Fundamentals Of Electricity

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Fundamentals Of Electricity. Simple DC Series Circuit, . R t = R 1 +R 2 +R 3. Simple DC Parallel Circuit, . R t = (R 1 .R 2 .R 3 ) /(R 2 .R 1 +R 3 .R 2 +R 1 .R 3 ) . Fundamentals Of Electricity. Simple AC Series Circuit, . Simple AC Parallel Circuit, . Fundamentals Of Electricity.

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## Fundamentals Of Electricity

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Fundamentals Of Electricity

Simple DC Series Circuit,

Rt = R1+R2+R3

Simple DC Parallel Circuit,

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

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

Fundamentals Of Electricity

Simple AC Series Circuit,

Simple AC Parallel Circuit,

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

Fundamentals Of Electricity

Three Phase (AC) Transformer Configurations

Note:

a = Turns Ratio = Np/Ns

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

Fundamentals Of Electricity

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 - jXc

Where, jXl = Zl and, -jXc =Zc

• Unit for Impedance: Ohms or s.

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

Fundamentals Of Electricity

Ohms Law:

• Mathematical Statement of the Ohm’s Law:

V= I Rfor DC circuits

V = I Z for AC Circuits

Note:BOLD letters, in general, represent Vectoral quantities

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

Impedance Calculation:

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

Fundamentals Of Electricity

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= 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 orS= (P)2+(Q)2
• Magnitude of Total (3  ) Power = S= 3. VL.IL

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

Fundamentals Of Electricity

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( - ).

PF = P/S or

PF = cos( - ),

• where  is the angle of voltage V, whereV = VRMS 
•  is the angle of current i = I RMS 

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

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

Fundamentals Of Electricity

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:

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

Fundamentals Of Electricity

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:

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Fundamentals Of Electricity

Classifications of Motors:

• Motor categorization by NEMA, National Electrical Manufacturers Association:
• Speed:
• Constant Speed
• Multispeed
• Varying Speed
• Service Classification:
• General
• Definite
• Special Purpose
• Varying Speed

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Fundamentals Of Electricity

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 C
• Class B: 130 C
• Class F: 155 C
• Class H: 180 C

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Fundamentals Of Electricity

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:

 VDrops =  VSource

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Fundamentals Of Electricity

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:

 iin =  iout

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

Fundamentals Of Electricity

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

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

Fundamentals Of Electricity

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-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.

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

Fundamentals Of Electricity

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.

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

Fundamentals Of Electricity

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)

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

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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Fundamentals Of Electricity

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.

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

Electronics

Semiconductor Diode:

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

Electronics

Outputs From Simple Diode Circuits:

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

Outputs From Simple Diode Circuits:

Electronics

Special Types of Diodes:

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

Electronics

Bipolar Junction Transistors:

Bipolar Junction Transistor Operating Regions

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

Standards
• 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 electrotechnical field

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

Standards
• IEEE: Institute of Electrical and Electronic Engineers; www.ieee.org
• The IEEE is a non-profit, technical professional association for Electrical and Electronics Engineers.

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

Power Distribution Systems

Power Distribution Systems Consist of:

• MCC or Motor Control Centers
• Loop Switches
• Transformers
• Voltage Regulators
• Capacitor Banks
• Circuit Breakers
• OCB’s, Oil Circuit Breakers
• Air Circuit Breakers
• Disconnect Switches
• Fuses
• Starters and Combination Starters
• Power Monitoring and Control Systems

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

### Power Factor Correction

• 1

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

3/10/2014

Topics

Power Factor, Definition, Concept and Formulas

Power Factor Correction / Improvement Example

Power Factor and Loss Calculation Example

• 2

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

3/10/2014

Fundamentals Of Electricity

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( - ).

PF = P/S or

PF = cos( - ),

where  is the angle of voltage V, whereV = VRMS 

 is the angle of current i = I RMS 

% PF = (PF) x 100

• 3

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

3/10/2014

Fundamentals Of Electricity

Power Factor, contd.:

Power factor is said to be leading when,  the angle of the current, exceeds , the angle of the voltage.

In other words, ( - ) is negative.

Impedance, Zc, due to pure capacitance reactance, Xc, has a negative angle. Or, Zc = Xc  -90

I

Zc= Xc  -90=-j Xc

 - 

V

• 4

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3/10/2014

Fundamentals Of Electricity

Power Factor, contd.:

Lagging Power Factor:

Power factor is said to be lagging when,  the angle of the current, is less than , the angle of the voltage.

In other words, ( - ) 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.

V

Zl= Xl  +90=+j Xl

Pf Angle

=  - 

I

V

90 Deg.

I

• 5

V

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

3/10/2014

Fundamentals Of Electricity

Power Factor, contd :

C = ( Q1 - Q2 )

2  f V2

Where,

C = Capacitance (F) required to reduce the

Reactive or Imaginary Power from Q1 toQ2

Q1 = Initial, higher Reactive Power, in VARs

Q2 = Improved, lower Reactive Power, in VARs

V = Voltage, in Volts

f = Frequency, in Hz

• 6

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3/10/2014