Environment-friendly digital high-voltage-class current transformer design method and current transformer

Abstract

The invention discloses a green digital high-voltage-class current transformer design method and a current transformer, and the design method comprises the steps: deducing a measurement error theoretical calculation formula of the current transformer, and determining the relation between digital load output and an electromagnetic unit according to the measurement error theoretical calculation formula; determining a secondary side rated capacity value according to digital load output requirements; determining parameters of an electromagnetic unit and an electromagnetic winding by combining a measurement error theoretical calculation formula of the current transformer and a relation between digital load output and the electromagnetic unit; the measurement error of the current transformer obtained through design is verified; if the verification is passed, the structure composition of an electromagnetic unit and an electromagnetic winding of the current transformer is completed, and non-SF6 insulating gas is adopted. Current measurement is achieved at the secondary side output end of the current transformer, the digital load output requirement is met, and digital transformation is promoted; and meanwhile, theoretical support is provided for large-scale application of clean air in measuring equipment insulating media and green development of high-voltage metering equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-voltage electrical equipment, in particular to a green and digital high-voltage level current transformer design method and a current transformer. BACKGROUND

[0002] The current transformer is an important current measurement device in the power system, and its measurement accuracy and stability are of great significance to the safe and stable operation of the power system and the construction of the smart grid.

[0003] The conventional digital access scheme flow of the current transformer is shown in Figure 1 The current transformer design has the problem that the secondary side rated capacity design value is too high to realize digitalization, which also leads to large equipment size, high cost, difficulty in transportation, and high probability of insulation failure, which is in sharp contradiction with the low power and micro-signal input requirements of digital relay devices.

[0004] Pure SF6 greenhouse gas is the main medium for gas-insulated medium current transformers in the current power system, and its strong greenhouse effect and long life characteristics pose a significant threat to climate change. Reducing the dependence on SF6 greenhouse gas by using clean air is a necessary measure to promote the transformation of green power grids. Compared with pure SF6 gas insulation, the advantages of clean air insulation are:

[0005] (1) Significant environmental protection. Zero greenhouse gas emissions, global warming potential (GWP) fully complies with the double carbon target and international environmental protection regulations, no recycling pressure, and reduces the carbon emissions of the whole life cycle;

[0006] (2) Improved economy. Clean air is low-cost, no need for SF6 gas procurement and high recycling processing fees, maintenance is simplified, no need to monitor gas leakage or regular air replenishment, and improves operation and maintenance efficiency;

[0007] (3) Good safety. No risk of suffocation or decomposition (such as SOF2) toxicity due to SF6 leakage, and has certain fireproof performance. Clean air itself is not flammable and can be applied to high fire risk scenarios.

[0008] The research and development of green and digital current transformers is a core environmental protection challenge and transformation direction faced by the global power industry, especially the power transmission and distribution field.

[0009] The disclosure of the above background technology content is only used to assist in understanding the concept and technical solutions of the present application, and it does not necessarily give technical teaching. SUMMARY

[0010] The application aims to provide a green digital high-voltage level current transformer design method, which can build a green and environmentally friendly power equipment solution while having the digitalization of power equipment.

[0011] To achieve the above-mentioned purpose, the technical solution adopted by the application is as follows:

[0012] A green digital high-voltage level current transformer design method, which is designed to obtain a current transformer of 500kV and above through the following steps:

[0013] The measurement error theoretical calculation formula of the current transformer is derived, and the relationship between the digital load output and the electromagnetic unit is determined based on the formula;

[0014] The secondary side rated capacity value is determined according to the digital load output requirement;

[0015] The parameters of the electromagnetic unit and the electromagnetic winding are determined in combination with the measurement error theoretical calculation formula of the current transformer, the relationship between the digital load output and the electromagnetic unit;

[0016] The measurement error of the designed current transformer is checked;

[0017] If the check is passed, the structure and composition of the electromagnetic unit and the electromagnetic winding of the current transformer are completed, and non-SF6 insulating gas is used.

[0018] Further, any of the above technical solutions or a combination of multiple technical solutions, the derivation method of the measurement error theoretical calculation formula of the current transformer is as follows:

[0019] According to the grid digitalization requirement, the following design is determined: the secondary side output capacity is related to the secondary side loop total impedance, the secondary side current, the electromagnetic unit size, and the electromagnetic winding number of turns, and the relationship formula is derived according to the vector diagram between each parameter of the current transformer: , wherein, S CSA represents the cross-sectional area of the electromagnetic unit, I 2n represents the rated secondary current, Z2 represents the secondary winding impedance, Z L represents the secondary load impedance, N2 represents the secondary winding number of turns, B represents the magnetic flux density of the electromagnetic unit core, and k represents a constant coefficient, which is 4.44 times the grid frequency.

[0020] The primary magnetic motive force is calculated according to the derived relationship formula, and the excitation current is determined accordingly;

[0021] The measurement error theoretical calculation formula of the current transformer is obtained according to the excitation current.

[0022] Furthermore, following any one or a combination of the aforementioned technical solutions, the magnetic flux density B is calculated based on the derived relational formula, and the magnetomotive force H per unit length corresponding to the calculated magnetic flux density B is determined based on the BH magnetization curve.

[0023] The average magnetic circuit length is determined based on the size of the electromagnetic unit and is defined as L. c ;

[0024] The primary magnetomotive force E1 is determined by the following formula: E1 = H × L c ;

[0025] The excitation current I is determined by the following formula. e = (H×L) c Substituting ε / N2 into the proportional error formula of the current transformer, we get ε≈I. e / I 2n Thus, the theoretical calculation formula for the measurement error of the current transformer is obtained.

[0026] Furthermore, based on any one or a combination of the aforementioned technical solutions, the excitation magnetomotive force H per unit length is determined using the following formula: H = B / μ, where μ is the permeability;

[0027] The theoretical formula for calculating the measurement error of a current transformer is as follows:

[0028]

[0029] Or simplified to .

[0030] Furthermore, following any one or a combination of the aforementioned technical solutions, after determining the secondary-side rated capacity value based on the digital load output requirements, the method further includes:

[0031] The secondary winding impedance Z2 is calculated using the following formula: Z2 = P 2n / (I 2n ) 2 , where P 2n This indicates the rated capacity value of the secondary side.

[0032] Furthermore, following any one or a combination of the aforementioned technical solutions, based on the secondary side rated capacity value required by the design and the maximum measurement error limit, the number of turns of the secondary winding, the average magnetic circuit length, and the permeability of the electromagnetic unit are first determined, thereby determining the minimum value of the core cross-sectional area of ​​the electromagnetic unit.

[0033] Furthermore, based on any or a combination of the aforementioned technical solutions, the iron core is designed as a ring structure;

[0034] The values ​​of the height and width of the iron core are optimized with the goal of balancing the control of consumable materials and the average magnetic circuit length.

[0035] The inner and outer diameters of the iron core are optimized within their respective ranges with the goal of minimizing the average magnetic circuit length.

[0036] Furthermore, based on any one or a combination of the aforementioned technical solutions, the electromagnetic unit of the current transformer is structurally optimized, including:

[0037] The secondary winding of the electromagnetic unit is designed as multiple independent windings, and the number of turns of the windings may be the same or different.

[0038] The secondary coil of the core assembly of the electromagnetic unit is insulated and encapsulated, and then assembled into the electromagnetic shielding cavity: a shielding cylinder made of aluminum alloy material is made, and an air gap is reserved for the core assembly to be assembled therein.

[0039] The end edge of the shielding cylinder adopts a curved transition structure, and the radius of curvature of the curved transition structure is between 20 and 40 mm.

[0040] Furthermore, based on any one or a combination of the aforementioned technical solutions, the parameters of the electromagnetic unit and the electromagnetic winding are determined in the following manner:

[0041] The magnetic flux density B of the iron core of the electromagnetic unit is determined by the following formula: B = B k / b, where B k Let be the magnetic flux near the knee of the core material, and b be the rated accuracy limit coefficient.

[0042] The average magnetic circuit length L is determined by the following formula. c =π×D avg , where D avg This is the arithmetic mean of the outer and inner diameters of the toroidal iron core.

[0043] According to another aspect of the present invention, a green and digital high-voltage current transformer is provided, which is designed using the method described above.

[0044] The beneficial effects of the technical solution provided by this invention are as follows:

[0045] a. In response to the shortcomings of traditional 500kV SF6 current transformers, such as high secondary side rated capacity redundancy making it difficult to digitize and insufficient environmental performance, clean air is innovatively used to replace pure SF6 or SF6 / N2 insulating gas. At the same time, the structural design of the current transformer is optimized to make the secondary side output parameters easy to digitize and meet the IEC61850 standard.

[0046] b. The method proposed in this invention for digital load output design of the secondary side of a current transformer can effectively reduce equipment size and manufacturing materials;

[0047] c. Directly realize current measurement at the output terminal of the secondary side of the current transformer to meet the requirements of digital load output and promote digital transformation: Based on the development requirements of digital grid and the actual secondary load of current transformer in 500kV substation, a design method for digital output requirements of secondary load is proposed, which can directly realize current measurement to meet digital requirements, accurately connect with the low-power signal transmission needs in the digital construction of smart grid, and promote the digital transformation of current transformer.

[0048] d. Using clean air as the insulating medium to replace pure SF6 or SF6 / N2: By controlling the air pressure and reconstructing the structural parameters of the core components of the current transformer, the greenhouse gas SF6 can be effectively replaced while ensuring that the insulation strength and thermal stability requirements are met. This eliminates problems such as toxic gas leakage, gas recovery and treatment, and carbon emissions, thereby improving the environmental performance and optimizing the environmental friendliness of the equipment. The solution provided by this invention provides theoretical support for the large-scale application of clean air as the insulating medium in high-voltage metering equipment.

[0049] e. Digital relay protection systems have power and level signal requirements for current transformer input. Traditional current transformer secondary output signals require the installation of precision sampling resistors, signal conditioning circuits, or the use of expensive dedicated CT interface chips for power matching and signal level conversion to meet the requirements of digital load output. At the same time, their rated power consumption is too high and their environmental performance is insufficient. This invention proposes a design method for digital output of current transformer secondary loads that fully meets the requirements of digital load output. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 A schematic diagram of the conventional solution for digitally connecting traditional current transformers;

[0052] Figure 2 A flowchart illustrating a green and digital high-voltage current transformer design method provided as an exemplary embodiment of the present invention;

[0053] Figure 3A schematic diagram illustrating the design features of the electromagnetic unit and electromagnetic winding structure of a current transformer, provided as an exemplary embodiment of the present invention.

[0054] Figure 4 A schematic diagram of the overall design features of a current transformer provided for an exemplary embodiment of the present invention. Detailed Implementation

[0055] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0056] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0057] Employing alternative technologies such as clean air to gradually phase out SF6 gas in power grid equipment is an inevitable trend and key measure for building a green and sustainable power system. Accelerating the research and development of green and digital current transformers will further speed up the transformation to an SF6-free green power grid. This invention aims to optimize the secondary load design of traditional 500kV SF6 current transformers based on digital load output requirements, thereby improving the equipment's environmental performance.

[0058] In one embodiment of the present invention, a green and digital design method for high-voltage current transformers is provided, such as... Figure 2 As shown, a current transformer of 500kV and above is designed through the following steps:

[0059] S100: Derive the theoretical calculation formula for the measurement error of the current transformer, and use it to determine the relationship between the digital load output and the electromagnetic unit;

[0060] The specific derivation method is as follows:

[0061] Based on the requirements of power grid digitalization, the following design is determined: the secondary side output capacity is related to the total impedance of the secondary side circuit, the secondary side current, the size of the electromagnetic unit, and the number of turns of the electromagnetic winding. Based on the vector diagram of the parameters of the current transformer, the following relationship is derived: , among which, S CSA I represents the cross-sectional area of ​​the iron core of the electromagnetic unit. 2n Z represents the rated secondary current, Z2 represents the secondary winding impedance, and Z... L N represents the secondary load impedance, N2 represents the number of turns in the secondary winding, B represents the magnetic flux density of the core of the electromagnetic unit, and k represents a constant coefficient, which is 4.44 times the power grid frequency.

[0062] The above formula The derivation process is as follows:

[0063] The secondary induced electromotive force Es = I of the current transformer 2n ×(Z2+Z L The following transformations are performed using Faraday's law of electromagnetic induction:

[0064] The standard form of Faraday's law is: Es = 4.44f × N² × B × S CSA ,get ;

[0065] That is, we can further obtain .

[0066] The primary magnetomotive force (MTF) is calculated based on the derived formula, and the excitation current is determined accordingly. Specifically, the MTF H per unit length corresponding to the calculated magnetic flux density B is determined based on the BH magnetization curve. The average magnetic circuit length, defined as L, is determined based on the electromagnetic unit dimensions. c The primary magnetomotive force E1 is determined by the following formula: E1 = H × L c ;

[0067] In this embodiment, the excitation magnetomotive force H per unit length is determined using the following formula: H = B / μ, where μ is the permeability; that is... Further determination .

[0068] According to Ampere's circuital law, the excitation current I... e The generated magnetomotive force is equal to the magnetic field strength multiplied by the magnetic circuit length, i.e., I e ×N2=H×L c ,Right now

[0069] The theoretical formula for calculating the measurement error of the current transformer is derived from the excitation current: the measurement error is the ratio error of the current transformer, and its fundamental source is the excitation current I. e Its simplest approximate definition is:

[0070] ε≈I e / I 2n ×100%; the above excitation current I e Substituting the expression, we obtain the theoretical formula for calculating the measurement error of the current transformer:

[0071]

[0072] Or simplified to .

[0073] S200: Determine the rated capacity value of the secondary side according to the digital load output requirements;

[0074] This also includes calculating the secondary winding impedance Z2 using the following formula: Z2 = P 2n / (I 2n ) 2 , where P 2n This indicates the rated capacity value of the secondary side.

[0075] S300: Determine the parameters of the electromagnetic unit and electromagnetic winding by combining the theoretical calculation formula of the measurement error of the current transformer and the relationship between the digital load output and the electromagnetic unit;

[0076] Based on the required secondary side rated capacity and the maximum measurement error limit, the number of turns, average magnetic circuit length, and permeability of the secondary winding of the electromagnetic unit are first determined, thereby determining the minimum value of the core cross-sectional area of ​​the electromagnetic unit. In one embodiment of the invention, the core is designed as a ring structure; the height and width of the core are optimized with the goal of balancing control materials and average magnetic circuit length; the inner diameter and outer diameter of the core are optimized within their respective ranges with the goal of minimizing the average magnetic circuit length. Furthermore, the electromagnetic unit of the current transformer is structurally optimized, including: designing the secondary winding of the electromagnetic unit as multiple independent windings with the same or different numbers of turns; completing the insulation encapsulation of the secondary coil of the core assembly of the electromagnetic unit, and then assembling it into the electromagnetic shielding cavity; fabricating a shielding cylinder made of aluminum alloy material, and reserving an air gap for assembling the core assembly therein; the end edge of the shielding cylinder adopts a curved transition structure, the radius of curvature parameter of the curved transition structure being between 20 and 40 mm. Specifically, the parameters of the electromagnetic unit and electromagnetic winding are determined as follows: the magnetic flux density B of the iron core of the electromagnetic unit is determined by the following formula: B = B k / b, where B k Let be the magnetic flux near the knee of the core material, and b be the rated accuracy limit coefficient; the average magnetic path length L is determined by the following formula. c =π×D avg , where D avg This is the arithmetic mean of the outer and inner diameters of the toroidal iron core.

[0077] S400: Verify the measurement error of the designed current transformer;

[0078] S500: If the verification passes, complete the structural composition of the current transformer electromagnetic unit and electromagnetic winding, using a non-SF6 insulating gas. After completing the structural design of the current transformer electromagnetic unit and single electromagnetic winding, a clean air insulating medium solution is adopted to replace pure SF6 or SF6 / N2 gas. Compared with the traditional SF6 current transformer that uses pure SF6 as the insulating medium, the operating conditions of this invention are 0.6 MPa gas pressure conditions, using clean air as the insulating medium, directly avoiding the use of the greenhouse gas SF6, and effectively reducing carbon emissions.

[0079] This embodiment includes the theoretical calculation of the current transformer winding error formula, the design of the digital load output on the secondary side of the current transformer, the design of the specific structural parameters of the electromagnetic unit and electromagnetic winding, and the innovative use of clean air insulation medium. By employing clean air insulation technology, the measurement error formula of the current transformer and the relationship between the digital output and the electromagnetic unit are calculated, thereby optimizing the secondary side output and structural parameters. This method, while ensuring the dielectric withstand voltage characteristics, thermal balance parameters, and meeting measurement error requirements, successfully reduces the size of traditional electromagnetic devices and the weight of electromagnetic units, improving equipment operational reliability and promoting the digital and green transformation of high-voltage metering equipment. Specifically, this embodiment mainly focuses on the design of the electromagnetic unit and electromagnetic winding. Their structural parameters are highly correlated with the secondary side digital load output. By calculating the measurement error formula, their quantitative relationship can be further obtained, facilitating the design of the specific structural parameters of the current transformer. This method can provide a theoretical basis for the structural design and error control of current transformers in high-voltage power metering devices, further optimizing the accuracy and stability of power metering.

[0080] The following is a more detailed explanation of step S300:

[0081] The relationship between the digital load output requirements of the current transformer and the electromagnetic unit can be seen from the formula derivation process and results in step S100:

[0082] To improve the measurement accuracy of a current transformer, i.e., to reduce the measurement error ε, the secondary winding impedance Z2 and / or the average magnetic path length L can be reduced. c Alternatively, increase the permeability μ and / or the number of turns N2 in the secondary winding and / or the core cross-sectional area S of the electromagnetic unit. CSA Accordingly, the design steps for secondary digital load output are as follows:

[0083] First, reducing the design value of the secondary load decreases the secondary load impedance, and according to the core cross-section calculation formula, the core cross-section decreases. Under the condition of keeping the error constant, combined with the above variable changes, it can be seen that the average magnetic path length decreases.

[0084] Finally, based on the above results, further derivation is made. After reducing the design value of the rated load on the secondary side, it can be seen from the calculation formula of the average magnetic circuit length that the inner and outer radii of the iron core winding and the cross-section of the iron core are reduced accordingly. This can effectively reduce the size of the electromagnetic unit, electromagnetic winding, and equipment, reduce manufacturing materials, and enable the secondary load to meet the requirements of digital output.

[0085] After revealing the relationship between the digital load output of the current transformer and the electromagnetic unit, and completing the analysis of the design and implementation ideas for the digital output of the secondary load, the specific structural parameters of the electromagnetic unit, electromagnetic winding, and shielding cylinder are designed. The specific calculation steps are as follows:

[0086] (I) Design of Electromagnetic Unit

[0087] (1) Working magnetic flux density B of the iron core:

[0088] The magnetization curve has good linearity, and the magnetic flux density of the iron core during normal operation can be calculated using the following formula: B = B k / b, where B k For the magnetic flux near the knee of the core material, protection level: B k =0.80~0.95, in T; b is the rated accuracy limit coefficient, which can be 30 in this embodiment.

[0089] This invention is designed for the digital requirements of 500kV current transformers. According to the measurement requirements of the current transformer, its measurement accuracy should meet the requirements of level 5P30. Taking the magnetic flux near the knee of the iron core material as 0.90T, and substituting it into formula (3), the magnetic flux density of the iron core during normal operation is about 0.03T.

[0090] (2) The cross-sectional area S of the iron core of the electromagnetic unit CSA :

[0091] As can be seen from the working principle of electromagnetic current transformers, the rated load output of the secondary winding of a current transformer is closely related to the material of the electromagnetic induction unit, the winding design, and the total impedance of the transformer and the secondary winding. For digital load output requirements, the rated load output on the secondary side should be lower than 2VA. Therefore, based on the measurement accuracy requirements of the 500kV current transformer 5P30 and reference engineering experience, the electromagnetic unit winding can be designed with 1200 turns and the total impedance of the electromagnetic unit is 8.0Ω. The core cross-sectional area S can be calculated using the formula derived above. CSA The minimum value is 11cm 2 .

[0092] The design thickness of the electromagnetic unit material is 26mm. The design values ​​for the height h and width w of the toroidal core structure need to be balanced. Appropriately increasing the core height h can reduce the average magnetic path length and improve electromagnetic conversion efficiency, but it will increase the material consumption of the secondary winding. Considering the above factors and engineering practice, a core cross-sectional height h of 44mm is chosen, resulting in a core cross-sectional area design value of 11.44cm. 2 .

[0093] (3) Inner diameter of iron core D i Outer diameter D o With average magnetic path length L c :

[0094] In the structural optimization process of power measurement devices, after the iron core assembly completes the insulation encapsulation process of the secondary coil, it needs to be precisely assembled into the electromagnetic shielding cavity. In actual engineering practice, the design of the iron core cavity geometry is highly correlated with the actual engineering project; the specifications of the shielding cylinder that meet the insulation performance requirements largely determine the size of the iron core cavity geometry. Based on extensive engineering experience, the inner diameter of the primary guide rod shielding cylinder is taken as 175mm. The shielding cylinder material designed in this invention is made of aluminum alloy with a thickness of 5mm, while reserving a certain air gap with a width of 18mm. Based on these parameters, the inner diameter D of the iron core is designed... i Outer diameter D o Through design, the inner diameter of the iron core is 221mm, the outer diameter of the iron core is 309mm, and the average magnetic circuit length is approximately 832mm.

[0095] To meet the requirements of multiple transformation ratios in practical applications, the secondary winding of the current transformer is designed as multiple independent windings with different numbers of turns.

[0096] The current transformer designed in this embodiment balances insulation strength and heat dissipation requirements, effectively improving operational reliability. Taking into full account the heat generated during transformer operation and the influence of various factors on the field strength distribution, the electromagnetic unit, electromagnetic winding, and shielding shell are designed to ensure excellent heat dissipation performance. This ensures that the operating field strength and temperature of the core components remain within acceptable ranges, achieving a synergistic improvement in insulation strength and heat dissipation performance, and guaranteeing the long-term stability and safety of the transformer.

[0097] (II) Design of Electromagnetic Single Winding

[0098] As shown by the derived theoretical formula for calculating measurement error, the measurement error of the current transformer is affected by the number of turns in the secondary winding. Based on the measurement accuracy and digital load output requirements, the rated transformation ratio is designed to be 2×600:1, the electromagnetic winding has 1200 turns, the secondary current is 1A, and the winding is uniformly wound in a single layer on the electromagnetic unit, using single-strand copper wire with a diameter of 1.18mm. From the design parameters, the conductor length of each layer and each turn of the winding is 8212mm.

[0099] Based on the above calculation results, the electromagnetic unit and electromagnetic winding structure of the current transformer are designed. Specific structural design features are as follows: Figure 3 As shown: The end edge of the shielding cylinder 100 adopts a curved transition structure, the electromagnetic unit 200 is set inside the shielding cylinder, and is designed as multiple independent electromagnetic single windings 300.

[0100] (III) Design of Shielding Cylinder

[0101] In the electromagnetic protection structure of high-voltage current transformers, the electromagnetic shielding sleeve performs multiple functions. Its main roles are to isolate the electromagnetic unit and electromagnetic winding from stray electric field coupling, and to provide mechanical positioning support and dielectric isolation protection. According to electromagnetic compatibility design principles, the inner cavity size of the shielding sleeve must form an insulating coordination relationship with the primary conductor, while the outer diameter parameter is determined by the electromagnetic unit size, winding air gap, and shielding sleeve material thickness. Calculations based on structural parameters determine the sleeve's outer diameter to be 349 mm.

[0102] The edge transition region employs a continuous curved surface transition structure. Based on electromagnetic field distribution theory, the radius of curvature of the transition surface directly affects the field strength gradient distribution characteristics inside the equipment. When the radius of curvature is below a critical value, the edge field strength distortion will significantly increase the probability of dielectric breakdown; conversely, an excessively large curvature value may weaken the spatial layout efficiency of the device. Based on practical engineering experience, an engineering optimization range of 20-40mm was ultimately selected, with the median value of 30mm taken as the design benchmark. This design achieves a balanced optimization of protective effectiveness and equipment integration while ensuring dielectric strength and structural rigidity.

[0103] Based on the calculation results of the specific structural parameters mentioned above, the overall design characteristics of the current transformer are as follows: Figure 4 As shown: The current transformer is installed inside the housing 500, and a conductor 400 is provided to electrically connect to the current transformer. A basin-type insulator 600 is also provided on the lower inner surface of the housing.

[0104] According to another aspect of the present invention, a green and digital high-voltage current transformer is provided, which is designed using the method described above.

[0105] This invention relates to a green and digital design method for high-voltage current transformers, aiming to solve the defects of traditional 500kV SF6 current transformers, such as high secondary side rated capacity redundancy making digitalization difficult and insufficient environmental performance. It innovatively uses clean air instead of pure SF6 or SF6 / N2 insulating gas, optimizes the secondary design according to digital load output requirements, and realizes that the secondary side output parameters are easy to digitally interface, complying with the IEC61850 standard, thus promoting the digital and green transformation of equipment.

[0106] Firstly, over 80% of traditional SF6 current transformers in 500kV substations have a rated capacity of over 10VA. However, the actual measured secondary output power is mostly below 2VA, less than 20% of the rated capacity. The actual operating load is far lower than the design capacity, which is inconsistent with the trend of small signal, low power, and lightweight development in digital power grids. Furthermore, a larger rated capacity design leads to a larger current transformer size, making the equipment bulky and contradicting the trend towards miniaturization and compactness in power equipment. A larger rated capacity design also requires more electromagnetic units and winding materials, resulting in larger and heavier equipment. Larger cores increase the difficulty of manufacturing and insulation design, and also increase the difficulty of transportation and installation, leading to a series of reliability issues. This invention analyzes the relationship between digital load output requirements and electromagnetic units, revealing the design principles for digital load output in the secondary side of current transformers.

[0107] Secondly, SF6 current transformers are gradually replacing oil-immersed current transformers in the market. The most common internal insulation media for electromagnetic current transformers are mainly of two types: insulating oil and SF6 gas. SF6 gas-insulated current transformers are oil-free products, offering higher reliability and preventing explosions and combustion compared to oil-immersed current transformers, with lower maintenance costs throughout their life cycle. However, their disadvantages are also obvious: SF6 gas has an extremely high greenhouse effect potential, 23,900 times that of CO2, and is difficult to decompose. Electrical equipment using pure SF6 gas will inevitably be gradually replaced in the future, making the search for environmentally friendly alternative gaseous media an urgent need for the power industry. This patent proposes a solution using clean air to replace SF6, effectively improving the environmental performance of current transformers and promoting their green development.

[0108] To achieve green and digital design of current transformers, this invention derives a theoretical calculation formula for current transformer measurement errors. Based on this formula, a quantitative analysis of the relationship between digital load output requirements and the electromagnetic unit is performed. Rated capacity values ​​are designed according to the digital load output requirements, and the structural parameters of the current transformer are redesigned. Specifically, the structural parameters of the secondary digital load output of the current transformer are given. This method successfully reduces the size of traditional electromagnetic devices, lowers the core weight, and reduces the insulation failure rate while ensuring the dielectric withstand voltage characteristics, thermal balance parameters, and meeting measurement error requirements. Simultaneously, the winding errors of the current transformer designed using this method are verified.

[0109] This invention considers the size requirements of clean air insulation equipment, resulting in a compact solution that is smaller, lighter, and uses fewer materials than conventional equipment, thus improving operational reliability. By reconfiguring the structural parameters of the core components of the current transformer, clean air is used as the insulating medium while meeting insulation requirements. This effectively reduces the cross-sectional area of ​​the electromagnetic unit and the overall equipment size, lowering material consumption and costs. It also solves problems related to difficult transportation and installation, effectively reducing the probability of equipment failure. Based on digitalization and green technology, the current transformer designed in this invention conforms to the IEC 61869-2 accuracy standard, with a measurement accuracy class of 5P30, 2VA, 600 / 1A, ensuring the measurement accuracy of the current transformer.

[0110] Specifically, the present invention discloses the following key points:

[0111] 1. Theoretical Calculation Formula for Current Transformer Error and Design Ideas for Secondary Digital Load Output. The requirements for digital load output are highly correlated with the electromagnetic unit. This invention first derives the theoretical error calculation formula for current transformers and quantitatively analyzes the relationship between the secondary digital load output and the electromagnetic unit structural design. Based on the quantitative relationship between the digital load output and the electromagnetic unit, the magnetic circuit is designed, revealing the design principles and methods of the electromagnetic unit and electromagnetic windings.

[0112] 2. Feasibility of large-scale application of clean air as an insulating medium in high-voltage metering equipment. The innovative use of clean air as an insulating medium can effectively replace pure SF6 gas or SF6 / N2 gas while meeting insulation and heat dissipation requirements. This directly avoids the use of greenhouse gases, effectively reduces carbon emissions, and proposes a solution that simultaneously achieves low power consumption and environmental friendliness.

[0113] Compared with existing traditional SF6 current transformers, the advantages of this invention are:

[0114] First, promote digital transformation: through the design of digital load output on the secondary side, accurately meet the low-power signal transmission needs in the construction of smart grids, promote the evolution of measurement equipment towards compact architecture and low-power mode, and conform to the trend of digital transformation of power system.

[0115] Secondly, improved environmental performance: The innovative use of clean air insulation technology replaces pure SF6 gas or SF6 / N2 gas as the insulation medium, directly avoiding the use of greenhouse gases and eliminating the risk of toxic gas leakage. This greatly improves the environmental performance of current transformers and provides theoretical support for the large-scale application of clean air in the insulation medium of measuring equipment.

[0116] Third, improved operational reliability: By reconfiguring the structural parameters of the core components of the current transformer, the electric field strength distribution and temperature distribution of the current transformer are improved, achieving a synergistic improvement in insulation strength and heat dissipation performance. At the same time, by reducing the rated capacity, the volume of the current transformer can be effectively reduced, the weight and cost of the equipment can be reduced, the difficulty of production, transportation and installation can be reduced, and the probability of equipment failure can be significantly reduced.

[0117] Fourth, improve economic efficiency: Using clean air insulation effectively simplifies the operation and maintenance process. After the equipment is decommissioned, the gas recovery does not require treatment, which improves the efficiency of equipment operation and maintenance and results in high economic benefits in the long run.

[0118] This invention provides theoretical and practical guidance for the green and digital design of high-voltage current transformers, and ensures the reliability and accuracy of high-voltage power metering devices.

[0119] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0120] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A green digital high voltage class current transformer design method, characterized by, The method comprises the following steps: deduce a measurement error theoretical calculation formula of the current transformer, and determine the relationship between the digitized load output and the electromagnetic unit based on the formula; determine the secondary side rated capacity value according to the requirement of the digitized load output; determine the parameters of the electromagnetic unit and the electromagnetic winding in combination with the measurement error theoretical calculation formula of the current transformer, the relationship between the digitized load output and the electromagnetic unit; verify the measurement error of the designed current transformer; if the verification is passed, complete the structure of the electromagnetic unit and the electromagnetic winding of the current transformer, and adopt non-SF6 insulation gas.

2. The current transformer design method of claim 1, wherein, The deduction mode of the measurement error theoretical calculation formula of the current transformer is as follows: According to the digital demand of power grid, the following design is determined: the output capacity of secondary side is related to the total impedance of secondary side circuit, the secondary side current, the size of electromagnetic unit and the number of turns of electromagnetic winding. According to the vector diagram of each parameter of current transformer, the relationship is derived as follows: Wherein, S CSA represents the cross-sectional area of the core of electromagnetic unit, I 2n represents the rated secondary current, Z2 represents the impedance of secondary winding, Z L represents the impedance of secondary load, N2 represents the number of turns of secondary winding, B represents the magnetic flux density of the core of electromagnetic unit, and k represents a constant coefficient, which is 4.44 times of the grid frequency; calculate the primary magnetomotive force according to the derived relationship, and determine the excitation current based on the primary magnetomotive force; obtain the measurement error theoretical calculation formula of the current transformer according to the excitation current.

3. The current transformer design method of claim 2, wherein, calculate the magnetic flux density B according to the derived relationship, and determine the unit length excitation magnetomotive force H corresponding to the calculated magnetic flux density B according to the B-H magnetization curve; According to the size of the electromagnetic unit, the average magnetic path length is determined, defined as L c ; The primary magnetomotive force E1 = H x L is determined by the following equation c ; The excitation current I is determined by the following equation e = (H x L c ) / N2, and the proportional error formula ε of the current transformer is substituted into the equation e = I 2n , to obtain the theoretical calculation formula of the measurement error of the current transformer.

4. The current transformer design method of claim 3, wherein, determine the unit length excitation magnetomotive force H by using the following formula: H=B / μ, wherein, μ is the magnetic permeability; the measurement error theoretical calculation formula of the current transformer is as follows: ； or simplified to .

5. The current transformer design method of any one of claims 2 to 4, wherein, after determining the secondary side rated capacity value according to the requirement of the digitized load output, the method further comprises the following steps: The secondary winding impedance Z2 is calculated by the following equation: Z2 = P 2n / (I 2n ) 2 where P 2n represents the secondary side rated capacity value.

6. The current transformer design method of claim 5, wherein, determine the secondary winding turns, the average magnetic path length and the magnetic permeability of the electromagnetic unit according to the required secondary side rated capacity value and the maximum limit of the measurement error, so as to determine the minimum value of the cross-sectional area of the core of the electromagnetic unit.

7. The current transformer design method of claim 6, wherein, design the core as a ring structure; optimize the values of the height and the width of the core with the goal of balancing the control material consumption and the average magnetic path length; optimize the values of the inner diameter and the outer diameter of the core within their respective ranges with the goal of minimizing the average magnetic path length.

8. The current transformer design method of claim 7, wherein, perform structure optimization on the electromagnetic unit of the current transformer, including: design the secondary winding of the electromagnetic unit as a plurality of independent windings, and configure the same or different winding turns; complete the insulation packaging of the secondary coil of the core assembly of the electromagnetic unit, and then assemble the core assembly into the electromagnetic shielding cavity: manufacture a shielding cylinder made of aluminum alloy, and reserve an air gap gap for assembling the core assembly into the shielding cylinder; the end edge of the shielding cylinder adopts a curved transition structure, and the curvature radius parameter of the curved transition structure is between 20 mm and 40 mm.

9. The current transformer design method of claim 1, wherein, The parameters of the electromagnetic unit and the electromagnetic winding are determined by using the method in any one of claims 1 to 9. The magnetic flux density B of the core of the electromagnetic unit is determined by the following formula: B = B k / b, wherein B k is the knee point magnetic flux of the core material, and b is a rated accuracy limit coefficient. The average magnetic path length L is determined by the following equation c = π x D avg where D avg is the arithmetic mean of the outer diameter and the inner diameter of the toroidal core.

10. A green digitized high voltage class current transformer, characterized by, ​

Images