In Main line service

Question

Examoogle · Accepted Answer

Option D: Both B and C

Explanation & Concepts:
In main line electric traction, trains travel long distances between stops, which necessitates long periods of free running and coasting to maintain speed and energy efficiency. Consequently, the relative time spent in acceleration and braking is short compared to the total journey duration.

Working Principle: The speed-time curve for main line service is characterized by a very long free-running period (constant speed) and a significant coasting period, where the motor is cut off and the train decelerates gradually due to friction and air resistance. Because stops are infrequent, the frequent acceleration/braking phases found in urban services are minimized, resulting in a low acceleration-to-coasting ratio.

Key Formulas: $T_{total} = T_a + T_{fr} + T_c + T_b$; $\frac{T_a + T_b}{T_{total}} \ll 1$

Key Points: Main line service has very low frequency of stops per kilometer.; The energy consumption is primarily dominated by overcoming air resistance during free running.; Coasting is used extensively to reduce energy consumption by utilizing the kinetic energy of the train.; Acceleration and braking periods are relatively negligible compared to the total trip time.

Advantages: Higher energy efficiency due to long coasting periods; Less wear on mechanical braking systems; Consistent power demand during free-run phase

Disadvantages: Not suitable for urban transit with frequent stops; Requires high power overhead to attain desired cruise speeds; Longer journey time if acceleration is restricted

Applications: Inter-city Express trains; High-speed rail corridors; Long-distance freight haulage

Additional Info: In urban service, the speed-time curve is dominated by acceleration and braking, whereas in main line service, free running is the dominant phase.. Option B is incorrect because acceleration and braking periods are short in duration relative to the total service interval, not the driving force of the operation.

Answer: D is correct — Main line electric traction is characterized by long distances between stops, leading to extended free-running and coasting periods while keeping the relative acceleration and braking times short.

Exam Tip: Always remember: 'Urban Service' = High Acceleration/Braking (frequent stops); 'Main Line' = High Free Running/Coasting (infrequent stops).

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Option A: Acceleration and braking periods are long

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Option B: Acceleration and braking periods are short

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Option C: Free run and coasting periods are long

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