Structure suitable for converting Vx wiring traction transformer into flexible single-phase wiring

Abstract

The invention provides a structure suitable for converting a Vx wiring traction transformer into flexible single-phase wiring, based on two single-phase transformers and an in-phase power supply device, an a1x1 winding and an a2x2 winding on the primary side of the transformer are connected in parallel to form a parallel winding 1; a b1y1 winding and a b2y2 winding on the secondary side of the transformer are connected in parallel to form a parallel winding 2; the parallel winding 2 and the in-phase power supply device are connected in parallel to form a parallel in-phase winding; and the parallel winding 1 and the parallel in-phase winding are connected in series, the series connection point is grounded, and the non-series connection end points are respectively connected with a contact network and a positive feeder line, so that a 2 * 27.5 kV power supply framework is formed. Flexible single-phase wiring transformation of the three-phase Vx wiring traction substation is achieved, utilization of the existing three-phase Vx wiring traction transformer can be achieved, related transformation and abandoned engineering caused by replacement of the traction transformer are avoided, high-voltage side transformation is avoided, and the influence on normal operation organization of a railway during transformation is reduced. And meanwhile, the cost for re-evaluating the electric energy quality can be saved.

Description

Technical Field

[0001] This invention belongs to the technical field of traction power supply systems, and in particular relates to a structure suitable for converting a Vx-connected traction transformer into a flexible single-phase connection. Background Technology

[0002] A three-phase Vx-connected traction transformer is a transformer used in electrified railways for AT power supply. It is usually composed of two single-phase transformers for AT power supply, with the two single-phase transformers supplying power to the two power supply arms of the traction substation respectively. Each single-phase transformer is a 3-winding transformer, with two secondary windings per phase. The two secondary windings output ±27.5kV respectively, and the winding neutral point is grounded.

[0003] Compared to Scott connection traction transformers, three-phase Vx connection traction transformers can save on the need for an autotransformer (AT) at the outlet, and compared to cross-connection traction transformers, they offer higher capacity utilization. The maturity of this connection type has been recognized by the industry, and it has been widely used in projects employing AT power supply methods, such as high-speed railways and heavy-haul railways.

[0004] In-phase power supply, also known as in-phase power supply technology, refers to a traction power supply method where the contact network voltage phase is the same in sections supplied by adjacent substations on a line, and there are no phase-splitting links on the line. Theoretically, in-phase power supply could be achieved by using single-phase transformers at all traction substations along the entire line. However, because single-phase loads induce negative sequence currents in the power system, this can lead to severe three-phase imbalance when the power system is weak. Therefore, using only single-phase transformers would not be approved by the power sector. Thus, the key technology for in-phase power supply is to achieve three-phase to single-phase symmetrical conversion at the traction substations and to use in-phase power supply devices.

[0005] Most existing high-speed or heavy-haul railways use AT power supply for their main lines, and traction substations mostly use three-phase Vx connection. If flexible single-phase connection upgrades are to be implemented, there are generally two methods: one is to directly replace the traction transformer with a balanced connection type; the other is to adjust the high-voltage side connection of the traction transformer, changing the connection of one traction transformer originally connected to the common phase to the middle of the high-voltage side of another traction transformer. However, both of these upgrade methods face the following problems in practice: first, directly replacing the traction transformer with a balanced connection type requires replacing two Vx-connected transformers to bear the load of the entire traction substation, resulting in a large transformer capacity and requiring extensive civil engineering modifications to the original traction substation; second, adjusting the high-voltage side connection of the traction transformer requires assessment and approval from the power grid department.

[0006] In existing technologies, flexible single-phase traction substations often use unequal-capacity balanced connection type traction transformers. If the existing three-phase Vx connection traction substations are upgraded to same-phase power supply, directly using the above-mentioned unequal-capacity balanced connection type traction transformers will cause problems such as abandonment of existing traction transformers, civil engineering renovation, and high-voltage side renovation of traction transformers. This is not conducive to the promotion and application of same-phase power supply technology in high-speed railways and heavy-haul railways that use a large number of three-phase Vx connection type traction transformers. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a structure suitable for converting Vx-connected traction transformers to flexible single-phase connections, so as to solve the problems of traction transformer abandonment, large-scale civil engineering renovation, and high-voltage side connection renovation caused by converting existing three-phase Vx-connected traction substations to flexible single-phase connections.

[0008] In a first aspect, embodiments of the present invention provide a structure applicable to converting a Vx-connected traction transformer into a flexible single-phase connection, based on two single-phase transformers and a same-phase power supply device, including: The a1x1 winding and the a2x2 winding on the primary side of the transformer are connected in parallel to form parallel winding 1; The b1y1 winding and b2y2 winding on the secondary side of the transformer are connected in parallel to form parallel winding 2; The parallel winding 2 is connected in parallel with the same-phase power supply device to form a parallel same-phase winding; The parallel winding 1 is connected in series with the parallel in-phase winding, the series connection point is grounded, and the non-series connection points are connected to the contact network and the positive feeder respectively, forming a 2×27.5kV power supply structure.

[0009] Preferably, the phase of the parallel winding 1 is consistent with the AB phase of the primary side of the transformer A, and the phase of the parallel winding is 180° out of phase with the CB phase of the primary side of the transformer B after phase shifting by the in-phase power supply device.

[0010] Preferably, the in-phase power supply device includes a step-down transformer, an AC-DC-AC converter and a matching transformer connected in sequence, used to shift the phase of the input voltage of the parallel winding 2 by 120° and output a voltage with a phase difference of 180° from that of the parallel winding 1.

[0011] Preferably, the AC-DC-AC converter adopts a three-level NPC topology and achieves dynamic phase adjustment through SPWM modulation, with an adjustment range of ±5°.

[0012] A non-phase power supply device, comprising: The step-down transformer has a parallel winding 2 connected to the input side and an AC-DC-AC converter connected to the output side. An AC-DC-AC converter, comprising a rectifier, a DC bus, and an inverter, is used to achieve a 120° basic phase offset. The matching transformer is connected to the inverter output on the input side, and the output side generates the z1c1 winding.

[0013] Preferably, the AC-DC-AC converter is equipped with a harmonic suppression module, and the total harmonic distortion of the output is less than 3%.

[0014] A flexible single-phase connection structure includes: the primary sides of transformer A and transformer B are respectively connected to phases AB and CB of a three-phase power grid; the secondary sides form a 2×27.5kV output through parallel-series reconfiguration and in-phase power supply devices, and the neutral point is grounded through a nonlinear resistor.

[0015] The embodiments of the present invention bring the following beneficial effects: This invention enables flexible single-phase wiring conversion of three-phase Vx-connected traction substations, allowing the utilization of existing three-phase Vx-connected traction transformers. This avoids the associated modifications and abandoned projects caused by replacing traction transformers, eliminates the need for high-voltage side modifications, and minimizes the impact on normal railway operations during the conversion process. It also saves on the cost of re-evaluating power quality.

[0016] Other features and advantages of the invention will be set forth in the following description, and some features will be obvious from the description or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description, claims, and drawings.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the terminal connection of a three-phase Vx wiring type in the prior art; Figure 2 This is a schematic diagram of the phase angle of a three-phase Vx connection type in the prior art; Figure 3 This is a schematic diagram of the conversion of the Vx-connected traction transformer to a flexible single-phase connection scheme according to an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the conversion of the Vx-connected traction transformer to a flexible single-phase terminal block in an embodiment of the present invention. Figure 5 The phase angle diagram for converting the Vx-connected traction transformer to a flexible single-phase connection is shown in this embodiment of the invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See Figure 1 and Figure 2 In current high-speed and heavy-haul railways, the Vx connection traction transformer structure consists of two single-phase transformers forming a three-phase Vx connection structure. The three-phase Vx connection configuration and phase angle are as follows: The three-phase Vx wiring configuration is as follows: One single-phase transformer has its high-voltage side connected to the A and B phases of external power. The a1x1 winding and a2x2 winding on the secondary side are connected in series. The series connection point of the two windings is grounded to R. The non-series connection points of the two windings are connected to the contact wire T and the positive feeder F, respectively. That is, the x1 terminal and the a2 terminal are connected and then grounded, the a1 terminal is connected to the contact wire T, and the x2 terminal is connected to the positive feeder F. Another single-phase transformer has its high-voltage side connected to the B and C phases of external power. The b1y1 winding and b2y2 winding on the secondary side are connected in series. The series connection point of the two windings is grounded to the R terminal. The non-series connection points of the two windings are connected to the contact wire T and the positive feeder F, respectively. That is, the y1 terminal and the b2 terminal are connected and then grounded, the y2 terminal is connected to the contact wire T, and the b1 terminal is connected to the F busbar.

[0021] The phase angles of the three-phase Vx connection are as follows: the phase angle between phases AB and CB on the primary side is 60 degrees; the secondary winding a1-(a2,x1)-x2 is in phase with AB, with terminals a2 and x1 grounded, and terminals a1 and x2 being 180 degrees apart, corresponding to 27.5kV and -27.5kV respectively, supplying power to the contact network T and positive feeder F respectively; the secondary winding y2-(b2,y1)-b1 is in phase with CB, with terminals b2 and y1 grounded, and terminals y2 and b1 being 180 degrees apart, corresponding to 27.5kV and -27.5kV respectively, supplying power to the contact network T and F busbars respectively.

[0022] See Figure 3 The structure for converting a Vx-connected traction transformer to a flexible single-phase connection in this embodiment includes a single-phase transformer A, a single-phase transformer B, and a same-phase power supply device. The same-phase power supply device includes a step-down transformer, an AC-DC-AC conversion device, and a matching transformer. The same-phase power supply device has an AC-DC-AC structure and is used to realize AC-DC-AC conversion.

[0023] See Figure 3 and Figure 4 The wiring configuration for the flexible single-phase connection structure is as follows: The primary windings A and B of single-phase transformer A are connected to the incoming power grid phases A and B, respectively. The secondary windings a1x1 and a2x2 of single-phase transformer A are connected in parallel and are designated as parallel winding 1. The primary windings B and C of single-phase transformer B are connected to the incoming power grid phases B and C, respectively. The secondary windings b1y1 and b2y2 of single-phase transformer B are connected in parallel and are designated as parallel winding 2. Parallel winding 2 is connected in parallel with the same-phase power supply device and is designated as parallel same-phase winding, i.e., winding c1z1. Parallel winding 1 and parallel same-phase winding are connected in series, with the series connection point being the neutral point and grounded. The non-parallel connection point of parallel winding 1 is connected to bus T to supply power to the contact network, and the non-series connection point of parallel same-phase winding is connected to bus F to supply power to the positive feeder.

[0024] Specifically, the x1 and x2 terminals of the secondary side of single-phase transformer A are connected to the c1 terminal of the parallel in-phase winding and then connected to the grounding R; the a1 and a2 terminals of the secondary side of single-phase transformer A are connected to the contact network T; the z1 terminal of the parallel in-phase winding is connected to the positive feeder F; the y1 and y2 terminals of the secondary side of single-phase transformer B are connected to the in-phase power supply device; and the b1 and b2 terminals of the secondary side of single-phase transformer B are connected to the in-phase power supply device.

[0025] See Figure 3 and Figure 5 Schematic diagram of the phase angle of single-phase transformer A connection Figure 5 As shown in Figure a, the phase angle between phases AB and CB on the primary side of single-phase transformer A is 60 degrees. The a1(a2)x1(x2) winding after the parallel connection of the secondary side windings a1x1 and a2b2 of single-phase transformer A is in phase with phase AB.

[0026] Single-phase transformer B connection phase angle diagram Figure 5 As shown in b, the phase angle between phases AB and CB on the primary side of single-phase transformer B is 60 degrees. The y2 (y1)b1 (b2) winding, which is formed by parallel connection of the b1y1 and b2y2 windings on the secondary side of single-phase transformer B, is in phase with phase CB. The in-phase power supply device shifts the phase of the power input to the y2 (y1)b1 (b2) winding by 120 degrees to obtain power supply z1c1. The c1z1 winding is connected in series with the a1 (a2)x1 (x2) winding. The series connection point x1 (x2)c1 is grounded. The phase difference between terminals a1 (a2) and z1 is 180 degrees, corresponding to 27.5kV and -27.5kV respectively, which are the power supplies for the contact network T and the positive feeder F respectively.

[0027] In this embodiment of the invention, the working principle is as follows: Transformer reconfiguration: Disconnect all series connection points of the secondary windings in the original Vx connection, and change the secondary windings of the two single-phase transformers A and B from series to parallel. That is, short-circuit the x1 and x2 terminals of the a1x1 and a2x2 windings of single-phase transformer A, and output the a1 and a2 terminals in parallel. Connect the a1x1 and a2x2 windings in parallel through phase conversion and parallel connection to form parallel winding 1 (phase AB is maintained); short-circuit the y1 and y2 terminals of the b1y1 and b2y2 windings of single-phase transformer B, and output the b1 and b2 terminals in parallel. Connect the b1y1 and b2y2 windings in parallel to form parallel winding 2 (phase CB is maintained); connect the parallel connection point of parallel winding 2 to the input side of the same-phase power supply device, and adjust its output voltage phase by 180° through the AC-DC-AC converter equipment to form a parallel same-phase winding that is complementary to parallel winding 1.

[0028] In-phase power supply reconfiguration: A step-down transformer is connected to parallel winding 2 on the input side and an AC-DC-AC converter on the output side, reducing the voltage from 27.5kV to a level suitable for power electronic devices. The AC-DC-AC converter includes a rectifier, DC bus, and inverter, achieving a 120° phase shift. A matching transformer is connected to the inverter output on the input side, boosting the voltage to 27.5kV and outputting the z1c1 winding. The AC-DC-AC converter is equipped with a harmonic suppression module, achieving a total harmonic distortion (THD) of less than 3%. Furthermore, the AC-DC-AC converter adopts a three-level NPC topology, using SPWM modulation to achieve dynamic phase adjustment within a range of ±5°.

[0029] System Integration: Parallel winding 1 and parallel winding 2 together form a 2×25kV power supply architecture. Dynamic current distribution between the two windings is achieved by controlling the voltage amplitude and phase of the parallel in-phase windings. Specifically: the x1 / x2 terminals of parallel winding 1 are connected in series with the c1 terminal of the parallel in-phase winding and then grounded; the a1 / a2 terminals of transformer A's output end are connected to the T bus (+27.5kV) to supply power to the contact network; the z1 terminal of the in-phase power supply device's output end is connected to the F bus (-27.5kV) to supply power to the positive feeder, ultimately forming a 2×27.5kV power supply architecture with a phase difference of 180°.

[0030] When the same-phase power supply device fails, the system directly switches to standby mode: the same-phase power supply device and the single-phase transformer B connected in parallel with it are taken out of operation, while the single-phase transformer A continues to operate. The two windings of the single-phase transformer A are changed from parallel to series connection, the series connection point is grounded, and the non-series connection points of the two windings are connected to the T bus and the F bus respectively.

[0031] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A structure for converting a Vx-connected traction transformer to a flexible single-phase connection, based on single-phase transformer A, single-phase transformer B, and a same-phase power supply device, characterized in that, The a1x1 winding and the a2x2 winding on the primary side of the transformer are connected in parallel to form parallel winding 1; The b1y1 winding and b2y2 winding on the secondary side of the transformer are connected in parallel to form parallel winding 2; The parallel winding 2 is connected in parallel with the same-phase power supply device to form a parallel same-phase winding; The parallel winding 1 is connected in series with the parallel in-phase winding, the series connection point is grounded, and the non-series connection points are connected to the contact network and the positive feeder respectively to form a 2×27.5kV power supply structure. The in-phase power supply device includes a step-down transformer, an AC-DC-AC converter and a matching transformer connected in sequence, which are used to shift the phase of the input voltage of the parallel winding 2 by 120° and output a voltage with a phase difference of 180° from that of the parallel winding 1.

2. The structure according to claim 1, characterized in that, The step-down transformer has a parallel winding 2 connected to the input side and an AC-DC-AC converter connected to the output side. An AC-DC-AC converter, comprising a rectifier, a DC bus, and an inverter, is used to achieve a 120° basic phase offset. The matching transformer is connected to the inverter output on the input side, and the output side generates the z1c1 winding.

3. The structure according to claim 2, characterized in that, The AC-DC-AC converter adopts a three-level NPC topology and achieves dynamic phase adjustment through SPWM modulation, with an adjustment range of ±5°.

4. The structure according to claim 2, characterized in that, The AC-DC-AC converter is equipped with a harmonic suppression module, and the total harmonic distortion rate of the output is less than 3%.

5. The structure according to claim 1, characterized in that, The phase of the parallel winding 1 is consistent with the AB phase of the primary side of the transformer A, and the phase of the parallel winding is 180° different from the CB phase of the primary side of the transformer B after being phase-shifted by the power supply device.

6. The structure according to claim 1, characterized in that: The primary sides of transformer A and transformer B are respectively connected to phases AB and CB of a three-phase power grid; The secondary side forms a 2×27.5kV output through parallel-series reconfiguration and in-phase power supply devices, and the neutral point is grounded through a nonlinear resistor.

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