Effect on efficiency due to series – parallel control : When two traction motors employ for series – parallel control, the efficiency of the motor is increased from 50% to 66.7%. The efficiency is increased almost 16.7% thereby 15-20% saving of energy is achieved.
Why the regenerative braking is most efficient than any other electrical
braking system?
The regenerative braking is most efficient than other
method because in
Plugging : Energy is drawn from the supply source.
Rheostatic braking : The kinetic energy of the rotor is wasted into external resistor.
Regenerative braking : No electrical energy is drawn from the supply but some energy is fed back to the supply source.
What is efficiency of the traction motor at starting?
The efficiency of the traction motor is approximately
50% at starting because half of electrical energy is wasted in the starting
resistor.
What are the different types of passenger services in the traction
system?
Types of passenger services
Main line service : Distance between two stops is more than 10 km.
Urban service : Distance between two stops is more than 1 km.
Sub-urban service : Distance between two stops is approximately 1 km to 8 km.
Describe the different periods of speed – time curve for the main line
service.
Speed – time periods of the
main line service
- Constant acceleration or notching period
- Acceleration
- Free running period
- Coasting period
- Braking period
Explain the following terms related to the electrical traction system: (
a ) Notch up period ( b ) Free running period ( c ) Coasting period
Notch up period
During this period, current taken by the traction
motor is approximately constant and voltage is gradually increased by cutting
out starting resistance. As the current taken by the motor is constant,
acceleration is also constant. Therefore, this period is known as constant
acceleration or notch up period.
Free running period
The traction motor draws constant power from the
supply lines during this period therefore the speed of the train remains constant.
Coasting period
The supply of the traction motor will be cut off
resulting motor speed falls due to friction during this period. The rate of
decrease of the traction motor is known as coasting period.
In which type of service system there is no free running period?
The distance between two stops is less than 1 km in
the urban service therefore there is no free running period.
Explain the following terms regarding to electrical traction : ( a ) Crest
speed ( b ) Average speed ( c ) Schedule speed ( d ) Schedule time
Crest speed : The maximum speed attained by the train during running is known as crest speed.
Average speed : It is defined as ratio of the distance covered by the train between start and stop station to the time during this distance.
Schedule speed : It is defined as the ratio of the distance covered by the train between two stations to the time required for the run and stop of the train.
Schedule time : It is defined as the time required by the train for actual the run and stop.
What are the factors affecting schedule speed of the train?
Factors
affecting schedule speed of the train
Distance between two stops
- Time duration of the stop
- Crest speed
- Acceleration
- Braking retardation
Explain the following terms : ( a ) Tractive effort ( b ) Specific
energy consumption ( c ) Dead weight ( d ) Adhesive weight and ( e ) Co – efficient
of adhesive
Tractive effort : It is defined as the effective force acting on the locomotive to propel the train.
Specific energy consumption : It is defined as the ratio of the total energy consumption by the traction motor to the product of the weight of train and distance covered by the train. The unit of specific energy consumption is watt - hour / ton / km.
Dead weight : It is defined as the total weight of train to be propelled by the locomotive.
Adhesive weight : It is defined as the total weight to be carried out on the wheel of a locomotive.
Co – efficient of adhesive : It is the ratio of the tractive effort required to propel the train to the adhesive Weight.
State the different types of current collector used in electrical
locomotives.
Different types of current
collectors
- Trolley collector
- Bow collector and
- Pantograph collector
What are limitations of trolley collectors?
Limitations of trolley collectors : The trolley collectors are used only for speed limit of 22 – 30 kmph. The main drawback of the trolley collector is that it has to rotate through 1800 whenever vehicle turns into reverse direction.
Explain : Catenary
Catenary : The trolley wire is supported by another wire for short distance ( which is made of seven strands of steel ) is known as catenary.
Why the small sag is provided in overhead contact wire for high-speed
traction system?
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