Electromagnetic Waves (EX-603 (C)) - Unit 4 Short Notes

UNIT 4: UTILIZATION OF ELECTRICAL ENERGY AND ENERGY MANAGEMENT

(Based on past exam analysis for EX-603(C) Electromagnetic Waves)

A. ILLUMINATION ENGINEERING

1. Basic Photometry

[!TIP]

Common Confusion:

• Illuminance (lux) = light falling on a surface.

• Luminance (cd/m²) = light leaving a surface (brightness).

2. Fundamental Laws of Illumination

• Inverse Square Law:

$$E \propto \frac{I}{d^2}$$

Illuminance varies inversely with square of distance from a point source.

$$\boxed{E = \frac{I}{d^2}}$$

• Lambert's Cosine Law:

$$E \propto \cos\theta$$

Illuminance on a surface is proportional to cosine of angle of incidence.

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

[!NOTE]

For a surface tilted at angle $\theta$, effective illuminance combines both laws.

3. Lighting Design Calculations

Key Parameters:

• Required Illuminance Level ($E$): Specified in lux for the task.

• Utilization Factor (UF): Fraction of luminous flux reaching the working plane (0.4–0.8).

• Maintenance Factor (MF): Accounts for dirt, aging (0.6–0.9). Depreciation Factor (DF) = $1/\text{MF}$.

• Candle Power (CP) per Lamp:

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

where $A$ = area, $N$ = number of lamps.

• Spacing-to-Height Ratio (SHR):

$$\text{Spacing} = \text{SHR} \times \text{Mounting Height}$$

Ensures uniform illuminance (typical SHR = 0.7–1.5).

Example (Past Paper):

Room: 60 m × 15 m, $$\displaystyle E = 100 $$ lux, $$\displaystyle h = 4 $$ m, UF = 0.5, MF = 0.8 (20% depreciation).

• Area $$\displaystyle A = 900 $$ m² → Total flux $$\displaystyle \Phi_{\text{total}} = E \times A = 90,000 $$ lm.

• Assume SHR = 1.5 → Spacing = $$\displaystyle 1.5 \times 4 = 6 $$ m.

• Lamps along length: $$\displaystyle 60/6 = 10 $$; along width: $$\displaystyle 15/6 = 2.5 \rightarrow 3 $$.

• Total lamps $$\displaystyle N = 10 \times 3 = 30 $$.

• Flux per lamp: $$\displaystyle \Phi_{\text{lamp}} = \frac{90,000}{30 \times 0.5 \times 0.8} = 7,500 $$ lm.

• Candle power per lamp (assuming downward only): $$\displaystyle I \approx \frac{\Phi_{\text{lamp}}}{2\pi} \approx 1,194 $$ cd.

4. Types of Lighting Schemes

5. Design Considerations

• Illuminance Uniformity: Ratio $$\displaystyle E_{\text{min}}/E_{\text{avg}} > 0.7 $$.

• Glare Index: Unified Glare Rating (UGR) < 19 for comfort.

• Color Rendering Index (CRI): >80 for accurate color perception.

• Mounting Height: Affects spacing and uniformity.

6. Energy-Efficient Lighting

• LEDs: High efficacy (100–150 lm/W), long life, instant start.

• CFLs: 50–70 lm/W, contain mercury (disposal issues).

• Electronic Ballasts: Reduce losses, no flicker, enable dimming.

• Occupancy Sensors: Turn off lights in unoccupied zones.

• Daylight Harvesting: Adjust artificial light based on natural light.

[!TIP]

Exam Focus: Compare LED vs CFL in terms of efficacy, lifetime, environmental impact.

B. ELECTRIC HEATING AND WELDING

1. Electric Heating Methods

Advantages of Electric Heating:

• Clean, no combustion products.

• Precise control, fast response.

• High efficiency (90–95%).

• No moving parts, low maintenance.

Losses in Heating Systems:

• Radiation/convection from hot surfaces.

• Heat loss through insulation.

• Stray losses in induction.

2. Induction Heating (Detailed)

• Principle: Alternating magnetic field induces eddy currents in conductive workpiece → $$\displaystyle I^2R $$ heating. Also hysteresis loss in magnetic materials.

• Frequency Selection:

$$\delta = \sqrt{\frac{\rho}{\pi f \mu}}$$

where $\delta$ = depth of penetration, $\rho$ = resistivity, $\mu$ = permeability.

• High $f$ → shallow heating (surface hardening).

• Low $f$ → deep heating (melting).

• Furnace Types:

  | Type | Core | Typical Use | |----------|----------|-----------------| | Core-type | Magnetic core | Melting non-ferrous metals | | Coreless | No core (crucible) | Melting steel, precious metals |

• Applications:

  • Melting (foundries).

  • Surface hardening.

  • Soldering/brazing.

  • Annealing.

• Advantages: Rapid, localized, no contact → no contamination.

• Limitations: High initial cost, limited to conductive materials, skin effect.

3. Welding Process Classification

4. Welding Equipment

• Welding Transformers:

  • Drooping V-I characteristic (stable arc).

  • Types: Rectifier (AC→DC), Inverter (high-frequency AC→DC→HF AC).

• Welding Generators: DC output, used where no AC supply.

• Accessories: Electrodes (coated, bare), gas cylinders (Ar, CO₂), wire feeders.

5. Electrochemical Processes

• Faraday's Laws:

  1. Mass deposited proportional to charge: $$\displaystyle m \propto Q = I t $$.

  2. For same $Q$, masses $\propto$ chemical equivalents.

$$\boxed{m = Z \cdot I \cdot t}$$

where $Z$ = electrochemical equivalent (g/C or kg/A·s).

• Electroplating: Deposit metal layer for corrosion resistance, appearance, wear resistance.

• Electroforming: Make precise metal molds.

• Electrowinning: Extract metal from solution (e.g., copper, zinc).

Example (Past Paper):
$$\displaystyle m = ? $$, $$\displaystyle I = 3 $$ A, $$\displaystyle t = 30 $$ min = 1800 s, $$\displaystyle Z = 0.065 $$ mg/A·s (typical for gold ≈ 0.068 mg/A·s).

$$m = 0.065 \times 3 \times 1800 = 351 \text{ mg} = 0.351 \text{ g}$$

6. Welding Transformers (Dedicated)

Requirements:

• High current (100–1000 A), low voltage (15–50 V).

• Drooping characteristic: Voltage decreases as current increases → stable arc.

• Portable, robust, with thermal protection.

C. ELECTRIC TRACTION AND ELECTRIC VEHICLES

1. Fundamentals of Electric Traction

• Advantages over Steam/Diesel:

  • High efficiency (70–80% vs 25–30%).

  • No local pollution, regenerative braking possible.

  • Smooth acceleration, high starting torque.

  • Lower maintenance.

• Types:

  • DC Traction: 600/750 V third rail or overhead.

  • AC Traction: 15–25 kV overhead, 50 Hz.

  • Diesel-Electric: Diesel engine drives generator → traction motors.

• Characteristics of Good Traction System:

  • High starting torque.

  • Simple speed control.

  • Overload capacity.

  • Robustness to vibrations.

2. Traction Mechanics and Speed-Time Curve

Typical Trapezoidal Curve (Main Line):

Speed (v)

  ↑

  |       /¯¯¯¯¯¯¯\

  |      /         \

  |_____/           \______→ Time (t)

       t₁   t₂   t₃

• $$\displaystyle t_1 $$: Acceleration period (constant acceleration $\alpha$).

• $$\displaystyle t_2 $$: Constant speed period.

• $$\displaystyle t_3 $$: Braking period (constant retardation $\beta$).

Derivation of Maximum Speed ($$\displaystyle v_{\text{max}} $$):

Given total distance $d$, total time $T$, acceleration $\alpha$, braking $\beta$.

• $$\displaystyle v_{\text{max}} = \alpha t_1 = \beta t_3 $$.

• $$\displaystyle t_1 = v_{\text{max}}/\alpha $$, $$\displaystyle t_3 = v_{\text{max}}/\beta $$.

• $$\displaystyle t_2 = T - t_1 - t_3 $$.

• Distance:

$$d = \frac{1}{2}\alpha t_1^2 + v_{\text{max}} t_2 + \frac{1}{2}\beta t_3^2$$

Substitute $$\displaystyle t_1, t_2, t_3 $$:

$$d = \frac{v_{\text{max}}^2}{2\alpha} + v_{\text{max}}\left(T - \frac{v_{\text{max}}}{\alpha} - \frac{v_{\text{max}}}{\beta}\right) + \frac{v_{\text{max}}^2}{2\beta}$$

Rearranged:

$$\boxed{\frac{v_{\text{max}}^2}{2}\left(\frac{1}{\alpha} + \frac{1}{\beta}\right) - v_{\text{max}} T + d = 0}$$

Solve quadratic for $$\displaystyle v_{\text{max}} $$.

Parameters:

• Dead Weight ($$\displaystyle W_d $$): Total weight of train.

• Acceleration Weight ($$\displaystyle W_a $$): $$\displaystyle W_d $$ + rotating parts (≈ 5–10% extra).

• Train Resistance (Davis Equation):

$$R = a + bv + cv^2$$

where $a, b, c$ depend on train type.

• Specific Energy Consumption:

$$\text{Wh/ton-km} = \frac{\text{Total energy consumed}}{\text{Weight} \times \text{Distance}}$$

Affected by acceleration, gradient, resistance, regenerative braking.

Example (Past Paper):
$$\displaystyle d = 1400 $$ m, $$\displaystyle v_{\text{avg}} = 42 $$ km/h = 11.67 m/s, $$\displaystyle \alpha = 1.7 $$ km/h/s = 0.472 m/s², $$\displaystyle \beta = 3.3 $$ km/h/s = 0.917 m/s².
$$\displaystyle T = d / v_{\text{avg}} = 1400 / 11.67 = 120 $$ s.

Solve:

$$\frac{v_{\text{max}}^2}{2}\left(\frac{1}{0.472} + \frac{1}{0.917}\right) - v_{\text{max}} \times 120 + 1400 = 0$$

$$\frac{v_{\text{max}}^2}{2}(2.119 + 1.090) = \frac{v_{\text{max}}^2}{2} \times 3.209 = 1.6045 v_{\text{max}}^2$$

Equation: $$\displaystyle 1.6045 v_{\text{max}}^2 - 120 v_{\text{max}} + 1400 = 0 $$.

Solve: $$\displaystyle v_{\text{max}} = \frac{120 \pm \sqrt{14400 - 4 \times 1.6045 \times 1400}}{2 \times 1.6045} = \frac{120 \pm \sqrt{14400 - 8985.2}}{3.209} = \frac{120 \pm \sqrt{5414.8}}{3.209} = \frac{120 \pm 73.58}{3.209} $$.

Take positive root: $$\displaystyle v_{\text{max}} = (120 - 73.58)/3.209 = 14.46 $$ m/s ≈ 52 km/h.

Then $$\displaystyle t_1 = 14.46/0.472 = 30.6 $$ s, $$\displaystyle t_3 = 14.46/0.917 = 15.8 $$ s, $$\displaystyle t_2 = 120 - 46.4 = 73.6 $$ s.

3. Traction Motors

• DC Series Motor:

  • Torque $$\displaystyle \propto I^2 $$, speed $\propto 1/I$ → high starting torque, speed varies with load.

  • Simple speed control via armature voltage/field flux.

  • Suitable for traction due to high starting torque and ability to handle overloads.

• AC Motors:

  • Induction Motors: Robust, low maintenance, with VFD for speed control.

  • Synchronous Motors: Constant speed, used in high-power AC traction.

• Selection: Based on torque-speed requirements, efficiency, control complexity.

4. Electrical Braking Methods

[!TIP]

Regenerative braking is most efficient; requires compatible power supply (DC or AC with inversion).

5. Load Equalization

• Need: Traction motors draw high current during acceleration → peak demand charges.

• Methods:

  • Flywheel Storage: Store kinetic energy during braking, release during acceleration.

  • Motor-Generator Sets: Store energy in rotating inertia.

• Reduces peak power from grid, smooths load.

6. Electric Vehicles (EVs)

Components:

• Traction Battery: Li-ion (high energy density), NiMH, lead-acid.

• Electric Motor: AC induction or permanent magnet synchronous.

• Power Electronics Controller: Inverter (DC→AC), converter (AC→DC).

• Charger: On-board or off-board.

Types:

• BEV: Battery Electric Vehicle (fully electric).

• HEV: Hybrid Electric Vehicle (ICE + electric).

• PHEV: Plug-in Hybrid (larger battery, plug-in charge).

7. Hybrid Vehicles

8. Transmission Systems in EVs

• Single-Speed Reduction Gear: Most common (motor wide torque-speed range).

• Multi-speed Transmission: Improves efficiency at high speeds, but adds complexity.

• Direct Drive: Motor integrated into wheel hub (in-wheel motors).

D. ENERGY MANAGEMENT AND CONSERVATION

1. Energy Audit

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

• Types:

  • Preliminary Audit: Walk-through, quick estimate.

  • Detailed Audit: Comprehensive measurement, analysis, reporting.

  • Special Audits: Thermal (HVAC), Process (industrial).

• Steps:

  1. Data collection (energy bills, equipment inventory).

  2. Analysis (energy end-use, losses).

  3. Reporting (recommendations, savings).

  4. Implementation and monitoring.

• Significance: Reduces costs, emissions, improves efficiency.

2. Energy Manager

• Roles:

  • Develop energy policy and plans.

  • Conduct audits and implement measures.

  • Monitor consumption, train staff.

  • Ensure compliance with regulations.

• Qualifications: Engineering degree, energy management certification (e.g., CEM), analytical skills.

3. Energy Policy

• Need: Organizational commitment, resource allocation, target setting.

• Development: Based on audit findings, set SMART goals (Specific, Measurable, Achievable, Relevant, Time-bound).

• Primary Energy Resources:

  • Conventional: Coal, oil, natural gas, nuclear.

  • Renewable: Solar, wind, biomass, hydro, geothermal.

4. Thermodynamics in Energy Conservation

• First Law (Energy Balance):

$$\text{Energy input} = \text{Useful output} + \text{Losses}$$

Example: Boiler: Fuel energy = steam energy + flue gas loss + radiation loss.

• Second Law (Entropy):

  • Entropy of isolated system never decreases.

  • No process 100% efficient; maximum efficiency given by Carnot:

$$\eta_{\text{Carnot}} = 1 - \frac{T_c}{T_h}$$

• Significance: Highlights irreversibilities, guides recovery of waste heat.

5. Energy Auditing Instruments

6. Demand Side Management (DSM)

• Load Curve Analysis:

  • Shape: Peak, off-peak, base load.

  • Load Factor = $$\displaystyle \frac{\text{Average load}}{\text{Peak load}} $$ (higher = better).

  • Diversity Factor = $$\displaystyle \frac{\text{Sum of individual peaks}}{\text{System peak}} $$.

• Tariff Structures:

  • Time-of-Day (TOD): Different rates for peak/off-peak.

  • Seasonal: Higher in summer/winter.

  • Block Tariff: Slab rates (increasing with consumption).

• DSM Techniques:

  • Load Shifting: Move load to off-peak.

  • Peak Clipping: Reduce peak demand.

  • Valley Filling: Increase off-peak consumption.

  • Energy Conservation: Reduce overall consumption.

7. Energy-Efficient Motors

• Premium Efficiency Classes: IE3 (premium), IE4 (super premium).

• Losses: Stator copper, rotor copper, core (hysteresis + eddy), friction, stray.

• Reduction Strategies:

  • Thinner laminations (reduce core loss).

  • Larger conductors (reduce copper loss).

  • Optimized design, better bearings.

• Selection: Right size (avoid oversized), high efficiency class, consider part-load efficiency.

8. Power Factor Improvement

• Causes of Poor PF: Inductive loads (motors, transformers) draw reactive power ($Q$).

• Disadvantages:

  • Increased current → higher $$\displaystyle I^2R $$ losses.

  • Reduced system capacity.

  • Voltage drop, poor regulation.

  • Penalty charges from utilities.

• Correction Methods:

  | Method | Principle | Pros/Cons | |------------|---------------|---------------| | Capacitor Banks | Provide leading $Q$ | Cheap, easy, but over-correction risk | | Synchronous Condensers | Overexcited sync motor | Adjustable, but costly, losses | | Phase Advancers | Improve PF of induction motor | Used with motor only |

• Benefits: Reduced losses, better voltage, lower demand charges.

9. Variable Speed Drives (VSD)

• Types:

  • VFD (AC): Rectifier → DC bus → Inverter (variable $f$ and $V$).

  • DC Drives: Adjust armature voltage/field.

• Principle: For AC motors, $f$ control → speed control ($N \propto f$).

• Applications: Pumps, fans (affinity laws: $$\displaystyle P \propto N^3 $$), compressors, conveyors.

• Energy Savings: Match motor speed to load, avoid throttling/dampers. Typical savings 20–50%.

10. Maintenance Strategies

• Predictive Maintenance:

  • Condition monitoring (vibration, thermography, oil analysis).

  • Schedule maintenance based on actual condition.

• Preventive Maintenance:

  • Scheduled servicing (e.g., quarterly cleaning, lubrication).

• Role in Conservation: Maintains efficiency, prevents degradation, extends equipment life.

11. Waste Heat Recovery

• Sources: Flue gases (200–500°C), cooling water, exhaust steam, engine coolant.

• Techniques:

  • Heat Exchangers: Recover heat to preheat fluids (air, water).

  • Regenerative Burners: Preheat combustion air using exhaust.

  • Waste Heat Recovery Boilers (WHRB): Generate steam from exhaust gases.

• Applications: In boilers, furnaces, diesel engines, gas turbines.

12. Cogeneration

• Principle: Simultaneous generation of electricity and useful heat (steam/hot water).

• Types:

  | Type | Steam Extraction | Efficiency | |----------|---------------------|----------------| | Back Pressure | All steam at process pressure | High (70–90%) | | Extraction-Condensing | Extract at intermediate pressure, rest to condenser | Flexible | | Double Extraction Back Pressure | Two extraction points | For multiple processes | | Combined Cycle | Gas turbine + steam turbine | Very high (>60%) |

• Benefits:

  • Overall efficiency 70–90% (vs 30–40% in separate generation).

  • Fuel savings, reduced emissions, lower operating cost.

• Energy Conservation in Power Plants:

  • Improve thermal efficiency (supercritical steam parameters, reheat).

  • Reduce auxiliary consumption (efficient pumps, fans, LED lighting).

13. Industrial Energy Conservation

Sugar Industry:

• Processes: Juice extraction, evaporation, crystallization, drying.

• Conservation:

  • Bagasse cogeneration (steam + power).

  • Efficient multiple-effect evaporators.

  • Waste heat recovery from flue gases.

  • LED lighting, efficient motors.

Textile Industry:

• Processes: Spinning, weaving, dyeing, drying.

• Conservation:

  • Heat recovery from dryer exhaust.

  • Variable speed drives in compressors/fans.

  • High-efficiency motors, LED lighting.

  • Process optimization (e.g., low-liquor ratio dyeing).

Cement Industry:

• Processes: Kiln, preheater, cooler, grinding.

• Conservation:

  • WHRB from kiln exhaust (generate power).

  • Alternative fuels (waste tires, biomass).

  • Preheater towers for heat recovery.

  • Efficient grinding (vertical roller mills).

Agriculture Waste Utilization:

• Biomass Power: Direct combustion, gasification.

• Biogas: Anaerobic digestion of dung/crop residue.

• Co-firing: Biomass with coal in boilers.

Lubrication and Tribological Innovations:

• Reduce friction losses in bearings, gears.

• Synthetic lubricants (longer life, lower friction).

• Proper maintenance (clean oil, correct viscosity).

14. Building Energy Conservation

• HVAC Systems:

  • Audit: Identify inefficiencies in chillers, pumps, ducts.

  • Efficient Practices:

    • Variable Air Volume (VAV) systems.

    • Heat Recovery Ventilators (HRV).

    • High-efficiency chillers (magnetic bearings).

    • Proper insulation, sealing.

• Lighting: LED, occupancy sensors, daylight harvesting.

• Building Envelope:

  • Insulation (walls, roof).

  • High-performance windows (low U-value, high SHGC).

  • Air sealing to reduce infiltration.

• Housekeeping Measures:

  • Regular filter cleaning.

  • Equipment scheduling (turn off when not needed).

  • Maintain optimal temperature setpoints.

• Electrical Load Calculation for AC:

$$\text{Total Load} = \text{Area} \times \text{Watts per m²} + \text{Occupancy Load} + \text{Equipment Load} + \text{Solar Gain}$$

Typical: 100–150 W/m² for offices.

15. Transportation Energy Conservation

• Electric Vehicles:

  • Higher efficiency (60–70% vs 20–30% for ICE).

  • Regenerative braking recovers energy.

  • Battery technology (Li-ion energy density improving).

• Public Transport:

  • Higher occupancy → lower per capita energy.

  • Electric buses, metros.

• Conventional Vehicles:

  • Aerodynamics (drag reduction).

  • Weight reduction (aluminum, composites).

  • Engine efficiency (turbocharging, direct injection).

• Role of Electric Drives:

  • High efficiency, regenerative braking, silent operation.

  • Enables energy recovery in hybrids/EVs.

16. Project Evaluation

• Payback Period (PBP):

$$\text{PBP} = \frac{\text{Initial Investment}}{\text{Annual Savings}}$$

Simple, ignores time value of money.

• Net Present Value (NPV):

$$\text{NPV} = \sum_{t=0}^{n} \frac{C_t}{(1+r)^t}$$

where $$\displaystyle C_t $$ = cash flow year $t$, $r$ = discount rate. Positive NPV = profitable.

• Internal Rate of Return (IRR): Rate $r$ where NPV = 0. Compare with hurdle rate.

• Depreciation:

  • Straight Line (SL): $$\displaystyle \frac{\text{Cost} - \text{Salvage}}{n} $$.

  • Written Down Value (WDV): $$\displaystyle \text{Depreciation} = \text{Rate} \times \text{Book Value} $$.

• Risk Analysis:

  • Sensitivity Analysis: Vary key assumptions (energy cost, savings).

  • Scenario Analysis: Best, worst, most likely cases.

  • Monte Carlo Simulation: Probabilistic outcomes.

17. Energy Management Tools

• Matrix Chart: Prioritize measures by cost vs savings.

• Load Energy Balance Diagram: Material and energy flows in a process.

• Energy Flow Networks: System-wide mapping of energy inputs/outputs.

• Simulation and Modeling:

  • Software (e.g., EnergyPlus, DOE-2) to predict savings.

  • Model HVAC, lighting, envelope interactions.

[!CAUTION]

Exam Focus Areas (From Past Papers):

1. Illumination Laws & Design Calculations – Inverse square, Lambert’s cosine, UF/MF, SHR.

2. Induction Heating – Principle, frequency selection, furnace types.

3. Traction Mechanics – Speed-time curve derivation, train run calculations.

4. Energy Audit – Types, steps, instruments.

5. DSM & Tariffs – Load curve, TOD, block tariff.

6. Cogeneration – Types, benefits, power plant conservation.

7. Industry-Specific Conservation – Sugar, textile, cement.

8. Project Evaluation – Payback, NPV, depreciation.

Always show units in calculations and convert consistently (e.g., km/h → m/s, minutes → seconds).