Electric Traction

Electric traction refers to the use of electric power to propel railway vehicles. It offers
advantages such as high efficiency, quick acceleration, regenerative braking, and reduced
pollution.

✅ 1. Requirements of an Ideal Traction System

An ideal electric traction system should have the following features:

Requirement Description

High Starting Torque For quick acceleration and heavy loads

Wide Speed Range Low speed for starting, high speed for running

Smooth Speed Control For passenger comfort and energy efficiency

Overload Capacity To manage gradients and acceleration

Regenerative Braking For energy saving and better braking

Reliability & Low Maintenance Essential for continuous operation

Low Capital & Operating Cost Economically viable

Less Pollution & Noise Eco-friendly and suitable for urban areas

2. Supply Systems for Electric Traction

There are different supply systems based on voltage, frequency, and type (AC or DC):

✅ a. DC Supply Systems

 600–750 V DC (used in metros and trams)

 1500 V DC, 3000 V DC (used in mainline railways in some countries)

✅ b. AC Supply Systems

 Single-phase 25 kV, 50 Hz AC – most commonly used worldwide.

 3-phase AC – used with induction motors in modern systems.

✅ c. Composite / Diesel-Electric
  Diesel engine generates electricity for traction motors.
 Used where electrification is not feasible.

3. Train Movement and Speed-Time Curves

✅ a. Speed-Time Curve

Shows speed of the train vs. time. Consists of:

1. Acceleration
2. Constant speed (free run)
3. Coasting (power off, slows due to resistance)
4. Braking

✅ b. Simplified Speed-Time Curve

 Ignores minor transitions.

 Approximates entire journey into 3 main parts: acceleration, coasting, braking.

✅ c. Average Speed

Average Speed=Total DistanceTotal Time\text{Average Speed} = \frac{\text{Total

Distance}}{\text{Total Time}}Average Speed=Total TimeTotal Distance

✅ d. Schedule Speed

Includes stop time (station halts):

Schedule Speed=Total DistanceTotal Time including stops\text{Schedule Speed} = \frac{\text{Total

Distance}}{\text{Total Time including
stops}}Schedule Speed=Total Time including stopsTotal Distance

4. Mechanism of Train Movement

✅ a. Energy Consumption

 Depends on acceleration, gradient, resistance, and number of stops.

 More stops or rapid acceleration increases energy use.

✅ b. Tractive Effort (TE)

Force exerted by the motor at the wheels to move the train.

i. During Acceleration:
TE=m⋅aTE = m \cdot aTE=m⋅a

Where:

 mmm = mass
 aaa = acceleration

ii. On Gradient:
TEgradient=m⋅g⋅sin (θ)≈m⋅g⋅G100TE_{\text{gradient}} = m \cdot g \cdot \sin(\theta) \approx m
\cdot g \cdot \frac{G}{100}TEgradient=m⋅g⋅sin(θ)≈m⋅g⋅100G

Where GGG is the gradient in %.

iii. For Resistance:

TEresistance=m⋅rTE_{\text{resistance}} = m \cdot rTEresistance=m⋅r

rrr = train resistance per tonne (depends on speed, track, curves, wind, etc.)

✅ c. Power Output at Driving Axles

P=TE×vP = TE \times vP=TE×v

Where vvv = train speed (in m/s)

✅ d. Energy Output

E=∫P dtE = \int P \, dtE=∫Pdt

Or calculated over the journey using mean power.

✅ e. Factors Affecting Specific Energy Consumption

(Specific Energy = Energy consumed per tonne per km)

 Train load
 Track profile (level, gradient, curves)
 Acceleration and braking rates
 Schedule speed
 Driving habits (manual vs automated control)
 Regenerative braking efficiency

✅ f. Coefficient of Adhesion
  Ratio of tractive effort to adhesive weight (weight on driven wheels)

Coefficient of Adhesion=TEAdhesive Weight\text{Coefficient of Adhesion} = \frac{TE}{Adhesive\

Weight}Coefficient of Adhesion=Adhesive WeightTE

 Typical values: 0.25 to 0.35 for steel wheel on steel rail.

 Affects maximum possible tractive effort before slipping.

Summary Table
Concept Formula / Key Point

DistanceTotal Time\frac{\text{Distance}}{\text{Total
Average Speed
Time}}Total TimeDistance

DistanceTime + Halts\frac{\text{Distance}}{\text{Time +
Schedule Speed
Halts}}Time + HaltsDistance

TE (acceleration) TE=m⋅aTE = m \cdot aTE=m⋅a

TE (gradient) TE=m⋅g⋅G100TE = m \cdot g \cdot \frac{G}{100}TE=m⋅g⋅100G

Power Output P=TE⋅vP = TE \cdot vP=TE⋅v

Specific Energy EnergyTonne-km\frac{\text{Energy}}{\text{Tonne-km}}Tonne-kmEnergy

Coefficient of
TEAdhesive Weight\frac{TE}{\text{Adhesive Weight}}Adhesive WeightTE
Adhesion
 Electric Traction Motors & Their Control
Electric traction systems commonly use DC Series motors, DC Shunt motors, AC Series
motors, and 3-phase Induction motors. These motors drive electric trains, trams, and other
railway vehicles due to their high torque characteristics and controllability.

Parallel and Series Operation of Motors

✅ 1. DC Series Motors

 Series Operation:
o Motors are connected in series; same current flows through each motor.
o Speed may vary if wheel diameters are unequal: the motor with a smaller
wheel rotates faster.
o Unequal torque sharing can damage the motors.
 Parallel Operation:
o Same voltage, different currents.
o Motors must be closely matched.
o Unequal wheel diameters cause speed mismatch → may cause circulating
currents and overloading.

✅ 2. DC Shunt Motors

 Parallel Operation:
o Most common, as these motors are naturally parallel-fed.
o Unequal wheel diameters again cause torque and speed imbalance.
 Series Operation:
o Not suitable for traction due to their poor torque at low speeds and poor
starting performance.

Effect of Unequal Wheel Diameters

When wheel diameters are unequal:

 The motors attempt to run at different speeds.

 Causes uneven torque distribution.
 Leads to overheating or motor damage.
 Special differential gear systems or speed compensation methods are required.

Effect of Sudden Change in Supply Voltage

  Sudden Rise in Voltage:
o Causes a spike in speed and torque.
o May damage the armature or winding insulation.
 Sudden Drop in Voltage:
o Sharp drop in torque.
o Risk of stalling under load.
o Protective relays may trip to prevent damage.

Temporary Interruption of Supply

 If supply is lost momentarily:
o Traction motors freewheel (run without power).
o Sudden re-application of power may cause shock load.
o Requires:
 Smooth re-energization.
 Proper circuit breakers and auto-reset protection.
 Flywheel systems in older trains or capacitive buffers in modern
EMUs.

Tractive Effort and Horsepower

 Tractive Effort (TE): Force at the wheel to move the train.
o Depends on torque and wheel radius.
o TE = (Motor Torque) / (Wheel Radius)
 Horsepower (HP): Power output.
o HP = (TE × Speed) / 375 (in ft-lb/sec)
o More HP → higher acceleration and ability to maintain speed on gradients.

Use of AC Series Motor and Induction Motor in

Traction
✅ 1. AC Series Motor

 Similar to DC Series motor.

 Operates on single-phase AC.
 High starting torque, variable speed.
 Suitable for old AC electric trains.
 Disadvantage: Requires commutator → frequent maintenance.

✅ 2. 3-Phase Induction Motor (Modern Choice)

  Used in modern EMUs and metro systems.
 Advantages:
o Robust and maintenance-free (no brushes/commutator).
o Regenerative braking capability.
o Controlled by Variable Frequency Drives (VFDs) or inverters for smooth
acceleration.
 Types:
o Squirrel Cage: Common, rugged.
o Slip Ring: Previously used where variable speed was needed.

✅ Summary Table:
Feature DC Series DC Shunt AC Series 3-Ph Induction
Motor Motor Motor Motor
Starting Very High Low High High
Torque
Speed Control Easy Good Limited Via VFD
Maintenance High Moderate High Low
Used in Old trains Rare Legacy AC Modern trains
systems
 Traction Motor Control
Traction motor control is essential to achieve smooth acceleration, deceleration, speed
regulation, braking, and safety in electric trains and locomotives.

1. DC Series Motor Control

DC Series motors are widely used in traction due to their high starting torque. Control is
achieved using:

✅ a. Rheostatic Control (Manual / Resistance Control)

 Adds resistance in series with the motor during start.

 Wastes energy as heat.
 Used in old systems.

✅ b. Series-Parallel Control

 Multiple motors connected in:

o Series at low speed (high torque, low voltage).
o Parallel at high speed (each motor gets full voltage).
 Efficient stepwise control.

✅ c. Field Weakening Control

 Reduces field current → increases speed beyond base speed.

 Used for high-speed running after full voltage is applied.

2. Multiple Unit (MU) Control

 Used in EMUs and metro trains.

 One driver’s cab controls all motors in all connected coaches.
 Each unit has its own motors and control systems.
 Control signals (not power) are sent via cables to each unit.
 Benefits:
o Easy expansion.
o Uniform acceleration.
o Centralized control of the whole train.

3. Braking of Electric Motors

Electric braking helps in energy saving and reducing wear on mechanical brakes. Three main
types:

✅ a. Regenerative Braking

 Motor works as a generator.

 Converts kinetic energy to electrical energy and feeds it back to the supply.
 Used in 3-phase induction motors.

✅ b. Rheostatic Braking

 Motor acts as a generator.

 Generated energy is dissipated as heat in resistors.
 Used where regeneration is not possible.

✅ c. Plugging (Reverse Current Braking)

 Supply polarity is reversed.

 Motor exerts braking torque and stops quickly.
 Not energy efficient; used for emergency.

4. Electrolysis by Current Through Earth

 In DC traction systems, return current flows through rails.

 If insulation is poor, some current leaks through earth.
 Causes electrolysis:
o Chemical decomposition of underground metallic structures like pipes and
cables.
o Leads to corrosion, damaging infrastructure.
 Mitigation:
o Use of insulated return conductors.
o Track bonding and earth leakage protection.

5. Current Collection in Traction Systems

Traction vehicles collect power using:

✅ a. Overhead Line Equipment (OHLE)

 Common in electric railways.

 Power collected via pantograph or trolley pole.
✅ b. Third Rail System

 Used in metros and underground systems.

 Power collected via a sliding shoe.
 Safer in confined spaces; requires insulation and protection.

✅ c. Battery / Hybrid

 Some modern systems use battery-electric or hybrid traction.

 Used for last-mile operation or areas without OHLE.

6. Power Electronic Controllers in Traction System

Modern traction uses power electronics for efficient control:

✅ a. Chopper Control (for DC Motors)

 Replaces resistance control.

 Uses IGBT/MOSFET to switch power supply on and off rapidly.
 Controls average voltage and motor speed.

✅ b. Inverter Control (for AC Motors)

 Converts DC to variable-frequency AC.

 Controls speed and torque of 3-phase induction motors.
 V/f control or vector control used.

✅ c. Rectifiers

 Convert AC supply to DC for DC traction systems.

✅ d. Benefits:

 Smooth acceleration and deceleration.

 Energy efficient.
 Compact and lightweight.
 Enables regenerative braking.

Summary Table
Topic Key Point

DC Series Motor Control Rheostatic, Series-Parallel, Field Weakening

 Topic Key Point

MU Control One driver controls multiple motorized coaches

Braking Regenerative, Rheostatic, Plugging

Electrolysis Caused by leakage current through earth

Current Collection Pantograph (OHLE), Third rail, Battery

Power Electronics Choppers, Inverters, Rectifiers for control and efficiency

 Electric Lighting – Key Topics Explained

1. Definition of Terms
Term Description
Total light energy emitted per second by a source. Measured in
Luminous Flux (Φ)
lumens (lm).
Luminous Intensity (I) Light intensity in a specific direction. Unit: candela (cd).
Light falling per unit area on a surface. Measured in lux
Illuminance (E)
(lm/m²).
Luminance (L) Perceived brightness of a surface. Measured in cd/m².
Efficacy Efficiency of a lamp: lumens per watt (lm/W).
Color Temperature Indicates warmth/coolness of light in Kelvin (K).
Color Rendering Index A measure of how well a light source shows colors realistically.
(CRI) Scale: 0–100.
Glare Discomfort or reduced visibility caused by excessive brightness.

2. Laws of Illumination
A. Inverse Square Law

 E=Id2E = \frac{I}{d^2}E=d2I
 Illuminance decreases with square of the distance.

B. Cosine Law

 E=Icos θd2E = \frac{I \cos \theta}{d^2}E=d2Icosθ

 Illuminance also depends on the angle between light direction and normal to the
surface.

3. Luminaries
 Definition: Fixtures that house and position the lamp, often with reflectors/diffusers
to direct light.
 Types:
o Open reflectors: High efficiency.
o Diffusing luminaries: Even distribution, soft light.
o Industrial luminaries: Rugged design, high intensity.
o Decorative: Residential, aesthetic use.
 4. Lighting Requirements
 Based on:
o Nature of task (precision vs. general visibility).
o Visual comfort.
o Safety and security.
o Energy efficiency.
 Considerations:
o Uniformity of light.
o Glare control.
o Color accuracy.
o Lighting level (lux requirement).
o Maintenance cost.

5. Illumination Levels (Standard Lux Values)

Application Lux Level
Corridor 50 – 100
Classroom 300 – 500
Office Work 500 – 750
Workshop/Factory 750 – 1500
Street 10 – 30
Stadium 1000 – 3000

6. Lamp Selection and Maintenance

A. Types of Lamps

Lamp Type Features

Incandescent Low cost, high heat loss, poor efficacy.
Fluorescent Good efficacy, requires ballast.
CFL Compact, efficient, mercury content.
LED High efficacy, long life, low power.
HID (High Intensity Discharge) Industrial use, includes Mercury Vapor, Metal Halide.

B. Maintenance Considerations

 Cleaning fixtures/luminaries regularly.

 Replacing lamps before failure (group replacement).
  Monitoring lumen depreciation.

7. Lighting Schemes
Scheme Description
Direct 90–100% light directed down. Efficient, harsh shadows.
Indirect 90–100% upward reflection. Soft, glare-free.
Semi-direct 60–90% downward. Balanced lighting.
Semi-indirect 60–90% upward. Aesthetic, used in homes.
General diffuse Even light distribution.

8. Lighting Calculations & Design

A. Lumen Method (Average Method)

Used for uniform illumination.

E=(F×UF×MF)/A = \frac{F \times UF \times MF}{A}E=AF×UF×MF

Where:

 E = Illuminance (lux)
 F= Total lumens
 UF = Utilization Factor
 MF = Maintenance Factor
 A = Area in m²

B. Point-by-Point Method

 Calculates light level at specific points using inverse square and cosine law.
 Useful in street, display lighting.

9. Interior Lighting
A. Residential Lighting

 Ambient Lighting: General illumination (LED bulbs, ceiling lights).

 Task Lighting: Reading, cooking (desk lamp, kitchen light).
 Accent Lighting: Decorative focus (spotlights).

B. Industrial/Factory Lighting
  Needs high illumination.
 Robust fixtures (dust, vibration resistant).
 Focus on:
o Vertical and horizontal surface lighting.
o Color rendering for quality control.
o Emergency lighting.

10. Exterior Lighting

Type Application
Flood Lighting Sports arenas, building facades.
Roads, highways. Uses pole spacing, mounting height, and cut-off
Street Lighting
type fixtures.
Display Lighting Sign boards, shop displays.
Signaling Lights Railway signals, traffic lights.
Beacons Navigation, aviation, lighthouse.
Surveillance
Security cameras need consistent lighting; IR + LED often used.
Lighting
Neon Signs Colorful displays, gas discharge tubes.
LED-LCD Displays Smart advertising panels.

11. Energy Conservation Codes for Lighting

A. ECBC – Energy Conservation Building Code (India)

 Limits on Lighting Power Density (LPD).

 Promotes:
o Use of LEDs and energy-efficient luminaries.
o Daylight integration.
o Automatic controls (dimming, motion sensors).

12. Lighting Controls

Type Function
Daylight Sensors Reduce artificial lighting when sunlight is adequate.
Occupancy Sensors Auto ON/OFF based on room occupancy.
Dimmers Adjust brightness.
Timers Scheduled switching.
Smart Controls IoT-based, app controlled lighting.
 13. Controller Design
 Microcontroller/PLC-Based Lighting Systems
o Input from sensors (motion, light).
o Output to relays or dimmers.
o Control algorithm: ON/OFF, brightness adjustment.
o Communication: Zigbee, Wi-Fi, Bluetooth.
 Example Applications:
o Smart home lighting.
o Street lights with ambient light sensors.
o Automatic classroom lighting with presence detection.

✅ Summary Table
Topic Key Focus
Definitions Terms like lumen, lux, efficacy, CRI
Laws Inverse square & cosine law
Luminaries Fixtures and types
Requirements Standards per application
Levels Lux values by use
Lamp Selection Lamp types, criteria, maintenance
Schemes Direct, indirect, general lighting
Calculations Lumen & point-by-point method
Interior Residential, industrial lighting
Exterior Flood, street, display, surveillance
Energy Codes ECBC, LPD, efficient design
Controls Sensors, dimmers, smart switches
Controller Design Microcontroller-based systems
 Electric Heating
✅ Advantages of Electric Heating

 Clean: No pollution, smoke, or ash.

 Efficient: Almost 100% of electrical energy is converted to heat.
 Controllable: Easy to regulate temperature and time.
 Uniform Heating: Ensures even distribution of heat.
 No Pre-heating Required: Instant heat generation.
 Space Saving: Equipment is compact.
 Safe: No flame, fire risk is minimal.

Heating Methods

1. Resistance Heating
2. Induction Heating
3. Dielectric Heating
4. Arc Heating
5. Infrared Heating
6. Microwave Heating

Resistance Heating

🔄 Direct Resistance Heating:

 Current passes directly through the charge.

 Eg: Salt bath furnace, electrode boilers.

🔁 Indirect Resistance Heating:

 Current flows through a heating element which transfers heat to the charge by
conduction/convection/radiation.
 Eg: Electric ovens, room heaters.

🔌 Electric Ovens:

 Use resistance coils to generate heat.

 Temperature Range: Up to 1000°C for general use; above 1500°C for special
furnaces.

🔧 Properties of Resistance Heating Elements:

 High resistivity
  High melting point
 Oxidation resistance
 Low temperature coefficient of resistance
Materials used: Nichrome, Kanthal, Silicon carbide, Tungsten

Domestic Water Heaters & Appliances

 Water heaters (Geysers): Use immersion rods.

 Appliances: Electric iron, toaster, kettle, etc.
 Thermostat Control: Maintains desired temperature by switching off/on supply
using a bimetallic strip.

Induction Heating

1. Core Type Induction Furnace:

 Magnetic core surrounds the charge.

 Suitable for low-frequency heating and large quantities.

2. Coreless Induction Furnace:

 No magnetic core, uses crucible surrounded by coil.

 Used for high-frequency melting of small batches (steel, bronze, etc.).

Electric Arc Heating

➤ Direct Arc Heating:

 Arc formed between electrodes and the charge.

 Eg: Electric Arc Furnace used in steel production.

➤ Indirect Arc Heating:

 Arc formed between two electrodes, heat radiates to the charge.

 Eg: Used in melting non-ferrous metals.

🔧 Construction & Working:

 Consists of carbon/graphite electrodes, refractory lining, and tilting mechanism.

 Dielectric Heating

 Also known as capacitive heating or RF heating.

 High-frequency electric field causes heating in non-conducting materials (plastics,
wood).
 Frequency: 10 – 100 MHz.

🏭 Applications:

 Plastic welding
 Drying textiles, wood
 Food processing

Infrared Heating

 Heat is transferred via infrared radiation.

 No direct contact with the product.

🔧 Applications:

 Paint drying
 Curing of coatings
 Baking food

Microwave Heating

 Uses microwave frequency (0.3 – 300 GHz).

 Causes molecular vibration (especially water molecules), generating heat.

🏭 Applications:

 Cooking
 Drying paper/textiles
 Chemical and food industries

Simple Design Problems of Resistance Heating Element

To calculate heating element parameters:

1. Heat Energy Required (Q):

Q=m⋅c⋅ΔTQ = m \cdot c \cdot \Delta TQ=m⋅c⋅ΔT

2. Electrical Power (P):

P=QtP = \frac{Q}{t}P=tQ

3. Resistance (R):

R=V2PR = \frac{V^2}{P}R=PV2

4. Length of Element (L):

L=R⋅AρL = \frac{R \cdot A}{\rho}L=ρR⋅A

o ρ\rhoρ: Resistivity of material

o AAA: Cross-sectional area
 Electric Welding
✅ Advantages of Electric Welding

 Simple and economical

 Portable and easy to operate
 Can join dissimilar metals
 No need for fuel gas (like in gas welding)
 More control over heat and welding speed
 Clean process with fewer emissions

Welding Methods

1. Resistance Welding
2. Arc Welding
3. Gas Welding (non-electric)
4. TIG (Tungsten Inert Gas) Welding
5. MIG (Metal Inert Gas) Welding

Resistance Welding
Principle:

 Heat is produced due to resistance to electric current at the joint.

 No filler material used.

Types:

1. Spot Welding:
o Workpieces pressed between electrodes.
o Suitable for sheet metal.
2. Projection Welding:
o Localized welds at embossed points.
o Used in nut/bolt welding to sheets.
3. Seam Welding:
o Rotating wheels produce a continuous weld seam.
o Used in making fuel tanks, drums.
4. Butt Welding:
o Ends of rods/wires are joined by heating and pressing.
o Used in joining wires, rods.

🛠 Equipment Used:
 Welding transformer
 Electrodes (copper alloy)
 Pressure device
 Control panel

Electric Arc Welding

Principle of Arc Production:

 Arc is formed between electrode and workpiece.

 Intense heat melts metal and forms a weld pool.

Characteristics of Arc:

 Requires high current and low voltage

 Stable arc is needed for smooth weld
 Arc temperature: ~3500°C

Types of Arc Welding

1. Carbon Arc Welding:

o Uses carbon electrode.
o No filler or non-consumable.
o Suitable for non-ferrous metals.
2. Metal Arc Welding (MMAW or SMAW):
o Uses metal (consumable) electrode.
o Commonly used for steel structures.
3. Hydrogen Arc Welding:
o Uses hydrogen gas as shielding.
o Extremely high temperature.
o Used for special alloys.

Power Supply for Arc Welding

 AC or DC can be used.
 Low voltage (20–80 V), High current (50–1000 A).
 Welding transformers (for AC)
 Welding rectifiers or generators (for DC)
➕ Advantages of Coated Electrodes

 Easier arc initiation

 Produces protective slag
 Stabilizes arc
 Provides filler metal
 Reduces oxidation and contamination

AC vs DC Arc Welding

Feature AC Welding DC Welding

Cost Cheaper Costlier

Arc Stability Less stable More stable

Electrode Types Limited Wider variety

Equipment Simple (transformer) Complex (rectifier)

Polarity Control Not possible Possible

Welding Control Circuits

 Used to control current, timing, and pressure.

 Consist of:
o Thyristor-based controllers
o Timers
o Heat control relays

Welding of Aluminum and Copper

Challenges:

 High thermal conductivity

 Formation of oxide layers

Methods:

 Use of inert gas shielding (TIG/MIG)

 Special flux and filler rods
 Introduction to TIG and MIG Welding

1. TIG (Tungsten Inert Gas) Welding

 Non-consumable tungsten electrode

 Inert gas (Argon/Helium) shields the weld
 Used for precision welding (Aluminum, Stainless Steel)

2. MIG (Metal Inert Gas) Welding

 Consumable wire electrode fed continuously

 Inert gas (CO₂/Argon) protects weld
 Fast and suitable for mass production