--- title: "Self-contained electric vehicle and transmission" subject: "Utilization of Electrical Energy" chapter: 4 key: "semester_7/utilization_of_electrical_energy:self-contained-vehicle-transmission" source: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/self-contained-vehicle-transmission site: BCT Engineering --- # Self-contained electric vehicle and transmission Utilization of Electrical Energy · Chapter 4: Electric Traction - Asked in: 2073 Shrawan; 2070 Chaitra (asked 2 times) - 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/self-contained-vehicle-transmission - Whole chapter: https://www.bctengineer.com/md/semester_7/utilization_of_electrical_energy/chapter-4 ## Question What is self-contained electric vehicle? What are transmission system employed in these types of electric vehicle? Explain. ## Short answer A self-contained electric vehicle carries its own energy source on board. Transmission systems include DC–DC (diesel engine–DC generator–DC motors), AC–DC (alternator–rectifier–DC motors), AC–AC (alternator–rectifier–inverter–three-phase induction motor), and battery-electric with chopper or inverter driving the motor. ## Answer A **self-contained electric vehicle** (self-contained locomotive) carries its own source of electrical energy on board, so it needs no overhead wire or third rail. The energy is produced or stored on the vehicle and supplied to electric traction motors that drive the wheels. #### Types - **Diesel-electric locomotive**: diesel engine drives a generator/alternator; output feeds traction motors. - **Battery electric vehicle**: lead-acid or lithium-ion batteries feed dc motors (shunting locos, mine locos, e-cars, e-rickshaws). - **Petrol-electric / hybrid vehicles**: engine plus generator and battery. - **Steam/gas-turbine electric** locomotives (rare). #### Transmission systems The transmission connects the prime mover to the driving axles. In electric vehicles it is mainly electrical, followed by a gear drive. **1. DC–DC transmission (diesel-electric)** ```text Diesel -> DC generator -> DC series motors -> gear -> axle engine (sep. excited) (axle hung) ``` - Generator voltage varied by its field; engine runs at its best speed. - Simple and robust, but generator commutator limits power. **2. AC–DC transmission** ```text Diesel -> 3-ph alternator -> rectifier -> DC series motors ``` - Alternator is lighter and cheaper, no commutator on the generator; widely used. **3. AC–DC–AC (AC–AC) transmission** ```text Diesel -> alternator -> rectifier -> inverter (VVVF) -> 3-ph IM ``` - Uses rugged cage induction motors, high adhesion, regenerative/rheostatic braking; modern locomotives. **4. Battery vehicles**: battery → chopper (dc motor) or inverter (ac motor) → motor → reduction gear/differential. **Mechanical part**: a single-reduction spur gear (gear ratio about 3–5) between motor pinion and axle, with axle-hung nose-suspended or frame-mounted motors. #### Advantages - Independent of track electrification; can run on any route; low initial cost of line. - Electric transmission gives smooth control and high starting torque. #### Disadvantages - Heavy and costly per kW; low overall efficiency (diesel 25–30 %). - Limited overload capacity; maintenance of engine; fuel cost and pollution; battery vehicles have limited range. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What defines a self-contained electric vehicle? A. It takes power from an overhead wire B. It uses a third rail C. It carries its own source of energy on board, so no overhead wire or third rail is needed D. It has no traction motors Answer: C. Diesel-electric locomotives and battery vehicles produce or store the energy on board and feed electric traction motors. (Key point: Definition) 2. What does AC-DC transmission in a diesel locomotive consist of? A. A dc generator feeding induction motors B. Battery feeding an inverter C. Alternator feeding a transformer only D. Diesel engine, three-phase alternator, rectifier, and dc series motors Answer: D. The alternator is lighter and cheaper than a dc generator and has no commutator; the rectified output drives dc series motors. (Key point: AC-DC transmission) 3. Why is AC-DC-AC transmission used in modern locomotives? A. It uses cage induction motors fed from a VVVF inverter, giving rugged motors, high adhesion and regenerative/rheostatic braking B. It avoids using a rectifier C. It uses a commutator-type generator D. It needs no control electronics Answer: A. The inverter supplies variable voltage and frequency to rugged three-phase induction motors. (Key point: AC-DC-AC benefit) 4. Which is a disadvantage of self-contained vehicles? A. Need for track electrification B. Heavy and costly per kW, with low overall efficiency (diesel 25 to 30 percent) C. Poor starting torque D. Dependence on supply interruptions Answer: B. On-board generation adds weight and cost, and the diesel engine is inefficient; line-fed vehicles avoid these but need electrification. 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