JPH0326790B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrode for dielectric breakdown testing used in AC voltage breakdown testing of sheet-like samples. Conventionally, this type of electrode is shown in Fig. 1 a to f.
The ones shown are known. In the figure, numeral 1 is a high-voltage side electrode, 2 is a low-voltage side electrode, and 3 is a sheet-like sample. In the above electrodes, in order to prevent dielectric breakdown at the electrode ends, the ends of electrodes 1 and 2 are rounded with an appropriate radius of curvature, and the geometric structure prevents the electric field from concentrating at the electrode ends. The electrode end effect can be prevented by relaxing the electrodes (see Figure 1 a to e), or by rounding the ends of the electrodes 1 and 2 and wrapping them with water-impregnated cotton cloth 4. (See figure f). However, the ones shown in Figures a to d have the problem that the electrode end effect can hardly be prevented, and the one shown in Figure e has the problem that the charged area of the sheet sample 3 is very small, and the one shown in Figure f In the case shown in FIG. 1, there was a problem in that the cotton cloth 4 existed between the electrodes 1 and 2 and the sheet-like sample 3, making it impossible to obtain a uniform electrode surface. Furthermore, in these electrodes, when the applied voltage becomes high, dielectric breakdown does not occur, and creeping discharge may occur on the surface of the sheet-like sample. It is also known to prevent the electrode end effect by immersing the electrode and sample in a high-resistance liquid or by inserting the electrode into the sample, but in the former case, xylene is used as a high-resistance liquid. In the latter case, there was a problem in that a chemical harmful to the human body, such as acetone, had to be used, and in the latter case, there was a problem in that voids were likely to be formed at the interface between the electrode and the sample after the electrode was inserted. Furthermore, Rogowski type electrodes are also known,
Even with this electrode, there was a problem that the electrode end effect could not be sufficiently prevented. The present invention has been made in view of the above circumstances, and its purpose is to provide an electrode for dielectric breakdown testing that can reliably prevent the electrode end effect without causing the various problems described above. be. That is, in the present invention, the high voltage side electrode is composed of a cylindrical high voltage side main electrode and a plurality of cylindrical voltage dividing electrodes arranged coaxially around the high voltage side main electrode. It is characterized by preventing extreme effects. An embodiment of the present invention will be described below with reference to the drawings. FIGS. 2 and 3 show an example of an electrode for dielectric breakdown testing of the present invention. Reference numeral 5 in the figure is a high voltage side electrode, in which a plurality of cylindrical voltage dividing electrodes 7a to 7g are arranged coaxially around a cylindrical high voltage side main electrode 6, and the high voltage side main electrode 6 and its It is constructed by winding oil-impregnated paper 8, which is an insulator impregnated with insulating oil, between the outer partial pressure electrode 7a and each of the partial pressure electrodes 7a to 7g. Further, reference numeral 9 in the figure is a low voltage side electrode, which is formed into a flat plate shape and is electrically connected to the outermost voltage dividing electrode 7g via a lead wire 10. The above-mentioned high voltage side electrode 5 is brought into close contact with one surface of the sheet-like sample 11, and the low voltage side electrode 9 is brought into close contact with the other surface on the opposite side of the sheet-like sample 11, and the high voltage side electrode 5 and the sheet are brought into close contact with each other. An alternating current voltage is applied between the high voltage side main electrode 6 and the low voltage side electrode 9 while the sample 11 is immersed in the insulating oil 13 in the glass container 12. As a result, as shown in FIG. 4, capacitance division is performed between the high-voltage side main electrode 6, the voltage-dividing electrodes 7a to 7g, and the low-voltage side electrode 9, forcing each voltage-dividing electrode to 7a to 7g each have a potential. In this embodiment, these potentials are set as follows. That is, 95%, 90%, and 80% of the voltage applied between the high-voltage side main electrode 6 and the low-voltage side electrode 9 (the voltage applied to the sheet-like sample 10)
%, 70%, 50%, 30%, and 0% voltage. Each of these potentials is determined by the capacitances C ₁ to C 7 and Ca to Cg between the high voltage side main electrode 6, the voltage dividing electrodes 7a to _7g , and the low voltage side electrode 9. FIG. 5 shows an equivalent circuit of FIG. 4, and a method for determining capacitances C ₁ to C ₇ and Ca to Cg based on this equivalent circuit will be explained. In the same figure, applied voltage V and currents I ₁ to _{I 7} , Ia to
The relationships between Ig and capacitance C ₁ to _{C 7} and Ca to Cg are (1), (2),
It becomes as shown in equation (3). Ia=V・ω・Ca Ib=0.95・V・ω・Cb Ic=0.9・V・ω・Cc Id=0.8・V・ω・Cd Ie=0.7・V・ω・Ce If=0.5・V・ω・Cf Ig＝0.3・V・ω・Cg ……(1) I ₁ =0.05・V・ω・C ₁ I ₂ =0.05・V・ω・C ₂ I ₃ =0.1・V・ω・C ₃ I ₄ =0.1・V・ω・C ₄ I ₅ =0.2・V・ω・C ₅ I ₆ =0.2・V・ω・C ₆ I ₇ =0.3・V・ω・C ₇ ……(2) I= I ₁ + Ia I ₁ = I ₂ + Ib I ₂ = I ₃ + Ic I ₃ = I ₄ + Id I ₄ = I ₅ + Ie I ₅ = I ₆ + If I ₆ = I ₇ + Ig ...(3) However, ω = 2・π・f Solving equations (1), (2), and (3) yields equation (4). 2C ₆ = 3Cg + 3C ₇ 2C ₅ = 5Cf + 3Cg + 3C ₇ C ₄ = 7Ce + 5Cf + 3Cg + 3C ₇ C ₃ = 8Cd + 7Ce + 5Cf + 3Cg + 3C ₇ C ₂ = 18Cc + 16Cd + 14Ce + 10Cf + 6Cg + 6C ₇ C ₁ = 19Cb + 1 8Cc+16Cd+14Ce +10Cf+6Cg+6C ₇
...(4) Calculate C ₁ to _{C 6} from this equation (4). Also, Cb~
Cg is the thickness of the sheet sample 11 and the partial pressure electrode 7a
Calculated from the thickness of ~7b. Also, for C ₇ , first set an appropriate value, and substitute this into equation (4) to calculate C ₁
Next, consider whether it is possible to construct a capacitor with a capacitance of C ₁ with the high voltage side main electrode 6 and the voltage dividing electrode 7a, and if possible, calculate the capacitance of C ₇ at this time. Obtained by selecting the set value. Note that C ₇ needs to have a larger value than the stray capacitance. Further, the diameters φa to φg of each of the partial voltage electrodes 7a to 7g described above are set as follows. That is, it is made to have a potential gradient that does not cause creeping discharge between the high-voltage side main electrode 6 and the partial voltage electrode 7a on the surface of the sheet-like sample 10 and between each of the partial voltage electrodes 7a to 7g. For example, the dielectric breakdown strength is 40KV/mm
When using the insulating oil 13 of approximately
Set diameters φa to φg of 7g. This is the minimum necessary value, and it may be set larger. Next, the operation of the above embodiment will be explained. When an AC voltage is applied from the AC high voltage generator 14 between the high voltage side electrode 5 and the low voltage side electrode 9 in the state shown in FIG. As a result, as shown by the dotted line in FIG. 6, the high voltage side main electrode 6
The potential distribution near the end of the main electrode 6 becomes rough, preventing the electric field from concentrating near the end of the high voltage side main electrode 6.
Dielectric breakdown occurs within the range where the two contact each other. Also, at this time, the partial pressure electrodes 7a to 7g
Between the high voltage side main electrode 6 and the partial pressure electrode 7a on the surface of the sheet-like sample 11 and each partial pressure electrode 7a to 7g
A predetermined potential gradient is generated between the two and the creeping discharge is prevented. When the partial pressure electrodes 7a to 7g are not arranged,
As shown in Figure 7, even if the end of the high voltage side electrode 1 is rounded, an electrode edge effect occurs near the end, and the potential distribution becomes dense and the electric field is concentrated as shown by the dotted line in the figure. As a result, dielectric breakdown occurs near the ends. Additionally, when the AC voltage is increased, creeping discharge occurs. In the above embodiment, since the oil-impregnated paper 8 is used to increase the dielectric constant, the high voltage side electrode 5 can be downsized. Moreover, creeping discharge is reliably prevented by the oil-impregnated paper 8 coming into close contact with the sheet-like sample 11. FIG. 8 shows a second embodiment of the invention. In the same embodiment, the oil-impregnated paper 8 is omitted and each partial pressure electrode 7 is
This shows the case where the diameters φa to φg of a to 7g are set large. The other configurations are the same as the first embodiment described above. In this case, the diameter φa of each partial pressure electrode 7a to 7g
Since ~φg is set to a large value, even if the oil-impregnated paper 8 is omitted, capacitance partial pressure is generated and the electrode end effect can be sufficiently prevented, and creeping discharge can also be prevented. Next, specific examples of the present invention will be explained. An AC dielectric breakdown test was conducted using the electrodes of the first and second examples. 0.05 for partial voltage electrodes 7a to 7g
mm aluminum foil was used. The dimensions of the partial pressure electrodes 7a to 7g and the high voltage side main electrode 6 were as shown in Table 1 (first example) and Table 2 (second example) below.

【table】

[Table] The AC dielectric breakdown test was conducted using 10 polyethylene sheets with a thickness of 0.5 mm. The test results were as shown in Table 3 below. For comparison, the electrode shown in Figure 1a (JIS standard C2110-1975)
A similar test was carried out by immersing it in insulating oil, and the results are also listed.

[Table] As explained above, according to the present invention, the high voltage side electrode is composed of a cylindrical high voltage side main electrode and a plurality of voltage dividing electrodes coaxially arranged around the high voltage side main electrode. The partial voltage electrode prevents the electric field from concentrating near the end of the high voltage side main electrode, so the electrode end effect can be prevented and the high voltage side main electrode of the sheet-like sample can be Dielectric breakdown occurs within the area in which the two contacts come into contact, and therefore an accurate dielectric breakdown voltage can be measured. Furthermore, since the electric field distribution is forcibly determined, unlike the case where the electric field distribution is determined by a geometric structure, it is not affected by the external atmosphere, and reliability can be improved and creeping discharge can be prevented. Furthermore, there is no need to use chemicals harmful to the human body, such as xylene, and there is a degree of design freedom in that the electrode area can be set arbitrarily. Furthermore, if an insulator impregnated with insulating oil is interposed between the high voltage side main electrode and the partial voltage electrode and between each partial voltage electrode, the dielectric constant can be increased by the insulator and the electrode can be made smaller. can be achieved.

[Brief explanation of drawings]

Figures 1 a to f are side views showing conventional electrodes;
The figure is a cross-sectional view showing the first embodiment of the present invention, FIG. 3 is a plan view of the high voltage side electrode 5, and FIG. 4 is an operation explanatory diagram.
FIG. 5 is an equivalent circuit diagram of FIG. 4, FIG. 6 is an explanatory diagram explaining the action and effect, FIG. 7 is an explanatory diagram explaining the action of the conventional electrode, and FIG. 8 is a cross section showing the second embodiment. It is a diagram. 5...High voltage side electrode, 6...High voltage side main electrode,
7a to 7g... Electrode for partial pressure, 8... Insulator (oil immersed paper), 9... Low voltage side electrode, 11... Sheet-like sample, 14... AC high pressure generator.

Claims (1)

[Claims] 1. An insulation device comprising a high-voltage side electrode and a low-voltage side electrode, and performing an AC dielectric breakdown test with a sheet-like sample interposed between the high-voltage side electrode and the low-voltage side electrode. In the electrode for destructive testing, the high voltage side electrode includes a cylindrical high voltage side main electrode and a plurality of cylindrical shapes arranged coaxially and mutually insulated around the high voltage side main electrode. The outermost voltage dividing electrode and the low voltage side electrode are short-circuited, and the voltage dividing electrode prevents the electric field from concentrating near the end of the high voltage side main electrode. An electrode for dielectric breakdown testing characterized by: 2. Dielectric breakdown according to claim 1, characterized in that an insulator impregnated with insulating oil is interposed between the high voltage side main electrode and the voltage dividing electrode and between each voltage dividing electrode. Test electrode.