MET Chapter 3 Signaling and Train Lighting
Q1.
With neat sketch explain the four aspects of colour light signalling.
Ans:
Four aspects of colour light signaling:
· 4 th aspect is
attention aspect given by 2 yellow lights in vertical fashion interpreted as
“prepared to pass next signal at restricted speed”.
·
Signal-1 & 2 located less than braking distance apart. Signal- 3 shows
attention aspect, when signal-2 is at caution.
· A driver
sighting signal-3, must pass signal-2 at restricted speed, stop has to be made
at signal-1.
Q2. With the help of neat diagram,
explain the method to obtain unidirectional polarity in train lighting.
Ans:
Method to Obtain Unidirectional Polarity in Train Lighting:
Dynamo has
rocker arm mounted on the shaft, friction tight. When the direction of rotation
of the shaft is clockwise, terminal X (positive) touches P1 while terminal Y
(negative) touches N. Thus, giving the output polarity as shown in figure. When
the direction of rotation is anticlockwise, X (negative) terminal of the rocker
arm will now touch to N1 brush and Y (positive) terminal of the rocker arm will
touch to P. Thus, the output polarities will be obtained as shown in figure.
Thus, unidirectional polarity is obtained.
Q3. Explain with neat diagram the
working of double battery parallel block system in train lighting.
Ans: Working of Double Battery Parallel Block System in Train Lighting: 1. When
train is stationary or runs slowly, generator contacts B1 and B2 are open and
both batteries supply the load through closed contacts L1 and L2, short
circuiting lamp resistance D as shown in following figure.
2.
When train is in motion and lights on, generator is connected to battery 1
through closed contact B1 and lighting load is connected to battery 2 through
closed contact L2, as shown in following figure.
3.
When train is in motion and lighting and other loads are switched off, switches
L1 and L2 are open, lamp resistance D is short circuited when both generator
contacts B1 and B2 are closed and both batteries will then be charged in
parallel.
Q4. State any
four ideal requirements of signaling system.
Ans: Ideal Requirements of Signaling System: 1.
Unless the whole section of track governed by the signal is clear & safe,
it should not be possible to display „safe‟ indication.
2. Failure of any component of signaling scheme
should give danger indication.
3. There should be provision of automatic application
of brakes to the train, should the driver ignore the danger indication of the
signal.
4. Electric lock should be provided on the lever
working the home signal.
5. All traction signals are located on the left side
of the track.
6. The signal units are so fixed that the height of
the center line of the red signal shall be approximately 3.65m above the track.
7. No part of the signal without track indicator
shall normally be higher than 5.2m above the track.
8. If signals are located between the tracks, no OHE
structures shall be provided in the same track space for at least 600m in the
rear of the signal.
Q5. Give any
four advantages of voice frequency signaling over DC signaling system.
Ans: Advantages of Voice Frequency Signaling Over DC
Signaling System:
1. Large number of circuits can be easily derived
over a single pair of wires (single pair can control 18 stations).
2. Signal attenuation can be compensated by use of
repeater stations.
3. No interference and cross talk over adjacent
conductors.
4. Can be used over long distances.
5. Can be used where large number of equipment can
be controlled.
Q6. Draw neat labeled diagram of AC
track circuit. Also give two advantages of AC track circuit.
Ans:
AC Track Circuit:
Advantages
of AC Track Circuit:
1.
Free from effects of stray currents.
2.
Track circuit is up to a long length of track in one section length up to 3km
to 5 km.
3.
Cheaper in costs as compared to DC track circuit.
4.
Easy to install than DC track circuit.
Q7.
List different types of signals. State application of each.
Ans:
Different Types of Signals:
1) Flag signals: This is shown by signalman if
green flag is raised; it means to proceed with caution. Green flag shown down,
it means there is track defect; the train should not go ahead.
2)
Denoting signals: These signals are used in foggy / cloudy weathers to indicate
the positions of a signal to the drivers of approaching locomotive. They are
placed across the tracks and explode when the engine pass over them, which
makes aloud sound and attracts the attention of driver.
3)
Warner signals: ‘ON‟ position indicates the signal ahead is at danger and
driver can pass signal with caution and be prepared to stop at the next signal.
„OFF‟ position indicates A signal ahead is to proceed position and driver can
take the train at speed.
4)
Fixed Signals: Each section (or block section as it is often called) is
protected by a fixed signal placed at its entrance for display to the driver of
an approaching train. If the section is clear, e.g. there is no train in it,
the signal will show a “Proceed” indication. If, however, the section is
occupied by a train, the signal will show a “Stop” indication, usually a red
aspect.
5)
Two-aspect colour-light signals: In this, each signal has two lamps (one above
the other). The higher of the two is a green lamp, and the lower one is a red
lamp. The green lamp when lit indicates clear (the proceed indication), and
when the red lamp is used for STOP indication.
6)
Three-aspect colour-light signals: – In this, each signal has three lamps
arranged vertically. The top one is green, the middle one yellow, and the
bottom one is red. The red and green lamps indicate indications as in the
2-aspect system, and the yellow lamp shows the caution indication.
Q8. Compare DC
and AC track circuits on: i) Length of circuit ii) Application iii) Effect of
stay currents iv) Maintenance
Q9. Define
mimic diagram and explain how it enables TPC to visualize the whole of the
power supply system.
Ans:
Mimic diagram: Definition: The diagram that depicts the power supply arrangement
for the overhead 25 kV traction systems in the remote control centre on a small
scale in the traction power control centre. Use of the mimic diagram:
·
Gives actual position of electric supply system visually. It describes
diagrammatically overhead system as well as various substations and control
posts.
·
Remote controlled equipment in the mimic diagram are represented by a control
discrepancy switch (DS). The tele-command for opening and closing of C.B. and
interrupter is transmitted by actuating the DS.
·
DS is in line with the busbar- closed position for C.B.
·
Glowing of built in lamp of DS- discrepancy between position of DS and the
actual position of the apparatus.
·
Non remote controlled apparatus like substation isolators are represented by
hand operated dummy switches.
The
TPC gets a complete visual indication of the conditions of the various
components of the system by following:
i)Milky white lamp lights up when alarm is
received from any station in the panel.
ii)
Green lamp lights up whenever impulse train is being transmitted from or
received by remote control centre.
iii)
Red lamp lights up when either send or receive channel fails.
iv) Annunciation window indicates the nature
of fault which is inscribed separately on each window.
Q10. Explain with neat sketch, the
three aspect colour light signaling.
Ans:
Points to be compulsorily covered: In three aspect signal; (R → Red, Y → Yellow
and G → Green) i) Red light on indicates – STOP, ii) Yellow or amber light
indicates PROCEED WITH CAUTION, iii) Green light ON indicates proceed.
Q11. What are the advantages of VF
signaling over DC signaling for remote control operation.
Ans:
Advantages of VF signaling over DC signaling for remote control operation:
1)
Large number of circuits can be easily derived over a single pair of wires
(single pair can control 18 stations).
2)
Signal attenuation can be compensated by use of repeater stations.
3)
No interference and cross talk over adjacent conductors.
4)
Can be used over long distances.
5)
Can be used where large number of equipment’s can be controlled.
Q12. Give any two advantages of
remote control system.
Ans:
Advantages of remote control system:
1)
As substations and control posts are unattended (due to remote controls) there
is considerable savings due to less manpower.
2)
Central control station houses the complete info of the route (supervision of
all individual posts is simple) hence coordination is very good.
3)
As oral instructions are very less, human error based problems are minimized,
otherwise oral instructions given over phone may lead to errors.
4)
Correct and rapid supervision is possible.
5)
Switching operations are carried out safely, quickly, and economically.
6)
Maintenance cost is low.
Q13. )State the significance of
mimic diagram.
Ans: Significance of mimic diagram: The mimic
diagram provides the operator with an overview of the status of the power
supply arrangement for overhead 25 kV system. The dynamic data shown on the
mimic is updated automatically with telemetered, calculated and manually
updated data from the database. The mimic diagram can also accommodate analog
meters, digital displays, directional power flow indicators and chart
recorders. The mimic diagram control equipment, mimic controller is used
together with dedicated software, normally residing in the application servers,
as the mimic driver unit. The mimic diagram shows and overview comprising
static and dynamic information about equipment in station. The static
information shows devices such as transmission lines, bus-bars and
transformers. The dynamic information shows the current state of the devices
such as circuit breakers, interrupters, etc. The circuit-breaker, interrupter
etc. are represented by control Discrepancy switch (DS). The tele-command for
closing or tripping of circuit-breakers is transmitted by actuating the
discrepancy switches.
Benefits:
•The operator is able to scan the overall status of the complete system at a
glance.
•The
mimic diagram provides a pictorial view of the system network.
Q14. With the help of circuit
diagram, explain the working of the dc track circuit.
Ans:
DC track circuit:
Working:
·
Insulated rail joints are obtained by placing fiber pieces in between abutting
rail ends. In the insulated section, continuity between the adjacent rails is
kept by bonds to keep the track resistance low. The two rails of the insulated
track are insulated from each other by wooden sleepers.
·
Track relay is connected across two rails of insulated track at the start end
and dc source along with the regulating resistance across the very same rails
at the other end.
·
When the track is not occupied, circuit is completed through track relay and
current flows, thereby functions on the required signal are carried out.
·
When the track is occupied by the train a circuit parallel to the relay coil is
established by the vehicle wheels and axles due to which the relay current
falls below the hold up value of the relay to give the required indication.
·
It is used for non-electrified track lines
Q 15. Give the functions of the
impedance bond present in AC track circuit.
Ans:
Functions of impedance bonds: i) To provide path of low resistance for traction
currents to pass through insulated track. ii) To provide path of high impedance
for AC signaling currents between two rails of track. iii) To keep signaling
currents restricted to the insulated track circuits.
Q16. List four special features of
train lighting dynamo.
Ans:
Special features of train lighting dynamo: 1) Robust construction for the
conditions in which it is used, 2) Constant polarity irrespective of direction
of motion of train, 3) Nearly constant output at varying speeds, 4) As it is in
parallel with the batteries charging them, it is inherently self regulating, 5)
It has two field windings namely: main field (weaker) between the positive and
negative brushes, and the aid field (stronger) between the positive and third
brush.
Q 17. State the necessity of the
signaling system.
Ans:
Necessity of signaling system: Control the movement of trains to avoid
hazardous movements, avoid accidents, operate optimally by the following:
·
Indicate to the driver when to stop
·
Indicate to the driver when to proceed on a certain rail route,
·
Indicate to the driver when to proceed with caution on a certain rail route,
·
Indicate to the driver when to proceed with full speed,
·
Indicate to the driver position of a hidden or obscured signal,
·
Indicate to the driver his action during shunting operations.
Q18. List any four advantages of
multi aspect color light signals.
Ans: Advantages of multi aspect color light
signals:
1.
Economical
2.
Simplicity of indication to drivers
3.
Better ability to deal with traffic of varying speed
4.
Simpler and easier in operation
5.
Control on large signals at heavily worked stations
6.
Provide increased line capacity
Q19. Differentiate DC and AC track
circuits on the basis of i) Length of circuit ii) Application iii) Effect of
stray currents iv) Maintenance
Ans:
i) Length of circuit : AC track
circuit is having long length up to 3 to 5 km while DC track circuit is having
short length.
ii) Application :
AC track circuit is used where tracks are electrified while DC track circuit is
used for electrified as well as non- electrified lines.
iii) Effect of stray currents:
Stray currents have no effect on AC track circuit while DC track lines are not
recommended for use in places where fear exists for circulation of stray direct
currents. They cause voltage drop in the un insulated rail, which limits the
length of the DC track.
iv) Maintenance :
AC track circuit has easier and economical maintenance while DC track circuit
has comparatively complex maintenance activities.
Q20. State what is meant by mimic
diagram and what is the indication in mimic diagram of following coloured
lamps. 1) Green lamp, 2) Milky white lamp, 3) Red lamp.
Ans:
Mimic diagram: It depicts the power
supply arrangement for the overhead 25 kV traction system in the remote control
centre on a small scale in the traction power control centre.
·
Mimic diagram is installed at each control centre to give actual visual
position of electric supply system. It describes diagrammatically overhead
system as well as various substations and control posts.
·
Remote controlled equipments in the mimic diagram are represented by a control
discrepancy switch (DS).
1)
Green lamp lights up whenever impulse train is being transmitted from or
received by remote control centre. 2) Milky white lamp lights up when alarm is
received from any station in the panel.
3)
Red lamp lights up when either send or receive channel fails.
