Direct-current cable sample multi-time rapid charging and discharging test device and method

Abstract

The invention discloses a multi-time rapid charging and discharging test device and method for a direct-current cable sample, and relates to the technical field of direct-current cables. The device comprises a sample cavity and a test circuit, a high-voltage electrode is arranged in the sample cavity, and the test circuit comprises an alternating current source, a transformer, a half-wave rectification circuit, a high-voltage relay and a control circuit; through on-off sequential control of the high-voltage relay, continuous multiple charging and discharging tests can be carried out on the direct-current cable sample, so that the cumulative effect that insulation of the direct-current cable is impacted by sudden voltage change in the whole life cycle is simulated, and the direct-current cable sample after continuous charging and discharging is obtained; the method is of great significance to design of a direct-current cable power transmission system, especially design of a hybrid power transmission line system of an overhead line and a submarine cable and design of cable structure type selection.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current cables, and in particular to a device and method for performing multiple rapid charge and discharge tests on direct current cable samples. Background Art

[0002] High-voltage DC cables often suffer grounding faults due to external damage, insulation breakdown, lightning tripping of connected overhead lines, etc. When a DC line fault occurs, it is necessary to cut off the DC current to quickly extinguish the arc generated by the flashover, thereby quickly clearing the fault. For hybrid DC lines composed of long-length cables and long-length overhead lines, the number of lightning tripping of overhead lines is very high during the entire life cycle, which may reach dozens or even hundreds of times. The cable lines connected to them will discharge and charge due to fault clearing. Under the influence of multiple rapid charges and discharges, the performance of the insulation material will deteriorate, reducing the service life of the submarine cable.

[0003] There is a cumulative effect of multiple impulse voltages on the insulation performance of insulating materials. After multiple impulse voltages, even if the insulating material is not broken down, the insulation structure inside the sample is damaged to a considerable extent, resulting in a decrease in the insulation resistance of the cable. In addition, the polarization process of a large number of impurities leads to an increase in the polarization current component, which makes the overall current curve decay more slowly. Multiple impulse voltages may also destroy the surface structure of the insulation, causing the electrode to inject charge into the interior of the dielectric, and the space charge accumulation phenomenon is significantly increased. However, at this stage, the research on cable insulation charging and discharging in various test projects such as DC cable formal tests, pre-qualification tests, and sampling tests mainly focuses on the optimization of the discharge device after the DC cable test and the optimization of the discharge strategy. The impact of multiple charging and discharging on the insulation performance of the cable is not considered, and there is also a lack of relevant DC cable sample charging and discharging test equipment. Summary of the Invention

[0004] The present invention provides a device and method for testing multiple rapid charge and discharge of a DC cable sample, aiming to obtain a DC cable sample after continuous charge and discharge.

[0005] The DC cable sample multiple rapid charge and discharge test device provided by the present invention comprises:

[0006] Sample chamber and test circuit;

[0007] A high voltage electrode is provided in the sample chamber;

[0008] The test circuit includes an AC source, a transformer, a half-wave rectifier circuit, a high-voltage relay and a control circuit;

[0009] The primary side of the transformer is connected to the AC source, the secondary side of the transformer is connected to the input end of the half-wave rectifier circuit, the output end of the half-wave rectifier circuit is connected to the high-voltage relay and the high-voltage electrode, and the ground wires of the AC source, the transformer, the half-wave rectifier circuit and the high-voltage electrode are connected to a common ground terminal;

[0010] The high-voltage relay is arranged on the path between the half-wave rectifier circuit and the high-voltage electrode; the high-voltage relay includes a common end, a normally closed end, a normally open end and a control end, the common end is connected to the high-voltage electrode, the normally closed end is connected to the output end of the half-wave rectifier circuit, the normally open end is connected to the common ground end, and the control end is connected to the control circuit; the control circuit is used to control the on-off timing of the high-voltage relay.

[0011] Optionally, the half-wave rectifier circuit includes a rectifier diode and a first capacitor, and a first resistor is further provided between the secondary side of the transformer and the half-wave rectifier circuit, and a first end of the first resistor is connected to a non-grounded end of the secondary side of the transformer;

[0012] The anode of the rectifier diode is connected to the second end of the first resistor, and the cathode of the rectifier diode is connected to the normally closed end;

[0013] A first end of the first capacitor is connected to the cathode of the rectifier diode, and a second end of the first capacitor is connected to the common ground terminal.

[0014] Optionally, the high-voltage relay is a single-pole double-throw high-voltage relay.

[0015] Optionally, the DC cable sample multiple rapid charge and discharge test device further includes a constant temperature bath;

[0016] The side wall of the sample chamber is provided with two connecting holes, each of which is connected to a hose, and the hose is connected to the constant temperature bath; the sample chamber forms a closed fluid circulation path with the constant temperature bath through the hose;

[0017] The constant temperature bath is configured to circulate a constant temperature medium into the sample cavity.

[0018] Optionally, the constant temperature medium is transformer oil.

[0019] Optionally, the DC cable sample multiple rapid charge and discharge test device further includes a temperature sensor; a sensing end of the temperature sensor is immersed in the constant temperature medium in the sample cavity.

[0020] Optionally, the temperature control range of the thermostatic bath is -30°C to 100°C, and the temperature control accuracy is 0.1°C.

[0021] The present invention provides a method for testing a DC cable sample for multiple rapid charge and discharge, using the DC cable sample multiple rapid charge and discharge test device described above. The method comprises the following steps:

[0022] S1, fixing a DC cable sample in a sample chamber and connecting the sample to a high-voltage electrode;

[0023] S2, switch the high-voltage relay to the normally closed end, apply a DC voltage of a preset amplitude and a preset pressurization time to the sample, then switch the high-voltage relay to the normally open end to maintain the preset discharge time, complete one cycle of the pressurization process, and repeat the pressurization process to a preset number of times.

[0024] Optionally, the preset amplitude is 3.6 kV, the preset pressurization time is 160 s, and the preset discharge time is 2 s.

[0025] Optionally, the DC cable is a DC XLPE cable.

[0026] The present invention has the following beneficial effects:

[0027] The device proposed in the present invention controls the charging and discharging of the sample through a high-voltage relay. When the high-voltage relay is switched to the normally closed end, the test circuit charges the sample. When the high-voltage relay is switched to the normally open end, the sample is discharged. By controlling the on-off timing of the high-voltage relay, it is possible to carry out multiple continuous charging and discharging tests on the DC cable sample, thereby simulating the cumulative effect of voltage mutation shock on the insulation of the DC cable throughout its life cycle, and obtaining the DC cable sample after continuous charging and discharging; the DC cable sample after continuous charging and discharging can be used for subsequent material and electrical tests and analyses such as breakdown voltage test, thermogravimetric analysis, differential scanning calorimetry analysis and infrared spectroscopy analysis, providing a reliable basis for evaluating the degree of insulation degradation of the DC cable, which is of great significance for the design of DC cable transmission systems, especially the design of hybrid transmission line systems of overhead lines and submarine cables, and the selection and design of cable structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of the structure of a device for multiple rapid charge and discharge testing of DC cable samples provided in some embodiments of the present invention;

[0030] Figure 2 This is a schematic diagram of the voltage waveform when the high-voltage DC cable fault is cleared;

[0031] Figure 3 Schematic diagram of the charge and discharge voltage waveforms during the test process of Example 1 of the present invention.

[0032] Description of reference numerals:

[0033] 101. AC source; 102. Transformer; 103. Half-wave rectifier circuit; 104. High-voltage relay; 105. Control circuit; 200. Sample chamber; 300. Constant temperature bath; 400. Temperature sensor. DETAILED DESCRIPTION

[0034] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] In the present invention, all expressions involving "connection" must be defined in conjunction with the specific technical objects and application scenarios to which they refer: if the "connection" is for electrical-related components or structures such as circuits, electrical elements, signal transmission paths, etc., the "connection" specifically refers to electrical connection, that is, through electrical means such as wires and conductive terminals, current conduction or electrical characteristic coupling between components is achieved to ensure the normal realization of electrical functions; if the "connection" is for mechanical-related parts such as mechanical components, structural components, supporting components, etc., the "connection" specifically refers to physical connection, that is, through mechanical means such as bolts, welding, bonding, mortise and tenon joints, snaps, bearings, hinges, etc., to achieve position fixation, relative positioning or movable assembly between components, thereby ensuring the stability of the mechanical structure, assembly accuracy and reliable execution of mechanical movement functions.

[0036] In the present invention, the terms "first" and "second" (if any) are used for descriptive purposes only and cannot be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features; therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0037] High-voltage DC cable lines often suffer grounding faults due to external damage, insulation breakdown, lightning tripping of connected overhead lines, and other reasons. When a DC line fault occurs, it is necessary to cut off the DC current to quickly extinguish the arc generated by the flashover, thereby quickly clearing the fault.

[0038] The fault clearing process of the DC line is divided into two processes: arc extinguishing and deionization, and restart logic; see Figure 2 During the arc extinguishing process, a short period of negative voltage will appear on the line voltage, and the fault current will drop rapidly to achieve the purpose of arc extinguishing. After a deionization process of 100ms to 500ms, as the insulation performance of the fault point recovers, the DC voltage station attempts to establish a DC voltage on the line (voltage reduction restart). When the DC voltage and current return to the pre-fault values, the DC line fault restart is completed; if the DC voltage fails to be established, it means that the DC fault still exists, and it is necessary to repeat the arc extinguishing and deionization process, and then restart at full voltage, and appropriately increase the deionization time.

[0039] For hybrid DC lines consisting of long DC cables (such as submarine cables) and long overhead lines, the number of lightning tripping times on the overhead lines during their entire life cycle is very high, possibly reaching dozens or even hundreds of times. The connected cable lines will discharge and charge due to fault clearing. Currently, DC cable insulation generally uses cross-linked polyethylene (XLPE) solid insulation. Under the influence of multiple rapid charges and discharges, the insulation material performance will deteriorate, reducing the service life of the DC cable.

[0040] At present, research on cable insulation discharge mainly focuses on the optimization of discharge devices after cable testing, as well as the optimization of discharge strategies such as discharge rate and discharge time interval, without considering the impact of multiple charge and discharge on cable insulation. Moreover, for high-voltage cables, multiple charge and discharge tests are carried out using prototype cables, which takes a long time and has high test costs.

[0041] In response to the above problems, the present invention proposes a device and method for multiple rapid charge and discharge testing of DC cable samples, aiming to obtain DC cable samples after continuous charge and discharge.

[0042] See Figure 1 In some embodiments, a DC cable sample multiple rapid charge and discharge test device includes a sample chamber 200 and a test circuit.

[0043] A high voltage electrode (not shown in the figure) is provided in the sample cavity 200 , and the high voltage electrode is used to connect a DC cable sample.

[0044] The test circuit includes an AC source 101 , a transformer 102 , a half-wave rectifier circuit 103 , a high-voltage relay 104 and a control circuit 105 .

[0045] The primary side of the transformer 102 is connected to the AC source 101, the secondary side of the transformer 102 is connected to the input end of the half-wave rectifier circuit 103, and the output end of the half-wave rectifier circuit 103 is connected to the high-voltage relay 104 and the high-voltage electrode; the ground wires of the AC source 101, the transformer 102, the half-wave rectifier circuit 103 and the high-voltage electrode are connected to a common ground terminal.

[0046] The high-voltage relay 104 is arranged on the path between the half-wave rectifier circuit 103 and the high-voltage electrode; the high-voltage relay 104 includes a common terminal (COM), a normally closed terminal (NC), a normally open terminal (NO) and a control terminal. The common terminal is connected to the high-voltage electrode, the normally closed terminal is connected to the output terminal of the half-wave rectifier circuit 103, the normally open terminal is connected to the common ground terminal, and the control terminal is connected to the control circuit 105; the control circuit 105 is used to control the on-off timing of the high-voltage relay 104. The on-off timing refers to the time logic such as the maintenance time, sequence, and interval of the high-voltage relay 104 switching to the normally closed terminal and the normally open terminal.

[0047] Among them, the control circuit 105 is composed of a timer (or a main control chip with a timing logic control function) and related components (such as switch drive units such as transistors, timing trigger signal elements, isolation protection elements, status indication elements, etc.); the specific circuit structure and component selection of the control circuit 105 are not particularly limited in the embodiments of the present invention. Those skilled in the art can purchase relevant components on the market and design the circuit structure based on existing public information. The core function of the control circuit 105 is to send a control level to the high-voltage relay 104 according to the set time logic (such as periodic pressurization), thereby realizing the control of the on and off of the high-voltage relay 104.

[0048] The device proposed in the embodiment of the present invention controls the charging and discharging of the sample through a high-voltage relay. When the high-voltage relay is switched to the normally closed end, the test circuit charges the sample. When the high-voltage relay is switched to the normally open end, the sample discharges. By controlling the on-off timing of the high-voltage relay, it is possible to carry out multiple continuous charging and discharging tests on the DC cable sample, thereby simulating the cumulative effect of voltage mutation shocks on the insulation of the DC cable throughout its life cycle, and obtaining the DC cable sample after continuous charging and discharging.

[0049] See Figure 1 Furthermore, in some embodiments, the half-wave rectifier circuit 103 includes a rectifier diode (D) and a first capacitor (C), and a first resistor (R) is further provided between the secondary side of the transformer 102 and the half-wave rectifier circuit 103, and the first end of the first resistor (R) is connected to the non-grounded end of the secondary side of the transformer 102; the anode of the rectifier diode (D) is connected to the second end of the first resistor (R), and the cathode of the rectifier diode (D) is connected to the normally closed end (NC) of the high-voltage relay 104; the first end of the first capacitor (C) is connected to the cathode of the rectifier diode (D), and the second end of the first capacitor (C) is connected to the common ground end.

[0050] Among them, the rectifier diode (D) is used for unidirectional conductive rectification to convert AC power into pulsating DC power; the first capacitor (C) is used for filtering and voltage stabilization, smoothing the pulsating DC power output by the rectifier diode (D), reducing voltage fluctuations, and outputting a more stable DC voltage; by adjusting the direction of the silicon stack of the half-wave rectifier circuit 103, periodic DC voltages of different polarities can be obtained.

[0051] In some embodiments, the high voltage relay 104 is a single-pole double-throw high voltage relay.

[0052] The single-pole double-throw high-voltage relay contains a moving contact (common end) and two static contacts (normally closed end and normally open end). The single contact realizes dual-circuit switching. When the single-pole double-throw high-voltage relay is switched to the normally closed end, the AC source, transformer, half-wave rectifier circuit and sample form a circuit. The test circuit applies high-voltage DC to the sample, and the sample begins to "charge"; when the single-pole double-throw high-voltage relay is switched to the normally open end, the sample is grounded and the sample "discharges".

[0053] In some implementations, the DC cable sample multiple rapid charge and discharge test apparatus further includes a constant temperature bath 300 .

[0054] Specifically, two connecting holes are provided on the side wall of the sample chamber 200, each of which is connected to a hose, which is connected to the constant temperature bath 300; the sample chamber 200 forms a closed fluid circulation passage with the constant temperature bath 300 through the hose; the constant temperature bath 300 is configured to circulate a constant temperature medium into the sample chamber 200. During the test, the sample is in the constant temperature medium, which can avoid surface flashover that may occur in the sample during the test on the one hand, and on the other hand provide a stable constant temperature environment for the test, thereby improving the reliability of the test.

[0055] In some preferred embodiments, the constant temperature medium is transformer oil; transformer oil has excellent thermal stability, insulation properties, heat transfer uniformity and compatibility with cable materials; transformer oil is one or more alkane and cycloalkane compounds.

[0056] In other embodiments, other types of mineral oil or silicone oil, perfluoropolyether, or perfluoroalkane media may be used instead of transformer oil.

[0057] In some preferred embodiments, the temperature control range of the thermostatic bath 300 is -30°C to 100°C, and the temperature control accuracy is 0.1°C.

[0058] In some embodiments, since the temperature controller of the constant temperature bath 300 can only monitor the temperature of the constant temperature medium in the bath, in order to avoid the situation where the temperature of the constant temperature medium in the sample cavity 200 is inconsistent with the temperature in the constant temperature bath 300, the DC cable sample multiple rapid charge and discharge test device also includes a temperature sensor 400. The temperature sensor 400 is arranged above the sample cavity, and the sensing end of the temperature sensor 400 is immersed in the constant temperature medium in the sample cavity 200.

[0059] The DC cable sample multiple rapid charge and discharge test device provided in the embodiment of the present invention performs a charge and discharge test on the DC cable by the following method, specifically comprising the steps of:

[0060] S1, fix the DC cable sample in the sample chamber and connect the sample to the high voltage electrode.

[0061] S2: Switch the high-voltage relay to the normally closed end, apply a DC voltage of a preset amplitude and preset pressurization duration to the sample, then switch the high-voltage relay to the normally open end to maintain the preset discharge duration to complete one cycle of the pressurization process, and repeat the pressurization process to the preset number of times.

[0062] It should be noted that before conducting a power-on test on the sample, it is necessary to wait until the temperature of the transformer oil (or other constant temperature medium) in the sample cavity reaches the test set temperature and remains stable.

[0063] Based on the device and method for multiple rapid charge and discharge tests of DC cable samples provided in the above embodiments, the present invention also proposes the following specific embodiments for explaining in detail the implementation process of the technical solution of the present invention. It should be noted that the following specific embodiments are only illustrative and do not constitute any form of limitation on the scope of protection of the present invention.

[0064] Example 1

[0065] Select DC XLPE cable and cut a sample with a thickness of 0.2mm.

[0066] Place the sample in the sample cavity, connect the high-voltage electrode, turn on the constant temperature bath and temperature sensor, and wait until the transformer oil in the sample cavity reaches the preset test temperature and remains stable.

[0067] Turn on the power of the test circuit and set the pressurization process of the sample through the control circuit; the specific pressurization process is as follows: Figure 3As shown, the amplitude of the applied DC voltage is 3.6kV. The DC voltage required for the test is applied to the sample and maintained for 160s. After that, the common end of the high-voltage relay is quickly switched from the normally closed end to the normally open end and maintained for 2s, that is, the switching of the sample from the charging state to the discharging state is completed once; after the 2s discharge is completed, the common end of the high-voltage relay is switched back to the normally closed end, and the sample is pressurized for the next cycle. This pressurization process is repeated cyclically 15 times, and a DC cable sample that is continuously charged and discharged multiple times is obtained.

[0068] After obtaining a DC cable sample that has been continuously charged and discharged multiple times, the sample can be subjected to subsequent material and electrical tests and analyses such as breakdown voltage testing, thermogravimetric analysis, differential scanning calorimetry analysis, and infrared spectroscopy analysis, to evaluate the impact of multiple charge and discharge cycles on the insulation performance of the DC cable sample.

[0069] As can be seen from the above examples, the device and method for the DC cable sample multiple rapid charge and discharge test proposed in the present invention can simulate the cumulative effects of sudden voltage shocks on the cable insulation over the entire life cycle of the DC cable at a certain temperature. This fills a gap in the field of DC cable testing and is of great significance for the design of DC cable transmission systems, especially hybrid transmission line systems combining overhead lines and submarine cables (submarine cables), and the selection of cable structures.

[0070] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A DC cable sample multiple rapid charge and discharge test device, characterized in that: Including sample chamber and test circuit; A high voltage electrode is provided in the sample chamber; The test circuit includes an AC source, a transformer, a half-wave rectifier circuit, a high-voltage relay and a control circuit; The primary side of the transformer is connected to the AC source, the secondary side of the transformer is connected to the input end of the half-wave rectifier circuit, the output end of the half-wave rectifier circuit is connected to the high-voltage relay and the high-voltage electrode, and the ground wires of the AC source, the transformer, the half-wave rectifier circuit and the high-voltage electrode are connected to a common ground terminal; The high-voltage relay is arranged on the path between the half-wave rectifier circuit and the high-voltage electrode; the high-voltage relay includes a common end, a normally closed end, a normally open end and a control end, the common end is connected to the high-voltage electrode, the normally closed end is connected to the output end of the half-wave rectifier circuit, the normally open end is connected to the common ground end, and the control end is connected to the control circuit; the control circuit is used to control the on-off timing of the high-voltage relay.

2. The DC cable sample multiple rapid charge and discharge test device according to claim 1, characterized in that: The half-wave rectifier circuit includes a rectifier diode and a first capacitor. A first resistor is further provided between the secondary side of the transformer and the half-wave rectifier circuit. The first end of the first resistor is connected to the non-grounded end of the secondary side of the transformer. The anode of the rectifier diode is connected to the second end of the first resistor, and the cathode of the rectifier diode is connected to the normally closed end; A first end of the first capacitor is connected to the cathode of the rectifier diode, and a second end of the first capacitor is connected to the common ground terminal.

3. The DC cable sample multiple rapid charge and discharge test device according to claim 1, characterized in that: The high-voltage relay is a single-pole double-throw high-voltage relay.

4. The DC cable sample multiple rapid charge and discharge test device according to claim 1, characterized in that: Also includes a constant temperature bath; The side wall of the sample chamber is provided with two connecting holes, each of which is connected to a hose, and the hose is connected to the constant temperature bath; the sample chamber forms a closed fluid circulation path with the constant temperature bath through the hose; The constant temperature bath is configured to circulate a constant temperature medium into the sample cavity.

5. The DC cable sample multiple rapid charge and discharge test device according to claim 4, characterized in that: The constant temperature medium is transformer oil.

6. The DC cable sample multiple rapid charge and discharge test device according to claim 4, characterized in that: Also includes a temperature sensor; The sensing end of the temperature sensor is immersed in the constant temperature medium in the sample cavity.

7. The DC cable sample multiple rapid charge and discharge test device according to claim 4, characterized in that: The temperature control range of the thermostatic bath is -30°C to 100°C, and the temperature control accuracy is 0.1°C.

8. A method for multiple rapid charge and discharge tests on DC cable samples, characterized in that: The DC cable sample multiple rapid charge and discharge test device according to any one of claims 1 to 7 is used, and the method comprises the steps of: S1, fixing a DC cable sample in a sample chamber and connecting the sample to a high-voltage electrode; S2, switch the high-voltage relay to the normally closed end, apply a DC voltage of a preset amplitude and a preset pressurization time to the sample, then switch the high-voltage relay to the normally open end to maintain the preset discharge time, complete one cycle of the pressurization process, and repeat the pressurization process to a preset number of times.

9. The DC cable sample multiple rapid charge and discharge test method according to claim 8, characterized in that: The preset amplitude is 3.6 kV, the preset pressurization time is 160 s, and the preset discharge time is 2 s.

10. The DC cable sample multiple rapid charge and discharge test method according to claim 8, characterized in that: The DC cable is a DC XLPE cable.

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