A method for selecting the capacitance voltage of the grading ring of a high-voltage bushing and a signal acquisition device

Abstract

The present invention discloses a method for selecting the capacitance voltage of the end screen of a high-voltage bushing and a signal acquisition device. Among them, the method includes: determining the maximum peak voltage U of the recording device at the maximum range in‑max and the selected peak voltage U at the selected range choice‑max ; according to the maximum peak voltage U in‑max , determining the impulse withstand voltage U of the external capacitor on the secondary side C3‑w ; according to the selected peak voltage U choice‑max , determining the value C3 of the external capacitor on the secondary side; according to the impulse withstand voltage U of the external capacitor on the secondary side C3‑w and the value C3 of the external capacitor on the secondary side, selecting the external capacitor on the secondary side to be measured; after selecting the external capacitor on the secondary side to be measured, determining the transformation ratio k of the recording device according to the value C3 of the external capacitor on the secondary side. Thus, the secondary voltage signal is within a reasonable output range under normal conditions; abnormal voltages are restricted under abnormal conditions, ensuring personal safety and equipment safety.

Description

Technical Field

[0001] The present invention relates to the field of online monitoring of bushing voltage of primary power equipment such as transformers and high-voltage reactors, and more specifically, to a method for selecting the voltage of a high-voltage bushing end screen capacitor and a signal acquisition device. Background Art

[0002] With the development of intelligent technology in power systems, online monitoring systems for bushing voltage of primary power equipment such as transformers and high-voltage reactors are becoming more and more widely used. Figure 1 As shown: The medium between the bushing core and the bushing end screen can be equivalent to a capacitor C 1 (1) The equivalent stray capacitance between the bushing end screen and the ground is C 2 (2) Connect an external capacitor C 3 (3) C 3 With C 2 Connect in parallel with C 1 The capacitor voltage divider unit is formed. If the primary input voltage amplitude is U 1 , then the secondary side output voltage U 2 The following relations are satisfied:

[0003] U 2 =U 1 C 1 / (C 1 +C 2 +C 3 )

[0004] Because C 1 and C 2 The capacitance value is in the pF to nF level, C 3 In μF level, C 1 and C 2 Much smaller than C 3 , the above formula can be simplified as:

[0005] U 2 ≈U 1 C 1 / C 3

[0006] Voltage U 2 It is transmitted to the recording device through the signal cable. Among them, 1 is the equivalent capacitance between the bushing core and the bushing end screen, 2 is the stray capacitance between the bushing end screen and the ground, 3 is the external capacitor, 4 is the signal line, and 5 is the recording device.

[0007] There are some aspects that need to be improved in the existing on-line monitoring system for bushing voltage: (1) There is a lack of a reasonable method for selecting the parameters of the external capacitor; (2) The problem of voltage traveling wave reflection is not considered; (3) There is a lack of a voltage limiting unit; (4) The anti-electromagnetic interference ability is poor; (5) Single-point grounding measures should be adopted; (6) There is a lack of an electromagnetic isolation unit. Summary of the Invention

[0008] In order to solve the technical problems in the prior art that there is a lack of a reasonable method for selecting the parameters of the external capacitor in the on-line monitoring system for bushing voltage; the problem of voltage traveling wave reflection is not considered; there is a lack of a voltage limiting unit; the anti-electromagnetic interference ability is poor; single-point grounding measures should be adopted; and there is a lack of an electromagnetic isolation unit, the present invention provides a signal acquisition device for a method of selecting the voltage of the end screen capacitor of a high-voltage bushing.

[0009] According to the first aspect of the present invention, there is provided a method for selecting the voltage of the end screen capacitor of a high-voltage bushing. The method includes:

[0010] Determine the maximum peak voltage U of the recording device at the maximum range in-max and the selected peak voltage U at the selected range choice-max ;

[0011] According to the maximum peak voltage U in-max , determine the impulse withstand voltage U of the external capacitor on the secondary side C3-w ;

[0012] According to the selected peak voltage U choice-max， determine the value C of the external capacitor on the secondary side 3 ;

[0013] According to the impulse withstand voltage U of the external capacitor on the secondary side C3-w and the value C of the external capacitor on the secondary side 3 , select the external capacitor on the secondary side to be measured;

[0014] After selecting the external capacitor on the secondary side to be measured, according to the value C of the external capacitor on the secondary side 3 , determine the transformation ratio k of the recording device.

[0015] Optionally, according to the maximum peak voltage U in-max , determine the impulse withstand voltage U of the external capacitor on the secondary side C3-w , including:

[0016] According to the maximum peak voltage U in-max , determine the type selection of the varistor, where the varistor voltage U MOV satisfies the following relationship:

[0017] U in-max <U MOV≤1.2U in-max ;

[0018] According to the varistor voltage U MOV Determine the impulse withstand voltage U of the secondary side external capacitor C3-w , where the secondary side external capacitor impulse withstand voltage U C3-w The following relations are satisfied:

[0019] U C3-w ≥1.1U MOV .

[0020] Optionally, according to the selected peak voltage U choice-max , determine the value of the secondary side external capacitor C 3 ,include:

[0021] Determine the maximum input voltage U of the recording device under the selected range choice-max , U choice-max is the peak voltage;

[0022] According to the AC voltage level U level Select the maximum operating overvoltage U allowed by the system s-max ;

[0023] Determine the capacitance value C of the bushing end screen to ground 1 ;

[0024] According to the bushing end screen to ground capacitance value C 1 , determine the value of the secondary side external capacitor C 3 :

[0025] C 3 =C 1 U s-max / U choice-max .

[0026] Optionally, according to the impulse withstand voltage U of the secondary side external capacitor C3-w and the secondary side external capacitance value C 3 , select the secondary side external capacitor to be tested, including:

[0027] Determine that the impulse withstand voltage of the secondary side external capacitor to be tested is not less than the impulse withstand voltage U of the secondary side external capacitor C3-w；

[0028] Determine that the secondary side external capacitance to be measured is not less than the secondary side external capacitance value C 3 .

[0029] Optionally, after selecting the secondary-side external capacitor to be tested, according to the secondary-side external capacitor value C 3 , determine the transformation ratio k of the recording equipment, including:

[0030] Determine the transformation ratio k of the oscillographic recording device according to the following formula

[0031] k = C 3 / C 1 .

[0032] Optionally, it further includes:

[0033] Apply a power frequency voltage or switching impulse voltage at the high-voltage electrode of the bushing, compare the amplitude of the applied voltage with the waveform amplitude on the oscillographic recording device, and correct the transformation ratio k;

[0034] After the measured bushing is energized and put into operation, compare the measurement data of other voltage measuring devices with the waveform data on the oscillographic recording device, and correct the transformation ratio k.

[0035] According to another aspect of the present invention, there is also provided a device for collecting the voltage signal of the end screen of a high-voltage bushing. The device includes an end screen adapter, a short lead wire, a secondary voltage dividing box, a signal cable, an oscillographic recording device, and an isolation transformer;

[0036] Among them, the secondary voltage dividing box is a fully metal-sealed box, and a signal input port and a signal output port are arranged on the surface of the box body, which are respectively used to connect the wiring terminals of the short lead wire and the signal cable;

[0037] The secondary voltage dividing box is internally provided with a signal wire, a matching resistor, a varistor, and a capacitor. The signal wire is a cable with an insulating outer skin, one end is connected to the core of the signal input port, and the other end is connected to the matching resistor; the matching resistor uses a color ring resistor, and the resistance value of the matching resistor is consistent with the wave impedance value of the signal cable, and is connected to the core of the signal output port; there are two varistors, both close to the signal input port, one end is connected to the signal wire, and the other end is connected to the metal of the outer shell of the secondary voltage dividing box; the capacitor is arranged between the varistor and the matching resistor, one end is connected to the signal wire, and the other end is connected to the metal of the outer shell of the secondary voltage dividing box.

[0038] Optionally, the end screen adapter is of a fully sealed type, and there is a signal port at the output end to lead out the end screen voltage signal, and the outer shell of the end screen adapter is connected to the outer shell of the bushing.

[0039] Optionally, the short lead wire is a coaxial cable with a shielding layer, one end is connected to the signal port of the end screen adapter, and the other end is connected to the signal input port of the secondary voltage dividing box.

[0040] Optionally, the signal cable is a coaxial cable with a shielding layer, one end is connected to the signal output port of the secondary voltage dividing box, and the other end is connected to the signal input port of the oscillographic recording device.

[0041] Optionally, the isolation transformer is arranged between the power supply line of the oscillographic recording device and the public network, and the power of the isolation transformer meets the requirements of the oscillographic recording device.

[0042] Optionally, the outer shell of the last screen adapter, the shielding layer of the short lead wire, the outer shell of the secondary voltage dividing box, the shielding layer of the signal cable and the outer shell of the signal input port of the oscillograph device are closely connected to each other to maintain the same ground potential, and at the same time are completely wrapped around the metal body for transmitting voltage signals inside.

[0043] Thus, according to the method for selecting the capacitance voltage of the last screen of the high-voltage bushing, the secondary voltage signal is made to be within a reasonable output range under normal circumstances; in abnormal circumstances, the abnormal voltage is limited to ensure personal safety and equipment safety. According to a device for collecting the voltage signal of the last screen of a high-voltage bushing, the problem of voltage traveling wave reflection between the external capacitor and the signal cable is eliminated, the anti-electromagnetic interference ability is improved, and the voltage waveform bias distortion is prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The exemplary embodiments of the present invention can be more fully understood by referring to the following drawings:

[0045] Figure 1 It is a schematic diagram of the measurement circuit described in the background art;

[0046] Figure 2 It is a schematic flow chart of a method for selecting the capacitance voltage of the last screen of a high-voltage bushing according to this specific embodiment;

[0047] Figure 3 It is a flow chart of a method for selecting parameters of a programmed external capacitor and a voltage limiting unit according to this specific embodiment;

[0048] Figure 4 It is a schematic structural diagram of a device for collecting the voltage signal of the last screen of a high-voltage bushing according to this specific embodiment;

[0049] Among them, the main element symbols in this embodiment are as follows:

[0050] Last screen adapter - 1, short lead wire - 2, secondary voltage dividing box - 3, signal cable - 4, oscillograph device - 5, isolation transformer - 6, bushing outer shell - 7, signal input port - 8, signal output port - 9, signal line - 10, matching resistor - 11, varistor - 12, capacitor - 13. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Reference is now made to the accompanying drawings to describe exemplary embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not limitations on the present invention. In the drawings, the same units / components are denoted by the same reference numerals.

[0052] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention.

[0053] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. In addition, it can be understood that the terms defined in the commonly used dictionary should be understood to have a meaning consistent with the context of the relevant field, and should not be understood as idealized or overly formal meanings.

[0054] According to the first aspect of the present embodiment, a method for selecting the capacitance voltage of the end screen of a high-voltage bushing is provided. Refer to Figure 2 As shown, the method 100 includes:

[0055] S101: Determine the maximum peak voltage U of the recording device at the maximum range in-max and the selected peak voltage U at the selected range choice-max ;

[0056] S102: According to the maximum peak voltage U in-max , determine the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w ;

[0057] S103: According to the selected peak voltage U choice-max , determine the value C of the externally connected capacitor on the secondary side 3 ;

[0058] S104: According to the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w and the value C3 of the externally connected capacitor on the secondary side, select the externally connected capacitor to be measured on the secondary side;

[0059] S105: After selecting the externally connected capacitor on the secondary side to be measured, determine the transformation ratio k of the recording device according to the value C of the externally connected capacitor on the secondary side. 3 , and determine the transformation ratio k of the recording device.

[0060] Specifically, as shown in Figure 3 , step 1: Determine the maximum input voltage U of the recording device at the maximum range in-max , where U in-max is the peak voltage;

[0061] Step 2: Determine the type selection of the varistor according to U in-max , and the varistor voltage U MOV of the varistor satisfies the following relationship:

[0062] 1.2U in-max ≤ U MOV ≤ 1.5U in-max

[0063] Step 3: Determine the impulse withstand voltage U of the externally connected capacitor on the secondary side according to U MOV , and there is: C3-w

[0064] U C3-w ≥ 1.1U MOV

[0065] Step 4: Determine the maximum input voltage U of the recording device at the selected range choice-max , where U choice-max is the peak voltage;

[0066] Step 5: Select the maximum allowable switching overvoltage U of the system according to the voltage level U level , and referring to GB / T50064-2014, U s-max can be determined by Table 1 below: s-max

[0067] Table 1

[0068]

[0069]

[0070] Step 6: Determine the capacitance value C of the bushing end screen to ground 1 , and C 1 can be obtained from the bushing manufacturer's manual or the bushing nameplate;

[0071] Step 7: Obtain the capacitance value C according to the following formula 3 :

[0072] C 3 = C 1 U s-max / U choice-max ​​

[0073] Step 8: U obtained from Step 3 C3-w and C obtained from Step 7 3 Determine the selection of the external capacitor on the secondary side. The impulse withstand voltage of the selected capacitor should be not less than U calculated in Step 3 C3-w , and the capacitance value should be not less than C calculated in Step 7 3 . Select the capacitor with the closest C 3 and U C3-w in the first gear.

[0074] Step 9: After the equipment is installed, the transformation ratio k of the oscillographic equipment is:

[0075] k = C 3 / C 1

[0076] In order to obtain a more accurate transformation ratio k, further verification is required, which can be divided into two methods:

[0077] Method ①: Apply a power frequency voltage or an operating impulse voltage at the high-voltage electrode of the bushing, and compare the amplitude of the applied voltage with the waveform amplitude on the oscillographic equipment to correct the transformation ratio k.

[0078] Note: The amplitude of the applied voltage should be less than U s-max , and a clear waveform can be recorded on the oscillographic equipment. The range of the oscillographic equipment can be appropriately reduced to improve the waveform recording accuracy.

[0079] Method ②: After the measured bushing is energized and put into operation, compare the measurement data of other voltage measuring devices with the waveform data on the oscillographic equipment to correct the transformation ratio k.

[0080] Use the voltage data at the steady state of the system for comparison.

[0081] Thus, according to the method for selecting the voltage of the capacitor at the end shield of the high-voltage bushing, the secondary voltage signal is located within a reasonable output range under normal conditions; the abnormal voltage is restricted under abnormal conditions to ensure personal safety and equipment safety.

[0082] Optionally, according to the maximum peak voltage U in-max , determine the impulse withstand voltage U C3-w of the external capacitor on the secondary side, including:

[0083] According to the maximum peak voltage U in-max , determine the type selection of the varistor, where the varistor voltage U MOV of the varistor satisfies the following relationship:

[0084] U in-max ≤U MOV ≤1.5U in-max ;

[0085] According to the piezoresistive voltage U MOV determine the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w , where the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w satisfies the following relationship:

[0086] U C3-w ≥1.1U MOV .

[0087] Optionally, according to the selected peak voltage U choice-max， determine the value C of the externally connected capacitor on the secondary side 3 , including:

[0088] Determine the maximum input voltage U of the oscillograph in the selected range choice-max , U choice-max is the peak voltage;

[0089] According to the AC voltage level U level select the maximum operating overvoltage U allowed by the system s-max ;

[0090] Determine the capacitance value C of the bushing end screen to ground 1 ;

[0091] According to the capacitance value C of the bushing end screen to ground 1 , determine the value C of the externally connected capacitor on the secondary side 3 :

[0092] C 3 = C 1 U s-max / U choice-max .

[0093] Optionally, according to the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w and the value C of the externally connected capacitor on the secondary side 3 , select the externally connected capacitor on the secondary side to be measured, including:

[0094] Determine that the impulse withstand voltage of the externally connected capacitor on the secondary side to be measured is not less than the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w ;

[0095] Determine that the externally connected capacitor on the secondary side to be measured is not less than the value C of the externally connected capacitor on the secondary side 3 .

[0096] Optionally, after selecting the externally connected capacitor on the secondary side to be measured, according to the value C of the externally connected capacitor on the secondary side 3 , determine the transformation ratio k of the oscillograph, including:

[0097] Determine the transformation ratio k of the oscillographic recording device according to the following formula

[0098] k = C 3 / C 1 。

[0099] Optionally, it further includes:

[0100] Apply a power frequency voltage or an operating impulse voltage at the high-voltage electrode of the bushing, compare the amplitude of the applied voltage with the waveform amplitude on the oscillographic recording device, and correct the transformation ratio k;

[0101] After the bushing under test is energized and put into operation, compare the measurement data of other voltage measurement devices with the waveform data on the oscillographic recording device to correct the transformation ratio k.

[0102] According to another aspect of this embodiment, a device for collecting the voltage signal of the end screen of a high-voltage bushing is also provided. Refer to Figure 4 As shown, the device includes an end screen adapter 1, a short lead 2, a secondary voltage divider box 3, a signal cable 4, an oscillographic recording device 5, and an isolation transformer 6;

[0103] Among them, the secondary voltage divider box 3 is a fully metal-sealed box, and a signal input port 8 and a signal output port 9 are arranged on the surface of the box body, which are respectively used to connect the wiring terminals of the short lead 2 and the signal cable 4;

[0104] Inside the secondary voltage divider box 3, there are a signal line 10, a matching resistor 11, a varistor 12, and a capacitor 13. The signal line 10 is a cable with an insulating outer skin, one end is connected to the core of the signal input port 8, and the other end is connected to the matching resistor 11; the matching resistor 11 is a color-ring resistor, and the resistance value of the matching resistor 11 is consistent with the wave impedance value of the signal cable 4, and it is connected to the core of the signal output port 9; there are two varistors 12, both of which are close to the signal input port 8, one end is connected to the signal line 10, and the other end is connected to the metal of the outer shell of the secondary voltage divider box 3; the capacitor 13 is arranged between the varistor 12 and the matching resistor 11, one end is connected to the signal line 10, and the other end is connected to the metal of the outer shell of the secondary voltage divider box 3.

[0105] Optionally, the end screen adapter 1 is of a fully sealed type, and there is a signal port at the output end to lead out the end screen voltage signal, and the outer shell of the end screen adapter is connected to the bushing outer shell 7.

[0106] Optionally, the short lead 2 is a coaxial cable with a shielding layer, one end is connected to the signal port of the end screen adapter 1, and the other end is connected to the signal input port of the secondary voltage divider box 3.

[0107] Optionally, the signal cable 4 is a coaxial cable with a shielding layer, one end is connected to the signal output port 9 of the secondary voltage divider box, and the other end is connected to the signal input port of the oscillographic recording device 5.

[0108] Optionally, the isolation transformer 6 is arranged between the power line of the oscillograph device 5 and the public network, and the power of the isolation transformer 6 meets the requirements of the oscillograph device 5.

[0109] Optionally, the outer shell of the end screen adapter 1, the shielding layer of the short lead 2, the outer shell of the secondary voltage dividing box 3, the shielding layer of the signal cable 4 and the outer shell of the signal input port of the oscillograph device 5 are tightly connected to each other to maintain the same ground potential, and at the same time are completely wrapped around the metal body for transmitting voltage signals inside.

[0110] Thus, according to a device for collecting the end screen voltage signal of a high-voltage bushing, the problem of voltage traveling wave reflection between the external capacitor and the signal cable is eliminated, the anti-electromagnetic interference ability is improved, and the offset distortion of the voltage waveform is prevented.

[0111] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0112] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate for implementing in the process Figure 1 one process or multiple processes and / or blocks Figure 1 a device for the functions specified in one block or multiple blocks.

[0113] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements in the process Figure 1 one process or multiple processes and / or blocks Figure 1 a device for the functions specified in one block or multiple blocks.

[0114] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are executed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions for implementing the steps of the process Figure 1 a process or processes and / or blocks Figure 1 steps for the functions specified in a block or blocks.

[0115] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to cover the preferred embodiments as well as all changes and modifications that fall within the scope of the present application.

[0116] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A method for selecting the capacitance voltage of the grading ring of a high-voltage bushing, characterized in that, the method includes: Determine the maximum peak voltage U of the oscillographic recording device at the maximum range in-max and the selected peak voltage U at the selected range choice-max ; According to the maximum peak voltage U in-max , determine the impulse withstand voltage U C3-w of the externally connected capacitor on the secondary side; According to the selected peak voltage U choice-max， determine the value of the externally connected capacitor C on the secondary side 3 ; According to the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w and the value C of the externally connected capacitor on the secondary side 3 , select the externally connected capacitor on the secondary side to be measured; After selecting the externally connected capacitor on the secondary side to be measured, according to the value C of the externally connected capacitor on the secondary side 3 , determine the transformation ratio k of the recording device; According to the maximum peak voltage U in-max , determine the impulse withstand voltage U C3-w of the externally connected capacitor on the secondary side, including: According to the maximum peak voltage U in-max , determine the type selection of the varistor, where the varistor voltage U MOV satisfies the following relationship: U in-max <U MOV ≤1.2U in-max ; According to the piezoresistive voltage U MOV determine the impact withstand voltage U of the externally connected capacitor on the secondary side C3-w , where the impact withstand voltage U of the externally connected capacitor on the secondary side C3-w satisfies the following relationship: U C3-w ≥1.1U MOV ; According to the selected peak voltage U choice-max， Determine the value of the externally connected capacitor C on the secondary side 3 , including: Determine the maximum input voltage U of the oscillographic recording device under the selected range choice-max , U choice-max is the peak voltage; According to the AC voltage level U level Select the maximum switching overvoltage U allowed by the system s-max ; Determine the capacitance value C of the bushing grading capacitor to the ground 1 ; According to the capacitance value C of the bushing grading capacitor to ground 1 , determine the capacitance value C 3 connected externally on the secondary side: C 3 = C 1 U s-max / U choice-max ; It is characterized in that, according to the impulse withstand voltage U of the externally connected capacitor on the secondary side C3-w and the value C of the externally connected capacitor on the secondary side 3 , an externally connected capacitor on the secondary side to be measured is selected, including: Determine that the impulse withstand voltage of the secondary side external capacitor to be measured is not less than the impulse withstand voltage U of the secondary side external capacitor C3-w； Determine that the externally connected capacitance on the secondary side to be measured is not less than the externally connected capacitance value C on the secondary side 3 .

2. According to the method described in claim 1, characterized in that, After selecting the secondary-side external capacitor to be measured, according to the value C of the secondary-side external capacitor 3 , determining the turns ratio k of the recording device, including: determine the transformation ratio k of the recording device according to the following formula k = C 3 / C 1 .

3. According to the method described in claim 1, characterized in that, further includes: apply a power frequency voltage or an operating impulse voltage at the high-voltage electrode of the bushing, compare the amplitude of the applied voltage with the waveform amplitude on the recording device, and correct the transformation ratio k; after the bushing under test is energized and put into operation, compare the measurement data of other voltage measuring devices with the waveform data on the recording device, and correct the transformation ratio k.

Images