The advantages
of 25 kV, 50 Hz AC supply system is shown as below.
Light overhead catenary
- As the system voltage is high, the line current for a given traction demand is very less. This will result in cross section of over head conductor is reduced.
- As the size of conductor is reduced, line conductor support and foundation are also light.
- The high voltage needs higher insulation of over head equipment this will be compensated by reduction in the size of conductors.
Less number of sub stations
- As the line current is less in the 25 - kV supply system, this will result in less voltage drop and improves voltage regulation of the line which makes larger spacing between sub stations.
- The distance between two sub stations due to 25 kV is approximately 50 – 80 km as against 5 – 15 km for 1500 V DC and 15 – 30 km for 3000 V DC system.
- As the number of sub stations is reduced, the capital cost of track electrification is also reduced.
Flexibility for location of sub station
- The sub station can be located near the high voltage grid which is close to main railway track.
- These sub stations are fed from high voltage grid which results in saving in cost of special transmission line for substation.
Low cost of installations
- The cost of fixed installation for 25 kV AC system as compared to DC system.
Co – efficient of Adhesion
- The DC locomotive has co – efficient of adhesion about 27% as compared to rectifier locomotive which is closely 45%.
- This will result in lighter AC locomotive can takes the same load as heavier straight DC locomotive.
Higher starting efficiency
- As the AC locomotive has higher string efficiency as compared to straight DC locomotive.
- The supply voltage at starting in the DC locomotive is reduced by means of ohmic resistors but it is changed by using tap changer in AC locomotives.
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