Bipolar direct current high voltage oscillation wave generating device for testing power cable insulation

Abstract

The application discloses a bipolar direct-current high-voltage oscillation wave generating device for power cable insulation test, relates to the technical field of power equipment insulation state detection and its technical application, and comprises an alternating current inversion unit, a polarity-adjustable direct-current generating unit, a polarity-adjustable high-voltage switch unit, a reactor unit, a measuring unit, a total control unit and an operation host computer. The application can generate oscillation wave voltage under positive and negative polarity alternation charging with adjustable levels, eliminates the risk of damage to cable insulation state caused by space charge accumulation in traditional single-polarity oscillation wave test, and has important engineering practical value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power equipment insulation state detection technology and its technical application field, and in particular to a bipolar DC high-voltage oscillation wave generating device for transmission cable insulation testing. BACKGROUND

[0002] Damped AC (DAC) is a new technology for power cable testing proposed by Dutch scholars in 1995. Compared with the traditional frequency conversion resonance technology, the DAC device has the outstanding advantages of small size and light weight, facilitating transportation, on-site installation and on-site testing. In the past two decades, DAC testing has been highly recognized by the academic and industrial circles, and has been widely applied in power distribution cable testing in many countries and regions including China, and has achieved excellent application results. It has gradually been popularized to the field of transmission cables. As of May 2022, China's power companies are operating hundreds of power distribution cable DAC and dozens of transmission cable DAC testing equipment.

[0003] However, in September 2021, the CIGRE TB841 transmission cable testing standard published by the International Large Grid Organization (CIGRE) clearly states that for the widely used cross-linked polyethylene (XLPE) insulated transmission cable testing around the world, the single-pole DAC testing technology proposed by Dutch scholars is no longer allowed, and the bipolar DAC method must be used. The main reason is that the single-pole DC charging method can cause the accumulation of space charge in the XLPE cable, which can cause fatal damage to the healthy insulation of the cable during the DAC phase. In this way, the technology of transmission cable testing has to rely on the frequency conversion resonance testing method again, which is 20 years old.

[0004] Therefore, the present application provides a bipolar DC high-voltage oscillation wave generating device for transmission cable insulation testing, which can adjust the output voltage level, fully meet the requirements of CIGRE TB 841, eliminate the risk of space charge accumulation damaging the insulation of the measured cable in the traditional single-pole DAC test, and fully retain all the advantages of the traditional DAC voltage device portability and test effect power frequency equivalence. It completely reverses the difficult situation faced by the single-pole DAC testing technology and has a broad application prospect. SUMMARY

[0005] Therefore, the present application provides a bipolar DC high-voltage oscillation wave generating device for transmission cable insulation testing, which can adjust the output voltage level, fully meet the requirements of CIGRE TB 841, eliminate the risk of space charge accumulation damaging the insulation of the measured cable in the traditional single-pole DAC test, and fully retain all the advantages of the traditional DAC voltage device portability and test effect power frequency equivalence. It completely reverses the difficult situation faced by the single-pole DAC testing technology and has a broad application prospect.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The bipolar DC high-voltage oscillation wave generating device for power cable insulation test comprises an AC inversion unit, a polarity-adjustable DC generating unit, a polarity-adjustable high-voltage switch unit, a reactor unit, a measurement unit, a total control unit and an operation host; wherein the AC inversion unit is connected with the polarity-adjustable DC generating unit, the polarity-adjustable DC generating unit is connected with the reactor unit through the polarity-adjustable high-voltage switch unit, and the reactor unit is connected to the measured cable through the measurement unit; the total control unit sends control signals to the AC inversion unit, the polarity-adjustable DC generating unit and the polarity-adjustable high-voltage switch unit, receives measurement signals of the polarity-adjustable DC generating unit and the measurement unit, and sends the measurement signals to the operation host.

[0008] Optionally, the AC inversion unit is composed of a rectifier circuit, a DC-DC conversion circuit, a high-frequency inversion circuit and a high-frequency transformer in series.

[0009] Optionally, the polarity-adjustable DC generating unit is composed of a three-stage voltage multiplier circuit, a voltage feedback circuit, a current-limiting resistor and a high-voltage isolation switch in series.

[0010] Optionally, the polarity-adjustable high-voltage switch unit is composed of two columns of high-voltage semiconductor switches, the two columns of high-voltage semiconductor switches have the same structure, and the two columns of high-voltage semiconductor switches are placed in parallel.

[0011] Optionally, the reactor unit adopts an air-core modular design and is composed of three sub-modules without partial discharge in series.

[0012] Optionally, the sub-modules are wound in a layer-by-layer winding manner from bottom to top to wind the reactor.

[0013] Optionally, the measurement unit is composed of a resistance-capacitance voltage divider and a partial discharge coupling detection unit, and the partial discharge coupling detection unit is connected to the low-voltage arm of the resistance-capacitance voltage divider.

[0014] Optionally, the total control unit comprises an FPGA control circuit board based on ARM control and an optoelectronic signal converter, and the total control unit sends control signals to the AC inversion unit, the polarity-adjustable DC generating unit and the polarity-adjustable high-voltage switch unit through the optoelectronic signal converter.

[0015] Optionally, the total control unit further comprises N A / D converters, which receive voltage feedback signals, cable oscillation wave voltage signals and partial discharge signals of the polarity-adjustable DC generating unit and transmit them to the operation host for cable insulation state evaluation.

[0016] According to the above technical solution, compared with the prior art,

[0017] 1. The bipolar DC high-voltage oscillating wave generating device for power cable insulation test of the present application can produce specified positive and negative alternating bipolar oscillating wave voltage on the measured cable through the cooperation of the AC inverter unit, the polarity adjustable DC generating unit and the polarity adjustable high-voltage switch unit, and the insulation state of the measured cable under the oscillating wave is evaluated through the measurement unit detecting the partial discharge signal generated by the measured cable.

[0018] 2. The bipolar DC high-voltage oscillating wave generating device for power cable insulation test of the present application has adjustable output voltage level and selectable positive and negative polarity, can produce specified positive and negative alternating bipolar oscillating wave voltage on the measured cable, fully meets the requirements of CIGRE TB 841, and can effectively eliminate the risk of damaging the cable insulation level caused by the introduction of space charge in the monopolar oscillating wave charging link.

[0019] 3. The bipolar DC high-voltage oscillating wave generating device for power cable insulation test of the present application fully retains all the advantages of the portability of the conventional oscillating wave voltage device and the good power frequency equivalence of the test effect, completely reverses the difficult situation faced by the monopolar oscillating wave test technology, and has broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0021] Figure 1 The structure schematic diagram of the bipolar DC high-voltage oscillating wave generating device for power cable insulation test provided by the present application is shown in the figure.

[0022] Figure 2 The bipolar oscillating wave shape schematic diagram adopted by the bipolar DC high-voltage oscillating wave generating device for power cable insulation test provided by the present application is shown in the figure.

[0023] Figure 3 The circuit diagram of the AC inverter unit in the bipolar DC high-voltage oscillating wave generating device for power cable insulation test provided by the present application is shown in the figure.

[0024] Figure 4 The circuit diagram of the polarity adjustable DC generating unit of the bipolar DC high-voltage oscillating wave generating device for power cable insulation test provided by the present application is shown in the figure.

[0025] Figure 5The schematic diagram of the polarity-adjustable high-voltage switch unit of the bipolar DC high-voltage oscillation wave generating device for insulating test of power transmission cable is provided. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0027] In the present application, the relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations, the term "comprising", "containing" or any other variant thereof is intended to cover non-exclusive containing, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the elements defined by the statement "comprising" do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

[0028] Referring to Figure 1 As shown in the figure, the present application discloses a bipolar DC high-voltage oscillation wave generating device for insulating test of power transmission cable, which comprises an AC inversion unit 1, a polarity-adjustable DC generating unit 2, a polarity-adjustable high-voltage switch unit 3, a reactor unit 4, a measuring unit 5, a general control unit 6 and an operation host; wherein the AC inversion unit 1 is connected with the polarity-adjustable DC generating unit 2, the polarity-adjustable DC generating unit 2 is connected with the reactor unit 4 through the polarity-adjustable high-voltage switch unit 3, and the reactor unit 4 is connected to the measured cable 7 through the measuring unit 5; the general control unit 6 sends control signals to the AC inversion unit 1, the polarity-adjustable DC generating unit 2 and the polarity-adjustable high-voltage switch unit 3, receives the measurement signals of the polarity-adjustable DC generating unit 2 and the measuring unit 5, and sends the measurement signals to the operation host.

[0029] Further, referring to Figure 3 As shown in the figure, the AC inversion unit 1 is composed of a rectifier circuit, a DC-DC conversion circuit, a high-frequency inversion circuit and a high-frequency transformer connected in series.

[0030] Specifically, the rectifier circuit is a bridge rectifier circuit composed of four diodes, and a 310V DC voltage is output after being connected to the mains. The DC-DC conversion circuit includes two filter and voltage stabilizing capacitors, an IGBT, a current limiting resistor, and a diode. The collector of the IGBT is connected to capacitor 15, and the emitter is connected to capacitor 19 through the current limiting resistor 17. The output voltage is adjusted by the duty cycle of the on-time, and the output range is 0-310V. The high-frequency inverter circuit is composed of an inverter bridge composed of four IGBTs with a withstand voltage of 3.3kV and diodes in reverse parallel connection, which is used to generate a high-frequency square wave voltage. The high-frequency transformer has a transformation ratio of 310V:35kV and a working frequency of 10kHz.

[0031] Further, referring to Figure 4 As shown, the polarity adjustable DC generation unit 2 is composed of a three-stage voltage doubler circuit, a voltage feedback circuit, a current limiting resistor, and a high voltage isolation switch in series.

[0032] Specifically, the three-stage voltage doubler circuit has the same structure and is composed of two charging capacitors and two direction controllable rectifier switches. The output voltage polarity is adjusted by changing the direction of the rectifier switch. The rectifier switch is composed of two high-voltage silicon stacks of 70kV series relay in reverse parallel connection. The high-voltage silicon stack has a withstand voltage of 70kV and a current carrying capacity of 10A. The silicon stack in the voltage doubler circuit is selected by controlling the on-off of the two relay switches, thereby changing the output DC high voltage polarity. The voltage feedback circuit has a transformation ratio of 40000:1, and the high voltage arm resistor is 180MΩ. The current limiting resistor 215 is a high-voltage glass enamel resistor with a resistance of 2MΩ and a power of 500W. The high-voltage isolation switch K1 is a relay switch with a withstand voltage of 420kV and a current carrying capacity of 10A.

[0033] Further, referring to Figure 5 As shown, the polarity adjustable high voltage switch unit 3 is composed of two columns of high voltage semiconductor switches. The two columns of high voltage semiconductor switches have the same structure and are placed in parallel.

[0034] Specifically, the two columns of switches are each composed of 24 optically triggered thyristors with a maximum withstand voltage of 7.5kV and a current carrying capacity of 200A. The thyristors are equipped with a voltage equalization circuit with a resistance of 10MΩ, and are connected to the driving circuit powered by a battery through an optical fiber. The control signal is transmitted to the driving circuit through an optical fiber to control the on-off of the switch unit by the total control unit 6.

[0035] Further, the reactor unit 4 is designed in an air-core modular manner and is composed of three sub-modules without partial discharge.

[0036] Further, the sub-modules are wound in a layer-by-layer winding manner from bottom to top to wind the reactor.

[0037] Specifically, the single sub-module inductance value is 1.5H, the resistance is 50Ω, the withstand voltage is not less than 60kV, and the partial discharge amount is not greater than 5pC.

[0038] Further, the measuring unit 5 is composed of a resistance-capacitance voltage divider and a partial discharge coupling detection unit, and the partial discharge coupling detection unit is connected to the low-voltage arm of the resistance-capacitance voltage divider.

[0039] Specifically, the resistance-capacitance voltage divider has a transformation ratio of 40000:1, the high-voltage arm capacitor is 2nF, and the resistance is 180MΩ; the partial discharge coupling detection unit is composed of an RLC type capacitive detection unit and a 7th order elliptical high-pass filter in series.

[0040] Further, the total control unit 6 includes an FPGA control circuit board based on ARM control and an optical-electric signal converter, and the total control unit 6 sends control signals to the alternating current inversion unit 1, the polarity adjustable direct current generation unit 2 and the polarity adjustable high-voltage switch unit 3 through the optical-electric signal converter.

[0041] Further, the total control unit 6 further includes three A / D converters, which receive the voltage feedback signal of the polarity adjustable direct current generation unit 2, the cable oscillation wave voltage signal and the partial discharge signal and transmit them to the operation host for cable insulation state evaluation.

[0042] Further, the device can generate a bipolar oscillation wave voltage of 20-500Hz, and the voltage waveform is as shown in Figure 2 .

[0043] Further, as shown in Figure 2 , the process of generating a bipolar high-voltage direct current oscillation wave on the measured cable 7 by the bipolar direct current high-voltage oscillation wave generation device for power cable insulation test is as follows:

[0044] Step 1: t0-t1 stage, the polarity adjustable direct current generation unit 2 outputs positive polarity direct current high voltage, and the measured cable 7 is in a positive polarity charging stage;

[0045] Step 2: t1-t2 stage, the polarity adjustable direct current generation unit 2 stops outputting, the polarity adjustable high-voltage switch unit 3 is turned on, and a positive polarity charging oscillation wave voltage is generated on the measured cable 7 through resonance;

[0046] Step 3: t2-t3 stage, the polarity adjustable direct current generation unit 2 outputs negative polarity direct current high voltage, and the measured cable 7 is in a negative polarity charging stage;

[0047] Step 4: t3-t4 stage, the polarity adjustable direct current generation unit 2 stops outputting, the polarity adjustable high-voltage switch unit 3 is turned on, and a negative polarity charging oscillation wave voltage is generated on the measured cable 7 through resonance.

[0048] Further, the bipolar DC high-voltage oscillation wave can be divided into four processes, and the voltage waveform satisfies the following expression:

[0049]

[0050] wherein U0 is the output voltage waveform of the bipolar oscillation wave generating device, V m is a preset test voltage amplitude, a is the inverse of the charging time constant, determined by the current limiting resistance R1 in the polarity adjustable DC generating unit 2, the equivalent capacitance C of the measured cable 7 and the resistance R2 of the reactor unit 4, β1 is the decay index, determined by the resistance R2 and the inductance L of the reactor unit 4, the calculation of a, β1, α and ω should satisfy a = 1 / ((R1+R2)C), β1 = R2 / (2L),

[0051] In a specific embodiment, the total control unit 6 controls the frequency and pulse width of the AC inverter unit 1 to generate square wave voltages of different amplitudes, which are output to the polarity adjustable DC generating unit 2; the total control unit 6 controls the switching rectification direction of the polarity adjustable DC generating unit 2 to generate DC high-voltage of different polarities, which is charged to the measured cable 7 through the polarity adjustable high-voltage switching unit 3, the reactor unit 4 and the measurement unit 5; the total control unit 6 obtains the charging voltage amplitude through the measurement unit 5; the total control unit 6 triggers the on-off of the high-voltage semiconductor switch at a specified test voltage, and the capacitance of the measured cable 7 and the inductance of the reactor unit 4 form a series resonance circuit to generate an oscillation wave voltage; the total control unit 6 obtains the oscillation wave voltage and partial discharge information through the measurement unit 5, and uploads them to the operation host to complete the test.

[0052] Each of the embodiments in the specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments.

[0053] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bipolar DC high-voltage oscillating wave generator for insulation testing of power transmission cables, characterized in that, It includes an AC inverter unit, a polarity-adjustable DC generator unit, a polarity-adjustable high-voltage switch unit, a reactor unit, a measurement unit, a central control unit, and an operating host. The AC inverter unit is connected to the polarity-adjustable DC generator unit, which is connected to the reactor unit via the polarity-adjustable high-voltage switch unit. The reactor unit is connected to the cable under test via the measurement unit. The central control unit sends control signals to the AC inverter unit, the polarity-adjustable DC generator unit, and the polarity-adjustable high-voltage switch unit, receives measurement signals from the polarity-adjustable DC generator unit and the measurement unit, and sends the measurement signals to the operating host. The AC inverter unit consists of a rectifier circuit, a DC-DC converter circuit, a high-frequency inverter circuit, and a high-frequency transformer connected in series.

2. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 1, characterized in that, The polarity-adjustable DC generator unit consists of a three-stage voltage multiplier circuit, a voltage feedback circuit, a current-limiting resistor, and a high-voltage disconnect switch connected in series.

3. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 1, characterized in that, The polarity-adjustable high-voltage switch unit consists of two rows of high-voltage semiconductor switches. The two rows of high-voltage semiconductor switches have the same structure and are placed in parallel.

4. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 1, characterized in that, The reactor unit adopts a hollow modular design and consists of three partial discharge-free sub-modules connected in series.

5. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 4, characterized in that, The submodule uses a bottom-up, layer-by-layer winding method to wind the reactor.

6. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 1, characterized in that, The measurement unit consists of a resistive-capacitive voltage divider and a partial discharge coupling detection unit, which is connected to the low-voltage arm of the resistive-capacitive voltage divider.

7. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 1, characterized in that, The main control unit includes an FPGA control circuit board based on ARM control and a photoelectric signal converter. The main control unit sends control signals to the AC inverter unit, the polarity adjustable DC generator unit, and the polarity adjustable high voltage switch unit through the photoelectric signal converter.

8. The bipolar DC high-voltage oscillating wave generator for power transmission cable insulation testing according to claim 7, characterized in that, The main control unit also includes N A / D converters, which receive voltage feedback signals from the polarity-adjustable DC generator, cable oscillation wave voltage signals, and partial discharge signals, and transmit them to the host computer for cable insulation condition assessment.

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