Electromagnetic Waves (EX-603 (C)) - Unit 2 Short Notes

UNIT 2: ELECTRICAL ENERGY UTILIZATION AND CONSERVATION

I. ENERGY MANAGEMENT FUNDAMENTALS

Energy Audit

• Definition: A systematic procedure to evaluate how energy is consumed in a facility and identify opportunities to reduce consumption without affecting output or comfort.

• Objectives: Establish energy baseline, identify wastage, recommend conservation measures, estimate savings, and prioritize actions.

• Significance: First step in energy management; provides data for decision-making, reduces operational costs, and lowers environmental impact.

• Types:

  • Preliminary (Walk-through) Audit: Quick visual inspection, low cost, identifies obvious savings.

  • Detailed Audit: Comprehensive data collection (2-4 weeks), detailed analysis, precise savings calculation, and implementation plan.

• Steps: Data collection → Analysis → Reporting → Implementation → Verification.

• Instruments: Power meter, data logger, thermographic camera, lux meter, flue gas analyzer, anemometer.

[!TIP] Exam Focus: Differentiate between audit types. Instruments are frequently asked (e.g., "Name instruments used for energy auditing").

Energy Manager

• Roles: Coordinate audit, implement measures, monitor performance, train staff, ensure compliance with policies.

• Responsibilities: Prepare energy policy, manage budget for conservation, report to management, maintain records.

• Qualities: Technical knowledge, analytical skills, communication, project management, commitment to sustainability.

Thermodynamics in Energy Conservation

• First Law (Energy Balance): Energy cannot be created/destroyed; input = output + accumulation + losses.

  • Example: Boiler: Heat input from fuel = Heat absorbed by steam + Losses (flue gases, radiation).

• Second Law (Entropy): Energy quality degrades; heat flows spontaneously from hot to cold. Defines maximum possible efficiency (Carnot).

  • Significance: Explains why 100% efficiency is impossible; guides recovery of high-grade energy from waste heat.

[!TIP] Common Pitfall: First law is about quantity; second law is about quality/direction of energy flow.

Maintenance Strategies

• Predictive Maintenance: Condition-based (vibration, thermography, oil analysis). Prevents failures, reduces downtime, optimizes spare parts.

• Preventive Maintenance: Scheduled tasks (cleaning, lubrication, part replacement). Reduces degradation, extends equipment life, cost-effective for critical assets.

Primary Energy Resources & Policy

• Classification: Fossil (coal, oil, gas), Renewable (solar, wind, biomass, hydro), Nuclear.

• Conservation: Shift to renewables, improve extraction/ conversion efficiency, promote sustainable use.

• Energy Policy: National/organizational framework with targets, incentives (subsidies for efficient tech), regulations (standards, labeling), and awareness programs.

Energy Conservation: Benefits & Practices

• Benefits:

  • Economic: Lower bills, reduced operational costs.

  • Environmental: Lower emissions (CO₂, pollutants), reduced resource depletion.

  • Social: Improved energy security, job creation in green tech.

• Daily Practices: Use LED bulbs, switch off idle equipment, optimize HVAC settings, use natural light, maintain appliances.

II. BUILDING AND FACILITY ENERGY EFFICIENCY

Lighting Systems

• Laws of Illumination:

  • Inverse Square Law: $$\displaystyle E = \frac{I}{d^2} $$ (Illuminance $E$ ∝ 1/distance²).

  • Lambert's Cosine Law: $$\displaystyle E = \frac{I \cos \theta}{d^2} $$ (θ = angle to normal).

• Design Factors:

  • Utilization Factor (UF): Ratio of lumens reaching work plane to total lumens emitted.

  • Maintenance Factor (MF): Accounts for lumen depreciation due to dirt/aging (usually 0.7-0.8).

  • Space-Height Ratio (SHR): Spacing between lamps / mounting height. Guides layout.

• Illumination Calculation (Average):

$$\text{Total Lumens Required} = \frac{E \times A}{UF \times MF}$$

where $E$ = required lux, $A$ = area.

$$\text{Number of Lamps} = \frac{\text{Total Lumens}}{\text{Lumens per Lamp}}$$

• Energy-Efficient Lighting: LED (high efficacy, long life), CFL, T5/T8 tubes, electronic ballasts, occupancy sensors, daylight harvesting.

[!TIP] Exam Focus: Numerical problems on point illumination or lamp number estimation are common. Always use $$\displaystyle E = I \cos^3 \theta / h^2 $$ for point source at height $h$.

Heating, Ventilation, and Air Conditioning (HVAC)

• Electrical Load Calculation: Sum of fan, pump, compressor, and auxiliary loads. Consider diversity factor.

• Energy Conservation Measures:

  • Insulation: Ducts, pipes, building envelope.

  • Efficient Compressors: Variable speed drives, high-COP units.

  • Thermostats & Controls: Programmable, zone control.

  • Heat Recovery: From exhaust air (enthalpy wheels).

• Thermal Energy Audit in HVAC: Measures temperature, humidity, airflow, pressure drops; identifies insulation gaps, equipment inefficiencies, and control flaws.

Housekeeping & Operational Practices

• Efficient Housekeeping: Regular cleaning of filters, coils, lamps; proper equipment upkeep; sealing air/water leaks.

• Impact of Poor Maintenance: Increased friction (pumps/fans), reduced heat transfer (coils), higher pressure drops → increased energy use.

Integrated Building Energy Management

• Load Curve Analysis: Plot of power demand vs. time. Identifies peak demand, base load, and idle periods.

• Energy Flow & Loss Identification: Map energy inputs (electricity, fuel) to useful outputs (lighting, cooling) and losses (transmission, conversion, wastage).

III. INDUSTRIAL ENERGY EFFICIENCY

Industry-Specific Conservation Measures

• Cement: Preheater/precalciner optimization, high-efficiency grinding (vertical mills), waste heat recovery from kiln exhaust.

• Sugar: Cogeneration (bagasse), process integration (juice heating), efficient multiple-effect evaporators.

• Textile: Motor-driven systems (VSDs for fans/compressors), efficient dyeing (low-liquor ratio), heat recovery from drying.

Waste Heat Recovery (WHR)

• Techniques:

  • Heat Exchangers: Recuperator (gas-gas), economiser (water heating).

  • WHR Boilers: Generate steam from exhaust gases.

  • Thermal Oil Heaters: For low-temperature heat.

• Applications: Furnace flue gases, engine exhaust, cooling water, compressed air dryers.

Co-generation (Combined Heat and Power - CHP)

• Principle: Simultaneous generation of electricity and useful thermal energy (steam/heat) from a single fuel source.

• Systems:

  • Back-Pressure Turbine: Steam expands to a pressure suitable for process use; no condenser.

  • Extraction-Condensing Turbine: Steam extracted for process; remainder condensed.

  • Double Extraction Back-Pressure: Two extraction points for different temperature levels.

• Benefits: Overall efficiency 70-90% (vs. 30-40% for separate generation), fuel saving, reduced emissions.

Material and Energy Balance

• Load Energy Balance Diagram (LEBD): Sankey diagram showing energy inputs, useful output, and losses (stack, radiation, unaccounted).

• Material Load Energy Balance Diagram: Tracks both material flow (input, output, accumulation) and associated energy flows.

• Losses in Material Flow: Spillage, evaporation, incomplete reaction, scrap. Mitigation: closed loops, better process control, recycling.

IV. ELECTRIC MOTORS, DRIVES, AND TRANSPORTATION SYSTEMS

Electric Motors and Drives

• Selection Criteria: Torque-speed characteristic, duty cycle (continuous, intermittent), starting/braking requirements, environment.

• Advantages over Mechanical/Hydraulic: Precise speed control, high efficiency, remote operation, less maintenance.

• Group vs. Individual Drive:

  | Group Drive | Individual Drive | |---|---| | Single motor drives multiple machines via line shaft | Each machine has its own motor | | Low initial cost, simple | High flexibility, independent control | | Poor efficiency at partial load, high maintenance | Better efficiency, easier to start/stop | | Used in textile mills, flour mills | Used in conveyors, CNC machines |

Energy Efficient Motors

• Design Features: Thinner, high-grade steel laminations (reduce core loss), larger conductors (reduce I²R loss), optimized cooling, better bearings.

• Standards (IEC): IE1 (Standard), IE2 (High Efficiency), IE3 (Premium Efficiency), IE4 (Super Premium).

• Selection: Choose IE3/IE4 for long operating hours; consider life-cycle cost, not just purchase price.

Traction Systems

• DC Series Motor Suitability:

  • High starting torque (T ∝ I²).

  • Speed self-adjusts with load (high load → low speed).

  • Simple, robust, easy speed control via voltage.

• Parameters:

  • Dead Weight: Total weight of locomotive/coach.

  • Acceleration Weight: Dead weight + rotating parts (equivalent).

  • Train Resistance: Sum of rolling, gradient, curve resistances (in N/tonne).

• Specific Energy Consumption (SEC): Energy per tonne-km. Affected by acceleration, braking, gradient, speed, auxiliary loads.

Speed-Time Curves

• General Speed-Time Curve (Main-line Service): Acceleration (constant) → Coasting (speed constant) → Braking (constant deceleration) → Stop.

• Trapezoidal Curve Derivation:

  Let:

  $$\displaystyle V_m $$ = max speed (km/h)

  $\alpha$ = acceleration (km/h/s)

  $\beta$ = braking retardation (km/h/s)

  $$\displaystyle t_1 $$ = acceleration time = $$\displaystyle V_m / \alpha $$

  $$\displaystyle t_3 $$ = braking time = $$\displaystyle V_m / \beta $$

  $$\displaystyle t_2 $$ = coasting time

  Total time $$\displaystyle T = t_1 + t_2 + t_3 $$

  Distance $$\displaystyle D = \frac{1}{2}(V_m t_1) + V_m t_2 + \frac{1}{2}(V_m t_3) $$

  \boxed{D = \frac{V_m}{2}\left(\frac{V_m}{\alpha} + \frac{V_m}{\beta}\right) + V_m t_2}

  For given $D$ and $T$, solve for $$\displaystyle V_m $$, $$\displaystyle t_2 $$.

[!TIP] Exam Focus: Derivation of trapezoidal curve parameters (max speed, acceleration time) is a 7-mark question. Convert km/h to m/s for distance in meters: 1 km/h = 0.2778 m/s.

Electrical Braking

• Plugging (Reverse Current): Motor connections reversed; acts as brake but dissipates energy as heat in resistors. Wastes energy.

• Rheostatic (Dynamic): Motor acts as generator; energy dissipated in external resistor. Used in DC drives.

• Regenerative Braking: Motor acts as generator; energy fed back to supply (inverter/rectifier). Used in EVs, AC drives with VFD. Energy recovery key benefit.

Load Equalization

• Need: Smooth peak demand → reduce demand charges, avoid oversized equipment.

• Methods:

  • Flywheel: Stores kinetic energy during light load, releases during peak.

  • Secondary Batteries: Store electrical energy.

  • Motor-Generator Sets: Motor draws constant power; generator supplies variable load.

Electric and Hybrid Vehicles

• EV Components: Traction motor (AC/DC), power electronics (inverter/controller), battery pack (Li-ion), charger, reduction gear.

• Types:

  • BEV: Battery only.

  • HEV: Combines ICE + electric motor.

    • Series: ICE drives generator; motor drives wheels.

    • Parallel: Both ICE and motor can drive wheels.

• Transmission: Single-speed (most EVs), multi-speed (for performance), in-wheel motors (direct drive).

• Energy Conservation: Regenerative braking, high motor efficiency, lightweight design, public transport shift.

Variable Speed Drives (VSD)

• Types:

  • AC Drive (VFD): Rectifier → DC bus → Inverter (variable frequency/voltage).

  • DC Drive: Adjust armature voltage/field.

  • Soft Starter: Reduces voltage at start.

• Energy-Saving Applications: Pumps, fans, compressors (affinity laws: power ∝ speed³). Reduces energy by 20-50% at partial load.

• Selection: Match motor rating, consider torque/speed profile, harmonics filtering.

V. ELECTROLYTIC AND WELDING PROCESSES

Electrolysis and Electroplating

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

$$m = Z \cdot Q = Z \cdot I \cdot t$$

where $Z$ = electrochemical equivalent.

• Faraday's Second Law: For same $Q$, masses ∝ equivalent weights.

• Electroplating: Deposition of metal layer for corrosion resistance, wear resistance, aesthetics. Uses electrolyte containing metal ions.

• Calculation: $$\displaystyle m = I \cdot t \cdot E.C. $$ (E.C. in g/A-s or kg/A-h).

Welding Methods Classification

Welding Transformers

• Types: Drooping characteristic (manual), constant current (automatic), rectifier type (DC).

• Characteristics:

  • Open-Circuit Voltage (OCV): 60-80V (safe).

  • Short-Circuit Current (SCC): High current at zero voltage.

  • Duty Cycle: % of time can weld in 10 min (e.g., 60% at 300A).

• Application: OCV affects ease of striking arc; SCC determines max current.

VI. DEMAND SIDE MANAGEMENT AND POWER QUALITY

Load Curve Analysis

• Importance: Identifies peak demand periods, load factor ($$\displaystyle \text{LF} = \frac{\text{Avg load}}{\text{Peak load}} $$), energy pattern.

• Use in DSM: Load shaping (shifting, clipping), forecasting, tariff design.

Demand Side Management (DSM) Techniques

Electricity Tariffs

• Types:

  • Flat Rate: Fixed charge per unit.

  • Block Rate: Increasing blocks (slab).

  • Two-Part: Fixed charge + energy charge.

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

• Restructuring for Conservation: Higher peak tariffs, lower off-peak rates, incentives for efficient equipment, penalty for low power factor.

Power Factor Improvement

• Causes of Poor PF: Inductive loads (motors, transformers), harmonic distortion, lightly loaded systems.

• Disadvantages: Increased current → higher I²R losses, reduced system capacity, penalty tariffs, voltage regulation issues.

• Correction Methods:

  • Shunt Capacitors: Most common; supply leading VARs.

  • Synchronous Condensers: Over-excited synchronous motor.

  • Phase Advancers: For induction motors.

  • Active Filters: For harmonics.

• Role in DSM: Reduces losses, defers capacity upgrades, improves voltage stability.

[!TIP] Common Pitfall: Power factor correction reduces current for same real power, not necessarily energy (kWh). Savings come from reduced losses and lower demand charges.

VII. ECONOMIC ANALYSIS FOR ENERGY PROJECTS

Project Evaluation Methods

• Payback Period (PBP):

  • Simple: $$\displaystyle \text{PBP} = \frac{\text{Initial Investment}}{\text{Annual Savings}} $$.

  • Discounted: Considers time value of money; sum discounted cash flows until cumulative = investment.

  • Merits: Simple, liquidity focus. Demerits: Ignores cash flows beyond PBP, time value (simple).

• Net Present Value (NPV): Sum of discounted cash flows (inflows - outflows). Accept if NPV > 0.

• Internal Rate of Return (IRR): Discount rate that makes NPV = 0. Accept if IRR > required rate.

• Comparison: NPV gives absolute value; IRR gives percentage return. NPV preferred for mutually exclusive projects.

Depreciation

• Straight Line Method (SLM):

$$\text{Annual Depreciation} = \frac{\text{Cost} - \text{Salvage Value}}{\text{Useful Life}}$$

Book value = Cost - (Annual Depreciation × year).

• Written Down Value (WDV) Method:

$$\text{Depreciation}_{year} = \text{Book Value}_{start} \times \text{Rate}$$

Rate = $$\displaystyle 1 - \left(\frac{\text{Salvage}}{\text{Cost}}\right)^{1/n} $$.

Book value reduces geometrically.

• Comparison: SLM → equal annual charge; WDV → higher initial charge, tax advantage early.

Cost-Benefit-Risk Analysis

• Inclusion: Inflation (adjust cash flows), discount rate (cost of capital), risk factors (add risk premium or use sensitivity analysis).

• Special Problems: Uncertainty in future energy prices, technology obsolescence, regulatory changes.

• Sensitivity Analysis: Vary key assumptions (savings, cost, discount rate) to see impact on NPV/IRR.

• Scenario Planning: Best-case, worst-case, most-likely scenarios.

Financial Metrics

• Return on Investment (ROI): $$\displaystyle \text{ROI} = \frac{\text{Annual Savings}}{\text{Investment}} \times 100\% $$.

• Life Cycle Costing (LCC): Total cost over project life (investment + O&M + disposal - salvage). Used to compare alternatives.

VIII. ADVANCED TOOLS AND EMERGING TRENDS

Simulation and Modeling

• Role: Predict energy use, evaluate conservation measures before implementation, optimize system design.

• Types: Building energy simulation (DOE-2, EnergyPlus), process modeling (Aspen Plus), CFD for airflow/heat transfer.

Renewable and Alternative Energy

• Agriculture Waste: Biomass (direct combustion), biogas (anaerobic digestion), gasification (syngas).

• Applications: Rural energy, cogeneration (bagasse in sugar mills), sustainable cooking, bio-CNG.

Tribology and Lubrication Innovations

• Energy Savings: Reduce friction in bearings, gears, engines → lower motor load.

• Innovations: Synthetic lubricants, solid lubricants (graphite, MoS₂), surface coatings (DLC), magnetic bearings.

Analytical Tools and Diagrams

• Matrix Charts: Prioritize energy-saving opportunities by impact vs. cost.

• Load Energy Balance Diagram (LEBD): Sankey diagram for energy flows in a process/plant.

• Energy Flow Networks: System-wide map of energy inputs, conversions, outputs, losses.

• Material and Energy Balance Tables: Tabular form for mass and energy inputs/outputs per process unit.