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
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