A polyhedral zigzag coupled phase-shifting transformer

Abstract

The invention provides a multi-edge zigzag connection phase-shifting transformer, which comprises a star connection excitation winding connected at the three-phase power supply side, and two phase-modulation windings provided with excitation from the excitation winding. The turns of the phase-modulation windings are adjusted by linearly modulated voltage regulating switches to change the voltage vector of the phase-modulation windings. The voltage of the power supply after the introduction of the transformer is sequentially connected to the voltage of the other two phase-modulation windings, and a voltage with a changed phase angle and an unchanged amplitude is obtained by the synthesis of the three-phase voltage vectors to supply the load side, so as to realize the function of the voltage phase angle change and the amplitude constancy of the power supply side and the load side. The polarity of the phase-modulation windings is changed by ARS polarity conversion switches, and the turns of the phase-modulation windings are selected by linear voltage regulating switches to control the step-by-step advancement of the load side voltage phase angle leading or lagging the power supply side and the phase-shifting angle.

Description

Technical Field

[0001] This invention belongs to the field of transformer technology, and particularly relates to a phase-shifting transformer with a polygonal tortuous connection. Background Technology

[0002] High-voltage phase-shifting transformers can control the power flow distribution of specific lines in complex transmission networks by changing the phase of the voltage on the power supply side and the load side of the transmission line. Although phase-shifting transformers with a single-body, zigzag connection structure have the advantages of simple structure and high reliability, adjusting the phase angle will cause a change in voltage amplitude, and the phase shift angle will be clamped to a small range. In many applications, it is necessary to ensure a constant voltage amplitude and a large phase shift angle, so this structure is not suitable for such application scenarios. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a phase-shifting transformer with a polygonal tortuous connection.

[0004] This invention discloses a phase-shifting transformer with a polygonal tortuous connection, comprising,

[0005] Excitation winding, phase adjustment unit I and phase adjustment unit II;

[0006] The transformer has an excitation winding, phase adjustment unit I, and phase adjustment unit II installed sequentially on each core column of the three-phase structure.

[0007] The three-phase excitation windings SA phase excitation winding, SB phase excitation winding and SC phase excitation winding are star connected, and three input terminals are led out to connect to the three phases of the power supply side: SA, SB and SC respectively.

[0008] The three phases on the load side, LA, LB, and LC, are led out from the output terminal of the phase adjustment unit II.

[0009] In some embodiments, the phase modulation unit I includes:

[0010] The first phase-adjusting winding, the first ARS switch, and the first linear adjustment switch;

[0011] The first phase-adjusting winding includes: an SA phase first phase-adjusting winding, an SB phase first phase-adjusting winding, and an SC phase first phase-adjusting winding;

[0012] The first ARS switch includes: SA phase first ARS switch, SB phase first ARS switch and SC phase first ARS switch;

[0013] The first linear adjustment switch includes: SA phase first linear adjustment switch, SB phase first linear adjustment switch and SC phase first linear adjustment switch;

[0014] The first terminal of the SA phase first ARS switch is connected to the output terminal of the SA phase excitation winding, the second terminal of the SA phase first ARS switch is connected to the first terminal of the SA phase first phase adjustment winding, the second terminal of the SA phase first phase adjustment winding is connected to the first terminal of the SA phase first linear adjustment switch, and the second terminal of the SA phase first linear adjustment switch is connected to the third terminal of the SA phase first ARS switch.

[0015] The first terminal of the SB phase first ARS switch is connected to the output terminal of the SB phase excitation winding, the second terminal of the SB phase first ARS switch is connected to the first terminal of the SB phase first phase adjustment winding, the second terminal of the SB phase first phase adjustment winding is connected to the first terminal of the SB phase first linear adjustment switch, and the second terminal of the SB phase first linear adjustment switch is connected to the third terminal of the SB phase first ARS switch.

[0016] The first terminal of the SC phase first ARS switch is connected to the output terminal of the SC phase excitation winding, the second terminal of the SC phase first ARS switch is connected to the first terminal of the SC phase first phase adjustment winding, the second terminal of the SC phase first phase adjustment winding is connected to the first terminal of the SC phase first linear adjustment switch, and the second terminal of the SC phase first linear adjustment switch is connected to the third terminal of the SC phase first ARS switch.

[0017] In some embodiments, the phase modulation unit II includes:

[0018] Second phase-adjusting winding, second ARS switch, and second linear adjustment switch;

[0019] The second phase-adjusting winding includes: the SA phase second phase-adjusting winding, the SB phase second phase-adjusting winding, and the SC phase second phase-adjusting winding;

[0020] The second ARS switch includes: an SA phase second ARS switch, an SB phase second ARS switch, and an SC phase second ARS switch;

[0021] The second linear adjustment switch includes: SA phase second linear adjustment switch, SB phase second linear adjustment switch and SC phase second linear adjustment switch;

[0022] The first terminal of the second ARS switch of the SA phase is connected to the fourth terminal of the first ARS switch of the SA phase, the second terminal of the second ARS switch of the SA phase is connected to the first terminal of the second phase-adjusting winding of the SA phase, the second terminal of the second phase-adjusting winding of the SA phase is connected to the first terminal of the second linear adjustment switch of the SA phase, and the second terminal of the second linear adjustment switch of the SA phase is connected to the third terminal of the second ARS switch of the SA phase.

[0023] The first terminal of the SB phase second ARS switch is connected to the fourth terminal of the SB phase first ARS switch, the second terminal of the SB phase second ARS switch is connected to the first terminal of the SB phase second phase adjustment winding, the second terminal of the SB phase second phase adjustment winding is connected to the first terminal of the SB phase second linear adjustment switch, and the second terminal of the SB phase second linear adjustment switch is connected to the third terminal of the SB phase second ARS switch.

[0024] The first terminal of the SC phase second ARS switch is connected to the fourth terminal of the SC phase first ARS switch, the second terminal of the SC phase second ARS switch is connected to the first terminal of the SC phase second phase adjustment winding, the second terminal of the SC phase second phase adjustment winding is connected to the first terminal of the SC phase second linear adjustment switch, and the second terminal of the SC phase second linear adjustment switch is connected to the third terminal of the SV phase second ARS switch.

[0025] In some embodiments, the first phase-adjusting winding is made of multiple levels of wires with different numbers of turns wound together.

[0026] In some embodiments, the second phase-adjusting winding is made of multiple levels of wires with different numbers of turns wound together.

[0027] In some embodiments, the load-side voltage phase angle is controlled to lead or lag the power supply-side voltage through the cooperation of the first ARS switch, the second ARS switch, the first linear adjustment switch, and the second linear adjustment switch.

[0028] In some embodiments, the relationship between the number of turns of the first phase-adjusting winding and the second phase-adjusting winding and the number of turns of the excitation winding is as follows:

[0029]

[0030] or

[0031] Where θ: phase shift angle under no-load conditions for each stage;

[0032] N E : Number of turns in the excitation winding;

[0033] N T The number of turns of the first and second phase-adjusting windings in phase-adjusting unit I or II when the nth tap is connected;

[0034] n: Number of phase-shifting taps.

[0035] In some embodiments, the number of turns of the first phase-adjusting winding and the second phase-adjusting winding can be obtained from equations (1-a) and (1-b) as follows:

[0036]

[0037] or

[0038] In some embodiments, the operating logic of the different tap-down phase winding turns and the ARS polarity selector specifically includes:

[0039] First operation logic: advance phase angle, tap position from n to 1, the polarity of phase adjustment unit I is negative, and it is sequentially inserted using equation (2-b), the polarity of phase adjustment unit II is positive, and it is sequentially inserted using equation (2-a).

[0040] Second operating logic: In the original position, no phase-adjusting winding is inserted;

[0041] The third operation logic is: lag phase shift angle, tap position from -1 to -n, the polarity of phase adjustment unit I is positive, and it is sequentially inserted using equation (2-a), the polarity of phase adjustment unit II is negative, and it is sequentially inserted using equation (2-b).

[0042] In some embodiments, when the number of turns of the voltage regulating winding is small, a cascade winding method is adopted to ensure the axial symmetry of the winding. The winding is divided into two groups by an even number of parallel wires and wound to the upper and lower ends respectively. After each stage of winding is completed, a tap is led out until all the turns are wound.

[0043] As can be seen, the solution proposed in this invention adopts a novel polygonal tortuous phase-shifting transformer structure, which can solve the requirement of maintaining a constant voltage amplitude in the line while shifting phases within a large phase angle range. The phase-shifting transformer with this structure is a single-body structure with fewer windings and simpler wiring, which is much simpler than the traditional double-body phase-shifting transformer that achieves the same function, reducing the design and manufacturing difficulty and improving the reliability of system operation. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the transformer wiring according to an embodiment of the present invention;

[0046] Figure 2 This is a structural layout diagram of a transformer according to an embodiment of the present invention;

[0047] Figure 3 This is a polygonal tortuous voltage vector diagram according to an embodiment of the present invention.

[0048] In the diagram, 1—excitation winding, 2—first phase adjustment winding, 3—first ARS switch, 4—first linear adjustment switch, 5—second phase adjustment winding, 6—second ARS switch, 7—second linear adjustment switch, 8—power supply output terminals SA, SB, SC, 9—load output terminals LA, LB, LC, 10—transformer core, 11—transformer tank, 12—phase adjustment unit I, 13—phase adjustment unit II. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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.

[0050] This invention discloses a multi-winding zig-zag PST, specifically as follows: Figure 1 As shown,

[0051] Excitation winding 1, phase adjustment unit I12 and phase adjustment unit II13;

[0052] The transformer has an excitation winding, a phase adjustment unit I12, and a phase adjustment unit II13 installed sequentially on each core column of the three-phase structure.

[0053] The three-phase excitation windings SA phase excitation winding, SB phase excitation winding and SC phase excitation winding are star connected, and three input terminals are led out to connect to the three phases of the power supply side: SA, SB and SC respectively.

[0054] The three phases on the load side, LA, LB, and LC, are led out from the output terminal of the phase adjustment unit II.

[0055] In some embodiments, the phase modulation unit I12 includes:

[0056] The first phase-adjusting winding 2, the first ARS switch 3, and the first linear adjustment switch 4;

[0057] The first phase-adjusting winding 2 includes: an SA phase first phase-adjusting winding, an SB phase first phase-adjusting winding, and an SC phase first phase-adjusting winding;

[0058] The first ARS switch 3 includes: an SA phase first ARS switch, an SB phase first ARS switch, and an SC phase first ARS switch;

[0059] The first linear adjustment switch 4 includes: an SA phase first linear adjustment switch, an SB phase first linear adjustment switch, and an SC phase first linear adjustment switch;

[0060] The first terminal of the SA phase first ARS switch is connected to the output terminal of the SA phase excitation winding, the second terminal of the SA phase first ARS switch is connected to the first terminal of the SA phase first phase adjustment winding, the second terminal of the SA phase first phase adjustment winding is connected to the first terminal of the SA phase first linear adjustment switch, and the second terminal of the SA phase first linear adjustment switch is connected to the third terminal of the SA phase first ARS switch.

[0061] The first terminal of the SB phase first ARS switch is connected to the output terminal of the SB phase excitation winding, the second terminal of the SB phase first ARS switch is connected to the first terminal of the SB phase first phase adjustment winding, the second terminal of the SB phase first phase adjustment winding is connected to the first terminal of the SB phase first linear adjustment switch, and the second terminal of the SB phase first linear adjustment switch is connected to the third terminal of the SB phase first ARS switch.

[0062] The first terminal of the SC phase first ARS switch is connected to the output terminal of the SC phase excitation winding, the second terminal of the SC phase first ARS switch is connected to the first terminal of the SC phase first phase adjustment winding, the second terminal of the SC phase first phase adjustment winding is connected to the first terminal of the SC phase first linear adjustment switch, and the second terminal of the SC phase first linear adjustment switch is connected to the third terminal of the SC phase first ARS switch.

[0063] In some embodiments, the phase modulation unit II13 includes:

[0064] Second phase adjustment winding 5, second ARS switch 6, and second linear adjustment switch 7;

[0065] The second phase-adjusting winding 5 includes: an SA phase second phase-adjusting winding, an SB phase second phase-adjusting winding, and an SC phase second phase-adjusting winding;

[0066] The second ARS switch 6 includes: an SA phase second ARS switch, an SB phase second ARS switch, and an SC phase second ARS switch;

[0067] The second linear adjustment switch 7 includes: an SA phase second linear adjustment switch, an SB phase second linear adjustment switch, and an SC phase second linear adjustment switch;

[0068] The first terminal of the second ARS switch of the SA phase is connected to the fourth terminal of the first ARS switch of the SA phase, the second terminal of the second ARS switch of the SA phase is connected to the first terminal of the second phase-adjusting winding of the SA phase, the second terminal of the second phase-adjusting winding of the SA phase is connected to the first terminal of the second linear adjustment switch of the SA phase, and the second terminal of the second linear adjustment switch of the SA phase is connected to the third terminal of the second ARS switch of the SA phase.

[0069] The first terminal of the SB phase second ARS switch is connected to the fourth terminal of the SB phase first ARS switch, the second terminal of the SB phase second ARS switch is connected to the first terminal of the SB phase second phase adjustment winding, the second terminal of the SB phase second phase adjustment winding is connected to the first terminal of the SB phase second linear adjustment switch, and the second terminal of the SB phase second linear adjustment switch is connected to the third terminal of the SB phase second ARS switch.

[0070] The first terminal of the SC phase second ARS switch is connected to the fourth terminal of the SC phase first ARS switch, the second terminal of the SC phase second ARS switch is connected to the first terminal of the SC phase second phase adjustment winding, the second terminal of the SC phase second phase adjustment winding is connected to the first terminal of the SC phase second linear adjustment switch, and the second terminal of the SC phase second linear adjustment switch is connected to the third terminal of the SV phase second ARS switch.

[0071] In some embodiments, the first phase-adjusting winding 2 is made of multiple levels of wires with different numbers of turns wound together.

[0072] In some embodiments, the second phase-adjusting winding 5 is made of multiple levels of wires with different numbers of turns wound together.

[0073] In some embodiments, the load-side voltage phase angle is controlled to lead or lag the power supply-side voltage through the cooperation of the first ARS switch 3, the second ARS switch 6, the first linear adjustment switch 4, and the second linear adjustment switch 7.

[0074] In some embodiments, the relationship between the number of turns of the first phase-adjusting winding 2 and the second phase-adjusting winding 5 and the number of turns of the excitation winding is as follows:

[0075]

[0076] or

[0077] Where θ: phase shift angle under no-load conditions for each stage;

[0078] N E : Number of turns in the excitation winding;

[0079] N T: The number of turns of the first phase-adjusting winding 2 and the second phase-adjusting winding 5 in phase-adjusting unit I12 or phase-adjusting unit II13 when the nth tap is connected;

[0080] n: Number of phase-shifting taps.

[0081] In some embodiments, the number of turns of the first phase-adjusting winding 2 and the second phase-adjusting winding 5 can be obtained from equations (1-a) and (1-b) as follows:

[0082]

[0083] or

[0084] In some embodiments, as shown in Table 1, the specific operating logic of the phase winding with different taps and the ARS polarity selector includes:

[0085] First operation logic: advance phase angle, tap position from n to 1, the polarity of phase adjustment unit I12 is negative, and it is sequentially inserted using equation (2-b), the polarity of phase adjustment unit II13 is positive, and it is sequentially inserted using equation (2-a).

[0086] Second operating logic: In the original position, no phase-adjusting winding is inserted;

[0087] The third operation logic is as follows: the phase shift angle is delayed, the tap position is from -1 to -n, the polarity of the phase adjustment unit I12 is positive, and it is sequentially inserted using equation (2-a), the polarity of the phase adjustment unit II13 is negative, and it is sequentially inserted using equation (2-b).

[0088] Table 1

[0089]

[0090] Figure 2 The structural layout diagram (top view) shows that all windings and cores (1, 2, 3, 10) are placed inside the oil tank (11). All switches (3, 4, 6, 7) are placed at the end of the long shaft of the oil tank. The power output terminal (8) and the load output terminal (9) are placed on both sides of the short shaft of the oil tank and led out from the top of the tank cover.

[0091] Figure 3 The voltage vector diagram is a polygonal, zigzag shape.

[0092] In some embodiments, when the number of turns of the voltage regulating winding is small, a cascade winding method is adopted to ensure the axial symmetry of the winding. The winding is divided into two groups by an even number of parallel wires and wound to the upper and lower ends respectively. After each stage of winding is completed, a tap is led out until all the turns are wound.

[0093] In summary, the technical solutions of this invention have the following advantages compared with the prior art:

[0094] This invention provides a phase-shifting transformer with a polygonal tortuous connection. It adopts a novel phase-shifting transformer structure with a polygonal tortuous connection, which can solve the problem of maintaining a constant voltage amplitude in the line while shifting phases over a large phase angle range. The phase-shifting transformer with this structure is a single-body structure with fewer windings and simpler wiring. It is much simpler than the traditional double-body phase-shifting transformer with the same function, which reduces the design and manufacturing difficulty and improves the reliability of system operation.

[0095] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A phase-shifting transformer with a polygonal tortuous connection, characterized in that, The transformer includes: Excitation winding, phase adjustment unit I and phase adjustment unit II; The transformer has the excitation winding, phase adjustment unit I and phase adjustment unit II installed sequentially on each core column of the three-phase structure; The three-phase excitation windings SA phase excitation winding, SB phase excitation winding and SC phase excitation winding are star connected, and three input terminals are led out to connect to the three phases of the power supply side: SA, SB and SC respectively. The three phases on the load side, LA, LB, and LC, are led out from the output terminal of phase modulation unit II; The phase modulation unit I includes: The first phase-adjusting winding, the first ARS switch, and the first linear adjustment switch; The first phase-adjusting winding includes: an SA phase first phase-adjusting winding, an SB phase first phase-adjusting winding, and an SC phase first phase-adjusting winding; The first ARS switch includes: SA phase first ARS switch, SB phase first ARS switch and SC phase first ARS switch; The first linear adjustment switch includes: SA phase first linear adjustment switch, SB phase first linear adjustment switch and SC phase first linear adjustment switch; The first terminal of the SA phase first ARS switch is connected to the input terminal of the SC phase excitation winding, the second terminal of the SA phase first ARS switch is connected to the first terminal of the SA phase first phase adjustment winding, the second terminal of the SA phase first phase adjustment winding is connected to the first terminal of the SA phase first linear adjustment switch, and the second terminal of the SA phase first linear adjustment switch is connected to the third terminal of the SA phase first ARS switch. The first terminal of the SB phase first ARS switch is connected to the input terminal of the SA phase excitation winding, the second terminal of the SB phase first ARS switch is connected to the first terminal of the SB phase first phase adjustment winding, the second terminal of the SB phase first phase adjustment winding is connected to the first terminal of the SB phase first linear adjustment switch, and the second terminal of the SB phase first linear adjustment switch is connected to the third terminal of the SB phase first ARS switch. The first terminal of the SC phase first ARS switch is connected to the input terminal of the SB phase excitation winding, the second terminal of the SC phase first ARS switch is connected to the first terminal of the SC phase first phase adjustment winding, the second terminal of the SC phase first phase adjustment winding is connected to the first terminal of the SC phase first linear adjustment switch, and the second terminal of the SC phase first linear adjustment switch is connected to the third terminal of the SC phase first ARS switch. The phase modulation unit II includes: Second phase-adjusting winding, second ARS switch, and second linear adjustment switch; The second phase-adjusting winding includes: the SA phase second phase-adjusting winding, the SB phase second phase-adjusting winding, and the SC phase second phase-adjusting winding; The second ARS switch includes: an SA phase second ARS switch, an SB phase second ARS switch, and an SC phase second ARS switch; The second linear adjustment switch includes: SA phase second linear adjustment switch, SB phase second linear adjustment switch and SC phase second linear adjustment switch; The first terminal of the SA phase second ARS switch is connected to the fourth terminal of the SC phase first ARS switch, the second terminal of the SA phase second ARS switch is connected to the first terminal of the SA phase second phase-adjusting winding, the second terminal of the SA phase second phase-adjusting winding is connected to the first terminal of the SA phase second linear adjustment switch, and the second terminal of the SA phase second linear adjustment switch is connected to the third terminal of the SA phase second ARS switch. The first terminal of the SB phase second ARS switch is connected to the fourth terminal of the SA phase first ARS switch, the second terminal of the SB phase second ARS switch is connected to the first terminal of the SB phase second phase-adjusting winding, the second terminal of the SB phase second phase-adjusting winding is connected to the first terminal of the SB phase second linear adjustment switch, and the second terminal of the SB phase second linear adjustment switch is connected to the third terminal of the SB phase second ARS switch. The first terminal of the SC phase second ARS switch is connected to the fourth terminal of the SB phase first ARS switch, the second terminal of the SC phase second ARS switch is connected to the first terminal of the SC phase second phase-adjusting winding, the second terminal of the SC phase second phase-adjusting winding is connected to the first terminal of the SC phase second linear adjustment switch, and the second terminal of the SC phase second linear adjustment switch is connected to the third terminal of the SC phase second ARS switch. All windings and cores are placed inside the oil tank, all switches are located at the end of the long shaft of the oil tank, and the power output terminals and load output terminals are located on both sides of the short shaft of the oil tank and lead out from the top of the tank cover.

2. The phase-shifting transformer with a polygonal tortuous connection according to claim 1, characterized in that, The first phase-adjusting winding is made of multiple levels of wires with different numbers of turns wound in parallel.

3. The phase-shifting transformer with a polygonal tortuous connection according to claim 2, characterized in that, The second phase-adjusting winding is made of multiple levels of wires with different numbers of turns wound in parallel.

4. The phase-shifting transformer with a polygonal tortuous connection according to claim 3, characterized in that, By coordinating the first ARS switch, the second ARS switch, the first linear adjustment switch, and the second linear adjustment switch, the phase angle of the load-side voltage is controlled to lead or lag the voltage on the power supply side.

5. The phase-shifting transformer with a polygonal tortuous connection according to claim 4, characterized in that, The relationship between the number of turns of the first phase-adjusting winding and the second phase-adjusting winding and the number of turns of the excitation winding is as follows: ； or ; in Phase shift angle under no-load conditions at each stage; : Number of turns in the excitation winding; The number of turns of the first phase-adjusting winding and the second phase-adjusting winding in phase-adjusting unit I or II when the nth tap is connected; : Number of phase-shifting taps.

6. The phase-shifting transformer with a polygonal tortuous connection according to claim 5, characterized in that, From equations (1-a) and (1-b), the number of turns of the first phase-adjusting winding and the second phase-adjusting winding can be obtained as follows: 。 7. The phase-shifting transformer with a polygonal tortuous connection according to claim 6, characterized in that, The specific operating logic of the phase winding with different taps and the ARS polarity selector includes: First operation logic: advance phase angle, tap position from n to 1, the polarity of the phase adjustment unit I is negative, and it is sequentially inserted using equation (2-b), the polarity of the phase adjustment unit II is positive, and it is sequentially inserted using equation (2-a). Second operating logic: In the original position, no phase-adjusting winding is inserted; The third operation logic is: lag phase shift angle, tap position from -1 to -n, the polarity of phase adjustment unit I is positive, and it is sequentially inserted using equation (2-a), the polarity of phase adjustment unit II is negative, and it is sequentially inserted using equation (2-b).

8. The phase-shifting transformer with a polygonal tortuous connection according to claim 7, characterized in that, When the number of turns in the voltage regulating winding is small, a cascade winding method is adopted to ensure the axial symmetry of the winding. The winding is divided into two groups by an even number of parallel wires, and the winding is performed on the upper and lower ends respectively. After the required number of turns for each stage is completed, a tap is led out until all the turns are completed.

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