21. The efficiency of diesel locomotives is nearly
A. 20 to 25 percent
B. 30 to 40 percent
C. 45 to 55 percent
D. 60 to 70 percent
Answer: A. 20 to 25 percent
Explanation:
- Thermal efficiency is the ratio of how effectively an engine converts a fuel’s heat energy into usable work.
- Each fuel has a certain amount of heat or thermal energy.
- The energy of the fuel has the potential to produce a certain amount of work when burned in the engine.
- This thermal efficiency is a theoretical value.
- Diesel fuel has more heat energy than coal and gasoline. Diesel engines also have higher compression ratios.
- Both of these are the reason why diesel gets better fuel economy than gasoline engines and steam engines.
- The efficiency of the diesel-electric locomotive (26 to 30%) is more than that of the steam locomotive (6 to 8%) and less than that of an electric locomotive (34 to 38%).
22. The speed of a superfast train is
A. 60 kmph
B. 75 kmph
C. 100 kmph
D. more than 100 kmph
Answer: D. more than 100 kmph
Explanation:
The average speed of express trains, range from 36 kilometres per hour (22 mph) to 113 kilometers per hour (70 mph).
23. The number of passengers coaches that can be attached to a diesel engine locomotive on broad gauge is usually restricted to
A. 5
B. 10
C. 14
D. 17
Answer: B. 10
Explanation:
The number of passengers coaches that can be attached to a diesel engine locomotive on broad gauge is usually restricted to 10.
24. Which of the following state capitals is not on broad gauge track?
A. Lucknow
B. Bhopal
C. Jaipur
D. Chandigarh
Answer: C. Jaipur
Explanation:
Jaipur state capitals is not on broad gauge track.
Broad gauge, meter gauge, narrow gauge indicate the width between two rails.
The difference in their width is as follows:
- Broad gauge: 1.676 meters.
- Narrow gauge: 0.762 meters.
- Metre gauge: 1 meter.
Important Notes:
What is Plugging in DC motor breaking?
- In this method, the motor is reconnected to the supply in such a way that it has to develop torque in opposite direction to the movement of the rotor, it can be done by reversing the connections of the armature
- The motor will decelerate until the speed is zero and then accelerates in opposite direction; Immediately, it is necessary to disconnect the motor from the supply as soon as the system comes to rest
- The kinetic energy of the rotating parts of the motor is wasted and an additional amount of energy from the supply is required to develop the torque in the reverse direction, i.e. the motor should be connected to the supply during braking
- It can be applied to both DC and AC motors.
- During plugging the effective voltage across the armature will be (V + Eb) which is almost twice the supply voltage. The armature current is reversed, and high braking torque is produced.
The Plugging is commonly used for the following applications:
- Controlling elevators
- Rolling Mills
- Printing Presses
- Machine tools
25. Which of the following is the advantage of electric braking?
A. It avoids wear of track
B. Motor continues to remain loaded during braking
C. It is instantaneous
D. More heat is generated during braking
Answer: A. It avoids wear of track
Explanation:
Advantages of Electrical Braking Over Mechanical Braking:
- In mechanical braking due to excessive wear on the brake drum, liner, etc., it needs frequent and costly replacement. This is not needed in electrical braking and so electrical braking is more economical than mechanical braking.
- Due to the wear and tear of the brake liner frequent adjustments are needed thereby making the maintenance cost.
- Mechanical braking produces metal dust, which can damage bearings. Electrical braking has no such problems.
- If mechanical brakes are not correctly adjusted it may result in shock loading of machine or machine parts in case of lift, trains which may result in discomfort to the occupants.
- Electrical braking is smooth.
- In mechanical braking the heat is produced at the brake liner or brake drum, which may be a source of failure of the brake. In electric braking, the heat is produced at a convenient place, which in no way is harmful to a braking system.
- In regenerative braking electrical energy can be returned back to the supply which is not possible in mechanical braking.
- The noise produced is very high in mechanical braking.
- Only disadvantage of electrical braking is that it is ineffective in applying holding torque.
26. Which of the following braking systems on the locomotives is costly?
A. Regenerative braking on electric locomotives
B. Vacuum braking on diesel locomotives
C. Vacuum braking on steam locomotives
D. All braking systems are equally costly
Answer: A. Regenerative braking on electric locomotives
Explanation:
In case of electric locomotives, additional equipment should be needed for the provision of regenerative braking, it will increase the overall cost of installation.27. Tractive effort is required to
A. overcome the gravity component of train mass
B. overcome friction, windage and curve resistance
C. accelerate the train mass
D. do all of the above
Answer: D. do all of the above
Explanation:
Functions of the Tractive effort
- Tractive effort required to accelerate the train mass horizontally (in newtons).
- The tractive effort required to accelerate the rotating parts: The rotating parts consist of wheels, gears, axles and rotor of the motor.
- The tractive effort required to overcome the force due to gravity: When moving up in the slope the drive has to produce tractive effort to overcome the force due to gravity.
- The tractive effort required to overcome train resistance: The resistance of the train is mainly due to various kinds of friction.
- The total tractive effort required to move the train
28. For given maximum axle load tractive efforts of A.C. locomotive will be
A. less than that of D.C. locomotive
B. more than that of D.C. locomotive
C. equal to that of D.C. locomotive
D. none of the above
Answer: B. more than that of D.C. locomotive
Explanation:
- Tractive effort is defined as the force at the rims or the outer edges of the driving wheels of moving trains.
- In other words, it is the sum of the tractive force and rolling effort on the road surface.
- In the main line train, tractive effort is caused by the locomotive, and in a suburban train, it is caused by motor coaches.
- The draw pull bar force is the horizontal force available for the vehicles for pulling the load.
- This force is less than the tractive effort required to move the locomotive.
- For given maximum axle load tractive efforts of A.C. locomotive will be more than that of D.C. locomotive.
29. Coefficient of adhesion reduces due to the presence of which of the following?
A. Sand on rails
B. Dew on rails
C. Oil on the rails
D. both B and C
Answer: D. both B and C
Explanation:
Coefficient of adhesion (μ): It is defined as the ratio of the tractive effort (Ft) to propel the wheel of a locomotive to its adhesive weight (W).
The coefficient of the adhesion improves due to the presence of:
- Dry sand on rails
- Rust on rails
- Dust on rails
The coefficient of the adhesion reduces due to the presence of:
- Dew on rails
- Oil and grease on rails
30. Due to which of the following co-efficient of adhesion improves?
A. Rust on the rails
B. Dust on the rails
C. Sand on the rails
D. All of the above
Answer: D. All of the above
Explanation:
The coefficient of the adhesion improves due to the presence of:
- Dry sand on rails
- Rust on rails
- Dust on rails
The coefficient of the adhesion reduces due to the presence of:
- Dew on rails
- Oil and grease on rails
More Objective Questions in Electrical Traction