Utilization of Electrical Engineering (EX-603 (A)) - Unit 1 Short Notes

UNIT 1: UTILIZATION OF ELECTRICAL ENGINEERING

I. FUNDAMENTALS OF ILLUMINATION

A. Laws of Illumination

1. Inverse Square Law

   The illuminance \( E \) at a point on a surface is inversely proportional to the square of the distance \( d \) from the source, provided the surface is perpendicular to the line of propagation.

$$ E = \frac{I}{d^2} \quad \text{(for point source, perpendicular surface)} $$

where \( I \) = luminous intensity (candela).

2. Lambert's Cosine Law

   The illuminance \( E \) on a surface is proportional to the cosine of the angle \( \theta \) between the normal to the surface and the direction of the incident light.

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

For an extended source, the effective luminous intensity is \( I \cos\theta \).

[!TIP]

Common Pitfall: In calculations, ensure the surface is perpendicular for inverse square law; otherwise combine both laws: \( E = \frac{I \cos\theta}{d^2} \).

B. Photometric Quantities and Units

C. Types of Lighting Schemes

• General (Ambient) Lighting: Uniform overall illumination (e.g., ceiling fixtures).

• Local (Task) Lighting: Focused on specific work areas (e.g., desk lamps).

• Mixed Lighting: Combination of general and local for balanced illumination.

Design Factors: Utilization Factor (UF), Maintenance Factor (MF), Space-Height Ratio (SHR), reflectance of walls/ceiling.

D. Light Sources and Luminaires

Luminaire Efficiency: Ratio of light output to lamp output. Affected by design, reflectance, diffusers.

II. ILLUMINATION DESIGN AND CALCULATIONS

A. Design Procedures

1. Lumen Method (Utilization Factor Method)

   Used for uniform illumination over large areas.

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

where \( E \) = required illuminance (lux), \( A \) = area (m²), UF = utilization factor, MF = maintenance factor.

Number of lamps \( N = \frac{\Phi_{\text{total}}}{\Phi_{\text{lamp}}} \).

2. Point-by-Point Method

   Calculates illuminance at specific points using inverse square and cosine laws. Suitable for non-uniform layouts or localized tasks.

B. Key Design Parameters

• Utilization Factor (UF): Fraction of lamp flux reaching the work plane. Depends on room cavity ratio (RCR), reflectance of ceiling, walls, floor. Obtained from manufacturer tables.

• Maintenance Factor (MF): Accounts for depreciation due to dirt, aging, lamp failure. Typically 0.6–0.8.

• Space-Height Ratio (SHR): Ratio of spacing between luminaires to mounting height above work plane. Ensures uniform illumination; typical SHR = 0.5–1.5.

C. Numerical Problems

• Number of lamps: Use lumen method formula.

• Spacing: \( \text{Spacing} = \text{SHR} \times h \), where \( h \) = mounting height.

• Layout: Arrange in grid; number of rows = room width / spacing, lamps per row = room length / spacing.

[!TIP]

Exam Focus: Always check if UF and MF are given; if not, estimate from typical values or calculate RCR. For point calculations, draw diagram showing \( d \) and \( \theta \).

D. Energy-Efficient Lighting

• LED & CFL: Higher efficacy, longer life, lower heat. CFL contains mercury (disposal issue).

• Lighting Controls:

  • Occupancy sensors (PIR/microwave) – switch off unoccupied areas.

  • Daylight harvesting – photosensors dim artificial light when sufficient daylight.

  • Time scheduling – automated on/off.

• Efficacy: \( \text{Efficacy} = \frac{\Phi_{\text{lamp}}}{\text{Power}} \) (lm/W). Compare life-cycle cost (initial + operating cost).

III. ELECTRICAL HEATING

A. Advantages and Applications

• Advantages: Clean, quiet, precise control, high efficiency (80-95%), no combustion byproducts.

• Applications: Industrial processes (melting, drying, heat treatment), domestic (cookers, water heaters), defrosting, medical.

B. Resistance Heating

• Direct Resistance Heating: Current passes through the material (e.g., water heater, soldering iron). Power \( P = I^2 R \) where \( R \) is resistance of material.

• Indirect Resistance Heating: Heating element (nichrome, Kanthal) radiates/convects heat to charge.

  • Radiant heaters (infrared panels, tube heaters).

  • Panel heaters (convection).

  Power: \( P = \frac{V^2}{R} \) for AC/DC.

C. Induction Heating

• Operating Principle:

  • Eddy Currents: Alternating magnetic field induces circulating currents in conductive material, heating by \( I^2R \).

  • Hysteresis Loss: In magnetic materials, domain reversal causes heat (only below Curie temperature).

• High-Frequency Induction Furnace:

  • Core-type: With laminated iron core, used for low-frequency (50 Hz) heating of bars, billets.

  • Coreless (Crucible): No core; high-frequency (1-10 kHz) AC through coil induces eddy currents in charge. Used for melting metals (steel, aluminum, precious metals).

  Advantages: Rapid, localized, no contact.

  Limitations: High initial cost, noise, requires high-frequency supply (inverter).

D. Dielectric Heating

• Principle: High-frequency (10-100 MHz) electric field causes molecular friction in non-conductors (wood, plastics, food).

• Applications: Wood gluing, plastic welding, food processing (drying, baking).

E. Arc Heating

• Direct Arc Furnace: Arc between electrodes and charge (e.g., steelmaking). Low voltage, high current.

• Indirect Arc Furnace: Arc between two electrodes; heat radiated to charge (e.g., foundry). Higher voltage.

F. Numerical Problems

• Resistance heating: Series/parallel combinations.

  Example: Two 100 Ω elements in 250 V supply:

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

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

• Efficiency: \( \eta = \frac{\text{Useful heat output}}{\text{Electrical input}} \times 100\% \).

IV. WELDING TECHNOLOGIES

A. Classification of Welding Processes

B. Arc Welding

• Shielded Metal Arc Welding (SMAW): Consumable electrode with flux coating. Manual, versatile, outdoor use.

• Gas Metal Arc Welding (GMAW/MIG): Continuous wire electrode, inert gas shield (Ar/CO₂). High deposition, automated.

• Gas Tungsten Arc Welding (GTAW/TIG): Non-consumable tungsten electrode, inert gas. High quality, thin materials, manual/automatic.

C. Resistance Welding

• Spot Welding: Two electrodes press sheets; current passes through overlap. Used in automotive bodies.

• Seam Welding: Rotating wheel electrodes for continuous weld (e.g., tanks).

• Projection Welding: Localized heating on projections (e.g., nuts, wires).

D. Special Welding Processes

• Electron Beam Welding (EBW): Focused electron beam in vacuum. Deep penetration, precision (aerospace, medical).

• Laser Beam Welding: Focused laser beam. High speed, automation (automotive, electronics).

• Ultrasonic Welding: High-frequency vibration under pressure. Plastics, thin metals (electronics).

E. Welding Transformers

• Characteristics: Drooping V-I curve (constant current) to stabilize arc against voltage fluctuations.

• Types:

  • Tap-changing: Adjustable primary taps for current control.

  • Rectifier Type: AC to DC for GTAW/SAW (smoother arc).

• Selection: Based on welding current range, duty cycle, portability.

V. ELECTROLYSIS AND ELECTROPLATING

A. Faraday's Laws of Electrolysis

1. First Law: Mass of substance deposited \( m \) is proportional to charge \( Q \) passed.

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

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

2. Second Law: For same charge, masses deposited are proportional to chemical equivalents.

$$ \frac{m_1}{m_2} = \frac{E_1}{E_2} $$

where \( E \) = equivalent weight.

Faraday Constant: \( F = 96500 \text{ C/mol} \).

$$ Z = \frac{E}{F} $$

B. Electroplating Process

• Setup: Anode (metal to deposit), Cathode (workpiece), Electrolyte (salt solution of anode metal).

• Principle: Electrolytic deposition. Anode dissolves: \( \text{M} \rightarrow \text{M}^{n+} + n e^- \); Cathode: \( \text{M}^{n+} + n e^- \rightarrow \text{M} \).

• Applications: Corrosion resistance (zinc, nickel), aesthetics (gold, chrome), wear resistance (hard chrome).

C. Electrochemical Deposition Calculations

• Using \( m = Z I t \).

  Example: \( I = 3 \text{ A}, t = 30 \times 60 = 1800 \text{ s}, Z_{\text{gold}} = 0.065 \text{ g/C} \) (given).

  \( m = 0.065 \times 3 \times 1800 = 351 \text{ g} \).

  Note: Check units; often \( Z \) given in g/A-h or mg/C.

VI. ELECTRIC TRACTION SYSTEMS

A. Introduction to Electric Traction

• DC Traction: DC series motors, 600-750 V supply (urban, metros).

• AC Traction: 25 kV AC, induction motors (mainline, high-speed).

• Diesel-Electric: Diesel engine drives generator; electric motors drive wheels.

B. Speed-Time Curves

• Trapezoidal: Acceleration → constant speed → braking.

  Derive \( V_{\text{max}} = \alpha \cdot t_a \), where \( \alpha \) = acceleration (m/s²).

  Distance during acceleration: \( d_a = \frac{1}{2} \alpha t_a^2 \).

• Triangular: No constant speed; acceleration and braking only. Used for short distances.

C. Train Motion and Resistance

• Dead Weight (W): Weight of locomotive + train.

• Acceleration Weight (Wₐ): \( W_a = W \left(1 + \frac{w_e}{W}\right) \), where \( w_e \) = rotating mass allowance (5-10%).

• Train Resistance (R):

$$ R = R_r + R_g + R_c $$

• Rolling resistance \( R_r = 0.0016 W \) (N/tonne).

• Gradient resistance \( R_g = W \cdot \text{gradient} \) (e.g., 1% = 10 N/tonne).

• Curve resistance \( R_c = 0.3 \times \text{radius factor} \times W \) (N/tonne).

D. Specific Energy Consumption (SEC)

$$ \text{SEC} = \frac{\text{Total energy consumed (Wh)}}{\text{Ton-km}} $$

For trapezoidal curve:

$$ \text{SEC} = \frac{0.0107 \cdot R \cdot d + 0.278 \cdot \alpha \cdot V_{\text{max}}^2 \cdot W_a}{W \cdot D} \quad \text{(kWh/ton-km)} $$

where \( d \) = distance (km), \( D \) = ton-km.

Factors: Acceleration, gradient, speed, regenerative braking (reduces SEC).

E. Electrical Braking Methods

• Plugging (Reverse Current): Reverse motor polarity while rotating; high deceleration, high energy loss as heat.

• Rheostatic Braking: Motor acts as generator; energy dissipated in resistor.

• Regenerative Braking: Energy fed back to supply. Most efficient; used in EVs, metros.

F. Traction Motors

• DC Series Motor:

  • Characteristics: High starting torque (\( T \propto I^2 \)), speed varies inversely with load.

  • Suitability: Matches traction demand (high torque at start, speed increases as load decreases).

  • Simple speed control via series-parallel or field weakening.

• Comparison:

  • DC shunt: Constant speed, low starting torque → unsuitable.

  • AC induction: Robust, low maintenance; requires variable frequency supply (VFD).

G. Electric Vehicles (EVs)

Components:

• Battery: Li-ion (high energy density). Voltage 200-400 V.

• Motor: AC induction or Permanent Magnet Synchronous Motor (PMSM).

• Controller: Inverter (DC to AC) for speed/torque control.

• Charger: On-board or off-board (AC/DC).

Advantages: Zero tailpipe emissions, quiet, high efficiency (60-80%).
Limitations: Limited range, long charging time, battery cost/weight.

H. Hybrid Electric Vehicles (HEVs)

• Series Hybrid: Engine → generator → battery → motor. Engine runs at optimal speed.

• Parallel Hybrid: Engine and motor both drive wheels (e.g., Toyota Prius).

• Series-Parallel: Combines both; power split device (e.g., Toyota Hybrid Synergy Drive).

I. Transmission Systems for EVs

• Single-Speed Gearbox: Fixed ratio; motor operates over wide speed range (most EVs).

• Multi-Speed Transmission: Improves efficiency at high/low speeds (e.g., Porsche Taycan 2-speed).

VII. ELECTRIC DRIVES

A. Advantages over Other Drives

• Flexible control: Wide speed range, quick response.

• High efficiency: 80-95% vs mechanical (60-70%).

• Remote operation: Easy automation, no mechanical linkages.

• Low maintenance: No gears, belts.

• Environment friendly: No exhaust.

B. Types of Electric Drives

C. Selection Criteria for Motor Drives

1. Nature of Load:

   • Constant torque (cranes, conveyors).

   • Variable torque (fans, pumps: \( T \propto N^2 \)).

   • Constant power (machine tools).

2. Duty Cycle: Continuous (S1), intermittent (S3), periodic (S6) per IS/IEC.

3. Environmental Conditions: Dust, moisture, explosive (choose enclosure: TEFC, explosion-proof).

4. Starting/braking requirements: High inertia loads need high starting torque.

D. Load Equalization

• Concept: Use flywheel or motor-generator set to store energy during light loads and release during peak loads, smoothing demand on supply.

• Necessity: Reduces peak demand charges, prevents voltage dips, allows smaller supply capacity.

• Applications: Presses, shears, rolling mills with fluctuating loads.

VIII. ELECTRICAL LOAD ESTIMATION FOR HVAC SYSTEMS

A. Principles of Load Calculation

• Cooling Load: Rate of heat removal to maintain indoor conditions.

  • Sensible Heat: Causes temperature rise (conduction, solar, equipment).

  • Latent Heat: Causes humidity rise (occupants, infiltration).

• Total Cooling Capacity: Sum of sensible and latent loads.

B. Factors Influencing Cooling Load

1. Solar Radiation: Through windows, walls, roof.

2. Occupancy: Sensible/latent heat from people.

3. Equipment: Lighting, appliances, machinery.

4. Infiltration: Outdoor air entering through leaks.

5. Ventilation: Required fresh air.

C. Numerical Problems

• Sensible Load: \( Q_s = U \cdot A \cdot \Delta T \) (W), where \( U \) = U-value (W/m²·K), \( A \) = area, \( \Delta T \) = temperature difference.

• Latent Load: \( Q_l = \text{occupants} \times \text{latent heat per person} + \text{infiltration} \times \text{humidity ratio} \).

• Total Load: \( Q_{\text{total}} = Q_s + Q_l \).

• Sizing: Select compressor and fan based on total load with safety factor (10-20%).

[!TIP]

Common Mistake: Forgetting latent load from occupants and infiltration; always check both sensible and latent components. Use standard values from ASHRAE/CIBSE guides.