UNIT 3: UTILIZATION OF ELECTRICAL ENGINEERING - EXAM-FOCUSED NOTES

1.0 ILLUMINATION ENGINEERING

1.1 Fundamental Laws of Illumination

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

| Holds for point sources. For extended sources, valid when distance >> source dimensions. | | Lambert's Cosine Law | Illuminance on a surface is proportional to the cosine of the angle of incidence (θ) between the normal to the surface and the direction of the incident flux. |

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

| Combined with inverse square law: $$\displaystyle E = \frac{I \cos^3\theta}{h^2} $$ for a source at height h directly above a horizontal plane. |

[!TIP] Common Pitfall: Students often forget the $\cos\theta$ term when the surface is tilted, or misuse the combined formula $$\displaystyle \frac{I \cos^3\theta}{h^2} $$ without ensuring the source is directly above the point.

1.2 Lighting Design & Calculations

Key Definitions:

• Luminous Flux (Φ): Total light energy emitted per second, measured in Lumens (lm).

• Luminous Intensity / Candle Power (I): Flux emitted per unit solid angle, measured in Candela (Cd). $$\displaystyle I = \frac{d\Phi}{d\omega} $$.

• Illuminance (E): Luminous flux incident per unit area, measured in Lux (1 Lux = 1 lm/m²).

• Utilization Factor (UF): Ratio of luminous flux reaching the working plane to the total flux emitted by the lamp(s). Depends on room geometry, surface reflectances, and luminaire type. (0 < UF < 1).

• Maintenance Factor (MF): Ratio of illuminance at a given time to the initial illuminance. Accounts for dirt accumulation and lamp aging. (0 < MF < 1).

• Space-Height Ratio (SHR): Ratio of the distance between luminaires (center-to-center) to their mounting height above the working plane. Used for preliminary layout.

$$SHR = \frac{\text{Luminaire Spacing}}{\text{Mounting Height}}$$

• Depreciation Factor: Often used interchangeably with Maintenance Factor (MF). It is the reciprocal of the factor by which initial illumination must be multiplied to get maintained illumination.

General Formula for Number of Lamps:

$$\text{Number of Lamps (N)} = \frac{E \times A}{N \times UF \times MF \times \text{Lumen Output per Lamp}}$$

Where:

• $E$ = Required illumination (Lux)

• $A$ = Area of working plane (m²)

• $N$ = Number of lamps (to be found)

• $UF$ = Utilization Factor

• $MF$ = Maintenance Factor

• Lumen Output = Φ (lm) per lamp

Point-by-Point Illumination (Multiple Sources):

For n point sources, total illuminance at a point is the scalar sum of illuminance from each source.

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

Where $$\displaystyle I_i $$, $$\displaystyle d_i $$, $$\displaystyle \theta_i $$ are the candle power, distance, and angle of incidence for the i-th source.

[!TIP] Exam Strategy: For numericals, first draw a clear diagram showing heights, distances, and angles. Calculate $d$ and $\theta$ for each lamp separately. Remember $$\displaystyle \cos\theta = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{h}{d} $$ for a horizontal plane.

1.3 Lighting Schemes & Systems

Factors for Designing Lighting Scheme:

1. Nature of Task: Precision work requires higher lux.

2. Room Dimensions & Reflectances: Affects UF.

3. Mounting Height: Determines SHR and direct/indirect ratio.

4. Glare & Color Rendering: Luminaire type, CRI.

5. Energy Efficiency & Cost: Initial vs. operating cost.

1.4 Energy-Efficient Lighting

[!TIP] Comparison Focus: Be ready to compare Incandescent vs. Fluorescent vs. LED on parameters: Efficacy (lm/W), Lifetime, Color Rendering Index (CRI), Cost, and Heat Emission.

2.0 WELDING PROCESSES

2.1 Classification Based on Process

2.2 Specific Welding Methods

A. Arc Welding

• Principle: Heat generated by an electric arc between an electrode and the workpiece.

• Process: Electrode (consumable or non-consumable) creates arc (~5000°C). Shielding gas/flux protects molten pool.

• Types: SMAW (Stick), GMAW (MIG), GTAW (TIG), FCAW.

• Applications: Structural steel, pipelines, shipbuilding, general fabrication.

B. Resistance Welding

• Principle: Heat generated by electrical resistance at the interface of materials under pressure ($$\displaystyle H = I^2 R t $$).

• Types:

  • Spot Welding: Two electrodes press sheets together at discrete points.

  • Seam Welding: Rotating wheel electrodes create continuous weld.

  • Projection Welding: Uses projections on one workpiece to localize heat.

  • Flash/Butt Welding: Ends brought together with pressure after flashing.

• Applications: Automotive bodies, appliances, wire joining.

C. Electron Beam Welding (EBW)

• Principle: Kinetic energy of a high-velocity electron beam (accelerated in vacuum) is converted to thermal energy upon impact.

• Process: Requires high vacuum (10⁻⁵ mbar). Deep, narrow penetration (high power density).

• Applications: Aerospace components, nuclear reactors, high-value precision parts (gears, turbine blades).

• Limitations: High equipment cost, vacuum chamber size limits, requires precise joint preparation, X-ray shielding needed.

2.3 Welding Equipment - Welding Transformers

• Function: Step-down transformer to provide high current (100-1000A) at low voltage (15-45V) for arc stability.

• Characteristics:

  • Drooping Characteristic: Voltage decreases as current increases. Essential for self-adjustment: if arc length increases (resistance ↑), current ↓, pulling arc back to set length.

  • Types: AC transformers (with rectifier for DC), DC generators (obsolete), Inverter-based (modern, lightweight, electronic control).

• Application: Power source for most manual arc welding processes (SMAW, GTAW).

3.0 ELECTRIC HEATING

3.1 Advantages & Losses

Advantages:

1. Clean & Controllable: No combustion byproducts, precise temperature control.

2. High Efficiency: Nearly 100% at point of use (no flue losses).

3. Automatic Operation: Easy to automate and integrate with process control.

4. High Temperature & Special Atmosphere: Can achieve very high temps; suitable for inert/reducing atmospheres.

5. Safety & Comfort: No open flames, less operator fatigue.

6. Uniform Heating: Possible with proper design (e.g., induction).

Losses in Electric Heating Systems:

1. Distribution Losses: I²R losses in supply cables and busbars.

2. Radiation & Convection Losses: From hot surfaces to surroundings.

3. Loss in Heating Element: Due to oxidation, scaling (in resistance heating).

4. Loss in Workpiece: Heat conducted away to supports, fixtures.

5. Loss in Furnace Walls: Through conduction and radiation (reduced by insulation).

3.2 Types of Heating Methods

A. Resistance Heating

• Principle: $$\displaystyle H = I^2 R t $$. Heat generated when current flows through a resistive element.

• Types:

  • Direct Resistance: Current passes through the workpiece itself (e.g., salt bath furnace). Requires good electrical contact.

  • Indirect Resistance: Current passes through a separate resistor (Nichrome, Kanthal) which radiates/convects heat to the workpiece. Most common (e.g., ovens, toasters).

• Applications: Domestic cooking, industrial furnaces, room heaters, toasters.

B. Induction Heating

• Principle: Based on electromagnetic induction. High-frequency AC in primary coil induces eddy currents ($$\displaystyle I_e $$) in the conductive workpiece. Heat generated by $$\displaystyle I_e^2 R $$ in the workpiece (Joule heating). Also includes hysteresis losses in magnetic materials.

$$P \propto f B^2 d^2$$

(Power ∝ frequency², flux density², material thickness²)

• Key Feature: Skin Effect - Current concentrates on surface. Depth of penetration $$\displaystyle \delta \propto \frac{1}{\sqrt{f}} $$.

• Applications: Surface hardening, melting (induction furnaces), soldering/brazing, induction cooktops.

• Limitations: Works only on conductive materials. Expensive high-frequency power supply (inverter). Limited penetration depth.

C. High-Frequency Induction Furnace

• Principle: Induction heating used for melting metals.

• Types:

  1. Coreless Furnace: Workpiece itself forms a short-circuited secondary. No magnetic core. Used for melting and holding.

  2. Channel Furnace: Has a magnetic core and a single-turn secondary (the molten metal channel). Used for holding and superheating.

  3. Plasma Arc Furnace: Uses plasma torch (ionized gas) for ultra-high temperatures.

• Description: AC supply (50 Hz to 10 kHz) converted to high-frequency AC by oscillator/inverter. Primary coil surrounds refractory crucible containing charge. Efficient, rapid heating, clean process.

3.3 Applications & Load Calculations

Electrical Load Calculation for Air Conditioning:

1. Calculate Cooling Load (in BTU/hr or Watts): Consider heat gain from:

   • Transmission through walls/windows (Q = U A ΔT)

   • Solar radiation through windows

   • Occupants (sensible + latent heat)

   • Equipment/appliances (lights, motors)

   • Infiltration/ventilation

2. Select AC Unit: Total cooling load determines tonnage (1 Ton = 12,000 BTU/hr ≈ 3.5 kW).

3. Estimate Electrical Power: $$\displaystyle P_{elec} = \frac{\text{Cooling Load (W)}}{\text{COP}} $$ or $$\displaystyle P_{elec} = \frac{\text{ Cooling Load (BTU/hr)}}{12,000 \times \text{EER}} $$

   • EER (Energy Efficiency Ratio): BTU/hr / Watt.

   • COP (Coefficient of Performance): Cooling output (W) / Electrical input (W). COP = EER / 3.412.

Example: Toaster with Series/Parallel Elements

• Given: Two 100Ω elements, 250V supply.

• Parallel Connection:

  $$\displaystyle R_{eq} = \frac{100 \times 100}{100+100} = 50\Omega $$

  $$\displaystyle P = \frac{V^2}{R_{eq}} = \frac{250^2}{50} = 1250 \text{ W} $$

• Series Connection:

  $$\displaystyle R_{eq} = 100 + 100 = 200\Omega $$

  $$\displaystyle P = \frac{250^2}{200} = 312.5 \text{ W} $$

[!TIP] Key Insight: Parallel connection gives higher total power (and faster toasting) because equivalent resistance is lower. Series connection gives lower power but each element gets full voltage (250V), while in parallel each gets 125V.

4.0 ELECTROLYSIS & ELECTROPLATING

4.1 Fundamental Principles

Basic Principle: Decomposition of an electrolyte by passing direct electric current, causing chemical changes at electrodes.

First Law of Electrolysis (Faraday's First Law):

The mass (m) of substance deposited or liberated at an electrode is directly proportional to the quantity of electricity (charge Q) passed.

$$m \propto Q \quad \Rightarrow \quad m = Z Q$$

Where:

• $Z$ = Electrochemical Equivalent (E.C.E.) = mass deposited per unit charge (kg/Coul or gm/Coul).

• $$\displaystyle Q = I \times t $$ (Current in Amperes × time in seconds).

Second Law of Electrolysis (Faraday's Second Law):

When the same quantity of electricity is passed through different electrolytes, the masses of different substances deposited are proportional to their chemical equivalent weights ($E$).

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

Where $$\displaystyle E = \frac{\text{Atomic Weight}}{\text{Valency}} $$.

Faraday Constant (F): Charge required to deposit 1 gram-equivalent of any substance. $$\displaystyle F = 96500 $$ Coulombs ≈ charge of 1 mole of electrons.

Relation between Z and E:

$$Z = \frac{E}{F} \quad \text{(in consistent units)}$$

4.2 Electroplating

• Definition: Process of depositing a thin layer of a superior metal (like Cr, Ni, Au, Ag) onto a base metal object using electrolysis.

• Purpose:

  1. Protection: Prevent corrosion (e.g., Zn on iron → galvanization).

  2. Appearance: Decorative finish (gold/silver plating).

  3. Wear Resistance: Hard chrome plating.

  4. Conductivity: Silver plating on copper conductors.

• Process:

  1. Cleaning: Object (cathode) thoroughly cleaned (degreasing, pickling) to remove oxides/oils.

  2. Electroplating Bath: Electrolyte contains salt of the plating metal. Anode is made of the plating metal (soluble anode). Sometimes inert anodes (Pb, Pt) used with complex salts.

  3. Current: DC current passed. Metal ions ($$\displaystyle M^{n+} $$) migrate to cathode, gain electrons ($$\displaystyle M^{n+} + ne^- \rightarrow M $$), and deposit.

  4. Post-Treatment: Rinsing, drying, polishing.

4.3 Numerical Problems - Weight of Deposition

Standard Formula:

$$\boxed{m = \frac{I \times t \times E}{96500}} \quad \text{(mass in grams, I in A, t in sec, E in gram-equivalent weight)}$$

Or using E.C.E. ($Z$):

$$m = Z \times I \times t$$

Steps:

1. Write electrode reaction, find valency (n).

2. Calculate Chemical Equivalent $$\displaystyle E = \frac{\text{Atomic Weight (or Molecular Weight for salts)}}{\text{Valency (n)}} $$.

3. Convert time to seconds.

4. Apply $$\displaystyle m = \frac{I t E}{96500} $$.

[!TIP] Common Error: Forgetting to convert time to seconds. For salts like CuSO₄, use Molecular Weight (159.5 for CuSO₄) and valency of Cu (2), so $$\displaystyle E = 159.5/2 = 79.75 $$ g/equivalent.

5.0 ELECTRIC DRIVES (GENERAL)

5.1 Advantages of Electric Drives

Key Advantages: Precise speed/torque control, high efficiency, flexible layout, automatic protection, easy start/stop, regenerative braking capability.

5.2 Selection of Motor Drive

Factors for Selection:

1. Nature of Load:

   • Constant Torque: Cranes, conveyors, elevators (DC series, AC slip-ring).

   • Constant Power: Machine tools, winding machines (DC shunt, synchronous).

   • Variable Torque (Fan/Pump): Centrifugal fans, pumps (Squirrel cage induction with VFD).

2. Starting Torque Requirement: High starting torque → DC series, slip-ring induction.

3. Speed Range & Control: Wide speed range → DC shunt, slip-ring with rotor resistance, VFD induction.

4. Duty Cycle: Continuous, intermittent, short-time. Affects motor rating (thermal capacity).

5. Environmental Conditions: Hazardous area (flame-proof), dusty (TEFC), corrosive (special coatings).

6. Power Supply: Available voltage, AC/DC, frequency.

7. Cost & Efficiency: Initial cost vs. operating cost (premium efficiency motors for long running hours).

8. Installation & Maintenance: Ease of maintenance, availability of spares.

5.3 Drive Configurations

[!TIP] Exam Differentiation: Emphasize that individual drive is the norm today due to flexibility, better speed control, higher reliability, and easier maintenance. Group drive is only of historical interest or for very specific, synchronized processes.

6.0 ELECTRIC TRACTION

6.1 Traction System Fundamentals

Characteristics of a Good Traction System:

1. High Starting Torque: To accelerate heavy train quickly.

2. Simple & Robust Speed Control: Wide speed range without overheating.

3. High Overload Capacity: To handle gradients and sudden acceleration.

4. Ability to Handle Frequent Starts/Stops: Regenerative braking desirable.

5. High Efficiency: Especially during regenerative braking.

6. Low Maintenance & Cost.

7. Smooth Acceleration & Braking.

8. Good Adhesion: High tractive effort without wheel slip.

Suitability of DC Series Motor for Electric Traction:

• High Starting Torque: $$\displaystyle T \propto I_a^2 $$ (since $$\displaystyle \phi \propto I_a $$). Excellent for starting heavy loads.

• Speed-Torque Characteristic: Speed decreases sharply with increase in load (almost constant power). Matches traction requirement: high speed on level track, low speed on gradient.

• Simple Speed Control: Varying field flux (via field weakening) or armature voltage gives wide speed range.

• High Overload Capacity: Can withstand temporary overloads.

• Regenerative Braking: Possible with proper control circuitry (motors act as generators).

• Disadvantage: Poor performance at very high speeds (due to commutation issues). Hence, often used with geared drives to keep motor speed within limits.

6.2 Train Motion & Speed-Time Curves

General Speed-Time Curve for Main Line Service (Trapezoidal):

Speed (v)

  ^

  |       /

  |      /|
|     / |
|    /  |
|   /   | Coasting

  |  /    |
| /     |
|/      |

  +-------+----------------> Time (t)

  0   t1  t2   t3   t4

• 0 → t₁: Acceleration period (constant acceleration α). Motor draws constant current → constant torque → linear speed rise.

• t₁ → t₂: Constant Speed (free-running) period. Motor at rated voltage, field at full strength.

• t₂ → t₃: Coasting period. Motor disconnected, train coasts under inertia against resistance.

• t₃ → t₄: Braking period (constant deceleration β). Brakes applied to bring train to stop.

Derivation of Equation for Maximum Speed ($$\displaystyle V_{max} $$):

Let:

• $$\displaystyle M_e $$ = Effective mass (in kg) = Dead Weight (W) + Acceleration Weight (αW/g)

  • Dead Weight (W): Actual weight of train (in kg or tonnes).

  • Acceleration Weight: Rotating mass equivalent (ωJ/g). For simplicity, often taken as 5-10% of dead weight.

• $α$ = Acceleration (m/s²)

• $β$ = Braking retardation (m/s²)

• $D$ = Distance between stops (m)

• $r$ = Train resistance per unit mass (N/kg) - includes friction, air resistance.

• $$\displaystyle F_t $$ = Tractive effort (N)

During Acceleration (0 to t₁):

Net force = $$\displaystyle F_t - r M_e = M_e α $$

Time for acceleration: $$\displaystyle t_a = \frac{V_{max}}{α} $$

Distance covered: $$\displaystyle d_a = \frac{1}{2} α t_a^2 = \frac{V_{max}^2}{2α} $$

During Coasting (t₂ to t₃):

Net force = $$\displaystyle - r M_e = M_e α_c $$ (where $$\displaystyle α_c $$ is negative, deceleration due to resistance alone)

Time of coasting: $$\displaystyle t_c = \frac{V_{max}}{|α_c|} $$ (where $$\displaystyle |α_c| = \frac{r M_e}{M_e} = r $$ in m/s² if r is in N/kg)

Distance: $$\displaystyle d_c = \frac{V_{max}^2}{2|α_c|} $$

During Braking (t₃ to t₄):

Net force = $$\displaystyle - (F_b + r M_e) = -M_e β $$ (F_b is braking force)

Time for braking: $$\displaystyle t_b = \frac{V_{max}}{β} $$

Distance: $$\displaystyle d_b = \frac{V_{max}^2}{2β} $$

Total Distance D = d_a + d_c + d_b

$$D = \frac{V_{max}^2}{2} \left( \frac{1}{α} + \frac{1}{|α_c|} + \frac{1}{β} \right)$$

Solving for $$\displaystyle V_{max} $$:

$$\boxed{V_{max} = \sqrt{\frac{2D}{\frac{1}{α} + \frac{1}{|α_c|} + \frac{1}{β}}}}$$

[!TIP] Numerical Approach: In problems, you are often given:

• D (distance between stops)

• Acceleration (α) in km/h/s or m/s² → CONVERT to m/s².

• Braking retardation (β) similarly.

• Train resistance (r) in N/tonne or kg/tonne → convert to N/kg.

• Dead weight (W) in tonnes.

1. Calculate $$\displaystyle |α_c| = r $$ (if r is in N/kg, it's directly deceleration in m/s²).

2. Plug into formula above to get $$\displaystyle V_{max} $$ (m/s) → convert to km/h if needed (×3.6).

3. Calculate times: $$\displaystyle t_a = V_{max}/α $$, $$\displaystyle t_b = V_{max}/β $$, $$\displaystyle t_c = V_{max}/|α_c| $$.

4. Distances: $$\displaystyle d_a = \frac{1}{2}α t_a^2 $$, etc., verify sum = D.

6.3 Train Resistance & Energy Consumption

• Dead Weight (W): Actual weight of locomotive + coaches/wagons (in kg or tonnes).

• Acceleration Weight: Equivalent weight accounting for rotational inertia of wheels, motors, etc. $$\displaystyle \text{Acceleration Weight} = \text{Dead Weight} \times (1 + \frac{\text{Rotating Inertia Factor}}{g}) $$. Typically 5-10% of dead weight.

• Train Resistance (R): Sum of mechanical resistance (friction in bearings, wheel flanges) + air resistance (∝ v²). Expressed as $$\displaystyle R = r_0 + r_1 v + r_2 v^2 $$ (N/tonne or N/kg).

• Specific Energy Consumption (SEC): Energy consumed per tonne-km (Wh/tonne-km or kJ/tonne-km).

$$\text{SEC} = \frac{\text{Total Energy Input (Wh)}}{\text{Total Weight (tonnes)} \times \text{Distance (km)}}$$

Includes energy for acceleration, running against resistance, and braking losses (if not regenerative).

Factors Affecting SEC:

1. Distance between stops: Shorter stops → more acceleration/braking → higher SEC.

2. Acceleration & Braking rates: Higher rates require more power/energy.

3. Maximum speed: Air resistance ∝ v³, so SEC increases sharply with speed.

4. Gradient: Uphill increases resistance, downhill may allow regenerative braking.

5. Train resistance: Rolling friction, wind.

6. Efficiency of drive & braking: Regenerative braking reduces net consumption.

7. Dead weight vs. payload: Higher payload ratio reduces SEC.

6.4 Electrical Braking

Types:

1. Plugging (or Reverse Current Braking): Motor connections reversed while running. Acts as a brake, but consumes energy (power is dissipated in resistors). Very high braking torque, used for emergency/quick stop.

2. Rheostatic Braking: Motor disconnected from supply, connected to a braking resistor in the armature circuit. Kinetic energy dissipated as heat in resistor. Common in DC drives and AC drives with DC link.

3. Regenerative Braking: Motor acts as generator. Generated power fed back to the supply line (AC system) or to a braking resistor/chopper (if grid not receptive). Most energy-efficient. Requires compatible drive system (VFD, DC drive with regenerative converter).

Explanation of Regenerative Braking (DC Series Motor Example):

• Motor disconnected from supply, field remains excited.

• Train momentum drives motor as generator.

• Generated EMF ($$\displaystyle E_g $$) drives current from armature into the supply line (if supply is AC, need converter/inverter to feed back).

• Braking torque is proportional to product of field flux and armature current (which is now in opposite direction to motoring).

• Condition: $$\displaystyle E_g > V_{supply} $$ (for DC) or proper phase angle (for AC) to feed power back.

• Limitation: At very low speeds, $$\displaystyle E_g $$ drops below supply voltage → braking ineffective → need to switch to rheostatic braking.

6.5 Load Equalization

• Concept: In traction, power demand is highly pulsating due to frequent acceleration (high current) and coasting/braking (low/no current). This causes severe fluctuations in the substation load and line voltage drop.

• Need: To smooth out these fluctuations, reduce peak demand on power supply, improve power factor, and reduce voltage flicker.

• Method: Use a motor-generator (MG) set or static storage (batteries, flywheels, supercapacitors) between the supply and the traction motors.

  • During acceleration, MG set draws power from supply and also from its own inertia (if flywheel) to meet high demand.

  • During braking (regenerative), MG set absorbs excess generated power (or charges battery).

  • The net effect is that the supply sees a nearly constant load equal to the average power requirement.

7.0 ELECTRIC VEHICLES & HYBRID SYSTEMS

7.1 Electric Vehicle (EV)

• Explanation: A vehicle propelled wholly or partly by one or more electric motors, using energy stored in batteries (or other on-board storage like fuel cells).

• Components:

  1. Energy Source: Battery Pack (Li-ion, NiMH, Lead-acid). Fuel Cell (H₂ + O₂ → Electricity + Water).

  2. Electric Drive Motor: AC induction motor, Permanent Magnet Synchronous Motor (PMSM), or Brushed DC motor.

  3. Power Controller / Inverter: Converts DC from battery to AC (for AC motors) with variable frequency/voltage for speed control. Also handles regenerative braking (converts AC from motor to DC for battery charging).

  4. Charger: On-board or off-board to charge battery from AC grid.

  5. Transmission: Often single-speed reduction gear (electric motors have wide torque-speed range, no need for multi-gear transmission). Some use multi-speed for efficiency/power.

  6. Auxiliary Systems: 12V battery, DC-DC converter, power steering (electric), air conditioning (electric compressor).

  7. Vehicle Control Unit (VCU): Manages overall operation, energy flow, safety.

Transmission System Used in EVs:

• Most Common: Single-speed reduction gearbox with a fixed gear ratio. Simple, compact, efficient.

• Reason: Electric motors produce maximum torque at zero speed and have a very wide constant power speed range (up to 3-4 times base speed). Hence, a single gear covers the entire speed range (0 to max vehicle speed).

• Exceptions: Some high-performance EVs (e.g., Porsche Taycan) use a 2-speed transmission to improve efficiency at very high speeds and acceleration.

7.2 Hybrid Electric Vehicles (HEV)

• Definition: Vehicle that combines a conventional internal combustion engine (ICE) with one or more electric motor-generators, using both as propulsion sources. Cannot be plugged in to charge (battery charged by ICE/regeneration). (Plug-in Hybrids - PHEVs - are a sub-class that can be plugged in).

• Types:

  1. Series Hybrid (S-HEV):

     • Configuration: ICE → Generator → Electricity → Motor → Wheels. Battery also powers motor. ICE never mechanically connected to wheels.

     • Operation: ICE runs at constant optimal speed to generate electricity. Motor provides all traction. Battery buffers energy.

     • Example: Diesel-electric locomotives, some buses (e.g., Volvo B5LH).

  2. Parallel Hybrid (P-HEV):

     • Configuration: ICE and Electric Motor both mechanically connected to wheels (via transmission). Can operate independently or together.

     • Operation: Motor assists ICE during acceleration, recovers energy during braking. Simple, but ICE and motor speeds are linked.

     • Example: Honda Insight (early), mild hybrids (48V systems).

  3. Series-Parallel (Power-Split) Hybrid (SP-HEV):

     • Configuration: Uses a planetary gear set to split power between ICE, generator, and motor. Allows independent control of ICE speed and vehicle speed.

     • Operation: Can operate in pure electric (battery → motor), series (ICE → gen → motor), parallel (ICE + motor), or charge-sustaining mode.

     • Example: Toyota Prius (Hybrid Synergy Drive), Ford Escape Hybrid.

Basic Configuration & Operation (Series-Parallel - Most Common):

• Key Component: Power Split Device (planetary gear).

  • Sun Gear: Connected to Motor Generator 1 (MG1, primarily generator).

  • Ring Gear: Connected to wheels (via final drive).

  • Planetary Carrier: Connected to ICE.

• Operation Modes:

  • Low Speed/Start: MG2 (traction motor) drives wheels from battery. ICE off.

  • Cruise: ICE drives wheels directly (mechanical path) and also drives MG1 to generate electricity for MG2 if needed.

  • Acceleration: ICE + MG2 power combined to wheels.

  • Braking: MG2 acts as generator to recharge battery (regenerative braking). MG1 may also generate.

  • Battery Charge: ICE drives MG1 to generate electricity for battery (while vehicle stationary or moving).

[!TIP] Key Differentiator: In Series HEV, ICE only generates electricity. In Parallel HEV, ICE directly drives wheels. In Series-Parallel, both are possible via a mechanical split.