Traction network is a power supply network composed of feeder, catenary, track and return line, as shown in the following figure:
In general, the catenary voltage should not be lower than 2 1kv, the rated voltage of trunk line is 25kv, and the voltage to ground is 27.5kv.
Single transformer power supply: each power supply partition only takes power from the traction substation at one end (the switch of the partition kiosk equipment is turned on).
Bilateral power supply: two power supply arms take power from two traction substations at the same time (the switch of kiosk equipment is turned off).
Cross-regional power supply: when the traction substation can't supply power normally, it is a temporary measure (abnormal state) to supply power to the adjacent substations on both sides through the partition booth switch.
Direct power supply mode, traction network has no special protection measures, and is generally only used in mountainous areas with few communication lines. The power supply modes of AT and BT are more complicated, so the electrification transformation of Shanghai-Hangzhou, Zhejiang-Jiangxi and Beijing-Shanghai lines adopts the direct power supply mode of return line.
Backflow direct power supply mode cancels the current-absorbing transformer in BT power supply mode and retains the return line. By using the mutual inductance between the catenary and the return line, the return flow in the rail can be as much as possible from the return line to the traction substation, thus partially offsetting the interference of the catenary to the adjacent communication lines. Its anti-interference effect is not as good as that of BT power supply mode, and it is usually used in sections with low anti-interference requirements for communication lines. This power supply mode is simple and improves the reliability of power supply equipment; Because the current absorption transformer is cancelled and only the return line is kept, the traction network impedance is lower than that of the direct supply mode, the power supply performance is better and the cost is not too high, so this power supply mode has been widely used in electrified railways in China.
Direct power supply mode
Advantages:
Simple and save investment.
Disadvantages:
Because the traction power supply system is a single-phase load, the power supply
Traction reflux of electric mode is rail, which is unbalanced.
Power supply mode I≠I? ), communication line production
Sensory influence.
Power supply mode of autotransformer (AT power supply mode)
Due to the effect of autotransformer, the current of catenary and positive feeder is I/2, and the directions are opposite, which effectively reduces the interference of traction network to communication lines.
Since the neutral point of autotransformer is connected to the rail, the power supply voltage of traction network is 2x25kV, and the voltage is doubled, so the distance between traction substations is doubled theoretically.
For example, if the distance between traction substations is 20-30km in the direct supply+return line power supply mode, then the AT power supply mode is 40-60km. AT power supply mode is used in traction power supply system with heavy load, high speed and large current.
Feeder current is only half that of direct supply mode.