A. 22 V B. 440 VC. 5kV D. 15 kVAnswer: A. 22 V
Explanation: Electric Traction Systems:- Electric traction is meant locomotion in which the driving (or tractive) force is obtained from electric motors. It is used in electric trains, tramcars, trolleybuses, diesel-electric vehicles, etc.
- They involve the use of electric energy at some stage or the other.
- Examples: battery-electric drive, diesel-electric drive, railway electric locomotive fed from overhead AC supply, tramways, and trolly buses supplied with DC supply.
- Direct Current Traction System:
- In all cases, contact systems are fed from substations which are spaced 3 to 5 km for suburban lines and 40-50 km for main lines Service.
- Substations receive power from 110/132 kV, 3-phase network (or grid). At these substations, this high-voltage 3-phase supply is converted into a low-voltage single-phase supply with the help of Scott-connected or V-connected 3-phase transformers.
- Next low AC voltage is converted to the suitable DC voltage by using suitable rectifiers or converters (like rotary converters, mercury-arc rectifiers, metal or semiconductor rectifiers).
- DC motors are better suited for frequent and rapid speed control than AC motors.
- DC train equipment is lighter, less costly, and more efficient than similar AC equipment.
- When operating under the same conditions, the DC train consumes less energy than a Single-phase AC train.
- The erection cost and maintenance cost of the conductor rail is less than that of a single-phase AC system.
- No electrical interference with overhead communication lines in the DC traction system.
- The only disadvantage of the DC system is the necessity of locating AC/DC conversion sub-stations at relatively short distances apart.
- Single-Phase Low-frequency AC Traction System:
- In this system, AC voltages from 11 to 15 kV at the frequency (50 Hz), (50/2 Hz), (50/3 Hz) Hz are used.
- Electric supply is taken from the high voltage transmission lines at 50 Hz, then in addition to a step-down transformer, the substation is provided with a frequency converter.
- supply is fed to the electric locomotor via a single over-head wire (running rail providing the return path).
- A step-down transformer carried by the locomotive reduces the 15-kV voltage to 300-400 V for feeding the AC series motors.
- To overcome the low power factor and commutation problem in the AC Series motor, a low-frequency AC supply is used.
- Another advantage of employing low frequency is that it reduces telephonic interference.
- Substations are 50 to 80 km apart.
- Three-phase Low-frequency AC System:
- It uses 3-phase induction motors which work on a 3 kV to 3.6 kV at (50/3 Hz) supply.
- Sub-stations receive power at a very high voltage from 3-phase transmission lines at the usual industrial frequency of 50 Hz.
- This high voltage is stepped down to (3 kV to 3.6 kV) by transformers and frequency is reduced from 50 Hz to (50/3 Hz) by frequency converters.
- This system employs two overhead contact wires and the track rail forming the third phase.
- Induction motors used in the system are quite simple and robust and give trouble-free operation.
- The induction motor used in this traction system has high efficiency and the ability of automatic regenerative braking.
- Kando System (Single-phase AC to Three-phase AC):
- In this system, the single-phase 16-kV, 50 Hz supply from the sub-station is picked up by the locomotive through the single overhead contact wire.
- It is then converted into a 3-phase AC supply at the same frequency by means of phase converter equipment carried on the locomotives.
- This 3-phase supply is then fed to the 3-phase induction motors.
- Kando system is likely to be developed further.
- Single-phase AC to DC System:
- This system combines the advantages of high-voltage AC distribution at the industrial frequency with the DC series motors traction.
- It employs an overhead 25-kV, 50-Hz supply which is stepped down by the transformer installed in the locomotive itself.
- The low-voltage AC supply is then converted into a DC supply by the rectifier which is also carried on the locomotive.
- This DC supply is finally fed to the DC series traction motor fitted between the wheels.
- The system of traction employing 25-kV, 50-Hz, 1-phase AC supply has been adopted by Indian Railway.
A. 22 V
B. 440 V
C. 5kV
D. 15 kV
Answer: A. 22 V
Explanation:
Electric Traction Systems:
- Electric traction is meant locomotion in which the driving (or tractive) force is obtained from electric motors. It is used in electric trains, tramcars, trolleybuses, diesel-electric vehicles, etc.
- They involve the use of electric energy at some stage or the other.
- Examples: battery-electric drive, diesel-electric drive, railway electric locomotive fed from overhead AC supply, tramways, and trolly buses supplied with DC supply.
- Direct Current Traction System:
- In all cases, contact systems are fed from substations which are spaced 3 to 5 km for suburban lines and 40-50 km for main lines Service.
- Substations receive power from 110/132 kV, 3-phase network (or grid). At these substations, this high-voltage 3-phase supply is converted into a low-voltage single-phase supply with the help of Scott-connected or V-connected 3-phase transformers.
- Next low AC voltage is converted to the suitable DC voltage by using suitable rectifiers or converters (like rotary converters, mercury-arc rectifiers, metal or semiconductor rectifiers).
- DC motors are better suited for frequent and rapid speed control than AC motors.
- DC train equipment is lighter, less costly, and more efficient than similar AC equipment.
- When operating under the same conditions, the DC train consumes less energy than a Single-phase AC train.
- The erection cost and maintenance cost of the conductor rail is less than that of a single-phase AC system.
- No electrical interference with overhead communication lines in the DC traction system.
- The only disadvantage of the DC system is the necessity of locating AC/DC conversion sub-stations at relatively short distances apart.
- Single-Phase Low-frequency AC Traction System:
- In this system, AC voltages from 11 to 15 kV at the frequency (50 Hz), (50/2 Hz), (50/3 Hz) Hz are used.
- Electric supply is taken from the high voltage transmission lines at 50 Hz, then in addition to a step-down transformer, the substation is provided with a frequency converter.
- supply is fed to the electric locomotor via a single over-head wire (running rail providing the return path).
- A step-down transformer carried by the locomotive reduces the 15-kV voltage to 300-400 V for feeding the AC series motors.
- To overcome the low power factor and commutation problem in the AC Series motor, a low-frequency AC supply is used.
- Another advantage of employing low frequency is that it reduces telephonic interference.
- Substations are 50 to 80 km apart.
- Three-phase Low-frequency AC System:
- It uses 3-phase induction motors which work on a 3 kV to 3.6 kV at (50/3 Hz) supply.
- Sub-stations receive power at a very high voltage from 3-phase transmission lines at the usual industrial frequency of 50 Hz.
- This high voltage is stepped down to (3 kV to 3.6 kV) by transformers and frequency is reduced from 50 Hz to (50/3 Hz) by frequency converters.
- This system employs two overhead contact wires and the track rail forming the third phase.
- Induction motors used in the system are quite simple and robust and give trouble-free operation.
- The induction motor used in this traction system has high efficiency and the ability of automatic regenerative braking.
- Kando System (Single-phase AC to Three-phase AC):
- In this system, the single-phase 16-kV, 50 Hz supply from the sub-station is picked up by the locomotive through the single overhead contact wire.
- It is then converted into a 3-phase AC supply at the same frequency by means of phase converter equipment carried on the locomotives.
- This 3-phase supply is then fed to the 3-phase induction motors.
- Kando system is likely to be developed further.
- Single-phase AC to DC System:
- This system combines the advantages of high-voltage AC distribution at the industrial frequency with the DC series motors traction.
- It employs an overhead 25-kV, 50-Hz supply which is stepped down by the transformer installed in the locomotive itself.
- The low-voltage AC supply is then converted into a DC supply by the rectifier which is also carried on the locomotive.
- This DC supply is finally fed to the DC series traction motor fitted between the wheels.
- The system of traction employing 25-kV, 50-Hz, 1-phase AC supply has been adopted by Indian Railway.
