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1
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What
is meant by Electrical traction?
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Electrical traction
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It is a
system that causes propulsion of a vehicle in which the driving force is
obtained by steam engine drive, diesel engine drive, traction motor etc.
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2
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What
are the different types of traction systems in the India?
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Types of traction system
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Electrical
traction system : Steam
electric drive and Diesel electrical drive
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Non – electrical
traction system : Direct steam
engine drive and Direct internal combustion engine drive
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3
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What
do you mean by the Tramways and Trolley buses?
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Tramway
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The
tramway is ordinary buses or vehicle but the only difference is that these
buses are run only on the designed track.
·
The
tramway is operated by single phase 500V DC supply.
·
The single overhead conductor acts as a
positive which is fed from suitable substation / power station and track acts
as a return path.
Trolley bus
·
The main
drawback of the tramway is that it runs along the designed track path. This
difficulty is overcome by using two overhead collectors.
·
The
trolley buses are electrical operated vehicle and the operating voltage is
600V DC.
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4
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What
are the supply systems for track electrification?
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Supply system for track
electrification
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DC
system
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Single
phase ac
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Three
phase ac and
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Composite
supply system
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5
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Which
is first electrical traction in India?
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The electrical traction in India was first introduced between Bombay
VT to kurla harbour in 1925 on 1.5 kV DC system.
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6
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What
is the operating Direct voltage in the traction system?
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DC Voltage in the Traction
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The
operating direct voltage for traction system is 600 V, 750 V, 1500 V and 3000
V.
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The
direct voltage of 600 V – 750 V is employed for tramways in the urban areas
and1500 V – 3000 V for main line system.
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7
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What
are the operating voltage and frequency for single phase AC and three phase
AC traction system?
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Single Phase
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15 kV – 20
kV at 16.7 Hz
Three phase
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3000 V –
3600 V at normal operating frequency or reduced frequency at 16.7 Hz
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8
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What
are the features required for electrical traction motor?
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Features of the electrical
traction motors
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High
starting torque
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Easy
speed control
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Overload
capacity
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Better
commutation
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Series-parallel
control
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Capability
to withstand higher temperature under transient conditions
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9
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Why
the three phase induction motor is not suitable in electrical traction
system?
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The induction motor suffers from
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Low
starting torque
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High
starting current and
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Absence
of speed control
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The
track electrification for the three phase induction motor requires high
capital cost because the distribution system consists of two overhead phase
wire and track rail acts as third phase.
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10
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Which
characteristics of DC series motor is suitable for traction system than DC
shunt motor?
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DC series motor
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The
output power in the DC series motor is directly proportional to √ torque
whereas in it is directly proportional to the torque in the DC shunt motor
therefore for the same amount of torque DC shunt motor draws more current
from the supply than in the DC series motor.
·
The
torque in the DC shunt motor is directly proportional to flux per pole and
armature current. But the field flux depends upon the supply voltage
therefore small variation in the supply voltage resulting torque is affected.
·
When the
two DC shunt motor are running in parallel, the torque – speed and speed – armature current characteristics
must be same otherwise both motors draw unequal current from the supply and
resulting unequal sharing of load.
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11
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Why
the DC series motor does not work satisfactory when it is operated at AC
supply?
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When the DC series motor is operated on AC supply it will rotates but
the operation of the motor is not satisfactory due to following reasons
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Unidirectional
torque is developed at double frequency.
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The
alternating flux causes excessive eddy current loss in the yoke and field
core resulting excessive heating of the motor.
·
Poor
power factor due to inductance of the armature and field coil.
·
Sparking
occurs at the brushes due to high voltage and current induced in the short
circuited armature coil during commutation period.
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12
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What
is the design modifications made to operate DC series motor on AC supply?
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The following modifications are made to operate DC series motor on the
AC supply
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To
reduce eddy current, yoke and field cores must be laminated.
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Power
factor is improved by reducing the reactance of armature and field winding.
·
To
reduce inductive reactance, the field winding is designed with few turns.
This will reduce air - gap flux resulting speed of the motor increase but
torque decrease. To obtain same torque, numbers of armature turns increase
proportionally. This increase in armature turns increase inductance,
therefore net inductance.
·
The
inductive reactance of the armature is neutralized by providing compensating
winding in series with armature.
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13
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Why
the AC series motor is not employed for sub – urban services?
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AC Series motor
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The AC
series motor develops low torque at the time of starting for a given current
as compared to the DC motor due to low power factor.
·
Therefore
AC series motor is not suitable in sub – urban a service in which frequent
stop is necessary.
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14
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Explain
the term : Linear synchronous speed
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Linear synchronous speed
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When the
primary (stator) winding is energized by the three phase alternating supply, magnetic
field is produced which is rotate at linear synchronous speed.
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Therefore
the linear synchronous speed is given by
Vs = 2τf
meter / sec
τ = pole pitch and
f = frequency
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15
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Which
parameters greatly affect the linear synchronous speed?
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Linear synchronous speed
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The
linear synchronous speed does not depend upon numbers of poles, but its value
depends upon pole pitch and frequency.
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