CN115421013A - A Method for Insulation Moisture and Aging Evaluation of Inverted Current Transformer - Google Patents

Abstract

The invention discloses an insulation damp and aging evaluation method for an inverted current transformer, which belongs to the technical field of power equipment insulation state evaluation and comprises the steps of obtaining imaginary part and real part basic data of composite dielectric constants of oil-impregnated paper with different water contents and different aging degrees, correcting the influence of water phase state change on dielectric parameters, establishing a dielectric parameter characteristic frequency band only influenced by the aging degree, carrying out frequency Wen Fanxiang translation on a main dielectric parameter curve, respectively carrying out fitting calculation on the characteristic frequency band influenced by the moisture and the characteristic frequency band influenced by the aging in an actually measured loss factor curve through a theoretical calculation expression of a total capacitance CA of the current transformer, and obtaining the moisture content and the polymerization degree when the fitting goodness of the curve is less than or equal to 3%. A direct measuring and calculating method is provided for the difference evaluation of the inverted current transformer distinguishing the insulation aging or damp state under wide temperature.

Description

A Method for Insulation Moisture and Aging Evaluation of Inverted Current Transformer

technical field

The invention belongs to the technical field of evaluating the insulation state of electric equipment, and in particular relates to an evaluation method for damp and aging of the insulation of an inverted current transformer.

Background technique

Inverted current transformers are more prone to insulation defects from the product manufacturing process. Compared with power transformers, although they are both oil-paper insulated power equipment, the oil-paper insulation of power transformers is concentrated in the relatively narrow inner space of the porcelain sleeve, and its oil-paper insulation The sandwich structure has large capacitance and thick insulation characteristics, and there is a big difference between the insulation structure and the ratio of oil and paper to the transformer. During production, due to the difficulty in controlling the winding process of the insulating part of the transformer during the manufacturing process, the winding is soft and there are pits or the insulation paper has wrinkles, which will lead to uneven distribution of the electric field, and the local field strength is too high. In severe cases, it may cause local Discharge, forming a hidden trouble in the operation of the transformer. At the same time, when the oil-immersed transformer is running, especially when the temperature is low in winter in the north, the volume of the sealing ring and insulating oil will shrink, and the outside gas and moisture may be sucked into the insulation. The interior causes the insulation to be damp; at the same time, the aging of the oil-paper insulation causes the molecular chain of the insulating material to break, and the formed low-molecular products will also generate a large amount of moisture and accelerate the aging process, which seriously affects the normal operation of the transformer and poses a certain threat to the safe operation of the power grid.

Most of the existing transformer field tests are high-voltage power frequency performance assessment (10kV, 50Hz). The test has certain damage, especially the cumulative effect of withstand voltage, which will also have a certain impact on the oil-paper insulation of the transformer, especially when the temperature is low. When water is analyzed, testing under high voltage may also cause faults such as insulation creepage and abnormal discharge breakdown.

When evaluating the insulation state of traditional inverted current transformers, the high-voltage bridge balance method is used, but the measurement data at a single frequency has a small amount of information, and it cannot give exact information on potential problems of the measured object, and it is impossible to distinguish Differences in insulation aging or damp condition. Moreover, the change rule of the dielectric properties of oil-paper insulation at low temperature is very different from the evaluation at normal temperature. The single temperature equivalent translation method is not applicable at low temperature. At present, it is still necessary to disassemble the mutual inductance for testing the moisture content and aging polymerization degree of the main insulating paper. It is measured by chemical titration analysis of paper samples taken by the device. The operation is complicated, the detection and evaluation cost is extremely high, and it cannot meet the requirements of my country's high-cold and low-temperature construction, commissioning and equipment operation status diagnosis.

Therefore, there is an urgent need for a novel technical solution in the prior art to solve this problem.

Contents of the invention

In order to overcome the deficiencies in the prior art, the present invention provides a method for evaluating the dampness and aging of the insulation of the inverted current transformer, which is used to solve the inability to distinguish the difference between the insulation aging or the damp state and the inability to evaluate the inverted current transformer under high cold and low temperature. The problem of accurate assessment of the insulation state.

In order to achieve the above object, the technical solution adopted by the present invention is: a method for evaluating the damp and aging of the insulation of an inverted current transformer, comprising the following steps, and the following steps are carried out in sequence,

Step 1. Conduct frequency-domain dielectric response tests on oil-impregnated papers with different moisture contents and aging degrees through the frequency-domain dielectric response test system at different test temperatures, and obtain the basic data of the imaginary part and real part of the complex dielectric constant;

Step 2. Using the basic dielectric response data of oil-impregnated paper with different water content obtained in step 1, construct a representation method for the dielectric parameters of the oil-impregnated paper-moisture composite medium system in the temperature ranges above zero degrees Celsius and below zero degrees Celsius respectively. Correct the influence of water phase change on dielectric parameters;

Step 3. Comparatively analyze the dielectric response data of oil-impregnated paper foundations with different aging degrees obtained in step 1, and establish a characteristic frequency band of dielectric parameters that is only affected by the degree of aging, so as to distinguish the influence of moisture and aging on the dielectric properties of oil-impregnated paper foundations. Effects on electrical response data;

Step 4. Calculate the total capacitance CA of the Ι main screen to the Λ main screen inside the inverted current transformer according to the voltage level and size of the current transformer;

Step 5. At a certain test temperature, obtain the spectrum loss factor curve of the inverted current transformer actually tested, and perform frequency-temperature reverse translation on the main curve of the dielectric parameter to obtain the basic dielectric data of the oil-immersed paper at this temperature. The basic dielectric data is complex permittivity;

Step 6. Combining the expression method of the dielectric parameters of the oil-impregnated paper-moisture composite medium system constructed in step 2, through the theoretical calculation expression of the total capacitance CA of the current transformer in step 4, the measured loss factor curve affected by moisture The characteristic frequency band is used for fitting calculation, and when the fitting degree of the curve is less than or equal to 3%, the moisture content of the oil-impregnated paper in the main insulation is obtained;

Step 7. Combining the aging basic data in step 3, through the theoretical calculation expression of the total capacitance CA of the current transformer in step 4, the characteristic frequency band affected by aging in the measured loss factor curve is fitted and calculated, and the fitting of the curve is excellent. When the degree of polymerization is less than or equal to 3%, the degree of polymerization of the oil-impregnated paper in the main insulation is obtained.

In said step 4, the total capacitance _CA of the inverted current transformer from the 1st main screen to the Λ main screen is obtained through the following steps,

① According to the voltage level and size of the current transformer, calculate the upper main insulation capacitance C _T of the inverted current transformer, which is equivalent to the series connection of an eccentric ring capacitance C _P , the outer cylinder capacitance C _W and the inner cylinder capacitance C _L structure, the calculation expression of each capacitor is as follows:

C _T ＝C _P +C _W +C _L (2)

In the formula, ε is the complex permittivity of oil-impregnated paper; ε0 is the vacuum permittivity, _8.854 ×10 ^-12 method/m; r _{x (Λ)} is the radius of the equivalent circle of the Λth main screen, unit: mm ; r _{x (Ι)} is the radius of the main screen of Ι outside the secondary winding of the ring, unit: mm; d _(Λ-Ι) is the eccentric distance between the main screen of Λ and the main screen of Ι, unit: mm; R _{x (Ι)} is the eccentricity of the main screen of Ι The distance from the center of the circle to the center of the busbar, unit: mm; R _{x (Λ)} is the distance from the eccentric center of the Λ main screen to the center of the busbar, unit: mm; R _{w (Λ)} is the distance from the outside of the eccentric circle of the Λ main screen to the center of the busbar , unit: mm; H _L is the thickness of the inner cylinder, unit: mm; H _w is the thickness of the outer cylinder, unit: mm;

② Calculate the lead capacitance C _n according to the structural size of the current transformer, which can be mainly divided into the capacitance C _m of the unterminated screen segment and the capacitance C _d of the end screen segment. The capacitance C _m of the unterminated screen segment can be calculated by concentric cylindrical capacitors calculate:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/meter; r _Λ is the equivalent radius of the Λ main screen at the lead section, unit: mm; r _i is the equivalent radius of the i-th end screen at the lead segment, unit: mm; L _(Λ) is the length of the Λ main screen without end screen segment, unit: mm;

Capacitance C _d of the end screen segment can be calculated according to the number of end screens, and the calculation expression for the main capacitance of the i-th end screen segment is:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/m; L _d is the length of the end screen, unit: mm; ΔL is the ladder difference of each end screen , unit: mm; δ _d is the insulation thickness between end screens, unit: mm;

Therefore, the lead capacitance C _kn of the current transformer with n end screens between the k-th main screen and the k-1 main screen can be expressed as:

In the formula, n is the number of end screens, unit: piece;

③The total capacitance C _A of the Ι main screen to the Λ main screen inside the inverted current transformer can represent the parallel calculation of the upper main insulation capacitance C _T and the lead capacitance C _kn ,

The specific method of the fifth step is to carry out the frequency-temperature translation calculation of the basic dielectric parameters of the oil-impregnated paper in different temperature zones, such as formula (7), to obtain the main curve of the basic data, and in the actual test through the frequency-temperature reverse Translation reduction, such as formula (8), can obtain the basic oil-impregnated paper dielectric response data under the actual test temperature;

In the formula, f _T is the frequency required to be translated to T temperature, unit: Hz; f ₀ is the test frequency, unit: Hz; T is the temperature required to be translated, unit: Kelvin; T ₀ is the test temperature, unit: Kelvin; ΔE(τ) is the relaxation activation energy of oil-impregnated paperboard, unit: kJ/mole; k is Boltzmann's constant, the magnitude is 1.38×10 ^-23 Joule/Kelvin.

Through the above design scheme, the present invention can bring the following beneficial effects:

1. Provide a direct calculation method for the difference evaluation of the inverted current transformer to distinguish the insulation aging or the damp state.

2. The effect of temperature on the viscosity of transformer oil and the change of water phase state on the dielectric parameters of oil-impregnated paper has been fully considered. It can be applied in a wide temperature range and meet the requirements of ambient temperature in domestic and foreign tests.

Description of drawings

Fig. 1 is a flow chart of a method for evaluating the insulation of an inverted current transformer exposed to moisture and aging according to the present invention.

Fig. 2 is a schematic diagram of the structure of the upper part of the inverted current transformer and the end of the lead wire in a method for evaluating the insulation of the inverted current transformer against moisture and aging according to the present invention.

Fig. 3 is a test wiring diagram of an inverted current transformer insulation damping and aging evaluation method according to the present invention.

FIG. 4 is a frequency-domain dielectric response loss factor curve diagram of an inverted current transformer at different temperatures in an embodiment of an inverted current transformer insulation damping and aging evaluation method according to the present invention.

Fig. 5 is a curve diagram of the fitting calculation curve of the frequency domain dielectric response loss factor calculated by the method of the present invention according to the actual measurement curve in an embodiment of the method for evaluating the insulation of an inverted current transformer exposed to moisture and aging of the present invention.

detailed description

Below in conjunction with accompanying drawing, specific embodiment of the present invention is described in detail

In order to illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art. The content specifically described below is illustrative rather than restrictive. Users can make various changes to the following parameters without departing from the mechanism and scope of the invention set forth in the claims. In order not to obscure the essence of the present invention, well-known methods and procedures have not been described in detail.

As shown in the accompanying drawings 1 to 5: a method for evaluating the damp and aging of the insulation of an inverted current transformer, including the following steps, and the following steps are carried out in sequence,

Step 1. Conduct frequency-domain dielectric response tests on oil-impregnated papers with different moisture contents and aging degrees through the frequency-domain dielectric response test system at different test temperatures, and obtain the basic data of the imaginary part and real part of the complex dielectric constant;

Step 2. Using the basic dielectric response data of oil-impregnated paper with different water content obtained in step 1, construct a representation method for the dielectric parameters of the oil-impregnated paper-moisture composite medium system in the temperature ranges above zero degrees Celsius and below zero degrees Celsius respectively. Correct the influence of water phase change on dielectric parameters;

Step 3. Comparatively analyze the dielectric response data of oil-impregnated paper foundations with different aging degrees obtained in step 1, and establish a characteristic frequency band of dielectric parameters that is only affected by the degree of aging, so as to distinguish the influence of moisture and aging on the dielectric properties of oil-impregnated paper foundations. Effects on electrical response data;

Step 4. Calculate the total capacitance CA of the Ι main screen to the Λ main screen inside the inverted current transformer according to the voltage level and size of the current transformer;

Step 5. At a certain test temperature, obtain the spectrum loss factor curve of the inverted current transformer actually tested, and perform frequency-temperature reverse translation on the main curve of the dielectric parameter to obtain the basic dielectric data of the oil-immersed paper at this temperature. The basic dielectric data is complex permittivity;

Step 6. Combining the expression method of the dielectric parameters of the oil-impregnated paper-moisture composite medium system constructed in step 2, through the theoretical calculation expression of the total capacitance CA of the current transformer in step 4, the measured loss factor curve affected by moisture The characteristic frequency band is used for fitting calculation, and when the fitting degree of the curve is less than or equal to 3%, the moisture content of the oil-impregnated paper in the main insulation is obtained;

Step 7. Combining the aging basic data in step 3, through the theoretical calculation expression of the total capacitance CA of the current transformer in step 4, the characteristic frequency band affected by aging in the measured loss factor curve is fitted and calculated, and the fitting of the curve is excellent. When the degree of polymerization is less than or equal to 3%, the degree of polymerization of the oil-impregnated paper in the main insulation is obtained.

In said step 4, the total capacitance _CA of the inverted current transformer from the 1st main screen to the Λ main screen is obtained through the following steps,

① According to the voltage level and size of the current transformer, calculate the upper main insulation capacitance C _T of the inverted current transformer, which is equivalent to the series connection of an eccentric ring capacitance C _P , the outer cylinder capacitance C _W and the inner cylinder capacitance C _L structure, the calculation expression of each capacitor is as follows:

C _T ＝C _P +C _W +C _L (2)

In the formula, ε is the complex permittivity of oil-impregnated paper; ε0 is the vacuum permittivity, _8.854 ×10 ^-12 method/m; r _{x (Λ)} is the radius of the equivalent circle of the Λth main screen, unit: mm ; r _{x (Ι)} is the radius of the main screen of Ι outside the secondary winding of the ring, unit: mm; d _(Λ-Ι) is the eccentric distance between the main screen of Λ and the main screen of Ι, unit: mm; R _{x (Ι)} is the eccentricity of the main screen of Ι The distance from the center of the circle to the center of the busbar, unit: mm; R _{x (Λ)} is the distance from the eccentric center of the Λ main screen to the center of the busbar, unit: mm; R _{w (Λ)} is the distance from the outside of the eccentric circle of the Λ main screen to the center of the busbar , unit: mm; H _L is the thickness of the inner cylinder, unit: mm; H _w is the thickness of the outer cylinder, unit: mm;

② Calculate the lead capacitance C _n according to the structural size of the current transformer, which can be mainly divided into the capacitance C _m of the unterminated screen segment and the capacitance C _d of the end screen segment. The capacitance C _m of the unterminated screen segment can be calculated by concentric cylindrical capacitors calculate:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/meter; r _Λ is the equivalent radius of the Λ main screen at the lead section, unit: mm; r _i is the equivalent radius of the i-th end screen at the lead segment, unit: mm; L _(Λ) is the length of the Λ main screen without end screen segment, unit: mm;

Capacitance C _d of the end screen segment can be calculated according to the number of end screens, and the calculation expression for the main capacitance of the i-th end screen segment is:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/m; L _d is the length of the end screen, unit: mm; ΔL is the ladder difference of each end screen , unit: mm; δ _d is the insulation thickness between end screens, unit: mm;

Therefore, the lead capacitance C _kn of the current transformer with n end screens between the k-th main screen and the k-1 main screen can be expressed as:

In the formula, n is the number of end screens, unit: piece;

③The total capacitance C _A of the Ι main screen to the Λ main screen inside the inverted current transformer can represent the parallel calculation of the upper main insulation capacitance C _T and the lead capacitance C _kn ,

The specific method of the fifth step is to carry out the frequency-temperature translation calculation of the basic dielectric parameters of the oil-impregnated paper in different temperature zones, such as formula (7), to obtain the main curve of the basic data, and in the actual test through the frequency-temperature reverse Translation reduction, such as formula (8), can obtain the basic oil-impregnated paper dielectric response data under the actual test temperature;

In the formula, f _T is the frequency required to be translated to T temperature, unit: Hz; f ₀ is the test frequency, unit: Hz; T is the temperature required to be translated, unit: Kelvin; T ₀ is the test temperature, unit: Kelvin; ΔE(τ) is the relaxation activation energy of oil-impregnated paperboard, unit: kJ/mole; k is Boltzmann's constant, the magnitude is 1.38×10 ^-23 Joule/Kelvin.

The different test temperature of step 1 is -40°C to 40°C; the frequency range of the frequency domain dielectric response test is 10 ^-3 Hz to 10 ³ Hz; the moisture content of the oil-soaked paper ranges from 0.5% to 5%; The aging degree of oil-impregnated paper refers to the degree of polymerization of oil-impregnated paper ranging from 300 to 1000.

In the specific implementation, the schematic diagram of the upper part and the structure size of the lead end in the calculation of the total capacitance of the oil-paper insulation in the inverted current transformer is shown in Fig. 2, where the four-layer end screen is taken as an example in the structure of the lead end in Fig. 2 .

The specific method for obtaining the frequency-domain dielectric response curve of the inverted current transformer is as follows: in Figure 3, Hi is the voltage electrode, Lo is the measurement electrode, and Ground is the ground electrode. Short-circuit and ground all the secondary side terminals 3 of the transformer, and disconnect the zero screen terminal 2 from the ground at the same time. During the test, connect the voltage output Lo of the insulation diagnostic analyzer FDS and the measurement terminal to the primary side bus terminal 1 of the transformer, and connect the current input Hi to the secondary side zero screen terminal 2 of the transformer. The specific wiring method is as follows: Figure 3 shows.

Place the tested current transformer with a voltage level of 66kV in a high and low temperature test oven, simulate the actual ambient temperature, and test its frequency domain dielectric response curve at three typical temperatures of 40°C, 0°C, and -40°C. Test, the test frequency range is 10 ^-3 Hz to 10 ³ Hz, and according to the curve, the method of the present invention is used to quantitatively analyze its insulation state. The loss factor test curves at three test temperatures are shown in Figure 4. As shown in the change law of the curve, it can be seen that with the decrease of the test temperature, the test curve of the low frequency band gradually decreases, while the test curve of the high frequency band gradually increases.

Adopt the method of the present invention to carry out the fitting calculation under different temperature zones to the test curve, the fitting calculation result is as shown in Figure 5, the moisture content in the oil-soaked paper in the mutual inductor calculated under three kinds of temperatures is respectively 1.25%, 1.15% %, 1.1%, the degree of polymerization is 685, 660, 670 respectively, the absolute error of calculation of moisture content at different test temperatures is 0.15%, and the absolute error of calculation of degree of polymerization is 25, which eliminates the influence of test temperature on calculation results and satisfies engineering requirements. Test requirements have proved the effectiveness of the method of the present invention.

Through the above method, a direct calculation method is provided for the evaluation of the insulation state of the oil-paper insulation system of the inverted current transformer, and the problem of being unable to distinguish the difference in insulation aging or damp state is solved. Using relevant theories and technical means such as frequency-domain dielectric response change rules in a wide temperature range, the moisture content and aging degree in the oil-paper insulation of inverted current transformers can be quantitatively evaluated in the high and low temperature range.

Apparently, the above-described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Claims (4)

1. A kind of inverted current transformer insulation be affected with damp and aging evaluation method, it is characterized in that: comprise the following steps, and following steps are carried out sequentially, Step 1. Conduct frequency-domain dielectric response tests on oil-impregnated papers with different moisture contents and aging degrees through the frequency-domain dielectric response test system at different test temperatures, and obtain the basic data of the imaginary part and real part of the complex dielectric constant; Step 2. Using the basic dielectric response data of oil-impregnated paper with different water content obtained in step 1, construct a representation method for the dielectric parameters of the oil-impregnated paper-moisture composite medium system in the temperature ranges above zero degrees Celsius and below zero degrees Celsius respectively. Correct the influence of water phase change on dielectric parameters; Step 3. Comparatively analyze the dielectric response data of oil-impregnated paper foundations with different aging degrees obtained in step 1, and establish a characteristic frequency band of dielectric parameters that is only affected by the degree of aging, so as to distinguish the influence of moisture and aging on the dielectric properties of oil-impregnated paper foundations. Effects on electrical response data; Step 4, according to current transformer voltage level, size, calculate the total capacitance C _A of the Ι main screen to the Λ main screen inside the inverted current transformer; Step 5. At a certain test temperature, obtain the spectrum loss factor curve of the inverted current transformer actually tested, and perform frequency-temperature reverse translation on the main curve of the dielectric parameter to obtain the basic dielectric data of the oil-immersed paper at this temperature. The basic dielectric data is complex permittivity; Step 6. Combining the expression method of the dielectric parameters of the oil-impregnated paper-moisture composite medium system constructed in step 2, through the theoretical calculation expression of the total capacitance C _A of the current transformer in step 4, the influence of moisture in the measured loss factor curve The characteristic frequency band is fitted and calculated, and the moisture content of the oil-impregnated paper in the main insulation is obtained when the goodness of fit of the curve is less than or equal to 3%. Step 7. In combination with the aging basic data in step 3, through the theoretical calculation expression of the total capacitance C _A of the current transformer in step 4, the characteristic frequency band affected by aging in the measured loss factor curve is fitted and calculated, and the fitting of the curve The degree of polymerization of the oil-impregnated paper in the main insulation is obtained when the degree of excellence is less than or equal to 3%. 2. according to claim 1, a kind of inverted current transformer insulation be affected with damp and aging evaluation method, it is characterized in that, the total capacitance _CA of the Ι main screen to the Λ main screen inside the inverted current transformer described in the step 4 Obtained by the following steps, ① According to the voltage level and size of the current transformer, calculate the upper main insulation capacitance C _T of the inverted current transformer, which is equivalent to the series connection of an eccentric ring capacitance C _P , the outer cylinder capacitance C _W and the inner cylinder capacitance C _L structure, the calculation expression of each capacitor is as follows:

L _(I-Λ) = 2πR _x(Λ) (1) R _A(I-Λ) ＝(r _x(Λ) +r _x(I) ) ² -d _(I-Λ) ² +R _G R _B(I-Λ) ＝(r _x(Λ) +r _{x (I)} ) ² -d _(I-Λ) ² -R _G C _T ＝C _P +C _W +C _L (2) In the formula, ε is the complex permittivity of oil-impregnated paper; ε0 is the vacuum permittivity, _8.854 ×10 ^-12 method/m; r _{x (Λ)} is the radius of the equivalent circle of the Λth main screen, unit: mm ; r _{x (Ι)} is the radius of the main screen of Ι outside the secondary winding of the ring, unit: mm; d _(Λ-Ι) is the eccentric distance between the main screen of Λ and the main screen of Ι, unit: mm; R _{x (Ι)} is the eccentricity of the main screen of Ι The distance from the center of the circle to the center of the busbar, unit: mm; R _{x (Λ)} is the distance from the eccentric center of the Λ main screen to the center of the busbar, unit: mm; R _{w (Λ)} is the distance from the outside of the eccentric circle of the Λ main screen to the center of the busbar , unit: mm; H _L is the thickness of the inner cylinder, unit: mm; H _w is the thickness of the outer cylinder, unit: mm; ② Calculate the lead capacitance C _n according to the structural size of the current transformer, which can be mainly divided into the capacitance C _m of the unterminated screen segment and the capacitance C _d of the end screen segment. The capacitance C _m of the unterminated screen segment can be calculated by concentric cylindrical capacitors calculate:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/meter; r _Λ is the equivalent radius of the Λ main screen at the lead section, unit: mm; r _i is the equivalent radius of the i-th end screen at the lead segment, unit: mm; L _(Λ) is the length of the Λ main screen without end screen segment, unit: mm; Capacitance C _d of the end screen segment can be calculated according to the number of end screens, and the calculation expression for the main capacitance of the i-th end screen segment is:

In the formula, ε is the complex dielectric constant of oil-impregnated paper; ε ₀ is the vacuum dielectric constant, 8.854×10 ^-12 method/m; L _d is the length of the end screen, unit: mm; ΔL is the ladder difference of each end screen , unit: mm; δ _d is the insulation thickness between end screens, unit: mm; Therefore, the lead capacitance C _kn of the current transformer with n end screens between the k-th main screen and the k-1 main screen can be expressed as:

In the formula, n is the number of end screens, unit: piece; ③The total capacitance C _A of the Ι main screen to the Λ main screen inside the inverted current transformer can represent the parallel calculation of the upper main insulation capacitance C _T and the lead capacitance C _kn ,

3. according to claim 1, a kind of inverted current transformer insulation be affected with damp and aging evaluation method, it is characterized in that, the specific method of described step 5 is, the basic dielectric parameter of oil-soaked paper is carried out in different temperature zones The frequency-temperature shift reduction, such as formula (7), obtains the main curve of the basic data, and in the actual test, through the frequency-temperature reverse shift reduction, such as formula (8), the dielectric response data of the basic oil-impregnated paper at the actual test temperature can be obtained ;

In the formula, f _T is the frequency required to be translated to T temperature, unit: Hz; f ₀ is the test frequency, unit: Hz; T is the temperature required to be translated, unit: Kelvin; T ₀ is the test temperature, unit: Kelvin; ΔE(τ) is the relaxation activation energy of oil-impregnated paperboard, unit: kJ/mole; k is Boltzmann's constant, the magnitude is 1.38×10 ^-23 Joule/Kelvin. 4. A method for evaluating insulation of an inverted current transformer according to claim 1, wherein the different test temperatures in step 1 are -40°C to 40°C; the frequency domain dielectric response test frequency is The range is 10 ⁻³ Hz to 10 ³ Hz; the water content of the oil-soaked paper ranges from 0.5% to 5%; the aging degree of the oil-soaked paper, that is, the degree of polymerization of the oil-soaked paper ranges from 300 to 1000.

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