How does the traction substation of transformer happen? What is the relationship between transformer

How does the traction substation of transformer happen?

The main transformer for tracTIon substaTIon in traction substation usually refers to the large-capacity power transformer which transforms the high-voltage electricity of power system into suitable for traction power. It is the main electrical facility of AC traction substation.

The connection modes of main transformer can be classified into single-phase traction substation and three-phase traction substation according to the number of phases of power supply introduced by traction substation. The connection of main transformer in single-phase traction substation is the simplest. It introduces single-phase power supply from power system. Usually, the secondary voltage of main transformer with single-phase connection is reduced to the voltage of traction network. In this way, the two power supply arms of traction substation supply power with the same phase voltage, resulting in a larger negative sequence current, and the three-phase power supply used in traction substation needs to be introduced separately.

Three-phase traction substation is introduced by power system into three-phase power supply, which is transformed to supply power to both sides of traction network with different phase voltages. The main transformer wiring of three-phase traction substation can be divided into two categories: one is composed of three common symmetrical winding transformers or single-phase transformers, which belongs to YN, D11 and V wiring, and the other is to realize the conversion of secondary single-phase load and primary three-phase balanced load of traction substation by various asymmetrical winding wiring. This kind of wiring is called "three-phase-two-phase balanced wiring". These include Scott, Wood Bridge, Leblame and three-phase impedance matching (see three-phase-two-phase balanced connection transformer). A scheme of transforming the secondary single-phase load and the primary three-phase balanced load of traction substation by means of capacitance and inductance is being studied and tested. This method can realize that the whole electrified railway section is supplied by the same phase without increasing the burden of negative sequence current on the power system, thus greatly reducing the number of electrical segments in the catenary, which is very important for the safe operation of high-speed electrified railway. Yes.

The characteristics of AC traction substations with different main transformers are as follows: (1) The relative negative sequence current of various connections is shown in the following figure when the load ratio of two arms (n) takes different values based on heavy arm load. In the figure, the negative sequence current generated by all kinds of balanced connection transformers is the smallest, followed by YN, DLL and V, V connection, and single-phase connection. (2) In terms of transformer installation capacity utilization, single-phase traction substation is the most abundant, not only the installation capacity can be 100% used, but also the average load rate of traction transformer is higher; the installation capacity of V, V and balanced connection traction substation can also be fully utilized, but the average load rate is smaller; the utilization rate of installation capacity of YN, D11 connection traction substation is only 79%, and the average load of transformer is only 79%. The rate is the worst. (3) In terms of voltage drop of traction bus, besides the voltage drop of the phase bus, the two arm loads of YN and D11 connection traction substation can also change the voltage of the other arm bus. Specifically, one third of the current component of the arm load supplied by the leading phase voltage will flow through the transformer lagging phase winding, thus causing additional voltage drop in the lagging phase bus. On the contrary, the arm load powered by lagging phase voltage also has 1/3 current flowing through the leading phase winding, and the voltage rises on the leading phase bus. The calculation shows that the additional voltage drop or voltage rise caused by the same arm load on the bus of the lagging phase or the leading phase are different in value, and the former is much larger than the latter. Therefore, the bus voltage drop of YN, D11 connection traction substation is larger. (4) In the aspect of providing three-phase power supply, YN and D11 wiring are the most convenient. The Scott wiring traction transformer needs special wiring inversion Scott transformer to convert the two-phase voltage system vertically to three-phase voltage system. The cost is high.

(100% negative sequence current of heavy arm)

The reliability of the power supply of the first-class traction load of the standby electrified railway can be guaranteed by the following measures: (1) There should be two power supply rounds of high-voltage transmission lines which do not belong to the same substation buses in the same area. Usually, the main supply and the other one are in the hot standby state, and the relationship between the main supply and the standby is alternated regularly. There is an automatic switching device of standby power supply between two transmission lines. (2) There are two ways to reserve the main transformer of traction substation: one is to connect 100% power to set up a second transformer, which is called "fixed reserve" mode, and the other is to set up a mobile transformer train for every 3-5 traction substations, whose capacity should be the same as that of the largest traction transformer in its jurisdiction. The "mobile standby" mode usually needs to set up railway bifurcation lines specially introduced into traction substations for mobile vehicles, and the normal power supply can not be restored immediately after the accident.

What is the relationship between transformer turns and voltage?

Relation between Turn Ratio and Voltage Ratio of Ferrite Transformer

I want to use TL494 to make a switching power supply, imitate the circuit of TL494 inverter, use 494 to drive two field effect transistors, transformer primary with central tap, if the AC voltage is 300V, primary 15 + 15 turns is OK? So is it 20V per turn? How many turns does it take to get a 15V voltage secondary?

The relationship between turn ratio and voltage ratio of ferrite transformer is the same as that of ordinary silicon steel sheet, and it is also the turn ratio = voltage ratio. The design of switching power supply is totally different from that of ordinary power frequency transformer. It is not so simple to determine the number of coils. The inductance of coils and other parameters should be taken into account, and the requirements for fabrication are also very high. In view of the difficulty of making switching transformer, it is suggested that we should not attempt to make self-made switching power supply.