31
|
Describe
the effect on the efficiency of the traction motors due to series – parallel control.
|
|
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.
|
32
|
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.
|
33
|
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.
|
34
|
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.
|
35
|
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
|
36
|
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.
|
37
|
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.
|
38
|
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.
|
39
|
What
are the factors affecting schedule speed of the train?
|
|
Factors affecting schedule speed
of the train
·
Distance
between two stop
·
Time
duration of the stop
·
Crest
speed
·
Acceleration
·
Braking
retardation
|
40
|
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.
|
41
|
State
the different types of current collector used in electrical locomotives.
|
|
Different types of current
collectors
·
Trolley
collector
·
Bow
collector and
·
Pantograph
collector
|
42
|
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.
|
43
|
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.
|
44
|
Why
the small sag is provided in overhead contact wire for high speed traction
system?
|
|
The small sag is provided in order to achieve current collection
without any interruption in high speed traction system.
|
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