⚡Basics of Traction
1. What is Traction?
Traction means pulling a vehicle (like a train or tram) using a power source.
2. Types of Traction Systems
Type Description
Steam Traction Uses steam engines. Obsolete now.
Diesel Traction Uses diesel engines to drive wheels.
Electric Traction Uses electric motors powered by electricity. Most efficient and eco-friendly.
3. Electric Traction
What is Electrical Traction?
Electrical traction refers to the use of electric power to move vehicle. In India, electric traction
is the backbone of the railway system, especially for mainline trains, suburban trains, and
metro rail systems.
Electric traction is widely used in trains, trams, and metros. It uses electric motors for
movement, powered by:
Overhead lines (OHE) – 25 kV AC is common
Third rail – used in metros (DC supply)
Battery – used in light-duty or hybrid vehicles
4. Advantages of Electric Traction
High efficiency
Pollution-free
Quick acceleration and braking
Regenerative braking possible
Low maintenance
5. Electric Motors Used
Motor Type Application
DC Series Motor Old electric locomotives
AC Motors (3-phase Induction) Modern trains and metros
Synchronous Motors High-speed trains
6. Power Supply Systems
Type of Supply Voltage Used in
AC Supply 25 kV, 50 Hz Railways (mainlines)
DC Supply 750V / 1500V Metros, trams
7. Braking in Traction
Mechanical Brakes – Traditional method
Electric Brakes:
o Dynamic Braking – Converts kinetic energy to heat
o Regenerative Braking – Sends power back to the supply system
8. Important Terms
Tractive Effort – Force used to pull the train
Acceleration – Speed increase rate
Adhesion – Grip between wheels and rail
Haulage – Total load pulled
9. Applications of Electric Traction
Railways
Metro systems
Trams
Electric buses and trucks (future mobility)
Timeline of Electric Traction in India
1. Early Experiments (1920s – 1930s)
1925: The first electric train in India ran on 3rd February 1925 between Bombay VT
(now CSMT) and Kurla on the Harbour Line.
o It operated on 1.5 kV DC overhead system.
o The train was hauled by a WCG-1 type electric locomotive, imported from
Europe.
2. Expansion of DC Traction (1930s – 1950s)
Gradual electrification spread across Bombay suburban routes.
By 1936, the Bombay-Poona line was partially electrified.
DC traction was dominant, especially in the Western and Central Railway zones.
3. Shift to AC Traction (1950s – 1960s)
1957: Indian Railways began shifting to 25 kV AC traction, which was more
economical and efficient over long distances.
o The first AC electric train ran between Rajkharswan and Dongoaposi in Bihar
(now in Jharkhand).
This shift required installing new infrastructure and retraining staff.
Indian Railways adopted 25 kV AC as the standard for future electrification.
4. Mixed Systems and Gradual Transition (1960s – 1990s)
For decades, India used a mix of DC and AC systems, especially in Mumbai.
The dual-voltage locomotives like WCAM series were developed to run on both DC and
AC networks.
Expansion of electric traction to more routes across India continued during this period.
5. Full Transition to AC & Modernization (2000s – 2020s)
Indian Railways initiated projects to convert all DC sections to 25 kV AC.
2016: Western Railway completed DC to AC conversion in the Mumbai suburban
section.
Mumbai became fully AC electrified, eliminating the need for dual-voltage
locomotives.
6. Electrification Push & Green Railways (2020s – Present)
A major push for complete electrification of Indian Railways was launched.
As of 2024, over 93% of the broad-gauge network is electrified.
Indian Railways aims to achieve 100% electrification and become a net-zero carbon
emitter by 2030.
Key Milestones
Year Event
1925 First electric train (Bombay VT to Kurla)
1957 First 25 kV AC line (Rajkharswan – Dongoaposi)
1960s–90s Mixed AC/DC operation with dual-voltage locomotives
2016 Mumbai fully converted to 25 kV AC
2023–24 Electrification crosses 90% of broad gauge routes
Power Supply System
India uses a 25 kV, 50 Hz, single-phase AC system for most of its railway electrification.
Source of Power:
Electricity is taken from state electricity boards.
It is stepped down and converted in traction substations.
Power is supplied via Overhead Equipment (OHE) to the pantograph of the
locomotive.
Components of Indian Electrical Traction
Component Function
Overhead Line (OHE) Carries 25 kV AC
Pantograph Collects current from OHE
Transformer Steps down voltage
Electric Locomotive Houses traction motors
Traction Motors Converts electric energy to mechanical energy
Control System Controls speed, direction, and braking
Types of Electrified Trains in India
Electric Locomotives – e.g., WAP, WAG series
EMU (Electric Multiple Unit) – Suburban trains like Mumbai locals
Metro Systems – Delhi Metro, Kolkata Metro, etc. (usually 750V DC or 25kV AC)
MEMU/DEMU – Mainline Electric Multiple Units
✅Advantages of Electric Traction in India
Cheaper operation cost than diesel
Pollution-free
Higher acceleration
Suitable for high-speed trains
Supports regenerative braking
Future Plans
100% Railway electrification by 2030 (Target)
Use of green energy sources like solar and wind
Electrification of all broad-gauge routes
⚡1. Electric Drive (Pure Electric Traction)
✅Advantages:
High efficiency
Pollution-free operation
Lower maintenance (fewer moving parts)
Regenerative braking possible (energy-saving)
High starting torque – good for heavy loads
Faster acceleration – suitable for suburban and high-speed trains
❌Disadvantages:
Requires continuous electrified track (OHE or third rail)
High initial cost for infrastructure (lines, substations)
Power failure = no operation
Less flexible (limited to electrified routes)
2. Diesel-Electric Drive
✅Advantages:
No overhead wires needed – flexible movement
Can run on non-electrified routes
Good for long-distance haulage
Quick to deploy in new areas
❌Disadvantages:
Lower efficiency than pure electric
Pollution and noise
Higher fuel cost
More maintenance (engine + generator + motors)
No regenerative braking
3. Battery Drive (Battery-Electric Drive)
✅Advantages:
Zero emissions at point of use
Silent operation
Ideal for short routes or shunting (yard work)
No overhead equipment needed
Can be charged using renewable energy
❌Disadvantages:
Limited range
Battery replacement cost is high
Long charging times
Lower power output – not suitable for heavy loads
Heavier weight due to batteries
Summary Table:
Feature Electric Drive Diesel-Electric Battery Drive
Efficiency High Medium Low to Medium
Pollution No Yes No
Range Unlimited (if electrified) High Low
Maintenance Low High Medium
Infrastructure Cost High Low Low
Flexibility Low High Medium
Regenerative Braking Yes No Possible
Problems in AC Traction System & Their Remedies
1. Voltage Balance
What Is It?
Voltage balance refers to keeping the voltages of all three phases in a 3-phase AC system
equal in magnitude and 120° apart in phase.
In Railway Traction:
Most electric trains use single-phase AC (25 kV, 50 Hz) drawn from the 3-phase
national grid.
This creates unbalanced loading, as only one or two phases are used.
Result: Voltage imbalance in the grid → inefficient and potentially damaging to other
equipment.
Problems Caused:
Overheating of motors/transformers.
Reduced equipment lifespan.
System instability.
✅Mitigation:
Use of Scott or V-V transformers to balance loads.
Phase staggering at different substations (e.g., Substation A uses R-Y, B uses Y-B).
Autotransformer systems reduce imbalance.
2. Current Balance
What Is It?
Current balance means ensuring that supply and return currents are equal and follow the
designed path, not leaking into the earth or nearby structures.
In Railway Traction:
Return current from trains should ideally flow through rails or return conductors, not
through the earth.
Any deviation causes current imbalance.
Problems Caused:
Stray currents → corrosion of metal pipes or structures.
Electromagnetic interference (EMI) with signaling and communication.
Heating of unintended paths (e.g., ground wires, earth).
✅Mitigation:
Booster transformers + return conductors in AC systems.
Impedance bonds in both AC and DC to guide return current and preserve track circuit
isolation.
Earthing and bonding of rails and equipment.
3. Production of Harmonics
What Are Harmonics?
Harmonics are voltage or current waveforms at multiples of the fundamental frequency (e.g.,
150 Hz, 250 Hz when the main frequency is 50 Hz).
In Railway Traction:
Trains use power electronic converters (IGBTs, thyristors) to control motors.
These non-linear loads distort the waveform and inject harmonics into the power
supply.
Problems Caused:
Overheating of equipment.
Resonance in the system.
Malfunctioning of relays or protective devices.
Degraded power quality → higher losses.
✅Mitigation:
Harmonic filters (passive or active).
Use of multi-pulse converters (e.g., 12-pulse, 24-pulse).
Designing substations with proper reactive compensation.
Monitoring with power quality analyzers.
4. Induction Effect (Electromagnetic Induction)
What Is It?
Induction effect is the phenomenon where a changing current in one conductor induces a
voltage in a nearby conductor, as described by Faraday’s Law.
In Railway Traction:
High traction currents flowing in overhead lines and rails create changing magnetic
fields.
These can induce voltages in nearby parallel lines, like:
o Telecommunication cables
o Signaling circuits
o Pipelines or fences
Problems Caused:
Induced voltages can cause interference or even damage in telecom or signal systems.
Can be a safety hazard (e.g., touch potential).
Can disrupt track circuits or signaling relays.
✅Mitigation:
Return conductors and booster transformers (for balanced magnetic fields).
Use of screened or twisted-pair signal cables.
Maintaining separation between traction and communication systems.
Earthing and shielding of sensitive cables.
What is a Metro Rail System?
A Metro Rail (also known as rapid transit, subway, or urban rail) is a high-capacity public
transport system designed to carry large numbers of passengers in urban and suburban areas.
It operates on exclusive tracks, free from road traffic, with frequent and fast service, and
usually has automated systems for operations and safety.
Key Components of a Metro System
Component Description
Standard gauge or broad gauge tracks, often elevated, underground, or at-
Tracks
grade
Rolling Stock Trains or coaches – lightweight, energy-efficient, usually electric
Power Supply Mostly 750V DC (third rail) or 25 kV AC (OHE)
Advanced systems like CBTC (Communication-Based Train Control) for
Signaling System
safe, driverless or semi-automatic operation
Designed for high throughput, includes platforms, escalators, elevators, AFC
Stations
(Automatic Fare Collection)
Control Center Centralized monitoring and command of trains and stations
Depot For train maintenance, cleaning, and storage
⭐ Features of Metro Rail System
1. Electric Traction
Powered by electricity, often through third rail or overhead wires
Enables clean, silent, and efficient operation
2. High Frequency
Trains run every 2–5 minutes during peak hours
Ideal for mass transportation
3. Dedicated Track
No level crossings or road intersections
Ensures uninterrupted service
4. Automatic Operation
Uses Automatic Train Operation (ATO) and CBTC
Some metros are fully driverless
5. Energy Efficiency
Uses regenerative braking
Trains convert braking energy back to electrical energy
6. Safety Systems
Automatic doors, platform screen doors (in advanced systems)
Fire detection, CCTV, emergency alarms, and PA systems
7. Accessibility
Lifts, ramps, tactile paths for visually impaired
Suitable for all passengers, including elderly and differently abled
8. Environmentally Friendly
Reduces road traffic, pollution, and fuel usage
Promotes sustainable urban mobility
Metro Systems in India (Examples)
City Metro System Power Supply
Delhi Delhi Metro 25 kV AC / 750 V DC
Bengaluru Namma Metro 750 V DC (Third Rail)
Mumbai Mumbai Metro Both AC and DC
Kolkata Kolkata Metro 750 V DC
Hyderabad Hyderabad Metro 25 kV AC OHE
