--- title: "Types of traction system by supply source" subject: "Utilization of Electrical Energy" chapter: 4 key: "semester_7/utilization_of_electrical_energy:traction-systems-supply-source" source: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/traction-systems-supply-source site: BCT Engineering --- # Types of traction system by supply source Utilization of Electrical Energy · Chapter 4: Electric Traction - Asked in: 2069 Chaitra - Video: [Type of Traction- Utilization of Electrical Power by Piyush Mathur](https://www.youtube.com/watch?v=14N54b6FOco) — Arya College of Engineering and IT - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/traction-systems-supply-source - Whole chapter: https://www.bctengineer.com/md/semester_7/utilization_of_electrical_energy/chapter-4 ## Question What is electric traction? Explain the types of electric traction system based on the types of supply source. Also discuss their advantages and disadvantages. ## Short answer Electric traction uses electric motors for propulsion. Systems: self-contained (diesel-electric: independent but low efficiency, pollution; battery-electric: clean but limited range) and electrified track (DC, AC, composite). Advantages of line supply: clean, high acceleration, low maintenance, regenerative braking, high efficiency. Disadvantages: high initial cost, supply failure stops all trains, route restriction, telecom interference (AC). ## Answer **Electric traction** is the propulsion of vehicles (trains, trams, trolley buses, electric buses) using electric motors, with the electrical energy taken from a supply line or produced or stored on the vehicle. #### Types of electric traction based on supply source **A. Self-contained (non-electrified track) systems** — the vehicle carries its own source. 1. **Diesel-electric:** a diesel engine drives a generator that feeds dc or ac traction motors. - Advantages: no overhead line, can run on any route, low line cost, high availability. - Disadvantages: low overall efficiency (about 25%), heavy locomotive, high running and maintenance cost, pollution, limited overload capacity. 2. **Battery-electric:** batteries feed dc motors. - Advantages: no pollution, simple, quiet; good for short distances, shunting, mines and e-rickshaws/e-buses. - Disadvantages: limited range, heavy batteries, long charging time, high battery replacement cost. **B. Electrified track (supply from distribution network)** — power is taken from an overhead wire or third rail. 1. **DC system:** 600–750 V (tramways, metro), 1500–3000 V (suburban, main line), using dc series motors. 2. **AC system:** single-phase 25 kV, 50 Hz (most common), single-phase low frequency, or three-phase. 3. **Composite system:** ac in the line and rectifier or inverter on board. #### Advantages of electric traction from line supply - Clean, no smoke; ideal for cities and tunnels. - High starting torque and acceleration, so higher schedule speed. - Low maintenance and running cost; long life of locomotives. - Regenerative braking returns energy to the line. - Higher overall efficiency when fed from hydro power (important for Nepal). #### Disadvantages - Very high initial cost of overhead line, substations and electrification. - Failure of supply stops all trains on the section. - Trains can run only on electrified routes. - Interference with telecommunication lines (ac systems). - Additional cost of signalling changes. | Source | Example | Main merit | Main demerit | |---|---|---|---| | Diesel-electric | Main-line locomotives | Independent of line | Low efficiency, smoke | | Battery | E-bus, shunter | Clean, quiet | Limited range | | DC line | Metro, tram | Simple motors | Many substations | | AC 25 kV line | Main line rail | Cheap line, few substations | Interference | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Electric traction means propulsion of vehicles using: A. Steam engines with electric lighting B. Electric motors, with energy from a supply line or produced/stored on the vehicle C. Only overhead-line fed ac motors D. Diesel engines only Answer: B. Electric traction uses electric motors, and the energy may come from a line or from on-board generation or storage. (Key point: Definition of electric traction) 2. What is a main disadvantage of diesel-electric traction? A. It needs an overhead line B. Low overall efficiency (about 25%) and pollution C. It cannot run on non-electrified tracks D. It has no starting torque Answer: B. Diesel-electric locomotives run on any route but have low efficiency, are heavy and pollute. (Key point: Diesel-electric disadvantage) 3. Why is battery-electric traction limited to short distances, shunting and mines? A. It produces smoke B. Dc motors cannot be used C. It needs substations D. Batteries are heavy, charge slowly and give limited range Answer: D. Limited range, heavy batteries and long charging time restrict it to short-duty applications. (Key point: Battery traction limits) 4. Which is a disadvantage of electrified-line traction? A. Poor starting torque B. Smoke in tunnels C. Supply failure stops all trains in the section D. Cannot use regenerative braking Answer: C. Dependence on the line means a supply failure halts every train on that section, along with high initial cost. (Key point: Disadvantage of line-fed traction) ## Related in Utilization of Electrical Energy - [Key components of electric traction system](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Acomponents-electric-traction-system) — Utilization of Electrical Energy, chapter 4 - [DC vs AC electric traction systems](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Adc-vs-ac-traction-systems) — Utilization of Electrical Energy, chapter 4 - [Advantages of electric traction; trains, trolley, tramways](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aadvantages-traction-trains-trolley-tramways) — Utilization of Electrical Energy, chapter 4 - [Electric traction in Nepal; self-contained vehicles](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aelectric-traction-nepal-self-contained-vehicles) — Utilization of Electrical Energy, chapter 4 - [Electric traction; current collection arrangements](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aelectric-traction-current-collection) — Utilization of Electrical Energy, chapter 4 - [Electric braking in AC and DC traction drives](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aelectric-braking-traction-drives) — Utilization of Electrical Energy, chapter 4 ## Related in other subjects - [Electric vehicle architecture and traction motors](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Aev-architecture-and-motors) — Automotive Technology, chapter 12 - [Microprocessor based system and bus organization](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Amp-based-system-bus-organization) — Microprocessor, chapter 1, asked 5× - [Types of electric wiring system compared](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Awiring-systems-comparison) — Industrial Power Distribution and Illumination, chapter 5 - [Typical water supply system and components](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Atypical-ws-system-components) — Water Supply Engineering, chapter 1, asked 4×