Module-1
Page 1: Introduction to Electrical Theory
Course Code: CE 228
Module Title: Engineering Utilities 1 - Electrical Theory.
Page 2: Quizzes and Problem Solving
Assessment Format:
Quiz 1: Problem Solving (Short & Long)
Quiz 2: Presentation
Page 3: Phenomenon of Electricity
Classical Theory
Flow of Electrons:
Electrons in inner shells: high attraction to nucleus, not easily released.
Electrons in outer shells: weaker attraction, more easily freed.
Energy addition can elevate electrons to higher shells; excessive energy can expel a valence electron, making it a free electron that contributes to electrical current flow.
Modern Theory
Flow of Charged Particles:
Electricity involves subatomic particles with positive or negative charges.
Only charged particles interact with electricity.
The electromagnetic force governs the flow of these particles, overcoming gravitational forces.
Law of Charges
Opposite charges attract; like charges repel.
Atoms with equal electrons and protons are neutral; imbalances lead to ions.
Positive ions: fewer electrons than protons.
Negative ions: more electrons than protons.
Page 4: Electrical Current
Definition: Flow of electric charge through a conductor.
Direction of flow: Negatively charged particles move from a negative to positive charge.
Speed of Flow: Actual particle movement is slow (~0.5 inches/sec), but the effect travels at light speed (~186,000 miles/sec).
Page 5: Producing Current Flow
Methods to Generate Current:
Static Electricity: Created by friction between materials, freeing surface electrons.
Thermoelectricity: Created by heating dissimilar metals (thermocouples).
Piezoelectricity: Generated when pressure deforms certain crystals, causing electron movement.
Electrochemistry: Produced from chemical reactions in solutions.
Photoelectricity: Caused by light photons freeing electrons in materials.
Magnetoelectricity: Generated by moving conductors through magnetic fields causing electron flow.
Page 6: Conductors, Insulators, and Semiconductors
Conductors: Materials that allow electrical current flow with minimal resistance.
Insulators: Materials that resist electricity movement, retaining electrons on their atoms (e.g., rubber, glass).
Semiconductors: Materials that behave as insulators at low temperatures and conductors when heated (e.g., silicon).
Page 7: Units of Electricity
Key Definitions
Voltage (V): Electrical pressure; higher voltage = increased current flow.
Current (A): Rate of charge flow, measured in amperes (1 A = 1 coulomb/second).
Resistance (Ω): Depends on conductor length, diameter, material type, and temperature. (Ohm’s Law: E=IR)
Power (W): Rate of energy transfer (P=EI).
Energy (Wh): Power consumed over time (q=Pt).
Page 8: Sample Problem
American Wire Gauge (AWG)
Conductors’ resistance varies inversely with AWG number.
#12 AWG copper:
100 ft: R = 0.162Ω
500 ft: R = 0.810Ω
#10 AWG copper:
100 ft: R = 0.102Ω
500 ft: R = 0.510Ω
Page 9: Sample Problem
Lamp Power Calculation:
Voltage (V) = 120V
Current (A) = 0.5A
Power (P) = EI = 120V x 0.5A = 60W.
Page 10: Electric Circuit
Definition
An interconnected path for electrical flow, also known as an electric network.
Components
Branches: Comprised of one or more elements in series.
Nodes: Points where branches meet.
Loops: Form closed paths.
Page 11: Circuit Configurations
Types of Circuits
Series: Components linked end-to-end.
Parallel: Components share the same voltage source.
Key Points
In parallel circuits, voltage remains equal while current adds up.
Page 12: Kirchoff’s Laws
Current Law
The total current entering a node equals the current leaving.
Voltage Law
The sum of voltage rises and drops in a closed loop equals zero.
Page 13: Electromagnetism
Induction: Voltage production when a conductor moves through a magnetic field or vice versa, causing current flow.
Page 14: DC and AC
Types of Current
Direct Current (DC): Flows in one direction.
Alternating Current (AC): Flows alternately in two directions.
Frequency
Measured in hertz (Hz), representing cycles per second.
Page 15: Ideal Transformer
Function
Transfers AC and voltage between circuits via induction.
Principle
For an ideal transformer, input power equals output power; VpIp = VsIs.
Page 16: Sample Problem
Transformer Calculation
Primary voltage (Vp) = 7200V; turns ratio = 30:1.
Building voltage: Vs = 7200V * (1/30) = 240V.
Current drawn by the building: Is = 225,000W / 240V = 937.5A.
Page 17: Impedance
Components
Inductors: Coils creating electromagnetic fields; phase lag in AC circuits.
Capacitors: Store electrostatic energy; phase lead in AC circuits.
Impedance (Z)
Resistance measure in AC circuits, incorporates resistance, inductance, and capacitance effects.
Page 18: Power Factor
Definitions
Real Power (W): Effective work accomplished (heat, light).
Reactive Power (VAR): Power for electromagnetic fields.
Apparent Power (VA): Total power encompassing both real and reactive power.
Power Factor (pf)
Ratio of real power to apparent power, indicating efficiency.
Page 19: Sample Problem
Power Factor Calculation
Real Power = 3,000W; Apparent Power = 3,600VA.
pf = 3000 / 3600 = 0.833 or 83.3%.
Phase angle Φ = cos⁻¹(0.833) = 33.6º.
Page 20: Sample Problem
Real Power Calculation
Voltage = 240V; Current = 10A; pf = 0.833.
PA = EI * pf = 240 V * 10 A * 0.833 = 1,999W.
Page 21: Power Factor Correction
Importance
Higher power factor reduces load currents, saving costs on equipment.
Correcting low power factors avoids penalties from power companies.
Page 22: Electrical Power System
Components:
Electrical consumers (commercial, industrial, domestic).
Electricity distribution via substations, transformers, and main transmission lines.
Page 23: Power Formulas Overview
DC and AC Power Formulas
Real Power (W), Apparent Power (VA), Current (A) calculations provided.
Page 24: Energy Costs Calculation
Example
Lamp Consumption: 60W for 24 hours/day, 30 days.
Total Energy = 43.2kWh; Cost = $5.06 at $0.1172/kWh.
Page 25: Large Residence Energy Charge
Cost Breakdown
Total charge calculation based on energy consumption and tiered pricing structure provided.
Page 26: Demand Charges
Pricing Structure
Detailed rates for service charge, energy charges, and scenario calculations.
Page 27: Demand Management Strategies
Load Shedding: Shutting off non-essential loads.
Load Shifting: Moving loads to off-peak hours.
Peak Shaving: Using storage and alternative energy to reduce peak demand.
Time-of-Use Rates: Incentives for reducing consumption during peak demand.