Why 25kv is used in railway traction system?
25kV is globally accepted voltage level for electric locomotives. The main reason for 25kV voltage used in railway is, that 25 kV AC more economical than 1.5kV DC voltage system. Since 25kV voltage system has higher voltage, the higher voltage reduces the current flow through conductor; this reflects to reduce the conductor size. The cost of the conductor gets less. However, there are 7 major advantages for using 25kV voltage system in railway. Let see…
- High voltage:
As the voltage increases, the current flow get decreases. Since the size of the conductor will be reduced.
Here you can see that, the cross section of the conductor gets reduced, as the voltage increase. Therefore, the lesser cross section of the conductor causes less cost of conductor as well as Catenary wires.
- Reduction in losses:
As the current flow decreases, the ohmic losses (I2 * R) get decreases. Refer the formula…That, the square of the current flow through the conductor is directly proportional to the ohmic losses. Therefore, by reducing the size of the current flow through the conductor we can reduce the power losses.
- Free from neutral voltage:
In AC voltage distribution, the neutral wire is used as simply current return path, therefore it does not have any potential as DC negative has.
- Reduction in stray current:
Stray current is the current which flows to buildings, ground or equipment due to electrical supply system imbalances or wiring flaws. Higher flow of stray current causes corrosive on the metal structure. As we increase the voltage the net stray current flow can be reduced.
- Voltage Regulation Improvement:
Due to less line voltage drop (IR), the line voltage regulation can be improved.
- Less Conversation cost:
Fixed AC can be converted into variable AC with the help of VFDs. So that the VFDs can be placed at locomotive itself. Therefore, any other conversion solid state equipment does not require.
AC voltage is universally available, so that we can change any voltage level with the help of AC transformers. But In case DC needs Special conversion equipment.
Key Points of Why 25kv is used in railway traction system:
To take advantage of high voltage distribution, generally railway locomotive is used 25kV AC voltage distribution.