Method, medium and system for determining phase selection vacuum switching inductive load closing speed

Abstract

The application discloses a method, medium and system for determining the closing speed of a phase-selected vacuum switch for closing a capacitive load, comprising: repeatedly performing multiple closing experiments on the fast vacuum switch at different closing speeds and at different closing phases under a power frequency voltage; collecting the minimum pre-breakdown voltage and the power frequency voltage corresponding to the closing process of each closing speed; drawing the curve of the minimum pre-breakdown voltage corresponding to each closing speed of the fast vacuum switch changing with time and the curve of the power frequency voltage changing with time; if the closing process corresponding to at least one closing speed meets a first preset requirement, selecting the smallest closing speed as the lower limit of the closing speed of the fast vacuum switch; and the first preset requirement is that the slope of the curve of the minimum pre-breakdown voltage changing with time is greater than the slope of the curve of the power frequency voltage changing with time at the same time. The application determines the minimum closing speed, and reduces the pre-breakdown high-frequency inrush current in the process of closing the capacitive load by the vacuum switch.

Description

Technical Field

[0001] This invention relates to the field of phase-selective vacuum switch closing technology, and in particular to a method, medium, and system for determining the closing speed of a phase-selective vacuum switch for capacitive loads. Background Technology

[0002] In power systems, switching operations cause electromagnetic oscillation transients, resulting in switching overvoltages and inrush currents that endanger the insulation of power equipment and the stability of the power system. Phase-controlled closing technology monitors the phase of the line voltage and controls the closing time of the switch to the optimal phase, thereby suppressing switching overvoltages and inrush currents in the power grid and fundamentally solving the electromagnetic transient effects during switch closing. Compared with high-voltage SF6 switchgear, vacuum switches have significant advantages such as economy and environmental friendliness, maintenance-free operation, and suitability for frequent operation, making them an important direction for the development of high-voltage switchgear under the dual carbon targets.

[0003] During the switching process, when the contact gap is less than a certain critical value and cannot withstand the applied voltage, a pre-breakdown phenomenon will occur, causing the switching equipment to fail to perform selective closing at the expected target phase. Therefore, the pre-breakdown characteristic of vacuum switches is one of the keys to achieving accurate selective closing. The timing of pre-breakdown is closely related to the closing insulation characteristics of the switch and the applied voltage. The closing pre-breakdown characteristic of vacuum switches is non-linear and exhibits a certain degree of dispersion, resulting in low control accuracy of phase selection closing. The closing speed directly affects the slope of the closing insulation characteristics, i.e., the rate of decrease in insulation strength of the contact gap (RDDS). Increasing the closing speed can reduce the dispersion of the pre-breakdown voltage during closing, which is of great significance for improving the accuracy of selective closing; however, excessively high closing speeds can cause the operating mechanism or related components to exceed their mechanical stress tolerance, resulting in component damage or shortened service life. Therefore, selecting an appropriate closing speed is very important for the selective closing process.

[0004] Fast vacuum switches, driven by eddy current repulsion mechanisms, offer comparable operational precision to power electronic switches while boasting lower operating losses and manufacturing costs. They are essential power switching devices for the rapid vacuum closing and opening of capacitive or inductive loads in power systems. Fast vacuum switching technology, with fast vacuum switches as its core component, is currently a research hotspot in the field of high-capacity switch technology both domestically and internationally, and has broad application prospects in many fields, including phase-controlled switches.

[0005] The main problems with selective closing of existing vacuum switches include: 1. Although the breakdown voltage of a vacuum gap is high, its dispersion is higher than that of a gas gap; 2. Vacuum switch selective closing strategies are mostly based on the effective value of the DC pre-breakdown voltage or the power frequency breakdown voltage. During selective closing, the instantaneous value of the power frequency voltage changes instantaneously with the contact gap distance and time. The above-mentioned basis has a large deviation, and there are even cases where closing is expected at the voltage zero point, but breakdown occurs at the voltage peak. This causes severe ablation of the contact surface by the high-frequency inrush current arc of the pre-breakdown, which often leads to re-breakdown and delayed breakdown after the capacitive load is disconnected. It is also very easy for the overvoltage caused by the breakdown level to cause damage to the reactive power compensation capacitor bank or the converter station filter equipment. Summary of the Invention

[0006] This invention provides a method, medium, and system for determining the closing speed of a phase-selective vacuum switch capacitive load, in order to solve the problem that the phase-selective closing strategy of the prior art is not conducive to the phase-selective closing of vacuum switches.

[0007] Firstly, a method for determining the closing speed of a phase-selective vacuum-closing capacitive load is provided, including:

[0008] Under power frequency voltage, the fast vacuum switch was repeatedly tested for closing multiple times at different closing speeds and different closing phases;

[0009] Collect the minimum pre-breakdown voltage and power frequency voltage of the closing process corresponding to each closing speed;

[0010] Plot the curves of minimum pre-breakdown voltage versus time and power frequency voltage versus time for each closing speed of the fast vacuum switch.

[0011] If the closing process corresponding to at least one closing speed meets the first preset requirement, then the smallest closing speed is selected as the lower limit of the closing speed of the fast vacuum switch.

[0012] The first preset requirement is that the slope of the curve showing the minimum pre-breakdown voltage changing with time during the closing process is greater than the slope of the curve showing the power frequency voltage changing with time at the same moment.

[0013] In a second aspect, a computer-readable storage medium is provided, wherein computer program instructions are stored on the computer-readable storage medium; when the computer program instructions are executed by a processor, the method for determining the closing speed of a phase-selective vacuum shut-off capacitive load as described in the first aspect embodiment above is implemented.

[0014] Thirdly, a system for determining the closing speed of a phase-selective vacuum-closing capacitive load is provided, comprising: a computer-readable storage medium as described in the second aspect embodiment above.

[0015] Thus, in this embodiment of the invention, a suitable lower limit for closing speed can be selected, thereby effectively suppressing the inrush current caused by premature breakdown before the voltage zero point during the switch closing process, and achieving synchronous closing. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention 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.

[0017] Figure 1 This is a flowchart of a method for determining the closing speed of a phase-selective vacuum closing capacitive load according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram showing the relationship between the pre-breakdown voltage and the pre-breakdown gap of a fast vacuum switch;

[0019] Figure 3 This is a schematic diagram of the design of the closing speed characteristics of a fast vacuum switch. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Existing technologies use switches with slow closing speeds, and the opening distance at the voltage peak cannot withstand the instantaneous voltage at that time. Therefore, this invention employs a fast vacuum switch, which has the advantages of simple structure, short closing time, and low dispersion of closing time. Due to its high closing speed, the opening distance at the same moment when closing at zero voltage is higher than that of a switch with a slower closing speed, resulting in a lower probability of pre-breakdown and reduced dispersion of pre-breakdown voltage. This facilitates further exploration of the variation of pre-breakdown voltage with opening distance under power frequency voltage, and provides guidance for the design of subsequent closing speeds.

[0022] Based on this, embodiments of the present invention disclose a method for determining the closing speed of a phase-selective vacuum-closing capacitive load. For example... Figure 1 As shown, the method of this embodiment of the invention includes the following steps:

[0023] Step S101: Under power frequency voltage, the fast vacuum switch is repeatedly tested for closing multiple times at different closing speeds and different closing phases.

[0024] Specifically, the fast vacuum switch is driven by eddy current electromagnetic repulsion. By changing the capacitance or voltage of the drive closing coil of the fast vacuum switch, the magnitude of the electromagnet current can be affected, thereby changing the magnitude of the electromagnetic force and thus adjusting the closing speed of the fast vacuum switch.

[0025] Step S102: Collect the minimum pre-breakdown voltage and power frequency voltage of the closing process corresponding to each closing speed.

[0026] This invention employs a fast vacuum switch to close a capacitive load. Closing tests revealed that, due to the different closing phases, the pre-breakdown voltage is dispersed, resulting in multiple pre-breakdown voltages occurring simultaneously. This invention selects the minimum pre-breakdown voltage at each moment.

[0027] Step S103: Plot the curves of the minimum pre-breakdown voltage versus time and the power frequency voltage versus time for each closing speed of the fast vacuum switch.

[0028] Step S104: If the closing process corresponding to at least one closing speed meets the first preset requirement, then the smallest closing speed is selected as the lower limit of the closing speed of the fast vacuum switch.

[0029] Specifically, the first preset requirement is:

[0030] The slope of the curve showing the minimum pre-breakdown voltage during the closing process versus time is greater than the slope of the curve showing the power frequency voltage versus time at the same moment.

[0031] Furthermore, closing experiments revealed that, due to the different closing phases, the pre-breakdown voltage and pre-breakdown gap of the fast vacuum switch under power frequency voltage exhibit a non-linear relationship. Because pre-breakdown is dispersed, the pre-breakdown voltage and pre-breakdown gap are distributed within a band, such as... Figure 2 As shown. The following relationship was obtained through fitting between the pre-breakdown voltage and the pre-breakdown gap:

[0032] u b (d)=B×d β (1)

[0033] u b+ (d)=D×dγ (2)

[0034] u b- (d)=A×dα (3)

[0035] Among them, u b (d) represents the pre-breakdown voltage corresponding to the pre-breakdown gap d, u b+ (d) represents the maximum pre-breakdown voltage corresponding to the pre-breakdown gap d, u b-(d) represents the minimum pre-breakdown voltage corresponding to the pre-breakdown gap d, A represents the first coefficient, α represents the second coefficient, B represents the third coefficient, β represents the fourth coefficient, D represents the fifth coefficient, and γ represents the sixth coefficient. These coefficients are all obtained by fitting.

[0036] Based on the relationship between the pre-breakdown gap and the contact stroke, the above equations (1) to (3) can be transformed into the following formulas:

[0037] u b (t)=B×(Ss(t)) β (4)

[0038] u b+ (t)=D×(Ss(t)) γ (5)

[0039] u b- (t)=A×(Ss(t))α (6)

[0040] Among them, u b (t) represents the pre-breakdown voltage at time t, u b+ (t) represents the maximum pre-breakdown voltage at time t, u b- (t) represents the minimum pre-breakdown voltage at time t, s(t) represents the contact travel at time t, and S represents the full opening distance of the fast vacuum switch, which can be determined by the factory parameters of the fast vacuum switch.

[0041] like Figure 3 As shown, disregarding the influence of voltage polarity, taking the absolute value of the power frequency voltage, the curves of the applied power frequency voltage versus time and the curves of the pre-breakdown voltage versus time (i.e., the RDDS characteristic curves) are plotted on the same coordinate system, and the endpoint of the RDDS characteristic curve falls at the zero point of the power frequency voltage (i.e., the horizontal axis of the curve is flipped about the zero point). To achieve the ideal closing target, that is, closing at the zero voltage point without pre-breakdown occurring before the zero point, this embodiment of the invention proposes that the closing speed of the fast vacuum switch must meet the following requirements throughout the entire travel time:

[0042]

[0043] The above u b- (-t) is based on u b -(t) is obtained by flipping the x-coordinate of the curve of time about zero.

[0044] Simplifying equation (7) yields the expression that serves as the criterion for the preset requirements:

[0045]

[0046] Therefore, the second preset requirement can be obtained in the embodiments of the present invention, as follows:

[0047] During the closing process, at every moment the following condition is met:

[0048]

[0049] Where u(t) represents the power frequency voltage at time t. C represents the preset redundancy, which can be preset based on experience; generally, C = 1.1 or 1.2. s(t), A, α, and S are as described above and will not be repeated here.

[0050] In this way, the closing process corresponding to the closing speed that meets the first preset requirement also meets the second preset requirement.

[0051] The lower limit of the closing speed is determined through the above process. If the closing speed is lower than this lower limit, the vacuum switch will experience pre-breakdown and generate a high-frequency inrush current when closing at the voltage zero crossing point.

[0052] Thus, without falling below the lower limit of closing speed, increasing the closing speed can provide technical support for improving the phase-controlled closing accuracy of fast vacuum switches from the perspective of reducing insulation dispersion, and help them achieve closing at the expected closing point where the inrush current meets the system requirements.

[0053] Furthermore, while increasing the closing speed can reduce insulation dispersion and help improve the accuracy of closing capacitive loads at zero point, excessively high closing speeds can seriously damage the operating mechanism. Therefore, provided the system can withstand the inrush current caused by insulation dispersion, a lower closing speed should be selected. Economic cost can also be considered when making the selection.

[0054] Furthermore, embodiments of the present invention also provide a computer-readable storage medium storing computer program instructions; when the computer program instructions are executed by a processor, they implement the method for determining the closing speed of a phase-selective vacuum shut-off capacitive load as described in the above embodiments.

[0055] Furthermore, embodiments of the present invention also provide a system for determining the closing speed of a phase-selective vacuum-closed capacitive load, comprising: a computer-readable storage medium as described in the above embodiments.

[0056] In summary, by determining a lower limit for the closing speed, a suitable closing speed not lower than the lower limit can be selected according to specific needs. This can suppress the high-frequency inrush current caused by premature breakdown before the voltage zero point during the closing of capacitive loads by the vacuum switch, thereby avoiding the burning of the contacts by the inrush current arc and reducing the probability of re-breakdown during the opening process of capacitive loads.

[0057] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the closing speed of a phase-selective vacuum-operated capacitive load, characterized in that, include: Under power frequency voltage, the fast vacuum switch was repeatedly tested for closing multiple times at different closing speeds and different closing phases; Collect the minimum pre-breakdown voltage and power frequency voltage of the closing process corresponding to each closing speed; Plot the curves of minimum pre-breakdown voltage versus time and power frequency voltage versus time for each closing speed of the fast vacuum switch. If the closing process corresponding to at least one closing speed meets the first preset requirement, then the smallest closing speed is selected as the lower limit of the closing speed of the fast vacuum switch. The first preset requirement is that the slope of the curve showing the minimum pre-breakdown voltage changing with time during the closing process is greater than the slope of the curve showing the power frequency voltage changing with time at the same moment. The closing process corresponding to the closing speed that meets the first preset requirement also meets the second preset requirement, wherein the second preset requirement is: during the closing process, at every moment, the closing speed meets the second preset requirement. , Indicates time t The contact stroke, Indicates time t power frequency voltage, S This indicates the full opening distance of the fast vacuum switch. A Indicates the first coefficient. Indicates the second coefficient. C This indicates the preset redundancy amount.

2. The method for determining the closing speed of a phase-selective vacuum-closed capacitive load according to claim 1, characterized in that: The closing speed of the fast vacuum switch can be adjusted by changing the capacitance or voltage of the drive closing coil of the fast vacuum switch.

3. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer program instructions; when the computer program instructions are executed by a processor, they implement the method for determining the closing speed of a phase-selective vacuum shut-off capacitive load as described in any one of claims 1 to 2.

4. A system for determining the closing speed of a phase-selective vacuum-operated capacitive load, characterized in that, include: The computer-readable storage medium as described in claim 3.

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