Ceramic capacitor medium, preparation method and phase sequence electronic voltage transformer

Abstract

The invention provides a ceramic capacitor medium, a preparation method and a phase sequence electronic voltage transformer, and the ceramic capacitor medium comprises the following raw material components in percentage by weight: 16% of BaCO3, 68% of TiO2, and 16% of Nd2O3 and Bi2O3, wherein the ratio of Nd2O3 in the total molar weight of Nd2O3 and Bi2O3 is a, the ratio of Bi2O3 in the total molar weight of Nd2O3 and Bi2O3 is b, a + b = 1, and 0.5 < = a < = 0.65. The raw materials Nd2O3 and Bi2O3 in the ceramic capacitor dielectric are adjusted in a specific proportion range, the dielectric property and the high voltage resistance of the ceramic capacitor dielectric are greatly improved, the dielectric constant of the prepared ceramic capacitor dielectric is larger than or equal to 120 under the test conditions of 1kHz and 1V, the change rate of the dielectric constant is within + / -0.5% within the temperature range of-40 DEG C to + 70 DEG C, the dielectric loss is lower than 0.05%, and the dielectric constant of the prepared ceramic capacitor dielectric is larger than or equal to 90% within the temperature range of-40 DEG C to + 70 DEG C under the test conditions of 1kHz and 1V. And the withstand voltage can reach more than power frequency 10 kV / mm, so that the dielectric property and the withstand voltage property of the ceramic capacitor dielectric are integrally improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical equipment, and particularly relates to a ceramic capacitor dielectric, a preparation method thereof, and a phase-sequence electronic voltage transformer. Background Art

[0002] Compared with traditional electromagnetic voltage transformers, electronic voltage transformers have the advantages of no ferromagnetic resonance, small volume, and easy integration, and are currently widely promoted in smart grids. Among them, ceramic capacitors are key measuring devices, which convert high-voltage signals into low-voltage signals using the voltage division principle of ceramic capacitors, and further convert them into digital signals through analog-to-digital converters.

[0003] Generally, the requirement for phase-sequence measurement accuracy is 0.5 level. However, the current temperature coefficient of ceramic capacitors is relatively large, and it is difficult to meet the phase-sequence accuracy requirements within the grid operating temperature range (-40°C to +70°C). In addition, for electronic voltage transformers, their capacitance should be as large as possible, and the corresponding dielectric constant is also required to be large (such as above 120), and low loss should also be achieved. Existing ceramic capacitor dielectrics are difficult to meet the above requirements simultaneously. Some high-frequency and microwave ceramic materials have high dielectric constants and temperature stabilities, but their application scenarios are different. For example, they were originally applied to high-frequency (≥1 MHz) and low-voltage scenarios. When applied to the low-frequency (≤1 kHz) and high-voltage (≥10 kV) scenarios of transformers, their performance indicators change and cannot meet the requirements of transformers.

[0004] Therefore, aiming at the requirements of electronic voltage transformers, especially for precise phase-sequence measurement, it is urgent to develop ceramic capacitor dielectrics and ceramic capacitors with high dielectric constants, high temperature stabilities, low losses, and high voltage resistances in this scenario. Summary of the Invention

[0005] The purpose of the present invention is to solve or alleviate the problem of poor dielectric properties of ceramic capacitor dielectrics in existing electronic voltage transformers.

[0006] The purpose of the present invention is achieved by the following solutions: The present invention provides a ceramic capacitor dielectric. By percentage, the raw material components of the ceramic capacitor dielectric include: the molar ratio of BaCO3 accounts for 16%, the molar ratio of TiO2 accounts for 68%, and the total molar ratio of Nd2O3 and Bi2O3 accounts for 16%; wherein, in the total molar amount of Nd2O3 and Bi2O3, the ratio of Nd2O3 is a, and in the total molar amount of Nd2O3 and Bi2O3, the ratio of Bi2O3 is b, a + b = 1, and 0.5 ≤ a ≤ 0.65.

[0007] Preferably, 0.57 ≤ a ≤ 0.6.

[0008] Based on the same inventive concept, the present invention also provides a method for preparing a ceramic capacitor, comprising: grinding and calcining: weighing the raw materials of the ceramic capacitor dielectric according to a ratio, and successively performing grinding treatment, drying treatment and calcining treatment to obtain a primary mixture; secondary grinding: subjecting the primary mixture to the grinding treatment and the drying treatment again to obtain a fine mixture; granulating and compacting: granulating the fine mixture to obtain raw material particles, and subjecting the raw material particles to screening treatment and pressing and forming treatment to obtain a ceramic blank; debinding and sintering: subjecting the ceramic blank to debinding treatment and sintering treatment successively to obtain the ceramic capacitor dielectric.

[0009] Preferably, in the grinding and calcining step and the secondary grinding step, the grinding treatment is carried out by a planetary ball mill, the rotational speed of the ball mill is 300 r / min - 400 r / min, and the ball milling time is 12 h - 24 h.

[0010] Preferably, the grinding aid of the ball mill comprises anhydrous ethanol or deionized water.

[0011] Preferably, in the grinding and calcining step, the calcining temperature of the calcining treatment is 900 °C - 1100 °C, and the calcining time is 6 h - 8 h.

[0012] Preferably, in the granulating and compacting step, the binder used in the granulating treatment is a polyvinyl alcohol solution with a mass fraction of 4% - 6%.

[0013] Preferably, in the granulating and compacting step, the screening treatment of the raw material particles is carried out using a sieve with 80 meshes - 120 meshes.

[0014] Preferably, in the granulating and compacting step, the pressure of the pressing and forming treatment is 100 MPa - 200 MPa, and the pressure holding time is 60 s - 180 s.

[0015] Preferably, in the debinding and sintering step, the heating rate of the debinding treatment is 2 °C / min, the debinding temperature is 550 °C - 650 °C, and the debinding time is 6 h - 12 h.

[0016] Preferably, in the debinding and sintering step, the heating rate of the sintering treatment is 3 °C / min, the sintering temperature is 1200 °C - 1320 °C, and the sintering time is 2 h - 6 h.

[0017] Preferably, the preparation method further comprises: sintering and infiltrating a silver electrode on the surface of the ceramic capacitor dielectric to obtain a ceramic capacitor, and the sintering and infiltration temperature is 550 °C - 650 °C.

[0018] Based on the same inventive concept, the present invention also provides a phase-sequence electronic voltage transformer, comprising the ceramic capacitor prepared by the preparation method of the ceramic capacitor dielectric.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a ceramic capacitor dielectric, a preparation method and a phase-sequence electronic voltage transformer. By percentage, the raw material components of the ceramic capacitor dielectric include: the molar ratio of BaCO3 is 16%, the molar ratio of TiO2 is 68%, and the total molar ratio of Nd2O3 and Bi2O3 is 16%; wherein, the ratio of Nd2O3 in the total molar amount of Nd2O3 and Bi2O3 is a, and the ratio of Bi2O3 in the total molar amount of Nd2O3 and Bi2O3 is b, a + b = 1, 0.5 ≤ a ≤ 0.65. By adjusting the raw materials Nd2O3 and Bi2O3 in the ceramic capacitor dielectric within a specific ratio range, the prepared ceramic capacitor dielectric has a dielectric constant ≥ 120 under the test conditions of 1 kHz and 1 V, the dielectric constant change rate is within ±0.5% in the temperature range of -40 to +70 degrees, and the dielectric loss is less than 5 per ten thousand. This ceramic capacitor dielectric has good high voltage withstand performance, and the voltage withstand can reach more than 10 kV / mm at power frequency, overall improving the dielectric performance and voltage withstand performance of the ceramic capacitor dielectric. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 SEM diagram of the ceramic capacitor dielectric in Embodiment 1 of the present invention; Figure 2 SEM diagram of the ceramic capacitor dielectric in Embodiment 2 of the present invention; Figure 3 SEM diagram of the ceramic capacitor dielectric in Embodiment 3 of the present invention; Figure 4 SEM diagram of the ceramic capacitor dielectric in Embodiment 4 of the present invention; Figure 5 SEM diagram of the ceramic capacitor dielectric in Embodiment 5 of the present invention; Figure 6 SEM diagram of the ceramic capacitor dielectric in Comparative Example 1; Figure 7 SEM diagram of the ceramic capacitor dielectric in Comparative Example 2; Figure 8 SEM diagram of the ceramic capacitor dielectric in Comparative Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following embodiments are provided to better understand the present invention further. They are not limited to the best embodiment, and do not limit the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0022] For those without specific experimental steps or conditions noted in the present invention, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed.

[0023] The present invention provides a ceramic capacitor dielectric. By percentage, the raw material components of the ceramic capacitor dielectric include: the molar proportion of BaCO3 is 16%, the molar proportion of TiO2 is 68%, and the total molar proportion of Nd2O3 and Bi2O3 is 16%; among them, the proportion of Nd2O3 in the total molar amount of Nd2O3 and Bi2O3 is a, and the proportion of Bi2O3 in the total molar amount of Nd2O3 and Bi2O3 is b, a + b = 1, and 0.5 ≤ a ≤ 0.65.

[0024] The preparation method of the ceramic capacitor dielectric of the present invention includes: S1. Grinding and calcining: Weigh the raw materials of the above-mentioned ceramic capacitor dielectric and perform grinding treatment, drying treatment, and calcining treatment in sequence to obtain a primary mixture. S2. Secondary grinding: Subject the primary mixture to grinding treatment and drying treatment again to obtain a fine mixture. S3. Granulation and pressing: Granulate the fine mixture to obtain raw material particles, and after screening treatment and pressing and forming treatment of the raw material particles, a ceramic green body is obtained. S4. Debinding and sintering: Subject the ceramic green body to debinding treatment and sintering treatment in sequence to obtain the ceramic capacitor dielectric.

[0025] Specifically, in the S1 grinding and calcining step and the S2 secondary grinding step, the grinding treatment uses a planetary ball mill. The rotation speed of the ball mill is set to 300 r / min - 400 r / min, the ball milling time is 12 h - 24 h, the grinding aids of the ball mill include anhydrous ethanol or deionized water, and the mixed material after ball milling is dried using a drying oven. The drying temperature is set to 90°C - 110°C to remove the grinding aids. The calcining temperature of the calcining treatment is set to 900°C - 1100°C, and the calcining time is 6 h - 8 h.

[0026] The treatment of the raw materials of the ceramic capacitor dielectric through two stages of grinding and calcining and secondary grinding greatly improves the uniformity of the mixing and dispersion of each component.

[0027] In the S3 granulation and pressing step, the granulation treatment uses a granulator. Among them, a polyvinyl alcohol solution with a mass fraction of 4% - 6% is used as the binder, a sieve with 80 - 120 meshes is used to screen the particles, and then according to different sizes and shapes of pressing, the mold filled with the screened particles is placed on a hydraulic press for pressing and forming treatment. The pressure of pressing and forming is maintained at 100 MPa - 200 MPa, and the pressure holding time is 10 s - 30 s. Finally, the required ceramic green body is obtained.

[0028] It should be noted that the ceramic green body is preferably in a cylindrical or disc-shaped structure.

[0029] In the S4 debinding and sintering step, the ceramic green body is placed in a sintering furnace and heated at a heating rate of 2 °C / min to the debinding temperature of 550 °C - 650 °C, and the debinding time is 6 h - 12 h for debinding treatment to discharge the polyvinyl alcohol binder from the ceramic green body. When the debinding treatment is completed, it is directly heated at a heating rate of 3 °C / min to continue heating to the sintering temperature of 1200 °C - 1320 °C, and the sintering time is 2 h - 6 h to complete the sintering treatment. Finally, it is cooled to room temperature with the furnace to obtain the ceramic capacitor dielectric.

[0030] The preparation method of the ceramic capacitor dielectric of the present invention further includes: S5. Silver electrode firing, that is, firing and infiltrating a silver electrode on the surface of the ceramic capacitor dielectric to obtain a ceramic capacitor.

[0031] Specifically, the fired ceramic capacitor dielectric in the above step S4 is taken, and silver layers are fired and infiltrated on both surfaces of the ceramic capacitor dielectric to produce a ceramic capacitor, and the firing and infiltration temperature is 550 °C - 650 °C.

[0032] It should be noted that this preparation method is simple in operation, easy to implement, and greatly improves the quality of the ceramic capacitor dielectric and the ceramic capacitor.

[0033] The raw material ratios and preparation process parameters of the ceramic capacitor dielectric in the above different ranges are selected to obtain the following specific examples.

[0034] Examples 1 - 5 Table 1 shows the comparison of the raw material ratios of the ceramic capacitor dielectric and the preparation process parameters of the ceramic capacitor dielectric in Examples 1 - 5 as follows: Table 1

[0035] Continued from the previous page table

[0036] It should be noted that in Examples 1 - 5 of the raw material components, the molar ratio of BaCO3 to TiO2 is a fixed value, so only the ratio values (a and b) between Nd2O3 and Bi2O3 are listed.

[0037] Comparative Example 1 The difference between the ceramic capacitor dielectric in this Comparative Example 1 and Example 1 is that in the raw materials of the ceramic capacitor dielectric in Comparative Example 1, the ratio values of Nd2O3 to Bi2O3 are a = 0.75 and b = 0.25 respectively.

[0038] The preparation method of the ceramic capacitor dielectric in this Comparative Example 1 is exactly the same as the process parameters of the preparation method in Example 1, so it will not be elaborated here.

[0039] Comparative Example 2 The difference between the ceramic capacitor dielectric in this Comparative Example 2 and that in Example 1 lies in that in the raw materials of the ceramic capacitor dielectric in Comparative Example 2, the ratio of Nd2O3 to Bi2O3 is a = 0.45 and b = 0.55 respectively.

[0040] The preparation method of the ceramic capacitor dielectric in this Comparative Example 2 is exactly the same as the process parameters of the preparation method in Example 1, so it will not be elaborated here.

[0041] Comparative Example 3 The difference between the ceramic capacitor dielectric in this Comparative Example 3 and that in Example 1 lies in that La2O3 is used to replace Nd2O3 in the raw materials of the ceramic capacitor dielectric in Comparative Example 3.

[0042] The preparation method of the ceramic capacitor dielectric in this Comparative Example 3 is exactly the same as the process parameters of the preparation method in Example 1, so it will not be elaborated here.

[0043] Performance Test Take the ceramic capacitor dielectric specimens obtained in Examples 1 to 5 and Comparative Examples 1 to 3, and test the scanning electron microscope images of the specimens respectively, and measure the dielectric constant and dielectric loss of the specimens at 20°C. The test conditions are 1 kHz and 1 V. If the dielectric constant ≥ 120 and the dielectric loss ≤ 0.05%, then proceed to the next test, otherwise stop the next test.

[0044] Further test the temperature change rate of the samples that meet the dielectric constant and dielectric loss. Test the dielectric constant of the materials at -40°C, 20°C and 70°C respectively, and then calculate the change rate relative to the dielectric constant at 20°C.

[0045] Finally, conduct a power frequency withstand voltage test on all specimens to determine whether the specimens meet the requirement of being greater than 10 kV / mm.

[0046] Table 2 is a comparison table of the dielectric constant, dielectric loss, dielectric constant change rate at different temperatures and withstand voltage performance of Examples 1 to 5 and Comparative Examples 1 to 3.

[0047] Table 2

[0048] According to the content of Table 2 above, the ceramic capacitor dielectrics of Examples 1 to 5 simultaneously meet the requirements that the dielectric constant is greater than 120, the loss is lower than 0.05%, the temperature change rate is within ±0.5%, and the withstand voltage ≥ 10 kV / mm. It can be seen from the SEM images that they also have a dense structure.

[0049] Among them, the dielectric constant of Example 4 at 20°C is 127, and its dielectric loss is only 0.01%.

[0050] In addition, in Comparative Example 1, since the ratio of Bi2O3 is b = 0.25, the molar ratio of Bi2O3 after conversion is 4%. Because Bi 3+ ions have a relatively high polarizability and can significantly enhance the polarization effect in the ceramic, thereby increasing the dielectric constant. Since the content of Bi element in Comparative Example 1 is too low, the polarization contribution of Bi element is reduced, resulting in the difficulty of achieving a relatively high dielectric constant (120) for the ceramic capacitor dielectric in Comparative Example 1 (110).

[0051] Relatively, in Comparative Example 2, since the ratio of Bi2O3 is b = 0.55, the molar ratio of Bi2O3 after conversion is 8.8%. The excessive Bi content leads to the easy volatilization of Bi element during the sintering process, making it difficult to control the sintering atmosphere, resulting in uneven local composition distribution of the material and affecting the stability of the crystal phase structure. As a result, the specimen in Comparative Example 2 deforms after sintering, the sample is prone to warping, and the dielectric loss increases abnormally, with the dielectric loss reaching 10 and the breakdown voltage not exceeding 10 kV / mm.

[0052] In Comparative Example 3, since La2O3 is used to replace the raw material Nd2O3 in Example 1, and La element which has a greater impact on dielectric loss is adopted, the dielectric loss of Comparative Example 3 exceeds 0.05%.

[0053] In addition, as Figures 1 - 5 shown Figures 1 - 5 are the SEM images of the ceramic capacitor dielectrics of Examples 1 - 5 respectively. The grain sizes of the ceramic capacitor dielectrics of Examples 1 - 5 are relatively uniform and dense as a whole, which is beneficial for the ceramic capacitor dielectric to obtain a lower dielectric loss. Among them, Figure 5 in

[0054] As Figure 6 shown, the Bi content in Comparative Example 1 is small and the structure is dense, but the dielectric constant is low. As Figure 7 shown, the Bi content in Comparative Example 2 is higher and the grain structure is more porous.

[0055] As Figure 8 shown, in Comparative Example 3, La element replaces Nd element in Comparative Example 1, and due to its relatively porous structure, the dielectric loss is also high. In comparison, the Nd 3+ radius in this example is smaller than that of La 3+Small, resulting in the shrinkage of the unit cell volume to obtain a dense structure and achieve low loss, and its temperature coefficient is closer to zero; Bi element can form a liquid-phase sintering environment during the sintering process to obtain a denser structure, which is beneficial to suppressing dielectric loss, and has a large polarizability and strong electron cloud distortion ability, which helps to enhance displacement coupling, increase the dielectric constant, and finally effectively suppress the temperature coefficient, dielectric loss and increase the dielectric constant.

[0056] By comparison, it can be seen that in Examples 1-5 of the present invention, the ratio of Nd2O3 to Bi2O3 is controlled within a set range, and a ceramic capacitor dielectric with good comprehensive performance such as high dielectric constant, low temperature change rate, low dielectric loss and high breakdown voltage can be prepared.

[0057] Among them, it is preferably 0.57 ≤ a ≤ 0.6, that is, the overall comprehensive performance of the ceramic capacitor dielectrics in Examples 2-4 is the best in terms of dielectric, loss, change rate and breakdown voltage.

[0058] Example 6 Based on the same inventive concept, this embodiment also provides a phase-sequence electronic voltage transformer, which uses a ceramic capacitor prepared by the preparation method of the ceramic capacitor dielectric in Examples 1-5.

[0059] The phase-sequence electronic voltage transformer uses this ceramic capacitor to convert a high-voltage signal into a low-voltage signal, greatly improving the phase-sequence measurement accuracy of the voltage transformer.

[0060] It should be noted that according to the actual application requirements of the electronic voltage transformer, leads or bolts are welded to both ends of the ceramic capacitor to facilitate the installation and connection of the circuit.

[0061] The above are only examples of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention pending approval.

Claims

1. A ceramic capacitor dielectric, characterized in that, By percentage, the raw material components of the ceramic capacitor dielectric include: The molar proportion of BaCO3 is 16%, the molar proportion of TiO2 is 68%, and the total molar proportion of Nd2O3 and Bi2O3 is 16%; Among them, the proportion of Nd2O3 in the total molar amount of Nd2O3 and Bi2O3 is a, and the proportion of Bi2O3 in the total molar amount of Nd2O3 and Bi2O3 is b, a + b = 1, 0.5 ≤ a ≤ 0.

65.

2. The ceramic capacitor dielectric according to claim 1, wherein, 0.57≤a≤0.6。 3. A preparation method of a ceramic capacitor dielectric, characterized in that, Including: Grinding and calcination: Weigh the raw materials of the ceramic capacitor dielectric according to the ratio of Claim 1 or Claim 2, and perform grinding treatment, drying treatment, and calcination treatment in sequence to obtain a primary mixture; Secondary grinding: Subject the primary mixture to the grinding treatment and the drying treatment again to obtain a fine mixture; Granulation and compacting: Granulate the fine mixture to obtain raw material particles, and after screening treatment and pressing and forming treatment of the raw material particles, obtain a ceramic blank; Debinding and sintering: Subject the ceramic blank to debinding treatment and sintering treatment in sequence to obtain the ceramic capacitor dielectric.

4. The preparation method of the ceramic capacitor dielectric according to claim 3, characterized in that, In the grinding and calcination step and the secondary grinding step, the grinding treatment uses a planetary ball mill, the rotation speed of the ball mill is 300 r / min - 400 r / min, and the ball milling time is 12 h - 24 h.

5. The preparation method of the ceramic capacitor dielectric according to claim 4, characterized in that, The grinding aid of the ball mill includes anhydrous ethanol or deionized water.

6. The preparation method of the ceramic capacitor dielectric according to claim 4, wherein, In the grinding and calcination step, the calcination temperature of the calcination treatment is 900 °C - 1100 °C, and the calcination time is 6 h - 8 h.

7. The preparation method of the ceramic capacitor dielectric according to claim 3, characterized in that, In the granulation and compacting step, the binder used in the granulation treatment is a polyvinyl alcohol solution with a mass fraction of 4% - 6%.

8. The preparation method of the ceramic capacitor dielectric according to claim 4, characterized in that, In the granulation and compacting step, the screening treatment of the raw material particles uses a sieve mesh with 80 - 120 meshes.

9. The preparation method of the ceramic capacitor dielectric according to claim 4, characterized in that In the granulation and compacting step, the pressure of the pressing and forming treatment is 100 MPa - 200 MPa, and the pressure holding time is 60 s - 180 s.

10. The preparation method of the ceramic capacitor dielectric according to claim 4, characterized in that, In the debinding and sintering step, the heating rate of the debinding treatment is 2 °C / min, the debinding temperature is 550 °C - 650 °C, and the debinding time is 6 h - 12 h.

11. The preparation method of the ceramic capacitor dielectric according to claim 4, characterized in that, In the debinding and sintering step, the heating rate of the sintering treatment is 3 °C / min, the sintering temperature is 1200 °C - 1320 °C, and the sintering time is 2 h - 6 h.

12. The preparation method of the ceramic capacitor dielectric according to claim 3, characterized in that, The preparation method further includes: Burning and infiltrating a silver layer on the surface of the ceramic capacitor dielectric to obtain a ceramic capacitor, and the burning and infiltration temperature is 550 °C - 650 °C.

13. An electronic voltage transformer for phase sequence, characterized in that, Including the ceramic capacitor prepared by the preparation method of the ceramic capacitor dielectric according to Claim 12.

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