CN203630174U - High precision capacitive voltage divider applied in live-line verification - Google Patents

Abstract

The utility model discloses a high-precision capacitive voltage divider used in live calibration, which belongs to the technical field of capacitive voltage dividers. It includes high-voltage arm capacitor C ₁ , low-voltage arm capacitor C ₂ , low-voltage capacitor leads, high-voltage side shielding sleeve and low-voltage side shielding sleeve. The high-voltage arm capacitor C ₁ is a coaxial cylindrical capacitor, and the low-voltage arm capacitor C ₂ is a parallel plate capacitor. The arm capacitor C ₁ is connected to the low-voltage arm capacitor C ₂ through the low-voltage capacitor lead. The high-voltage side shielding sleeve covers the high-voltage arm capacitor C ₁ . The low-voltage side shielding sleeve covers the low-voltage arm capacitor C ₂ and the low-voltage capacitor lead. The high-voltage side shielding sleeve Together with the low-voltage side shield cover the entire capacitive divider. Due to the introduction of shielding, the capacitive voltage divider can effectively reduce the influence of external interference on the intermediate voltage value of the capacitive voltage divider, and improve the accuracy and stability of measurement.

Description

A High-Precision Capacitive Voltage Divider Applied to Live Calibration

technical field

The utility model relates to the technical field of capacitor voltage dividers, in particular to a high-precision capacitor voltage divider applied to live calibration.

Background technique

Capacitive voltage transformer (capacitor voltage transformer) is mainly used in high-voltage level circuits of power systems, referred to as CVT. The main structure of CVT includes standard capacitive voltage divider, intermediate voltage measuring transformer and subsequent circuits. The intermediate voltage measuring transformer and the follow-up circuit can be considered as a low-voltage electromagnetic voltage transformer, and its measurement accuracy can be very high under the current production conditions, so under normal working conditions, it will affect the CVT measurement accuracy The factors focus on standard capacitive voltage dividers.

The standard capacitive voltage divider is generally composed of the main capacitor of the high-voltage arm and the main capacitor of the low-voltage arm in series. Since the main capacitance of the high-voltage arm is relatively large, a structure of connecting several low-capacity capacitors in series can also be used in the high-voltage arm. A structure in which several capacitors are connected in parallel can be used. When a voltage is applied across an ideal capacitor, only displacement current exists in the capacitor. However, when a voltage is applied to both ends of the actual capacitor, some leakage current will flow through the insulating material of the capacitor, and this part of the leakage current will change the voltage division ratio of the standard capacitor voltage divider, causing errors in the measurement. In order to obtain a high-precision standard capacitor voltage divider, it is necessary to reduce the leakage current of the standard capacitor voltage divider as much as possible.

The standard capacitive voltage divider is used in high voltage occasions. Due to its large size, stray capacitance will be generated between the surrounding equipment and the ground. Under normal operating conditions, these stray capacitances cause stray currents to flow in standard capacitive dividers. These stray currents also change the divider ratio of standard capacitive dividers, affecting measurement accuracy. Especially for capacitive voltage transformers used in online calibration, the on-site working environment is complex and changeable, and changes in the surrounding environment will also affect stray capacitance. Therefore, in order to obtain a high-precision standard capacitive voltage divider, measures need to be taken to reduce the stray capacitance between the standard capacitive voltage divider and the surrounding environment, and reduce the influence of the charged state of adjacent equipment on the measurement accuracy of the standard capacitive voltage divider.

Due to the many advantages of CVT in high-voltage lines, scholars and companies at home and abroad have done a lot of research on capacitive voltage transformers. The direction of research includes analyzing the cause of errors in steady state and improving measurement accuracy, research on transient characteristics, improving transient response and weakening ferromagnetic resonance, etc. However, the influence of the external electromagnetic environment and nearby equipment on the standard capacitive voltage divider is still very prominent.

The main components of a capacitive voltage transformer include a two-stage standard capacitive voltage divider, an A/D conversion module, a data processing module, and a data display output module. Its structural principle is shown in Figure 1.

When the capacitive electronic voltage transformer measures the voltage, it first reduces the high voltage on the bus to the intermediate voltage at both ends of the low-voltage arm capacitor through a two-stage standard capacitive voltage divider, and then converts the intermediate voltage analog signal through the A/D conversion module It is converted into a digital signal, and the signal data is processed in the data processing module of the secondary side to obtain the voltage signal of the primary side, and its amplitude and phase are calculated, and finally output through the data display output module.

In the basic structure of CVT, the accuracy and stability of the standard capacitive voltage divider has a very important influence on the measurement accuracy of the CVT. The content of this chapter mainly focuses on the shielding measures of the standard capacitive voltage divider.

The ideal structural circuit diagram of a standard capacitive voltage divider is shown in Figure 2(a). In the ideal case, only displacement current flows through the capacitor, and the voltage relationship between the low-voltage arm and the high-voltage arm is shown in formula (1). However, in actual operation, due to the leakage current in the standard capacitor, the leakage current is equivalent to a resistor connected in parallel with the standard capacitor, and the structure of the standard capacitor voltage divider in actual operation is shown in Figure 2(b).

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000430175760000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Ideally, the voltage division ratio of the standard capacitor voltage divider has nothing to do with frequency, but the voltage division ratio of the standard voltage divider in actual operation is related to frequency, such as formulas (2) and (3).

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000430175760000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; j\&omega;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; j\&omega;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; j\&omega;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000430175760000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; J\&omega;</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="HDA0000430175760000014.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; j\&omega;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

It can be seen that due to the existence of the equivalent resistance of the leakage current, the accuracy of the voltage division ratio of the actual standard capacitor voltage divider will be affected, and the accuracy of the standard capacitor voltage divider can be improved by reducing the leakage current.

Utility model content

In order to solve the above problems, the utility model proposes a high-precision capacitive voltage divider applied to live calibration by reducing the stray capacitance between the capacitive electrode and adjacent equipment to improve measurement accuracy and measurement stability.

The high-precision capacitive voltage divider used in live calibration provided by the utility model includes a high-voltage arm capacitor C ₁ , a low-voltage arm capacitor C ₂ , a low-voltage capacitor lead wire, a high-voltage side shielding sleeve, and a low-voltage side shielding sleeve. The high-voltage arm capacitor C ₁ is a coaxial cylindrical capacitor, the low-voltage arm capacitor C ₂ is a parallel plate capacitor, the high-voltage arm capacitor C ₁ is connected to the low-voltage arm capacitor C ₂ through a low-voltage capacitor lead, and the high-voltage side shielding sleeve covers the high-voltage arm Capacitor C ₁ , the low-voltage side shielding sleeve covers the low-voltage arm capacitor C ₂ and the lead wire of the low-voltage capacitor, and the high-voltage side shielding sleeve and the low-voltage side shielding sleeve together cover the entire capacitor voltage divider.

Preferably, the high-voltage arm capacitor _C1 is smoothed.

Preferably, an SF ₆ air gap is filled between the electrodes of the high-voltage arm capacitor C ₁ .

As a preference, the filling medium of the low-voltage arm capacitor _C2 is a film-paper composite medium with a dielectric constant of 3.5.

Preferably, the capacitive voltage divider further includes a plurality of temperature sensors for indicating the temperature in the capacitive voltage divider.

The high-accuracy capacitive voltage divider used in live calibration provided by the utility model can effectively reduce the influence of external interference on the intermediate voltage value of the capacitive voltage divider due to the introduction of shielding, and improve the accuracy and stability of measurement.

Description of drawings

Fig. 1 is a schematic diagram of a CVT structure in the prior art;

Figure 2(a) is a schematic diagram of the CVT structure in the prior art under ideal conditions;

Fig. 2(b) is a schematic diagram of the actual situation of the CVT structure in the prior art;

Fig. 3 is a schematic structural diagram of a high-precision capacitive voltage divider applied to live calibration provided by Embodiment 1 of the utility model;

Fig. 4 is a schematic structural diagram of a high-precision capacitive voltage divider applied to live calibration provided by Embodiment 2 of the present invention;

Fig. 5 is a temperature error-temperature line graph of the high-precision capacitive voltage divider applied to live calibration provided by the second embodiment of the present invention.

Detailed ways

In order to deeply understand the utility model, the utility model will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Embodiment one

The high-precision capacitive voltage divider used in live calibration provided by the utility model includes high-voltage arm capacitor C ₁ 2, low-voltage arm capacitor C ₂ 4, low-voltage capacitor lead wire 6, high-voltage side shielding sleeve 1 and low-voltage side shielding sleeve 3, high-voltage The arm capacitor C ₁ 2 is a coaxial cylindrical capacitor, the low-voltage arm capacitor C ₂ 4 is a parallel plate capacitor, the high-voltage arm capacitor C ₁ 2 is connected to the low-voltage arm capacitor C ₂ 4 through the low-voltage capacitor lead 6, and the high-voltage side shielding sleeve 1 covers the The high-voltage arm capacitor C ₁ 2, the low-voltage side shielding sleeve 3 covers the low-voltage arm capacitor C ₂ 4 and the low-voltage capacitor lead 6, the high-voltage side shielding sleeve 1 and the low-voltage side shielding sleeve 3 together cover the entire capacitor voltage divider, and the label 5 is Intermediate voltage signal output terminal. The simulation is carried out with ANSOFT software. After calculation and simulation, the maximum value of the electric field appears between the electrodes of the parallel plate capacitor, and the electric field strength value of the rest is relatively low, which meets the insulation requirements.

The capacitive voltage divider under the four conditions of shielded without interference, shielded with interference, unshielded without interference, and unshielded with interference are respectively simulated, and the obtained intermediate voltage values are shown in Table 1:

Table 1 Comparison table of intermediate voltage simulation results

It can be seen from Table 1 that external interference has no effect on the intermediate voltage value, and the difference between the intermediate voltage with and without interference is 0.00%. When adopting the capacitive voltage divider provided by the prior art, when there is interference and no interference, the intermediate voltage difference is 10.79%, so it can be seen that the high-precision capacitive voltage divider applied to live calibration provided by the utility model is due to The introduction of shielding can effectively reduce the influence of external interference on the intermediate voltage value of the capacitor voltage divider, and improve the accuracy and stability of the measurement.

Among them, the high-voltage arm capacitor C ₁ 2 can be smoothed to reduce the electric field intensity.

Among them, the SF ₆ air gap can be filled between the electrodes of the high-voltage arm capacitor C ₁ to take advantage of its good electrical insulation performance and excellent arc extinguishing performance.

Among them, the low-voltage arm capacitor C ₂ is filled with a film-paper composite medium with a dielectric constant of 3.5 to take advantage of its small temperature coefficient, stable capacitance, and good moisture resistance.

Embodiment two

Referring to Figure 4, the difference between the high-precision capacitive voltage divider applied to the live calibration provided by the second embodiment of the present invention and the high-precision capacitive voltage divider applied to the live calibration provided by the first embodiment of the present invention is that,

The utility model capacitive voltage divider also comprises a plurality of temperature sensors 7, and in the present embodiment, temperature sensor 7 is respectively arranged in 6 different positions in this capacitive voltage divider, is used for indicating the temperature of different positions in the capacitive voltage divider. temperature, thereby further reducing the influence of temperature and improving the stability of the partial pressure ratio.

The method for measuring the intermediate voltage by using the capacitive voltage divider provided in Embodiment 2 of the present invention includes the following steps:

According to the temperature measured by each temperature sensor 7, adopt the interpolation method to obtain the temperature error in the temperature error-temperature line graph as shown in Figure 5;

According to the temperature error, the intermediate voltage actually measured by the capacitor voltage divider is corrected to obtain the true value of the intermediate voltage.

Wherein, the method for obtaining the temperature error-temperature line graph as shown in Figure 5 comprises the following steps:

Put the capacitor voltage divider into the temperature control room, apply the rated voltage to the capacitor voltage divider at different temperature points, and measure the temperature characteristic data of the capacitor voltage divider. The temperature characteristic data of the capacitor voltage divider include temperature value, test voltage value, Intermediate voltage value and temperature error value, in the present embodiment, the temperature characteristic data of capacitive voltage divider are as shown in Table 2:

Table 2 temperature characteristic data

temperature (°C) Rated voltage (KV) Intermediate voltage (V) Temperature error (%) 0.1 50.641 11.6263 0.034 15.3 50.527 11.6002 0.035 30.1 50.769 11.6549 0.027 45.2 50.749 11.6504 0.028 59.6 50.970 11.7034 0.048 ;

Draw the temperature error-temperature line graph shown in Figure 5 according to the temperature error value and the temperature value.

Wherein, the temperature range of the temperature control chamber is 0-60°C.

Wherein, there are multiple temperature points, and in this embodiment, the temperature points are 5 as shown in Table 2, wherein, the more the number of temperature points is, the more accurate the temperature error-temperature line graph is.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present utility model in detail. For the utility model, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the utility model shall be included in the protection scope of the utility model.

Claims (5)

1. A high-precision capacitive voltage divider applied to live calibration, characterized in that it comprises a high-voltage arm capacitor C ₁ , a low-voltage arm capacitor C ₂ , a low-voltage capacitor lead wire, a high-voltage side shielding sleeve and a low-voltage side shielding sleeve, the The high-voltage arm capacitor C ₁ is a coaxial cylindrical capacitor, the low-voltage arm capacitor C ₂ is a parallel plate capacitor, the high-voltage arm capacitor C ₁ is connected to the low-voltage arm capacitor C ₂ through a low-voltage capacitor lead wire, and the high-voltage side shielding sleeve covers The high-voltage arm capacitor C ₁ is covered, the low-voltage arm capacitor C ₂ and the low-voltage capacitor leads are covered by the low-voltage side shielding sleeve, and the high-voltage side shielding sleeve and the low-voltage side shielding sleeve together cover the entire capacitor voltage divider. 2. The capacitive voltage divider according to claim 1, wherein the high voltage arm capacitor _C1 has been smoothed. 3. The capacitive voltage divider according to claim 1, characterized in that, the SF ₆ air gap is filled between the electrodes of the high voltage arm capacitor C ₁ . 4. The capacitive voltage divider according to claim 1, characterized in that, the filling medium of the low-voltage arm capacitor _C2 is a film-paper composite medium with a dielectric constant of 3.5. 5. The capacitive voltage divider according to any one of claims 1-4, characterized in that, the capacitive voltage divider further comprises a plurality of temperature sensors for indicating the temperature inside the capacitive voltage divider.

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