An impedance balanced multi-winding transformer power supply system

Abstract

The present invention belongs to the technical field of power equipment, and discloses an impedance-balanced multi-winding transformer power supply system, which is applied to urban rail transit subways, and includes two multi-winding transformers with the same structure, which are connected in parallel, and their high-voltage ends are connected to an external power grid, wherein the low-voltage end of one multi-winding transformer is connected to a low-voltage power grid that supplies power to the subway through a rectifier module, and its energy-feeding winding is vacant or replaced by an insulating support, and the low-voltage end of the other multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway by tapping the rectifier module and the energy-feeding module. The overall structure of the present invention is simple, easy to implement, and low-cost.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment, and in particular to an impedance-balanced multi-winding transformer power supply system. Background Art

[0002] In the field of subway traction power supply, two 12-phase rectifier transformers with a phase shift of 30° are generally used to step down the power supply to the traction rectifier. After rectification, an equivalent 24-pulse DC power supply system is formed. The primary and secondary winding capacities and structural types of these two transformers are consistent. The difference is that the primary winding phase shift angles are +7.5° and -7.5° respectively, and the number of turns of the phase-shift windings of the two rectifier transformers is also the same. Since the impedance voltage of the transformer is determined by the number of winding turns and the structural size, the impedance voltage of these two rectifier transformers can be kept consistent.

[0003] In order to meet the needs of train braking energy recovery, the new multi-winding transformer needs to add an energy feedback winding on the basis of the original 12-phase rectifier transformer of the same capacity. After adding an energy feedback winding, the overall structure of the transformer is changed. The impedance of the rectifier winding of the multi-winding transformer is difficult to keep the same as the impedance of the original 12-phase rectifier transformer. In some occasions, the multi-winding transformer and the 12-phase rectifier transformer need to be connected to the rectifier and powered in parallel after rectification, which will lead to an unbalanced output power of the two power supply groups after rectification. Summary of the invention

[0004] The present invention provides an impedance-balanced multi-winding transformer power supply system, which solves the problem of unbalanced output power caused by different structures of two transformers in the existing power supply system.

[0005] The present invention can be achieved through the following technical solutions:

[0006] An impedance-balanced multi-winding transformer power supply system is applied to urban rail transit subways, comprising two multi-winding transformers with the same structure, which are connected in parallel, and their high-voltage ends are connected to an external power grid. The low-voltage end of one of the multi-winding transformers is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and its energy feed winding is vacant or replaced by an insulating support. The low-voltage end of the other multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway through a rectifier module and an energy feed module respectively.

[0007] Further, the two combined transformers are respectively denoted as T1 and T2, wherein the multi-winding transformer T1 includes a high-voltage side winding, two low-voltage side windings and an idle energy feedback winding, or a high-voltage side winding, two low-voltage side windings and an insulating support; the multi-winding transformer T2 includes a high-voltage side winding, two low-voltage side windings and an energy feedback winding.

[0008] Furthermore, the energy-feed winding adopts a delta connection or a star connection structure.

[0009] The beneficial technical effects of the present invention are:

[0010] By designing the 12-phase rectifier transformer to be exactly the same as the multi-winding transformer or using an insulating support to replace the energy-feeding winding that is missing in the 12-phase rectifier transformer compared to the multi-winding transformer, the overall structure of the two transformers can be ensured to be the same, thereby ensuring the impedance balance between the two transformers, and solving the problem of rectifier winding impedance imbalance caused by adding the energy-feeding winding. The present invention can be extended to a transformer power supply system with multiple windings of different numbers and balanced main winding impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of a 24-pulse rectifier power supply system in the prior art;

[0012] Figure 2 A schematic diagram of a power supply system in which a 12-phase rectifier transformer and a multi-winding transformer are connected in parallel in the prior art;

[0013] Figure 3 Schematic diagram of the transformer winding structure cross section for calculating the impedance associated with the split transformer;

[0014] Figure 4 for Figure 2 Schematic diagram of the cross-section of the winding structure of transformer T1;

[0015] Figure 5 for Figure 2 Schematic diagram of the cross-section structure of the transformer T2 winding;

[0016] Figure 6 This is a schematic diagram of a power supply system according to solution 1 of the present invention;

[0017] Figure 7 It is a schematic cross-sectional diagram of the winding structure of transformer T1 in scheme 2 of the present invention. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0019] In the field of subway traction power supply, generally Figure 1 As shown in the figure, two 12-phase wave rectifier transformers T1 and T2 are used to step down the power supply to the traction rectifier to form an equivalent 24-pulse DC power supply system. The transformer in the subway traction power supply system often adopts a split transformer structure, in which X1 is the high-voltage side winding, and X2 and X3 are the low-voltage side windings. In order to meet the needs of train braking energy recovery, such as Figure 2 As shown, the new multi-winding transformer T2 needs to add an energy-feeding winding on the basis of the original 12-phase rectifier transformer of the same capacity, that is, Figure 2The X4 winding in the circuit can be connected in delta or in star.

[0020] In the impedance of the transformer, the reactance component accounts for a large proportion. As the transformer capacity increases, this proportion will also increase. In large transformers, the reactance value can be used to replace the impedance value. Figure 3 Take the reactance calculation formula of split transformer as an example.

[0021] like Figure 3 As shown, X1 and X2 are high-voltage side windings, X3 and X4 are low-voltage side windings, and B q1 , B q2 , B q3 , B q4 is the radial dimension of each coil, A 13 , A 24 H is the main air path size between each pair of coils, k is the average reactance height, λ is the leakage width, R p1 , R p2 , R p3 , R p4 is the average radius of each coil, R p13 , R p24 is the average radius of each main air channel, D0 is the diameter of the core circle, and s' is the distance from the core to the low-voltage winding.

[0022] Then the reactance height expression is:

[0023]

[0024]

[0025] The expression of leakage width is:

[0026] λ=λ 13 =λ 24 =B q1 +A 13 +B q3 (3)

[0027] λ s12 =B q1 =B q2 (4)

[0028] λ s34 =B q3 =B q4 (5)

[0029] The Rockwell coefficient expression is:

[0030]

[0031]

[0032]

[0033]

[0034] In formulas (6) to (9), u s12 =λ s12 / H k12 ,u s34 =λ s34 / H k34 , v 12 =(s'+D0+B q3 +A 13 ) / H k12 , v 34 =(s'+D0) / H k34 ,u 13 =u 24 =H k13 / λ 13 =H k24 / λ 24 , u=H k / λ.

[0035] Then the transformer leakage magnetic equivalent total area ∑D R The expression is:

[0036]

[0037] When the number of turns of the line segments and the oil channels between segments are evenly distributed:

[0038]

[0039]

[0040] Among them, B t1 , B t2 , B t3 , B t4 is the height of high pressure 1, 2 and low pressure 3, 4 line segments, n g1 、n g2 、n g3 、n g4 is the number of high voltage 1, 2 and low voltage 3, 4 line segments, h dy1 、h dy2 、h dy3 、h dy4 It is the oil channel between the high pressure 1, 2 and low pressure 3, 4 segments.

[0041] Then the reactance expression of each pair of windings is:

[0042]

[0043]

[0044]

[0045] Where f is the rated frequency, I1W1 and I2W2 are the tapped ampere-turns per phase, and K x is the reactance correction factor, e t is the potential per turn.

[0046] When two low-voltage windings are connected in parallel, the short-circuit reactance between the high-voltage and low-voltage windings is the through reactance X. k %, and its expression is:

[0047]

[0048] When one of the two low-voltage windings is open-circuited, the short-circuit reactance of the other low-voltage winding to the high-voltage winding is the semi-through reactance X B %, and its expression is:

[0049]

[0050] Combining equations (1) to (17), it can be seen that when the current, number of winding turns, and coil parameters are the same, the short-circuit reactance X between the high-voltage and low-voltage windings of the transformer is k %, X B % is only related to the winding structure size.

[0051] For Figure 2 In the power supply system with energy recovery function shown in FIG. 1 , transformer T1 is a 12-phase rectifier transformer, and its winding structure is as follows: Figure 4 Compared to the example of calculating transformer-related reactance Figure 3 , Figure 4 The difference is that the lead wire indicating the winding connection method is added. Figure 4 Medium X 1_1 and X 1_2 Parallel connection Figure 2 The high-voltage side windings X1, X2 and X3 of the transformer T1 are two low-voltage side windings. From the perspective of transformer structure, Figure 4 X in 1_1 correspond Figure 3 X1 in Figure 4 X in 1_2 correspond Figure 3 X2 in Figure 4 X2 in corresponds to Figure 3 X3 in Figure 4 X3 in Figure 3 X4 in the figure. Transformer T2 is a multi-winding transformer with a power-feed winding, and its winding structure is as follows: Figure 5 As shown. Figure 4 and Figure 5It can be seen that since the transformer T2 adds the energy-feed winding X4 (the X4 winding can be delta-connected or star-connected), the distance between the windings X2 and X3 of the transformer T2 and the iron core has changed compared to the transformer T1. Due to the difference in winding structure, the impedance of the transformers T1 and T2 is difficult to balance. In practical applications, the impedance imbalance is ≥10%, which will lead to unbalanced output power of the two groups of power supplies after rectification.

[0052] To solve this problem, the present invention proposes an impedance-balanced multi-winding transformer power supply system, which includes two multi-winding transformers with the same structure, which are connected in parallel, and their high-voltage ends are connected to the external power grid. The low-voltage end of one multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and its energy-feeding winding is vacant or replaced by an insulating support. The low-voltage end of the other multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway through a rectifier module and an energy-feeding module. This can be achieved through the following technical solutions:

[0053] Option 1: Figure 2 The transformer T1 in the figure is designed as a multi-winding transformer like the transformer T2, such as Figure 6 As shown, during operation, the energy-feed winding X4 (the X4 winding can be delta-connected or star-connected) of the transformer T1 is idle. Figure 6 The transformers T1 and T2 are exactly the same, and the impedance of the main winding of the transformer is determined by the number of turns and the structural size, so the impedance of the main windings of the two transformers can be kept consistent. This solution is simple and easy to implement, but the disadvantage is that the energy-feeding winding is left idle and wasteful.

[0054] Option 2: Figure 2 The transformer T1 in the figure is designed to use an insulating support to replace the energy feeding winding, and its winding structure is as follows: Figure 7 As shown, the original energy-feeding winding is replaced by an insulating support, such as Figure 7 In the shaded area, transformer T2 still uses Figure 5 The winding structure is shown.

[0055] Since the transformer is a concentric structure with the core in the middle and the other windings wound around the core from the inside to the outside, it can be seen from the previous transformer impedance calculation that when the current flowing, the number of winding turns, and the coil parameters are the same, the short-circuit reactance between the high and low voltage windings of the transformer is only related to the size of the winding structure. Figure 7 The limiting requirements for the insulating support in the Figure 7 The distance from the middle core to the X2 and X3 windings is Figure 5 The distance from the middle core to the X2 and X3 windings is the same, that is, Figure 7 d in core23 and Figure 5 d in core23 same.

[0056] Since the X1~X3 windings of transformers T1 and T2 have the same structure and size, as long as Figure 7 d in core23 and Figure 5 d in core23 The same can ensure that Figure 7 The transformer T1 shown in the structure is Figure 5 The transformer T2 of the structure shown has the same winding structure and size. When it is necessary to connect the multi-winding transformer T2 and the 12-phase rectifier transformer T1 to parallel power supply after rectification in some occasions, the two transformers connected to the system have the same number of turns and structure, which ensures the impedance balance between the two transformers and solves the problem of rectifier winding impedance imbalance caused by adding energy-feeding windings.

[0057] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. An impedance balanced multi-winding transformer power supply system, characterized in that: Applied to urban rail transit subways, including two multi-winding transformers with the same structure, which are connected in parallel, and the high-voltage end of which is connected to the external power grid, the low-voltage end of one of the multi-winding transformers is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and its energy-feed winding is idle, and the low-voltage end of the other multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and the energy-feed winding is connected to the low-voltage power grid that supplies power to the subway through an energy-feed module; Or it is applied to urban rail transit subways, including two multi-winding transformers, which are connected in parallel, and their high-voltage ends are connected to an external power grid. The low-voltage end of one of the multi-winding transformers is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and its energy feedback winding is replaced by an insulating support. At this time, the distance from the winding at the low-voltage end to the iron core is the same as the distance from the winding at the low-voltage end of the other multi-winding transformer to the corresponding iron core. The low-voltage end of the other multi-winding transformer is connected to the low-voltage power grid that supplies power to the subway through a rectifier module, and the energy feedback winding is connected to the low-voltage power grid that supplies power to the subway through the energy feedback module.

2. The impedance balanced multi-winding transformer power supply system according to claim 1, characterized in that: The two multi-winding transformers are respectively denoted as T1 and T2, wherein the multi-winding transformer T1 includes a high-voltage side winding, two low-voltage side windings and an idle energy feedback winding, or a high-voltage side winding, two low-voltage side windings and an insulating support; the multi-winding transformer T2 includes a high-voltage side winding, two low-voltage side windings and an energy feedback winding.

3. The impedance balanced multi-winding transformer power supply system according to claim 2, characterized in that: The energy-feed winding adopts a delta connection or a star connection structure.

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