In the former Soviet Union, increasing traction network voltage level through series capacitor compensation (SCC) in their traction feeder caused even higher equalizing current (or penetrating power) [15].
The units were ordered to be used on the intercity Bergen, Dovre and Sørland Lines, but were plagued with technical faults (overheating traction equipment, transient voltages, etc).
The thyristor a rapid-action, high-power switch with which the "on" and "off" periods of each cycle can be fractionally varied achieved smoothly graduated application of voltage to traction motors.
As the modern trains have been widely adopted in China high-speed and heavy-haul railways, the low-frequency voltage fluctuation of traction network has been found frequently, which affects both traction power supply system (TPSS) and utility system seriously.
Drops in the line voltage consistent with traction current being drawn were observed however, which suggests that the traction equipment had been isolated on the vehicle with the measuring equipment, with other vehicles in the train providing all of the tractive effort.
The no-load voltage of direct traction power supply network is 27.5 kV.
However, the voltage loss of traction bus is increased from 730 to 5,790 V.
Lastly, the power factor can be adjusted to ensure a proper voltage level of traction network.
This is hard to be achieved in practice, particularly when traction loads fluctuate sharply: the voltage increases at no load and drops at heavy load.
In Fig. 1, U A, U B, U C are three phase voltage of the traction transformer primary side; U α, U β the load voltage of two power supply arms; φ α and φ β the impedance angles of α-phase and β-phase.
