QUESTION ANSWER OF BASIC MAGNETIC CIRCUITS

BASIC TERMINOLOGY OF MAGNETIC CIRCUITS

Modern electric Traction chapter 3 Notes ( Signaling and Train Lighting)

 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.

Modern electric Traction chapter 4 Notes ( Electric Locomotives)

Chapter 4. Electric Locomotives 

Q1. List any 8 equipment used in auxiliary circuit of electric locomotive. 

 Ans: Equipment Used in Auxiliary Circuit of Electric Locomotive: 

1. Batteries 

2. Compressor 

3. Blowers 

4. Exhausters 

5. Pumps 

6. Cab ventilating fans 

7. Locomotive heating (if any) 

8. Transformer oil cooling radiator 

9. Head light 

10. Flasher light 

11. Marker light 

12. Engine Horn 

Q2.Draw neat labeled diagram of 1-ϕ AC locomotive showing its various equipment of power circuit and give the function of each equipment used in power circuit. 

 Ans: Diagram of 1-ϕ AC Locomotive:

Functions of Equipment: 1. Circuit Breaker: Disconnects the locomotive equipment from the supply in the event of fault in the equipment / loco. 

2. On Load Tap Changer: Used to control the voltage to the traction motors through the rectifier for speed control. 

3. Traction Transformer: Steps down the voltage to the suitable value for the traction motor. It has a ratio of 20:1. 

4. Rectifier: Converts input AC to DC for further use by series traction motors. 

5. Smoothing reactor/choke: Smoothen out the ripples in the DC output current of rectifier. 

6. Traction motor: Operates as per the requirement to take the traction load. 

Q3. List any eight equipment used in auxiliary circuit of electric locomotive. 

 Ans: 1) Batteries , 2) Compressor , 3) Blowers , 4) Exhausters , 5) Pumps , 6) Cab ventilating fans. 7) Locomotive heating (if any) , 8) Transformer oil cooling radiator. 9) Head light , 10) Flasher light , 11) Marker light , 12) Engine Horn 

Q4. Explain the meaning of the terms WAM1, WAV3, YAV1, WAG1. 

 Ans: 

• WAM1: Broad gauge AC locomotive for mixed freight (goods) and people design class 1. 

• ( WAV3) WAU3: Broad gauge AC locomotive EMU design class 3. 

• (YAV1) YAU1: Meter gauge AC locomotive EMU design class 1 

• WAG1: Broad gauge AC locomotive for goods freight design class 1. 

Q5. Write any 4 equipment and their function in auxiliary circuits of electric locomotive. 

Ans: Auxiliaries with function: 

1) Batteries – to run baby compressor which supplies air for initial raising of pantograph and closing of air blast circuit breaker. 

2) Air compressor – operation of air control and application of brakes. 

3) Exhausters – for vacuum brakes.

4) Blowers – as transformer blower, reactor blower, SCR blower, traction motor blower etc. 

5) Pumps – transformer oil pump, water pump etc. 

6) Fan – cab ventilation 

7) Heater – locomotive heating

Q6. State any 4 limitations of Arno converter. 

Ans: Limitations of Arno converter: 

1. Unbalanced current in the 3-phase of stator winding 

2. Undue heat produced in the winding. 

3. Voltage fluctuation and voltage unbalance. Output voltage obtained from Arno converter fluctuates from 290 V to 460 V. 

4. When output voltage of Arno converter raises to 460 V, because of excessive magnetizing current, p.f. is poor. 

5. Stator winding carries single phase motoring current and 3ph generating current. 

6. Motoring phases carry both motoring and generating currents, resultant current is small, whereas generating phase carries only generating current, its magnitude is higher than that of motoring phases. 7. Negative sequence torque has pronounced effect on starting torque. 8. Problem in starting. 

Q7. List any four contactors and their purpose. 

Ans: Types of Contactors in traction and their purpose : Each contactor makes or breaks the power circuit. List any four contactors and their purpose. 

i) Electromagnetic Contactor : When operating coil is energized, it attracts a soft iron armature which in turn operates moving power contact. When coil is de-energized moving contact drops. 

ii) Electro-pneumatic Contactor: Moving power contact operates to close the circuit when compressed air acts on a piston in cylinder. Releasing air pressure, spring forces the piston to open the contact. 

iii) Cam and Roller operated Contactor: Moving contact is carried at one end of hinged arm and roller is carried at other end. Roller is engaged with cam on shaft. Cam shaft can be moved by air engine or vane motor. 

Q8. State any four points of differences between circuit breaker and an interrupter. 

Ans: Difference between Circuit breaker and Interrupter:

Q9. State the reason for employing air blast type circuit breaker in electric locomotive. 

Ans: The main function of any circuit breaker is to operate under normal and abnormal circuit conditions as per the requirements of the electrical machines/equipment by switching or for protection purpose. As the AC electric locomotive is powered by a 25 kV overhead line, it is necessary to have a proper switching device that will provide the above mentioned facilities. Also the overhead line is in open air where the pantograph makes contact with it and draws power. The air blast circuit breaker is placed between the pantograph and the transformer which is in the locomotive. Also the circuit breaker has to isolate the locomotive whenever there is a voltage change or phase change point in the path. Thus the breaker used here has to operate frequently. Oil or other types of breakers (other than air blast) will need more frequent maintenance or replenishment of oil etc. hence air blast breakers are employed. 

Q10. State the function of earthing switch and tap changer in electric locomotive. 

Ans: 1) Earthing switch: Earthing switch (has a number of electromagnetic and electro-pneumatic interlocks with the HT areas in the locomotive) is to be closed for safety to discharge the line charge to earth before working for maintenance. Also the doors of these unsafe areas do not open for maintenance unless the earthing switch is operated. The switch has to be opened before energizing the locomotive equipment at 25 kV when the safety doors lock. 

2) Tap changer: Used to control the voltage to the traction motors through the rectifier for speed control. LV or HV side tap changing is precisely done. Due to the variable voltage available from the tap changer, the smooth speed control is possible without losses in rheostatic devices leading to efficient running of the locomotives