Suburban railways use

Suburban railways use

Right Answer is:

750 V DC


The system used for traction is a combination of both AC and DC, you must be knowing that the overhead power cable above the train is fed with AC supply (in India it’s 25kV) which is received by the transformer inside the railway engine which is stepped down, i.e the voltage level is reduced (this also causes the current level to increase and this increased current level is the driving force of the traction motor) and this power is fed to a device which converts AC power to DC power which is known as Rectifier. Now this DC supply is given to a given number of sets of DC Series & Shunt motors. 

Direct current at 600-750 V is universally employed for tramways in urban areas and for many suburban railways while 1500-3000 V dc is used for mainline railways. The current collection is from the third rail (or conductor rail) up to 750 V, where large currents are involved, and from overhead wire for 1500 V and 3000 V, where small currents are involved. 

It may be noted that for heavy suburban service, a low voltage dc system is undoubtedly superior to a 1-phase ac system due to the following reasons:

  1. DC motors are better suited for frequent and rapid acceleration of heavy trains than ac motors.
  2. DC train equipment is lighter, less costly, and more efficient than similar ac equipment.
  3. When operating under similar service conditions, a DC train consumes less energy than a 1-phase ac train.
  4. The conductor rail for the DC distribution system is less costly, both initially and in maintenance than the high-voltage overhead ac distribution system.
  5. DC system causes no electrical interference with overhead communication lines.

The only disadvantage of the dc system is the necessity of locating ac/dc conversion sub-stations at relatively short distances apart.

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