CN1912638B - Tank type capacitor voltage transformer - Google Patents

Abstract

The invention relates to a tank-type CVT, which is composed of a sealed tank body, a high-voltage electrode, a medium-voltage electrode, an outlet sleeve and an electromagnetic unit, and is insulated by SF ₆ gas. The sealed tank body, high-voltage electrodes and medium-voltage electrodes are all coaxial cylinders Shaped structure; the high voltage arm capacitor C ₁ is formed between the high voltage electrode and the medium voltage electrode cylinder, the medium voltage arm capacitor C ₂ is formed between the medium voltage electrode and the sealed tank cylinder, the high voltage arm capacitor C ₁ and the medium voltage arm Capacitor _C2 forms a capacitive voltage divider. The invention has simple structure and process, low cost, good transient characteristics, stable and recoverable insulation performance, large insulation margin, and improved safety and reliability of the power grid; no ferromagnetic resonance phenomenon occurs when running on the power grid, and the error characteristics are stable, The linear relationship of the partial pressure ratio is good. The invention solves the problem of voltage transformers used in UHV and EHV GIS, and is suitable for electric energy measurement, relay protection and power monitoring in GIS of 1000kV voltage level grid, and can also be extended to 750kV, 500kV and lower voltage level grids .

Description

Tank type capacitor voltage transformer

technical field

The invention belongs to the field of high-voltage electrical appliances for power transmission and transformation equipment, and relates to a high-voltage capacitive voltage transformer, in particular to a tank-type capacitor-type voltage transformer (referred to as tank-type CVT), which is suitable for gas-insulated substations of 1000kV voltage level power grids (hereinafter referred to as GIS), the electric energy metering, relay protection and power monitoring can also be extended to 750kV, 500kV and lower voltage level grids.

Background technique

At present, the voltage transformer widely used in GIS is the electromagnetic voltage transformer (hereinafter referred to as VT). As the voltage level increases, the manufacturing difficulty, process, cost, volume, and weight of VT will increase exponentially, and the insulation properties are also very bad. Poor overvoltage capability. As far as the applicant knows, the only GIS with a voltage level of 1000kV in the world is Japan's Shinharuna 1000kV AC UHV substation, which uses electronic voltage transformers (hereinafter referred to as EVTs). The 1000kV GIS developed by three well-known power equipment manufacturing companies for the Xinzheng 1000kV AC UHV substation uses EVT, which has the following problems: poor stability of error characteristics, large variation, poor ability to withstand overvoltage transmission, and two of the prototypes did not meet the requirements. Design requirements, it will be damaged during the simulation operation, that is, the long-term electrification assessment process; even the product of a company with the best performance, its error characteristics are much worse than the traditional VT, and the stability is not good. Compared with VT and high-voltage capacitive voltage transformer (referred to as CVT), the shortcomings of EVT, such as poor reliability and poor error characteristics, have not been completely resolved so far. Since the world has not yet developed a 1000kV VT prototype, Japan's 1000kV UHV GIS chooses EVT because of the difficulty of VT development, and Japan's 1000kV EVT accuracy level only reaches level 1.

In addition, the traditional CVT is a column structure, and the capacitive voltage divider for high voltage is composed of multi-stage capacitive units (that is, capacitor cores) installed in the porcelain bushing. Column structure CVT is mainly used in open substations (referred to as AIS), and its capacitive voltage divider mainly has two insulation structures: one is an oil-immersed capacitive voltage divider with an oil-paper insulation structure, also known as a coupling capacitor ; The other is a capacitive voltage divider in which the organic insulating medium is mostly polyester film and SF ₆ gas insulation composite. Oil-paper insulation structure and polyester film SF ₆ gas-insulation composite structure are not suitable for _use in GIS. The film and tin foil (electrode) are coaxially wound. The composite structure of two materials with different dielectric coefficients is far inferior to the single insulating SF ₆ gas insulation in terms of recoverability.

If an oil-immersed capacitor is installed in the GIS, not only the electric field distribution is uneven, but also because of the insulating oil, the sealing of the interface of different media and the electric field are not easy to handle, it is easy to pollute the GIS tank, and the SF ₆ gas cannot be fully utilized. Excellent characteristics for use in uniform electric fields or slightly inhomogeneous electric fields. The dielectric coefficients of oil paper and SF ₆ gas are different, and it is easy to distort the electric field strength near the two media, so that the effect of SF ₆ gas cannot be exerted. Another drawback of oil-immersed CVTs is the potential for explosive combustion. Polyester film SF ₆ gas-insulated composite structure CVT, the main insulation of the capacitive voltage divider that withstands high voltage is organic insulation material, once the insulation damage occurs, it is permanent, and its insulation performance cannot be recovered.

The capacitive voltage divider of the traditional column CVT has complex structure and difficult manufacturing process. The capacitive voltage divider is composed of hundreds or hundreds of capacitor units connected in series; The ambient temperature and temperature gradient, the degree of pollution 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 wires and temperature changes (including the temperature gradient difference between the upper and lower sides of the column capacitor voltage divider) have an influence of 0.3% on the error of the 765kV voltage level column CVT, and the combined influence is even greater.

Contents of the invention

The purpose of the present invention is to improve the defects of the prior art and provide a tank-type CVT with a new design concept, mainly to solve the problem of the transient overvoltage distribution of the primary winding of the voltage transformer used for UHV, EHV and HV GIS. Both of them cause problems such as lack of insulation performance, the risk of ferromagnetic resonance with the power grid, and difficult manufacturing processes.

The technical solution of the present invention is a tank-type CVT, which is composed of a sealed tank body, a high-voltage electrode, a medium-voltage electrode, an outlet sleeve and an electromagnetic unit. The high-voltage electrode and the medium-voltage electrode are in the sealed tank body, and the sealed tank body It adopts SF ₆ gas insulated tank structure, and the electromagnetic unit is externally mounted. It is characterized in that: the sealed tank body 1, the high-voltage electrode 2 and the medium-voltage electrode 3 are all coaxial cylindrical structures, and the high-voltage electrode 2 is in the innermost layer, and the medium-voltage electrode 3 is in the innermost layer. The electrode 3 is between the sealed tank 1 and the high-voltage electrode 2; the high-voltage arm capacitance C ₁ is formed between the high-voltage electrode 2 and the cylinder of the medium-voltage electrode 3, and the medium-voltage electrode 3 and the sealed tank 1 are ground potential electrode columns A medium-voltage arm capacitor C ₂ is formed between the surfaces. The high-voltage arm capacitor C ₁ and the medium-voltage arm capacitor C ₂ form a capacitor voltage divider. The medium-voltage arm capacitor C ₂ can be one or more combinations. The above-mentioned electrode length and layer number and the adjustment of the distance between the electrodes can change the voltage division ratio of the capacitive voltage divider; the lead-out line of the medium-voltage electrode 3 is connected in series with the small resistance inductive reactance 6 and then connected to the electromagnetic unit 5, and the small resistance inductive reactance 6 is installed in the outlet sleeve Inside tube 4.

It is characterized in that: the small resistance inductive reactance 6 presents a low impedance value under the condition of power frequency 50Hz, and it presents a high impedance value under the action of fast steep wave overvoltage (VFTO for short) and lightning impulse overvoltage, and the small resistance inductive reactance 6 has Insulation recoverable helical structure, there is an air gap between winding turns for filling SF ₆ gas.

It is characterized in that: under the premise of meeting the lightning impulse voltage, the insulation of the medium voltage electrode 3 and the outlet bushing 4 also meets the tolerance level of VFTO - the maximum field of the electrode surface under the action of VFTO under the gas supply pressure of 0.35MPa Strong not greater than 26kV/mm.

It is characterized in that: the SF ₆ gas-insulated tank structure is an independent cabin structure, and its shape is an independent cylindrical tank body. The two ends of the high-voltage electrode 2 in the sealed tank body 1 are arc-shaped, and one end is installed through the plum blossom contact 7 There is a basin-type insulator 8, which is used for the sealing isolation of the GIS pipeline and the connection of the high-voltage electrode; the other end of the high-voltage electrode 2 is supported on the base of the sealed tank 1 through an insulating support rod 9; the medium-voltage electrode 3 is connected to the sealed tank Several insulating supports 10 are used to fix the cylindrical surfaces of the body 1 .

It is characterized in that: the medium-voltage electrode 3 can be directly installed in the GIS bus pipe as the sealed tank body 1, the high-voltage electrode 2 adopts the high-voltage conductor in the GIS bus pipe, that is, the bus bar, and the medium-voltage electrode 3 is located in the sealed tank body 1, that is, the GIS Several insulating supports 10 are fixed between the bus pipe and the high-voltage electrode 2 and the cylindrical surface of the bus, and between the medium-voltage electrode 3 and the sealed tank 1, that is, the cylindrical surface of the GIS bus pipe.

It is characterized in that: the medium voltage electrode 3 is directly installed in the GIS bus pipe as the sealed tank body 1, the high voltage electrode 2 is fixedly sleeved outside the high voltage conductor, that is, the bus bar 12 through a number of insulators 11, and the high voltage electrode 2 and the bus bar 12 are connected by wires To be equipotential, the medium-voltage arm capacitor C2 is composed of multi-layer medium-voltage electrodes 3 and multi-layer coaxial ground potential electrodes 13, and the multi-layer medium-voltage electrodes 3 and multi-layer ground potential electrodes 13 are alternately installed in the sealed tank That is, between the GIS bus pipe and the high-voltage electrode 2, the multilayer medium-voltage electrodes 3 are fixed to each other by a number of equipotential metal connecting rods 14 and fixed on the wall of the sealed tank 1, that is, the GIS bus pipe, by a number of insulating supports 10 , the multi-layer ground potential electrode 13 is fixed on the pipe wall of the GIS bus pipe through several metal fixing plates 15 .

It is characterized in that: an independent adjustable capacitor 16 for fine-tuning the capacity and voltage division ratio of the pressure arm capacitor _C2 in the capacitor voltage divider can also be connected outside the sealed tank body 1 .

The invention solves the problem of voltage transformers used in UHV, EHV and high-voltage GIS. Its capacitive voltage divider has simple structure and process, low cost and good transient characteristics. The main insulation is pure SF ₆ gas medium, and its insulation performance is stable and stable. Recoverable, large insulation margin, greatly improving the safety and reliability of the power grid; there will be no ferromagnetic resonance phenomenon when running on the power grid, and the error characteristics are good. It can be used not only as a voltage transformer, but also as a voltage divider or sensor Use: It is not easily affected by adjacent objects, the arrangement of high-voltage leads, that is, the proximity effect, and is not affected by pollution and relative humidity on error characteristics. The influence of temperature is small, and the error characteristics are stable. The linearity of the voltage division ratio means that the relationship between the voltage division ratio and the voltage level is good, and the uncertainty including temperature influence, voltage linearity, and harmonic influence is better than 0.03%. This technology can also be used in the EVT primary sensor of GIS, which improves the safety and reliability of AC UHV GIS.

Description of drawings

Fig. 1, embodiment one of the present invention is the structural representation of independent tank type CVT;

Fig. 2, the second embodiment of the present invention is the structural schematic diagram of the small current GIS pipeline structure tank type CVT;

Fig. 3, embodiment three of the present invention is the structural schematic diagram of tank type CVT of large current GIS pipeline structure;

Fig. 4, the side view of embodiment two of the present invention;

Fig. 5 is a schematic circuit diagram of the fourth embodiment of the present invention, that is, an externally connected adjustable capacitor tank type CVT.

In the figure, 1 sealed tank, 2 high-voltage electrodes, 3 medium-voltage electrodes, 4 outlet sleeves, 5 electromagnetic units, 6 small resistance inductive reactance, 7 plum blossom contacts, 8 pot insulators, 9 insulating support rods, 10 Insulation support piece, 11 insulation piece, 12 bus bar, 13 ground potential electrode, 14 equipotential metal connecting rod, 15 metal fixing plate, 16 adjustable capacitor

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Example

The present invention is suitable for UHV and ultra-high voltage GIS, as shown in Fig. 1, Fig. 2, Fig. 3, Fig. 4 and Fig. Pole 3, outlet bushing 4 and electromagnetic unit 5, the high-voltage electrode 2 and the medium-voltage electrode 3 are both in the sealed tank 1, adopting the SF ₆ gas insulated tank structure, and the electromagnetic unit 5 is externally attached; the sealed tank 1, high-voltage The electrode 2 and the medium voltage electrode 3 are coaxial cylindrical structures and the high voltage electrode 2 is in the innermost layer, the medium voltage electrode 3 is between the sealed tank body 1 and the high voltage electrode 2; the high voltage electrode 2 and the medium voltage electrode 3 The high-voltage arm capacitance C ₁ is formed between the cylinders, the medium-voltage arm capacitance C 2 is formed between the medium-voltage electrode 3 and the sealed tank 1, that is, the ground potential electrode cylinder, and the high-voltage arm capacitance C ₁ and the medium-voltage arm capacitance C _{2 constitute} Capacitive voltage divider, medium-voltage arm capacitor _C2 can be one or more combinations, the adjustment of the above-mentioned electrode length, layer number and distance between electrodes can change the voltage division ratio of the capacitor voltage divider, and the high-voltage electrode is the primary electrode The length depends on the secondary output capacity. The basic size is between 2 and 3 meters; Inside casing 4. The small resistance inductive reactance 6 is used to damp the influence of VFTO, lightning impulse overvoltage, and operating overvoltage on the electromagnetic unit 5 in the GIS. The small-resistance inductive reactance 6 connected in series presents a low impedance value under the condition of a power frequency of 50 Hz, and a high impedance value under the action of VFTO and lightning impulse overvoltage, reducing the overvoltage of VFTO and lightning impulse overvoltage acting on the electromagnetic unit 5. The voltage amplitude is different according to the VFTO oscillation frequency of the GIS outgoing line and the capacitive reactance value of the capacitor voltage divider, and the inductance value of the small resistance inductive reactance 6 is also different. For a tank-type CVT with a VFTO oscillation frequency of 5MHz, a voltage divider rated medium voltage of 3kV, and a high-voltage arm capacitance of 1000pF, the inductance value of the small inductive reactance 6 connected in series is controlled within the range of 10μH to 20μH. The small resistance inductive reactance 6 is designed to be insulated and recoverable. It is a spiral structure, and there is an air gap between the winding turns for filling with SF ₆ gas. The insulation design of the medium-voltage electrode 3 and the outlet bushing 4 takes into account the tolerance level of VFTO, and the maximum field strength of the electrode surface under the action of VFTO under the gas supply pressure of 0.35MPa is not greater than 26kV/mm.

Figure 1 is a schematic diagram of the structure of a tank-type CVT that can be used independently after the bushing is configured in Embodiment 1 of the present invention. Composed of bushing 4 and electromagnetic unit 5, the high-voltage electrode 2 and the medium-voltage electrode 3 are both inside the sealed tank 1, and the electromagnetic unit 5 is externally attached; the main insulating medium is SF ₆ gas, which has the recoverability of insulating performance, and is used as an independent cabin structure The sealed tank 1 is an independent cylindrical tank filled with SF ₆ gas for insulation; the two ends of the high-voltage electrode 2 in the sealed tank 1 are arc-shaped, and one end is installed with a basin-type The insulator 8 is used for the sealing isolation of the GIS pipeline and the communication of the high-voltage electrode, that is, the connection with the insulating sleeve; the other end of the high-voltage electrode 2 is supported on the base of the sealed tank 1 through an insulating support rod 9; a layer of medium piezoelectric The electrode 3 and the sealed tank body 1, that is, the cylinder surface of the ground potential electrode, are fixed with two turns of a total of 8 insulating support members 10; the diameter of the sealed tank body 1 is between 1 and 1.4m. According to conventional calculations, 1000kV SF ₆ gas The diameter of the insulating tank type VT is about 1.8m, the self-weight is about 8 tons, and the pressure on the end flange is greater than 120 tons. If the 1000kV tank-type CVT of the present invention is adopted, the diameter of the sealed tank body 1 is 1.4m, and its self-weight will be less than 2 tons, the maximum pressure on the end flange is about 70 tons. Due to the coaxial electrode structure, the insulation resistance level of the primary high voltage winding is much higher than that of the tank type VT with a diameter of 1.8m.

Fig. 2 is the second embodiment of the present invention, that is, the structural schematic diagram of the small current GIS pipeline structure tank type CVT, and Fig. 4 is the side view of the second embodiment of the present invention; in the second embodiment, the present invention also consists of a sealed tank body 1, Composed of high-voltage electrode 2, medium-voltage electrode 3, outlet bushing 4 and electromagnetic unit 5, both high-voltage electrode 2 and medium-voltage electrode 3 are in the sealed tank 1, and the electromagnetic unit 5 is externally hung; the main insulating medium is SF ₆ gas, It has the recoverability of insulation performance; the tank type CVT of the present invention is directly installed in the GIS bus duct as the sealed tank body 1, and the GIS bus duct is filled with SF ₆ gas for insulation, and the GIS bus duct is both the sealed tank body 1, for Relax the error requirements or when the bus current is a small current less than 4000A, the high-voltage conductor in the GIS bus pipe, that is, the bus, is the high-voltage electrode 2, and a layer of medium-voltage electrode 3 is between the sealed tank body 1, which is the cylinder surface of the GIS bus pipe. Support and fix with a total of 8 insulating support members 10 in two circles.

Fig. 3 is the third embodiment of the present invention, that is, the structural schematic diagram of the large-current GIS pipeline structure tank type CVT. 4 and an electromagnetic unit 5, the high-voltage electrode 2 and the medium-voltage electrode 3 are all in the sealed tank 1, and the electromagnetic unit 5 is externally attached; the main insulating medium is SF ₆ gas, which has the recoverability of the insulating performance; the tank-type CVT of the present invention directly Installed in the GIS bus duct, the GIS bus duct is filled with SF6 gas for insulation, the GIS bus duct is a sealed tank 1, for the GIS with a large rated current such as greater than 4000A, it requires higher accuracy and stable error In this case, the high-voltage electrode 2 is fixedly set outside the high-voltage conductor, that is, the bus bar 12, through two turns of a total of 8 insulating parts 11. The high-voltage electrode 2 and the bus bar 12 are connected by wires to be equipotential, and there is a gap between the high-voltage electrode 2 and the bus bar 12 without direct contact. , to prevent the heat on the high-voltage conductor from being directly transferred to the high-voltage electrode ₂ , which can reduce the influence of temperature on the voltage division ratio of the capacitor voltage divider; The axial ground potential electrode 13 and the GIS bus pipe wall are composed of the GIS bus pipe wall. The GIS bus pipe wall is also a layer of ground potential electrodes. Between the high-voltage electrodes 2, the three-layer medium-voltage electrodes 3 are fixed to each other by two turns of a total of eight equipotential metal connecting rods 14, and are fixed to the sealed tank body 1, that is, the wall of the GIS busbar, by two turns of a total of eight insulating support members 10 , 2 layers of ground potential electrodes 13 are fixed on the pipe wall of the GIS busbar through two circles of 8 metal fixing plates 15 in total, and the pipe wall of the GIS busbar is the third layer of ground potential electrodes. The three-layer medium-voltage electrode 3 and the ground potential electrode 13 structure are used to adjust the voltage division ratio of the capacitor voltage divider. The adjustment of the electrode length, the number of layers, and the distance between the electrodes can change the voltage division ratio of the capacitor voltage divider, as shown in Figure 3. Medium voltage arm capacitance C ₂ =C ₂₁ +C ₂₂ +C ₂₃ +C ₂₄ +C ₂₅ . The design dimensions in Fig. 3 are: the length of the high-voltage electrode 2 is 4.2m and the diameter is 0.4m, the diameter of the innermost medium-voltage electrode 3 is 0.8m, and the diameter of the sealed tank 1, which is the GIS bus pipe, is 1.3m, which can meet the Insulation performance requirements for 1000kV tank-type CVT for GIS with rated current 4000A～8000A, short-time power frequency withstand voltage 1200kV, lightning impulse voltage 2400kV, and operating impulse withstand voltage 1960kV.

In Fig. 5, it is a schematic diagram of the circuit principle of the fourth embodiment of the present invention, that is, an externally connected adjustable capacitor tank type CVT, for the small adjustment of the voltage division ratio of the capacitor voltage divider, and an externally connected independent adjustable capacitor 16 can also be measured outside the tank , at this time the capacitance of the medium voltage arm is C ₂ +C ₂ ′.

The capacitive voltage divider of the present invention has a simple structure, and the electrodes constituting the high-voltage arm capacitor C1 and the medium-voltage arm capacitor C2 are coaxial electrodes, and SF6 inert gas is used between the electrodes. Even if electrical breakdown occurs between the electrodes, the insulating properties between the electrodes can be restored after the applied voltage is removed. Such a structure has extremely high insulation properties and high insulation reliability. At the same time, it does not need an external secondary power supply, and does not use semiconductors and electronic devices such as laser devices and integrated circuits, which improves the safety and reliability of power grid operation. The special measure adopted by the present invention is the mode of inductive reactance with small resistance connected in series with medium-voltage electrode lead-out wires, so that the present invention has a very high ability to withstand VFTO, lightning (atmosphere) overvoltage and anti-transfer overvoltage in GIS. Extremely high safety and reliability of the secondary (measurement, measurement and relay protection) system, which is extremely important for VFTO and 1000kV voltage level UHV GIS that have a serious impact on transmission overvoltage.

Since the capacitive voltage divider of the present invention is placed in the SF ₆ gas tank, it is not affected by factors such as high-voltage leads, adjacent objects, adjacent phase power supplies, temperature field gradients, etc., the additional error has little influence, and the error stability is much higher than that of the column type CVT. It is extremely important to improve the accuracy level of UHV grid measurement. Due to the stable error characteristics of the present invention, the rated capacitance _Cn (parallel capacitance of _C1 and _C2 ) can be selected to be smaller than that of the column type CVT, so the volume of the capacitor voltage divider can be miniaturized, and its internal energy storage elements (capacitor, compensation reactance device) has small energy storage, which is beneficial to suppress the occurrence of internal ferromagnetic resonance, and is beneficial to improve the level of CVT transient characteristics.

The invention is especially suitable for ultra-high voltage and ultra-high voltage GIS, suitable for electric energy metering, relay protection and power monitoring of 1000kV voltage level grid, and can also be extended to 750kV, 500kV and lower voltage level grids; it can also be used on tanks Install high-voltage bushings to lead out high-voltage wires, and use them as independent voltage transformers for AIS. The invention can take into account the protection system requirements of various power systems, and has wide adaptability. It can not only meet the power drive requirements of the traditional relay protection system, but also can be easily converted into small signal analog or digital for the microcomputer protection system. The quantity needs to provide signal and power, and there is no need to provide additional secondary drive power.

Claims (7)

1. The tank-type capacitive voltage transformer is composed of a sealed tank, high-voltage electrodes, medium-voltage electrodes, outlet bushings and electromagnetic units. The high-voltage electrodes and medium-voltage electrodes are both in the sealed tank, and the SF ₆ gas insulation tank is used. type structure, the electromagnetic unit is plugged in, and it is characterized in that: the sealed tank body (1), the high-voltage electrode (2) and the medium-voltage electrode (3) are all coaxial cylindrical structures, and the high-voltage electrode (2) is in the innermost layer, The medium-voltage electrode (3) is between the sealed tank body (1) and the high-voltage electrode (2); the high-voltage arm capacitance C ₁ is formed between the high-voltage electrode (2) and the cylindrical surface of the medium-voltage electrode (3), and the medium-voltage electrode The medium-voltage arm capacitance _{C 2 is formed between the pole (3) and the sealed tank body (1), that is, the ground potential electrode cylinder, the high-voltage arm capacitance C 1 and} the medium-voltage arm capacitance C ₂ form a capacitive voltage divider, and the medium-voltage arm capacitance C ₂ can be one or more combinations, the adjustment of the length of the electrodes, the number of layers and the distance between the electrodes can change the voltage division ratio of the capacitive voltage divider; 6) After connecting with the electromagnetic unit (5), the small resistance inductive reactance (6) is installed in the outlet bushing (4). 2. The tank-type capacitive voltage transformer according to claim 1, characterized in that: the inductive reactance (6) of small resistance in series presents a low impedance value under the condition of power frequency 50 Hz, and the fast and steep wave overvoltage ( Under the action of VFTO) and lightning impulse overvoltage, it presents a high impedance value, and the small resistance inductance (6) has an insulating and recoverable helical structure, and an air gap for filling SF ₆ gas is left between winding turns. 3. The tank-type capacitive voltage transformer according to claim 2, characterized in that: the insulation of the medium-voltage electrode (3) and the outlet bushing (4) also meets 0.35MPa under the premise of meeting the lightning impulse voltage The maximum field strength of the electrode surface under the gas supply pressure under the action of VFTO is not more than 28kV/mm. 4. The tank-type capacitive voltage transformer according to claim 3, characterized in that: the capacitor voltage divider can be used as an independent cabin structure, and the sealed tank (1) is an independent cylindrical tank, and the sealed tank (1) The two ends of the inner high-voltage electrode (2) are arc-shaped, and one end of the high-voltage electrode (2) is installed with a pot insulator (8) through the plum blossom contact (7), which is used for sealing with the pipeline of the gas-insulated substation (GIS) Isolation and connection of high-voltage electrodes; the other end of the high-voltage electrode (2) is supported on the base of the sealed tank (1) via an insulating support rod (9); a layer of medium-voltage electrodes (3) and the sealed tank (1) ) between the cylinders are fixed with several insulating supports (10). 5. The tank-type capacitive voltage transformer according to claim 3, characterized in that: the medium-voltage electrode (3) can also be directly installed in the GIS bus duct as the sealed tank body (1), and the GIS bus duct is both In order to seal the tank (1), the high-voltage conductor in the GIS bus pipe, that is, the bus, is the high-voltage electrode (2), and a layer of medium-voltage electrodes (3) is used between the sealed tank (1), that is, the cylindrical surface of the GIS bus pipe. Several insulating supports (10) are fixed. 6. The tank-type capacitive voltage transformer according to claim 3, characterized in that: the medium-voltage electrode (3) is directly installed in the GIS bus duct as a sealed tank (1), and the high-voltage electrode (2) passes through Several insulators (11) are fixedly sleeved outside the high-voltage conductor, that is, the busbar (12), and the high-voltage electrode (2) is connected to the busbar (12) with wires to be equipotential, and the medium-voltage arm capacitor C2 is formed by the multilayer medium-voltage electrode (3) and multi-layer coaxial ground potential electrodes (13), the multi-layer medium-voltage electrodes (3) and multi-layer ground potential electrodes (13) are installed alternately on the sealed tank body (1), that is, the GIS busbar pipe wall and the high-voltage electrodes (2 ), the multi-layer medium-voltage electrodes (3) are fixed to each other by a number of equipotential metal connecting rods (14) and are fixed on the wall of the sealed tank (1) that is the GIS busbar by a number of insulating supports (10). The multilayer ground potential electrodes (13) are fixed on the pipe wall of the GIS bus through several metal fixing plates (15). 7. The tank-type capacitive voltage transformer according to claim 4, 5 or 6, characterized in that: an independent medium-voltage arm for fine-tuning the capacitor voltage divider can also be connected outside the sealed tank body (1) The capacity of capacitor C2 and the adjustable capacitor (16) of voltage division ratio.

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