UNIT 5: UTILIZATION OF ELECTRICAL ENGINEERING

(Based on EX‑603(A) Past Examination Analysis)

I. ILLUMINATION ENGINEERING

A. Fundamental Laws of Illumination

1. Inverse Square Law

The illumination \( E \) on a surface is inversely proportional to the square of the distance \( d \) from the point source, provided the surface is normal to the direction of light.

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

where \( I \) = Candle Power (CP) of the source in the direction of the surface.

[!TIP] Common Pitfall: This law holds only when the receiving surface is perpendicular to the incident light. For an inclined surface, use Lambert’s Cosine Law.

2. Lambert’s Cosine Law

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

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

[!TIP] Combined Formula: For a surface at distance \( d \) and angle \( \theta \),

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

B. Illumination Design & Calculations

1. Determination of Lux Level on Working Plane

Total illumination \( E \) on a working plane from multiple sources is the sum of contributions from each lamp, considering room surface reflectances.

2. Calculation of Number of Lamps

Key formula for number of lamps \( N \):

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

Where:

• \( E \) = Required illumination level (Lux)

• \( A \) = Area of working plane (m²)

• \( \Phi \) = Luminous flux per lamp (Lumens)

• UF = Utilization Factor (fraction of light reaching work plane)

• MF = Maintenance Factor (accounts for dirt, aging; typically 0.7–0.8)

• Depreciation Factor = \( \frac{1}{MF} \) (older term)

[!TIP] Past Paper Pattern: Questions often provide UF, MF, and ask for number of lamps. Always check if Depreciation Factor is given instead of MF.

3. Point‑by‑Point Illumination Method

For multiple point sources, illumination at a point is the vector sum of contributions from each lamp:

$$ E_{total} = \sum_{i=1}^{n} \frac{I_i \cos\theta_i}{d_i^2} $$

C. Lighting Schemes & Design Considerations

1. Types of Lighting Schemes

2. Factors Influencing Lighting Design

• Room size and shape

• Mounting height of luminaires

• Reflectance of walls, ceiling, floor (light colors increase UF)

• Type of work (precision tasks need higher lux)

• Glare and uniformity requirements

• Energy efficiency and cost

D. Energy‑Efficient Lighting Methods

[!TIP] Exam Focus: Compare LED vs. CFL vs. HID in terms of efficacy, lifespan, environmental impact, and suitable applications.

II. WELDING PROCESSES

A. Classification of Welding Based on Processes

B. Arc Welding

1. Principle

An electric arc (3000–3500°C) between electrode and workpiece melts metal. Shielded by flux or inert gas.

2. Types & Applications

• Manual Metal Arc (MMA): Consumable electrode with flux coating. Versatile, used in construction, pipelines.

• Gas Shielded (MIG/MAG): Continuous wire electrode, inert (MIG) or active (MAG) gas shield. High deposition rate, automotive, shipbuilding.

• TIG (Tungsten Inert Gas): Non‑consumable tungsten electrode, inert gas. High quality, thin materials, aerospace.

• Submerged Arc Welding (SAW): Arc under flux blanket. High speed, thick plates, automated.

3. Limitations

• Requires skilled operator (except some automated)

• Fumes, UV radiation, spatter

• Not suitable for all metals (e.g., reactive metals need special shielding)

C. Resistance Welding

1. Spot Welding

• Two electrodes clamp sheets, current passes → localized heating → weld nugget.

• Applications: Sheet metal assemblies (auto bodies, appliances).

• Advantages: Fast, no filler, clean.

• Limitations: Limited thickness, requires access to both sides.

2. Seam Welding

• Rotating disc electrodes create continuous weld.

• Applications: Tanks, pipes, leak‑proof joints.

3. Projection Welding

• Projections on one piece concentrate current → weld at points.

• Applications: Welding studs, nuts, cross‑wire welding.

D. Electron Beam Welding

1. Principle

High‑velocity electron beam in vacuum (10⁻⁵ mbar) bombards workpiece → kinetic energy → heat → weld.

2. Equipment

• Electron gun (cathode, anode, electromagnetic lenses)

• Vacuum chamber

• Workpiece manipulator

• High voltage supply (30–200 kV)

3. Advantages

• Deep penetration (high depth‑to‑width ratio)

• Minimal distortion, precise

• No filler material

• Can weld refractory metals, dissimilar metals

4. Applications

Aerospace, nuclear, medical implants, high‑value precision components.

5. Limitations

• Expensive, requires vacuum

• X‑ray shielding needed

• Not suitable for large structures

E. Welding Transformers

1. Purpose

Provide low voltage, high current AC for arc welding (typically 15–40 V, 100–600 A).

2. Types

• Tap‑changing transformer: Manual tap selection for current control.

• Reactor type: Series reactor for smooth current regulation.

• Inverter welding transformer: High‑frequency AC → DC → high‑frequency AC. Lightweight, efficient, precise control.

3. Characteristics

• High current, low voltage output

• Drooping characteristic (stable arc)

• Portable or stationary

[!TIP] Past Question: "Welding transformers" – focus on their drooping V‑I characteristic and why it’s essential for stable arc.

III. ELECTRICAL HEATING

A. Types of Heating Methods

B. Advantages of Electrical Heating

• Precise control of temperature and distribution

• No combustion by‑products → clean, suitable for food/pharma

• High efficiency (nearly 100% at point of use)

• Safety (no open flame, automatic shut‑off)

• Rapid heating and response

• Ease of automation and remote operation

C. Induction Heating (Detailed)

1. Operating Principle

• Eddy Current Losses: Alternating magnetic field induces eddy currents in conductive workpiece → \( I^2R \) heating.

• Hysteresis Losses: In magnetic materials, domain reversal causes loss (significant below Curie temperature).

• Skin Effect: Current concentrates near surface → surface heating. Penetration depth:

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

where \( \rho \) = resistivity, \( f \) = frequency, \( \mu \) = permeability.

2. Applications

• Melting: Induction furnaces (coreless, channel) for metals.

• Surface Hardening: Gear teeth, shafts.

• Soldering/Brazing: Localized heating.

• Induction Cooktops: Direct pot heating.

3. Limitations

• Works only on conductive materials (metals, graphite).

• Skin effect limits depth → not for thick uniform heating.

• High‑frequency equipment costly.

• Magnetic materials heat more efficiently due to hysteresis.

4. High‑Frequency Induction Furnace

• Construction:

  • Crucible: Refractory lining, holds charge.

  • Primary coil: Water‑cooled copper, surrounding crucible.

  • Oscillator: High‑frequency AC source (e.g., thyristor/IGBT inverter).

  • Cooling system: For coil and power electronics.

• Working: High‑frequency current in primary → alternating magnetic field → eddy currents in charge → heating. Stirring action due to electromagnetic forces.

D. Numerical Problems in Heating

1. Power Calculation for Resistive Elements

• Series: \( P = \frac{V^2}{(R_1 + R_2 + ...)} \)

• Parallel: \( P = V^2 \left( \frac{1}{R_1} + \frac{1}{R_2} + ... \right) \)

2. Energy Consumption

$$ \text{Energy (kWh)} = \frac{P \times t}{1000} $$

where \( P \) in watts, \( t \) in hours.

[!TIP] Past Paper Example: "Electric toaster with two 100Ω elements at 250V" → Calculate power in series (\( P = 250^2/200 = 312.5 \, \text{W} \)) and parallel (\( P = 250^2/50 = 1250 \, \text{W} \)).

E. Air‑Conditioning Load Calculation

1. Electrical Load Estimation for HVAC

• Cooling Load (BTU/h or kW) → Compressor power input.

• Power Factor of compressor motor (typically 0.8–0.9 lag).

• Full Load Current (FLC):

$$ I = \frac{P_{input}}{\sqrt{3} \times V \times \cos\phi} $$

for 3‑phase.

• Include margin (10–20%) for startup and auxiliary loads (fans, pumps).

IV. ELECTROLYSIS AND ELECTROPLATING

A. Laws of Electrolysis (Faraday’s Laws)

First Law

Mass \( m \) of substance deposited at an electrode is directly proportional to quantity of electricity \( Q \) passed:

$$ m = Z \cdot Q $$

where \( Z \) = Electrochemical Equivalent (ECE) in kg/C.

Second Law

For same quantity of electricity, masses deposited are proportional to their chemical equivalent weights \( E \):

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

Relation between ECE and Equivalent Weight:

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

where \( F \) = Faraday constant = 96485 C/mol.

B. Electroplating

1. Process Description

• Anode: Metal to be plated (e.g., nickel).

• Cathode: Workpiece (e.g., steel).

• Electrolyte: Salt solution of anode metal (e.g., NiSO₄).

• DC Supply: Current flows → metal ions deposit on cathode.

2. Applications

• Corrosion protection: Zinc (galvanizing), chromium.

• Decoration: Gold, silver, rhodium plating.

• Wear resistance: Hard chrome.

• Conductivity improvement: Gold on contacts.

C. Electrochemical Deposition Calculations

Using ECE:

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

where \( I \) in amperes, \( t \) in seconds.

Using Faraday’s Law:

$$ m = \left( \frac{I \cdot t}{F} \right) \times \left( \frac{E}{n} \right) $$

where \( n \) = number of electrons exchanged per ion.

[!TIP] Past Paper Example: "50g gold deposition, 3A, 30 min, ECE=0.065" →

\( Q = 3 \times 1800 = 5400 \, \text{C} \), \( m = 0.065 \times 5400 = 351 \, \text{g} \).

Check: Is this realistic? Gold ECE is ~0.000065 g/C → likely question meant 0.065 mg/C or units mismatch. Always verify units.

V. ELECTRIC TRACTION

A. Speed‑Time Curves

1. General Speed‑Time Curve (Main Line Service)

2. Trapezoidal Speed‑Time Curve

• Periods:

  • Acceleration (0 → \( t_a \)): Constant acceleration \( \alpha \) (km/h/s).

  • Constant speed (\( t_a \) → \( t_c \)): \( V = V_{\max} \).

  • Coasting (\( t_c \) → \( t_o \)): Speed decays due to resistance.

  • Braking (\( t_o \) → \( t_b \)): Constant deceleration \( \beta \) to stop.

3. Derivation of Maximum Speed Equation

Let \( S \) = distance between stops (m), \( V_m \) = max speed (km/h).

Acceleration distance: \( S_a = \frac{V_m^2}{2 \times 3.6 \times \alpha} \) (convert km/h to m/s: divide by 3.6).

Braking distance: \( S_b = \frac{V_m^2}{2 \times 3.6 \times \beta} \).

Coasting/constant speed distance: \( S_c = S - S_a - S_b \).

Time at constant speed: \( t_c = \frac{S_c}{V_m / 3.6} \).

Total time: \( T = t_a + t_c + t_b \), where \( t_a = V_m / (3.6 \alpha) \), \( t_b = V_m / (3.6 \beta) \).

Solving for \( V_m \) from \( S \) and \( T \) gives quadratic.

[!TIP] Key Formulas (with consistent units):

Acceleration time: \( t_a = \frac{V_m}{\alpha} \) (if \( \alpha \) in km/h/s, \( V_m \) in km/h).

Distance during acceleration: \( S_a = \frac{V_m^2}{2\alpha} \) (in km, if \( \alpha \) in km/h/s).

Always convert to m/s for SI consistency: \( \alpha_{m/s^2} = \frac{\alpha_{km/h/s}}{3.6} \).

4. Numerical Analysis

Given: \( S \), \( \alpha \), \( \beta \), average speed \( V_{avg} = S/T \).

Steps:

1. Assume \( V_m \).

2. Compute \( S_a, S_b, S_c \).

3. Check if \( S_c \geq 0 \). If negative, \( V_m \) too high → recalc.

4. Compute times \( t_a, t_c, t_b \), total \( T \).

5. Iterate to match given \( V_{avg} \) or \( T \).

B. Traction Motors

1. DC Series Motor – Suitability for Traction

2. Comparison with Other Motors

• DC Shunt: Constant speed, low starting torque → not suitable.

• AC Motors (Induction/Synchronous): Require variable frequency for speed control → more complex (VFDs). Modern EVs use AC induction or permanent magnet synchronous motors with inverters.

• Universal Motors: High speed, light, but commutator wear → used in appliances, not main traction.

3. Characteristics of a Good Traction System

• High starting torque

• Wide speed range (including low speed)

• Simple speed control

• High overload capacity

• Regenerative braking capability

• Ruggedness, low maintenance

[!TIP] Exam Justification: "Why DC series motor?" → Emphasize \( T \propto I^2 \) for high starting torque and soft characteristic for load sharing in multiple unit trains.

C. Electrical Braking Methods

[!TIP] Compare: Regenerative is most energy‑efficient; plugging wastes energy but provides strong braking.

D. Electric Vehicles (EVs) and Hybrid Vehicles

1. Components of EVs

• Battery: Energy storage (Li‑ion common).

• Electric Motor: AC induction or permanent magnet synchronous.

• Controller (Inverter): Converts DC battery to AC for motor, controls speed/torque.

• Charger: AC/DC converter for battery charging.

• Transmission: Often single‑speed gear (EV motors have wide speed range).

• Regenerative Braking System: Recaptures energy.

2. Types of Hybrid Vehicles

3. Transmission Systems in EVs

• Single‑speed reduction gear: Simple, efficient (most EVs).

• Multi‑speed gearbox: For high‑performance EVs (e.g., Porsche Taycan) to optimize motor efficiency over wider speed range.

E. Train Resistance and Energy Consumption

1. Dead Weight, Acceleration Weight, Train Resistance

• Dead Weight \( W_d \): Total weight of locomotive + wagons (tonnes).

• Acceleration Weight \( W_a \): Portion of dead weight to be accelerated (includes rotating parts). \( W_a = (1 + \lambda) W_d \), where \( \lambda \) = rotating factor (0.06–0.1).

• Train Resistance \( R \): Sum of mechanical resistance (rolling, flange, air) expressed as \( R = r_0 + r_1 v + r_2 v^2 \) (N/tonne), where \( v \) in km/h.

2. Specific Energy Consumption (SEC)

Energy per tonne‑km:

$$ SEC = \frac{\text{Total energy consumed (kWh)}}{\text{Dead weight (tonnes)} \times \text{Distance (km)}} $$

Units: kWh/tonne‑km.

Factors Affecting SEC:

• Acceleration and braking rates (frequent stops increase SEC)

• Gradient (uphill increases energy)

• Train resistance (speed, aerodynamics)

• Regenerative braking (reduces net energy)

• Motor/drive efficiency

F. Load Equalization

1. Concept and Need

Traction loads are highly pulsating (high current during acceleration, zero during braking). This causes large voltage drops and strain on power supply. Load equalization smoothens the demand.

2. Methods

• Flywheel Energy Storage: During braking, motor drives flywheel (stores kinetic energy); during acceleration, flywheel assists motor.

• Regenerative Braking: Energy fed back to grid or used by other trains.

• Battery/UPS Systems: Buffer energy during peaks.

• Multiple Unit Operation: Current demand spread across multiple vehicles from different supply sections.

[!TIP] Past Question: "Load equalization" → Define as smoothing of pulsating traction load and mention flywheel as a mechanical method.

VI. ELECTRIC DRIVES

A. Advantages of Electric Drives Over Other Drives

B. Selection of Motor for Specific Applications

Considerations:

1. Load type: Constant torque (cranes), constant power (machining tools), variable torque (fans, pumps).

2. Duty cycle: Continuous, intermittent, short‑time.

3. Starting torque requirement: High → series DC, slip‑ring IM; Low → shunt DC, squirrel‑cage IM.

4. Speed control range: Wide → DC, VFD‑fed AC; Fixed → synchronous motor.

5. Environment: Hazardous (explosion‑proof), corrosive, clean.

6. Cost and maintenance: AC motors generally cheaper, less maintenance than DC.

7. Power factor and efficiency: High efficiency motors for continuous duty.

[!TIP] Match:

• Cranes/Hoists: DC series or slip‑ring IM (high starting torque).

• Fans/Pumps: Squirrel‑cage IM with VFD (variable torque).

• Precision tools: Servo motors or PMSM.

• Clocks/Conveyors: Small synchronous motors.

C. Group Drive vs. Individual Drive

[!TIP] Past Question: "Differentiate between group drive and individual drive" → Tabulate as above, emphasize flexibility and efficiency as key differentiators.

END OF UNIT 5 NOTES
Always cross‑check formulas with past paper numerical problems. Focus on derivation of trapezoidal curve and lamp calculation steps.