Superconducting and quench bubble, insulation barrier and liquid nitrogen composite insulation breakdown voltage testing method considering influence of bubble heat effect

Abstract

The invention relates to insulation performance testing of superconducting equipment of an electric power system, in particular to a superconducting quench bubble, insulation barrier and liquid nitrogen composite insulation breakdown voltage testing method considering the influence of a bubble heat effect. Comprising the following steps: S1, acquiring the relation between the resistance and the surface temperature of the superconducting conductor in a quenching interval; s2, arranging a dielectric barrier member between the superconducting current limiting unit and the electrode; and S3, driving the superconducting current limiting unit to quench, and measuring the breakdown voltage between the superconducting current limiting unit and the first electrode. And S4, determining the representative value of the surface temperature of the superconducting conductor in the quenching process. And S5, performing heat and force coupling numerical simulation. And S6, measuring the change relation of the parameters of the insulation barrier along with the temperature. And S7, obtaining a key electrical parameter corresponding to the temperature parameter T in the step S5. According to the invention, accurate quantification of the influence of the quench bubble heat effect on the composite insulation breakdown characteristic is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the insulation performance test of superconducting equipment in power system, and in particular to a test method for the insulation breakdown voltage of superconducting quench bubble, insulation barrier and liquid nitrogen composite insulation considering the influence of bubble thermal effect. BACKGROUND

[0002] With the development of high proportion of DC and high power flexible DC interconnection in power system, the peak value of DC short circuit current increases significantly, and the breaking capacity of traditional DC circuit breaker is difficult to meet the safety demand of power grid. The resistive superconducting current limiter, which has the characteristics of zero impedance in normal operation and resistance state in fault, becomes one of the core devices for limiting DC short circuit current, and its safe and stable operation directly determines the reliability of power grid.

[0003] At present, the core component of the resistive superconducting current limiter is the superconducting current limiting unit, which is placed in liquid nitrogen for cooling. However, after the superconducting quench triggered by short circuit fault, the resistance of superconducting tape increases rapidly, and the surrounding liquid nitrogen evaporates in large quantities due to Joule heat, forming hot bubbles. These hot bubbles not only change the dielectric properties of liquid nitrogen, but more importantly, the Joule heat carried by the bubbles changes the temperature distribution of the superconducting current limiting unit, the insulation barrier and the liquid nitrogen, i.e. the bubble thermal effect. The increase in temperature will further reduce the dielectric strength of liquid nitrogen, and will also cause the insulation performance of the insulation barrier to decay with the increase in temperature, which will easily lead to the breakdown of the superconducting quench bubble, insulation barrier and liquid nitrogen composite insulation system, and even cause equipment damage and power grid accidents.

[0004] In the prior art, the test of the composite insulation breakdown voltage of liquid nitrogen and insulation material of superconducting power equipment does not consider the key influencing factor of quench bubble. The response time of the sensor that can be applied to measure the temperature of liquid nitrogen temperature zone is in the order of milliseconds, which cannot meet the accuracy requirement of temperature measurement under the large temperature gradient transient change from superconducting tape to insulation barrier during the superconducting tape quench process. At the same time, there is no in-depth analysis of the effect of bubble thermal effect on the breakdown of composite insulation, which leads to the inability to establish the quantitative correlation of superconducting quench bubble thermal effect, insulation barrier and liquid nitrogen composite insulation breakdown voltage, and further makes the insulation design of superconducting current limiter rely on empirical value, which has the problems of insufficient safety redundancy or overdesign. SUMMARY

[0005] The present application is aimed at the defects in the prior art, and provides a test method for the composite insulation breakdown voltage of superconducting quench bubble, insulation barrier and liquid nitrogen considering the influence of bubble thermal effect. It is suitable for the insulation design optimization and safety performance evaluation of superconducting current limiter in flexible DC power grid, and can accurately quantify the influence of quench bubble thermal effect on the breakdown characteristics of the composite insulation.

[0006] In order to achieve the above object, the application adopts the following technical scheme, a superconducting quench-insulation barrier-liquid nitrogen composite insulation breakdown voltage test method considering bubble thermal effect, comprising the following steps: S1: obtaining the corresponding relationship between the resistance and surface temperature of the superconducting conductor in the quench interval.

[0007] S2: forming a superconducting current limiting unit by the superconducting conductor, setting a dielectric barrier member between the superconducting current limiting unit and a first electrode to form an insulation barrier; electrically connecting the superconducting current limiting unit with a large current source and electrically connecting the first electrode with a high potential source; and building a test environment in a low-temperature insulation medium, so that the superconducting current limiting unit, the insulation barrier and the first electrode are sequentially arranged along the target electric field direction.

[0008] S3: driving the superconducting current limiting unit to quench, measuring the breakdown voltage between the superconducting current limiting unit and the first electrode under different set-through conditions, and collecting electrical time sequence data of the quenching process, the electrical time sequence data at least including sequence data of resistance with time; and simultaneously obtaining the spatial position and shape information of the breakdown path and the bubble based on optical imaging.

[0009] S4: determining the surface temperature representative value of the superconducting conductor in the quenching process according to the electrical time sequence data of S3 and combining the corresponding relationship between the resistance and the temperature of S1, the surface temperature representative value at least including the highest surface temperature.

[0010] S5: based on the test arrangement of S2 and S3, taking the surface temperature representative value of S4 as the temperature boundary condition of the superconducting conductor surface bubble, performing numerical simulation of thermal and force coupling or multi-physical field coupling, and obtaining the surface temperature parameter T of the insulation barrier under the action of bubble thermal effect.

[0011] S6: measuring the change relationship of the key electrical parameters of the insulation barrier with temperature in the low-temperature to room-temperature temperature range.

[0012] S7: according to the temperature-parameter relationship of S6, obtaining the key electrical parameter corresponding to the temperature parameter T of S5, and establishing the quantitative mapping relationship between the key electrical parameter and the breakdown voltage.

[0013] Further, the low-temperature insulation medium is liquid nitrogen.

[0014] Further, the superconducting conductor is a high-temperature superconducting tape.

[0015] Further, the superconducting current limiting unit is composed of a single high-temperature superconducting tape, or the high-temperature superconducting tape is wound into multiple groups of coils and connected in series and / or parallel at the beginning and end.

[0016] Further, the insulating barrier adopts an insulating material suitable for liquid nitrogen working conditions, and the insulating material is one or more of G10 material, polyimide material, polytetrafluoroethylene or polypropylene laminated paper.

[0017] Further, the insulating barrier is arranged between the superconducting current limiting unit and the first electrode through an insulating support, and the area of the insulating barrier is greater than the projected area of the superconducting current limiting unit, and the insulating barrier has a predetermined thickness.

[0018] Further, the first electrode is a metal electrode and is used as a high-voltage electrode; the structure type of the first electrode is a flat plate electrode or a hollow cylindrical electrode.

[0019] Further, the high-potential source is a high-voltage direct current source, a high-voltage alternating current source or a lightning impulse power source.

[0020] Further, the optical imaging is realized by using a high-speed camera or a general camera to obtain the breakdown path and the position and shape information of the bubble.

[0021] Further, the key electrical parameters of the insulating barrier at least include relative dielectric constant, dielectric loss angle, volume resistivity and / or breakdown field strength.

[0022] Compared with the prior art, the present application has the following beneficial effects.

[0023] The present application realizes the precise quantification of the influence of the superconducting bubble thermal effect on the breakdown characteristics of the composite insulation, and provides key technical support for the insulation design optimization and safety performance evaluation of the superconducting current limiter in the flexible DC power grid, filling the gap in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described below in combination with the drawings and specific embodiments. The protection scope of the present application is not limited to the following descriptions.

[0025] Figure 1 It is a flowchart of the breakdown voltage test method in the embodiment. Figure 2 It is a schematic diagram of the first breakdown path. Figure 3 It is a schematic diagram of the second breakdown path. Figure 4 It is a schematic diagram of the method for obtaining the surface temperature of the superconducting tape during the superconducting current limiting unit superconducting loss process in the embodiment. DETAILED DESCRIPTION

[0026] The present application provides a superconducting loss-insulating barrier-liquid nitrogen composite insulation breakdown voltage test method considering the bubble thermal effect.

[0027] The test device is mainly composed of a low-temperature container, a superconducting current-limiting unit, an insulation barrier, a high-voltage electrode, an optical observation system and a multi-channel electric measurement system.

[0028] The low-temperature container is filled with liquid nitrogen, and an observation window is arranged for optical observation.

[0029] The superconducting current-limiting unit is made of yttrium barium copper oxide (YBCO) or bismuth strontium calcium copper oxide (BSCCO) high-temperature superconducting tape, which can be a single tape or a plurality of coils wound and connected in series or parallel. The insulation barrier is an insulation material with a certain thickness and area, which is larger than the area of the superconducting current-limiting unit and is fixed between the superconducting current-limiting unit and the high-voltage electrode by a low-temperature insulation support.

[0030] The superconducting current-limiting unit is connected in series with a large current source, and the high-voltage electrode is connected with a high potential source.

[0031] The test steps of the test method are as shown in Figure 1 The test steps of the test method are as shown in S1, select a certain type of high-temperature superconducting tape, measure and obtain the resistance change curve with surface temperature under the superconducting state of the tape.

[0032] S2, use the high-temperature superconducting tape to form a superconducting current-limiting unit, and arrange an insulation barrier and a high-voltage electrode above it; the whole test device is placed in a liquid nitrogen environment.

[0033] S3, measure the breakdown voltage value between the high-voltage electrode and the superconducting current-limiting unit by the first voltage measurement device, measure the voltage value between the two input and output terminals of the superconducting current-limiting unit by the second voltage measurement device, measure the current value flowing through the superconducting current-limiting unit by the first current measurement device, and observe the bubble generation dynamics behavior path of the superconducting current-limiting unit and the breakdown path between the superconducting current-limiting unit and the high-voltage electrode by the optical observation system.

[0034] The high-voltage power supply (i.e. high potential source) is adjusted to a certain voltage, and then the large current source in series with the superconducting current limiting unit is discharged to make the superconducting current limiting unit lose superconductivity. If breakdown occurs between the superconducting current limiting unit and the high-voltage electrode, the breakdown voltage value U1 is obtained by the first voltage measuring device, the voltage value U2 of the inlet and outlet of the superconducting current limiting unit is obtained by the second voltage measuring device, the current value I in the superconductivity loss process of the superconducting current limiting unit is obtained by the first current measuring device, the dynamic behavior path of the surface bubble in the superconductivity loss process of the superconducting current limiting unit is obtained by the optical observation system, and the position, shape and breakdown path between the superconducting current limiting unit and the high-voltage electrode of the superconductivity loss bubble at the time of breakdown are recorded.

[0035] The breakdown path between the superconducting current limiting unit and the high-voltage electrode is divided into a first breakdown path and a second breakdown path. The first breakdown path is a bulk breakdown through the insulating barrier, which constitutes an insulation breakdown between the superconducting current limiting unit and the high-voltage electrode, as shown in Figure 2 The second breakdown path is a surface creeping through the insulating barrier, which constitutes an insulation breakdown between the superconducting current limiting unit and the high-voltage electrode, as shown in Figure 3 The first voltage measuring device is used to obtain the breakdown voltage value U11 corresponding to the first breakdown path and the breakdown voltage value U12 corresponding to the second breakdown path.

[0036] S4, as shown in Figure 4 The voltage value U2 of the inlet and outlet of the superconducting current limiting unit obtained by the second voltage measuring device and the current value I in the superconductivity loss process of the superconducting current limiting unit obtained by the first current measuring device are used to calculate the resistance value Rt of the superconducting current limiting unit changing with time in the superconductivity loss process. With the obtained curve of the resistance value of the high-temperature superconducting tape changing with the surface temperature thereof and the obtained resistance value of the superconducting current limiting unit changing with temperature in the superconductivity loss process, the highest temperature T of the surface bubble of the superconducting tape in the superconductivity loss process of the superconducting current limiting unit is calculated.

[0037] The expected current value of the large current source is changed in the experiment process, and the breakdown voltage value U1 of the composite insulation system under different expected currents I' is obtained. The distribution law and filling volume of the bubbles between the superconducting current limiting unit and the insulating barrier under different expected currents I' are recorded by the optical observation system, and the highest temperature T of the surface of the superconducting tape in the superconductivity loss process of the superconducting current limiting unit under different expected currents is calculated.

[0038] At the same time, the material of the insulating barrier is changed in the experiment to obtain the influence law of different thermal conductivities, different dielectric constants, bulk resistivity and surface resistivity on the breakdown voltage.

[0039] S5, establish the electric-thermal-flow multi-physical field coupling simulation calculation model of the superconducting current limiting unit-bubble-insulation barrier-high voltage electrode and liquid nitrogen composite insulation system. The highest temperature T of the superconducting tape surface in the quenching process of the superconducting current limiting unit under different expected current conditions obtained through experiments and calculations is taken as a boundary condition, and the surface temperature T' of the insulation barrier under the influence of bubble thermal stress is calculated.

[0040] S6, test the electrical performance parameters of the insulation barrier of different materials under room temperature and liquid nitrogen temperature conditions, such as the relative dielectric constant, volume resistivity and surface resistivity, so as to obtain the electrical performance parameter table of the insulation barrier surface at different temperature values under the condition of slow temperature rise.

[0041] S7, according to the electrical performance parameter table of the insulation barrier surface at different temperature values, the relative dielectric constant, volume resistivity and surface resistivity of the insulation barrier surface under the condition of the temperature T' of the superconducting current limiting unit in the transient quenching process are found.

[0042] Finally, the quantitative relationship between the key parameters of the composite insulation system, such as the relative dielectric constant, volume resistivity and composite system breakdown voltage, under the first breakdown path condition is obtained. The results can provide a theoretical basis for the selection of insulation materials for superconducting power equipment.

[0043] It should be noted that in the experiment of the present application, the breakdown path can be divided into two categories: The first breakdown path: the breakdown channel passes through the inside of the insulation barrier body, forming volume breakdown; The second breakdown path: the breakdown occurs along the surface of the insulation barrier, forming surface creepage breakdown.

[0044] As an embodiment, to ensure the synchronization of experimental data, the electrical measurement system and the optical observation system are linked through a time reference trigger signal to ensure that the voltage, current and optical image correspond one by one at the moment of breakdown. Therefore, the evolution of the bubble shape and the change of the electrical parameters can be accurately associated, which provides experimental support for the quantitative modeling of the bubble thermal effect.

[0045] In the preferred embodiment, in step S5, the finite element analysis method is used for numerical calculation when establishing the electric-thermal-flow multi-physical field coupling simulation calculation model of the superconducting current limiting unit-bubble-insulation barrier-high voltage electrode and liquid nitrogen composite insulation system. Through the finite element analysis software, the highest temperature T of the superconducting tape surface obtained through experiments is taken as the boundary condition of the bubble heat source, and the highest temperature T' of the insulation barrier surface under the action of transient bubble thermal stress can be simulated and calculated. This simulation process can directly reveal the distribution of the temperature field on the insulation barrier, and provide key data for the subsequent correlation of temperature and electrical parameters.

[0046] To ensure the wide applicability of the experiment, the "high potential source" mentioned in steps S3 and S4 can be specifically a high-voltage alternating current source, a high-voltage direct current source, or a standard lightning impulse voltage generator, etc. to simulate electrical stress under different operating conditions.

[0047] Meanwhile, the "optical observation system" used is preferably a high-speed camera with high frame rate shooting capability, which can capture and record the transient dynamic behavior of the supercritical bubble and the instantaneous process of the breakdown discharge.

[0048] It can be understood that the above specific description of the present application is only used to illustrate the present application and is not limited to the technical solutions described in the embodiments of the present application. Those skilled in the art should understand that the present application can still be modified or replaced equivalently to achieve the same technical effect; as long as the use needs are met, it is within the protection scope of the present application.

Claims

1. A method for testing the breakdown voltage of a superconducting quenching-insulation barrier-liquid nitrogen composite insulation considering the thermal effect of air bubbles, characterized in that, The steps include: S1: Obtaining the relationship between the resistance and surface temperature of the superconducting conductor in the quenching region; S2: A superconducting current-limiting unit is formed by the superconducting conductor, and a dielectric barrier is provided between the superconducting current-limiting unit and the first electrode to form an insulating barrier; the superconducting current-limiting unit is electrically connected to a high current source, and the first electrode is electrically connected to a high potential source; and a test environment is established in a low-temperature insulating medium, such that the superconducting current-limiting unit, the insulating barrier, and the first electrode are arranged sequentially along the target electric field direction. S3: Drive the superconducting current limiting unit to lose quench, measure the breakdown voltage between the superconducting current limiting unit and the first electrode under different set current conditions, and collect electrical timing data of the quench process. The electrical timing data includes at least the sequence data of resistance over time. At the same time, acquire the breakdown path and the spatial position and morphology information of the bubble based on optical imaging. S4: Based on the electrical timing data of S3 and the correspondence between resistance and temperature in S1, determine the representative value of the surface temperature of the superconducting conductor during the quenching process. The representative value of the surface temperature includes at least the highest surface temperature. S5: Based on the experimental setup of S2 and S3, the surface temperature representative value described in S4 is used as the temperature boundary condition of the bubbles on the surface of the superconducting conductor. Numerical simulation of thermal and mechanical coupling or multi-physics field coupling is performed to obtain the surface temperature parameter T of the insulating barrier under the action of bubble thermal effect. S6: Determine the relationship between the key electrical parameters of the insulation barrier and temperature in the range from low temperature to room temperature; S7: Based on the temperature-parameter relationship in S6, obtain the key electrical parameters corresponding to the temperature parameter T in S5, and establish a quantitative mapping relationship between the key electrical parameters and the breakdown voltage.

2. The method according to claim 1, characterized in that: The cryogenic insulating medium is liquid nitrogen.

3. The method according to claim 1, characterized in that: The superconducting conductor is a high-temperature superconducting tape.

4. The method according to claim 1, characterized in that: The superconducting current limiting unit is composed of a single high-temperature superconducting tape, or the high-temperature superconducting tape is wound into multiple coils and connected in series and / or in parallel.

5. The method according to claim 1, characterized in that: The insulating barrier uses an insulating material suitable for liquid nitrogen conditions, which is one or more of G10 material, polyimide material, polytetrafluoroethylene or polypropylene laminated paper.

6. The method according to claim 1, characterized in that: The insulating barrier is disposed between the superconducting current limiting unit and the first electrode via an insulating support, and the area of ​​the insulating barrier is larger than the projected area of ​​the superconducting current limiting unit, and has a predetermined thickness.

7. The method according to claim 1, characterized in that: The first electrode is a metal electrode and is used as a high-voltage electrode; the structure of the first electrode is a flat plate electrode or a hollow cylindrical electrode.

8. The method according to claim 1, characterized in that: The high-potential source is a high-voltage DC source, a high-voltage AC source, or a lightning impulse power source.

9. The method according to claim 1, characterized in that: The optical imaging is achieved using a high-speed camera or a regular camera to acquire information on the breakdown path and the location and shape of the bubble.

10. The method according to claim 1, characterized in that: The key electrical parameters of the insulation barrier include at least the relative permittivity, dielectric loss angle, volume resistivity, and / or breakdown field strength.

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