Vacuum on-load tap-changer transition circuit and voltage regulating method

Abstract

The invention discloses a vacuum on-load tap-changer transition circuit and a voltage regulation method. The vacuum on-load tap-changer transition circuit comprises an on-load tap-changer comprising a first main switch and a second main switch, and a transition circuit comprising a change-over switch, a first transition branch, a second transition branch and a third transition branch, one end of the first main switch is connected with a first winding tap of a voltage regulating winding of the transformer, one end of the second main switch is connected with a second winding tap, and the other ends of the first main switch and the second main switch and the output end of the second transition branch are connected with a neutral point of the transformer; the first transition branch is connected in parallel with the first main switch; the third transition branch is connected in parallel with the second main switch; a static contact, a first moving contact and a second moving contact of the change-over switch are respectively connected with a first output end of the third transition branch, an input end of the first transition branch and an input end of the second transition branch in a one-to-one correspondence manner; according to the invention, the switching loss of the switch element in the on-load tap-changer can be effectively reduced, and the service life of the transition circuit is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a vacuum on-load tap changer transition circuit and a voltage regulation method. Background Art

[0002] On-load tap-changers are key components within power transformers. They operate under transformer excitation or load conditions, changing the effective turns ratio by connecting multiple taps in the transformer windings, thereby regulating the output voltage without interrupting the load current. On-load tap-changers are widely used, particularly in converter transformers for ultra-high voltage direct current (UHVDC) transmission projects, ensuring the rated trigger angle of the converter during normal operation. Vacuum-type on-load tap-changers primarily use vacuum tubes to extinguish the arc, avoiding the carbonization and contamination of the oil caused by arc extinguishing during traditional load transfer using copper-tungsten arc contacts. Due to the short arc-breaking time, low arc voltage, low arc energy consumption, and the recondensation of contact metal vapors, vacuum-type on-load tap-changers minimize contact corrosion and burnout, leading to their widespread use.

[0003] The core of an on-load tap-changer is the transition circuit, which utilizes its principles to implement tap-changing operations. Depending on the number of transition resistors, transitions can be single-resistor, dual-resistor, or multi-resistor. Based on UHVDC project experience, the interstage circulating current flowing through the transition resistors in the transition circuit during switching is approximately 900 to 1000A, generating significant heat in the transition resistors. The load current flowing through the main vacuum contacts of the converter transformer's on-load tap-changer is approximately 500 to 600A. Because the circulating current within the transition circuit is significantly greater than the load current, the vacuum contacts of the on-load tap-changer and its internal components in the transition circuit are susceptible to damage after repeated switching, shortening the life of the transition circuit. Summary of the Invention

[0004] In view of the problems existing in the prior art, embodiments of the present invention provide a vacuum on-load tap changer transition circuit and a voltage regulation method, which can effectively improve the service life of the on-load tap changer transition circuit.

[0005] In a first aspect, an embodiment of the present invention provides a vacuum on-load tap changer transition circuit, comprising: an on-load tap changer and a transition circuit; the on-load tap changer comprising: a first main switch and a second main switch; the transition circuit comprising: a transfer switch, a first transition branch, a second transition branch, and a third transition branch;

[0006] One end of the first main switch is connected to a first winding tap in a voltage regulating winding of a transformer, one end of the second main switch is connected to a second winding tap in a voltage regulating winding of the transformer, and the other ends of the first and second main switches are connected to the neutral point of the transformer; the first transition branch is connected in parallel with the first main switch; the third transition branch is connected in parallel with the second main switch; the static contact of the transfer switch is connected to a first output end of the third transition branch; the first moving contact of the transfer switch is connected to an input end of the first transition branch, the second moving contact of the transfer switch is connected to an input end of the second transition branch, and the output end of the second transition branch is connected to the neutral point of the transformer.

[0007] As an improvement of the above scheme, the first transition branch includes: a first auxiliary switching element and a first transition resistor; one end of the first auxiliary switching element is connected to the input end of the first transition branch, the other end of the first auxiliary switching element is connected to one end of the first transition resistor, and the other end of the first transition resistor is connected to the output end of the first transition branch; wherein, the input end of the first transition branch is used to be connected to the first winding tap in the voltage regulating winding of the transformer, and the output end of the first transition branch is used to be connected to the neutral point of the transformer.

[0008] As an improvement of the above solution, the second transition branch includes: a second transition resistor; one end of the second transition resistor is connected to the input end of the second transition branch, and the other end of the second transition resistor is connected to the output end of the second transition branch.

[0009] As an improvement to the above scheme, the third transition branch includes a second auxiliary switching element and a third auxiliary switching element; the input end of the second auxiliary switching element is connected to the input end of the third transition branch, the output end of the second auxiliary switching element and the input end of the third auxiliary switching element are connected to the first output end of the third transition branch, and the output end of the third auxiliary switching element is connected to the second output end of the third transition branch; wherein, the input end of the third transition branch is used to be connected to the second winding tap in the voltage regulating winding of the transformer, and the second output end of the third transition branch is used to be connected to the neutral point of the transformer.

[0010] In a second aspect, an embodiment of the present invention provides a voltage regulation method for a vacuum on-load tap changer transition circuit, which uses the vacuum on-load tap changer transition circuit described in the first aspect; the voltage regulation method includes:

[0011] Controlling the switching of the on-load tap changer between the first winding tap and the second winding tap by turning on and off the first main switch and the second main switch;

[0012] By turning on and off the first moving contact and the second moving contact in the switch, the connection or disconnection between the third transition branch and the first transition branch and the second transition branch is controlled;

[0013] By switching on and off the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element, the load current is controlled to be disconnected in each branch of the transition circuit of the vacuum on-load tap changer, so that the load current flows from the first winding tap or the second winding tap through the first main switch or the second main switch and out from the neutral point lead-out terminal, thereby adjusting the voltage of each switching element in the transition circuit during the switching process.

[0014] As an improvement to the above solution, the method includes:

[0015] When the first main switch, the third auxiliary switch element, and the first auxiliary switch element are in the on state, the second auxiliary switch element and the second main switch are in the off state, and the first moving contact of the transfer switch is in the on state, the first winding tap is connected, and the load current flows from the first winding tap through the first main switch and out of the neutral point lead-out terminal;

[0016] The first main switch is turned off, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switch element;

[0017] The third auxiliary switching element is disconnected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the first transition resistor;

[0018] The first moving contact of the transfer switch is disconnected, the second moving contact of the transfer switch is connected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor;

[0019] The second auxiliary switch element is turned on, the second moving contact of the transfer switch is turned on, the first winding tap and the second winding tap are both connected, and the load current flows out from the neutral point lead-out terminal through the first transition resistor and the second transition resistor;

[0020] The first auxiliary switching element is disconnected, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the two auxiliary switching elements, the transfer switch, and the second transition resistor;

[0021] Turning on the third auxiliary switching element, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element and the third auxiliary switching element;

[0022] The second main switch is turned on, the second winding tap is connected, and the load current flows from the second winding tap through the second main switch and out of the neutral point lead-out terminal, completing the switching process of the on-load tap changer from the first winding tap to the second winding tap.

[0023] As an improvement to the above solution, the method includes:

[0024] When the second main switch, the third auxiliary switch element, and the second auxiliary switch element are in the on state, the first auxiliary switch element is in the off state, and the second movable contact of the transfer switch is in the on state, the second winding tap is connected, and the load current flows from the second winding tap through the second main switch and out of the neutral point lead-out terminal;

[0025] The second main switch is turned off, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element and the second auxiliary switching element;

[0026] The third auxiliary switching element is disconnected, the second winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element, the transfer switch, and the second transition resistor;

[0027] Turning on the first auxiliary switching element, connecting the second winding tap and the first winding tap, and allowing the load current to flow out from the neutral point lead-out terminal through the first transition resistor and the second transition resistor;

[0028] The second auxiliary switching element is turned off, the first winding tap is turned on, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor;

[0029] The second moving contact of the transfer switch is disconnected, the first moving contact of the transfer switch is turned on, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor;

[0030] Turning on the third auxiliary switching element, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switching element;

[0031] The first main switch is turned on, the first winding tap is connected, the load current flows from the first winding tap through the first main switch and out from the neutral point lead-out terminal, completing the switching process of the on-load tap changer from the second winding tap to the first winding tap.

[0032] As an improvement to the above solution, the method includes:

[0033] When the first winding tap is connected and the load current flows from the first winding tap through the first main switch from the neutral point lead-out terminal, the voltage of the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element is zero, the current of the first auxiliary switching element and the third auxiliary switching element is zero, and the voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit.

[0034] When the first winding tap continues to be connected and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switching element, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, the current of the first auxiliary switching element and the second auxiliary switching element is zero, the voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit, and the current of the third auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit.

[0035] As an improvement to the above solution, the method includes:

[0036] When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the transfer switch and the first transition resistor, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, and the current of the second auxiliary switching element and the third auxiliary switching element is zero. The voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit, and the current of the first auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit.

[0037] When the load current flows out of the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, and the current of the second auxiliary switching element and the third auxiliary switching element is zero. The voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit and the voltage of the first transition resistor, and the current of the first auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit.

[0038] When the first winding tap and the second winding tap are both connected and the load current flows out of the neutral point lead-out terminal through the first transition resistor and the second transition resistor, the voltage of the first auxiliary switching element and the second auxiliary switching element is zero, and the current of the third auxiliary switching element is zero. The voltage of the third auxiliary switching element is determined according to the voltage and current of the vacuum on-load tap changer transition circuit and the resistance values of the first transition resistor and the second transition resistor. The current of the first auxiliary switching element and the second auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit and the resistance values of the first transition resistor and the second transition resistor.

[0039] As an improvement to the above solution, the method includes:

[0040] When the second winding tap is connected and the load current flows out of the neutral point lead-out terminal through the two auxiliary switching elements, the transfer switch, and the second transition resistor, the voltage of the second auxiliary switching element is zero, and the currents of the first and second auxiliary switching elements are zero. The voltage of the first auxiliary switching element is determined according to the voltage and current of the vacuum on-load tap changer transition circuit and the resistance value of the second transition resistor. The voltage of the third auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit and the resistance value of the second transition resistor. The current of the second auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit.

[0041] When the second winding tap is connected and the load current flows out from the neutral point lead-out terminal through the second and third auxiliary switching elements, the voltages of the second and third auxiliary switching elements are zero, and the current of the first auxiliary switching element is zero. The voltage of the first auxiliary switching element is determined according to the voltage of the vacuum on-load tap-changer transition circuit, and the currents of the second and third auxiliary switching elements are determined according to the current of the vacuum on-load tap-changer transition circuit.

[0042] When the second winding tap is connected and the load current flows from the second winding tap through the second main switch from the neutral point lead-out terminal, the voltage of the second auxiliary switching element and the third auxiliary switching element is zero, and the current of the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element is zero. The voltage of the first auxiliary switching element is determined according to the voltage of the transition circuit of the vacuum on-load tap changer.

[0043] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows: a vacuum on-load tap changer transition circuit includes an on-load tap changer and a transition circuit; the on-load tap changer includes: a first main switch and a second main switch; the transition circuit includes: a transfer switch, a first transition branch, a second transition branch and a third transition branch; wherein, one end of the first main switch is used to be connected to a first winding tap in a voltage regulating winding of a transformer, one end of the second main switch is used to be connected to a second winding tap in a voltage regulating winding of the transformer, and the other ends of the first main switch and the second main switch are used to be connected to the neutral point of the transformer; the first transition branch is connected in parallel with the first main switch; the third transition branch is connected in parallel with the second main switch; the static contact of the transfer switch is connected to the third transition branch. The first output ends of the three transition branches are connected; the first moving contact of the transfer switch is connected to the input end of the first transition branch, the second moving contact of the transfer switch is connected to the input end of the second transition branch, and the output end of the second transition branch is connected to the neutral point of the transformer; in an embodiment of the present invention, the third auxiliary switch element is responsible for interrupting the load current, and the first and second auxiliary switch elements are responsible for interrupting the load current superimposed on the inter-stage circulating current. By controlling the on and off of the first main switch, the second main switch, the first auxiliary switch element, the second auxiliary switch element, and the third auxiliary switch element to achieve reciprocating switching, the switching loss of the switch elements (i.e., the vacuum contacts) in the on-load tap changer can be effectively reduced, and the service life of the transition circuit can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings used in the implementation methods. Obviously, the drawings described below are only some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 This is a schematic block diagram of a vacuum on-load tap changer transition circuit provided by an embodiment of the present invention;

[0046] Figure 2 is a first circuit diagram of a vacuum on-load tap changer transition circuit provided by an embodiment of the present invention;

[0047] Figure 3 This is a flow chart of a voltage regulation method for a transition circuit of a vacuum on-load tap changer provided by an embodiment of the present invention;

[0048] Figure 4 This is a circuit diagram of a first switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0049] Figure 5 is a circuit diagram of the second switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0050] Figure 6 This is a circuit diagram of the third switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0051] Figure 7 This is a circuit diagram of the fourth switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0052] Figure 8 is a circuit diagram of the fifth switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0053] Figure 9 is a circuit diagram of the sixth switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0054] Figure 10 is a circuit diagram of the seventh switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0055] Figure 11 This is a circuit diagram of the eighth switching stage of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0056] Figure 12 This is a transition timing diagram of a vacuum on-load tap changer transition circuit from a first winding tap to a second winding tap provided by an embodiment of the present invention;

[0057] Figure 13 This is a transition timing diagram of a vacuum on-load tap changer transition circuit from the second winding tap to the first winding tap provided by an embodiment of the present invention;

[0058] Figure 14 is a second circuit diagram of a vacuum on-load tap changer transition circuit provided by an embodiment of the present invention;

[0059] Figure 15 This is a third circuit diagram of the vacuum on-load tap changer transition circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0061] It is understood that the various numbers used in the embodiments of the present invention are merely for ease of description and are not intended to limit the scope of this application. The order of execution of each process does not necessarily imply a specific order of execution. The order of execution of each process should be determined by its function and inherent logic.

[0062] In embodiments of the present invention, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The terms "include", "comprises", or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, the elements defined by the phrase "includes..." do not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the elements.

[0063] See Figure 1 , Figure 1 This is a schematic block diagram of a vacuum on-load tap changer transition circuit provided by an embodiment of the present invention. The vacuum on-load tap changer transition circuit includes: an on-load tap changer and a transition circuit; the on-load tap changer includes: a first main switch MC1 and a second main switch MC2; the transition circuit includes: a transfer switch T, a first transition branch 21, a second transition branch 22, and a third transition branch 23;

[0064] Among them, one end of the first main switch MC1 is used to connect to the first winding tap (N) in the voltage regulating winding of the transformer, one end of the second main switch MC2 is used to connect to the second winding tap (N+1) in the voltage regulating winding of the transformer, and the other ends of the first main switch MC1 and the second main switch MC2 are used to connect to the neutral point (0) of the transformer; the first transition branch 21 is connected in parallel with the first main switch MC1; the third transition branch 23 is connected in parallel with the second main switch MC2; the static contact 10 of the transfer switch T is connected to the first output end of the third transition branch 23; the first moving contact 11 of the transfer switch T is connected to the input end of the first transition branch 21, the second moving contact 12 of the transfer switch T is connected to the input end of the second transition branch 22, and the output end of the second transition branch 22 is used to connect to the neutral point (0) of the transformer.

[0065] In the embodiment of the present invention, both the first main switch MC1 and the second main switch MC2 are vacuum contacts. They take turns to perform switching tasks, which can achieve reciprocating switching, reduce the probability of failure, reduce component loss during the switching process of the on-load tap changer, and increase the service life of the transition circuit.

[0066] Take the example of a single-break vacuum contact as the switching element in the transition circuit. Figure 2 As shown, the first transition branch 21 includes: a first auxiliary switching element V1 and a first transition resistor R1; one end of the first auxiliary switching element V1 is connected to the input end of the first transition branch 21, the other end of the first auxiliary switching element V1 is connected to one end of the first transition resistor R1, and the other end of the first transition resistor R1 is connected to the output end of the first transition branch 21; wherein, the input end of the first transition branch 21 is used to be connected to the first winding tap (N) in the voltage regulating winding of the transformer, and the output end of the first transition branch 21 is used to be connected to the neutral point (0) of the transformer.

[0067] The second transition branch 22 includes: a second transition resistor R2 ; one end of the second transition resistor R2 is connected to the input end of the second transition branch 22 , and the other end of the second transition resistor R2 is connected to the output end of the second transition branch 22 .

[0068] The third transition branch 23 includes a second auxiliary switching element V2 and a third auxiliary switching element V3; the input end of the second auxiliary switching element V2 is connected to the input end of the third transition branch 23, the output end of the second auxiliary switching element V2 and the input end of the third auxiliary switching element V3 are connected to the first output end of the third transition branch 23, and the output end of the third auxiliary switching element V3 is connected to the second output end of the third transition branch 23; wherein, the input end of the third transition branch 23 is used to be connected to the second winding tap (N+1) in the voltage regulating winding of the transformer, and the second output end of the third transition branch 23 is used to be connected to the neutral point (0) of the transformer.

[0069] In this embodiment of the present invention, the use of two transition resistors (R1 and R2) in transition circuit 2 reduces heat generation from a single resistor, facilitates design and installation, and ensures insulation distance. Furthermore, among the switching elements (first auxiliary switching element V1, second auxiliary switching element V2, and third auxiliary switching element V3) within transition circuit 2, the third auxiliary switching element V3 is responsible for interrupting the load current, while the first and second auxiliary switching elements V1 and V2 are responsible for interrupting the load current superimposed on the inter-stage circulating current. By controlling the on-off state of the first main switch MC1, second main switch MC2, first auxiliary switching element V1, second auxiliary switching element V2, and third auxiliary switching element V3 according to a specific timing sequence, reciprocating switching of the on-load tap changer can be achieved. The reversible reciprocating switching timing improves the reliability of the on-load tap changer's operation, reduces switching losses in the on-load tap changer's switching elements (i.e., vacuum contacts), and increases the service life of the transition circuit.

[0070] For the above-mentioned vacuum on-load tap changer transition circuit, the embodiment of the present invention further provides a voltage regulation method for the vacuum on-load tap changer transition circuit, such as Figure 3 As shown, the specific voltage regulation methods include:

[0071] S11: Controlling the switching of the on-load tap changer between the first winding tap and the second winding tap by turning on and off the first main switch and the second main switch;

[0072] S12: Controlling the connection or disconnection between the third transition branch and the first transition branch and the second transition branch by switching the first moving contact and the second moving contact in the switch;

[0073] S13: By switching on and off the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element, the load current is controlled to be disconnected in each branch in the transition circuit of the vacuum on-load tap-changer, so that the load current flows out from the first winding tap or the second winding tap through the first main switch or the second main switch from the neutral point lead-out terminal, thereby adjusting the voltage of each switching element in the transition circuit during the switching process.

[0074] The transition circuit voltage regulation process is explained in detail using the example of an on-load tap changer switching from the first winding tap (N) to the second winding tap (N+1) of a transformer's voltage regulating winding. The transition circuit has a unique switching phase division, with the switching elements experiencing different electrical stresses in each phase. There are a total of eight switching phases.

[0075] In the first switching stage, the first main switch MC1, the third auxiliary switch element V3 and the first auxiliary switch element V1 are in the on state, the second auxiliary switch element V2 and the second main switch MC2 are in the off state, and the first moving contact 11 of the transfer switch T is in the on state (i.e., the static contact 10 is connected to the first moving contact 11), the first winding tap (N) is connected, and the load current flows from the first winding tap (N) through the first main switch MC1 and out of the neutral point (0) lead-out terminal, as shown in FIG. Figure 4 shown.

[0076] The power supply side of the transition circuit can be equivalent to a voltage source and a current source, and there is a certain phase difference between the two, which can be specifically expressed as the following formula:

[0077]

[0078] Among them, i n 、u n Represent the instantaneous values of the equivalent current source and equivalent voltage source respectively, I n 、U n They represent the peak values of the equivalent current source and the equivalent voltage source respectively, ω represents the angular velocity corresponding to the power frequency quantity, φ represents the phase angle of the voltage leading the current, and t represents time.

[0079] During the first switching phase, the voltage of the first auxiliary switching element V1, the second auxiliary switching element V2, and the third auxiliary switching element V3 are zero, and the current of the first auxiliary switching element V1 and the third auxiliary switching element V3 are zero. The voltage of the second auxiliary switching element V2 is determined by the voltage of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0080]

[0081] Among them, U V1 、U V2 、U V3 I represents the voltages borne by the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element, respectively. V1 , I V2 , I V3 They respectively represent the currents borne by the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element.

[0082] The second switching stage: the first main switch MC1 is turned off. At this time, the second main switch MC2 remains off, the third auxiliary switch element V3 and the first auxiliary switch element V1 remain on, the second auxiliary switch element V2 remains off, the transfer switch T remains in the first moving contact 11 state, the first winding tap (N) continues to be connected, and the load current flows out from the neutral point (0) lead-out terminal through the transfer switch T and the third auxiliary switch element V3. Figure 5 shown.

[0083] In the second switching phase, the voltage of the first auxiliary switching element V1 and the third auxiliary switching element V3 is zero, and the current of the first auxiliary switching element V1 and the second auxiliary switching element V2 is zero. The voltage of the second auxiliary switching element V2 is determined by the voltage of the vacuum on-load tap-changer transition circuit, and the current of the third auxiliary switching element V3 is determined by the current of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0084]

[0085] The third switching stage: the first main switch MC1 remains off, the second main switch MC2 remains off, and the third auxiliary switch element V3 is disconnected. At this time, an arc is generated in the third auxiliary switch element V3, the first auxiliary switch element V1 remains on, the second auxiliary switch element V2 remains off, the transfer switch T remains in the first moving contact 11 state, the first winding tap continues to be connected, and the load current flows out from the neutral point (0) terminal through the transfer switch T and the first transition resistor R1, as shown in FIG. Figure 6 shown.

[0086] In the third switching phase, the voltage of the first auxiliary switching element V1 and the third auxiliary switching element V3 is zero, and the current of the second auxiliary switching element V2 and the third auxiliary switching element V3 is zero. The voltage of the second auxiliary switching element V2 is determined by the voltage of the vacuum on-load tap-changer transition circuit, and the current of the first auxiliary switching element V1 is determined by the current of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0087]

[0088] In the fourth switching stage, the first main switch MC1 remains disconnected, the second main switch MC2 remains disconnected, the third auxiliary switch element V3 remains disconnected, the first auxiliary switch element V1 remains on, and the second auxiliary switch element V2 remains disconnected. After the arc in the third auxiliary switch element V3 is extinguished, the first moving contact 11 of the transfer switch T is disconnected, and the second moving contact 12 of the transfer switch T is turned on (i.e., the transfer switch T is switched from the first moving contact 11 state to the second moving contact 12 state). The first winding tap (N) continues to be connected, and the load current flows out from the neutral point (0) terminal through the first auxiliary switch element V1 and the first transition resistor R1, as shown in FIG. Figure 7 shown.

[0089] In the fourth switching phase, the voltage of the first auxiliary switching element V1 and the third auxiliary switching element V3 is zero, and the current of the second auxiliary switching element V2 and the third auxiliary switching element V3 is zero. The voltage of the second auxiliary switching element V2 is determined by the voltage of the vacuum on-load tap-changer transition circuit and the voltage of the first transition resistor R1, and the current of the first auxiliary switching element V1 is determined by the current of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0090]

[0091] Here, R1 represents the resistance value of the first transition resistor R1.

[0092] The fifth switching stage: the first main switch MC1 remains disconnected, the second main switch MC2 remains disconnected, the third auxiliary switch element V3 remains disconnected, the first auxiliary switch element V1 remains on, the second auxiliary switch element V2 is closed and turned on, the transfer switch T remains in the second moving contact 12 state, the first winding tap (N) and the second winding tap (N+1) are both connected, and the load current flows out from the neutral point (0) lead-out end through the two paths where the first transition resistor R1 and the second transition resistor R2 are located. The first path is the first auxiliary switch element V1 and the first transition resistor R1, and the second path is the second auxiliary switch element V2, the transfer switch T, and the second transition resistor R2; the transition circuit forms a bridge connection, generating an inter-stage circulating current I c ,like Figure 8 shown.

[0093] In the fifth switching phase, the voltage of the first auxiliary switching element V1 and the second auxiliary switching element V2 is zero, and the current of the third auxiliary switching element V3 is zero. The voltage of the third auxiliary switching element V3 is determined by the voltage and current of the vacuum on-load tap-changer transition circuit and the resistance values of the first transition resistor R1 and the second transition resistor R2. The current of the first auxiliary switching element V1 and the second auxiliary switching element V2 is determined by the current of the vacuum on-load tap-changer transition circuit and the resistance values of the first transition resistor R1 and the second transition resistor R2. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0094]

[0095] Here, R2 represents the resistance value of the second transition resistor R2.

[0096] The sixth switching stage: the first main switch MC1 remains open, the second main switch MC2 remains open, and the third auxiliary switch element V3 remains open, and the first auxiliary switch element V1 is disconnected. At this time, an arc is generated in the first auxiliary switch element V1, the second auxiliary switch element V2 remains closed, the transfer switch T maintains the second moving contact 12 state, the second winding tap (N+1) is connected, and the load current flows out from the neutral point (0) terminal through the second auxiliary switch element V2, the transfer switch T, and the second transition resistor R2, as shown in FIG. Figure 9 shown.

[0097] In the sixth switching phase, the voltage of the second auxiliary switching element V2 is zero, and the currents of the first and second auxiliary switching elements V1 and V2 are zero. The voltage of the first auxiliary switching element V1 is determined by the voltage and current of the vacuum on-load tapchanger transition circuit and the resistance value of the second transition resistor R2. The voltage of the third auxiliary switching element V3 is determined by the current of the vacuum on-load tapchanger transition circuit and the resistance value of the second transition resistor R2. The current of the second auxiliary switching element V2 is determined by the current of the vacuum on-load tapchanger transition circuit. The voltages and currents borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0098]

[0099] In the seventh switching stage, the first main switch MC1 remains open, and the second main switch MC2 remains open. After the arc in the first auxiliary switch element V1 is extinguished, the third auxiliary switch element V3 is closed and turned on. The first auxiliary switch element V1 remains open, the second auxiliary switch element V2 remains closed, and the transfer switch T maintains the second moving contact 12 state. The second winding tap (N+1) continues to be connected, and the load current flows out from the neutral point (0) terminal through the second auxiliary switch element V2 and the third auxiliary switch element V3. Figure 10 shown.

[0100] In the seventh switching phase, the voltage of the second auxiliary switching element V2 and the third auxiliary switching element V3 is zero, and the current of the first auxiliary switching element V1 is zero. The voltage of the first auxiliary switching element V1 is determined by the voltage of the vacuum on-load tap-changer transition circuit, and the current of the second auxiliary switching element V2 and the third auxiliary switching element V3 is determined by the current of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0101]

[0102] In the eighth switching stage, the first main switch MC1 remains open, the second main switch MC1 is closed and turned on, the third auxiliary switch element V3 remains closed, the first auxiliary switch element V1 remains open, the second auxiliary switch element V2 remains closed, the transfer switch T maintains the second moving contact 12 state, the second winding tap (N+1) continues to be connected, and the load current flows out from the second winding tap (N+1) through the second main switch MC2 from the neutral point (0) lead-out terminal, completing the switching process of the on-load tap changer from the first winding tap (N) to the second winding tap (N+1), as shown in FIG. Figure 11 shown.

[0103] In the eighth switching phase, the voltage of the second auxiliary switching element V2 and the third auxiliary switching element V3 is zero, and the current of the first auxiliary switching element V1, the second auxiliary switching element V2, and the third auxiliary switching element V3 is zero. The voltage of the first auxiliary switching element V1 is determined by the voltage of the vacuum on-load tap-changer transition circuit. The voltage and current borne by each switching element (V1, V2, V3) in the transition circuit are as follows:

[0104]

[0105] When the on-load tap changer switches from the second winding tap (N+1) to the first winding tap (N), the switching phase of the transition circuit can also be divided into eight switching phases. The specific voltage regulation process is as follows:

[0106] In the first switching stage, the first main switch remains open, the second main switch and the third auxiliary switch element remain closed and conductive, the first auxiliary switch element remains open, the second auxiliary switch element remains closed and conductive, the transfer switch maintains the second moving contact state, the second winding tap is connected, and the load current flows from the second winding tap through the second main switch to the neutral point lead-out terminal;

[0107] Second switching stage: The first main switch remains off, and the second main switch is turned off. At this time, the third auxiliary switch element remains closed and conductive, the first auxiliary switch element remains off, the second auxiliary switch element remains closed and conductive, the transfer switch remains in the second moving contact state, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switch element and the second auxiliary switch element;

[0108] Third switching stage: The first main switch remains off, the second main switch remains off, and the third auxiliary switch element is disconnected. At this time, an arc is generated in the third auxiliary switch element. The first auxiliary switch element remains off, the second auxiliary switch element remains closed and conductive, the transfer switch maintains the second moving contact state, the second winding tap continues to be connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switch element, the transfer switch, and the second transition resistor.

[0109] The fourth switching stage: the first main switch remains disconnected, the second main contact remains disconnected, and the third auxiliary switch element remains disconnected. After the arc in the third auxiliary switch element is extinguished, the first auxiliary switch element is closed and turned on, the second auxiliary switch element remains closed and turned on, the transfer switch remains in the second moving contact state, the first winding tap and the second winding tap are both connected, and the load current flows out from the neutral point lead-out end through the two paths where the first transition resistor and the second transition resistor are located; the first path is the first auxiliary switch element and the first transition resistor, and the second path is the second auxiliary switch element, the transfer switch, and the second transition resistor; the transition circuit forms a bridge, generating an inter-stage circulating current.

[0110] Fifth switching stage: the first main switch remains open, the second main contact remains open, the third auxiliary switch element remains open, the first auxiliary switch element remains closed and conductive, the second auxiliary switch element is disconnected, an arc is generated in the second auxiliary switch element, the transfer switch remains in the second moving contact state, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switch element and the first transition resistor;

[0111] Sixth switching stage: the first main switch remains open, the second main contact remains open, the third auxiliary switch element remains open, the first auxiliary switch element remains closed and conductive, and the second auxiliary switch element remains open. After the arc in the second auxiliary switch element is extinguished, the second moving contact of the transfer switch is opened, and the first moving contact of the transfer switch is conductive (i.e., the transfer switch switches from the second moving contact state to the first moving contact state). The first winding tap continues to be connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switch element and the first transition resistor.

[0112] Seventh switching stage: the first main switch remains open, the second main contact remains open, the third auxiliary switch element is closed and turned on, the first auxiliary switch element remains closed, the second auxiliary switch element remains open, the transfer switch maintains the first moving contact state, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switch element;

[0113] Eighth switching stage: The first main switch is turned on. At this time, the second main switch remains off, the third auxiliary switch element remains closed and turned on, the second auxiliary switch element remains off, the transfer switch remains in the first moving contact state, the first winding tap continues to be connected, and the load current flows from the first winding tap through the first main switch to the neutral point lead-out terminal, completing the switching process of the on-load tap changer from the second winding tap to the first winding tap.

[0114] It should be noted that the voltage and current calculation process of each switching element in the transition circuit in each stage when the on-load tap changer switches from the second winding tap (N+1) to the first winding tap (N) can be referred to the voltage and current calculation process of each switching element in the transition circuit in each stage when the on-load tap changer switches from the first winding tap (N) to the second winding tap (N+1), and will not be repeated here.

[0115] Among them, the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element can be any one of a single-break vacuum circuit breaker (also described as a single-break vacuum contact), a double-break vacuum circuit breaker (also described as a double-break vacuum contact), and a power electronic element with controllable on-off function.

[0116] Power electronic components with controllable on / off functions include but are not limited to insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs).

[0117] It should be understood that when the internal switching elements (V1, V2, V3) in the vacuum on-load tap-changer transition circuit are power electronic elements with controllable on-off functions, double-break vacuum contacts, or single-break vacuum contacts, the action timing and voltage regulation method of the switching elements are consistent.

[0118] In the embodiment of the present invention, the switching tasks of the transition circuit of the vacuum on-load tap changer using the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switch are shown in the following table:

[0119]

[0120]

[0121] Among them, I N Indicates load current; U Srepresents the inter-stage voltage of the on-load tap changer; R1 represents the resistance value of the first transition resistor R1, and R2 represents the resistance value of the second transition resistor R2.

[0122] When the on-load tapchanger switches from the first winding tap (N) to the second winding tap (N+1), the transition circuit conversion procedure is as follows: Figure 12 As shown;

[0123] When the on-load tapchanger switches from the second winding tap (N+1) to the first winding tap (N), the transition circuit conversion procedure is as follows: Figure 13 As shown;

[0124] Figure 14 The circuit diagram of the vacuum on-load tap-changer transition circuit (which can also be described as a reciprocating transition circuit of an on-load tap-changer with alternating switching of vacuum tubes) is formed when the switching elements (V1, V2, V3) in the transition circuit are power electronic elements. Figure 14 As shown, only Figure 2 The switching elements (V1, V2, V3) in the transition circuit are replaced from single-break vacuum contacts to power electronic elements with controllable on / off. Figure 2 The components are the same, the action sequence is the same, and the functions and effects are the same Figure 2 The functions and effects of the transition circuit shown are also the same and will not be repeated here.

[0125] Figure 15 The circuit diagram of the vacuum on-load tap-changer transition circuit is formed when the switching elements (V1, V2, V3) in the transition circuit are power electronic elements; Figure 15 As shown, only Figure 2 The switching elements (V1, V2, V3) in the transition circuit are replaced from single-break vacuum contacts to double-break vacuum contacts, and the other elements are the same as Figure 2 The components are the same, the action sequence is the same, and the functions and effects are the same Figure 2 The functions and effects of the transition circuit shown are also the same and will not be repeated here.

[0126] During the reciprocating switching process of the transition circuit of the vacuum on-load tap changer, the third auxiliary switching element V3 is responsible for interrupting the load current, while the first auxiliary switching element V1 and the second auxiliary switching element V2 are responsible for interrupting the load current superimposed on the inter-stage circulating current. The switching elements take turns to share the switching task, which can effectively reduce the switching loss of the switching elements (i.e., the vacuum contacts) and extend the service life of the transition circuit. At the same time, the reciprocating switching sequence is reversible, which can improve the reliability and switching efficiency of the on-load tap changer. At the same time, during the switching process, the embodiment of the present invention adjusts the withstand voltage and current of each switching element, improving the tolerance to overcurrent and overvoltage. It illustrates the unique characteristics of the switching elements in the switching process of the transition circuit, making it adaptable to different switching requirements.

[0127] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, many improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A vacuum on-load tap changer transition circuit, characterized in that: include: On-load tap-changers and transition circuits; The on-load tap changer includes: a first main switch and a second main switch; the transition circuit includes: a transfer switch, a first transition branch, a second transition branch and a third transition branch; One end of the first main switch is connected to a first winding tap in a voltage regulating winding of a transformer, one end of the second main switch is connected to a second winding tap in a voltage regulating winding of the transformer, and the other ends of the first and second main switches are connected to the neutral point of the transformer; the first transition branch is connected in parallel with the first main switch; the third transition branch is connected in parallel with the second main switch; the static contact of the transfer switch is connected to a first output end of the third transition branch; the first moving contact of the transfer switch is connected to an input end of the first transition branch, the second moving contact of the transfer switch is connected to an input end of the second transition branch, and the output end of the second transition branch is connected to the neutral point of the transformer.

2. The vacuum on-load tap changer transition circuit according to claim 1, characterized in that: The first transition branch includes: a first auxiliary switching element and a first transition resistor; one end of the first auxiliary switching element is connected to the input end of the first transition branch, the other end of the first auxiliary switching element is connected to one end of the first transition resistor, and the other end of the first transition resistor is connected to the output end of the first transition branch; wherein the input end of the first transition branch is used to be connected to the first winding tap in the voltage regulating winding of the transformer, and the output end of the first transition branch is used to be connected to the neutral point of the transformer.

3. The vacuum on-load tap changer transition circuit according to claim 2, characterized in that: The second transition branch includes: a second transition resistor; one end of the second transition resistor is connected to the input end of the second transition branch, and the other end of the second transition resistor is connected to the output end of the second transition branch.

4. The vacuum on-load tap changer transition circuit according to claim 3, characterized in that: The third transition branch includes a second auxiliary switching element and a third auxiliary switching element; the input end of the second auxiliary switching element is connected to the input end of the third transition branch, the output end of the second auxiliary switching element and the input end of the third auxiliary switching element are connected to the first output end of the third transition branch, and the output end of the third auxiliary switching element is connected to the second output end of the third transition branch; wherein, the input end of the third transition branch is used to be connected to the second winding tap in the voltage regulating winding of the transformer, and the second output end of the third transition branch is used to be connected to the neutral point of the transformer.

5. A method for regulating the voltage of a transition circuit of a vacuum on-load tap changer, characterized in that: The vacuum on-load tap changer transition circuit according to claim 4 is applied; the voltage regulation method comprises: Controlling the switching of the on-load tap changer between the first winding tap and the second winding tap by turning on and off the first main switch and the second main switch; By turning on and off the first moving contact and the second moving contact in the switch, the connection or disconnection between the third transition branch and the first transition branch and the second transition branch is controlled; By switching on and off the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element, the load current is controlled to be disconnected in each branch of the transition circuit of the vacuum on-load tap changer, so that the load current flows from the first winding tap or the second winding tap through the first main switch or the second main switch and out from the neutral point lead-out terminal, thereby adjusting the voltage of each switching element in the transition circuit during the switching process.

6. The voltage regulating method for a vacuum on-load tap changer transition circuit according to claim 5, characterized in that: The method comprises: When the first main switch, the third auxiliary switch element, and the first auxiliary switch element are in the on state, the second auxiliary switch element and the second main switch are in the off state, and the first moving contact of the transfer switch is in the on state, the first winding tap is connected, and the load current flows from the first winding tap through the first main switch and out of the neutral point lead-out terminal; The first main switch is turned off, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switch element; The third auxiliary switching element is disconnected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the first transition resistor; The first moving contact of the transfer switch is disconnected, the second moving contact of the transfer switch is connected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor; The second auxiliary switch element is turned on, the second moving contact of the transfer switch is turned on, the first winding tap and the second winding tap are both connected, and the load current flows out from the neutral point lead-out terminal through the first transition resistor and the second transition resistor; The first auxiliary switching element is disconnected, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the two auxiliary switching elements, the transfer switch, and the second transition resistor; Turning on the third auxiliary switching element, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element and the third auxiliary switching element; The second main switch is turned on, the second winding tap is connected, and the load current flows from the second winding tap through the second main switch and out of the neutral point lead-out terminal, completing the switching process of the on-load tap changer from the first winding tap to the second winding tap.

7. The voltage regulating method for a vacuum on-load tap changer transition circuit according to claim 6, characterized in that: The method comprises: When the second main switch, the third auxiliary switch element, and the second auxiliary switch element are in the on state, the first auxiliary switch element is in the off state, and the second movable contact of the transfer switch is in the on state, the second winding tap is connected, and the load current flows from the second winding tap through the second main switch and out of the neutral point lead-out terminal; The second main switch is turned off, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element and the second auxiliary switching element; The third auxiliary switching element is disconnected, the second winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the second auxiliary switching element, the transfer switch, and the second transition resistor; Turning on the first auxiliary switching element, connecting the second winding tap and the first winding tap, and allowing the load current to flow out from the neutral point lead-out terminal through the first transition resistor and the second transition resistor; The second auxiliary switching element is turned off, the first winding tap is turned on, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor; The second moving contact of the transfer switch is disconnected, the first moving contact of the transfer switch is turned on, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor; Turning on the third auxiliary switching element, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switching element; The first main switch is turned on, the first winding tap is connected, the load current flows from the first winding tap through the first main switch and out from the neutral point lead-out terminal, completing the switching process of the on-load tap changer from the second winding tap to the first winding tap.

8. The voltage regulating method for a vacuum on-load tap changer transition circuit according to claim 6, characterized in that: The method comprises: When the first winding tap is connected and the load current flows from the first winding tap through the first main switch from the neutral point lead-out terminal, the voltages of the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element are zero, the currents of the first auxiliary switching element and the third auxiliary switching element are zero, and the voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap-changer transition circuit; When the first winding tap continues to be connected and the load current flows out from the neutral point lead-out terminal through the transfer switch and the third auxiliary switching element, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, the current of the first auxiliary switching element and the second auxiliary switching element is zero, the voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit, and the current of the third auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit.

9. The voltage regulating method for a vacuum on-load tap changer transition circuit according to claim 8, characterized in that: The method comprises: When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the transfer switch and the first transition resistor, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, and the current of the second auxiliary switching element and the third auxiliary switching element is zero. The voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit, and the current of the first auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit. When the load current flows out of the neutral point lead-out terminal through the first auxiliary switching element and the first transition resistor, the voltage of the first auxiliary switching element and the third auxiliary switching element is zero, and the current of the second auxiliary switching element and the third auxiliary switching element is zero. The voltage of the second auxiliary switching element is determined according to the voltage of the vacuum on-load tap changer transition circuit and the voltage of the first transition resistor, and the current of the first auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit. When the first winding tap and the second winding tap are both connected and the load current flows out of the neutral point lead-out terminal through the first transition resistor and the second transition resistor, the voltage of the first auxiliary switching element and the second auxiliary switching element is zero, and the current of the third auxiliary switching element is zero. The voltage of the third auxiliary switching element is determined according to the voltage and current of the vacuum on-load tap changer transition circuit and the resistance values of the first transition resistor and the second transition resistor. The current of the first auxiliary switching element and the second auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit and the resistance values of the first transition resistor and the second transition resistor.

10. The voltage regulating method for a transition circuit of a vacuum on-load tap changer according to claim 9, characterized in that: The method comprises: When the second winding tap is connected and the load current flows out of the neutral point lead-out terminal through the two auxiliary switching elements, the transfer switch, and the second transition resistor, the voltage of the second auxiliary switching element is zero, and the currents of the first and second auxiliary switching elements are zero. The voltage of the first auxiliary switching element is determined according to the voltage and current of the vacuum on-load tap changer transition circuit and the resistance value of the second transition resistor. The voltage of the third auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit and the resistance value of the second transition resistor. The current of the second auxiliary switching element is determined according to the current of the vacuum on-load tap changer transition circuit. When the second winding tap is connected and the load current flows out from the neutral point lead-out terminal through the second and third auxiliary switching elements, the voltages of the second and third auxiliary switching elements are zero, and the current of the first auxiliary switching element is zero. The voltage of the first auxiliary switching element is determined according to the voltage of the vacuum on-load tap-changer transition circuit, and the currents of the second and third auxiliary switching elements are determined according to the current of the vacuum on-load tap-changer transition circuit. When the second winding tap is connected and the load current flows from the second winding tap through the second main switch from the neutral point lead-out terminal, the voltage of the second auxiliary switching element and the third auxiliary switching element is zero, and the current of the first auxiliary switching element, the second auxiliary switching element, and the third auxiliary switching element is zero. The voltage of the first auxiliary switching element is determined according to the voltage of the transition circuit of the vacuum on-load tap changer.

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