Transition circuit of double-resistor on-load tap-changer and voltage regulating method

Abstract

The invention discloses a dual-resistor on-load tap-changer transition circuit and a voltage regulation method. The circuit comprises an on-load tap-changer comprising a first main contact and a second main contact, and a dual-resistor transition circuit comprising a change-over switch, a first resistor transition branch and a second resistor transition branch. One end of the first main contact and the input end of the first resistance transition branch are connected with a first winding tap in a voltage regulating winding of the transformer; one end of the second main contact is connected with a second winding tap of a second moving contact of the change-over switch; a static contact and a first moving contact of the change-over switch are respectively connected with an input end of the second resistance transition branch and a second output end of the first resistance transition branch; the other ends of the first main contact and the second main contact, the first output end of the first resistance transition circuit and the output end of the second resistance transition circuit are connected with a neutral point; 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 dual-resistor transition circuit is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a dual-resistance 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 the on-load tapchanger is the dual-resistor transition circuit, which uses this principle to implement tap-changing operations. Depending on the number of transition resistors, single-resistor, dual-resistor, or multi-resistor transitions are employed. Based on UHVDC project experience, the interstage circulating current flowing through the transition resistors in the dual-resistor 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 tapchanger is approximately 500 to 600A. Because the circulating current within the dual-resistor transition circuit is significantly greater than the load current, the vacuum contacts of the on-load tapchanger and the internal components of the dual-resistor transition circuit are susceptible to damage after repeated switching, shortening the life of the dual-resistor transition circuit. Summary of the Invention

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

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

[0006] Among them, one end of the first main contact and the input end of the first resistance transition branch are used to connect to the first winding tap in the voltage regulating winding of the transformer; one end of the second main contact and the second moving contact of the conversion switch are used to connect to the second winding tap in the voltage regulating winding of the transformer; the static contact of the conversion switch is connected to the input end of the second resistance transition branch; the first moving contact of the conversion switch is connected to the second output end of the first resistance transition branch; the other ends of the first main contact and the second main contact, the first output end of the first resistance transition circuit, and the output end of the second resistance transition circuit are used to connect to the neutral point of the transformer.

[0007] As an improvement to the above scheme, the first resistance transition branch includes: a first switching element and a first transition resistor; the input end of the first switching element is connected to the input end of the first resistance transition branch, the output end of the first switching element and one end of the first transition resistor are connected to the second output end of the first resistance transition branch, and the other end of the first transition resistor is connected to the first output end of the first resistance transition branch.

[0008] As an improvement to the above scheme, the second transition branch includes: a second switching element, a third switching element, and a second transition resistor; one end of the second transition resistor and the input end of the second switching element are connected to the input end of the second resistance transition branch, the other end of the second transition resistor is connected to the input end of the third switching element, and the output ends of the second switching element and the third switching element are connected to the output end of the second resistance transition branch.

[0009] As an improvement to the above scheme, the first switching element, the second switching element, and the third switching element include any one of a single-break vacuum contact, a double-break vacuum contact, and a power electronic element with a controllable on-off function; the power electronic element with a controllable on-off function includes an insulated gate bipolar transistor IGBT and a metal oxide semiconductor field effect transistor MOSFET.

[0010] In a second aspect, an embodiment of the present invention provides a voltage regulation method for a dual-resistance on-load tap changer transition circuit, which uses the dual-resistance 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 switching the first main contact and the second main contact;

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

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

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

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

[0016] The first main contact is disconnected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the first switching element, the transfer switch, and the second switching element;

[0017] The second 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 first switching element and the first transition resistor;

[0018] Switching the transfer switch from the first moving contact conducting state to the second moving contact conducting 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 switching element and the first transition resistor;

[0019] The second switching element is closed and 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 transfer switch and the second switching element;

[0020] The third switch element is closed and turned on, so that 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 transfer switch and the second switch element;

[0021] The first 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 transfer switch and the second switching element;

[0022] The second main contact is closed and turned on, the second winding tap is connected, and the load current flows from the second winding tap through the second main contact 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 first main contact is in the open state, the second main contact and the second switch element are in the closed and conductive state, the first switch element is in the open state, the third switch element is in the closed and conductive state, and the transfer switch is in the second movable contact conductive state, the second winding tap is connected, and the load current flows from the second winding tap through the second main contact and out of the neutral point lead-out terminal;

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

[0026] The second 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 transfer switch, the second transition resistor, and the third switching element;

[0027] The first switching element is closed and turned on, the second winding tap and the first winding tap are both connected, and the load current flows out from the neutral point lead-out end through the first transition resistor and the path where the second switching element is located;

[0028] The third 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 switching element and the first transition resistor;

[0029] Switching the transfer switch from the second moving contact conducting state to the first moving contact conducting state, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the first switching element and the first transition resistor;

[0030] The second switching element is closed and turned on, 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 second switching element;

[0031] The first main contact is turned on, the first winding tap is connected, and the load current flows from the first winding tap through the first main contact and out of 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 contact and out of the neutral point lead-out terminal, the voltage of the first switching element, the second switching element, and the third switching element is zero, and the current of the first switching element, the second switching element, and the third switching element is zero;

[0034] When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the first switching element, the transfer switch, and the second switching element, the voltages of the first switching element, the second switching element, and the third switching element are zero, the current of the third switching element is zero, and the currents of the first switching element and the second switching element are determined according to the current of the dual-resistance 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 first switching element and the first transition resistor, the voltage of the first switching element is zero, and the currents of the second switching element and the third switching element are zero. The voltages of the second switching element and the third switching element are determined according to the current of the dual-resistor on-load tapchanger transition circuit and the resistance value of the first transition resistor, and the current of the first switching element is determined according to the current of the dual-resistor on-load tapchanger transition circuit.

[0037] When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the first switching element and the first transition resistor, the voltage of the first switching element is zero, and the currents of the second switching element and the third switching element are zero. The voltages of the second switching element and the third switching element are determined according to the voltage and current of the dual-resistor on-load tapchanger transition circuit and the resistance value of the first transition resistor, and the current of the first switching element is determined according to the current of the dual-resistor on-load tapchanger 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 transfer switch and the second switching element, the voltages of the first switching element, the second switching element, and the third switching element are zero, and the current of the third switching element is zero. The current of the first switching element is determined based on the voltage of the dual-resistor on-load tap changer transition circuit and the resistance value of the first transition resistor. The current of the second switching element is determined based on the voltage and current of the dual-resistor on-load tap changer transition circuit and the resistance value of the first transition resistor.

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

[0040] 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 transfer switch and the second switching element, the voltages of the first switching element, the second switching element, and the third switching element are zero, and the current of the third switching element is zero. The current of the first switching element is determined by the voltage of the dual-resistance on-load tap changer transition circuit and the resistance value of the first transition resistor. The current of the second switching element is determined by the voltage and current of the dual-resistance on-load tap changer transition circuit and the resistance value of the first transition resistor.

[0041] When the second winding tap is connected and the load current flows out of the neutral point lead-out terminal through the transfer switch and the second switching element, the voltage of the second switching element and the third switching element is zero, and the current of the first switching element and the third switching element is zero. The voltage of the first switching element is determined according to the voltage of the dual-resistance on-load tap changer transition circuit, and the current of the second switching element is determined according to the current of the dual-resistance 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 contact and out of the neutral point lead-out terminal, the voltage of the second switching element and the third switching element is zero, and the current of the first switching element, the second switching element, and the third switching element is zero. The voltage of the first switching element is determined according to the voltage of the transition circuit of the dual-resistance on-load tap changer.

[0043] Compared with the prior art, the beneficial effects of the embodiments of the present invention are: a dual-resistance on-load tap changer transition circuit is provided, including an on-load tap changer, a transfer switch and a dual-resistance transition circuit; the on-load tap changer includes: a first main contact and a second main contact; the dual-resistance transition circuit includes: a first resistance transition branch and a second resistance transition branch; wherein, one end of the first main contact and the input end of the first resistance transition branch are used to be connected to the first winding tap in the voltage regulating winding of the transformer; one end of the second main contact and the second moving contact of the transfer switch are used to be connected to the second winding tap in the voltage regulating winding of the transformer; the static contact of the transfer switch is connected to the input end of the second resistance transition branch; the transfer switch The first moving contact is connected to the second output end of the first resistance transition branch; the other ends of the first main contact and the second main contact, the first output end of the first resistance transition circuit, and the output end of the second resistance transition circuit are used to be connected to the neutral point of the transformer; in an embodiment of the present invention, the second switching element is responsible for breaking the load current, and the first switching element and the third switching element are responsible for breaking the load current superimposed on the inter-stage circulating current. By controlling the on and off of the first main contact, the second main contact, the first switching element, the second switching element, and the third switching element to achieve reciprocating switching, the switching loss of the switching elements (i.e., 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 dual-resistance on-load tap changer transition circuit provided by an embodiment of the present invention;

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

[0048] Figure 4 This is a circuit diagram of the first switching stage of a dual-resistance 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 5This is a circuit diagram of the second switching stage of a dual-resistance 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 dual-resistance 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 dual-resistance 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 This is a circuit diagram of the fifth switching stage of a dual-resistance 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 This is a circuit diagram of the sixth switching stage of a dual-resistance 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 This is a circuit diagram of the seventh switching stage of a dual-resistance 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 dual-resistance 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 dual-resistance 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 dual-resistance 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 dual-resistance 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 dual-resistance 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 dual-resistance on-load tapchanger transition circuit provided by an embodiment of the present invention. The dual-resistance on-load tapchanger transition circuit includes: an on-load tapchanger, a transfer switch T, and a dual-resistance transition circuit; the on-load tapchanger includes: a first main contact MC1 and a second main contact MC2; the dual-resistance transition circuit includes: a first resistor transition branch 21 and a second resistor transition branch 22;

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

[0065] In the embodiment of the present invention, both the first main contact MC1 and the second main contact MC2 are vacuum contacts, which take turns to perform switching tasks, thereby reducing the probability of failure. During the reciprocating switching process of the on-load tap changer, the current is interrupted in turn through the two resistance transition branches, which can 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 a dual-resistance transition circuit. Figure 2 As shown, the first resistance transition branch includes: a first switching element V1 and a first transition resistor R1; the input end of the first switching element V1 is connected to the input end of the first resistance transition branch, the output end of the first switching element V1 and one end of the first transition resistor R1 are connected to the second output end of the first resistance transition branch, and the other end of the first transition resistor R1 is connected to the first output end of the first resistance transition branch.

[0067] The second transition branch includes: a second switching element V2, a third switching element V3, and a second transition resistor R2; one end of the second transition resistor R2 and the input end of the second switching element V2 are connected to the input end of the second resistance transition branch, the other end of the second transition resistor R2 is connected to the input end of the third switching element V3, and the output ends of the second switching element V2 and the third switching element V3 are connected to the output end of the second resistance transition branch.

[0068] In the embodiment of the present invention, the use of two transition resistors (R1, R2) in the dual-resistance transition circuit can reduce the heat generation of a single resistor, facilitate design and installation, and ensure insulation distance. At the same time, among the switching elements (first switching element V1, second switching element V2, and third switching element V3) within the dual-resistance transition circuit 2, during reciprocating switching, the first switching element V1 and the second switching element V2 alternately interrupt the current, which can reduce the number of operations of a single contact and increase the overall service life of the contacts. By controlling the on-off of the first main contact MC1, the second main contact MC2, the first switching element V1, the second switching element V2, and the third switching element V3 according to a certain timing sequence, the on-load tap changer can be switched back and forth. The reciprocating switching timing is reversible, which improves the reliability of the on-load tap changer operation, reduces the switching loss of the switching elements (i.e., the vacuum contacts) in the on-load tap changer, and increases the service life of the dual-resistance transition circuit.

[0069] For the above-mentioned dual-resistance on-load tap-changer transition circuit, the embodiment of the present invention further provides a voltage regulation method for the dual-resistance on-load tap-changer transition circuit, such as Figure 3 As shown in FIG, the specific voltage regulation methods include:

[0070] S11: Controlling the switching of the on-load tap changer between the first winding tap and the second winding tap by switching the first main contact and the second main contact;

[0071] S12: Controlling the connection or disconnection between the second resistance transition branch and the first resistance transition branch and the second main contact by turning on and off the first moving contact and the second moving contact in the switch;

[0072] S13: By turning on and off the first switching element, the second switching element, and the third switching element, the load current is controlled to be disconnected in each branch in the dual-resistance on-load tap changer transition circuit, so that the load current flows from the first winding tap or the second winding tap through the first main contact or the second main contact and out from the neutral point lead-out terminal, thereby adjusting the voltage of each switching element in the dual-resistance transition circuit during the switching process.

[0073] The voltage regulation process of a dual-resistor transition circuit 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 dual-resistor 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.

[0074] In the first switching stage, the first main contact MC1, the second switching element V2 and the first switching element V1 are all in the on state, the third switching element V3 and the second main contact MC2 are in the off state, and when the transfer switch T is in the on state of the first moving contact 11 (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 contact MC1 and out of the neutral point (0) lead-out terminal, as shown in FIG. Figure 4 shown.

[0075] The power supply side of the dual-resistance on-load tap-changer transition circuit can be equivalent to a voltage source and a current source. There is a certain phase difference between the two, which can be specifically expressed as the following formula:

[0076]

[0077] Among them, i n 、u n They represent the instantaneous values of the equivalent current source and equivalent voltage source on the power supply side of the dual-resistance on-load tap-changer transition circuit, I n 、U n They represent the peak values of the equivalent current source and the equivalent voltage source on the power supply side of the dual-resistance on-load tap-changer transition circuit, 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.

[0078] In the first switching phase, the voltage of the first switching element V1, the second switching element V2, and the third switching element V3 is zero, and the current of the first switching element V1, the second switching element V2, and the third switching element V3 is zero. The voltage and current borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0079]

[0080] Among them, U V1 、U V2 、U V3 Respectively represent the voltages borne by the first switching element, the second switching element, and the third switching element, I V1 , I V2 , I V3 Respectively represent the currents borne by the first switching element, the second switching element, and the third switching element.

[0081] Second switching stage: disconnect the first main contact MC1. At this time, the second main contact MC2 remains disconnected, the second switch element V2 and the first switch element V1 remain on, the third switch element V3 remains disconnected, 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) terminal through the first switch element V1, the transfer switch T, and the second switch element V2. Figure 5 shown.

[0082] During the second switching phase, the voltages of the first switching element V1, the second switching element V2, and the third switching element V3 are zero, and the current of the third switching element V3 is zero. The currents of the first switching element V1 and the second switching element V2 are determined by the current of the dual-resistance on-load tapchanger transition circuit. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0083]

[0084] The third switching stage: the first main contact MC1 remains open, the second main contact MC2 remains open, and the second switching element V2 is disconnected. At this time, an arc is generated in the second switching element V2, the first switching element V1 remains on, the third switching element V3 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 first switching element V1 and the first transition resistor R1, as shown in FIG. Figure 6 shown.

[0085] In the third switching phase, the voltage of the first switching element V1 is zero, and the currents of the second and third switching elements V2 and V3 are zero. The voltages of the second and third switching elements V2 and V3 are determined by the current of the dual-resistor on-load tapchanger transition circuit and the resistance value of the first transition resistor R1. The current of the first switching element V1 is determined by the current of the dual-resistor on-load tapchanger transition circuit. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistor transition circuit are as follows:

[0086]

[0087] Here, R1 represents the resistance value of the first transition resistor R1.

[0088] The fourth switching stage: the first main contact MC1 remains disconnected, the second main contact MC2 remains disconnected, the second switching element V2 remains disconnected, the first switching element V1 remains on, and the third switching element V3 remains disconnected. After the arc in the second switching element V2 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 switching 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 switching element V1 is zero, and the currents of the second and third switching elements V2 and V3 are zero. The voltages of the second and third switching elements V2 and V3 are determined by the voltage and current of the dual-resistor on-load tapchanger transition circuit and the voltage of the first transition resistor R1. The current of the first switching element V1 is determined by the current of the dual-resistor on-load tapchanger transition circuit. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistor transition circuit are as follows:

[0090]

[0091] The fifth switching stage: the first main contact MC1 remains open, the second main contact MC2 remains open, the second switch element V2 is closed and turned on, the first switch element V1 remains on, the third switch element V3 remains open, 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) terminal through the transfer switch T and the second switch element V2, as shown in FIG. Figure 8 As shown. At this time, the dual-resistance transition circuit forms a bridge, generating an inter-stage circulating current I c The current flowing through the first switching element V1 is the interstage circulating current I c, the current I flowing through the second switching element V2 v =I N +I c , where I c =U s / R1,U s Indicates the inter-stage voltage of the on-load tapchanger, I N Indicates the load current.

[0092] In the fifth switching phase, the voltages of the first switching element V1 and the second switching element V2 are zero, and the current of the third switching element V3 is zero. The current of the first switching element V1 is determined by the voltage of the dual-resistance on-load tapchanger transition circuit and the resistance value of the first transition resistor R1. The current of the second switching element V2 is determined by the voltage and current of the dual-resistance on-load tapchanger transition circuit and the resistance value of the first transition resistor R1. The current of the third switching element V3 is zero. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0093]

[0094] The sixth switching stage: the first main contact MC1 remains open, the second main contact MC2 remains open, the second switch element V2 remains closed and turned on, the first switch element V1 remains turned on, the third switch element V3 is closed and turned on, the transfer switch T maintains the second moving contact 12 state, the first winding tap (N) and the second winding tap (N+1) are connected, and the load current flows out from the neutral point (0) lead-out terminal through the transfer switch T and the second switch element V2, as shown in FIG. Figure 9 As shown. At this time, the dual-resistance transition circuit forms a bridge, generating an inter-stage circulating current I c The current flowing through the first switching element V1 is the interstage circulating current I c , the current I flowing through the second switching element V2 v =I N +I c .

[0095] In the sixth switching phase, the voltages of the first switching element V1 and the second switching element V2 are zero, the voltage of the third switching element V3 is zero, the current of the first switching element V1 is determined by the voltage of the dual-resistance on-load tapchanger transition circuit and the resistance value of the first transition resistor R1, the current of the second switching element V2 is determined by the voltage and current of the dual-resistance on-load tapchanger transition circuit and the resistance value of the first transition resistor R1, and the current of the third switching element V3 is zero. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0096]

[0097] In the seventh switching stage, the first main contact MC1 remains disconnected, the second main contact MC2 remains disconnected, and the second switch element V2 remains closed and conductive, disconnecting the first switch element V1. The arc in the first switch element V1 is extinguished, the third switch element V3 remains closed and conductive, and the transfer switch T remains in 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) lead-out terminal through the transfer switch T and the second switch element V2, as shown in FIG. Figure 10 shown.

[0098] In the seventh switching phase, the voltage of the first switching element V1 is determined by the voltage of the dual-resistance on-load tapchanger transition circuit. The voltages of the second switching element V2 and the third switching element V3 are zero. The currents of the first switching element V1 and the third switching element V3 are zero. The current of the first switching element V1 is determined by the current of the dual-resistance on-load tapchanger transition circuit. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0099]

[0100] The eighth switching stage: the first main contact MC1 remains open. After the arc in the first switching element V1 is extinguished, the second main contact MC1 is closed and turned on. The second switching element V2 remains closed and turned on. The first switching element V1 remains open. The third switching element V3 remains closed and turned on. The transfer switch T maintains the second moving contact 12 state. The second winding tap (N+1) continues to be connected. The load current flows out from the second winding tap (N+1) through the second main contact 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). Figure 11 shown.

[0101] In the eighth switching phase, the voltage of the first switching element V1 is determined by the voltage of the dual-resistance on-load tapchanger transition circuit. The voltages of the second switching element V2 and the third switching element V3 are zero, and the currents of the first switching element V1, the second switching element V2, and the third switching element V3 are zero. The voltages and currents borne by each switching element (V1, V2, V3) in the dual-resistance transition circuit are as follows:

[0102]

[0103] 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 dual-resistance transition circuit can also be divided into eight switching phases. The specific voltage regulation process is as follows:

[0104] First switching stage: the first main contact remains open, the second main contact remains closed and conductive, the second switching element remains closed and conductive, the first switching element remains open, the third switching 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 contact to the neutral point lead-out terminal;

[0105] Second switching stage: The first main contact remains open, and the second main contact is opened. At this time, the second switching element remains closed and conductive, the first switching element remains open, the third switching 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 transfer switch and the second switching element;

[0106] Third switching stage: The first main contact remains open, the second main contact remains open, and the second switching element is disconnected. At this time, an arc is generated in the second switching element, the first switching element remains open, the third switching 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 transfer switch and the third switching element;

[0107] The fourth switching stage: the first main contact remains disconnected, the second main contact remains disconnected, and the second switching element remains disconnected. After the arc in the second switching element is extinguished, the first switching element is closed and turned on to generate inter-stage circulating current. The third switching element remains closed and turned on, and the transfer switch maintains 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 two paths; the first path is the path where the second winding tap, the transfer switch, the second transition resistor, and the third switching element are located, and the second path is the path where the first winding tap, the second switching element, and the first transition resistor are located; the dual-resistance transition circuit forms a bridge to generate inter-stage circulating current.

[0108] Fifth switching stage: the first main contact remains open, the second main contact remains open, the second switching element remains open, the first switching element remains closed and conductive, the third switching element is disconnected, an arc is generated in the third switching 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 switching element and the first transition resistor;

[0109] Sixth switching stage: the first main contact remains open, the second main contact remains open, the second switching element remains open, the first switching element remains closed and conductive, and the third switching element remains open. After the arc in the third switching element is extinguished, the second moving contact of the transfer switch is opened, and the first moving contact of the transfer switch is turned on (i.e., the transfer switch is switched 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 switching element and the first transition resistor.

[0110] Seventh switching stage: the first main contact remains open, the second main contact remains open, the second switching element is closed and turned on, the first switching element remains closed, the third switching element remains open, the transfer switch remains in 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 second switching element;

[0111] The eighth switching stage: the first main contact is closed and turned on. At this time, the second main contact remains open, the second switching element remains closed and turned on, the first switching element remains closed and turned on, the third switching element remains open, 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 contact and out of 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.

[0112] It should be noted that the voltage and current calculation process of each switching element in the dual-resistance transition circuit in each stage when the on-load tap changer switches from the second winding tap to the first winding tap can be referred to the voltage and current calculation process of each switching element in the dual-resistance transition circuit in each stage when the on-load tap changer switches from the first winding tap to the second winding tap, and will not be repeated here.

[0113] It should be understood that when the internal switching elements (V1, V2, V3) in the dual-resistance on-load tap changer transition circuit are power electronic elements with controllable on-off functions, double-break vacuum contacts, and single-break vacuum contacts, the action timing and voltage regulation method of the switching elements are the same and will not be repeated here.

[0114] In the embodiment of the present invention, the switching tasks of the transition circuit of the dual-resistance on-load tap changer using the first switching element, the second switching element, and the third auxiliary switch are shown in the following table:

[0115]

[0116]

[0117] 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.

[0118] During the reciprocating switching process of the embodiment of the present invention, by setting a timing to adjust the voltage, sufficient time can be reserved for the arc ignition and arc extinguishing processes in the vacuum contact, making the overall switching process safer and more reasonable.

[0119] When the on-load tapchanger switches from the first winding tap (N) to the second winding tap (N+1), the double resistor transition circuit conversion procedure is as follows: Figure 12 As shown;

[0120] When the on-load tapchanger switches from the second winding tap (N+1) to the first winding tap (N), the double resistor transition circuit conversion procedure is as follows: Figure 13 As shown;

[0121] Figure 14 The circuit diagram of the dual-resistor on-load tap-changer transition circuit (which can also be described as a dual-resistor three-vacuum-tube on-load tap-changer reciprocating transition circuit) is formed when the switching elements (V1, V2, V3) in the dual-resistor transition circuit are power electronic elements. Figure 14 As shown, only Figure 2 The switching elements (V1, V2, V3) in the double-resistance 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 dual-resistance transition circuit shown are the same and will not be repeated here.

[0122] Figure 15 The circuit diagram of the dual-resistance on-load tap-changer transition circuit is formed when the switching elements (V1, V2, V3) in the dual-resistance transition circuit are power electronic elements; Figure 15 As shown, only Figure 2 The switching elements (V1, V2, V3) in the double-resistance 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 dual-resistance transition circuit shown are the same and will not be repeated here.

[0123] During the reciprocating switching process of the dual-resistance on-load tap changer transition circuit, the first switching element, the second switching element, and the third switching element take turns to share the switching task, which can effectively reduce the switching loss of the switching element (i.e., the vacuum contact) and extend the service life of the dual-resistance transition circuit. In addition, the switching elements are reasonably distributed, and an optimized transition circuit switching sequence is provided, so that the switching steps are reduced, the element tasks are reasonably distributed, and reciprocating switching and reversible reciprocating switching sequence can be achieved. At the same time, sufficient time can be reserved for the arc ignition and arc extinction processes, thereby improving 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, improves the tolerance when bearing overcurrent and overvoltage, and clarifies the unique characteristics of the switching elements bearing electrical stress during the switching process of the dual-resistance transition circuit, so that it can adapt to different switching requirements.

[0124] 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 dual-resistance on-load tap-changer transition circuit, characterized in that: include: On-load tap-changers, transfer switches and double-resistance transition circuits; The on-load tap changer comprises: a first main contact and a second main contact; the dual-resistance transition circuit comprises: a first resistance transition branch and a second resistance transition branch; Among them, one end of the first main contact and the input end of the first resistance transition branch are used to connect to the first winding tap in the voltage regulating winding of the transformer; one end of the second main contact and the second moving contact of the conversion switch are used to connect to the second winding tap in the voltage regulating winding of the transformer; the static contact of the conversion switch is connected to the input end of the second resistance transition branch; the first moving contact of the conversion switch is connected to the second output end of the first resistance transition branch; the other ends of the first main contact and the second main contact, the first output end of the first resistance transition circuit, and the output end of the second resistance transition circuit are used to connect to the neutral point of the transformer.

2. The dual-resistance on-load tap-changer transition circuit according to claim 1, characterized in that: The first resistance transition branch includes: a first switching element and a first transition resistor; the input end of the first switching element is connected to the input end of the first resistance transition branch, the output end of the first switching element and one end of the first transition resistor are connected to the second output end of the first resistance transition branch, and the other end of the first transition resistor is connected to the first output end of the first resistance transition branch.

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

4. The dual-resistance on-load tap-changer transition circuit according to claim 3, characterized in that: The first switching element, the second switching element, and the third switching element include any one of a single-break vacuum contact, a double-break vacuum contact, and a power electronic element with a controllable on-off function; the power electronic element with a controllable on-off function includes an insulated gate bipolar transistor IGBT and a metal oxide semiconductor field effect transistor MOSFET.

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

6. The voltage regulation method for a dual-resistance on-load tap-changer transition circuit according to claim 5, characterized in that: The method comprises: When the first main contact, the second switching element, and the first switching element are in the on state, the second main contact and the third switching element are in the off state, and the transfer switch is in the first moving contact on state, the first winding tap is connected, and the load current flows from the first winding tap through the first main contact and out of the neutral point lead-out terminal; The first main contact is disconnected, the first winding tap is still connected, and the load current flows out from the neutral point lead-out terminal through the first switching element, the transfer switch, and the second switching element; The second 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 first switching element and the first transition resistor; Switching the transfer switch from the first moving contact conducting state to the second moving contact conducting 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 switching element and the first transition resistor; The second switching element is closed and 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 transfer switch and the second switching element; The third switch element is closed and turned on, so that 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 transfer switch and the second switch element; The first 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 transfer switch and the second switching element; The second main contact is closed and turned on, the second winding tap is connected, and the load current flows from the second winding tap through the second main contact 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 regulation method for a dual-resistance on-load tap-changer transition circuit according to claim 5, characterized in that: The method comprises: When the first main contact is in the open state, the second main contact and the second switch element are in the closed and conductive state, the first switch element is in the open state, the third switch element is in the closed and conductive state, and the transfer switch is in the second movable contact conductive state, the second winding tap is connected, and the load current flows from the second winding tap through the second main contact and out of the neutral point lead-out terminal; The second main contact is disconnected, the second winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the transfer switch and the second switching element; The second 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 transfer switch, the second transition resistor, and the third switching element; The first switching element is closed and turned on, the second winding tap and the first winding tap are both connected, and the load current flows out from the neutral point lead-out end through the first transition resistor and the path where the second switching element is located; The third 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 switching element and the first transition resistor; Switching the transfer switch from the second moving contact conducting state to the first moving contact conducting state, the first winding tap is connected, and the load current flows out from the neutral point lead-out terminal through the first switching element and the first transition resistor; The second switching element is closed and turned on, 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 second switching element; The first main contact is turned on, the first winding tap is connected, and the load current flows from the first winding tap through the first main contact and out of 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 regulation method for a dual-resistance 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 contact and out of the neutral point lead-out terminal, the voltage of the first switching element, the second switching element, and the third switching element is zero, and the current of the first switching element, the second switching element, and the third switching element is zero; When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the first switching element, the transfer switch, and the second switching element, the voltages of the first switching element, the second switching element, and the third switching element are zero, the current of the third switching element is zero, and the currents of the first switching element and the second switching element are determined according to the current of the dual-resistance on-load tap changer transition circuit.

9. The voltage regulation method for a dual-resistance 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 first switching element and the first transition resistor, the voltage of the first switching element is zero, and the currents of the second switching element and the third switching element are zero. The voltages of the second switching element and the third switching element are determined according to the current of the dual-resistor on-load tapchanger transition circuit and the resistance value of the first transition resistor, and the current of the first switching element is determined according to the current of the dual-resistor on-load tapchanger transition circuit. When the first winding tap continues to be connected and the load current flows out of the neutral point lead-out terminal through the first switching element and the first transition resistor, the voltage of the first switching element is zero, and the currents of the second switching element and the third switching element are zero. The voltages of the second switching element and the third switching element are determined according to the voltage and current of the dual-resistor on-load tapchanger transition circuit and the resistance value of the first transition resistor, and the current of the first switching element is determined according to the current of the dual-resistor on-load tapchanger 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 transfer switch and the second switching element, the voltages of the first switching element, the second switching element, and the third switching element are zero, and the current of the third switching element is zero. The current of the first switching element is determined based on the voltage of the dual-resistor on-load tap changer transition circuit and the resistance value of the first transition resistor. The current of the second switching element is determined based on the voltage and current of the dual-resistor on-load tap changer transition circuit and the resistance value of the first transition resistor.

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

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