Harmonic switching method for converter transformer vacuum on-load tap changer

Abstract

The application discloses a harmonic switching method of a converter transformer vacuum on-load tap changer, and comprises the following steps: setting test parameters of harmonic current breaking test according to the structural features of the converter transformer vacuum on-load tap changer; selecting harmonic components according to the harmonic current frequency spectrum of the converter transformer application site, and designing a high-frequency harmonic operating mechanism; controlling the closing and breaking of a vacuum arc-extinguishing chamber through the high-frequency harmonic operating mechanism to perform harmonic switching, so as to verify the influence of the test current value when the harmonic components change the breaking time on the breaking performance of the vacuum arc-extinguishing chamber; and the high-frequency harmonic operating mechanism is designed, so that whether the on-load tap changer can bear the harmonic current in the power grid system is effectively examined.

Description

Technical Field

[0001] This invention relates to the technical field of tap changers, and more particularly to a harmonic switching method for a converter-to-vacuum on-load tap changer. Background Technology

[0002] With the development of flexible DC technology, the operating conditions of on-load tap changers switching with harmonic currents are becoming increasingly prominent, which places higher demands on the reliability of tap changers. Currently, IEC and GB standards are based on research on conventional DC systems and do not propose load switching test requirements with harmonic currents. Summary of the Invention

[0003] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution, including: setting test parameters for harmonic current interruption test based on the structural characteristics of the converter transformer vacuum on-load tap changer; selecting harmonic components based on the harmonic current spectrum at the converter transformer application site and designing a high-frequency harmonic operation mechanism; and controlling the closing and opening of the vacuum interrupter through the high-frequency harmonic operation mechanism to perform harmonic switching, so as to verify the influence of harmonic components on the interruption performance of the vacuum interrupter when changing the test current value at the interruption time.

[0006] As a preferred embodiment of the harmonic switching method for the converter-vacuum on-load tap changer described in this invention, the test parameters include test voltage, test current, number of tests, and test current value at the time of interruption.

[0007] In a preferred embodiment of the harmonic switching method for the converter-vacuum on-load tap changer described in this invention, the test voltage includes:

[0008] U = U L +R×I L

[0009] Where U is the test voltage, U L R is the voltage level, R is the transition resistance, and I is the voltage level. L This is the load current.

[0010] As a preferred embodiment of the harmonic switching method for the converter-vacuum on-load tap changer described in this invention, the test current includes:

[0011] I = 0.5 × (IL +U L / R)

[0012] Where I is the test current.

[0013] As a preferred embodiment of the harmonic switching method of the converter-vacuum on-load tap changer described in this invention, the harmonic components include superimposed 5th and 7th harmonic currents, the amplitude of which is adjustable from 0 to 230A.

[0014] As a preferred embodiment of the harmonic switching method for the converter-vacuum on-load tap changer described in this invention, it further includes: controlling the amplitude, frequency, and phase angle of the 5th and 7th harmonic currents superimposed on the fundamental wave to meet the requirements of the required test current.

[0015] As a preferred embodiment of the harmonic switching method of the converter-vacuum on-load tap changer described in this invention, the method includes: switching using a power grid test power supply or a short-circuit generator via a high-frequency harmonic operation mechanism, with a vacuum interrupter connected in series in the switching circuit, and the power factor of the switching circuit power supply being less than or equal to 0.15.

[0016] As a preferred embodiment of the harmonic switching method for the converter-vacuum on-load tap changer described in this invention, the high-frequency harmonic operating mechanism includes a harmonic current source, a fundamental power supply, an inverter, and an isolation transformer; a 220V power electronic inverter is used to form the harmonic current source, and a bypass resistor is provided next to the harmonic current source; the harmonic current is injected by stepping up the voltage through the isolation transformer; wherein the turns ratio of the isolation transformer is 1:10, the rated voltage on the high-voltage side is 7.56kV, and the rated voltage on the low-voltage side is 756V.

[0017] As a preferred embodiment of the harmonic switching method of the converter-vacuum on-load tap changer described in this invention, the method includes: when the vacuum interrupter is closed, the currents of the harmonic current source and the fundamental power source flow through the vacuum interrupter; when the vacuum interrupter is open, the test current flows through the parallel resistor.

[0018] The beneficial effects of the present invention are as follows: By designing a high-frequency harmonic operation mechanism, the present invention effectively tests whether an on-load tap changer can withstand harmonic currents in the power grid system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0020] Figure 1 This is a schematic diagram of the on-load tap changer topology switching test circuit for the harmonic switching method of the converter-to-vacuum on-load tap changer described in the first embodiment of the present invention. Detailed Implementation

[0021] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] This invention is described in detail with reference to the schematic diagrams. When describing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0025] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Example 1

[0028] This embodiment provides a harmonic switching method for a converter-to-vacuum on-load tap changer, including:

[0029] S1: Based on the structural characteristics of the on-load tap changer of the converter transformer vacuum, set the test parameters for the harmonic current interruption test.

[0030] Based on the structural characteristics of the on-load tap changer of the converter transformer vacuum system, the key parameters during the switching process mainly include transfer interruption current, power frequency recovery voltage, transfer closing current, and closing voltage. The most severe situation for the vacuum interrupter during on-load tap changer switching is the superposition of the rated load current and the circulating current during the switching process. Similarly, the most severe situation for the vacuum interrupter during on-load tap changer switching is the superposition of the stage voltage and the voltage across the transition resistor. Specifically, the test parameters for the harmonic current interruption test are set (test voltage, test current, number of tests, and test current value at the interruption time):

[0031] Among them, (1) test voltage:

[0032] U = U L +R×I L

[0033] Where U is the test voltage, U L R is the voltage level, R is the transition resistance, and I is the voltage level. L This is the load current.

[0034] (2) Test current:

[0035] I = 0.5 × (I L +U L / R)

[0036] Where I is the test current.

[0037] The required test parameters are for verifying the harmonic current switching capability of the vacuum on-load tap changer under the most severe operating conditions.

[0038] S2: Select harmonic components based on the harmonic current spectrum at the converter transformer application site, and design a high-frequency harmonic operation mechanism.

[0039] Based on the harmonic current spectrum at the converter transformer application site, the amplitude of harmonic components above the 50th order is relatively small. The typical harmonic content with the highest proportion is usually the 5th and 7th harmonics, which is the harmonic content selected in this embodiment. Specifically, the harmonic content selected in this embodiment is: superimposed 5th and 7th harmonic currents, with the amplitude of the 5th and 7th harmonic currents adjustable from 0 to 230A.

[0040] The required test current is met by controlling the amplitude, frequency, and phase angle of the 5th and 7th harmonic currents superimposed on the fundamental wave.

[0041] Furthermore, a high-frequency harmonic operation mechanism is designed, which includes a harmonic current source, a fundamental power supply, an inverter, and an isolation transformer.

[0042] Specifically, (1) In this embodiment, a 220V power electronic inverter is used to form a harmonic current source, and there is a bypass resistor next to the harmonic current source; the harmonic current source can output a 5th harmonic current with an amplitude of 223A and a 7th harmonic current with an amplitude of 133A (or can be adjusted to other amplitudes).

[0043] (2) Inject harmonic current by stepping up the voltage through an isolation transformer; wherein the turns ratio of the isolation transformer is 1:10, the rated voltage on the high voltage side is 7.56kV, and the rated voltage on the low voltage side is 756V.

[0044] (3) The inverter uses IGBTs to form a single-phase H-bridge circuit.

[0045] A resistor is connected in parallel across the vacuum interrupter as a freewheeling current. When the vacuum interrupter is interrupted, the freewheeling current flows through the resistor. The resistance value is selected such that when the freewheeling current flows through the resistor, the voltage drop across the resistor does not exceed the high-voltage bus voltage.

[0046] When the vacuum interrupter is closed, the currents from the harmonic current source and the fundamental current source flow through the vacuum interrupter. When the vacuum interrupter is open, the test current flows through the parallel resistor.

[0047] Preferably, when the fundamental power supply impedance is not less than the parallel resistance value, the requirement of harmonic backflow into the power grid can be met regardless of whether the vacuum interrupter is closed.

[0048] S3: Harmonic switching is achieved by controlling the opening and closing of the vacuum interrupter through a high-frequency harmonic operation mechanism, in order to verify the effect of changing the test current value at the breaking time of the harmonic component on the breaking performance of the vacuum interrupter.

[0049] The switching is performed using a power grid test power supply or a short-circuit generator via a high-frequency harmonic operating mechanism. A vacuum interrupter is connected in series in the switching circuit, and the power factor of the switching circuit power supply is less than or equal to 0.15.

[0050] Example 2

[0051] To verify the effectiveness of the technology used in this method, this embodiment selects this method to conduct a harmonic switching test to verify the actual effect of this method.

[0052] Set the test parameters for the harmonic current interruption test:

[0053] Test voltage: 7560V; Test current: 1718A; Number of tests: 3000; Test current value at the time of interruption: 3A / us.

[0054] This embodiment uses a typical on-load tap changer topology as an example to test V1. Figure 1 In the table, X represents the connection that needs to be disconnected, R is the external resistor, R1 and R2 are resistors, R1 needs to be shorted, N is the time, A and B are the circuit switches, V1 and V2 are the test power supplies, T1 and T2 are the placement locations of the vacuum interrupter, and C is the high-frequency harmonic operation mechanism. The switching results are shown in Table 1.

[0055] Table 1: Switching Results.

[0056] Number of trials Transfer current half-cycle Steepness at zero point 0 times 112ms 15.73A / us 1000 times 127ms 12.1A / us 2000 times 263ms 7.6A / us 3000 times 480ms 1.2A / us

[0057] It can be seen that the half-cycle of the transfer current increases significantly and the zero-crossing steepness decreases, which meets the requirements of the load switching test.

[0058] It should be recognized that embodiments of the present invention can be implemented or carried out by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer-readable storage medium. The method can be implemented using standard programming techniques—including a non-transitory computer-readable storage medium configured with a computer program, wherein such a storage medium causes the computer to operate in a specific and predefined manner—according to the methods and drawings described in the specific embodiments. Each program can be implemented in a high-level procedural or object-oriented programming language to communicate with the computer system. However, if desired, the program can be implemented in assembly or machine language. In any case, the language can be a compiled or interpreted language. Furthermore, for this purpose, the program can run on a programmed application-specific integrated circuit (ASIC).

[0059] Furthermore, the procedures described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by the context. The procedures described herein (or variations and / or combinations thereof) may be executed under the control of one or more computer systems configured with executable instructions, and may be implemented by hardware or a combination thereof as code (e.g., executable instructions, one or more computer programs, or one or more applications) that commonly executes on one or more processors. The computer program comprises a plurality of instructions executable by one or more processors.

[0060] Furthermore, the method can be implemented in any suitable type of computing platform, including but not limited to personal computers, minicomputers, mainframes, workstations, networked or distributed computing environments, standalone or integrated computer platforms, or in communication with charged particle tools or other imaging devices, etc. Aspects of the invention can be implemented as machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optical read and / or write storage medium, RAM, ROM, etc., such that it is readable by a programmable computer, and when the storage medium or device is read by the computer, it can be used to configure and operate the computer to perform the processes described herein. Furthermore, the machine-readable code, or portions thereof, can be transmitted via wired or wireless networks. The invention described herein includes these and other different types of non-transitory computer-readable storage media when such media comprises instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor. When programmed according to the methods and techniques described herein, the invention also includes the computer itself. A computer program can be applied to input data to perform the functions described herein, thereby transforming the input data to generate output data stored in non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the invention, the converted data represents physical and tangible objects, including specific visual depictions of physical and tangible objects generated on a display.

[0061] As used herein, the terms “component,” “module,” “system,” etc., are intended to refer to a computer-related entity, which may be hardware, firmware, a combination of hardware and software, software, or running software. For example, a component may be, but is not limited to, a process running on a processor, a processor, an object, an executable file, a running thread, a program, and / or a computer. As an example, an application running on a computing device and the computing device itself can both be components. One or more components may reside in a running process and / or thread, and components may be located in a single computer and / or distributed among two or more computers. Furthermore, these components are capable of execution from various computer-readable media having various data structures thereon. These components may communicate locally and / or remotely via signals, such as based on one or more data packets (e.g., data from a component that interacts with a local system, another component in a distributed system, and / or signals that interact with other systems via a network such as the Internet).

[0062] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A harmonic switching method for a converter-to-vacuum on-load tap changer, characterized in that, include: Based on the structural characteristics of the on-load tap changer of the converter transformer vacuum, the test parameters for the harmonic current interruption test are set. Select harmonic components based on the harmonic current spectrum at the converter transformer application site, and design a high-frequency harmonic operation mechanism. Harmonic switching is achieved by controlling the opening and closing of the vacuum interrupter through a high-frequency harmonic operating mechanism, in order to verify the effect of changing the test current value at the breaking time of the harmonic component on the breaking performance of the vacuum interrupter. The test parameters include the test voltage, test current, number of tests, and test current value at the time of interruption; The test voltages include: U=U L +R×I L Where U is the test voltage, U L R is the voltage level, R is the transition resistance, and I is the voltage level. L This is the load current; The test current includes: I=0.5×(I L +U L / R) Where I is the test current; Harmonic components include: The 5th and 7th harmonic currents are superimposed, and the amplitude of the 5th and 7th harmonic currents is adjustable from 0 to 230A. The high-frequency harmonic operating mechanism includes a harmonic current source, a fundamental power supply, an inverter, and an isolation transformer; A harmonic current source is formed using a 220V power electronic inverter, and a bypass resistor is placed next to the harmonic current source. Harmonic current is injected by stepping up the voltage through an isolation transformer; the transformer has a turns ratio of 1:10, a rated voltage of 7.56kV on the high-voltage side, and a rated voltage of 756V on the low-voltage side. When the vacuum interrupter is closed, the currents from the harmonic current source and the fundamental current source flow through the vacuum interrupter. When the vacuum interrupter is open, the test current flows through the parallel resistor.

2. The harmonic switching method for a converter-to-vacuum on-load tap changer as described in claim 1, characterized in that, Also includes: The required test current is met by controlling the amplitude, frequency, and phase angle of the 5th and 7th harmonic currents superimposed on the fundamental wave.

3. The harmonic switching method for a converter-to-vacuum on-load tap changer as described in claim 2, characterized in that, include: The switching is performed using a power grid test power supply or a short-circuit generator via a high-frequency harmonic operating mechanism. A vacuum interrupter is connected in series in the switching circuit, and the power factor of the switching circuit power supply is less than or equal to 0.15.

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