A method for testing the ratio error of capacitor voltage transformer using equivalent method

Abstract

The present invention discloses a method for testing the ratio error of a capacitive voltage transformer using an equivalent method, belonging to the field of transformer measurement technology. Based on the Thevenin law, the CVT electromagnetic circuit is equivalent to a pure circuit, and the CVT ratio K is obtained to be equal to the product of the capacitive voltage divider CVD ratio K1 and the equivalent intermediate voltage transformer IVT ratio K2. The ratio error r% is approximately equal to the sum of r1% and r2%, simplifying the testing process. High-precision standard equipment and the differential measurement method are used to improve test accuracy. This method is applicable to CVTs with voltage levels of 110kV and above and is not restricted by environmental, spatial, and other factors.

Description

Technical Field

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

[0002] Capacitor voltage transformers (CVTs), also known as capacitive voltage transformers, are essential equipment for the safe, economical, and reliable operation of power systems and are a crucial component of electric energy metering and protection systems. To dynamically monitor the performance and ratio accuracy of CVT equipment during operation, periodic on-site preventive testing of CVT ratio errors is conducted in accordance with relevant national regulations. These tests include testing the capacitance and dielectric loss of the voltage divider capacitors, as well as on-site verification of CVT ratio errors. This ensures safe operation of the power system and the accuracy of measurement, metering, and protection. Capacitor voltage transformer error testing is a key indicator for determining whether the ratio error and phase angle error of the CVT meet accuracy requirements when converting high voltage to low voltage. Field testing of CVT ratio error is crucial for the economic operation of power systems, improving the economic efficiency of power grids, and ensuring safety and reliability.

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

[0004] Capacitor voltage transformers (CVTs) consist of two components: a capacitive voltage divider and an electromagnetic voltage transformer (EMT). They are suitable for measuring high and ultra-high voltage AC voltages. Their primary characteristic is their high dielectric strength. High-voltage CVTs are easier to manufacture than EMTs, resulting in smaller size, lighter weight, and lower price. Therefore, CVTs are often used for voltage transformers of 110 kV and above. According to DL / T956-1996, "Procedure for Preventive Testing of Electric Power Equipment," and other relevant regulations, CVT ratio errors must be tested on-site every two to four years to ensure safe, economical, and reliable operation of the power system.

[0005] Many scientific and technological researchers have devoted considerable effort to testing the ratio error of high-voltage and ultra-high-voltage CVTs, devising numerous methods, publishing numerous articles online and in relevant journals, and applying for patents. However, these methods can be categorized into the following two main types:

[0006] Method 1: The full voltage method is used to test the CVT's ratio error. This involves applying 80% Un / √3, 100% Un / √3, and 120% Un / √3 of the normal rated voltage to the CVT when testing the ratio error. This requires a complete set of series resonant boost test equipment: such as a variable frequency control power supply, excitation transformer, resonant reactor, compensation reactor, capacitive voltage divider, compensation capacitor, etc. In addition, a high-precision standard voltage transformer of the same voltage level is required. Due to insulation requirements, these ultra-high voltage devices are quite large in size and weight, and are filled with SF6 insulating gas or insulating oil. Many manufacturers install them on a large truck and convert them into a transformer field calibration vehicle. However, this method has the following problems:

[0007] 1. Since the electrical insulation level requirements of on-site boost equipment and standard voltage transformers are very high, these devices are large in size and heavy, making testing inconvenient and labor-intensive.

[0008] 2. A large capacity of working power is required on site, which is sometimes difficult to meet.

[0009] 2. The voltage is very high, the safety measures are complex, and safety control is difficult.

[0010] 3. Testing work is sometimes limited by space.

[0011] 4. The purchase cost is very high. A fully equipped transformer inspection vehicle is estimated to cost between 3 and 4 million RMB.

[0012] 5. Large supporting equipment filled with SF6 high-pressure gas or insulating oil will inevitably leak gas, leak oil or be damaged during long-term transportation, so the maintenance cost is high.

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

[0014] Method 2: Model extrapolation of CVT error. This involves applying low voltage only to the CVT secondary and using frequency conversion technology to obtain the excitation characteristic curve of the intermediate voltage transformer operating range. Combined with the measured error curve of the secondary low voltage, the transformer error is extrapolated using a mathematical model. This method is widely available in articles and equipment. However, it has the following issues:

[0015] 1. The CVT ratio error is composed of two parts: CVD and IVT. The model extrapolation method is also difficult to reflect the actual error of the CVD ratio.

[0016] 2. The IVT's ratio error is extrapolated from the transformer error using a mathematical model based on the excitation characteristic curve and the load error curve. The excitation characteristic curve is nonlinear and is affected by factors such as the core material, temperature, applied voltage frequency, voltage amplitude, number of winding turns, core structure, geometry, and core manufacturing process. The load error curve is influenced by factors such as the size and properties of the secondary load. However, the mathematical model is based on a limited number of characteristic quantities. Using this model extrapolation method, it is difficult to truly reflect the CVT's ratio error under rated voltage and actual field conditions.

[0017] 3. Without corresponding primary standard equipment, the transfer of measurement values ​​cannot be traced.

[0018] Therefore, how to provide a method for testing the capacitance voltage transformer ratio error using an equivalent method is a problem that those skilled in the art need to solve urgently. Summary of the Invention

[0019] In view of this, the present invention provides a method for testing the ratio error of a capacitive voltage transformer using an equivalent method. The method is simple and feasible, requires less equipment, 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 a capacitance voltage transformer ratio error using an equivalent method, comprising:

[0022] S100: The electromagnetic circuit of the capacitor voltage transformer (CVT) is equivalent to a pure circuit and split into the capacitor voltage divider (CVD) and the equivalent intermediate voltage transformer (IVT). Based on the Thevenin law, the relationship between the CVT transformation ratio (K), the no-load voltage divider ratio (K1) of the capacitor voltage divider (CVD), and the equivalent intermediate voltage transformer (IVT) transformation ratio (K2) is derived, and the correlation of the transformation ratio error is obtained.

[0023] S200: Perform an error test on the capacitance voltage divider CVD ratio K1. Use a 0.001-level two-stage inductive voltage divider and the differential measurement method to measure the ratio and phase angle difference of the capacitance voltage divider CVD ratio K1 relative to the standard voltage divider ratio Kf1 using a digital transformer calibrator.

[0024] S300: Perform an error test on the equivalent intermediate voltage transformer (IVT) ratio K2. A 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider are selected. The theoretical ratio K20 of the equivalent intermediate voltage transformer is calculated based on the CVT ratio K of the capacitive voltage transformer and the measured CVD ratio K1 of the capacitive voltage divider. The error in the CVD ratio K1 of the capacitive voltage divider is determined to determine whether the error in the CVD ratio K1 of the capacitive voltage divider is included in the comprehensive error. The ratio Kf2 of the two-stage inductive voltage divider is then calculated based on the theoretical ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt. The connection position of the two-stage inductive voltage divider is determined. After adjusting the voltage regulator, the error in the equivalent intermediate voltage transformer (IVT) ratio K2 is measured using a calibrator.

[0025] S400: Calculate the ratio difference and angle difference of the capacitance voltage transformer (CVT) according to the calculation method of the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer, and obtain the measured error.

[0026] Furthermore, the S100 includes:

[0027] S110: The electromagnetic circuit of the capacitor voltage transformer (CVT) is equivalent to a pure circuit. Based on the Thevenin law, the equivalent circuit is viewed from the output port of the capacitor voltage transformer (CVT) into the circuit. The capacitor voltage transformer (CVT) is effectively split into two parts: the capacitor voltage divider (CVD) and the equivalent intermediate voltage transformer (IVT).

[0028] S120: deriving a CVT transformation ratio K equal to the product of a no-load transformation ratio K1 of the capacitor voltage divider CVD and an equivalent intermediate voltage transformer IVT transformation ratio K2, and a CVT transformation ratio error r% equal to a sum of a CVD transformation ratio error r1% and an equivalent intermediate voltage transformer IVT transformation ratio error r2%, i.e., r% = r1% + r2%.

[0029] S130: Divide the transformation ratio error r% of the capacitive voltage transformer CVT into a ratio difference ε% and a phase angle difference δ, i.e., ε% = ε1% + ε2%; δ = δ1 + δ2, where ε1%, ε2%, δ1, and δ2 are respectively the ratio difference and phase angle difference between 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] Furthermore, S200 includes:

[0031] S210: A 0.001-level two-stage inductive voltage divider is selected as the standard test equipment. Based on the output difference measurement method between the standard equipment and the equipment under test, a digital transformer calibrator is used to measure the ratio of the difference and perform orthogonal analysis to obtain the relative ratio difference and phase angle difference between the capacitive voltage divider CVD ratio K1 and the high-precision 0.001-level two-stage inductive voltage divider voltage ratio Kf1.

[0032] 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.

[0033] Furthermore, 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 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.

[0035] If the nominal capacitance values ​​of the first high-voltage voltage divider capacitor C1 and the second high-voltage voltage divider capacitor C2 are known, calculate the theoretical K1' in advance and set the secondary dial of the two-stage inductive voltage divider, then adjust the last two dials to minimize the digital multimeter indication.

[0036] Furthermore, when performing an error test on the capacitor voltage divider CVD ratio K1, it is necessary to ensure that the differential pressure circuit input resistance of the calibrator is greater than 20 kilo-ohms to avoid changing the voltage divider ratio of the first high-voltage voltage divider capacitor C1 and the second high-voltage voltage divider capacitor C2 or introducing a test error.

[0037] Furthermore, S300 includes:

[0038] S310: Select a 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider. Calculate the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer based on the CVT transformation ratio K of the capacitor voltage transformer and the measured CVD transformation ratio K1 of the test capacitor voltage divider.

[0039] 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 capacitor voltage divider CVD ratio error r1% is not included in the calculation of the comprehensive error of the capacitor voltage transformer CVT;

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

[0041] S330: Calculate the two-stage inductive voltage divider ratio Kf2 based on the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt. 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 calibrator 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.

[0042] Furthermore, S400 includes:

[0043] Before performing the error test of the equivalent intermediate voltage transformer IVT transformation ratio K2, the low potential end of the second high-voltage voltage-dividing capacitor C2 is connected to a carrier and 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 fixed directly to the ground, 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.

[0044] Furthermore, S400 includes:

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

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

[0047] It can be seen from the above technical solution that compared with the prior art, the present invention discloses a method for testing the ratio error of a capacitive voltage transformer using an equivalent method. The method is simple and feasible, requires less equipment, has a wide range of test objects, is economical, safe, efficient and convenient, and is suitable for on-site testing of CVT errors at voltage levels of 110kV and above. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0049] Figure 1 Schematic diagram of the method flow of the present invention;

[0050] Figure 2 A schematic diagram of the structure of a CVT provided in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of an embodiment of the present invention showing that a CVT of an electromagnetic circuit is equivalent to a CVT of a pure circuit;

[0052] Figure 4 The embodiment of the present invention provides an embodiment that ignores Figure 3 Schematic diagram of pure electric circuit of CVT under the condition of IVT excitation impedance Zo;

[0053] Figure 5 A schematic diagram illustrating the equivalent of a pure electric circuit of a CVT using the Thevenin law provided in an embodiment of the present invention;

[0054] Figure 6 A schematic diagram of a detection circuit provided by an embodiment of the present invention;

[0055] Figure 7 A measurement diagram of a transformer calibrator provided in an embodiment of the present invention;

[0056] Figure 8 A schematic diagram of the losses of the high-voltage voltage-dividing capacitors C1 and C2 provided in an embodiment of the present invention;

[0057] Figure 9 A CVT wiring diagram provided in an embodiment of the present invention;

[0058] Figure 10 A wiring diagram for testing an IVT provided in an embodiment of the present invention;

[0059] Figure 11 A schematic diagram of a two-stage inductive voltage divider provided in an embodiment of the present invention connected to the secondary voltage terminal of an IVT;

[0060] Figure 12 This is the overall test diagram of the CVT ratio error provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0062] Example 1:

[0063] See also Figure 1 The embodiment of the present invention discloses a method for testing a capacitance voltage transformer ratio error using an equivalent method, comprising:

[0064] S100: The electromagnetic circuit of the capacitor voltage transformer (CVT) is equivalent to a pure circuit and split into the capacitor voltage divider (CVD) and the equivalent intermediate voltage transformer (IVT). Based on the Thevenin law, the relationship between the CVT transformation ratio (K), the no-load voltage divider ratio (K1) of the capacitor voltage divider (CVD), and the equivalent intermediate voltage transformer (IVT) transformation ratio (K2) is derived, and the correlation of the transformation ratio error is obtained.

[0065] S200: Perform an error test on the capacitance voltage divider CVD ratio K1. Use a 0.001-level two-stage inductive voltage divider and the differential measurement method to measure the ratio and phase angle difference of the capacitance voltage divider CVD ratio K1 relative to the standard voltage divider ratio Kf1 using a digital transformer calibrator.

[0066] S300: Perform an error test on the equivalent intermediate voltage transformer (IVT) ratio K2. A 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider are selected. The theoretical ratio K20 of the equivalent intermediate voltage transformer is calculated based on the CVT ratio K of the capacitive voltage transformer and the measured CVD ratio K1 of the capacitive voltage divider. The error in the CVD ratio K1 of the capacitive voltage divider is determined to determine whether the error in the CVD ratio K1 of the capacitive voltage divider is included in the comprehensive error. The ratio Kf2 of the two-stage inductive voltage divider is then calculated based on the theoretical ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt. The connection position of the two-stage inductive voltage divider is determined. After adjusting the voltage regulator, the error in the equivalent intermediate voltage transformer (IVT) ratio K2 is measured using a calibrator.

[0067] S400: Calculate the ratio difference and angle difference of the capacitance voltage transformer (CVT) according to the calculation method of the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer, and obtain the measured error.

[0068] For details, see Figure 2 The structural principle diagram of the CVT shown in the figure includes an intermediate voltage transformer IVT, a primary winding of the IVT, a compensating inductor, a regulating winding, a secondary winding, damping windings d and d2, and a protective discharger.

[0069] Depend on Figure 2 It can be seen 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 divider capacitors C1 and C2; the IVT is composed of the primary winding, secondary winding, iron core, damping winding, error adjustment winding, compensation reactor, protective discharger, etc. of the electromagnetic induction voltage transformer. Among them:

[0070] Primary winding, secondary winding, iron core: convert the CVD divided voltage into a secondary voltage that is acceptable to instruments and protection equipment and has a certain load capacity and meets the error level requirements.

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

[0072] The role of the regulating winding: Because capacitors have manufacturing tolerances, the voltage divider ratio of the capacitor divider is usually slightly different from the rated value, and the regulating winding can be used to compensate.

[0073] Function of the damping winding: When a capacitive voltage transformer is subjected to transient shocks such as a secondary short circuit or disconnection, it may generate ferromagnetic resonance. This ferromagnetic resonance can generate high currents and overvoltages in the intermediate voltage circuit, potentially damaging insulation, measuring instruments, and protective equipment. Therefore, a damping device must be used to suppress this.

[0074] Function of the protective spark gap: When a carrier device fails and the L and N terminals of the CVD are open, high voltages will appear at L and N terminals, endangering the carrier device, secondary equipment connected to the intermediate voltage transformer, and personnel. When a protective spark gap is present, it automatically switches on when the voltage reaches its critical operating value, protecting personnel and equipment.

[0075] The capacitive voltage divider (CVD) divides the grid's high voltage (U1) into a lower intermediate voltage (Ua) (between 10 and 20 kV, typically 13 kV). The intermediate voltage transformer (IVT) then converts this voltage Ua to a regulated low voltage acceptable to instrumentation and protection systems. This reduces insulation issues for high-voltage equipment, primarily focusing on the capacitive voltage divider and making them relatively easy to resolve. The intermediate voltage transformer, previously difficult to isolate, now operates at lower voltages, making accuracy easier to achieve.

[0076] Capacitor voltage transformers are generally classified into two types based on their structure: a unitized structure, in which the capacitor divider and electromagnetic unit are independent and can be assembled on site, with the medium-voltage line exposed; and an integral structure, in which the capacitor divider and electromagnetic unit are integrated, with the medium-voltage line not exposed. Capacitor voltage transformers for voltage levels of 500 kV and below are available in both integral and unitized structures. Capacitor voltage transformers for voltage levels of 750 kV and above generally adopt a unitized structure.

[0077] Specifically, based on Figure 2 Based on the principle of CVT, this embodiment analyzes the electromagnetic circuit of CVT. First, the electromagnetic circuit CVT is equivalent to the pure circuit CVT. Figure 3 The CVT circuit diagram includes the intermediate voltage transformer (IVT), its primary winding, compensating reactor, regulating winding, secondary winding, damping windings d and d2, and a protective arrester. For ease of analysis, the CVT's damping winding and multiple secondary windings are not considered, and only the single secondary winding is considered. This approach simplifies the analysis and makes it easier to understand without affecting the equivalent theory.

[0078] exist Figure 3 In the figure, C1 and C2 are high-voltage voltage-dividing capacitors, namely 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 converted secondary impedance, secondary inductive reactance, secondary resistance, secondary load impedance, and secondary voltage of the intermediate transformer respectively. From the theory of electrical machinery, we know that Zl2'=Zl2*K22, Xl2'=Xl2*K22, R2'=R2*K22, Zf2'=Zf2*K22, and U2'=U2*K2, K2 is the theoretical transformation ratio of the intermediate voltage transformer IVT, K2=Ua / U2; Zo is the excitation impedance of the intermediate transformer.

[0079] Since Zo>>Zl2'+Zf2', then Figure 3 Simplified to Figure 4 .

[0080] Bundle Figure 4 The pure electric circuit of the CVT is observed through the Thevenin law from the CVT output port U2' into the circuit, that is, Figure 5 Part A is equivalent to Figure 5 Part B. According to the no-load voltage theory in Thevenin's law, Figure 5 Ua in circuit B is Figure 5 The equivalent voltage when U2' is open circuit in A is Ua=U1 / K1, where K1 is the no-load voltage divider ratio of the capacitive voltage divider CVD:

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

[0082] C1 and C2 are two high-voltage capacitors of CVT. C1 and C2 form a voltage divider called a capacitor voltage divider (CVD). Figure 5 The equivalent capacitance Co in B is, according to Thevenin's law, Co is Figure 5 The equivalent capacitance of short-circuited U1 in A is the parallel connection of C1 and C2, Co = C1 + C2;

[0083] Bundle Figure 5 The equivalent circuit in B is called an equivalent intermediate voltage transformer, abbreviated as IVT (intermediate voltage transformer).

[0084] According to the theory of electrical machinery, the transformation ratio of IVT is: K2=Ua / U2(2)

[0085] In order to reduce the inductive error caused by the primary impedance of the IVT, the design is made so that Xc≈XL+XL1, forming a no-load resonance. Figure 5 shown.

[0086] The actual value is: Xc=XL+XL1+λ To *Z0

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

[0088] K2 load ratio error: 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, multiplying equations (1) and (2) yields K1*K2 = (U1 / Ua)*(Ua / U2) = U1 / U2 = K, which is exactly the CVT ratio. This means that, after calibration by Thevenin et al., the CVT ratio K equals the CVD ratio K1 multiplied by the IVT ratio K2. Furthermore, according to error theory, excluding the influence of higher-order micro-errors, the CVT ratio error r% is approximately equal to the sum of the CVD ratio error r1% and the IVT ratio error r2%. That is, r% = r1% + r2%. The ratio error is further divided into the ratio difference ε% and the phase angle difference δ(′), namely: ε% = ε1% + ε2% δ = δ1 + δ2(′); where ε1%, ε2%, δ1, and δ2 are the ratio difference and phase angle difference between the CVD and IVT ratios, respectively.

[0091] Specifically, regarding the feasibility of K1 and K2 tests, the details are as follows:

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

[0093] Depend on Figure 6As can be seen from B, the no-load voltage 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 greatly facilitates the testing of the capacitor voltage divider ratio. For example, for a (500 / √3)kV CVT, when testing the capacitor voltage divider ratio K1, it is sufficient to apply a voltage of several hundred volts (such as 600V). On the other hand, from the expression K1 = (C1 + C2) / C1 = 1 + C2 / C1, it can be seen that the no-load voltage divider ratio K1 is sensitive to the manufacturing error of the capacitor capacitance or the measurement error of the capacitance. This is the purpose of actual measurement of the manufacturing error of the capacitance; the measurement error of the capacitance is a consideration for the measurement method, measurement means, and measurement equipment.

[0094] While insensitive to small changes in the transformation ratio K2 and C1 and C2, it is also affected by the same factors as conventional electromagnetic voltage transformers, such as frequency, voltage amplitude, secondary load size, and power factor. Therefore, when testing IVT transformation ratio errors, to ensure measurement accuracy, the test voltage applied to the IVT must be close to the rated voltage Ua and its corresponding secondary load. Ua is the voltage obtained by dividing the grid voltage U1 by the CVD voltage divider, i.e., Ua = U1 / K1. Ua is generally between 10-20 kV, but varies between different manufacturers' CVTs. This voltage level is easily achieved on-site, making it easy to select equipment such as a booster or standard voltage transformer.

[0095] Through the above simple qualitative analysis, the error test of CVD's transformation ratio K1 and the error test of IVT's transformation ratio K2 are convenient and simple.

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

[0097] The accuracy of on-site CVTs is generally 0.5, 0.2, and 0.1 levels. To improve the measurement accuracy of the CVD ratio K1 error test, a 0.001-level two-stage inductive voltage divider is used when selecting standard test equipment. This means that the measurement error introduced by the standard test equipment is completely negligible. The test method uses the difference measurement method, which measures the output difference between the standard equipment (the secondary voltage output of the inductive voltage divider) and the device under test (the CVD voltage divider output). According to error testing theory, the difference measurement method can significantly improve measurement accuracy. A digital transformer calibrator is used to measure the difference. Ratio and quadrature analysis are performed on the difference, measuring the relative ratio and phase angle difference of K1 relative to the high-precision 0.001-level two-stage inductive voltage divider's voltage divider ratio Kf1.

[0098] like Figure 7As shown, T1 is an AC 220V voltage regulator; T2 is an AC booster: 200V / 1000V; DMT is a digital multimeter with high input impedance; T3 is a BFJ-3 inductive voltage divider with a grade of 0.001, a primary rated voltage of 600V, and a secondary output voltage of 0-600V; Y is a digital transformer calibrator; and D is an isolation switch.

[0099] If the capacitance values ​​of C1 and C2 are unknown, disconnect the isolation switch D ( Figure 7 ), power on the voltage regulator, and adjust the voltage regulator so that the output of the booster is the primary rated voltage of the two-stage inductive voltage divider, 600V. Repeatedly adjust the inductive voltage divider dial to make the DMT indication value minimum.

[0100] If the nominal values ​​of the capacitors C1 and C2, [C1] and [C2], are known, the theoretical K1' can be calculated in advance: K1' = 1 + [C2] / [C1]. Set the secondary dial of the two-stage inductive voltage divider so that the transformation ratio Kf' equals K1'. After powering on, adjust the last two digits of the inductive voltage divider again to minimize the DMT indication. This improves testing efficiency on site.

[0101] With switch D closed, the digital transformer calibrator measures the ratio error r1 (%) and phase angle error δ1 (minutes) of the true transformation ratio K1 of the CVD relative to Kf1. Kf1 is the transformation ratio after adjustment of the two-stage inductive voltage divider.

[0102] through Figure 7 The test shows that the CVD ratio K1 error is:

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

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

[0105] The angular difference δ1 is due to the fact that the dielectric loss of the two capacitors C1 and C2 may not be completely consistent. When testing the capacitors, the dielectric loss will introduce additional errors. The error introduced by the test K1 is called phase error. In other words, there is a certain phase difference between the divided voltage Ua and the total voltage U. Figure 8 .

[0106] Specifically, it should be noted that the input resistance of the differential pressure circuit of the calibrator must be large, greater than 20 kilo-ohms, otherwise the voltage divider ratio of C1 and C2 will be changed or test errors will be introduced.

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

[0108] CVT wiring diagram Figure 9If the low-potential end of the CVT capacitor C2 is connected to a carrier, please short-circuit the carrier; if the low-potential end of the CVT capacitor C2 is not connected to a carrier, the low-potential end of C2 is generally fixed and directly grounded; disconnect the connection tap between CVD and IVT in the CVT, and connect one end of the IVT (Ua) to the high-potential end of the booster; connect the high-potential end of the CVT high-voltage capacitor C1 to the low-potential end of C2; and connect the other end of the booster output to Ua'.

[0109] When selecting standard equipment, the accuracy of the standard voltage transformer is selected to be 0.01, and the accuracy of the two-stage inductive voltage divider is selected to be 0.001. The maximum accuracy of the on-site CVT does not exceed 0.1. According to error theory, when the standard equipment is two levels higher than the equipment under test (0.1 level is 0.05 and 0.02), the error introduced by the standard equipment is negligible. The measurement method is to measure the difference between the secondary output of the IVT of the equipment under test and the secondary output of the standard voltage transformer, and test the difference, which is called the difference measurement method. This improves measurement accuracy. For this difference measurement, a digital transformer calibrator is used. The difference is analyzed by ratio and quadrature analysis to measure the relative ratio difference and phase angle difference of K2 relative to the high-precision voltage transformer.

[0110] See the wiring diagram for testing IVT. Figure 10 , the equipment used in the figure are: single-phase voltage regulator

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

[0112] The CVT's nameplate shows its brand-name transformation ratio K = U1n / U2n, and the CVD's transformation ratio K1 can be determined from the test method in the previous section. Therefore, the theoretical transformation ratio of the equivalent intermediate voltage transformer, K20, is K / K1.

[0113] When K20 is calculated using K20=K / K1, because K1=(1+r1%)*Kf1, K1 has become a true value after being corrected by Kf1 and r1%, and is no longer included in the calculation of the CVT comprehensive error.

[0114] When K20 is calculated using K20=K / Kf1, because K1≠Kf1, K20 contains the error r1% of the transformation ratio K1, so the error r1% needs to be taken into account when calculating the CVT comprehensive error.

[0115] The calculated K20 may be a non-standard transformation ratio. Use a standard voltage transformer in conjunction with a high-precision two-stage inductive voltage divider to make its synthetic transformation ratio consistent with the theoretical transformation ratio K20 of the IVT under test. Assume that the transformation ratio of the standard voltage transformer is Kpt and the transformation ratio of the two-stage inductive voltage divider is Kf2, then K20=Kpt*Kf2,Kf2=K20 / Kpt. When Kf2>=1, the two-stage inductive voltage divider is connected to the secondary voltage of the standard voltage transformer. Figure 10 ; When Kf2<1, the two-stage inductive voltage divider is connected to the secondary voltage terminal of the IVT, see Figure 11 .

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

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

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

[0119] Power on the voltage regulator and adjust it so that the IVT secondary voltage reaches the required test voltage. The digital transformer calibrator measures the IVT's true transformation ratio K2 relative to Kf2*Kpt or K2*Kf2 relative to Kpt, with an error of r2 (%) and a phase angle error of δ2 (minutes). Since the two-stage inductive voltage divider box has high precision, its error is negligible. Therefore, the digital transformer calibrator measures the IVT's true transformation ratio K2 relative to Kpt, with an error of r2 (%) and a phase angle error of δ2 (minutes).

[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 CVT ratio

[0123] Since the CVT ratio K = K1 * K2, the CVT ratio error consists of two components: the r1% error in the CVD ratio K1 and the r2% error in the IVT ratio K2. The following analysis does not consider the minor errors introduced by standard voltage transformers, high-precision two-stage inductive dividers, and transformer calibrators.

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

[0125] Ratio difference: ε% = r2(%)

[0126] Angular difference: δ=δ1+δ2(minutes)

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

[0128] Ratio difference: ε% = r1% + r2(%)

[0129] Angular difference: δ=δ1+δ2(minutes)

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

[0131] Specifically, through the above technical solution, it can be seen that this application has the following effects:

[0132] Field testing is easy

[0133] Depend on Figure 7-10 、 Figure 11 As can be seen, 35kV equipment can be used for the booster and standard voltage transformer, and the on-site power supply capacity is very small. The test equipment is very small in both size and weight and is commonly used.

[0134] 1). Strong security

[0135] Low test voltage, safe and easy to ensure

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

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

[0138] 3). Low investment

[0139] 4) Not restricted by environment, space, on-site power capacity, transportation, etc.

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

[0141] shortcoming:

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

[0143] 2) When testing the CVD ratio error K1, the CVT stray capacitance interference may vary due to the use of low voltage testing.

[0144] 3) The medium voltage taps of CVD and IVT must have obvious detachable terminals on the outside.

[0145] Example 2:

[0146] This embodiment verifies the method provided by the present application for testing the capacitance voltage transformer ratio error using the equivalent method, as follows:

[0147] The schematic diagram of the overall method for testing CVT ratio error is shown in Figure 12 , requires an ultra-high voltage booster and a standard voltage transformer. Since these devices are large and heavy, they need to be transported by crane or car, which makes transportation extremely inconvenient. In addition, there needs to be enough working space on site, and the working power supply for testing should have a large enough capacity.

[0148] The schematic diagram of the equivalent method (new method) for testing CVT ratio error is shown in Figure 7 、 Figure 10 、 Figure 11 The equipment used are all conventional test equipment, which can easily complete the test task.

[0149] Specifically, a CVT manufacturer's comparison test was conducted at the Xi'an Capacitor Factory, a CVT manufacturer. Using both the overall CVT ratio error test and the equivalent method, the CVT ratio error test for 110kV CVT, 220kV CVT, and 330kV CVT was measured. The results were very similar. The Xi'an Capacitor Factory used a complete set of high-voltage test equipment imported from Switzerland (very expensive), while the only equipment required was what is used in daily operations (valued at tens of thousands of RMB). Specific test data is shown in Table 1-6:

[0150] Table 1 Data sheet for the TYD3330 / √3kV-0.005H model tested using the full voltage method

[0151]

[0152] Table 2 Data sheet for the TYD3220 / √3-0.0075H model tested using the full voltage method

[0153]

[0154]

[0155] Table 3 Data sheet for TYD3110 / √3-0.015H tested using the full voltage method

[0156]

[0157] Table 4 Data sheet of TYD3330 / √3kV-0.005H tested by the method of the present invention

[0158]

[0159]

[0160] Table 5 Data sheet of the TYD3220 / √3-0.0075H model tested by the method of the present invention

[0161]

[0162] Table 6 Data sheet of TYD3110 / √3-0.015H tested by the method of the present invention

[0163]

[0164] Specifically, the test and verification of the method of the present invention at the substation CVT installation site includes:

[0165] For the actual on-site test of the two 110kV CVTs at the Huangjiazhai substation, see Table 7-8.

[0166] Tested model: TYD110 / √3-0.008C

[0167] Primary rated voltage: 110 / √3kV Secondary rated voltage: 100 / √3V

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

[0169] Table 7 Capacitance: C1: 0.01uF; C2: 0.03794uF test table

[0170]

[0171] Table 8 Capacitance: C1: 0.009979uF; C2: 0.03801uF test table

[0172]

[0173]

[0174] Specifically, the Huayuan Substation uses a capacitor voltage transformer (CVT) manufactured by Alstom, France, as its 330kV voltage transformer. Using a new equivalent method, the CVT's ratio error was measured on-site at the substation. Since a complete test of the 330kV CVT was not possible on-site, the equivalent method test data could only be compared with the original factory-reported data (see Table 9-17).

[0175] Table 9 Hualong two-circuit CVT; Phase A; U1n: 330 / √3kK test table

[0176]

[0177] Table 10 Hualong two-circuit CVT; Phase B; U1n: 330 / √3kK test table

[0178]

[0179] Table 11 Hualong two-circuit CVT; Phase B; U1n: 330 / √3kK test table

[0180]

[0181]

[0182] Table 12 Huahaiyihui CVT; Phase A; U1n:330 / √3kK test table

[0183]

[0184] Table 13 Huahaiyihui CVT; Phase B; U1n: 330 / √3kK test table

[0185]

[0186] Table 14 Huahaiyihui CVT; Phase C; U1n: 330 / √3kK test table

[0187]

[0188] Table 15 Huahai two-circuit CVT; Phase A; U1n: 330 / √3kK test table

[0189]

[0190] Table 16 Huahai two-circuit CVT; Phase B; U1n: 330 / √3kK test table

[0191]

[0192] Table 17 Huahai two-circuit CVT; C phase; U1n:330 / √3kK test table

[0193]

[0194]

[0195] The above analysis and actual testing demonstrate that the testing method of the present invention is completely feasible and effective. Comparative testing at the Xi'an Capacitor Factory demonstrated that the error introduced by the method does not exceed 0.1% (actually, it is around 7%). The required equipment is simple and readily available in most electrical research institutes and power supply companies, making it easy to promote and apply. This method can calibrate 0.2-level CVTs of various voltage levels and is suitable for verifying CVT ratio errors derived from center taps. The successful development of this method has resolved a major domestic technical challenge, resulting in inestimable economic savings for the country. It also contributes positively to the safe and economical generation, supply, and consumption of electricity in the power system.

[0196] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0197] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for testing the capacitance voltage transformer ratio error 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 split into a capacitor voltage divider (CVD) and an equivalent intermediate voltage transformer (IVT). Based on the Thevenin law, the relationship between the CVT transformation ratio (K), the CVD transformation ratio (K1), and the equivalent intermediate voltage transformer (IVT) transformation ratio (K2) is derived, and the correlation of the transformation ratio errors is obtained. S200: Perform an error test on the capacitance voltage divider CVD ratio K1. Use a 0.001-level two-stage inductive voltage divider and the differential measurement method to measure the ratio and phase angle difference of the capacitance voltage divider CVD ratio K1 relative to the standard voltage divider ratio Kf1 using a digital transformer calibrator. S300: Perform an error test on the equivalent intermediate voltage transformer IVT ratio K2. A 0.01-level standard voltage transformer and a 0.001-level two-stage inductive voltage divider are selected. The theoretical ratio K20 of the equivalent intermediate voltage transformer is calculated based on the CVT ratio K of the capacitive voltage transformer and the measured CVD ratio K1 of the capacitive voltage divider. The error of the CVD ratio K1 of the capacitive voltage divider is determined to determine whether the error of the CVD ratio K1 of the capacitive voltage divider is included in the comprehensive error. The ratio Kf2 of the two-stage inductive voltage divider is then calculated based on the theoretical ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt. The connection position of the two-stage inductive voltage divider is determined. After adjusting the voltage regulator, the error of the equivalent intermediate voltage transformer IVT ratio K2 is measured using a calibrator. S4 00: Based on the calculation method of the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer, the ratio difference and angle difference of the capacitor voltage transformer CVT are calculated respectively to obtain the measured error.

2. The method for testing the capacitance voltage transformer ratio error by using the 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 equivalent circuit is viewed from the output port of the capacitor voltage transformer (CVT) into the circuit. The capacitor voltage transformer (CVT) is effectively split into two parts: the capacitor voltage divider (CVD) and the equivalent intermediate voltage transformer (IVT). S120: It is concluded that the CVT ratio K of the capacitor voltage transformer is equal to the product of the CVD ratio K1 of the capacitor voltage divider and the IVT ratio K2 of the equivalent intermediate voltage transformer, and the CVT ratio error r% of the capacitor voltage transformer is equal to the sum of the CVD ratio error r1% of the capacitor voltage divider and the IVT ratio error r2% of the equivalent intermediate voltage transformer, that is, r%=r1%+r2%; S130: The ratio error r% of the capacitive voltage transformer CVT is divided into the ratio difference ε% and the phase angle difference δ, that is: ε%=ε1%+ε2%; δ=δ1+δ2, where ε1%, ε2%, δ1, and δ2 are the ratio difference and phase angle difference between the capacitive voltage divider CVD ratio K1 and the equivalent intermediate voltage transformer IVT ratio K2, respectively.

3. The method for testing the capacitance voltage transformer ratio error by using the equivalent method according to claim 1, characterized in that: S200 includes: S210: Selecting a 0.001-level two-stage inductive voltage divider as a standard test device, and using a digital transformer calibrator to measure the difference between the outputs of the standard test device and the device under test, performing a ratio and orthogonal analysis to obtain a relative ratio difference and phase angle difference between the capacitive voltage divider CVD ratio K1 and 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.

4. The method for testing the capacitance voltage transformer ratio error by using the equivalent method according to claim 3, characterized in that: The 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 divider capacitor C1 and the second high-voltage voltage divider capacitor C2 are known, calculate the theoretical K1' in advance and set the secondary dial of the two-stage inductive voltage divider, then adjust the last two dials to minimize the digital multimeter indication.

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

6. The method for testing the capacitance voltage transformer ratio error by using the 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. Calculate the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer based on the CVT transformation ratio K of the capacitor voltage transformer and the measured CVD transformation ratio K1 of the test capacitor voltage divider. S320: When K20=K / K1, the capacitor voltage divider CVD ratio K1 is corrected to the true value, and the capacitor voltage divider CVD ratio error r1% is not included in the calculation of the capacitor voltage transformer CVT comprehensive error; S330: When K20=K / Kf1, the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer includes the capacitance voltage divider CVD transformation ratio error r1%. The capacitance voltage divider CVD transformation ratio error r1% is included in the calculation of the comprehensive error of the capacitance voltage transformer CVT. S340: Calculate the two-stage inductive voltage divider ratio Kf2 based on the theoretical transformation ratio K20 of the equivalent intermediate voltage transformer and the standard voltage transformer ratio Kpt. 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 calibrator 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 capacitance voltage transformer ratio error by using the equivalent method according to claim 6, characterized in that: S300 includes: Before performing the error test of the equivalent intermediate voltage transformer IVT transformation ratio K2, the low potential end of the second high-voltage voltage-dividing capacitor C2 is connected to a carrier and 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 fixed directly to the ground, 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 capacitance voltage transformer ratio error by using the 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 using 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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