Insulation material for a DC electrical component

Abstract

An insulation material for a DC electrical component. The insulation material includes a thermoset or thermoplastic matrix and a functional filler component. The functional filler component has a non-linear DC conductivity depending on an applied electrical field strength. At least in a temperature range of 0° C. to 120° C., the functional filler component has a bandgap in the range of 2 to 5 eV, and optionally in the range of 2 to 4 eV. Furthermore, a method for producing an insulation material, a use of an insulation material for a high voltage DC electrical component, a DC electrical component comprising the insulation material and the use of a DC electrical component comprising the insulation material in a high voltage DC gas insulated device are suggested.

Claims

1. An insulation material for a direct current (DC) electrical component, the insulation material comprising: a thermoset or thermoplastic matrix; a functional filler component combined with the thermoset or thermoplastic matrix and comprising any one of the group consisting of silica with antimony-doped tin oxide, titanium oxide with antimony doped tin oxide, and n-type tin oxide; and a bulk filler component, wherein the functional filler component has a non-linear DC conductivity depending on an applied electrical field strength, wherein at least in a temperature range of 0° C. to 120° C., the functional filler component has a bandgap in the range of 2 to 5 eV, wherein a DC conductivity of the insulation material measured after the application of a constant and homogeneous electric field of a field strength under normal DC operation for a time duration equal or longer than 10.sup.5 seconds, is within the range of 10.sup.−18 siemens per meter (S/m) to 10.sup.−10 S/m for 303 to 378 K, or a DC conductivity is dependent on the electric field strength applied to the insulation material at a temperature of the insulation material of any one temperature within the range between 303 and 378 K, for the electric field strength being in a range between a minimum electric field strength of 1 kV/mm and a maximum electric field strength of 10 kV/mm, such that the DC conductivity at the maximum electric field strength is less than 10.sup.5 times the DC conductivity at the minimum electric field strength.

2. The insulation material according to claim 1, wherein the total amount of the functional filler component within the insulation material is within the range of 30 to 80 wt.-%.

3. The insulation material according to claim 1, wherein the amount of the bulk filler component in the insulation material is within the range of up to 50 wt.-%.

4. The insulation material according to claim 3 wherein the bulk filler component is alumina.

5. The insulation material according to claim 1, wherein an average particle size of the functional filler component is within the range of 0.1 to 30 μm.

6. The insulation material according to claim 1, wherein a DC conductivity is dependent on the temperature of the insulation material at any one field strength within the range between 0 kV/mm and 10 kV/mm, such that the DC conductivity at the maximum temperature is less than 10.sup.4 times the DC conductivity at the minimum temperature.

7. A DC electrical component for high voltage DC power transmission or distribution, the DC electrical component comprising a conductor surrounded at least partially by an insulation layer of an insulation material according to claim 1.

8. The insulation material according claim 1, wherein the total amount of the functional filler component within the insulation material is within the range of 55 to 75 wt.-%.

9. The insulation material according to claim 1, wherein a DC conductivity is dependent on the temperature of the insulation material at any one field strength within the range between 0 kV/mm and 10 kV/mm, such that the DC conductivity at the maximum temperature is less than 10.sup.4 times the DC conductivity at the minimum temperature.

10. A method for producing an insulation material comprising the steps of: combining a functional filler component having a non-linear resistive behavior depending on an applied electrical field strength and/or a non-linear capacitive behavior depending on an applied electrical field strength and having, at least in a temperature range of 0° C. to 120° C., a bandgap in the range of 2 to 5 eV, optionally in the range of 2 to 4 eV; and comprising any one of the group consisting of silica with antimony-doped tin oxide, titanium oxide with antimony doped tin oxide, and n-type tin oxide, a bulk filler component, and a thermoset or thermoplastic matrix compounding the ingredients according to the type of matrix, and processing the compounded ingredients according to the type of matrix, wherein a DC conductivity of the insulation material measured after the application of a constant and homogeneous electric field of a field strength under normal DC operation for a time duration equal or longer than 10.sup.5 seconds, is within the range of 10.sup.−18 siemens per meter (S/m) to 10.sup.−10 S/m for 303 to 378 K, or a DC conductivity is dependent on the electric field strength applied to the insulation material at a temperature of the insulation material of any one temperature within the range between 303 and 378 K, for the electric field strength being in a range between a minimum electric field strength of 1 kV/mm and a maximum electric field strength of 10 kV/mm, such that the DC conductivity at the maximum electric field strength is less than 10.sup.5 times the DC conductivity at the minimum electric field strength.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a is a diagram showing conductivities of exemplary insulation materials according to embodiments of the present disclosure, in dependence of the electric field, at 30° C.;

(2) FIG. 1b is a diagram showing conductivities of exemplary insulation materials according to embodiments of the present disclosure, in dependence of the electric field, at 70° C.;

(3) FIG. 1c is a diagram showing conductivities of exemplary insulation materials according to embodiments of the present disclosure, in dependence of the electric field, at 105° C.;

(4) FIG. 2a is a diagram showing simulation results of the normalized electric field strength at the gas-solid interface under capacitive conditions, under ohmic conditions using a conventional insulation material, and under ohmic conditions using an exemplary insulation material according to an embodiment of the disclosure, in dependence of the radius of a modeled insulator;

(5) FIG. 2b is a diagram showing simulation results of the normalized maximum electric field strength at the gas-solid interface under ohmic conditions using a conventional insulation material, and under ohmic conditions using an exemplary insulation material according to an embodiment of the disclosure, in dependence of time, on the surface of a modeled insulator;

(6) FIG. 3 is a schematic sectional view of the modeled insulator used in the simulations shown in FIGS. 2a and 2b;

(7) FIG. 4a is a diagram showing a schematic view of the microstructure inside field grading materials based on SiC, for explanatory purposes.

(8) FIG. 4b is a diagram showing a schematic view of the microstructure inside field grading materials based on ZnO microvaristors, for explanatory purposes.

(9) FIG. 4c is a diagram showing a schematic view of the microstructure inside field grading materials based on Cr.sub.2O.sub.3, Fe.sub.2O.sub.3, TiO.sub.2, ZnS, and SnO2, for explanatory purposes.

EXAMPLES

(10) In the following, embodiments of the present disclosure are described by way of specific examples with reference to the drawings. The examples discussed below are not to be understood as limiting the scope of the disclosure to these specific embodiments. Rather, the examples are given for illustrating purposes, and the skilled person will understand that the disclosure can be implemented in a number of different ways and not only in the way as presented in the embodiments. For example, features illustrated or described as parts of one embodiment can be used in conjunction with any other embodiment or aspect, and the present disclosure includes any such variations and/or combinations.

(11) Insulation materials were prepared and casted into thin sample plates having a thickness of 2 mm. For the purpose of comparison, a reference sample was casted, containing, as a filler, only Al.sub.2O.sub.3 particles of an average particle size of 3.0 μm (D.sub.50, measured by laser diffraction, the same applies hereinafter). Various samples of insulation materials according to embodiments of the present disclosure were casted as well.

(12) The average particle size of the fillers components used in the experiment can be derived from the following table 2:

(13) TABLE-US-00002 TABLE 2 Average Particle size Filler component (D.sub.50) [μm] SPAN Al.sub.2O.sub.3 3.0 2.8 conductive Titnium oxide 1.6 3.7 (TiO.sub.2[SnO.sub.2, Sb.sub.2O.sub.3]) Titanium oxide core with 1.0 n/a antimony-doped tin oxide ZnS 0.3 2.2 TiO.sub.2 0.4 2.5 Cr.sub.2O.sub.3 0.6 2.8 Fe.sub.2O.sub.3 0.6 2.1 SnO.sub.2 0.5 2.7

(14) In a series of DC conductivity tests, the samples were applied a voltage resulting in a homogenous DC electric field having a field strength of 1, 3 and 5 kV/mm for the various temperature of 30° C. (303 K), 70° C. (343 K) 105° C. (378 K) for approximately 10.sup.5 seconds, approximately 28 hours. After that time, the voltage still applied to the sample, the current through the samples was measured by means of a picoammeter. This current was used to calculate the conductivity. The DC conductivities of the total DC conductivity tests thus calculated are given in the following table 3, wherein the functional filler component is given after the + (plus) symbol, and the second filler component is given before the + (plus) symbol:

(15) TABLE-US-00003 TABLE 3 DC E conductivity Filler formulation [kV/mm] T [° C.] [S/m] 60 wt.-% Al.sub.2O.sub.3 (comparative 1 30 1.0 × 10.sup.−18 example) 3 30 1.0 × 10.sup.−18 5 30 1.0 × 10.sup.−18 1 70 3.1 × 10.sup.−16 3 70 3.1 × 10.sup.−16 5 70 3.1 × 10.sup.−16 1 105 1.1 × 10.sup.−14 3 105 1.1 × 10.sup.−14 5 105 1.1 × 10.sup.−14 40 wt.-% Al.sub.2O.sub.3 + 20 wt.-% 1 30 3.1 × 10.sup.−17 conductive Titanium oxide (TiO.sub.2[SnO.sub.2, Sb.sub.2O.sub.3]) 3 30 1.6 × 10.sup.−16 5 30 1.4 × 10.sup.−15 1 70 1.5 × 10.sup.−16 3 70 4.0 × 10.sup.−16 5 70 5.5 × 10.sup.−15 1 105 5.35 × 10.sup.−16  3 105 5.1 × 10.sup.−15 5 105 5.9 × 10.sup.−14 20 wt.-% Al.sub.2O.sub.3 + 40 wt.-% Fe.sub.2O.sub.3 1 30 6.9 × 10.sup.−17 3 30 4.9 × 10.sup.−16 5 30 7.4 × 10.sup.−15 1 70 2.3 × 10.sup.−16 3 70 1.6 × 10.sup.−15 5 70 4.1 × 10.sup.−14 1 105 1.4 × 10.sup.−15 3 105 2.0 × 10.sup.−14 5 105 5.9 × 10.sup.−13 10 wt.-% Al.sub.2O.sub.3 + 55 wt.-% Cr.sub.2O.sub.3 1 30 6.2 × 10.sup.−17 3 30 3.7 × 10.sup.−16 5 30 5.1 × 10.sup.−15 1 70 2.0 × 10.sup.−16 3 70 1.4 × 10.sup.−14 5 70 1.5 × 10.sup.−13 1 105 3.5 × 10.sup.−15 3 105 2.4 × 10.sup.−13 5 105 1.6 × 10.sup.−12 30 wt.-% Al.sub.2O.sub.3 + 30 wt.-% SnO.sub.2 1 30 1.8 × 10.sup.−18 3 30 5.65 × 10.sup.−18  5 30 145 × 10.sup.−17  1 70 2.1 × 10.sup.−17 3 70 7.0 × 10.sup.−17 5 70 2.9 × 10.sup.−16 1 105 8.5 × 10.sup.−16 3 105 3.7 × 10.sup.−15 5 105 1.0 × 10.sup.−14

(16) FIGS. 1a, 1b, 1c are diagrams showing conductivities of exemplary insulation materials according to embodiments of the present disclosure, in dependence of the electric field for the various temperatures above. The conductivities of the DC conductivity tests for some materials are plotted in the graph of FIG. 1, i.e. for 1, 3, 5 kV/mm at 30, 70, 105° C.

(17) Here, 101 denotes a field-dependence line between the measurement values of a filler containing only 60 wt.-% of Al.sub.2O.sub.3. 111 denotes a field-dependence line between the measurement values of a filler containing 40 wt.-% Al.sub.2O.sub.3+20 wt.-% TiO.sub.2[SnO.sub.2, Sb.sub.2O.sub.3]. 112 denotes a field-dependence line between the measurement values of a filler containing 20 wt.-% Al.sub.2O.sub.3+40 wt.-% Fe.sub.2O.sub.3. 113 denotes a field-dependence line between the measurement values of a filler containing 10 wt.-% Al.sub.2O.sub.3+55 wt.-% Cr.sub.2O.sub.3. 114 denotes a fictive line between the measurement values of a filler containing 30 wt.-% Al.sub.2O.sub.3+30 wt.-% SnO.sub.2.

(18) As clearly derivable from the table 3 and the graph of FIG. 1, an insulation material containing a relatively high amount of filler comprising a functional filler component as suggested herein, exhibits advantageous properties. For the exemplary operating conditions shown, all lines 111 to 114 show the field-dependence and weak non-linear behavior, i.e. the conductivities of the insulation material suggested herein are superior to those of a conventional insulation material. Yet, a thermal runaway is avoided.

(19) In a DC breakdown strength test, the DC breakdown properties of a third selection of samples was measured in a standard test procedure.

(20) It was found that the DC breakdown strength decreased in all of the samples comprising one of the insulation materials suggested herein. As compared to the pure aluminum oxide filler, the breakdown strength results are still above the requirement for application in typical DC applications such as DC gas insulated systems.

(21) While these conductivities are still low enough in order to avoid any thermal runaway, the distribution of the electrical field on the insulator surface improves significantly. This makes charge accumulation on the surface more difficult, leading to better electrical properties in the DC regime. Also, the resistive field maximum will be reduced, e.g. after a switch-on operation of the DC voltage. Hence, the transition time needed in order to return to a stable equilibrium (a resistive DC field distribution) is lessened. This, in turn, alleviates a charge accumulation in the DC regime even more.

(22) In the diagram shown in FIG. 2a, the DC electric field strength on the surface of insulators having a standard shape is shown, dependent on the distance r from the center of the respective insulator. The diagram of FIG. 2b shows the maximum DC electric field strength on the same insulator dependent on time. The graphs shown in FIGS. 2a and 2b are simulation results of the electric field strength on a modeled standard-shaped insulator. The electric field strengths were normalized to the maximum electric field strength in the case of a pure capacitive field as discussed below.

(23) For convenience, a schematic sectional view of the insulator used in the simulations of FIGS. 2a and 2b is shown in FIG. 3. Here, reference numeral 400 denotes the insulator bulk of the respective material, r.sub.tot denotes the total radius, and r denotes the radial distance on the insulator surface, wherein a single r is shown as an example. A grounded enclosure is denoted by reference numeral 401.

(24) As seen in FIG. 2b, it could also be shown in the simulations that the transition time from a capacitive field after a switch-on transient to a resistive field, i.e. the transition time to a steady-state operation, is reduced significantly when a novel insulation material is used for a DC electrical component such as an insulator, compared to using a conventional insulation material.

(25) In the diagram of FIG. 2a, simulation results of the normalized DC electric field strength on the insulator surface dependent on the insulator radius are shown. For convenience of comparison, the simulation results when using a conventional insulator material are shown in the same graph as the simulation results when using some of the insulation materials suggested herein.

(26) For a conventional material, the normalized capacitive electric field strength (i.e. after a switch-on transient of the DC electric field) on the insulator surface of an insulation material containing only 60 wt.-% Al.sub.2O.sub.3 as a filler is shown as a solid-line reference curve 200. A dashed-line reference curve 201 is shown as the normalized resistive electric field strength of an insulation material containing only 60 wt.-% Al.sub.2O.sub.3 as a filler.

(27) The further curves show the normalized resistive electric field strengths on the insulator surface of insulation materials containing, as a filler, a mixture of 30 wt.-% Al.sub.2O.sub.3 as a bulk filler component and 30 wt.-% of a functional filler component, the functional filler component being Cr.sub.2O.sub.3 for the dashed-line curve 211; Fe.sub.2O.sub.3 for the solid-line curve 212; SnO.sub.2 for the dashed-line curve 213; and TiO.sub.2 for the dotted-line curve 214.

(28) The advantageous conductivity of the novel insulation material keeps the charge accumulation low, such that the maximum electric field strength on the insulator surface is only slightly higher than that of the pure capacitive field.

(29) In the diagram of FIG. 2b, simulation results of the normalized maximum DC electric field strength on the insulator surface dependent on time are shown. Time, on the abscissa, is logarithmically scaled; from time 0 on, a homogeneous DC electric field was applied, as discussed above. For convenience of comparison, the simulation result when using a conventional insulator material is shown in the same graph as the simulation results when using some of the insulation materials suggested herein.

(30) In FIG. 2b, the time-dependent charge accumulation on an insulator comprising a reference insulation material containing only 60 wt.-% Al.sub.2O.sub.3 as a filler is shown as a solid-line reference curve 301.

(31) Curves 311 through 313 show the normalized maximum DC electric field strength on the insulator surface of insulation materials containing, as a filler, a mixture of 30 wt.-% Al.sub.2O.sub.3 as a bulk filler component and 30 wt.-% of a functional filler component, the functional filler component being Cr.sub.2O.sub.3 for the dashed-line curve 311; Fe.sub.2O.sub.3 for the solid-line curve 312; and SnO.sub.2 for the dotted-line curve 313.

(32) For convenience, dash-dotted vertical lines indicate, from the left to the right, times corresponding to one day, one week, and three months after the beginning of an application of the DC electric field.

(33) As can be seen from the diagram in FIG. 2b, already after one day, the electric field strength increases considerably for the reference material (filler comprising 60 wt.-% Al.sub.2O.sub.3), whereas for the suggested insulation materials comprising Cr.sub.2O.sub.3 or Fe.sub.2O.sub.3 as a functional filler component, increases only slightly and remains on a lower level thereafter in a stable state.