Bipolar high voltage direct current generating device and method for cable insulation withstand test

Abstract

The present invention discloses a bipolar high-voltage direct current generating device and method for cable insulation resistance test, which relates to the field of power equipment insulation state test, and includes a voltage conversion module, a boost module, an oscillation waveform generating module, a measurement module and a master control module; there are multiple voltage conversion modules, and the multiple voltage conversion modules are grouped in pairs and matched with a boost module respectively, and the boost modules corresponding to the same group of voltage conversion modules are cascaded and the high-voltage end is connected to the oscillation waveform generating module; each group of voltage conversion modules is arranged in parallel; the voltage conversion module includes a variable frequency power supply unit, a capacitor unit, a protection unit and a bidirectional switch unit. The present application has the effect of improving the applicability of the bipolar high-voltage direct current generating device.

Description

Technical Field

[0001] The present application relates to the field of insulation status testing of power equipment, and in particular to a bipolar high-voltage direct current generating device and method for cable insulation withstand testing. Background Art

[0002] Insulation testing is an important means to ensure the safe operation of power cables. Take two testing technologies as examples:

[0003] The first one is the more traditional series resonant technology;

[0004] The second is what has been developed in the last twenty years called oscillating wave technology.

[0005] Among them, the disadvantage of series resonance technology is that the test device is large in size and weight. A 220kV device weighs tens of tons, which is relatively inconvenient to implement on site. However, the test device using oscillation wave technology, a 220kV device weighs only a few tons, is small in size and light in weight, and is relatively more convenient to implement on site.

[0006] In recent years, oscillatory wave technology has been widely recognized by power companies. In 2015, IEEE promulgated relevant standards (IEEE Std 400.4) to regulate and guide the research and application of oscillatory wave technology. However, in 2021, the CIGRE expert group, based on a comprehensive summary and systematic analysis of the experience and theoretical research results of oscillatory wave applications in the past 20 years, clearly pointed out in CIGRE TB841: The current oscillatory wave test technology uses single-polarity high-voltage DC charging, which has technical defects such as causing space charge accumulation in cross-linked polyethylene (XLPE) cables and damaging cable insulation. The existing technology must be modified to adopt a positive and negative alternating bipolar DC charging method.

[0007] Patent CN202310191859.4: A bipolar DC high-voltage oscillation wave generator for transmission cable insulation testing, comprising an AC inverter unit, a polarity-adjustable DC generator unit, a polarity-adjustable high-voltage switch unit, a reactor unit, a measurement module, a master control unit, and an operating host. The invention can generate an oscillation wave voltage with adjustable levels of positive and negative polarity alternating charging, eliminating the risk of space charge accumulation damaging the cable insulation state in traditional unipolar oscillation wave testing, and has important engineering practical value.

[0008] The above technical solution provides a bipolar DC charging method, but its scope of application is small. The device built last time may not meet the needs of the next use and needs to be rebuilt in advance or on-site. Therefore, this application proposes a new technical solution. Summary of the invention

[0009] In order to improve the applicability of a bipolar high-voltage direct current generating device, the present application provides a bipolar high-voltage direct current generating device and method for cable insulation withstand testing.

[0010] In a first aspect, the present application provides a bipolar high voltage direct current generating device for cable insulation withstand testing, which adopts the following technical solution:

[0011] A bipolar high voltage direct current generating device for cable insulation withstand test, comprising:

[0012] A voltage conversion module, which is used to convert bipolar direct current based on on-site power supply conditions;

[0013] A boost module, which is used to boost the preceding bipolar DC voltage;

[0014] An oscillation waveform generating module, which is used to complete cable charging or oscillation wave generation in response to a control signal;

[0015] A measuring module, which is used to collect the oscillation voltage and the feedback signal of the cable;

[0016] A master control module, which is connected to the voltage conversion module, the boost module, the oscillation waveform generation module and the measurement module, and is used for overall control and data interaction with a preset operation host;

[0017] There are multiple voltage conversion modules, which are grouped in pairs and matched with a boost module respectively. The boost modules corresponding to the same group of voltage conversion modules are cascaded and the high-voltage end is connected to the oscillation waveform generation module; each group of voltage conversion modules is arranged in parallel;

[0018] The voltage conversion module includes a variable frequency power supply unit, a capacitor unit, a protection unit and a bidirectional switch unit;

[0019] The variable frequency power supply unit includes a transformer 1, a rectifier bridge, an AC relay and a charging resistor. The primary side of the transformer 1 is connected to the on-site power supply connector and the secondary side is connected to the input side of the rectifier bridge. The output side of the rectifier bridge is connected to both ends of the capacitor unit. The capacitor unit is connected in series with a protection unit and then connected to a bidirectional switch unit. The charging resistor is connected in series to the primary side of the transformer 1, and the normally open contact of the AC relay is connected in series to another terminal on the primary side of the transformer 1. The transformer 1 is a voltage regulating transformer.

[0020] Optionally, the oscillation waveform generating module includes a reactor unit and a high-voltage semiconductor switch, the reactor unit includes a plurality of series-connected partial discharge-free sub-modules, and the high-voltage semiconductor switch is used to switch on and off the reactor unit and the boost module; one end of the high-voltage semiconductor switch is grounded.

[0021] Optionally, the capacitor unit includes a plurality of capacitor groups and an electronic switch, the capacitor group includes a plurality of electrolytic capacitors, at least two of the plurality of capacitor groups have different numbers of electrolytic capacitors, and the plurality of electrolytic capacitor groups are arranged in series;

[0022] The number of the electronic switches is less than the number of the capacitor banks and the difference is one;

[0023] Each of the capacitor banks except one capacitor bank is connected in parallel with an electronic switch, and the electronic switch is connected to the master control module and responds.

[0024] Optionally, the master control module is configured as follows:

[0025] Get the length parameters of the tested cable;

[0026] If the current length parameter meets the preset overlong cable condition, after the device completes at least one complete voltage wave application, the electronic switch is controlled to adjust the combination relationship of the capacitor group and complete at least one complete new voltage wave application.

[0027] Optionally, a partial discharge positioning test mechanism is further included, and the partial discharge positioning test mechanism includes:

[0028] An insulating movable sleeve, which is used to be sleeved on the cable under test;

[0029] A test knife, which penetrates the insulating movable sleeve and is connected to the insulating movable sleeve in a sliding manner;

[0030] A separate push mechanism, which is installed on the outer wall of the insulating movable sleeve and is used to push the test knife to move inside the insulating movable sleeve in response to the test execution period;

[0031] Wherein, the separate pushing mechanism is connected to the master control module, and the master control module is configured as follows:

[0032] If a partial discharge location verification request is received, the separate pushing mechanism is controlled to push the test knife to move and after the pushing amount reaches a preset moving amount, the separate pushing mechanism is controlled to separate from the test knife.

[0033] Optionally, the test knife includes a knife head and a knife handle, the knife head is detachably connected to the knife handle, the knife handle is slidably connected to the insulating movable sleeve, the end of the knife handle away from the cable to be tested is a wedge block and the wedge surface of the wedge block faces the side of the knife handle, and the separate pushing mechanism includes a hydraulic cylinder or an air cylinder and the piston rod end faces the wedge surface.

[0034] Optionally, the reactor unit is connected in parallel with a safety circuit, which includes a second current limiting resistor and a relay. The second current limiting resistor is connected in parallel to the reactor unit and in series with the coil of the relay. The normally closed contacts of the relay are connected in series with the power supply circuit of the separate driving mechanism.

[0035] The application provides a bipolar high voltage DC generation method for cable insulation withstand test, using the following technical solution:

[0036] A bipolar high-voltage direct current generating method for cable insulation withstand test uses any of the above-mentioned bipolar high-voltage direct current generating devices for cable insulation withstand test to power a tested cable.

[0037] To summarize, the present application includes the following beneficial technical effects: it can be used in a variety of different test site power supply environments, is relatively less affected by the site power supply frequency and voltage, does not require on-site device modification during the process, and can be adaptively adjusted and controlled; at the same time, a protection unit is used for circuit protection to reduce the chance of damage to the device due to misoperation or circuit failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the overall structure of the device of the present application;

[0039] Figure 2 is a schematic diagram of the circuit structure of the voltage conversion module of the present application;

[0040] Figure 3 It is a schematic diagram of the circuit structure of the oscillation wave generating module of the present application;

[0041] Figure 4 It is a structural schematic diagram of the partial discharge positioning test mechanism of the present application.

[0042] Explanation of the accompanying drawings: 1. Frequency conversion power supply unit; 11. Rectifier diode 1; 12. Rectifier diode 2; 13. Rectifier diode 3; 14. Rectifier diode 4; 15. Insulation movable sleeve; 16. Test knife; 17. Separate pushing mechanism; 101. AC relay; 102. Charging resistor; 103. Transformer 1; 2. Capacitor unit; 3. Protection unit; 31. Protection diode; 32. Current limiting resistor 1; 4. Bidirectional switch unit; 5. Boost module; 6. Oscillation wave generating module; 7. Measurement module; 8. Master control module; 9. Cable under test. DETAILED DESCRIPTION

[0043] The following is combined with Figure 1-4 This application is described in further detail.

[0044] The embodiment of the present application discloses a bipolar high-voltage direct current generating device for cable insulation withstand testing.

[0045] Reference Figure 1-3 , the bipolar high voltage DC generator used for cable insulation withstand test includes:

[0046] A voltage conversion module, which is used to convert bipolar direct current based on on-site power supply conditions;

[0047] A boost module 5, which is used to boost the preceding bipolar DC voltage;

[0048] An oscillation wave generating module 6, which is used to complete cable charging or oscillation wave generation in response to a control signal;

[0049] A measuring module 7, which is used to collect the oscillation voltage and the feedback signal of the cable;

[0050] The master control module 8 is connected to the voltage conversion module, the boost module 5, the oscillation wave generating module 6 and the measuring module 7, and is used for overall control and data interaction with a preset operating host.

[0051] Among them, the master control module 8 includes a microprocessor unit and an electro-optical conversion unit. The microprocessor unit includes a bus communication unit and adaptively configured capacitor charging control unit, capacitor power detection unit, bidirectional switch control unit, oscillation wave generation control unit, measurement data acquisition unit and other parts; the microprocessor is an FPGA control circuit board based on ARM control, which sends control signals to the voltage conversion module, oscillation wave generation module 6, and measurement module 7 through the photoelectric conversion unit, and receives the power detection signal of the capacitor unit, the cable oscillation wave voltage signal and the partial discharge signal through the internal inherited A / D converter and communication unit and transmits them to the operating host to cooperate with the cable insulation status evaluation.

[0052] In the present application, there are multiple voltage conversion modules, which are grouped in pairs and matched with a boost module 5 respectively. The boost modules 5 corresponding to the same group of voltage conversion modules are cascaded and the high-voltage end is connected to the oscillation wave generating module 6, and the low-voltage end is grounded. The high-voltage section of the output of the oscillation wave generating module 6 is connected to the measurement module 7 and the cable 9 under test.

[0053] The above-mentioned groups of voltage conversion modules are arranged in parallel. The voltage conversion module includes a variable frequency power supply unit 1, a capacitor unit 2, a protection unit 3 and a bidirectional switch unit 4.

[0054] The variable frequency power supply unit 1 includes a transformer 103, a rectifier bridge, an AC relay 101 and a charging resistor 102, wherein the primary side of the transformer 103 is connected to the on-site power supply connector (points a / b in the figure) and the secondary side is connected to the input side of the rectifier bridge; the output side of the rectifier bridge has two ends, which are respectively connected to the two ends of the capacitor unit 2, and the capacitor unit 2 is connected in series with the protection unit 3 and then connected to the bidirectional switch unit 4; the bidirectional switch unit 4 has two input ends and two output ends (points c and d in the figure), one end of the input end is connected in series with the protection unit 3 and then connected to one end of the capacitor unit 2, and the other end is connected to the other end of the capacitor unit 2.

[0055] The charging resistor 102 is connected in series to the primary side of the transformer 103. The coil of the AC relay 101 serves as the control part of the master control module 8 and the normally open contact is connected in series to another terminal on the primary side of the transformer 103. The transformer 103 is a voltage regulating transformer in this application.

[0056] According to the above settings, the device can be used in a variety of different test site power supply environments, and is relatively less affected by the site power supply frequency and voltage. There is no need to modify the device on site during the process, and adaptive adjustment and control are sufficient. At the same time, the protection unit 3 is also used for circuit protection to reduce the probability of damage to the device due to misoperation and circuit failure.

[0057] Reference Figure 2 In this embodiment, the rectifier bridge is composed of four rectifier diodes 11, rectifier diodes 2 12, rectifier diodes 3 13 and rectifier diodes 4 14 in a group of two, one group is connected in series, and two groups are connected in parallel. The protection unit 3 includes a protection circuit, which can be composed of a protection diode 31 and a current limiting resistor 1 32 connected in series. The bidirectional switch unit 4 can be composed of an inverter bridge composed of four IGBTs (41, 42, 43, 44 in the figure) and reverse parallel diodes; the withstand voltage value of the IGBT can be 3.3kV.

[0058] Reference Figure 3 The oscillation wave generating module 6 includes a reactor unit and a high-voltage semiconductor switch. The reactor unit includes a plurality of non-partial discharge submodules connected in series, for example, 3; the non-partial discharge submodules are wound layer by layer from bottom to top, which can effectively avoid the influence of inter-turn partial discharge on the partial discharge test of the transmission cable while ensuring uniform longitudinal voltage distribution. The high-voltage semiconductor switch can be another IGBT, which is connected to and receives the signal output by the master control module 8, and is used to turn on and off the reactor unit and the boost module 5, that is, to control the breaking and changing the circuit state, and complete the function of cable charging or oscillation wave generation.

[0059] According to the above content, it can be known that whether the device enters the test after power-on is controlled. This point is particularly effective when combined with the signal attenuation and distortion analysis in another embodiment.

[0060] In this embodiment, the measurement module 7 is composed of a resistor-capacitor voltage divider and a partial discharge coupling detection unit, the ratio of the resistor-capacitor voltage divider is 40000:1, the high-voltage arm capacitor is 2nF, and the resistor is 180MΩ; the partial discharge coupling detection unit is connected to the low-voltage arm of the voltage divider, and is composed of an RLC type capacitive detection unit and a 7th-order elliptical high-pass filter in series. One end of the high-voltage semiconductor switch is grounded.

[0061] In one embodiment of the present application, the capacitor unit 2 includes multiple capacitor groups and electronic switches, the capacitor groups include a number of electrolytic capacitors, at least two of the multiple capacitor groups have different numbers of electrolytic capacitors, and the multiple electrolytic capacitor groups are arranged in series.

[0062] The number of electronic switches is less than the number of capacitor banks and the difference is one; each capacitor bank except one capacitor bank is connected in parallel with an electronic switch, which is connected to the master control module 8 and responds. The electronic switch may be another IGBT.

[0063] In the context of this device, it is necessary to locate the partial discharge position of the cable, and the length of the measured cable 9 will affect the positioning accuracy, etc. This application starts from the fact that the longer the cable length, the higher the charging efficiency required during the charging process. Considering that the charging efficiency is affected by the frequency, the measured cable 9 and the air-core inductor form a series resonant circuit and Wherein, f is the frequency, L is the inductance value of the reactor unit, and C is the equivalent capacitance. With the above-mentioned setting of the device, the staff can actively control the number of electrolytic capacitors actually connected and change the charging efficiency to better meet the test requirements of the tested cables 9 of different lengths.

[0064] In one embodiment of the present device, considering the difference in attenuation distortion of signals caused by cables of different lengths, the longer the cables, the more likely it is that misleading attenuation distortion characteristic interference will occur. Therefore, in order to ensure the accuracy of the test analysis for cables 9 of different lengths, the master control module is configured as follows:

[0065] Obtain the length parameter of the tested cable 9 through the information actively input by the staff;

[0066] If the current length parameter meets the preset over-long cable condition (such as: exceeding the preset standard cable length threshold), then after the device completes at least one complete voltage wave application, the electronic switch is controlled to adjust the combination relationship of the capacitor group (i.e., change the charging efficiency and waveform) and complete at least one complete new voltage wave application.

[0067] Subsequently, the upper host may, in some cases, also use the master control module 8 to compare the feedback information of the measurement modules under the combination of different capacitor groups, and analyze the attenuation distortion characteristics; wherein the comparative analysis may be a waveform comparison to find out the position where the amplitude changes rapidly and decreases, so as to identify the abnormal signal points.

[0068] Reference Figure 4 In one embodiment of the device, the device further comprises a partial discharge positioning test mechanism, the partial discharge positioning test mechanism comprising:

[0069] An insulating movable sleeve 15, which is used to be sleeved on the cable 9 under test;

[0070] A test knife 16, which penetrates the insulating movable sleeve 15 and is connected to the insulating movable sleeve in a sliding manner;

[0071] The separate pushing mechanism 17 is installed on the outer wall of the insulating movable sleeve 15 and is used to push the test blade 16 to move inside the insulating movable sleeve 15 in response to the test execution period.

[0072] The separate push mechanism 17 is connected to the master control module 8, and the master control module 8 is configured as follows:

[0073] If a partial discharge location verification request is received, the separate pushing mechanism 17 is controlled to push the test blade 16 to move, and after the pushing amount reaches a preset moving amount, the separate pushing mechanism 17 is controlled to separate from the test blade 16 .

[0074] According to the above arrangement, during the insulation test, the staff can install the above insulating movable sleeve 15 on the cable, and then actively initiate a local discharge positioning verification request, so that the test knife 16 can actively destroy the cable casing at the specified position to cooperate with the oscillation wave for functional inspection; at the same time, because the separate pushing mechanism 17 will be actively separated during the insulation test, even in high-voltage detection, local discharge and leakage are relatively difficult to electrically break down and conduct electricity to the electrical structure of the mechanism, the mechanism is relatively difficult to be damaged, and the safety is relatively higher.

[0075] It should be noted that the insulating sleeve 15 may be in the shape of a cuboid and have a passage for the cable to pass through along the length. There should be a physical structure under the cable, at least under the test knife 16, to provide support for the cable to prevent the cable from being pulled or scraped and damaged at other locations when the outer shell is broken by the test knife 16. The insulating sleeve 15 is preferably installed at the end section of the cable.

[0076] Reference Figure 4 The test knife 16 includes a knife head and a knife handle, and the knife head is detachably connected to the knife handle, for example: there is an insert block at the tail of the knife head, and the insert block is inserted into the slot pre-opened in the knife handle; the knife handle is in the shape of a long strip and is slidably connected to the insulating movable sleeve 15; the end of the knife handle away from the tested cable is a wedge block and the wedge surface of the wedge block faces the side of the knife handle; the separate pushing mechanism 17 includes a hydraulic cylinder or a gas cylinder and the piston rod end faces the wedge surface. The reason for choosing a hydraulic cylinder or a gas cylinder is that the control valve can be remote from the cylinder body, and further away from the test knife 16, so as to reduce the safety hazard caused by accidental electrical breakdown during partial discharge.

[0077] In one embodiment of the device, the reactor unit is connected in parallel with a safety circuit, which includes a current limiting resistor 2 and a relay. The current limiting resistor 2 is connected in parallel to the reactor unit and in series with the coil of the relay. The normally closed contacts of the relay are connected in series with the power supply circuit of the separate driving mechanism 17.

[0078] According to the above arrangement, once the cable is charged, the partial discharge positioning test mechanism is powered off to prevent misoperation during the test, interference with the test results, and even potential safety hazards.

[0079] The embodiment of the present application also discloses a bipolar high voltage direct current generation method for cable insulation withstand testing.

[0080] A bipolar high-voltage direct current generating method for cable insulation withstand test comprises using any of the above-mentioned bipolar high-voltage direct current generating devices for cable insulation withstand test to supply power to the tested cable.

[0081] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A bipolar high voltage direct current generator for cable insulation withstand testing, characterized in that: include: A voltage conversion module, which is used to convert bipolar direct current based on on-site power supply conditions; A boost module (5), which is used to boost the preceding bipolar DC voltage; An oscillation waveform generating module, which is used to complete cable charging or oscillation wave generation in response to a control signal; A measuring module (7), which is used to collect the oscillation voltage and the feedback signal of the cable; A master control module (8) connected to the voltage conversion module, the boost module (5), the oscillation waveform generation module and the measurement module (7) for overall control and data exchange with a preset operating host; There are a plurality of voltage conversion modules, and the plurality of voltage conversion modules are grouped in pairs and are respectively matched with a boost module (5); the boost modules (5) corresponding to the same group of voltage conversion modules are cascaded and the high-voltage ends are connected to the oscillation waveform generation module; the groups of voltage conversion modules are arranged in parallel; The voltage conversion module comprises a variable frequency power supply unit (1), a capacitor unit (2), a protection unit (3) and a bidirectional switch unit (4); The variable frequency power supply unit (1) comprises a transformer (103), a rectifier bridge, an AC relay (101) and a charging resistor (102); the primary side of the transformer (103) is connected to an on-site power supply connector and the secondary side is connected to the input side of the rectifier bridge; the output side of the rectifier bridge is connected to both ends of a capacitor unit (2); the capacitor unit (2) is connected in series with a protection unit (3) and then connected to a bidirectional switch unit (4); the charging resistor (102) is connected in series to the primary side of the transformer (103); the normally open contact of the AC relay (101) is connected in series to another connection terminal on the primary side of the transformer (103); the transformer (103) is a voltage regulating transformer; The oscillation waveform generating module comprises a reactor unit and a high-voltage semiconductor switch, wherein the reactor unit comprises a plurality of non-partial discharge sub-modules connected in series, and the high-voltage semiconductor switch is used to switch on and off the reactor unit and the boost module (5); one end of the high-voltage semiconductor switch is grounded; The capacitor unit (2) comprises a plurality of capacitor groups and an electronic switch, the capacitor groups comprising a plurality of electrolytic capacitors, at least two of the plurality of capacitor groups having different numbers of electrolytic capacitors, and the plurality of electrolytic capacitor groups are arranged in series; The number of the electronic switches is less than the number of the capacitor banks and the difference is one; Each of the capacitor banks except one capacitor bank is connected in parallel with an electronic switch, which is connected to the master control module (8) and responds.

2. The bipolar high voltage direct current generator for cable insulation withstand test according to claim 1, characterized in that: The master control module (8) is configured as follows: Obtaining the length parameter of the cable under test (9); If the current length parameter meets the preset overlong cable condition, after the device completes at least one complete voltage wave application, the electronic switch is controlled to adjust the combination relationship of the capacitor group and complete at least one complete new voltage wave application.

3. The bipolar high voltage direct current generator for cable insulation withstand test according to claim 1, characterized in that: It also includes a partial discharge positioning test mechanism, the partial discharge positioning test mechanism comprising: An insulating movable sleeve (15) for being sleeved on the cable (9) to be tested; A test knife (16) which penetrates the insulating movable sleeve (15) and is slidably connected thereto; A separate pushing mechanism (17) is mounted on the outer wall of the insulating movable sleeve (15) and is used to push the test knife (16) toward the inner side of the insulating movable sleeve (15) in response to a test execution period; Wherein, the separate pushing mechanism (17) is connected to the master control module (8), and the master control module (8) is configured as follows: If a partial discharge positioning verification request is received, the separate pushing mechanism (17) is controlled to push the test knife (16) to move, and after the pushing amount reaches a preset moving amount, the separate pushing mechanism (17) is controlled to separate from the test knife (16).

4. The bipolar high voltage direct current generator for cable insulation withstand test according to claim 3 is characterized in that: The test knife (16) comprises a knife head and a knife handle, wherein the knife head is detachably connected to the knife handle, and the knife handle is slidably connected to the insulating movable sleeve (15), and the end of the knife handle away from the tested cable (9) is a wedge block, and the wedge surface of the wedge block faces the side of the knife handle, and the separate pushing mechanism (17) comprises a hydraulic cylinder or an air cylinder, and the piston rod end faces the wedge surface.

5. The bipolar high voltage direct current generator for cable insulation withstand test according to claim 4 is characterized in that: The reactor unit is connected in parallel with a safety circuit, the safety circuit comprising a second current limiting resistor and a relay, the second current limiting resistor is connected in parallel to the reactor unit and in series with the coil of the relay, and the normally closed contact of the relay is connected in series with the power supply circuit of the separate driving mechanism (17).

6. A bipolar high voltage direct current generation method for cable insulation withstand test, characterized in that: A bipolar high voltage direct current generator for cable insulation withstand testing as claimed in any one of claims 1 to 5 is used to power the cable (9) under test.

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