All-condition equivalent testing device for capacitor for direct-current power transmission

Abstract

The invention, which belongs to the technical field of high-voltage direct-current power transmission, discloses an all-condition equivalent test device for a capacitor for direct-current power transmission, comprising an alternating-current voltage test module and a direct-current voltage test module. After the alternating-current voltage test module and the direct-current voltage test module are connected in parallel, one end is connected with a capacitor to be tested, and the other end is grounded; the alternating-current voltage test module is used for outputting alternating-current voltage with adjustable amplitude and frequency; the direct-current voltage test module is used for outputting direct-current voltage with adjustable amplitude and boost rate; the alternating-current voltage test module is used for outputting alternating-current voltage with adjustable amplitude and frequency; the DC voltage test module is used for outputting a DC voltage with an adjustable amplitude and an adjustable boost rate. According to the invention, the problem that the test performance of the DC support capacitor does not accord with the practical application of engineering because the existing test device can only output single DC voltage or AC voltage is solved, and effective assessment of the full-working-condition stress of the capacitor is realized by inputting different working-condition voltage stress waveforms.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage direct current transmission, and more specifically, relates to a full-operating-condition equivalent testing device for capacitors used in direct current transmission. Background Art

[0002] Ultra-high voltage direct current transmission and flexible direct current grid have become effective technical means to solve the problems of renewable energy acceptance, long-distance and large-scale power transmission, and to build a new power system with new energy as the main body. The flexible direct current transmission system using voltage source converter (VSC) has independent, accurate, flexible and convenient active power and reactive power regulation capabilities and regulation characteristics, which is very suitable for new energy power generation grid connection, urban power supply, island power supply and other fields.

[0003] As the most widely used modular multi-level voltage source converter (MMC) in VSC structure, each submodule needs to be equipped with a DC capacitor to support and stabilize the voltage of the converter valve group submodule, suppress the ripple on the DC side, and buffer the energy exchange between the AC side and the DC side. The MMC submodule consists of two insulated gate bipolar transistor switching devices, a diode connected in anti-parallel with them, and a DC capacitor.

[0004] The voltage of a single DC capacitor for flexible DC transmission is usually 2200VDC or 2800VDC, the capacitance of a single capacitor is 7-10mF, the maximum can reach 13mF, and the weight of a single capacitor exceeds 100kg. For safety reasons, such capacitors generally adopt an oil-free design, and the dielectric material is metallized polypropylene film and filled resin solid material. It is estimated that DC capacitors in flexible DC transmission projects account for 60% of the weight and more than 50% of the volume of the converter valve assembly.

[0005] As one of the core components of the flexible DC transmission converter valve, the long-term operating performance of dry DC capacitors directly determines the quality and safety of power conversion, and plays a vital role in the safe operation of high-voltage DC transmission projects. In actual operation, the voltage stress of capacitors used in high-voltage DC transmission equipment shows the characteristics of AC and DC voltage superposition, and each working cycle is accompanied by a continuous charging and discharging process with large currents; at the same time, due to the switching of the converter valve, the capacitor will also withstand periodic large-value pulse currents. Therefore, the test assessment of the actual operating stress of high-voltage capacitors is a key test project to effectively verify the long-term operating performance of capacitors. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides a full-operating-condition equivalent test device for capacitors for DC transmission, thereby solving the technical problem that the existing test devices can only output a single DC voltage or AC voltage, resulting in the test performance of the DC support capacitor being inconsistent with actual engineering applications.

[0007] To achieve the above object, according to one aspect of the present invention, a full-operating-condition equivalent test device for a capacitor for direct current transmission is provided, comprising: an alternating current voltage test module and a direct current voltage test module;

[0008] After the AC voltage test module is connected in parallel with the DC voltage test module, one end of the AC voltage test module is connected to the capacitor to be tested, and the other end is grounded;

[0009] The AC voltage test module is used to output an AC voltage with adjustable amplitude and frequency;

[0010] The DC voltage test module is used to output a DC voltage with adjustable amplitude and voltage boost rate.

[0011] Preferably, the AC voltage test module comprises: an AC voltage source, a first voltage regulator, a first transformer, a first protection resistor and a DC blocking capacitor;

[0012] The output end of the AC voltage source is connected to one end of the first voltage regulator, and the other end of the first voltage regulator is connected to the primary side of the first transformer; the secondary side of the first transformer is connected to one end of the first protection resistor; the other end of the first protection resistor is connected to one end of the DC blocking capacitor, and the other end of the DC blocking capacitor is connected to the output end of the DC voltage test module.

[0013] Preferably, the AC voltage test module further includes an AC charging switch and an AC discharging switch, wherein the AC charging switch is arranged between the first protection resistor and the DC blocking capacitor, and the AC discharging switch is arranged between the DC blocking capacitor and the capacitor to be tested.

[0014] Preferably, the DC blocking capacitor includes a plurality of capacitors having the same specifications as the capacitor to be tested.

[0015] Preferably, the DC blocking capacitor is a capacitor group formed by connecting a plurality of capacitors in series and parallel.

[0016] Preferably, the DC voltage test module comprises: a DC voltage source, a second voltage regulator, a second transformer, a second protection resistor and an isolation inductor;

[0017] The output end of the DC voltage source is connected to one end of the second voltage regulator, and the other end of the second voltage regulator is connected to the primary side of the second transformer; the secondary side of the second transformer is connected to one end of the second protection resistor; the other end of the second protection resistor is connected to one end of the isolation inductor, and the other end of the isolation inductor is connected to the output end of the AC voltage test module.

[0018] Preferably, the DC voltage test module further includes a DC charging switch and a DC discharging switch, wherein the DC charging switch is arranged between the second protection resistor and the isolation inductor, and the DC discharging switch is arranged between the isolation inductor and the capacitor to be tested.

[0019] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0020] 1. The full-operating-condition equivalent test device for capacitors for DC power transmission proposed in the present invention connects the test end of the AC voltage test module and the DC voltage test module in parallel to the capacitor to be tested, thereby solving the problem that the existing test device can only output a single DC voltage or AC voltage, causing the test performance of the DC support capacitor to be inconsistent with the actual engineering application. By inputting voltage stress waveforms under different operating conditions, effective assessment of the full-operating-condition stress of the capacitor is achieved.

[0021] 2. The full-operating-condition equivalent test device for capacitors for DC power transmission proposed in the present invention can freely switch the charge and discharge circuits by respectively setting AC and DC charge and discharge switches in the AC voltage test module and the DC voltage test module, thereby ensuring the safety of test personnel and equipment.

[0022] 3. The full-operating-condition equivalent test device for capacitors for DC transmission proposed in the present invention, in order to ensure the safe, stable and reliable operation of the DC blocking capacitors, the DC blocking capacitors are connected in series and parallel to form a capacitor bank, thereby reducing the voltage and current that each DC blocking capacitor bears during the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a full-operating-condition equivalent test device for a capacitor for direct current transmission according to the present invention;

[0024] Figure 2 It is a circuit diagram of an AC voltage test module in a full-operating-condition equivalent test device for a capacitor for DC power transmission of the present invention;

[0025] Figure 3 The invention discloses a circuit diagram of a DC voltage test module in a full-operating-condition equivalent test device for a capacitor for DC power transmission. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] like Figure 1 As shown, the present invention provides a full-operating-condition equivalent test device for capacitors for DC power transmission, specifically comprising: an AC voltage test module and a DC voltage test module; the output ports of the AC voltage test module and the DC voltage test module are connected in parallel at both ends of the capacitor to be tested, and one end thereof is grounded; the AC voltage test module is used to output an AC composite voltage with adjustable amplitude and frequency; the DC voltage test module is used to output a DC voltage with adjustable amplitude.

[0028] To further explain, the role of the DC blocking capacitor located at the AC tail end in the present invention is that the AC component only accounts for about 10% of the total voltage. From the perspective of the DC end, the AC circuit reactor and the secondary resistance of the transformer are extremely small. Installing a DC blocking capacitor at the AC tail end can effectively block the DC voltage from being directly applied to the AC equipment, preventing the DC equipment from short-circuiting or even burning.

[0029] Furthermore, the principle of selecting the DC blocking capacitor is to ensure that the capacitor to be tested can withstand sufficient voltage division while ensuring matching with the loop inductance. The voltage across the capacitor to be tested is:

[0030]

[0031] In the formula, C t Indicates the capacitor to be tested, C g Indicates DC blocking capacitor.

[0032] It can be seen from the formula that the larger the DC blocking capacitor, the greater the voltage across the capacitor to be tested. In order to make full use of the test capacity, C g ≥5C t , so as to ensure that the test voltage is applied to the capacitor to be tested as much as possible. However, when the specifications of the capacitor to be tested are similar to those of the DC blocking capacitor, in order to ensure the reliability of the DC blocking capacitor, it is impossible to ensure that C g Much larger than C t .

[0033] Furthermore, in order to ensure the safe, stable and reliable operation of the DC blocking capacitors, the DC blocking capacitors are connected in series and parallel to form a capacitor bank, thereby reducing the voltage and current that each DC blocking capacitor is subjected to during the test.

[0034] To further explain, the function of the isolation inductor in the present invention is to increase the impedance of the DC end, thereby reducing the current generated by the negative half-wave of the AC in the DC circuit.

[0035] To further explain, the function of the charge and discharge switch in the present invention is: to ensure the safety of test personnel and equipment and to prevent the surge current during the capacitor discharge process from flowing into the power supply side, the DC blocking capacitor and the capacitor to be tested need to be discharged during the end of the test.

[0036] The technical solution of the present invention is further illustrated by specific embodiments below.

[0037] Specifically, Figure 2 As shown, the AC voltage test module includes a composite AC voltage source U1, a first voltage regulator T1, a first transformer T2, a first protection resistor R1 and a DC blocking capacitor C g The output end of the composite AC voltage source U1 is connected to one end of the first voltage regulator T1; the other end of the first voltage regulator T1 is connected to the primary side of the first transformer T2; the secondary side of the first transformer T2 is connected to one end of the first protection resistor R1; the other end of the first protection resistor R1 is connected to one end of the AC charging switch S1, and the other end of the AC charging switch S1 is connected to the DC blocking capacitor C g and the AC discharge switch S2; the DC blocking capacitor C g The other end is connected in parallel with the output end of the DC voltage test module.

[0038] Specifically, Figure 3 As shown, the DC voltage test module includes a DC voltage source U2, a second voltage regulator T3, a second transformer T4, a second protection resistor R2 and an isolation inductor L g The output end of the DC voltage source U2 is connected to one end of the second voltage regulator T3; the other end of the second voltage regulator T3 is connected to the primary side of the second transformer T4; the secondary side of the second transformer T4 is connected to one end of the second protection resistor R2; the other end of the second protection resistor R2 is connected to one end of the DC charging switch S3, and the other end of the DC charging switch S3 is connected to the isolation inductor L g One end of the DC discharge switch S4 is connected to the discharge resistor R3, and the isolation inductor L g The other end is connected in parallel with the output end of the AC voltage test module.

[0039] In order to ensure the capacity utilization rate and loop operation reliability of the full working condition equivalent test loop, the parameters of the blocking capacitor need to be reasonably designed. The implementation case of the present invention uses 2.8kV / 8mF DC support capacitor as the capacitor to be tested. This example selects 18 DC support capacitors with model specifications of 2.8kV / 8mF as blocking capacitors. The electrical connection of 18 capacitors is 3 strings of 6 and constitutes a capacitor bank, so the total capacitance value of the blocking capacitor is 16mF. When carrying out the full working condition equivalent test, the DC voltage between the poles of the blocking capacitor is only 66.7% of the test capacitor. In the AC circuit, the blocking capacitor is in series with the test product, but the blocking capacitor itself is 6 parallel connections, so the current passed by each blocking capacitor is also only 16.7% of the test capacitor. So it can be ensured that in the test process, the operating condition of each blocking capacitor is only half of the test capacitor, which can ensure its safe, stable and reliable operation.

[0040] For the isolation inductor, a dry discharge coil with a voltage of 11 / √3kV and a single-phase matching capacity of 4Mvar is selected as the isolation inductor. When the AC voltage applied to the test product is 280V, the AC current value passing through the DC circuit is about 35μA, which is much smaller than the tolerable current of 1.1A on the DC side.

[0041] In order to ensure the safety of test personnel, a charge-discharge circuit should be introduced into the circuit, and the charge-discharge circuit can be adjusted by opening and closing the above-mentioned AC and DC charge-discharge switches. Before the test, the discharge switches S2 and S4 are opened, and the charging switches S1 and S3 are closed. At this time, the circuit is a full-condition equivalent test charging circuit; after the test, the power supply is turned off first, and then the discharge switches S2 and S4 are closed, and the charging switches S1 and S3 are opened. At the same time, in order to ensure that the discharge time is as fast as possible, the discharge resistor is selected to be composed of 4 2kΩ resistors, 2 in parallel and 1 in series.

[0042] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A full-operating-condition equivalent test device for capacitors for DC transmission, characterized in that: include: AC voltage test module and DC voltage test module; After the AC voltage test module is connected in parallel with the DC voltage test module, one end of the AC voltage test module is connected to the capacitor to be tested, and the other end is grounded; The AC voltage test module is used to output an AC voltage with adjustable amplitude and frequency; The DC voltage test module is used to output a DC voltage with adjustable amplitude and voltage boost rate.

2. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 1, characterized in that: The AC voltage test module includes: an AC voltage source, a first voltage regulator, a first transformer, a first protection resistor and a DC blocking capacitor; The output end of the AC voltage source is connected to one end of the first voltage regulator, and the other end of the first voltage regulator is connected to the primary side of the first transformer; the secondary side of the first transformer is connected to one end of the first protection resistor; the other end of the first protection resistor is connected to one end of the DC blocking capacitor, and the other end of the DC blocking capacitor is connected to the output end of the DC voltage test module.

3. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 2, characterized in that: The AC voltage test module further includes an AC charging switch and an AC discharging switch. The AC charging switch is arranged between the first protection resistor and the DC blocking capacitor, and the AC discharging switch is arranged between the DC blocking capacitor and the capacitor to be tested.

4. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 3, characterized in that: The DC blocking capacitors include a plurality of capacitors having the same specifications as the capacitor to be tested.

5. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 4, characterized in that: The DC blocking capacitor is a capacitor group formed by combining multiple capacitors in series and parallel.

6. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 1, characterized in that: The DC voltage test module includes: a DC voltage source, a second voltage regulator, a second transformer, a second protection resistor and an isolation inductor; The output end of the DC voltage source is connected to one end of the second voltage regulator, and the other end of the second voltage regulator is connected to the primary side of the second transformer; the secondary side of the second transformer is connected to one end of the second protection resistor; the other end of the second protection resistor is connected to one end of the isolation inductor, and the other end of the isolation inductor is connected to the output end of the AC voltage test module.

7. A full-operating-condition equivalent test device for capacitors for direct current transmission according to claim 6, characterized in that: The DC voltage test module further includes a DC charging switch and a DC discharging switch. The DC charging switch is arranged between the second protection resistor and the isolation inductor, and the DC discharging switch is arranged between the isolation inductor and the capacitor to be tested.

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