A twenty-four pulse dry-type rectifier transformer

Abstract

The present application provides a kind of twenty-four pulse dry-type rectifier transformer, including two twelve pulse rectifier transformers.Single twelve pulse rectifier transformer is arranged from core to outside in turn winding unit, including valve side phase shift winding unit, valve side main winding unit, net side input winding unit.Net side input winding unit is star connection, and valve side phase shift winding unit and valve side main winding unit are extended side delta connection, wherein, one twelve pulse rectifier transformer is phase shifted-7.5° and-22.5°, and the other twelve pulse rectifier transformer is phase shifted+7.5 and +22.5°, and the phase shift angle is different by 15°.It can solve the technical problems of large parallel circulating current and large harmonic current to power grid caused by voltage difference of transformer ratio due to turn number rounding of traditional rectifier transformer star and delta winding.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and specifically to a 24-pulse dry-type rectifier transformer. Background Technology

[0002] A rectifier transformer converts AC grid voltage into the voltage required by the rectifier device, and meets the operational requirements of both the grid side and the valve side by changing the number of phases and phase angles. It is widely used in metallurgy, chemical industry, industrial drives, and transportation—fields requiring DC power. With the rapid development of industry and transportation, the demand for rectifier equipment is increasing daily. At the same time, the large number of harmonics generated by the rectifier system seriously pollutes the power grid. To effectively mitigate the pollution of the power grid by harmonics generated by the rectifier system, it is necessary to take measures to limit the frequency of harmonic currents injected into the grid by the rectifier system. One effective measure to limit the frequency of harmonic currents injected into the grid by the rectifier system is to increase the pulse number of the rectifier system.

[0003] Although traditional 24-pulse dry-type rectifier transformers increase the pulse number, they still have the following problems:

[0004] (1) Since one set of the two low-pressure valve-side coils is delta-connected and the other is star-connected, the turns ratio of the two sets of coils must be 1 when selecting the number of turns of the valve-side coils: In reality, rounding the number of turns to an integer will cause the turns ratio of the two sets of coils to deviate. The circulating current caused by the voltage difference in the transformer ratio will lead to current imbalance (or inequality) between parallel rectifiers. On the one hand, the current imbalance will reduce the working capacity of the parallel rectifier; on the other hand, the fifth and seventh harmonic currents on the grid side cannot completely cancel each other out, and will still transmit the uncancelled fifth and seventh harmonic currents to the grid.

[0005] Furthermore, in the design and manufacturing of parallel rectifier units, it is essential to reduce and control the circulating current due to the voltage difference between the turns ratio. Therefore, GB / T10411-2005 "DC Traction Power Supply System for Urban Rail Transit" stipulates that the voltage difference between the two y,d connected split coils on the valve side and the rated voltage should be <±0.2%. To meet the standard requirements for valve-side voltage and minimize the circulating current between the two sets of valve-side coils, the turns matching of the valve-side coils must follow certain rules. This results in extremely limited options for matching the turns of the two sets of low-voltage valve-side coils in the rectifier transformer, leading to high production costs.

[0006] (2) When the grid-side winding needs to be equipped with ±2×2.5% tap adjustment, in order to ensure the accuracy of the phase shift angle of each tap, ±2×2.5% tap adjustment must be performed simultaneously on the grid-side main winding section and the extension section winding, resulting in a complex product structure and uncontrollable internal electric field strength, partial discharge, etc.

[0007] (3) There is a gap between the main winding section and the extension section winding on the grid side. The gap will generate transverse leakage magnetic field, which increases the amount of engineering calculation and difficulty, and is prone to overheating, posing certain hidden dangers.

[0008] (4) Rectification often uses power electronic devices, with converters accounting for the largest proportion. During the conversion process, a large number of harmonics are generated. However, the large number of nonlinear electrical devices also makes the working environment of the power grid more severe. The converter on the transformer valve side forms a harmonic source for the transformer, while the filter is connected to the AC system bus on the grid side. Harmonic power and reactive power must pass through the primary and secondary windings of the transformer, which not only occupies the winding capacity of the transformer, but also increases the additional copper and iron losses of the windings, increases electromagnetic interference and insulation difficulties, and leads to mechanical vibration and noise. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the prior art by providing a 24-pulse dry-type rectifier transformer, which solves the problems of large parallel circulating current and large harmonic current transmitted to the power grid in traditional 24-pulse dry-type rectifier transformers.

[0010] This invention provides a 24-pulse dry-type rectifier transformer, comprising two 12-pulse rectifier transformers.

[0011] A single twelve-pulse rectifier transformer includes a core and winding units. The winding units include a grid-side input winding unit and a valve-side output winding unit. The valve-side output winding unit includes a valve-side phase-shifting winding unit and a valve-side main winding unit. The core and winding units are arranged concentrically, with the valve-side phase-shifting winding unit, valve-side main winding unit, and grid-side input winding unit arranged sequentially from the core outwards. The grid-side input winding unit includes two axially split sets of grid-side input windings, the valve-side phase-shifting winding unit includes two axially split sets of valve-side phase-shifting windings, and the valve-side main winding unit includes two axially split sets of... The valve-side main winding and grid-side input winding units are radially corresponding three-phase grid-side input windings connected in a star configuration. The two sets of radially corresponding grid-side input windings form two parallel input branches. The valve-side output winding units are radially corresponding three-phase valve-side phase-shifting windings and valve-side main windings connected in a delta configuration. The two sets of radially corresponding valve-side phase-shifting windings and valve-side main windings form two independent outputs. One twelve-pulse rectifier transformer shifts phases by -7.5° and -22.5°, and the other twelve-pulse rectifier transformer shifts phases by +7.5° and +22.5°, with a phase shift angle difference of 15°.

[0012] Preferably, the reactance heights of the grid-side input winding unit and the valve-side output winding unit correspond.

[0013] Preferably, the lamination method of the iron core adopts a 45° angled full-oblique five to nine-level step lamination, the iron core adopts a non-perforated screw iron core, and is fixed by a pull plate and binding structure.

[0014] Preferably, a valve-side winding air passage is provided between the radially corresponding valve-side phase-shifting winding and the valve-side main winding.

[0015] Preferably, insulating pads are provided between the two sets of axially split grid-side input windings, between the two sets of axially split valve-side phase-shifting windings, and between the two sets of axially split valve-side main windings.

[0016] The 24-pulse dry-type rectifier transformer of this invention has a lower output voltage deviation than that of conventional 24-pulse dry-type rectifier transformers. This solves the problems of large parallel circulating currents and the transmission of large harmonic currents to the grid caused by the rounding of turns ratio in conventional dry-type rectifier transformers. Furthermore, on the grid side, the 5th, 7th, 11th, and 13th harmonic currents of the parallel 24-pulse rectifier system composed of two rectifier transformers of this invention are theoretically completely canceled out. In addition, this rectifier transformer is simple to manufacture, has good heat dissipation, and is highly economical. Attached Figure Description

[0017] Figure 1(a) is a schematic diagram of the traditional 24-pulse dry-type rectifier transformer structure;

[0018] Figure 1(b) is a schematic diagram of the twenty-four-pulse dry rectifier transformer structure of Embodiment 1 of the present invention;

[0019] Figure 2 This is a front view of the 24-pulse dry-type rectifier transformer structure according to Embodiment 1 of the present invention;

[0020] Figure 3 This is a side view of the 24-pulse dry-type rectifier transformer structure according to Embodiment 1 of the present invention;

[0021] Figure 4 This is a top view of the 24-pulse dry rectifier transformer structure of Embodiment 1 of the present invention;

[0022] Figure 5 This is a wiring diagram of one transformer winding of the 24-pulse dry-type rectifier transformer according to Embodiment 1 of the present invention.

[0023] Figure 6 This is a wiring diagram of another transformer winding of the 24-pulse dry rectifier transformer in Embodiment 1 of the present invention.

[0024] In the diagram: 1-Iron core; 2-Grid-side input winding; 3-Valve-side phase-shifting winding; 4-Valve-side main winding; 5-Valve-side winding air passage; 6-Valve-side winding lead wire; 7-Inter-winding insulation pad. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example 1:

[0027] As shown in Figure 1(a), a traditional 24-pulse dry-type rectifier transformer consists of two 12-pulse rectifier transformers with phase-shifted grid-side input windings, and there is a gap between the grid-side main winding and the grid-side phase-shifted winding. One set of valve-side windings is delta-connected, and the other set is star-connected. Since the above-mentioned traditional 24-pulse dry-type rectifier transformer structure still has many problems, this embodiment provides a novel 24-pulse dry-type rectifier transformer.

[0028] As shown in Figure 1(b), Figures 2-6 As shown, the 24-pulse dry-type rectifier transformer in this embodiment includes two 12-pulse rectifier transformers connected in parallel.

[0029] A single twelve-pulse rectifier transformer includes a core 1 and winding units. The winding units include a grid-side input winding unit and a valve-side output winding unit. The valve-side output winding unit includes a valve-side phase-shifting winding unit and a valve-side main winding unit. (See Figure 1(b)). Figure 4 In one phase of the transformer shown, the core 1 and winding units are arranged concentrically, and the valve-side phase-shifting winding unit, valve-side main winding unit, and grid-side input winding unit are arranged sequentially from the core 1 outwards. (See Figure 1(b)). Figure 3 As shown, the grid-side input winding unit includes two sets of axially split grid-side input windings 2, the valve-side phase-shifting winding unit includes two sets of axially split valve-side phase-shifting windings 3, and the valve-side main winding unit includes two sets of axially split valve-side main windings 4.

[0030] like Figure 2 , Figure 5 , Figure 6 As shown, the grid-side input winding unit is a radially corresponding three-phase grid-side input winding 2 connected in a star configuration. The two radially corresponding grid-side input windings 2 form two parallel input branches. The valve-side output winding unit is a radially corresponding three-phase valve-side phase-shifting winding 3 and valve-side main winding 4 connected in a delta configuration. The two radially corresponding valve-side phase-shifting windings 3 and valve-side main winding 4 form two independent outputs. One twelve-pulse rectifier transformer is phase-shifted at -7.5° and -22.5°, and the other twelve-pulse rectifier transformer is phase-shifted at +7.5° and +22.5°, with a phase shift angle difference of 15°.

[0031] In this embodiment, since the valve-side output winding unit is connected in a delta configuration, the excitation current and the high-order harmonic current, mainly the 3n harmonic, during rectification are connected in a delta configuration within the triangle. This allows a circulating current to form within the valve-side main winding 4, preventing it from being injected into the common high-voltage grid. If the transformer grid contains 3n harmonics, these harmonics will still form a circulating current within the triangle, making the magnetic flux sinusoidal. The valve-side electromotive force and current are both sinusoidal, and the 3n harmonic current will not appear in the load. This achieves the flow of the 3n harmonic, which helps suppress high-order harmonic currents, reduce transformer power loss, and ensure the quality of the power supply waveform. Here, n represents the harmonic order. In this embodiment, the valve-side output winding units of a single twelve-pulse rectifier transformer are all dual-output and electrically unconnected; one of them is connected to a group labeled as follows: The other connection group number is: In this embodiment, the grid-side input winding units of both twelve-pulse rectifier transformers are star-connected; the valve-side output winding units are delta-connected. One valve-side output winding unit has phase shifts of -7.5° and -22.5° respectively, while the other has phase shifts of +7.5° and +22.5° respectively, with their effective line voltage values ​​being equal. The phase difference between the line voltages at the corresponding terminals of the valve-side output winding units is 2π / 24 (electrical angle of 15°). This embodiment can form a twelve-phase rectifier system with twenty-four pulses per cycle, achieving input multiplexing compared to the existing six-pulse three-phase rectifier system. Because the 24-pulse dry-type rectifier transformer in this embodiment uses phase shifting through the valve-side output winding unit, and the valve-side output winding unit adopts an extended delta connection, a lower output voltage deviation than traditional transformer structures can be obtained simply by selecting a reasonable number of turns for the valve-side phase-shifting winding and the valve-side main winding. This solves the technical problem of large parallel circulating current and large harmonic current transmission to the power grid caused by the rounding of the number of turns in the star and delta windings of traditional rectifier transformers. In addition, since the valve-side output winding units of one transformer are phase-shifted by -7.5° and -22.5° respectively, and the valve-side output winding units of the other transformer are phase-shifted by +7.5° and +22.5° respectively, the waveforms of the valve-side line currents of the two 12-pulse rectifier transformers in this embodiment, after Fourier decomposition, show that the 5th, 7th, 11th, and 13th harmonics of the two sets of valve-side output winding units are out of phase, and their magnetomotive forces can cancel each other out.

[0032] Optionally, the reactance heights of the grid-side input winding unit and the valve-side output winding unit correspond.

[0033] In this embodiment, as shown in Figure 1(b), the reactance heights of the grid-side input winding, the valve-side phase-shifting winding, and the valve-side main winding correspond. The grid-side input winding is wound with wire, while the valve-side phase-shifting winding and the valve-side main winding are wound with copper foil. Preferably, the reactance heights of the three are equal. Corresponding reactance heights help to balance local ampere-turns, effectively reducing impedance mismatch caused by differences in leakage reactance due to different winding structures, i.e., differences in winding position.

[0034] Optionally, the lamination method of the iron core adopts a 45° angle full-skew five to nine-stage step lamination, the iron core adopts a non-perforated screw iron core, and is fixed by a pull plate and binding structure to effectively reduce no-load current, excitation current, hysteresis loss and noise.

[0035] Optionally, a valve-side winding air passage 5 is provided between the radially corresponding valve-side phase-shifting winding 3 and the valve-side main winding 4 to facilitate heat dissipation of the winding unit.

[0036] Optionally, such as Figure 2 and Figure 3 As shown, insulating pads 7 are provided between the two axially split grid-side input windings 2, between the two axially split valve-side phase-shifting windings 3, and between the two axially split valve-side main windings 4. The insulating pads 7 provide reactive isolation and winding support. Furthermore, as... Figure 3 As shown, the two sets of valve-side winding leads 6 are led out from the top and bottom of the transformer winding unit, respectively, resulting in a compact structure.

[0037] The performance of a traditional 24-pulse dry-type rectifier transformer and the 24-pulse dry-type rectifier transformer of this embodiment will be compared below:

[0038] For traditional 24-pulse dry-type rectifier transformers to ensure that the voltage difference between the two y- and d-connected split coils on the valve side of the rectifier transformer and the rated voltage is ≤ ±0.2%, the number of turns can only be selected according to Table 1.

[0039] Table 1

[0040]

[0041] The unbalance rate of the no-load voltage difference between groups y and d on the valve side of the same transformer is ≤ ±0.2%. This is because the number of transformer turns must be an integer, and the phase voltage of the Δ-connected winding on the valve side is a fraction of the phase voltage of the y-connected winding. The turns potential E of the two windings is times that of the two windings. t Similarly, for example: selecting the optimal number of turns for the y-connection winding as 26 turns and the Δ-connection winding as 45 turns from Table 1, the following can be calculated:

[0042]

[0043] The 24-pulse dry-type rectifier transformer of this embodiment achieves a considerably low output voltage deviation by reasonably selecting the number of turns in the valve-side output winding unit, and the reasonable range for selecting the number of turns is large, as shown in Table 2 for some examples of turn selection. For example, selecting 39 turns and 13 turns for the valve-side phase-shifting winding and 23 turns and 68 turns for the valve-side main winding from Table 2, the no-load voltage difference can reach 0.015%, which is far lower than the output voltage deviation of existing traditional structures, and its phase shift angle is more accurate. Measurements show that when the 24-pulse 12-phase dry-type rectifier transformer of this embodiment is used, the current harmonic content caused to the power grid is reduced by more than 50% compared with the traditional 12-phase rectification. Therefore, the rectifier transformer of this embodiment can further reduce the characteristic and non-characteristic harmonic content, while significantly reducing the cost of filtering engineering. Moreover, any single transformer-rectifier can operate independently in 12-phase rectification mode, and the current harmonic content is also lower than that of the prior art.

[0044] Table 2

[0045]

[0046]

[0047] Traditional 24-pulse dry-type rectifier transformers use winding Y-connection and D-connection, but it is not easy to achieve complete load balance because the turns ratio of the two valve-side windings cannot be perfectly satisfied. Therefore, the magnetomotive forces in the two valve-side windings generated by non-characteristic harmonics will not completely cancel each other out, and the difference is compensated by the magnetomotive force of the grid-side winding. In this embodiment, the line voltages of the two valve-side windings of the 24-pulse dry-type rectifier transformer are phase-shifted through the extension winding, solving the problem that the turns ratio of traditional transformers cannot be completely satisfied. The problem is that its harmonic shielding function can further reduce the amplitude of the 5th, 7th, 11th, 13th, 23rd, and 25th harmonics. The distortion rate of its primary current waveform in steady state is already very low, and the flow path of harmonics has been effectively suppressed on the transformer valve side. The current waveform on its AC grid side is very close to a sine wave, and the harmonic elimination effect is more significant, thus greatly reducing the cost of filtering projects.

[0048] This embodiment of the 24-pulse dry-type rectifier transformer consists of two 12-pulse rectifier transformers with phase shifts in their valve-side output winding units. One 12-pulse rectifier transformer shifts phases by -7.5° and -22.5°, while the other shifts phases by +7.5° and +22.5°, with a phase shift angle difference of 15°. By rationally selecting the number of turns in the valve-side phase-shifting winding and the valve-side main winding, its output voltage deviation is lower than that of a traditional 24-pulse rectifier transformer. This solves the problem of large parallel circulating currents and the transmission of large harmonic currents to the grid caused by the rounding of the number of turns in the star and delta windings of traditional rectifier transformers. Furthermore, on the grid side, the 5th, 7th, 11th, and 13th harmonic currents of the parallel 24-pulse rectifier system composed of the two rectifier transformers are theoretically completely canceled out. Further, since the primary winding on the grid side is star-connected, its phase voltage is only a fraction of the line voltage. Its structure can be manufactured according to phase voltage, meaning it is easy to process and manufacture, has a low partial discharge initiation voltage, and the partial discharge quantity is easy to control. Because the valve side secondary side is a delta-connected winding, the main winding section and the delta-connected winding section can be continuously wound, eliminating lateral magnetic leakage, reducing engineering calculations, and minimizing the risk of localized overheating. The 24-pulse rectifier unit in this embodiment has a low ripple coefficient in its output DC voltage, significantly reducing filtering costs, the footprint of the rectifier transformer, and the overall project cost, resulting in significant economic benefits. Simultaneously, the amount of civil engineering work will be greatly reduced, accelerating the construction period and lowering costs. This rectifier transformer can significantly reduce non-characteristic harmonic content, improving the power supply quality of the power grid system. The application of this embodiment will not only improve system efficiency and reliability but also bring substantial economic benefits.

[0049] Furthermore, the transformer in this embodiment is an environmentally friendly and energy-saving product. By adopting an epoxy resin vacuum casting structure, it has the characteristics of strong thermal shock resistance, large overload capacity, flame retardancy, strong emergency overload capacity, convenient repair and maintenance, insensitivity to humidity and dust, no cracking, and safe and reliable performance. It is particularly suitable for harsh environments with large load fluctuation range and dirty and humid conditions.

[0050] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A 24-pulse dry-type rectifier transformer, comprising two 12-pulse rectifier transformers, characterized in that, A single twelve-pulse rectifier transformer includes an iron core (1) and winding units. The winding units include grid-side input winding units and valve-side output winding units. The valve-side output winding units include valve-side phase-shifting winding units and valve-side main winding units. The iron core (1) and the winding units are arranged concentrically, and the valve-side phase-shifting winding unit, the valve-side main winding unit, and the grid-side input winding unit are arranged sequentially from the iron core (1) outwards. The grid-side input winding unit includes two sets of axially split grid-side input windings (2). The valve-side phase-shifting winding unit includes two sets of axially split valve-side phase-shifting windings (3). The valve-side main winding unit includes two sets of axially split valve-side main windings (4). The grid-side input winding unit is a radially corresponding three-phase grid-side input winding (2) star-connected. The two radially corresponding grid-side input windings (2) constitute two branches connected in parallel. The valve-side output winding unit consists of three radially corresponding valve-side phase-shifting windings (3) and valve-side main windings (4) connected in a delta configuration. The two radially corresponding valve-side phase-shifting windings (3) and valve-side main windings (4) form two independent outputs. One twelve-pulse rectifier transformer shifts phases by -7.5° and -22.5°, and the other twelve-pulse rectifier transformer shifts phases by +7.5° and +22.5°, with a phase shift angle difference of 15°.

2. The rectifier transformer according to claim 1, characterized in that, The reactance of the grid-side input winding unit corresponds to that of the valve-side output winding unit.

3. The rectifier transformer according to claim 2, characterized in that, The lamination method of the iron core adopts a 45° angle full oblique five to nine-level step lamination, the iron core adopts a non-perforated screw iron core, and is fixed by a tie plate and binding structure.

4. The rectifier transformer according to claim 3, characterized in that, A valve-side winding air passage (5) is provided between the radially corresponding valve-side phase-shifting winding (3) and the valve-side main winding (4).

5. The rectifier transformer according to claim 4, characterized in that, Insulating pads (7) are provided between the two sets of axially split grid-side input windings (2), between the two sets of axially split valve-side phase-shifting windings (3), and between the two sets of axially split valve-side main windings (4).

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