Overvoltage protection device of single-core asymmetric phase-shifting transformer

Abstract

The invention discloses an overvoltage protection device for a single-core asymmetric phase-shifting transformer. The overvoltage protection device comprises a phase-shifting transformer branch, a first branch switch, a second branch switch and an overvoltage protection circuit, wherein the phase-shifting transformer branch comprises the single-core asymmetric phase-shifting transformer and the first branch switch; a winding of the single-core asymmetric phase-shifting transformer is connected in parallel with a corresponding internal voltage transformer; the lightning arrester branch comprises a lightning arrester and a second branch switch; the external voltage transformer branch comprises an external voltage transformer; when it is judged that the single-core asymmetric phase-shifting transformer does not have overvoltage, the first branch switch is switched on, and the second branch switch is switched off; when it is judged that the single-core asymmetric phase-shifting transformer has the external overvoltage, the first branch switch and the second branch switch are closed; and when the internal voltage transformer detects that the single-core asymmetric phase-shifting transformer has internal overvoltage, the first branch switch and the second branch switch are closed. According to the invention, overvoltage protection can be carried out on the single-core asymmetric phase-shifting transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and particularly relates to an overvoltage protection device for a single-core asymmetric phase-shifting transformer. Background Art

[0002] The large-scale access of new energy has brought many challenges to the power system. Among them, the power flow problem is particularly prominent. The intermittency and uncertainty of new energy make the power flow distribution in the power system more complex and difficult to predict. Traditional power regulation means often seem inadequate when dealing with these new changes. To solve this problem, the phase-shifting transformer, as an effective power flow regulation device, has gradually attracted attention. The phase-shifting transformer can provide a compensation voltage for the line, thereby realizing flexible control of the power flow. Compared with other types of power flow controllers, the phase-shifting transformer has the advantages of low cost and high reliability. The single-core asymmetric phase-shifting transformer is suitable for medium and low voltage lines. It can independently adjust the primary side regulating winding and the secondary side regulating winding, and has flexible voltage combinations. Therefore, compared with other types of phase-shifting transformers, the single-core asymmetric phase-shifting transformer has higher flexibility in power flow regulation. Therefore, it is crucial to study the single-core asymmetric phase-shifting transformer.

[0003] The phase-shifting transformer belongs to electrical equipment. When a fault occurs, it will cause inestimable losses to the power grid. Therefore, it is necessary to study the protection strategy of the phase-shifting transformer. At present, most protection strategies are proposed for overcurrent faults. However, in actual situations, the phase-shifting transformer also faces the problem of overvoltage protection during operation. Due to the voltage fluctuations that may be brought about by the grid connection of new energy and the working characteristics of the phase-shifting transformer itself, overvoltage phenomena occur frequently. In addition, it may also encounter external overvoltages, such as lightning overvoltages. Overvoltage will not only damage the phase-shifting transformer itself, but also may affect the safe and stable operation of the entire power system. Therefore, it is urgent to study the overvoltage protection measures for the overcurrent faults of the single-core asymmetric phase-shifting transformer. Summary of the Invention

[0004] The present invention provides an overvoltage protection device for a single-core asymmetric phase-shifting transformer to solve the technical problem that the existing protection strategy for a single-core asymmetric phase-shifting transformer only targets overcurrent faults and does not target overvoltage faults.

[0005] To solve the above technical problem, an embodiment of the present invention provides an overvoltage protection device for a single-core asymmetric phase-shifting transformer, including: the phase-shifting transformer branch, the lightning arrester branch, and the external voltage transformer branch are connected in parallel;

[0006] The phase-shifting transformer branch includes: a single-core asymmetric phase-shifting transformer and a first branch switch;

[0007] Corresponding internal voltage transformers are connected in parallel to the three-phase exciting windings, the three-phase primary-side regulating windings, and the three-phase secondary-side regulating windings of the single-core asymmetric phase-shifting transformer;

[0008] The arrester branch includes: an arrester and a second branch switch;

[0009] The external voltage transformer branch includes: an external voltage transformer;

[0010] When the absolute value of the voltage detected by the external voltage transformer is not greater than a preset voltage threshold and the internal voltage transformer does not detect an internal overvoltage in the single-core asymmetric phase-shifting transformer, it is determined that there is no overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch is closed, and the second branch switch is opened;

[0011] When the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that there is an external overvoltage in the single-core asymmetric phase-shifting transformer, and the first branch switch and the second branch switch are closed;

[0012] When the internal voltage transformer detects an internal overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch and the second branch switch are closed.

[0013] As a preferred solution, it further includes: a circuit breaker branch;

[0014] The circuit breaker branch is connected in parallel to the phase-shifting transformer branch, the arrester branch, and the external voltage transformer branch respectively;

[0015] The circuit breaker branch includes: a circuit breaker, a first power electronic switch, and a second power electronic switch;

[0016] The first end of the first power electronic switch is connected to the input end of the overvoltage protection device, the second end of the first power electronic switch is connected to the first end of the circuit breaker, the second end of the circuit breaker is connected to the first end of the second power electronic switch, and the second end of the second power electronic switch is connected to the output end of the overvoltage protection device.

[0017] As a preferred solution, the first branch switch includes: a third power electronic switch and a fourth power electronic switch;

[0018] The second branch switch includes: a fifth power electronic switch and a sixth power electronic switch;

[0019] The first terminal of the third power electronic switch is connected to the input terminal of the overvoltage protection device. The second terminal of the third power electronic switch is connected to the first terminal of the single-core asymmetric phase-shifting transformer. The second terminal of the single-core asymmetric phase-shifting transformer is connected to the first terminal of the fourth power electronic switch. The second terminal of the fourth power electronic switch is connected to the output terminal of the overvoltage protection device;

[0020] The first terminal of the fifth power electronic switch is connected to the input terminal of the overvoltage protection device. The second terminal of the fifth power electronic switch is connected to the first terminal of the lightning arrester. The second terminal of the lightning arrester is connected to the first terminal of the sixth power electronic switch. The second terminal of the sixth power electronic switch is connected to the output terminal of the overvoltage protection device.

[0021] As a preferred solution, the circuit breaker branch further includes: a first earthing switch and a second earthing switch;

[0022] The first terminal of the first earthing switch is located between the first power electronic switch and the circuit breaker. The first terminal of the second earthing switch is located between the circuit breaker and the second power electronic switch. The second terminals of the first earthing switch and the second earthing switch are grounded;

[0023] The phase-shifting transformer branch further includes: a third earthing switch and a fourth earthing switch;

[0024] The first terminal of the third earthing switch is located between the third power electronic switch and the single-core asymmetric phase-shifting transformer. The first terminal of the fourth earthing switch is located between the single-core asymmetric phase-shifting transformer and the fourth power electronic switch. The second terminals of the third earthing switch and the fourth earthing switch are grounded.

[0025] As a preferred solution, when the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that there is an external overvoltage in the single-core asymmetric phase-shifting transformer, and the first branch switch and the second branch switch are closed, including:

[0026] When the absolute value of the voltage value detected by the external voltage transformer is greater than the voltage threshold and the voltage value is positive, it is determined that there is an external overvoltage at the input end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is closed, and the sixth power electronic switch is opened;

[0027] When the absolute value of the voltage value detected by the external voltage transformer is greater than the voltage threshold and the voltage value is negative, it is determined that there is an external overvoltage at the output end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is opened, and the sixth power electronic switch is closed.

[0028] Preferably, the internal voltage transformer includes: three first internal voltage transformers, three second internal voltage transformers, and three third internal voltage transformers;

[0029] The first internal voltage transformers are respectively connected in parallel with the three-phase exciting windings of the single-core asymmetric phase-shifting transformer;

[0030] The second internal voltage transformers are respectively connected in parallel with the three-phase primary voltage regulating windings of the single-core asymmetric phase-shifting transformer;

[0031] The second internal voltage transformers are respectively connected in parallel with the three-phase secondary voltage regulating windings of the single-core asymmetric phase-shifting transformer;

[0032] When the exciting winding voltage detected by the first internal voltage transformer, the three-phase primary voltage regulating winding regulating voltage detected by the second internal voltage transformer, and the three-phase secondary voltage regulating winding regulating voltage detected by the second internal voltage transformer simultaneously meet the preset electrical balance three-phase voltage condition and magnetic balance voltage condition, it is determined that the internal voltage transformer does not detect an internal overvoltage in the single-core asymmetric phase-shifting transformer; otherwise, it is determined that the internal voltage transformer detects an internal overvoltage in the single-core asymmetric phase-shifting transformer.

[0033] Preferably, when the line connected to the overvoltage protection device does not require power flow regulation, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch, and the fourth grounding switch are opened.

[0034] Preferably, when the line connected to the overvoltage protection device requires power flow regulation, the third power electronic switch and the fourth power electronic switch are closed, and the first power electronic switch, the second power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch, and the fourth grounding switch are opened.

[0035] Preferably, when a fault occurs in the line connected to the overvoltage protection device, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the fifth power electronic switch, the sixth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch, and the fourth grounding switch are opened.

[0036] Preferably, when a fault occurs in the circuit breaker, the first power electronic switch, the second power electronic switch, the third grounding switch, and the fourth grounding switch are opened, and the third power electronic switch, the fourth power electronic switch, the first grounding switch, and the second grounding switch are closed;

[0037] When a fault occurs in the single-core asymmetric phase-shifting transformer, the third power electronic switch, the fourth power electronic switch, the first grounding switch and the second grounding switch are opened, and the first power electronic switch, the fourth power electronic switch, the third grounding switch and the fourth grounding switch are closed.

[0038] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0039] The present invention provides an overvoltage protection device for a single-core asymmetric phase-shifting transformer, including: a phase-shifting transformer branch, a lightning arrester branch and an external voltage transformer branch; the phase-shifting transformer branch, the lightning arrester branch and the external voltage transformer branch are connected in parallel; the phase-shifting transformer branch includes: a single-core asymmetric phase-shifting transformer and a first branch switch; corresponding internal voltage transformers are connected in parallel to the three-phase exciting windings, the three-phase primary side regulating windings and the three-phase secondary side regulating windings of the single-core asymmetric phase-shifting transformer; the lightning arrester branch includes: a lightning arrester and a second branch switch; the external voltage transformer branch includes: an external voltage transformer; when the absolute value of the voltage detected by the external voltage transformer is not greater than a preset voltage threshold and the internal voltage transformer does not detect an internal overvoltage in the single-core asymmetric phase-shifting transformer, it is determined that there is no overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch is closed, and the second branch switch is opened; when the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that there is an external overvoltage in the single-core asymmetric phase-shifting transformer, and the first branch switch and the second branch switch are closed; when the internal voltage transformer detects an internal overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch and the second branch switch are closed.

[0040] The protection method for the single-core asymmetric phase-shifting transformer in the prior art is mainly proposed for the overcurrent of the phase-shifting transformer. However, the present invention proposes a method for configuring a voltage transformer for monitoring overvoltage faults and a method for quickly switching the access mode of the phase-shifting transformer through a branch switch during overvoltage to realize the overvoltage protection of the single-core asymmetric phase-shifting transformer, effectively solving the problem of equipment damage caused by overvoltage. Description of the Drawings

[0041] Figure 1 is a schematic structural diagram of an overvoltage protection device for a single-core asymmetric phase-shifting transformer provided by an embodiment of the present invention;

[0042] Figure 2 is a schematic installation diagram of an internal voltage transformer of a single-core asymmetric phase-shifting transformer;

[0043] Figure 3 It is a diagram of overvoltage fault monitoring and protection action strategy for a single-core asymmetric phase-shifting transformer;

[0044] Figure 4 It is a diagram of response strategies under the operating states of different devices and lines;

[0045] Figure 5 It is a schematic diagram of lightning rod configuration for a single-core asymmetric phase-shifting transformer. Detailed implementation manners

[0046] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts shall fall within the protection scope of the present application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0048] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means two or more unless otherwise specifically defined.

[0049] Referring to "embodiments" herein means that specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase does not necessarily refer to the same embodiment at various positions in the specification, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0050] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships can exist, for example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0051] In the description of the embodiments of the present application, the term "plurality" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0052] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0053] Embodiment 1

[0054] Please refer to Figure 1 , which is a schematic structural diagram of an overvoltage protection device for a single-core asymmetric phase-shifting transformer provided by an embodiment of the present invention, including: the phase-shifting transformer branch, the arrester branch, and the external voltage transformer branch are connected in parallel;

[0055] The phase-shifting transformer branch includes: a single-core asymmetric phase-shifting transformer and a first branch switch;

[0056] Corresponding internal voltage transformers are connected in parallel on the three-phase exciting winding, the three-phase primary side regulating winding, and the three-phase secondary side regulating winding of the single-core asymmetric phase-shifting transformer;

[0057] The arrester branch includes: an arrester and a second branch switch;

[0058] The external voltage transformer branch includes: an external voltage transformer;

[0059] When the absolute value of the voltage detected by the external voltage transformer is not greater than a preset voltage threshold and the internal voltage transformer does not detect an internal overvoltage in the single-core asymmetric phase-shifting transformer, it is determined that there is no overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch is closed, and the second branch switch is opened;

[0060] When the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that there is an external overvoltage in the single-core asymmetric phase-shifting transformer, and the first branch switch and the second branch switch are closed;

[0061] When the internal voltage transformer detects an internal overvoltage in the single-core asymmetric phase-shifting transformer, the first branch switch and the second branch switch are closed.

[0062] Preferably, it further includes: a breaker branch; the breaker branch is respectively connected in parallel with the phase-shifting transformer branch, the arrester branch and the external voltage transformer branch; the breaker branch includes: a breaker, a first power electronic switch and a second power electronic switch; the first end of the first power electronic switch is connected to the input end of the overvoltage protection device, the second end of the first power electronic switch is connected to the first end of the breaker, the second end of the breaker is connected to the first end of the second power electronic switch, and the second end of the second power electronic switch is connected to the output end of the overvoltage protection device.

[0063] Preferably, the first branch switch includes: a third power electronic switch and a fourth power electronic switch; the second branch switch includes: a fifth power electronic switch and a sixth power electronic switch; the first end of the third power electronic switch is connected to the input end of the overvoltage protection device, the second end of the third power electronic switch is connected to the first end of the single-core asymmetric phase-shifting transformer, the second end of the single-core asymmetric phase-shifting transformer is connected to the first end of the fourth power electronic switch, and the second end of the fourth power electronic switch is connected to the output end of the overvoltage protection device; the first end of the fifth power electronic switch is connected to the input end of the overvoltage protection device, the second end of the fifth power electronic switch is connected to the first end of the arrester, the second end of the arrester is connected to the first end of the sixth power electronic switch, and the second end of the sixth power electronic switch is connected to the output end of the overvoltage protection device.

[0064] Preferably, the breaker branch further includes: a first earthing switch and a second earthing switch; the first end of the first earthing switch is located between the first power electronic switch and the breaker, the first end of the second earthing switch is located between the breaker and the second power electronic switch, and the second ends of the first earthing switch and the second earthing switch are grounded; the phase-shifting transformer branch further includes: a third earthing switch and a fourth earthing switch; the first end of the third earthing switch is located between the third power electronic switch and the single-core asymmetric phase-shifting transformer, the first end of the fourth earthing switch is located between the single-core asymmetric phase-shifting transformer and the fourth power electronic switch, and the second ends of the third earthing switch and the fourth earthing switch are grounded.

[0065] Specifically, the main wiring mode of the overvoltage protection device of the single-core asymmetric phase-shifting transformer of the present invention is as Figure 1As shown in the figure, the main wiring mainly includes three parallel branches: the breaker BK branch, the phase-shifting transformer branch, and the arrester branch. The breaker BK branch, the phase-shifting transformer branch, and the arrester branch are respectively provided with a first branch switch, a second branch switch, and a third branch switch. All branch switches each have two power electronic switches, one on the input side and one on the output side.

[0066] Among them, the first branch switch includes: a first power electronic switch K11 (located on the input side) and a second power electronic switch K12 (located on the output side); the second branch switch includes: a third power electronic switch K21 (located on the input side) and a fourth power electronic switch K22 (located on the output side); the third branch switch includes: a fifth power electronic switch K31 (located on the input side) and a sixth power electronic switch K32 (located on the output side). The power electronic switch can achieve rapid turn-off, thereby realizing the switching of the connection line mode of the phase-shifting transformer. The phase-shifting transformer equipment and the line are protected by changing the connection line mode of the phase-shifting transformer.

[0067] In a specific embodiment: when the breaker BK branch is connected to the line and operates stably, the power electronic switch of this branch is closed, that is, the mechanical switch of the current-limiting resistance branch of the power electronic switch is closed, and the mechanical switch of the anti-parallel thyristor branch is opened. When switching from the breaker BK branch connected to the line to the phase-shifting transformer branch connected to the line, it is necessary to disconnect the power electronic switch of the breaker BK branch and close the power electronic switch of the phase-shifting transformer branch. The specific operation process is as follows, and the switching of other connection methods follows the same switching principle.

[0068] 1) Simultaneously close the mechanical switches of the anti-parallel thyristor branches of the power electronic switches on both sides of the breaker BK branch;

[0069] 2) Simultaneously close the mechanical switches of the current-limiting resistance branches of the power electronic switches on both sides of the single-core asymmetric phase-shifting transformer branch;

[0070] 3) Simultaneously disconnect the mechanical switches of the current-limiting resistance branches of the power electronic switches on both sides of the breaker BK branch to complete the switching.

[0071] The breaker BK branch is provided with two sets of grounding devices. The grounding device includes a grounding switch and a grounding wire. Whether the two sides of the breaker BK are connected to the ground is controlled by the first grounding switch GS1 and the second grounding switch GS2. The first grounding switch GS1 and the second grounding switch GS2 are respectively located between the breaker BK and the power electronic switch K11 and between the breaker BK and the power electronic switch K12.

[0072] The phase-shifting transformer branch is also provided with two sets of grounding devices, which are located on both sides of the phase-shifting transformer respectively, and the third grounding switch GS3 and the fourth grounding switch GS4 are used to control whether both sides of the phase-shifting transformer are connected to the ground. In actual situations, when power equipment cuts off the line, there may be equipment circulating current inside the equipment. At this time, when maintenance personnel carry out maintenance, it is very likely to endanger the personal safety of the maintenance personnel. To solve this problem, the present invention is equipped with grounding devices on both sides of the circuit breaker BK and the phase-shifting transformer. When the circuit breaker BK or the phase-shifting transformer cuts off the line for maintenance, the grounding switches on both sides of the power equipment are closed to release the equipment circulating current to the ground, ensuring the personal safety of the maintenance personnel.

[0073] Preferably, when the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that there is an external overvoltage in the single-core asymmetric phase-shifting transformer, and the first branch switch and the second branch switch are closed, including: when the absolute value of the voltage value detected by the external voltage transformer is greater than the voltage threshold and the voltage value is positive, it is determined that there is an external overvoltage at the input end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is closed, and the sixth power electronic switch is disconnected; when the absolute value of the voltage value detected by the external voltage transformer is greater than the voltage threshold and the voltage value is negative, it is determined that there is an external overvoltage at the output end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is disconnected, and the sixth power electronic switch is closed.

[0074] Specifically, to solve the problem that the external line overvoltage damages the phase-shifting transformer, an external voltage transformer VT0 is installed outside the three parallel branches connected to the phase-shifting transformer to monitor the external voltage of the equipment. When an external line overvoltage occurs, it provides a fault criterion for the external line overvoltage protection device. The external line overvoltage mainly refers to the lightning arrester branch, which includes a lightning arrester connected to the ground and two sets of power electronic switches K31 and K32. Set the voltage limit value of the external voltage transformer VT0. By judging whether the voltage value monitored by the external voltage transformer VT0 exceeds the voltage limit value, when it exceeds the voltage limit value, it is judged that an overvoltage fault occurs in the external line, and then the external line overvoltage protection action is carried out. The external line overvoltage includes various types such as lightning overvoltage.

[0075] Such as Figure 1As shown in the figure, the external voltage transformer VT0 is connected in parallel across the phase-shifting transformer. Under normal operating conditions of the line, there will be no large voltage difference between the voltages on both sides. However, when an overvoltage occurs on the external line on one side, a large voltage difference will appear across the phase-shifting transformer. When overvoltage occurs on different sides, the external voltage transformer VT0 will show different monitoring results. When an overvoltage occurs at the input end, the external voltage transformer VT0 shows a positive value; when a lightning overvoltage occurs at the output end, it shows a negative value. Based on the positive and negative values and amplitudes of the voltages fed back by the external voltage transformer VT0, it is determined whether an external overvoltage has occurred and on which side the overvoltage has occurred, thereby controlling the opening and closing of the power electronic switches K31 and K32 of the arrester branch. When a lightning overvoltage occurs at the input end, K31 closes and K32 opens; when a lightning overvoltage occurs at the output end, K31 opens and K32 closes. By controlling the closing of the power electronic switch, the external overvoltage on the line is discharged to the ground through the arrester, thereby protecting the phase-shifting transformer equipment.

[0076] Preferably, the internal voltage transformer includes: three first internal voltage transformers, three second internal voltage transformers, and three third internal voltage transformers; the first internal voltage transformers are respectively connected in parallel with the three-phase exciting windings of the single-core asymmetric phase-shifting transformer; the second internal voltage transformers are respectively connected in parallel with the three-phase primary side regulating windings of the single-core asymmetric phase-shifting transformer; the second internal voltage transformers are respectively connected in parallel with the three-phase secondary side regulating windings of the single-core asymmetric phase-shifting transformer; when the exciting winding voltage detected by the first internal voltage transformer, the regulating voltage of the three-phase primary side regulating winding detected by the second internal voltage transformer, and the regulating voltage of the three-phase secondary side regulating winding detected by the second internal voltage transformer simultaneously meet the preset electrical balance three-phase voltage condition and magnetic balance voltage condition, it is determined that the internal voltage transformer does not detect an internal overvoltage in the single-core asymmetric phase-shifting transformer; otherwise, it is determined that the internal voltage transformer detects an internal overvoltage in the single-core asymmetric phase-shifting transformer.

[0077] Specifically, in addition to the harm of overvoltage on the external line, the phase-shifting transformer may also have an internal overvoltage fault. To solve this problem, the present invention also equips the phase-shifting transformer with an internal voltage transformer. Please refer to Figure 2 , which is a schematic installation diagram of the internal voltage transformer of the single-core asymmetric phase-shifting transformer. As Figure 2 shown, the internal voltage situation of the phase-shifting transformer is monitored through the internal voltage transformer, providing a criterion for internal overvoltage protection. Since the voltage transformer is installed in parallel, there is no need to change the structure of the phase shifter, nor to consider the installation space for the voltage transformer inside the phase-shifting transformer, which has the characteristic of high installation flexibility.

[0078] Three first voltage transformers VT12, VT23 and VT31 are installed in parallel on the three-phase exciting winding to monitor the exciting winding voltages U12, U23 and U31; three second voltage transformers VTSA, VTSB and VTSC are installed in parallel on the three-phase primary side regulating winding to monitor the three-phase primary side regulating winding regulating voltages ΔUSA, ΔUSB and ΔUSC; three third voltage transformers VTLA, VTLB and VTLC are installed in parallel on the three-phase secondary side regulating winding to monitor the three-phase secondary side regulating winding regulating voltages ΔULA, ΔULB and ΔULC.

[0079] According to Kirchhoff's voltage law and the principle of electromagnetic induction, the following electrical balance voltage relationship and magnetic balance voltage relationship exist:

[0080] 1) Electrical balance voltage relationship: When the single-core asymmetric phase-shifting transformer is operating normally, according to Kirchhoff's voltage law, the following electrical balance three-phase voltage relationship exists:

[0081]

[0082] When overvoltage occurs, fault voltages UEVA, UEVB and UEVC will be generated to break the original voltage balance, and the following three-phase voltage relationship will appear:

[0083]

[0084] 2) Magnetic balance voltage relationship: When the single-core asymmetric phase-shifting transformer is operating normally, according to the principle of electromagnetic induction, the following magnetic balance voltage relationship exists:

[0085]

[0086] When overvoltage occurs, fault voltages UMV11, UMV12, UMV21, UMV22, UMV31 and UMV32 will be generated to break the original voltage balance, and the following voltage relationship will appear:

[0087]

[0088] Among them, NC is the number of turns of the exciting winding, NSA, NSB and NSC respectively represent the number of turns of the three-phase primary side regulating winding connected to the line, and NLA, NLB and NLC respectively represent the number of turns of the three-phase secondary side regulating winding connected to the line.

[0089] When the line is operating normally, the values of the fault voltages UEVA, UEVB, UEVC, UMV11, UMV12, UMV21, UMV22, UMV31 and UMV32 are all zero. A fault voltage limit value is set. According to whether the values of the fault voltages UEVA, UEVB, UEVC, UMV11, UMV12, UMV21, UMV22, UMV31 and UMV32 are zero and whether they exceed the limit value, it is judged whether there is an overvoltage fault inside the phase-shifting transformer. When an overvoltage fault occurs inside the phase-shifting transformer, the phase-shifting transformer is cut out by controlling the opening and closing of the power electronic switches of each branch, so as to realize the protection of the phase-shifting transformer. Please refer to Figure 3 , which is a diagram of the overvoltage fault monitoring and protection action strategy for a single-core asymmetric phase-shifting transformer.

[0090] Preferably, when the line connected to the overvoltage protection device does not need to perform power flow regulation, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

[0091] Preferably, when the line connected to the overvoltage protection device needs to perform power flow regulation, the third power electronic switch and the fourth power electronic switch are closed, and the first power electronic switch, the second power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

[0092] Preferably, when a fault occurs in the line connected to the overvoltage protection device, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the fifth power electronic switch, the sixth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

[0093] Preferably, when a fault occurs in the circuit breaker, the first power electronic switch, the second power electronic switch, the third grounding switch and the fourth grounding switch are opened, and the third power electronic switch, the fourth power electronic switch, the first grounding switch and the second grounding switch are closed; when a fault occurs in the single-core asymmetric phase-shifting transformer, the third power electronic switch, the fourth power electronic switch, the first grounding switch and the second grounding switch are opened, and the first power electronic switch, the fourth second power electronic switch, the third grounding switch and the fourth grounding switch are closed.

[0094] Specifically, the internal overvoltage fault of the phase-shifting transformer and the external overvoltage fault of the line are only two operating states of the line or equipment. The wiring method proposed in the present invention can also consider various actual operating conditions such as line maintenance, whether the line needs power flow regulation, equipment fault repair, and direct lightning strike, and can make response strategies for each operating condition, that is, by controlling the power electronic switch to realize the access and disconnection of each device. Please refer to Figure 4 , which is the response strategy diagram for different device and line operating states. As Figure 4 shown, the specific operating conditions of the line and equipment, and the response strategies for each operating condition mainly include the following aspects:

[0095] 1) When the line is operating normally and no power flow regulation is required: The breaker BK branch is connected to the line, that is, the power electronic switches K11 and K12 of this branch are closed, and the grounding switches GS1 and GS2 are opened; the phase-shifting transformer branch is cut out, that is, the power electronic switches K21 and K22 of this branch are opened, and the grounding switches GS3 and GS4 are opened.

[0096] 2) When the line needs power flow regulation: The phase shifter branch is connected to the line, that is, the power electronic switches K21 and K22 of this branch are closed, and the grounding switches GS3 and GS4 are opened; the breaker BK branch is cut out, that is, the power electronic switches K11 and K12 of this branch are opened, and the grounding switches GS1 and GS2 are opened.

[0097] 3) When the breaker fails and needs to be repaired: The phase-shifting transformer branch is connected to the line, that is, the power electronic switches K21 and K22 of this branch are closed, and the grounding switches GS3 and GS4 are opened; the breaker BK branch is cut out for maintenance, that is, the power electronic switches K11 and K12 of this branch are opened, and the grounding switches GS1 and GS2 are closed, avoiding the generation of circulating current in the equipment during maintenance and ensuring the personal safety of maintenance personnel; adjust the gear according to the power flow regulation requirement, that is, adjust the phase-shifting transformer to the corresponding gear when power flow regulation is required, and adjust the phase-shifting transformer to the zero gear when power flow regulation is not required.

[0098] 4) When the phase-shifting transformer has an overvoltage fault or other conditions and needs to be cut out for repair or treatment: The phase-shifting transformer branch is cut out, that is, the power electronic switches K21 and K22 of this branch are opened, and the grounding switches GS3 and GS4 are closed; the breaker BK branch is connected to the line, that is, the power electronic switches K11 and K12 of this branch are closed, and the grounding switches GS1 and GS2 are opened; when the power flow regulation requirement is small, the breaker BK is closed and the line is conducted; when the power flow regulation requirement is large, the breaker is opened and the line is cut off and powered off.

[0099] 5) When encountering external line overvoltages including lightning overvoltages: When an external overvoltage at the input end is detected, the power electronic switch K31 of the arrester branch near the input end closes, and the power electronic switch K32 on the other side opens; when an external overvoltage at the output end is detected, the power electronic switch K32 of the arrester branch near the output end closes, and the power electronic switch K31 on the other side opens.

[0100] 6) When the phase-shifting transformer is struck by direct lightning: Please refer to Figure 5 , which is a schematic diagram of the lightning rod configuration for a single-core asymmetric phase-shifting transformer. A lightning rod is installed on the outer shell of the single-core asymmetric phase-shifting transformer equipment. When struck by direct lightning, the lightning is conducted into the ground, thus avoiding the harm of direct lightning.

[0101] 7) When the line needs to be repaired: The power electronic switches K11 and K12 of the breaker BK branch close; the breaker BK opens; the remaining power electronic switches and all earthing switches are opened, cutting off the power supply of the line.

[0102] Thus, the present invention provides an overvoltage protection device for a single-core asymmetric phase-shifting transformer. Through the present invention, the following beneficial effects can be achieved:

[0103] 1) Traditional protection methods are mainly proposed for overcurrent in the phase-shifting transformer, while the present invention proposes a voltage transformer configuration method that can reliably monitor overvoltage faults and a method for quickly switching the access mode of the phase-shifting transformer during overvoltage to achieve protection, effectively solving the problem of equipment damage caused by overvoltage.

[0104] 2) The voltage transformers are installed in parallel, so the voltage transformer configuration inside the phase-shifting transformer does not need to consider the space limitation of the phase-shifting transformer, having the advantage of high installation flexibility.

[0105] 3) The present invention fully considers various overvoltage situations such as internal overvoltage of the phase-shifting transformer, external line overvoltage, and lightning overvoltage, and provides coping strategies for each overvoltage, which can effectively protect the phase-shifting transformer.

[0106] 4) The new connection method of the phase-shifting transformer proposed by the present invention also fully considers various equipment and line operation situations such as line maintenance, phase-shifting transformer fault removal, normal line operation, line power flow regulation required, direct lightning strike on the phase-shifting transformer, and breaker fault repair, and gives the switch action strategies for each operation situation, which can effectively cope with various power system scenarios.

[0107] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An overvoltage protection device for a single-core asymmetric phase-shifting transformer, characterized in that: include: Phase-shifting transformer branch, lightning arrester branch and external voltage transformer branch; The phase-shifting transformer branch, the lightning arrester branch and the external voltage transformer branch are connected in parallel; The phase-shifting transformer branch comprises: a single-core asymmetric phase-shifting transformer and a first branch switch; The three-phase excitation winding, the three-phase first-side voltage regulating winding and the three-phase last-side voltage regulating winding of the single-core asymmetric phase-shifting transformer are all connected in parallel with corresponding internal voltage transformers; The arrester branch includes: an arrester and a second branch switch; The external voltage transformer branch includes: an external voltage transformer; When the absolute value of the voltage detected by the external voltage transformer is not greater than the preset voltage threshold, and the internal voltage transformer does not detect the existence of internal overvoltage in the single-core asymmetric phase-shifting transformer, it is determined that the single-core asymmetric phase-shifting transformer does not have overvoltage, the first branch switch is closed, and the second branch switch is opened; When the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that the single-core asymmetric phase-shifting transformer has an external overvoltage, and the first branch switch and the second branch switch are closed; When the internal voltage transformer detects that the single-core asymmetric phase-shifting transformer has an internal overvoltage, the first branch switch and the second branch switch are closed.

2. The overvoltage protection device for a single-core asymmetric phase-shifting transformer according to claim 1, characterized in that: Also includes: Circuit breaker branch; The circuit breaker branch is connected in parallel with the phase-shifting transformer branch, the lightning arrester branch and the external voltage transformer branch respectively; The circuit breaker branch comprises: a circuit breaker, a first power electronic switch and a second power electronic switch; The first end of the first power electronic switch is connected to the input end of the overvoltage protection device, the second end of the first power electronic switch is connected to the first end of the circuit breaker, the second end of the circuit breaker is connected to the first end of the second power electronic switch, and the second end of the second power electronic switch is connected to the output end of the overvoltage protection device.

3. The overvoltage protection device for a single-core asymmetric phase-shifting transformer according to claim 2, characterized in that: The first branch switch includes: a third power electronic switch and a fourth power electronic switch; The second branch switch includes: a fifth power electronic switch and a sixth power electronic switch; The first end of the third power electronic switch is connected to the input end of the overvoltage protection device, the second end of the third power electronic switch is connected to the first end of the single-core asymmetric phase-shifting transformer, the second end of the single-core asymmetric phase-shifting transformer is connected to the first end of the fourth power electronic switch, and the second end of the fourth power electronic switch is connected to the output end of the overvoltage protection device; The first end of the fifth power electronic switch is connected to the input end of the overvoltage protection device, the second end of the fifth power electronic switch is connected to the first end of the lightning arrester, the second end of the lightning arrester is connected to the first end of the sixth power electronic switch, and the second end of the sixth power electronic switch is connected to the output end of the overvoltage protection device.

4. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 3, characterized in that: The circuit breaker branch further includes: a first grounding switch and a second grounding switch; The first end of the first grounding switch is located between the first power electronic switch and the circuit breaker, the first end of the second grounding switch is located between the circuit breaker and the second power electronic switch, and the second ends of the first grounding switch and the second grounding switch are grounded; The phase-shifting transformer branch further includes: a third grounding switch and a fourth grounding switch; The first end of the third grounding switch is located between the third power electronic switch and the single-core asymmetric phase-shifting transformer, the first end of the fourth grounding switch is located between the single-core asymmetric phase-shifting transformer and the fourth power electronic switch, and the second ends of the third grounding switch and the fourth grounding switch are grounded.

5. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 4, characterized in that: When the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold, it is determined that the single-core asymmetric phase-shifting transformer has an external overvoltage, and the first branch switch and the second branch switch are closed, including: When the absolute value of the voltage value detected by the external voltage transformer is greater than the voltage threshold and the voltage value is a positive value, it is determined that an external overvoltage exists at the input end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is closed, and the sixth power electronic switch is opened; When the absolute value of the voltage detected by the external voltage transformer is greater than the voltage threshold and the voltage value is a negative value, it is determined that an external overvoltage exists at the output end of the single-core asymmetric phase-shifting transformer, the fifth power electronic switch is disconnected, and the sixth power electronic switch is closed.

6. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 5, characterized in that: The internal voltage transformer comprises: three first internal voltage transformers, three second internal voltage transformers and three third internal voltage transformers; The first internal voltage transformers are respectively connected in parallel with the three-phase excitation windings of the single-core asymmetric phase-shifting transformer; The second internal voltage transformer is respectively connected in parallel with the three-phase primary-side voltage regulating windings of the single-core asymmetric phase-shifting transformer; The second internal voltage transformer is respectively connected in parallel with the three-phase terminal voltage regulating windings of the single-core asymmetric phase-shifting transformer; When the excitation winding voltage detected by the first internal voltage transformer, the three-phase first-side regulating winding regulating voltage detected by the second internal voltage transformer, and the three-phase last-side regulating winding regulating voltage detected by the second internal voltage transformer simultaneously meet the preset electrical balance three-phase voltage condition and magnetic balance voltage condition, it is determined that the internal voltage transformer has not detected the existence of internal overvoltage in the single-core asymmetric phase-shifting transformer; otherwise, it is determined that the internal voltage transformer has detected the existence of internal overvoltage in the single-core asymmetric phase-shifting transformer.

7. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 6, characterized in that: When the line connected to the overvoltage protection device does not need to perform power flow regulation, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

8. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 7, characterized in that: When the line connected to the overvoltage protection device needs to perform power flow regulation, the third power electronic switch and the fourth power electronic switch are closed, and the first power electronic switch, the second power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

9. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 8, characterized in that: When a fault occurs in the line to which the overvoltage protection device is connected, the first power electronic switch and the second power electronic switch are closed, and the third power electronic switch, the fourth power electronic switch, the fifth power electronic switch, the sixth power electronic switch, the first grounding switch, the second grounding switch, the third grounding switch and the fourth grounding switch are opened.

10. The overvoltage protection device for a single-core asymmetrical phase-shifting transformer according to claim 9, characterized in that: When the circuit breaker fails, the first power electronic switch, the second power electronic switch, the third grounding switch and the fourth grounding switch are disconnected, and the third power electronic switch, the fourth power electronic switch, the first grounding switch and the second grounding switch are closed; When the single-core asymmetric phase-shifting transformer fails, the third power electronic switch, the fourth power electronic switch, the first grounding switch and the second grounding switch are disconnected, and the first power electronic switch, the fourth power electronic switch, the third grounding switch and the fourth grounding switch are closed.

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