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TYPES OF SERVICES 1. Main line service. 2. Urban or city service. 3. Suburban service.

TYPES OF SERVICES 1. Main line service. 2. Urban or city service. 3. Suburban service. Speed time curve: 1. Constant accelerating period. 2. Acceleration on speed curve. 3. Free-running period. 4. Coasting period. 5. Braking period. Average speed

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TYPES OF SERVICES 1. Main line service. 2. Urban or city service. 3. Suburban service.

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  1. TYPES OF SERVICES 1. Main line service. 2. Urban or city service. 3. Suburban service. Speed time curve: 1. Constant accelerating period. 2. Acceleration on speed curve. 3. Free-running period. 4. Coasting period. 5. Braking period.

  2. Average speed It is the mean of the speeds attained by the train from start to stop, i.e., it is defined as the ratio of the distance covered by the train between two stops to the total time of rum. It is denoted with ‘Va’. Schedule time It is defined as the sum of time required for actual run and the time required for stop.

  3. The factors that affect the schedule speed of a train are: 1. Crest speed. 2. The duration of stops. 3. The distance between the stops. 4. Acceleration. 5. Braking retardation.

  4. K.Karthikeyan

  5. Braking • The process of bringing the motor to rest within the pre-determined time is known as braking. • A good braking system must have the following features: • Braking should be fast and reliable. • The equipment to stop the motor should be in such a way that the kinetic energy of the rotating parts of the motor should be dissipated as soon as the brakes are applied.

  6. The advantages of the electric braking over the mechanical braking o The electric braking is smooth, fast, and reliable. o Higher speeds can be maintained; This leads to the higher capacity of the system. o The electric braking is more economical; o Heat produced in the electric braking is less and not harmful but heat produced in the mechanical braking will cause the failure of brakes. o In the electric braking, sometimes, it is possible to fed back electric energy during braking period to the supply system. This results in saving in the operating cost. This is not possible in case of mechanical braking.

  7. Dissadvantages • During the braking period, the traction motor acts generator and electric brakes can almost stop the motor but it cannot hold stationary. Hence, it is necessary to employ mechanical braking in addition to electric braking. • Traction motor has to work as a generator during braking period. So that, motor has to select in such a way that it should have suitable braking characteristics. • The initial cost of the electric braking equipment is costlier.

  8. 1. Electric braking - the kinetic energy of the rotating parts of the motor is converted into electrical energy which in turn is dissipated as heat energy in a resistance or in sometimes, electrical energy is returned to the supply. 2. Mechanical braking - the kinetic energy of the rotating parts is dissipated in the form of heat by the brake shoes of the brake lining that rubs on a wheel of vehicle or brake drum.

  9. TYPES OF ELECTRIC BRAKING • Plugging. • The electric motor is reconnected to the supply in such a way that it has to develop a torque in opposite direction to the movement of the rotor. • 2. Rheostatic braking. • The electric motor is disconnected from the supply during the braking period and is reconnected across same electrical resistance. • 3. Regenerative braking. • The kinetic energy of the motor is converted into electrical energy which is fed back to the supply systems.

  10. TRACTIVE EEFFORT (Ft) It is the effective force acting on the wheel of locomotive, necessary to propel the train is known as ‘tractive effort’. Ft = Fa+Fg+Fr 1. Required for linear and angular acceleration (Fa). 2. To overcome the effect of gravity (Fg). 3. To overcome the frictional resistance to the motion of the train (Fr). Gear ratio = Speed of motor pinion / Speed of driving motor

  11. SPECIFIC ENERGY CONSUMPTION The energy input to the motors is called the energy consumption. This is the energy consumed by various parts of the train for its propulsion. The energy drawn from the distribution system should be equals to the energy consumed by the various parts of the train and the quantity of the energy required for lighting, heating, control, and braking. This quantity of energy consumed by the various parts of train per ton per kilometer is known as specific energy consumption. It is expressed in watt hours per ton per km.

  12. Factors affecting the SEC • The distance between the stops • The acceleration and retardation • The maximum speed • Gradient • Train resistant • Type of train equipment • Home work • 1. An electric train is accelerated at 2 kmphps and is braked at 3 kmphps. The train has an average speed of 50 kmph on a level track of 2,000 min between the two stations. Determine the following: • 1. Actual time of run. 2. Maximum speed. • 3. The distance travelled before applying brakes 4. Schedule speed. • Assume time for stop as 12 sec, and run according to trapezoidal.

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