Electromagnetic Waves (EX-603 (C)) - Unit 5 Short Notes

UNIT 5: APPLICATIONS OF ELECTRICAL ENERGY & ENERGY MANAGEMENT

I. ILLUMINATION ENGINEERING

A. Fundamental Laws of Illumination

• Inverse Square Law: Illuminance \( E \) at a point on a surface is inversely proportional to the square of the distance \( d \) from the source.

$$ E = \frac{I}{d^2} \cos \theta $$

where \( I \) = candle power (cd), \( \theta \) = angle between normal to surface and direction to source.

• Lambert's Cosine Law: Illuminance on a surface is proportional to the cosine of the angle of incidence \( \theta \).

$$ E \propto \cos \theta $$

For a diffusing surface, intensity \( I_\theta = I_0 \cos \theta \).

[!TIP]

Combine both: \( E = \frac{I_0 \cos^3 \theta}{d^2} \) for a point source on an inclined plane. Common mistake: forgetting \( \cos \theta \) for surface orientation.

B. Illumination Design Methodology

• Required Illumination Level (E): Specified in lux (lumens/m²) based on task.

• Key Factors:

  • Room dimensions: Length \( l \), width \( w \), mounting height \( h \) above workplane.

  • Space-Height Ratio (SHR): \( \text{SHR} = \frac{\text{Maximum spacing between lamps}}{h} \). Determines number of rows.

  • Utilization Factor (UF): Fraction of emitted lumens reaching workplane (from manufacturer's tables, depends on room reflectances, SHR).

  • Maintenance Factor (MF): Accounts for dirt, lamp depreciation (typical 0.7–0.8).

  • Candle Power Deposition: Often synonymous with Light Loss Factor (LLF) = UF × MF. "Deposition of 20%" likely means 80% effective (MF = 0.8).

• Number of Lamps:

$$ N = \frac{E \times A}{\Phi \times \text{UF} \times \text{MF}} $$

where \( A \) = area (m²), \( \Phi \) = lumens per lamp.

• Layout: Determine rows from SHR, then lamps per row from spacing.

C. Point Source Illumination Calculations

• Directly under lamp (\( \theta = 0 \)):

$$ E = \frac{I}{h^2} $$

• At intermediate point (multiple sources): Use superposition principle—sum illuminance from all sources.

  For two lamps separated by distance \( s \), at point on ground:

$$ E = \frac{I_1}{d_1^2} \cos \theta_1 + \frac{I_2}{d_2^2} \cos \theta_2 $$

where \( d_i \) = distance from lamp to point, \( \theta_i \) = angle of incidence (for horizontal surface, \( \cos \theta_i = h/d_i \)).

D. Energy-Efficient Lighting Technologies

[!TIP]

LED dominates due to high efficacy, long life, instant start, dimmability. CRI > 80 for indoor visual comfort.

II. ELECTRICAL HEATING SYSTEMS

A. General Advantages and Losses

• Advantages: Clean, quiet, controllable, high efficiency (90–95%), no combustion byproducts.

• Losses: Conduction (through insulation), convection (to air), radiation (unintended).

B. Resistance Heating

• Principle: \( P = I^2 R = \frac{V^2}{R} \). Heat generated by current through resistor.

• Applications: Toasters, space heaters, furnaces.

• Numerical Example: Two 100 Ω elements in parallel/series from 250 V.

  • Parallel: \( R_{eq} = 50 \Omega \), \( P = \frac{250^2}{50} = 1250 \text{ W} \).

  • Series: \( R_{eq} = 200 \Omega \), \( P = \frac{250^2}{200} = 312.5 \text{ W} \).

C. Induction Heating

• Operating Principle: Alternating magnetic field induces eddy currents in conductive workpiece → Joule heating. Also hysteresis loss in magnetic materials.

• Skin Effect: High-frequency current flows near surface; depth \( \delta = \sqrt{\frac{\rho}{\pi f \mu}} \).

• Types:

  | Type | Frequency | Applications | |----------------|---------------|------------------------------------------| | Radio Frequency (RF) | 100–500 kHz | Surface hardening, soldering | | Medium Frequency (MF) | 1–10 kHz | Melting, through heating | | High-Frequency (HF) | 10–100 kHz | Precision hardening, semiconductor |

• Applications: Melting metals, heat treatment, brazing.

• Limitations: Only conductive materials, high initial cost, radio interference.

D. Other Heating Methods

• Dielectric Heating: High-frequency electric field heats non-conductors (wood, plastics). Uses RF waves.

• Arc Heating: Electric arc (3000–10,000°C) for steelmaking, welding.

III. ELECTROCHEMICAL PROCESSES

A. Laws of Electrolysis

• Faraday's First Law: Mass deposited \( m \propto Q \) (charge).

$$ m = Z Q = Z I t $$

where \( Z \) = electrochemical equivalent (kg/C), \( I \) = current (A), \( t \) = time (s).

• Faraday's Second Law: For same charge, masses \( \propto \) equivalent weights.

$$ Z = \frac{M}{n F} $$

where \( M \) = atomic mass, \( n \) = electrons per atom, \( F \) = Faraday constant (96,500 C/mol).

B. Electroplating and Electrodeposition

• Purpose: Corrosion resistance, wear resistance, aesthetics, conductivity.

• Process:

  • Anode: Metal to be deposited (e.g., gold).

  • Cathode: Workpiece.

  • Electrolyte: Solution containing metal ions (e.g., gold cyanide).

C. Numerical Problems

• Weight deposited:

$$ m = \frac{I \cdot t \cdot M}{n \cdot F} $$

Example: Gold (Au, \( M = 197 \), \( n = 1 \)), \( I = 3 \text{ A} \), \( t = 30 \times 60 \text{ s} \):

$$ m = \frac{3 \times 1800 \times 197}{1 \times 96500} = 11.62 \text{ g} $$

IV. WELDING TECHNOLOGIES

A. Classification of Welding Processes

B. Arc Welding and Resistance Welding

• Arc Welding: Consumable/non-consumable electrode, arc melts base & filler metal. Shielding gas/flux protects weld pool.

• Resistance Welding: Pressure + current → heat at interface. Spot welding: two electrodes, local melting. Seam welding: rotating wheels for continuous weld.

C. Advanced Welding Methods

• Electron Beam Welding (EBW): Focused high-velocity electron beam in vacuum → deep penetration, no filler. Used in aerospace, nuclear.

• Laser Beam Welding: Focused laser beam, high speed, automation. Used in automotive, electronics.

D. Welding Transformers and Power Sources

• Characteristics: Drooping V-I characteristic (high voltage at low current, low voltage at high current) stabilizes arc.

• Types:

  • AC transformers (step-down, high current).

  • DC rectifier-type (smoother arc, better control).

V. ELECTRIC TRACTION AND ELECTRIC VEHICLES

A. Train Motion and Speed-Time Curves

• General Speed-Time Curve (Main-line Service):

  • Acceleration (\( t_1 \)) → Constant speed (\( t_2 \)) → Coasting (\( t_3 \)) → Braking (\( t_4 \)).

  • Trapezoidal Curve: Simplest; assumes constant acceleration/retardation.

• Derivation of Maximum Speed:

  Let \( \alpha \) = acceleration (m/s²), \( \beta \) = retardation (m/s²), \( D \) = distance between stops (m).

  Distance covered:

$$ D = \frac{1}{2} \alpha t_1^2 + V_{\max} t_2 + \frac{V_{\max}^2}{2\beta} + \frac{1}{2} \alpha t_4^2 \text{ (if symmetric)} $$

For symmetric acceleration/braking (\( t_1 = t_4 \)):

$$ D = V_{\max} \left( t_2 + \frac{V_{\max}}{2} \left( \frac{1}{\alpha} + \frac{1}{\beta} \right) \right) $$

Solve quadratic for \( V_{\max} \).

B. Train Resistance and Weights

• Dead Weight (\( W_d \)): Actual weight of train.

• Acceleration Weight (\( W_a \)): \( W_a = W_d + \frac{W_d}{g} \cdot \alpha \) (rotating parts effect).

• Train Resistance Components:

  • Rolling resistance: \( r_r = a + bV \) (N/tonne).

  • Gradient resistance: \( r_g = g\% \times 9.81 \) (N/tonne).

  • Wind resistance: \( r_w = c V^2 \) (N/tonne).

• Specific Energy Consumption (SEC): kWh/tonne-km. Lower SEC = efficient.

C. Electrical Braking Methods

[!TIP]

Regenerative braking most efficient; dynamic simplest but wastes energy as heat.

D. Traction Motors

• DC Series Motor:

  • High starting torque (\( T \propto I_a^2 \)).

  • Speed-Torque: \( N \propto \frac{V - I_a R}{I_a} \) → speed drops sharply with load.

  • Self-protecting under overload.

• Others: AC induction (robust, low maintenance), PMSM (high efficiency, compact).

E. Electric Vehicle (EV) Systems

• Components:

  • Battery: Li-ion (high energy density).

  • Motor Controller: Inverter (DC to AC for AC motors).

  • Drive Motor: AC induction or PMSM.

  • Charger: On-board/off-board.

  • Transmission: Usually single-speed (motor wide speed range).

F. Hybrid Electric Vehicles (HEVs)

G. Load Equalization

• Need: Reduce peak demand from traction (high current during acceleration).

• Methods:

  • Flywheel: Stores kinetic energy during braking, releases during acceleration.

  • Motor-Generator Set: Stores energy in rotating inertia or battery.

VI. ENERGY AUDIT AND MANAGEMENT PRINCIPLES

A. Energy Audit

• Definition: Systematic examination of energy use to identify savings opportunities.

• Types:

  • Preliminary: Walk-through, identifies obvious ECOs.

  • Detailed: Measurements, data logging, detailed analysis.

  • Investment-Grade: Financial analysis, ROI, for major projects.

• Significance: Reduces costs, emissions, improves productivity.

• Procedure:

  1. Define audit scope.

  2. Collect data (energy bills, equipment inventory).

  3. Measure/analyze.

  4. Identify ECOs.

  5. Evaluate economics.

  6. Report & implement.

B. Role of Energy Manager

• Qualities: Technical knowledge, analytical, communication, project management.

• Functions:

  • Develop energy policy.

  • Monitor consumption.

  • Identify ECOs.

  • Train staff.

  • Ensure compliance.

• Responsibilities: Regular reporting, budget management, vendor evaluation.

C. Thermodynamic Laws in Energy Conservation

• First Law (Energy Balance):

$$ \Delta U = Q - W $$

Energy conserved; identify losses (e.g., exhaust heat).

• Second Law (Entropy):

$$ \Delta S \ge 0 \text{ (isolated system)} $$

Exergy analysis: maximum useful work. Example: Heat engine efficiency \( \eta \le 1 - \frac{T_c}{T_h} \). Real systems have irreversibilities (friction, heat loss).

[!TIP]

Second law explains why 100% energy conversion impossible; focus on reducing exergy destruction.

D. Thermal Energy Audit in HVAC Systems

• Scope:

  • Chillers (COP, part-load efficiency).

  • Pumps (affinity laws: \( P \propto N^3 \)).

  • Fans (VFD potential).

  • Distribution (insulation, leaks).

• ECOs:

  • Optimize setpoints (temperature, humidity).

  • Install VFDs.

  • Improve insulation.

  • Heat recovery wheels.

E. Load Curve Analysis and Demand Side Management (DSM)

• Load Curve: Plot of load (kW) vs. time (usually 24h).

  • Peak Demand: Maximum load.

  • Load Factor: \( \frac{\text{Average load}}{\text{Peak load}} \). Higher = better utilization.

• DSM Techniques:

  • Time-of-Use (TOU) Pricing: Different rates for peak/off-peak.

  • Load Shifting: Move non-urgent loads to off-peak.

  • Peak Clipping: Reduce load during peak (e.g., cycling AC).

  • Energy Efficiency: Permanent reduction via efficient equipment.

F. Electricity Tariff Structures

G. Maintenance Strategies

• Preventive Maintenance: Scheduled (time-based) servicing.

• Predictive Maintenance: Condition-based (vibration, thermography, oil analysis).

• Role: Prevents efficiency degradation (e.g., dirty coils, misalignment), extends life, reduces failures.

VII. ENERGY-EFFICIENT TECHNOLOGIES AND PRACTICES

A. Motors and Drives

• Energy-Efficient Motors (IE3/IE4):

  • Higher grade steel, optimized design, better cooling.

  • Loss reduction: core (thin laminations), stator/rotor (larger cross-section), friction (better bearings).

• Variable Speed Drives (VSD):

  • Types: VFD (voltage/frequency control for AC), slip power recovery (wound rotor induction).

  • Benefits: Energy savings at part-load (affinity laws), process control, soft start.

  • Selection: Match load torque-speed profile, consider harmonics.

B. Power Factor Management

• Causes of Poor PF:

  • Inductive loads (motors, transformers) → lagging PF.

  • Harmonic currents (non-linear loads) → distorted PF.

• Disadvantages:

  • Increased current → higher \( I^2R \) losses.

  • Reduced system capacity.

  • Penalty tariffs.

• Improvement Methods:

  • Shunt Capacitors: Most common; supply leading current.

  • Synchronous Condensers: Over-excited synchronous motor.

  • Phase Advancers: For induction motors.

  • Active PF Correction: For harmonics.

C. Energy Conservation in Buildings

• Housekeeping: Switch off idle equipment, regular cleaning (heat exchangers, filters), fix leaks.

• HVAC Optimization:

  • Setback temperatures (e.g., 18°C winter night).

  • Zonal control.

  • Economizer cycles (use outdoor air).

• Lighting: Use LEDs, daylight harvesting, occupancy sensors.

• Electrical Load for AC:

  • Calculate cooling load (sensible + latent).

  • Apply diversity factor: \( \text{Total Connected Load} \times \text{Demand Factor} / \text{Diversity Factor} \).

D. Energy-Efficient Housekeeping

• Simple operational changes with quick payback (<1 year):

  • Turn off lights/equipment when not needed.

  • Clean condenser coils, air filters.

  • Maintain proper refrigerant charge.

  • Seal air leaks in ducts.

VIII. CO-GENERATION AND WASTE HEAT RECOVERY

A. Co-generation (Combined Heat and Power – CHP)

• Principle: Generate electricity and useful thermal energy (steam, hot water) from same fuel.

• Benefits:

  • Fuel savings 20–50% vs. separate generation.

  • Reduced emissions.

  • Increased reliability.

• Configurations:

  | Type | Description | Application | |----------------------------|----------------------------------------------|------------------------------| | Back Pressure Turbine | Steam expanded to process pressure; no condenser | Constant heat demand | | Extraction-Condensing | Steam extracted at intermediate pressure; rest condensed | Variable heat/power ratio | | Double Extraction Back Pressure | Two extractions for two process levels | Multiple temperature levels |

B. Waste Heat Recovery

• Sources: Exhaust gases (200–600°C), cooling water (30–60°C), process streams.

• Techniques:

  • Waste Heat Boiler: Generate steam from exhaust.

  • Economizer: Preheat feedwater using flue gas.

  • Heat Exchanger: Recover heat between streams.

  • Thermoelectric Generators (TEG): Seebeck effect (direct heat→electricity), low efficiency.

• Applications: Preheating combustion air, feedwater, space heating.

IX. INDUSTRIAL ENERGY CONSERVATION

A. Industry-Specific Conservation

• Cement Industry:

  • Kiln optimization (temperature profile, length).

  • Preheater/precalciner to reduce kiln load.

  • Waste heat recovery from preheater exhaust, cooler vent.

• Sugar Industry:

  • Cogeneration from bagasse (high-pressure boilers, turbo-generator).

  • Multiple-effect evaporation with vapor bleeding.

  • Efficient drives for mills.

• Textile Industry:

  • Efficient motors with VFDs.

  • HVAC optimization (humidification, temperature).

  • Waste heat recovery in dyeing (drying, washing).

B. Biomass and Agricultural Waste Utilization

• Conversion Methods:

  • Direct combustion (boilers).

  • Biogas (anaerobic digestion of manure, crop residue).

  • Biofuels (ethanol from sugarcane, biodiesel from oilseeds).

• Role: Renewable, reduces fossil fuel use, waste management.

C. Process Optimization and Material Balance

• Material Load Energy Balance Diagram: Track energy input/output with material flow.

• Identify Losses: Inefficient heat transfer, leaks, standby losses.

• Lubrication Innovations: Low-friction coatings, synthetic oils → reduce friction losses in bearings, gears.

X. ENERGY ANALYSIS TOOLS AND ECONOMIC EVALUATION

A. Energy Auditing Instruments

• Power Analyzer: Voltage, current, power factor, harmonics.

• Infrared Camera: Thermal imaging for insulation leaks, hot spots.

• Lux Meter: Illumination levels.

• Flue Gas Analyzer: O₂, CO, CO₂, stack temperature → combustion efficiency.

• Data Loggers: Record parameters over time.

B. Energy Analysis Tools

• Energy Flow Networks (Sankey Diagrams): Visualize energy inputs, outputs, losses.

• Matrix Charts: Prioritize ECOs by cost, savings, payback.

• Load Energy Balance Diagrams: Energy in/out for a process.

C. Project Evaluation Methods

• Payback Period (PBP):

  • Simple: \( \text{PBP} = \frac{\text{Initial Investment}}{\text{Annual Savings}} \).

  • Discounted: Accounts for time value of money; solve for \( n \) where \( \sum \frac{S_t}{(1+i)^t} = I \).

• Depreciation:

  • Straight-Line: \( \text{Annual Depreciation} = \frac{I - S}{n} \).

  • Written-Down Value (Declining Balance): \( D_t = (I - \text{Accumulated Depreciation}) \times d \), where \( d = 1 - \sqrt[n]{\frac{S}{I}} \).

D. Risk and Financial Analysis

• Cost-Benefit-Risk: Evaluate ECOs beyond payback (NPV, IRR).

• Inflation Impact: Increases future costs, reduces real savings. Use real discount rate: \( (1+i) = (1+r)(1+f) \).

• Simulation: Monte Carlo for uncertainty in energy prices, savings.

XI. MISCELLANEOUS APPLICATIONS

A. Electrical Load Calculations

• For Air Conditioning:

  • Cooling load (kW) = Sensible + Latent heat.

  • Apply diversity factor: \( \text{Total Load} = \frac{\sum (\text{Connected Load} \times \text{Demand Factor})}{\text{Diversity Factor}} \).

B. Selection of Electric Drives

• Advantages over other drives: Quick start/stop, remote control, regenerative braking, precise speed control.

• Selection Factors:

  • Load torque-speed characteristic (constant torque, variable torque).

  • Duty cycle (continuous, intermittent).

  • Environment (hazardous, clean).

  • Cost, efficiency, maintenance.

• Group Drive vs. Individual Drive:

  • Group: One motor for multiple machines → lower cost, but less flexible, single point failure.

  • Individual: Each machine has motor → flexible, efficient, but higher cost.

C. Special Topics

• Simulation and Modeling: Software (e.g., EnergyPlus, RETScreen) to predict energy use, savings, ROI.

• Energy Flow Networks: Sankey diagrams showing energy transformations and losses; identify major loss sources.

• Matrix Charts: Prioritize ECOs by criteria (cost, savings, complexity).