Which one is more efficient for railways 750v DC or 25 KV AC and why?

For mainline and high-speed railways 25kV ac is now the most proven and widely used system. It offers a number of advantages, including reducing the cost of power supply equipment, improving efficiency, and using energy from braking more effectively which are all potentially attractive features to metro operators.



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Advantages of 25 kV AC System over DC System The 25 kV AC substations have lesser number equipment. The 25 kV AC system requires light overhead catenary (conductor) than the DC system. The use of high voltage (25 kV) in the overhead system reduces the current in the line which makes the use of small sized conductors.

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The choice of 25 kV was related to the efficiency of power transmission as a function of voltage and cost, not based on a neat and tidy ratio of the supply voltage. For a given power level, a higher voltage allows for a lower current and usually better efficiency at the greater cost for high-voltage equipment.

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DC motors are used on trains is because of their high torque and good speed control. Compared to AC motors, DC motors can provide industry applications with a fine balance of strong starting torque and controllable speed for seamless yet precise performance.

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A 25 kV AC traction system has several advantages compared to other traction systems, such as: Reduced power loss: The higher voltage reduces the power loss during transmission, which means that more power can be delivered to the locomotive or train.

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