In this system 1-phase high voltage of 25KV at 50Hz is required – This system needs a rectifier circuit to convert AC into DC .The step down transformer Changes the voltage from 25KV to the desired low voltage and rectifier circuit convert it from AC to DC.
DC series Motor are used or traction Motor because of its high starting torque and easy speed control 1-phase 25KV is supplied to the over head syestem (OHE) from traction sub-station .
At traction sub-station 3-phase 132KV or 110KV is taken from grid sub-station through transmission line. This 3-phase, 132KV is converted into 1-phase 25KV by two method
a :- Scott connected (3-phase, 2-phase)
b :- Rotational wise use of 3-phase at any sub-station at a time (R-Y ,Y-B ,B-R).
This system is adopted in all the areas of major traffic density on main lines in India and aboard.
• The line current for the given power demand is reduced because of high system voltage.
• Sub-station distance is 50-80KM so less no of sub-station required.
• Cost of sub-station design is simple and less than to other sub-station.
• Starting torque is high.
• Efficiency is high.
• 1-phase Ac system is unbalanced in the power supply system which is very important is consider.
• There is disturbance with communication line.
• There is disturbance with the television station and radio station.