Method for testing transformation ratio error of capacitor voltage transformer by using equivalent method

Abstract

The invention discloses a method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method, and belongs to the technical field of transformer measurement. Based on the Thevenin law, a CVT electromagnetic circuit is equivalent to a pure circuit, the transformation ratio K of the CVT is equal to the product of the transformation ratio K1 of a capacitive voltage divider CVD and the transformation ratio K2 of an equivalent intermediate voltage transformer IVT, the transformation ratio error r% is approximately equal to the sum of r1% and r2%, and the testing process is simplified. And high-precision standard equipment and a difference measurement method are selected, so that the test precision is improved. The method is suitable for the CVT with the voltage level of 110 kV and above, and is not limited by factors such as environment and space.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer measurement, and more particularly to a method for testing the ratio error of a capacitive voltage transformer by an equivalent method. Background Art

[0002] A capacitive voltage transformer, abbreviated as CVT (capacitor voltage transformer), is one of the main devices for the safe, economic and reliable operation of a power system and an important part of an electric energy metering device and a protection system. In order to dynamically master the performance and ratio accuracy of CVT equipment during operation, according to relevant national regulations, periodic on-site preventive tests are carried out on the ratio error of CVT, including the measurement of the capacitance of the voltage-dividing capacitor, the dielectric loss test, and the on-site inspection of the ratio error of CVT, etc., to ensure the safe operation of the power system and the accuracy of measurement, metering and protection. The error test of a capacitive voltage transformer is an important index for detecting whether the ratio error and phase angle error meet the accuracy requirements when the CVT transforms high voltage into low voltage. On-site testing of the ratio error of CVT is of great significance for the economic operation of the power system, improving the economic benefits of the power grid and ensuring safety and reliability.

[0003] The current status of on-site testing of CVT errors is as follows:

[0004] A capacitive voltage transformer consists of a capacitive voltage divider and an electromagnetic voltage transformer, and is suitable for measuring AC voltages of high voltage and extra-high voltage. The most important feature is its very high insulation impact strength. The manufacture of high-voltage-class CVT is easier than that of electromagnetic voltage transformers, with a smaller volume, lighter weight and lower price. Therefore, for voltage transformers with a voltage level of 110 kV and above, capacitive voltage transformers (CVTs) are mostly used. According to the DL / T956-1996 Regulations for Preventive Tests of Electric Equipment and other relevant specifications, the ratio error of CVT is tested on-site every 2-4 years to ensure the safe, economic and reliable operation of the power system.

[0005] Regarding the problem of testing the ratio error of high-voltage and extra-high-voltage CVTs, many scientific and technical workers have spent a great deal of energy on this, come up with many methods, published many articles on the Internet and in relevant journals, and also applied for some patents. However, in terms of their methods, they can be divided into the following two major categories:

[0006] Method 1: The full-voltage method for testing the transformation ratio error of a CVT, that is, when testing the transformation ratio error, apply 80% Un / √3, 100% Un / √3, and 120% Un / √3 of the normal rated voltage to the CVT. This requires a complete set of series resonance step-up test equipment: such as a frequency conversion control power supply, excitation transformer, resonance reactor, compensation reactor, capacitor voltage divider, compensation capacitor, etc. In addition, a high-precision standard voltage transformer of the same voltage level is also required. For these extra-high voltage devices, due to insulation requirements, their volume and weight are quite large and filled with SF6 insulating gas or insulating oil. Many manufacturers install them on a large truck and convert it into an on-site calibration vehicle for transformers. However, this method has the following problems:

[0007] 1. Due to the very high electrical insulation level requirements of on-site step-up equipment and standard voltage transformers, these devices are large in volume and heavy in weight, making testing inconvenient and the workload very large.

[0008] 2. It is required to provide a very large-capacity working power supply on-site, and sometimes the on-site power supply is difficult to meet.

[0009] 2. The voltage is very high, the safety measures are complex, and the difficulty of safety prevention and control is great.

[0010] 3. The testing work is sometimes restricted by space.

[0011] 4. The purchase cost is very high. The estimated price of a fully equipped transformer inspection vehicle is between 3 million and 4 million yuan.

[0012] 5. Large-scale supporting equipment filled with SF6 high-pressure gas or insulating oil is jolted during long-term transportation, and it is inevitable to form equipment air leakage, oil leakage or damage. Therefore, the maintenance cost is high.

[0013] 6. Affected by factors such as transportation, environment, and space.

[0014] Method 2: The method of extrapolating the error of a CVT by a model. Only apply a low-voltage voltage to the secondary of the CVT, use frequency conversion technology to obtain the excitation characteristic curve of the intermediate voltage transformer working area, and combine the error curve measured by the secondary low-voltage voltage to extrapolate the error of the transformer by a mathematical model. There are relatively many relevant articles and equipment for this type of method. However, this method has the following problems:

[0015] 1. The transformation ratio error of a CVT consists of two parts, CVD and IVT. The model extrapolation method is also difficult to reflect the true error situation of the transformation ratio of CVD.

[0016] 2. The transformation ratio error of the IVT is the error of the transformer deduced by using the mathematical models of the excitation characteristic curve and the load error curve. The excitation characteristic curve is a non-linear curve, which is affected by factors such as the material of the iron core, temperature, applied voltage frequency, voltage amplitude, number of winding turns, iron core structure, geometric dimensions, and iron core technology; the load error curve is affected by factors such as the magnitude and nature of the secondary load. The mathematical model is established based on limited characteristic quantities. Using the model extrapolation method, it is difficult to truly reflect the transformation ratio error of the CVT under the rated voltage and actual on-site working conditions.

[0017] 3. Without a corresponding primary standard device, the quantity transfer cannot be traced.

[0018] Therefore, how to provide a method for testing the transformation ratio error of a capacitive voltage transformer by the equivalent method is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0019] In view of this, the present invention provides a method for testing the transformation ratio error of a capacitive voltage transformer by the equivalent method. This method is simple and feasible, requires few devices, has a wide range of test objects, is economical, safe, efficient, and convenient, and can solve the technical defects existing in the above-mentioned prior art.

[0020] In order to achieve the above object, the present invention provides the following technical solutions:

[0021] A method for testing the transformation ratio error of a capacitive voltage transformer by the equivalent method, comprising:

[0022] S100: Equivalent the electromagnetic circuit of the capacitive voltage transformer CVT to a pure circuit, and split it into a capacitive voltage divider CVD and an equivalent intermediate voltage transformer IVT. Based on Thevenin's law, obtain the relationship between the transformation ratio K of the capacitive voltage transformer CVT, the no-load voltage division ratio K1 of the capacitive voltage divider CVD, and the transformation ratio K2 of the equivalent intermediate voltage transformer IVT, and obtain the correlation of the transformation ratio error;

[0023] S200: Conduct the error test of the transformation ratio K1 of the capacitive voltage divider CVD. Use a 0.001-level double-stage induction voltage divider and the differential measurement method to measure the ratio difference and phase angle difference between the transformation ratio K1 of the capacitive voltage divider CVD and the standard voltage division ratio Kf1 through a digital transformer calibrator.

[0024] S300: Conduct the error test on the transformation ratio K2 of the equivalent intermediate voltage transformer IVT. Select a 0.01 - level standard voltage transformer and a 0.001 - level double - stage induction voltage divider. Calculate the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer according to the transformation ratio K of the capacitive voltage transformer CVT and the measured transformation ratio K1 of the capacitive voltage divider CVD, and determine whether the error of the transformation ratio K1 of the capacitive voltage divider CVD is included in the comprehensive error; then calculate the transformation ratio Kf2 of the double - stage induction voltage divider according to the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer and the transformation ratio Kpt of the standard voltage transformer, determine the connection position of the double - stage induction voltage divider, and after adjusting the voltage regulator, measure the error of the transformation ratio K2 of the equivalent intermediate voltage transformer IVT with a calibrator.

[0025] S400: According to the calculation method of the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer, calculate the ratio error and phase angle error of the transformation ratio of the capacitive voltage transformer CVT respectively, and obtain the measured error.

[0026] Further, the S100 includes:

[0027] S110: Equivalent the electromagnetic circuit of the capacitive voltage transformer CVT to a pure circuit. Based on Thevenin's law, look into the circuit from the output port of the capacitive voltage transformer CVT for equivalence, and equivalently split the capacitive voltage transformer CVT into two parts: a capacitive voltage divider CVD and an equivalent intermediate voltage transformer IVT.

[0028] S120: Obtain that the transformation ratio K of the capacitive voltage transformer CVT is equal to the product of the no - load transformation ratio K1 of the capacitive voltage divider CVD and the transformation ratio K2 of the equivalent intermediate voltage transformer IVT, and the transformation ratio error r% of the capacitive voltage transformer CVT is equal to the sum of the transformation ratio error r1% of the capacitive voltage divider CVD and the transformation ratio error r2% of the equivalent intermediate voltage transformer IVT, that is, r% = r1% + r2%.

[0029] S130: Divide the transformation ratio error r% of the capacitive voltage transformer CVT into a ratio error ε% and a phase - angle difference δ, that is: ε% = ε1% + ε2%; δ = δ1 + δ2, where ε1%, ε2%, δ1, and δ2 are respectively the ratio error and phase - angle difference of the no - load transformation ratio K1 of the capacitive voltage divider CVD and the transformation ratio K2 of the equivalent intermediate voltage transformer IVT.

[0030] Further, S200 includes:

[0031] S210: Select a 0.001 - level double - stage induction voltage divider as the standard test equipment. According to the output quantity difference measurement method of the standard equipment and the device under test, use a digital transformer calibrator to measure the ratio and orthogonal analysis of the difference quantity, and obtain the relative ratio error and phase - angle difference of the transformation ratio K1 of the capacitive voltage divider CVD with respect to the voltage division ratio Kf1 of the high - precision 0.001 - level double - stage induction voltage divider.

[0032] S220: During testing, different adjustment operations are performed according to whether the capacitance values of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 in the capacitive voltage transformer CVT are known.

[0033] Further, S220 includes:

[0034] If the capacitance values of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 are unknown, disconnect the isolating switch, adjust the voltage regulator so that the output of the booster is the rated voltage of the primary of the double-stage induction voltage divider, and repeatedly adjust the induction voltage divider turntable to make the indicated value of the high-input impedance digital multimeter the smallest;

[0035] If the nominal capacitance values of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 are known, calculate the theoretical K1' in advance and set the secondary turntable of the double-stage induction voltage divider, and then adjust the last two turntables to make the indicated value of the digital multimeter the smallest.

[0036] Further, when performing the error test on the transformation ratio K1 of the capacitive voltage divider CVD, it is necessary to ensure that the input resistance of the differential pressure loop of the calibrator is greater than 20 kΩ to avoid changing the voltage division ratio of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 or introducing test errors.

[0037] Further, S300 includes:

[0038] S310: Select a 0.01-class standard voltage transformer and a 0.001-class double-stage induction voltage divider, and calculate the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer according to the transformation ratio K of the capacitive voltage transformer CVT and the measured transformation ratio K1 of the test capacitive voltage divider CVD;

[0039] S320: When K20 = K / K1, correct the no-load voltage division ratio K1 of the capacitive voltage divider CVD to the true value, and do not include the transformation ratio error r1% of the capacitive voltage divider CVD when calculating the comprehensive error of the capacitive voltage transformer CVT;

[0040] S330: When K20 = K / Kf1, the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer contains the transformation ratio error r1% of the capacitive voltage divider CVD, and the transformation ratio error r1% of the capacitive voltage divider CVD is included when calculating the comprehensive error of the capacitive voltage transformer CVT;

[0041] S330: Calculate the ratio Kf2 of the double-stage inductive voltage divider according to the theoretical ratio K20 of the equivalent intermediate voltage transformer and the ratio Kpt of the standard voltage transformer. When Kf2 ≥ 1, the double-stage inductive voltage divider is connected to the secondary voltage of the standard voltage transformer; when Kf2 < 1, the double-stage inductive voltage divider is connected to the secondary voltage terminal of the equivalent intermediate voltage transformer IVT. Adjust the voltage regulator to make the secondary voltage of the equivalent intermediate voltage transformer IVT the test voltage. The ratio error r2% and phase angle error δ2 measured by the digital transformer calibrator are the ratios of the actual ratio K2 of IVT to Kf2*Kpt or the ratio of K2*Kf2 to Kpt.

[0042] Further, S400 includes:

[0043] Before testing the error of the ratio K2 of the equivalent intermediate voltage transformer IVT, a carrier is connected to the low-potential end of the second high-voltage dividing capacitor C2, and the carrier needs to be short-circuited. If no carrier is connected, the low-potential end of the second high-voltage dividing capacitor C2 is directly grounded, and the connection tap between the capacitor voltage transformer CVT's capacitor voltage divider CVD and the equivalent intermediate voltage transformer IVT is disconnected.

[0044] Further, S400 includes:

[0045] When the theoretical ratio K20 of the equivalent intermediate voltage transformer is calculated using K20 = K / K1, the ratio error ε% of the capacitor voltage transformer CVT = r2%, and the phase angle difference δ = δ1 + δ2;

[0046] When the theoretical ratio K20 of the equivalent intermediate voltage transformer is calculated using K20 = K / Kf1, the ratio error ε% of the capacitor voltage transformer CVT = r1% + r2%, and the phase angle difference δ = δ1 + δ2.

[0047] Through the above technical solutions, compared with the prior art, the present invention discloses a method for testing the ratio error of a capacitor voltage transformer using the equivalent method. This method is simple and feasible, requires few equipment, has a wide range of test objects, is economical, safe, efficient, and convenient, and is suitable for on-site testing of the errors of CVTs with voltage levels of 110 kV and above. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0049] Figure 1 It is a schematic flow chart of the method of the present invention;

[0050] Figure 2 It is the structural schematic diagram of the CVT provided by the embodiment of the present invention;

[0051] Figure 3 It is the schematic diagram of the CVT that equivalent the electromagnetic circuit CVT to a pure circuit provided by the embodiment of the present invention;

[0052] Figure 4 It is provided by the embodiment of the present invention and ignores Figure 3 The schematic diagram of the pure electric circuit of the CVT in the case of the excitation impedance Zo of the IVT;

[0053] Figure 5 It is the schematic diagram after the pure electric circuit of the CVT is equivalent by the Thevenin's law provided by the embodiment of the present invention;

[0054] Figure 6 It is the schematic diagram of the detection circuit provided by the embodiment of the present invention;

[0055] Figure 7 It is the measurement schematic diagram of the mutual inductor calibrator provided by the embodiment of the present invention;

[0056] Figure 8 It is the loss schematic diagram of the high-voltage dividing capacitors C1 and C2 provided by the embodiment of the present invention;

[0057] Figure 9 It is the wiring diagram of the CVT provided by the embodiment of the present invention;

[0058] Figure 10 It is the wiring diagram for testing the IVT provided by the embodiment of the present invention;

[0059] Figure 11 It is the schematic diagram of the double-stage induction voltage divider connected to the secondary voltage terminal of the IVT provided by the embodiment of the present invention;

[0060] Figure 12 It is the overall test diagram of the CVT ratio error provided by the embodiment of the present invention. Specific embodiments

[0061] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] Embodiment 1:

[0063] See Figure 1 , the embodiment of the present invention discloses a method for testing the ratio error of a capacitive voltage transformer by the equivalent method, including:

[0064] S100: Equivalent the electromagnetic circuit of the capacitive voltage transformer (CVT) to a pure circuit, and split it into a capacitive voltage divider (CVD) and an equivalent intermediate voltage transformer (IVT). Based on Thevenin's law, obtain the relationship between the transformation ratio K of the CVT, the no-load voltage division ratio K1 of the CVD, and the transformation ratio K2 of the equivalent IVT, and get the correlation of the transformation ratio error.

[0065] S200: Conduct the error test of the transformation ratio K1 of the CVD. Use a 0.001-level double-stage induction voltage divider and the differential measurement method. Measure the ratio difference and phase angle difference between the transformation ratio K1 of the CVD and the standard voltage division ratio Kf1 through a digital transformer calibrator.

[0066] S300: Conduct the error test of the transformation ratio K2 of the equivalent IVT. Select a 0.01-level standard voltage transformer and a 0.001-level double-stage induction voltage divider. Calculate the theoretical transformation ratio K20 of the equivalent IVT according to the transformation ratio K of the CVT and the measured transformation ratio K1 of the CVD, and determine whether the error of the transformation ratio K1 of the CVD is included in the comprehensive error. Then, calculate the transformation ratio Kf2 of the double-stage induction voltage divider according to the theoretical transformation ratio K20 of the equivalent IVT and the transformation ratio Kpt of the standard voltage transformer, determine the connection position of the double-stage induction voltage divider, and measure the error of the transformation ratio K2 of the equivalent IVT with a calibrator after adjusting the voltage regulator.

[0067] S400: According to the calculation method of the theoretical transformation ratio K20 of the equivalent IVT, calculate the ratio difference and phase angle difference of the transformation ratio of the CVT respectively, and obtain the measured error.

[0068] Specifically, refer to Figure 2 the structural schematic diagram of the CVT shown, which includes an intermediate voltage transformer (IVT), the primary winding of the IVT, a compensation reactor, an adjustment winding, a secondary winding, damping windings d and d2, and a protective arrester.

[0069] It can be seen from Figure 2 that the CVT is mainly composed of a capacitive voltage divider (CVD) and an intermediate electromagnetic induction transformer (IVT). The CVD is composed of high-voltage voltage dividing capacitors C1 and C2; the IVT is composed of the primary winding, secondary winding, iron core, damping winding, error adjustment winding, compensation reactor, protective arrester, etc. of the electromagnetic induction voltage transformer. Among them:

[0070] The primary winding, secondary winding, and iron core: Convert the voltage divided by the CVD into a secondary voltage that can be accepted by instruments and protection equipment and has a certain load-carrying capacity and meets the requirements of the error grade specification.

[0071] Function of the compensating reactor: Since the voltage on the CVT varies with the load, an inductor is connected in series in the voltage dividing circuit to compensate for the internal impedance of the capacitor and stabilize the voltage.

[0072] Function of the regulating winding: Because capacitors have manufacturing tolerances, the voltage division ratio of the capacitive voltage divider usually slightly differs from the rated value, and the regulating winding is used for compensation.

[0073] Function of the damping winding: When the capacitive voltage transformer is subjected to instantaneous changes such as secondary side short - circuit and disconnection, ferromagnetic resonance may occur. Ferromagnetic resonance will generate large currents and over - voltages in the intermediate voltage circuit, causing harm to insulation, measuring instruments, and protection equipment. Therefore, a damping device must be used to suppress it.

[0074] Function of the protective arrester: When a fault occurs in the carrier equipment, causing the L and N at the tail of the CVD to open, high voltages will appear at L and N, endangering the carrier equipment, the secondary equipment connected to the intermediate voltage transformer, and personal safety. When there is a protective arrester, when the voltage rises to the action critical value of the protective arrester, it will automatically turn on to protect personal and equipment safety.

[0075] The capacitive voltage divider CVD divides the high voltage U1 of the power grid into a relatively low intermediate voltage Ua for output (the intermediate voltage is between (10 - 20) kV, generally 13 kV). Then the intermediate voltage transformer IVT further transforms the divided voltage Ua into a standard low voltage that can be received by instruments and protection. In this way, the insulation problem of high - voltage equipment is mainly concentrated on the capacitive voltage divider, which is relatively easy to solve. The intermediate voltage transformer with difficult - to - solve insulation now only bears a lower voltage, and the accuracy level is also easy to achieve.

[0076] Capacitive voltage transformers are generally classified into two types according to their structures: One is the unit type structure, where the capacitive voltage divider and the electromagnetic unit are independent of each other, can be assembled on - site, and the intermediate voltage line is exposed; the other is the integral type structure, where the capacitive voltage divider and the electromagnetic unit are an integral whole, and the intermediate voltage line is not exposed. For capacitive voltage transformers with voltage levels of 500 kV and below, both the integral type structure and the unit type structure are used. For capacitive voltage transformers with voltage levels of 750 kV and above, the unit type structure is mostly used.

[0077] Specifically, based on Figure 2 the principle, this embodiment analyzes the electromagnetic circuit of the CVT. First, the CVT of the electromagnetic circuit is equivalent to the CVT of the pure circuit, as shown in Figure 3 , including the intermediate voltage transformer IVT, the primary winding of the IVT, the compensating reactor, the regulating winding, the secondary winding, the damping windings d and d2, and the protective arrester. For the convenience of analysis, temporarily do not consider the damping winding and multiple secondary windings of the CVT, and only consider one secondary winding. This analysis is simple and easy to understand, and does not affect the equivalent theory.

[0078] In Figure 3 , C1 and C2 are high-voltage voltage-dividing capacitors, which are the first high-voltage capacitor and the second high-voltage capacitor respectively, U1 is the grid voltage, ZL, XL, and R are the resonant impedance, resonant reactance, and resonant resistance respectively; Zl1, Xl1, and R1 are the primary impedance, primary inductive reactance, and primary resistance of the intermediate transformer respectively; Zl2’, Xl2’, R2’, Zf2’, and U2’ are the secondary impedance, secondary inductive reactance, secondary resistance, secondary load impedance, and secondary voltage after conversion of the intermediate transformer respectively. According to the theory of electrical machinery, Zl2’ = Zl2 * K22, Xl2’ = Xl2 * K22, R2’ = R2 * K22, Zf2’ = Zf2 * K22, U2’ = U2 * K2, and K2 is the theoretical turns ratio of the intermediate voltage transformer IVT, K2 = Ua / U2; Zo is the exciting impedance of the intermediate transformer.

[0079] Since Zo >> Zl2’ + Zf2’, then Figure 3 is simplified to Figure 4 .

[0080] Regarding Figure 4 the pure electrical circuit of the CVT in Figure 5 the A part of Figure 5 is equivalent to Figure 5 the B part of Figure 5 by looking into the circuit from the output port U2’ of the CVT through Thevenin's theorem, that is

[0081] K1 = U1 / Ua = (C1 + C2) / C1 (1)

[0082] where C1 and C2 are the two high-voltage capacitors of the CVT respectively. C1 and C2 form a voltage divider, which is the capacitor voltage divider (abbreviation CVD: capacitor voltage divider); Figure 5 The equivalent capacitor Co in Figure 5 the B of

[0083] Regarding Figure 5 the equivalent circuit in

[0084] the B of

[0085] In order to reduce the inductive error caused by the primary impedance of the IVT, during the manufacturing design, make Xc≈XL+XL1 to form no-load resonance. See Figure 5 as shown.

[0086] While in reality: Xc=XL+XL1+λ To *Z0

[0087] where: λ To =(Xc-XL-XL1) / Z0 is the no-load resonance error

[0088] The load ratio error of K2: ε K2 ≈(R+R1) / Z0+(R-ZL1+Z2’) / Zf’+λTo.

[0089] K, K1, K2, U, Ua, and U2 in the above formula are all vectors.

[0090] Specifically, multiply formula (1) by (2), that is, K1*K2=(U1 / Ua)*(Ua / U2)=U1 / U2=K which is exactly the transformation ratio of the CVT. That is to say, through the circuit after Thevenin equivalence, the transformation ratio K of the CVT is equal to the transformation ratio K1 of the CVD multiplied by the transformation ratio K2 of the IVT. Also according to the error theory, excluding the influence of high-order small errors, the transformation ratio error r% of the CVT is approximately equal to the sum of the transformation ratio error r1% of the CVD and the transformation ratio error r2% of the IVT. That is, r%=r1%+r2%; and the transformation ratio error is further divided into ratio error ε% and phase angle difference δ(′), that is: ε%=ε1%+ε2% δ=δ1+δ2(′); where ε1%, ε2%, δ1, and δ2 are the ratio errors and phase angle differences of the transformation ratios of the CVD and the IVT respectively.

[0091] Specifically, regarding the feasibility of testing K1 and K2, it is as follows:

[0092] From the above analysis, it can be seen that a complete CVT can be equivalently split into two parts: the first part is the capacitor voltage divider CVD part, and the second part is the equivalent intermediate voltage transformer INT part. The transformation ratio K of the CVT is equal to the product of the transformation ratio K1 of the CVD and the transformation ratio K2 of the IVT. In this way, the error test of the transformation ratio K of the CVT is converted into the error tests of the transformation ratios K1 of the CVD and K2 of the IVT. The detection circuit is shown in Figure 6 , in the figure, 1 is the CVD, 2 is the IVT, 4 is the secondary load, 5 is the resonant reactance, and 6 is the equivalent capacitance.

[0093] From Figure 6As can be seen from B of the CVD, the no-load transformation ratio K1 of the CVD is independent of the load (i.e., the load across the secondary terminals of the intermediate voltage transformer) (the Ua output of the CVD is disconnected). In addition, it is independent of the frequency and amplitude of the power supply voltage. This characteristic brings great convenience to the test of the capacitor voltage division ratio. For example, for a CVT of (500 / √3) kV, when testing the capacitor voltage division ratio K1, only a voltage of several hundred volts (such as 600 V) needs to be applied. On the other hand, from the expression K1 = (C1 + C2) / C1 = 1 + C2 / C1, it can be seen that the no-load voltage division ratio K1 is sensitive to the manufacturing error of the capacitor capacitance or the measurement error of the capacitance. For the manufacturing error of the capacitance, this is the purpose of actual measurement; for the measurement error of the capacitance, the measurement method, measurement means and measurement equipment need to be considered.

[0094] The transformation ratio K2 is not sensitive to small changes in C1 and C2. On the other hand, it is also affected by the same factors as ordinary electromagnetic voltage transformers, such as frequency, voltage amplitude, secondary load size and its power factor, etc. Therefore, when testing the transformation ratio error of the IVT, in order to ensure the accuracy of the measurement, the test voltage applied to the IVT needs to be close to the rated voltage Ua and its corresponding secondary load. And Ua is the voltage after the grid voltage U1 is divided by the CVD, that is, Ua = U1 / K1, and Ua is generally (10 - 20) kV, and for CVTs of different manufacturers, Ua is different. For this voltage level of Ua, it is very easy to achieve on site, and it is very easy to select equipment such as step-up transformers and standard voltage transformers.

[0095] Through the above simple qualitative analysis, it is convenient and simple to test the error of the transformation ratio K1 of the CVD and the error of the transformation ratio K2 of the IVT.

[0096] Specifically, for the test of the CVD voltage division ratio K1, it is as follows:

[0097] The accuracy of on-site CVTs is generally 0.5, 0.2, 0.1 levels. In order to improve the measurement accuracy of the CVD transformation ratio K1 error test, when selecting standard test equipment, a 0.001-level double-stage induction voltage divider is used, that is, the measurement error introduced by the standard test equipment can be completely ignored; in the test method, the difference measurement method of the output quantities of the standard equipment (secondary voltage output of the induction voltage divider) and the equipment under test (CVD voltage division output) is selected, that is, the difference measurement method. According to the error test theory, the difference measurement method can greatly improve the measurement accuracy. For the measurement of the difference, a digital transformer calibrator is selected, and the ratio and orthogonal analysis of the difference quantity are carried out to measure the relative ratio difference and phase angle difference of K1 relative to the voltage division ratio Kf1 of the 0.001-level high-precision double-stage induction voltage divider.

[0098] Such as Figure 7As shown in the figure, T1 is an AC 220V voltage regulator; T2 is an AC step-up transformer: 200V / 1000V; DMT is a digital multimeter with high input impedance; T3 is a BFJ-3 inductive voltage divider, with a class of 0.001, a primary rated voltage of 600V, and a secondary output voltage: 0 - 600V; Y is a digital transformer calibrator; D is an isolating switch.

[0099] If the capacitance values of C1 and C2 are unknown. Disconnect the isolating switch D( Figure 7 ), energize the voltage regulator, and adjust the voltage regulator so that the output of the step-up transformer is the primary rated voltage of 600V of the double-stage inductive voltage divider. Repeatedly adjust the turntable of the inductive voltage divider so that the indication value of DMT is the smallest.

[0100] If the nominal values [C1] and [C2] of the capacitances of C1 and C2 are known, the theoretical K1’ can be calculated in advance, K1’ = 1 + [C2] / [C1]. Set the secondary turntable of the double-stage inductive voltage divider so that the turns ratio Kf’ of the double-stage inductive voltage divider is equal to K1’. After power-on, adjust the last two turntables of the inductive voltage divider again so that the indication value of DMT is the smallest. This can improve the test work efficiency on-site.

[0101] Close the switch D. What the digital transformer calibrator measures is the ratio error r1(%) of the true turns ratio K1 of CVD relative to Kf1 and the phase angle error: δ1 (minutes). Kf1 is the turns ratio after adjustment of the double-stage inductive voltage divider.

[0102] After Figure 7 testing, the turns ratio error of CVD K1 is:

[0103] r1(%) = (K1 - Kf1)*100 / Kf1

[0104] K1 = Kf1*(1 + r1(%))(1)

[0105] The angular difference δ1 is because the dielectric losses of the two capacitors C1 and C2 may not be exactly the same. When testing the capacitors, the dielectric losses will introduce additional errors. The error introduced when testing K1 is called the phase error. That is to say, there is a certain phase difference between the divided voltage Ua and the total voltage U. See Figure 8 .

[0106] Specifically, it should be noted here that the input resistance of the differential pressure circuit of the calibrator must be large, greater than 20 kΩ, otherwise it will change the voltage division ratio of C1 and C2 or introduce test errors.

[0107] Specifically, for the error test of the IVT equivalent intermediate voltage transformer, it is as follows:

[0108] The wiring diagram of the CVT is shown in Figure 9If there is a carrier connected to the low-potential terminal of the capacitor C2 of the CVT, short-circuit the carrier; if there is no carrier connected to the low-potential terminal of the capacitor C2 of the CVT, the low-potential terminal of C2 is generally fixedly directly grounded; disconnect the connection tap between CVD and IVT in the CVT, connect one end (Ua) of the IVT to the high-potential terminal of the step-up transformer; connect the high-potential terminal of the high-voltage capacitor C1 of the CVT to the low-potential terminal of C2; connect the other end of the output of the step-up transformer to Ua'.

[0109] In the selection of standard equipment, the accuracy of the standard voltage transformer is selected as 0.01 level, the double-stage inductive voltage divider is selected as 0.001 level, and the highest accuracy of the on-site CVT does not exceed 0.1 level. According to the error theory, when the standard equipment is two levels higher than the equipment under test (above 0.1 level are 0.05 level and 0.02 level), the error introduced by the standard equipment can be ignored. In the measurement method, the difference between the secondary output of the IVT of the equipment under test and the secondary output of the standard voltage transformer is selected, and the difference is tested, that is, the difference measurement method. To improve the measurement accuracy. For the measurement of the difference, a digital transformer calibrator is selected, and the ratio and orthogonal analysis are performed on the difference quantity to measure the relative ratio difference and phase angle difference of K2 relative to the high-precision voltage transformer.

[0110] The wiring diagram for testing the IVT is shown in Figure 10 , and the equipment used in the figure are: single-phase voltage regulator

[0111] (AC: 220V / (0 - 240)V, capacity 10kVA; step-up transformer (30kV / 200V, capacity 5kVA, the two output terminals are insulated from the ground); standard voltage transformer: (35kV / 100V, 0.01 level, the two output terminals are insulated from the ground); double-stage inductive voltage divider (primary 600V, secondary 0 - 600V, 0.001 level); load box; transformer calibrator. These equipment are all conventional test equipment.

[0112] From the nameplate of the CVT, it can be known that the nameplate turns ratio K of the CVT = U1n / U2n, and the turns ratio K1 of CVD can be obtained from the above test method. Then the theoretical turns ratio K20 of the equivalent intermediate voltage transformer = K / K1.

[0113] When K20 is calculated by K20 = K / K1, because K1 = (1 + r1%) * Kf1, after K1 has been error-corrected by Kf1 and r1%, it has become the true value and is no longer included when calculating the comprehensive error of the CVT.

[0114] When K20 is calculated by K20 = K / Kf1, because K1 ≠ Kf1, K20 contains the error r1% of the turns ratio K1, so the error of r1% needs to be included when calculating the comprehensive error of the CVT.

[0115] The calculated K20 may be a non-standard transformation ratio. A standard voltage transformer is used in conjunction with a high-precision double-stage induction voltage divider to make the combined transformation ratio consistent with the theoretical transformation ratio K20 of the IVT under test. Let the transformation ratio of the standard voltage transformer be Kpt and the transformation ratio of the double-stage induction voltage divider be Kf2, then K20 = Kpt * Kf2, and Kf2 = K20 / Kpt. When Kf2 >= 1, the double-stage induction voltage divider is connected to the secondary voltage of the standard voltage transformer, see Figure 10 ; when Kf2 < 1, the double-stage induction voltage divider is connected to the secondary voltage terminal of the IVT, see Figure 11 .

[0116] For example, for a 500 kV CVT, K = 500 kV / 100 V = 5000. Suppose the CVD voltage division ratio: K1 = 14, then K20 = 5000 / 14 = 357.1429. The standard voltage transformer is selected as 35 kV / 100 V with an accuracy of 0.01 class, and Kpt = 350. The transformation ratio Kf2 of the induction voltage divider: Kf2 = K20 / Kpt = 357.1429 / 350 = 1.020408 > 1, and the double-stage induction voltage divider is connected to the secondary voltage of the standard voltage transformer, see Figure 10 .

[0117] Suppose the CVD voltage division ratio: K1 = 18, then K20 = 5000 / 14 = 277.77778. The standard voltage transformer is selected as 35 kV / 100 V with an accuracy of 0.01 class, and Kpt = 350. The transformation ratio Kf2 of the induction voltage divider: Kf2 = K20 / Kpt

[0118] = 277.77778 / 350 = 0.793651 < 1, and the double-stage induction voltage divider is connected to the secondary voltage terminal of the IVT. See Figure 11 . Since the double-stage induction voltage divider has a very high accuracy, the measurement error introduced by itself can be ignored.

[0119] The voltage regulator is powered on and adjusted to make the secondary voltage of the IVT the required test voltage. The digital transformer calibrator measures the ratio error r2 (%) and phase angle error: δ2 (minutes) of the true transformation ratio K2 of the IVT relative to Kf2 * Kpt or K2 * Kf2 relative to Kpt. Since the double-stage induction voltage dividing box has a very high accuracy and its error can be ignored, the digital transformer calibrator measures the ratio error r2 (%) and phase angle error: δ2 (minutes) of the true transformation ratio K2 of the IVT relative to Kpt.

[0120] When Kf2 >= 1, r2 (%) = (K2 - Kpt * Kf2) * 100 / Kpt * Kf2

[0121] When Kf2 < 1, r2 (%) = (K2 * Kf2 - Kpt) * 100 / Kpt

[0122] Measured error of transformation ratio of CVT

[0123] Since the transformation ratio K of CVT = K1 * K2, the transformation ratio error of CVT consists of two parts, namely the error r1% of the transformation ratio K1 of CVD and the error r2% of the transformation ratio K2 of IVT. The following analysis does not consider the tiny errors introduced by the standard voltage transformer, high-precision double-stage induction voltage divider, and transformer calibrator.

[0124] When K20 is calculated using K20 = K / K1, since the true value of K1 of CVD (the ratio error part has been corrected) is used when calculating K20, the transformation ratio error of CVT does not contain the ratio error component of K1 of CVD. The CVT error is as follows:

[0125] Ratio error: ε% = r2(%)

[0126] Phase angle error: δ = δ1 + δ2 (minutes)

[0127] When K20 is calculated using K20 = K / Kf1, because K1 ≠ Kf1, K20 contains the error of the transformation ratio r1% of K1, so the transformation ratio error of CVT contains the error component of K1 of CVD. The CVT error is as follows:

[0128] Ratio error: ε% = r1% + r2(%)

[0129] Phase angle error: δ = δ1 + δ2 (minutes)

[0130] Through the above method, the true error of CVT can be measured.

[0131] Specifically, according to the above technical solution, the present application has the following effects;

[0132] On-site testing is very easy

[0133] From Figures 7 - 10 、 Figure 11 it can be seen that for the step-up transformer and the standard voltage transformer, 35 kV equipment can be selected, and the on-site power supply capacity is very small. Whether in terms of volume or weight, the testing equipment is very small and is some commonly used equipment.

[0134] 1). Strong safety

[0135] The test voltage is low, and safety is easy to ensure

[0136] 2). High precision and small introduced test error

[0137] For conventional equipment, its high precision and insulation strength are very easy to achieve.

[0138] 3). Less investment

[0139] 4). It is not restricted by the environment, space, on-site power supply capacity, transportation, etc.

[0140] 5). High working efficiency, saving manpower, material resources and financial resources.

[0141] Disadvantages:

[0142] 1). When testing the CVD transformation ratio error K1, because low voltage is used for testing, the dielectric loss of the capacitor may vary, which will affect the angular difference.

[0143] 2). When testing the CVD transformation ratio error K1, because low voltage is used for testing, the interference of the CVT stray capacitance may vary.

[0144] 3). For the intermediate voltage taps of CVD and IVT, obvious detachable terminals are required externally.

[0145] Embodiment 2:

[0146] This embodiment actually verifies a method for testing the transformation ratio error of a capacitive voltage transformer by the equivalent method provided in this application, specifically as follows:

[0147] The schematic diagram of testing the CVT transformation ratio error by the integral method is shown in Figure 12 , a booster with ultra-high voltage and a standard voltage transformer are required. Since these devices are large in volume and heavy in weight, they need to be transported with the help of a crane and a vehicle, and the traffic is extremely inconvenient. Moreover, there should be enough working space on site, and the working power supply for testing should have a large enough capacity.

[0148] The schematic diagram of testing the CVT transformation ratio error by the equivalent method (new method) is shown in Figure 7 , Figure 10 , Figure 11 . All the devices used are conventional testing devices, and it is very easy to complete the testing task.

[0149] Specifically, the comparison and verification of CVT manufacturers: A comparison test was conducted at the Xi'an Capacitor Factory where CVTs are produced. For three products of 110kV CVT, 220kV CVT, and 330kV CVT, the transformation ratio error of the CVT was measured by both the integral method and the equivalent method. The data are very close. The Xi'an Capacitor Factory uses a complete set of high-voltage testing equipment imported from Switzerland (which is very expensive), while the equipment required is only the equipment used in daily work (worth about tens of thousands of yuan). The specific test data are shown in Table 1-6:

[0150] Table 1 Data table of testing the model TYD3330 / √3kV - 0.005H by the full voltage method

[0151]

[0152] Table 2 Data Sheet of the Model TYD3220 / √3-0.0075H Tested by the Full Voltage Method

[0153]

[0154]

[0155] Table 3 Data Sheet of the Model TYD3110 / √3-0.015H Tested by the Full Voltage Method

[0156]

[0157] Table 4 Data Sheet of the Model TYD3330 / √3kV-0.005H Tested by the Method of the Present Invention

[0158]

[0159]

[0160] Table 5 Data Sheet of the Model TYD3220 / √3-0.0075H Tested by the Method of the Present Invention

[0161]

[0162] Table 6 Data Sheet of the Model TYD3110 / √3-0.015H Tested by the Method of the Present Invention

[0163]

[0164] Specifically, the test verification of the method based on the present invention at the on-site installation of CVT in the substation includes:

[0165] Conduct on-site actual tests on two 110kV CVTs in Huangjiazhai Substation. See Tables 7-8.

[0166] Model to be tested: TYD110 / √3-0.008C

[0167] Rated primary voltage: 110 / √3kV Rated secondary voltage: 100 / √3V

[0168] Secondary load: 300VA Grade: 1; 600VA Grade: 3

[0169] Table 7 Test Table with Capacitance: C1: 0.01uF; C2: 0.03794uF

[0170]

[0171] Table 8 Test Table with Capacitance: C1: 0.009979uF; C2: 0.03801uF

[0172]

[0173]

[0174] Specifically, the 330 kV voltage transformer of the garden substation selects the capacitive voltage transformer (CVT) produced by Alstom of France. For the ratio error of the CVT at the substation site, a new equivalent method is adopted for on-site actual measurement. For the 330 kV CVT, since the overall test cannot be carried out on-site, the test data of the equivalent method can only be compared with the data in the original factory report. See Table 9-17.

[0175] Table 9 Hualong Second Circuit CVT; Phase A; U1n: 330 / √3 kV Test Table

[0176]

[0177] Table 10 Hualong Second Circuit CVT; Phase B; U1n: 330 / √3 kV Test Table

[0178]

[0179] Table 11 Hualong Second Circuit CVT; Phase B; U1n: 330 / √3 kV Test Table

[0180]

[0181]

[0182] Table 12 Huahai First Circuit CVT; Phase A; U1n: 330 / √3 kV Test Table

[0183]

[0184] Table 13 Huahai First Circuit CVT; Phase B; U1n: 330 / √3 kV Test Table

[0185]

[0186] Table 14 Huahai First Circuit CVT; Phase C; U1n: 330 / √3 kV Test Table

[0187]

[0188] Table 15 Huahai Second Circuit CVT; Phase A; U1n: 330 / √3 kV Test Table

[0189]

[0190] Table 16 Huahai Second Circuit CVT; Phase B; U1n: 330 / √3 kV Test Table

[0191]

[0192] Table 17 Huahai Second-stage CVT; Phase C; U1n: 330 / √3 kV Test Table

[0193]

[0194]

[0195] From the above analysis and actual test verification, it can be seen that the test method of the present invention is completely feasible and effective. Through the comparison test of Xi'an Capacitor Factory, the error introduced by the method of the present invention does not exceed 0.1% (actually about 7‰). The required equipment is simple, and the test equipment is basically available in each electric power research institute and power supply company, which is easy to promote and apply. This method can calibrate 0.2-level CVTs of various voltage levels and is applicable to the calibration of the ratio error of CVTs with intermediate tap leads. The successful research of this method has solved a major technical problem in the country, and the funds saved for the country economically are inestimable. At the same time, it also plays a positive role in the safe and economic power generation, supply and use of the power system.

[0196] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts between the various embodiments, reference can be made to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and reference can be made to the description in the method part for related parts.

[0197] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for testing the ratio error of a capacitive voltage transformer using an equivalent method, characterized in that: include: S100: The electromagnetic circuit of the capacitor voltage transformer CVT is equivalent to a pure circuit, and is split into a capacitor voltage divider CVD and an equivalent intermediate voltage transformer IVT. Based on the Thevenin law, the relationship between the capacitor voltage transformer CVT ratio K, the capacitor voltage divider CVD no-load voltage divider ratio K1, and the equivalent intermediate voltage transformer IVT ratio K2 is obtained, and the correlation of the ratio error is obtained; S200: Perform error test on the capacitance voltage divider CVD ratio K1, using a 0.001-level two-stage inductive voltage divider and a differential measurement method, and measuring the ratio difference and phase angle difference of the capacitance voltage divider CVD ratio K1 relative to the standard voltage divider ratio Kf1 through a digital transformer tester; S300: Perform an error test on the equivalent intermediate voltage transformer IVT ratio K2, select a 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider, calculate the theoretical ratio K20 of the equivalent intermediate voltage transformer according to the CVT ratio K of the capacitive voltage transformer and the measured CVD ratio K1 of the capacitive voltage divider, and determine whether the error of the CVD ratio K1 of the capacitive voltage divider is included in the comprehensive error; then calculate the ratio Kf2 of the two-stage inductive voltage divider according to the theoretical ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt, determine the connection position of the two-stage inductive voltage divider, and use a calibrator to measure the error of the equivalent intermediate voltage transformer IVT ratio K2 after adjusting the voltage regulator; S4 00: According to the calculation method of the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer, the ratio difference and angle difference of the capacitance voltage transformer CVT are calculated respectively to obtain the measured error.

2. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 1, characterized in that: The S100 includes: S110: The electromagnetic circuit of the capacitor voltage transformer CVT is equivalent to a pure circuit. Based on the Thevenin law, the capacitor voltage transformer CVT is equivalently divided into two parts: a capacitor voltage divider CVD and an equivalent intermediate voltage transformer IVT from the output port of the capacitor voltage transformer CVT to the circuit input. S120: It is obtained that the transformation ratio K of the capacitor voltage transformer CVT is equal to the product of the transformation ratio K1 of the capacitor voltage divider CVD and the transformation ratio K2 of the equivalent intermediate voltage transformer IVT, and the transformation ratio error r% of the capacitor voltage transformer CVT is equal to the sum of the transformation ratio error r1% of the capacitor voltage divider CVD and the transformation ratio error r2% of the equivalent intermediate voltage transformer IVT, that is, r%=r1%+r2%; S130: Divide the transformation ratio error r% of the capacitive voltage transformer CVT into the ratio difference ε% and the phase angle difference δ, that is: ε%=ε1%+ε2%; δ=δ1+δ2, wherein ε1%, ε2%, δ1, δ2 are respectively the ratio difference and the phase angle difference between the transformation ratio K1 of the capacitive voltage divider CVD and the transformation ratio K2 of the equivalent intermediate voltage transformer IVT.

3. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 1, characterized in that: S200 includes: S210: Select a 0.001-level two-stage inductive voltage divider as a standard test device, and use a digital transformer tester to measure the ratio of the difference and orthogonal analysis according to the output difference measurement method between the standard device and the device under test, and obtain the relative ratio difference and phase angle difference of the capacitance voltage divider CVD ratio K1 relative to the high-precision 0.001-level two-stage inductive voltage divider voltage ratio Kf1; S220: During the test, different adjustment operations are performed according to whether the capacitance values ​​of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 of the capacitive voltage divider CVD in the capacitive voltage transformer CVT are known or not.

4. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 3, characterized in that: S220 includes: If the capacitance values ​​of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 are unknown, disconnect the isolation switch, adjust the voltage regulator so that the booster output is the primary rated voltage of the two-stage inductive voltage divider, and repeatedly adjust the inductive voltage divider dial to minimize the indication value of the high input impedance digital multimeter; If the nominal capacitance values ​​of the first high-voltage voltage-dividing capacitor C1 and the second high-voltage voltage-dividing capacitor C2 are known, the theoretical K1' is calculated in advance and the secondary dial of the two-stage inductive voltage divider is set, and then the last two dials are adjusted to minimize the indication value of the digital multimeter.

5. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 3, characterized in that: When performing an error test on the capacitance voltage divider CVD ratio K1, it is necessary to ensure that the differential pressure loop input resistance of the calibrator is greater than 20 kilo-ohms to avoid changing the voltage dividing ratio of the first high-voltage voltage divider capacitor C1 and the second high-voltage voltage divider capacitor C2 or introducing a test error.

6. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 5, characterized in that: S300 includes: S310: Select a 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider, and calculate the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer based on the transformation ratio K of the capacitive voltage transformer CVT and the measured transformation ratio K1 of the test capacitive voltage divider CVD; S320: when K20=K / K1, the no-load voltage divider ratio K1 of the capacitor voltage divider CVD is corrected to the true value, and the ratio error r1% of the capacitor voltage divider CVD is not taken into account when calculating the comprehensive error of the capacitor voltage transformer CVT; S330: When K20=K / Kf1, the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer contains the transformation ratio error r1% of the capacitor voltage divider CVD, and the transformation ratio error r1% of the capacitor voltage divider CVD is taken into account when calculating the comprehensive error of the capacitor voltage transformer CVT; S330: Calculate the transformation ratio Kf2 of the two-stage inductive voltage divider based on the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer and the transformation ratio Kpt of the standard voltage transformer. When Kf2≥1, the two-stage inductive voltage divider is connected to the secondary voltage of the standard voltage transformer. When Kf2<1, the two-stage inductive voltage divider is connected to the secondary voltage terminal of the equivalent intermediate voltage transformer IVT. Adjust the voltage regulator so that the secondary voltage of the equivalent intermediate voltage transformer IVT is the test voltage. The digital transformer tester is used to measure the ratio error r2% and the phase angle error δ2 of the actual transformation ratio K2 of the IVT relative to Kf2*Kpt or K2*Kf2 relative to Kpt.

7. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 6, characterized in that: S400 includes: Before performing the error test of the transformation ratio K2 of the equivalent intermediate voltage transformer IVT, the low potential end of the second high-voltage voltage-dividing capacitor C2 is connected to a carrier, and the carrier needs to be short-circuited; if the carrier is not connected, the low potential end of the second high-voltage voltage-dividing capacitor C2 is fixedly and directly grounded, and the connection tap between the capacitive voltage divider CVD in the capacitive voltage transformer CVT and the equivalent intermediate voltage transformer IVT is disconnected.

8. The method for testing the transformation ratio error of a capacitor voltage transformer by using an equivalent method according to claim 6, characterized in that: S400 includes: When the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer is calculated by K20=K / K1, the ratio difference ε%=r2% and the phase angle difference δ=δ1+δ2 of the capacitive voltage transformer CVT; When the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer is calculated using K20=K / Kf1, the ratio difference ε%=r1%+r2% and the phase angle difference δ=δ1+δ2 of the capacitive voltage transformer CVT.

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