEMA: National Electrical Manufacturers Association; 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, provides a forum for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical 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 Electronic Engineers; 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

Power Distribution Systems Consist of:MCC or Motor Control CentersLoop SwitchesTransformersVoltage RegulatorsCapacitor BanksCircuit Breakers– OCB’s, Oil Circuit Breakers– Air Circuit Breakers

Disconnect SwitchesFusesStarters and Combination Starters Power Monitoring and Control Systems

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Power Factor CorrectionPower Factor Correction

Bobby Rauf ©

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Electrical Engineering Fundamentals for Non-EE's; © B. Rauf

Topics Topics

Power Factor, Definition, Concept and FormulasPower Factor Correction / Improvement ExampleAdditional Comments / Discussion on Power FactorPower Factor and Loss Calculation Example

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Power Factor, Definition, Concept and Formula:Definition: Power Factor is defined as the Ratio of Real Power (kW) to Apparent Power (kVA). It is also defined as the quantity cos(θ - φ).

PF = P/S orPF = cos(θ - φ),

where θ is the angle of voltage V, where V = VRMS ∠ θφ is the angle of current i = I RMS ∠ φ% PF = (PF) x 100

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Power Factor, contd.:Leading Power Factor:

Power factor is said to be leading when, φthe angle of the current, exceeds θ, the angle of the voltage.In other words, (θ - φ) is negative.Impedance, Zc, due to pure capacitance reactance, Xc, has a negative angle. Or, Zc = Xc ∠ -90

Zc= Xc ∠ -90=-j Xc

I

Vθ - φ

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Power Factor, contd.:Lagging Power Factor:

Power factor is said to be lagging when, φ the angle of the current, is less than θ, the angle of the voltage.In other words, (θ - φ) 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 Inductive Reactance, Xl, and to Increase the PF.

Zl = Xl ∠ +90=+j Xl

90 Deg.

θV

I

V

V

I

Pf Angle = θ - φ


Power Factor, contd :

C = ( Q1 - Q2 )2 π f V2

Where, C = Capacitance (F) required to reduce the

Reactive or Imaginary Power from Q1 to Q2 Q1 = Initial, higher Reactive Power, in VARsQ2 = Improved, lower Reactive Power, in VARsV = Voltage, in Voltsf = Frequency, in Hz

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Fundamentals Of Electricity For Non-EE - Part 2.pdf · Fundamentals Of Electricity Power Factor : zDefinition: Power Factor is defined as the Ratio of Real Power (kW) to Apparent

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