Capacitive voltage transformer for gas insulated substation

Abstract

The invention discloses a capacitive voltage transformer for a gas insulated substation, which comprises a capacitive voltage divider and an electromagnetic unit, the capacitive voltage divider comprises a high-voltage capacitor C1 and a medium-voltage capacitor, the medium-voltage capacitor comprises a medium-voltage capacitor C21 and an externally connected medium-voltage capacitor C22, and the capacitance of the medium-voltage capacitor C22 is greater than that of the medium-voltage capacitor C21; the electromagnetic unit is connected with the capacitive voltage divider, an intermediate transformer and a compensation reactor are arranged in the electromagnetic unit, a full-shielding high-voltage shielding cover is arranged outside a high-voltage coil of the intermediate transformer, a damper and an overvoltage protector are arranged outside the electromagnetic unit, and the damper and the overvoltage protector are placed in an external junction box. The problem that in the prior art, an extra-high voltage transformer is low in lightning impulse overvoltage tolerance capacity is solved, the impulse overvoltage tolerance capacity is improved, and the breakdown risk is reduced.

Description

Technical Field

[0001] The invention relates to the field of high-voltage electrical appliances for power transmission and transformation equipment, and in particular to a capacitive voltage transformer for a gas-insulated transformer station. Background Art

[0002] UHV voltage transformer is an important device for realizing grid power metering, voltage measurement and system protection in UHV GIS equipment. However, due to structural limitations, the 1000kV column-type capacitor voltage transformer that is widely used in open substations cannot be directly installed on UHV GIS equipment. As the voltage level is increased to the UHV level, the production process and manufacturing difficulty of the conventional tank-type electromagnetic voltage transformer used in GIS equipment have increased significantly.

[0003] At present, the voltage transformer widely used in GIS is the tank-type electromagnetic voltage transformer. With the increase of voltage level, the manufacturing difficulty, process, cost, volume and weight of the tank-type electromagnetic voltage transformer will increase exponentially, and the insulation characteristics are also very poor. In particular, the tank-type electromagnetic voltage transformer is prone to ferromagnetic resonance with the power grid, and its ability to withstand lightning impulse overvoltage and operation impulse overvoltage is poor.

[0004] The capacitor voltage divider of the traditional column capacitor voltage transformer has a complex structure and a difficult manufacturing process. The capacitor voltage divider is composed of hundreds or thousands of capacitor units connected in series. The column capacitor voltage transformer is greatly affected by the high-voltage lead, adjacent objects and adjacent phase power supply. The ambient temperature and temperature gradient, the degree of contamination on the surface of the porcelain bushing and the relative humidity also have an impact on the error characteristics. Various factors such as high-voltage lead, temperature change (including the upper and lower temperature gradient of the column capacitor voltage divider) have an error influence of 0.3% on the 765kV voltage level column capacitor voltage transformer, and the combined influence is even greater.

[0005] In 2009, China Electric Power Research Institute (formerly Wuhan High Voltage Research Institute) and Shandong Taikai Instrument Transformer Co., Ltd. developed the first 1000kV tank CVT. From 2013 to 2014, the prototype was put into operation for one year at the live test site of the UHV AC test base. The insulation performance of the 1000kV tank capacitor voltage transformer was tested by applying the rated operating voltage and switching operations. During the operation, it was found that the product error caused by the change in ambient temperature exceeded the 0.2-level error range, but did not exceed the 0.5-level error range. Therefore, the product only met the 0.5-level voltage measurement requirement, but did not meet the 0.2-level measurement error requirement.

[0006] To this end, the Chinese invention patent application number CN200610020003.7 discloses a tank-type capacitor voltage transformer. However, there are still at least the following defects: the existing technology connects a small resistance inductor in series with the medium voltage lead wire to reduce the overvoltage amplitude of the VFTO and lightning impulse overvoltage acting on the electromagnetic unit. The hollow inductor of this structure will frequently break down and discharge under overvoltage, causing air chamber pollution, and ultimately leading to reduced insulation performance of the product. Summary of the invention

[0007] The embodiment of the present application solves the problems of low lightning impulse overvoltage tolerance of ultra-high voltage voltage transformers in the prior art by providing a capacitive voltage transformer for a gas-insulated substation, thereby improving the impulse overvoltage tolerance capability and reducing the breakdown risk.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solution: a capacitive voltage transformer for a gas-insulated substation, comprising a capacitive voltage divider and an electromagnetic unit, wherein the capacitive voltage divider comprises a high-voltage capacitor C1 and a medium-voltage capacitor, wherein the medium-voltage capacitor comprises a medium-voltage capacitor C 21 And the external medium voltage capacitor C 22 , medium voltage capacitor C 22 The capacitance is greater than the medium voltage capacitor C 21 The electromagnetic unit is connected to the capacitive voltage divider, an intermediate transformer and a compensating reactor are arranged inside the electromagnetic unit, a fully shielded high-voltage shielding cover is arranged outside the high-voltage coil of the intermediate transformer, a damper and an overvoltage protector are arranged outside the electromagnetic unit, and the damper and the overvoltage protector are placed in an external junction box.

[0009] In the electromagnetic unit, a fully shielded high-voltage shielding cover is set outside the high-voltage coil of the intermediate transformer, which can effectively improve the electric field distribution at the end of the high-voltage coil. When VFTO and lightning impulse overvoltage occur, the electric field is prone to distortion, and the fully shielded high-voltage shielding cover can make the electric field distribution more uniform, reducing the risk of insulation breakdown caused by excessive local electric field. The damper and overvoltage protector are placed in the external junction box, where the damper plays the role of absorbing energy in the circuit. When VFTO or lightning impulse overvoltage causes transient oscillations in the circuit, the damper can quickly absorb these oscillation energies, prevent the overvoltage from continuing to propagate and amplify in the circuit, and stabilize the circuit state.

[0010] As a further improvement of the above scheme, the high-voltage coil of the intermediate transformer adopts a rectangular structure; the rectangular structure of the high-voltage coil ensures that the impact potential gradient between coil layers is consistent, and no potential gradient distortion occurs under overvoltage impact, thereby avoiding the problem of local discharge, thereby improving the ability of the electromagnetic unit to withstand impact overvoltage.

[0011] As a further improvement of the above scheme, the differential tap adjustment winding is wound on the outer ring of the secondary low-voltage coil, and the high-voltage coil does not have an adjustment winding; thereby, the high-voltage coil structure can be relatively simple, without interference from additional adjustment components, and can be wound by a fully automatic winding machine.

[0012] As a further improvement of the above solution, the number of turns of each layer of wire is equal, and the secondary winding is wound in the order of 1a1n, 2a2n, 3a3n, ..., dadn from inside to outside.

[0013] As a further improvement of the above solution, the medium voltage capacitor C 22 NPO ceramic capacitors are used; NPO ceramic capacitors have excellent high-frequency characteristics and wide temperature stability. Therefore, by adjusting the formula ratio of ceramic capacitors and using a combination of positive temperature coefficient and negative temperature coefficient ceramic capacitors, the medium voltage capacitor C 22 The temperature coefficient of is close to that of the high voltage capacitor C1, thereby reducing the influence of temperature on product error.

[0014] As a further improvement of the above scheme, the insulating support at the end of the high-voltage capacitor C1 adopts an epoxy resin insulating cylinder, and the inner and outer walls of the epoxy resin insulating cylinder are provided with annular protrusions; epoxy resin itself has good mechanical strength, and it is made into an insulating cylinder for the insulating support at the end of the high-voltage capacitor C1, which can provide a stable physical support structure for the high-voltage capacitor. The annular protrusions on the inner and outer walls of the epoxy resin insulating cylinder increase the obstacles to the movement of impurities, effectively preventing impurities from forming a continuous conductive channel on the surface of the epoxy resin insulating cylinder, greatly improving the insulation reliability of the insulating support, and reducing the risk of surface discharge and flashover.

[0015] As a further improvement of the above scheme, it also includes an online error compensation module, which includes a compensation circuit, wherein two parts of voltage are extracted from the intermediate transformer coil of the electromagnetic unit, one part is used as the input of the isolated AC / DC power supply, and the other part is used as the input of the compensation circuit; the error compensation module can perform error compensation on the metering winding according to real-time conditions.

[0016] As a further improvement of the above solution, the output voltage of the isolated AC / DC power supply supplies power to the compensation circuit, and the compensation circuit has a temperature sensing element and an IC chip.

[0017] It can be seen from the above technical solutions that the present invention has at least the following technical effects or advantages: In the present invention, the electromagnetic unit is connected to the capacitive voltage divider, and a fully shielded high-voltage shielding cover is provided outside the high-voltage coil of the intermediate transformer of the electromagnetic unit, which can effectively improve the electric field distribution at the end of the high-voltage coil. When VFTO and lightning impulse overvoltage occur, the electric field is easily distorted, and the fully shielded high-voltage shielding cover can make the electric field distribution more uniform, reducing the risk of insulation breakdown caused by excessive local electric field. The damper and overvoltage protector are placed in the external junction box, where the damper plays the role of absorbing energy in the circuit. When VFTO or lightning impulse overvoltage causes transient oscillations in the circuit, the damper can quickly absorb these oscillation energies, prevent the overvoltage from continuing to propagate and amplify in the circuit, and stabilize the circuit state. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work: Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a structural schematic diagram of the electromagnetic unit; Figure 3 The medium voltage capacitor C 22 Schematic diagram of the structure; Figure 4 It is a structural schematic diagram of the insulation support; Figure 5 This is the schematic diagram of the online error compensation module.

[0019] Description of reference numerals: 1. Electromagnetic unit, 2. High-voltage capacitor C1, 3. Medium-voltage capacitor C 21 ,4. Medium voltage capacitor C 22 ,5. Intermediate transformer, 6. Compensating reactor, 7. Fully shielded high-voltage shielding cover. DETAILED DESCRIPTION In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments in this patent, other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this patent.

[0020] See also Figures 1 to 3The present invention discloses a capacitive voltage transformer for a gas-insulated substation, which includes a capacitive voltage divider and an electromagnetic unit 1. The capacitive voltage divider includes a high-voltage capacitor C12 and a medium-voltage capacitor, wherein the medium-voltage capacitor includes a medium-voltage capacitor C 21 3 and external medium voltage capacitor C 22 4. Externally connected medium voltage capacitor C 22 The capacitance of 4 is much larger than that of the medium voltage capacitor C 21 The capacitance of 3 is used to adjust the intermediate voltage (i.e. the voltage input to the electromagnetic unit).

[0021] Therefore, the medium voltage lead wire of the capacitor voltage divider is not connected in series with a small resistance inductance, and the overvoltage of VFTO and lightning impulse can be dealt with through the special structure of the electromagnetic unit 1.

[0022] The electromagnetic unit 1 is connected to the capacitive voltage divider, an intermediate transformer 5 and a compensating reactor 6 are arranged inside the electromagnetic unit 1, and a damper and an overvoltage protector are arranged outside the electromagnetic unit 1, and the damper and the overvoltage protector are placed in an external junction box.

[0023] A fully shielded high-voltage shielding cover 7 is provided outside the high-voltage coil of the intermediate transformer 5, and the high-voltage shielding cover 7 can improve the electric field distribution at the end of the high-voltage coil and improve the impact overvoltage tolerance level of the electromagnetic unit 1. At the same time, the high-voltage coil adopts a rectangular structure, and the number of turns of each layer of wire is equal, so as to ensure that the impact potential gradient between the coil layers is consistent and no distortion occurs.

[0024] The differential tap adjustment winding of the intermediate transformer 5 is wound on the outer ring of the secondary low-voltage coil, and the high-voltage coil does not have an adjustment winding, so it can be wound by a fully automatic winding machine to improve production efficiency. At the same time, the secondary winding is wound from the inside to the outside in the order of 1a1n, 2a2n, 3a3n, ...dadn, so as to achieve the minimum DC resistance of the metering winding 1a1n and improve the measurement accuracy (where "a" represents the positive polarity end of the secondary winding, and "n" represents the negative polarity end of the secondary winding).

[0025] The existing medium voltage capacitor structure is generally a thin film capacitor structure, which is prone to interlayer slippage during transportation. According to theoretical calculations and practical verification, the temperature coefficient of the high voltage capacitor C12 is 3×10 -5 K -1 In this embodiment, the medium voltage capacitor C 22 4. Using NPO ceramic capacitors, by adjusting the formula ratio of ceramic capacitors, using a combination of positive temperature coefficient and negative temperature coefficient ceramic capacitors, the temperature coefficient of the ceramic capacitor can be close to 3×10 -5 K -1 After calculation, the influence of temperature on product error is reduced to 0.05%, and the product error does not exceed the error requirement of 0.2 level ± 0.2% after temperature correction.

[0026] Moreover, NP0 ceramic capacitors have excellent high-frequency characteristics. According to actual tests, the capacitance deviation is only 0.63% at 50Hz-1MHz, and the maximum dielectric loss is 0.1%. Since NP0 ceramic capacitors have excellent high-frequency characteristics, they do not affect the transmission of high-frequency overvoltage, thus reducing the voltage of medium-voltage capacitors and the risk of breakdown.

[0027] The insulation support at the end of the high-voltage capacitor C12 adopts an epoxy resin insulation tube, and the inner and outer walls of the epoxy resin insulation tube are increased with circular protrusions (such as Figure 4 As shown). This can improve the support strength and block the movement of impurities along the surface, thus avoiding the occurrence of surface discharge and surface flashover.

[0028] In this embodiment, the gas-insulated substation capacitor voltage transformer further includes an online error compensation module, and the online error compensation module includes a compensation circuit. Figure 5 , the coil of the intermediate transformer 5 extracts two parts of voltage, one part as the input of the isolated AC / DC power supply, and the other part as the input of the compensation circuit. The output voltage of the isolated AC / DC power supply module powers the compensation circuit to drive the compensation circuit. The compensation circuit has a temperature sensing element and an IC chip. The compensation circuit sets the corresponding gain for the compensation input through the temperature sensing element and the IC chip, and outputs the required compensation amount. The compensation amount is finally compensated for the secondary circuit through the current transformer, thereby realizing the error temperature compensation of the metering winding 1a1n ( Figure 5 In the figure, a and a' are the positive polarity ends of the metering winding, and n and n' are the negative polarity ends of the metering winding).

[0029] Specifically in this embodiment, the effect of the inflation pressure on the product error also needs to be considered. 21 The insulating medium of 3 is SF6 gas. As the filling pressure increases, the capacitance also increases. However, the medium voltage capacitor C 22 4 is a ceramic capacitor, and its capacitance has nothing to do with the inflation pressure. Therefore, it is necessary to formulate a reasonable inflation pressure. After testing and calculation, when the pressure changes by 0.2MPa, the error changes by 0.04% (the maximum acceptable range of change). Therefore, considering the error limit, the acceptable range of pressure change is 0.2MPa. Therefore, the inflation pressure is 0.2MPa less than the rated inflation pressure. For example, if the rated inflation pressure is 0.4MPa, the inflation pressure is 0.38MPa.

[0030] In the description of the present invention, the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "vertical", "horizontal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the purpose of describing the present invention rather than requiring the present invention to be constructed or operated in a specific position, and therefore should not be construed as limiting the present invention. The terms "connected" and "connected" in the present invention should be understood in a broad sense, for example, it can be a connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in their embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novelties disclosed herein.

Claims

1. A capacitive voltage transformer for a gas insulated substation, characterized in that: The invention comprises a capacitive voltage divider and an electromagnetic unit (1), wherein the capacitive voltage divider comprises a high-voltage capacitor C1 (2) and a medium-voltage capacitor, wherein the medium-voltage capacitor comprises a medium-voltage capacitor C 21 (3) and the externally connected medium voltage capacitor C 22 (4) Medium voltage capacitor C 22 (4) The capacitance is greater than the medium voltage capacitor C 21 (3); the electromagnetic unit (1) is connected to the capacitive voltage divider, an intermediate transformer (5) and a compensating reactor (6) are arranged inside the electromagnetic unit (1), a fully shielded high-voltage shielding cover (7) is arranged outside the high-voltage coil of the intermediate transformer (5), and a damper and an overvoltage protector are arranged outside the electromagnetic unit (1), and the damper and the overvoltage protector are placed in an external junction box.

2. A gas-insulated capacitive voltage transformer for a substation according to claim 1, characterized in that: The high voltage coil of the intermediate transformer (5) adopts a rectangular structure.

3. A gas-insulated capacitive voltage transformer for a substation according to claim 2, characterized in that: The differential tap adjustment winding is wound on the outer ring of the secondary low-voltage coil, and the high-voltage coil does not have an adjustment winding.

4. A gas-insulated capacitive voltage transformer for a substation according to claim 3, characterized in that: The number of turns of each layer of wire is equal, and the winding order of the secondary winding from inside to outside is 1a1n, 2a2n, 3a3n, ...dadn.

5. A gas-insulated capacitive voltage transformer for a substation according to claim 1, characterized in that: Medium voltage capacitor C 22 (4) Use NPO ceramic capacitors.

6. A gas-insulated substation capacitor voltage transformer according to claim 1, characterized in that: The insulating support at the end of the high-voltage capacitor C1 (2) is an epoxy resin insulating tube, and both the inner and outer walls of the epoxy resin insulating tube are provided with circular protrusions.

7. A gas-insulated capacitive voltage transformer for a substation according to claim 1, characterized in that: It also includes an online error compensation module, which includes a compensation circuit, wherein two parts of voltage are extracted from the coil of the intermediate transformer (5) of the electromagnetic unit (1), one part is used as the input of the isolated AC / DC power supply, and the other part is used as the input of the compensation circuit.

8. A gas-insulated capacitive voltage transformer for a substation according to claim 7, characterized in that: The output voltage of the isolated AC / DC power supply supplies power to the compensation circuit, which has a temperature sensing element and an IC chip.

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