CN102136311A - Mixed gas insulating medium - Google Patents

Abstract

A mixed gas insulating medium, the volume percentage of its components is: 15%-20% of octafluorocyclobutane, 80%-85% of nitrogen. The mixed gas insulating medium can replace sulfur hexafluoride as a new generation of gas insulating medium, and is widely used in high-voltage power equipment such as gas-insulated transformers, gas-insulated combined electrical appliances, and gas-insulated transmission pipelines.

Description

A mixed gas insulating medium

technical field

The invention relates to a mixed gas insulating medium which can replace sulfur hexafluoride for high-voltage power equipment.

Background technique

SF ₆ gas has good insulation ability, arc extinguishing ability, chemical stability and non-toxicity, so it is widely used in gas-insulated equipment, such as gas-insulated transformers, gas-insulated circuit breakers, gas-insulated transmission pipelines, etc. However, pure SF ₆ gas is very sensitive to electric field inhomogeneity and has high requirements for equipment processing; and the discharge decomposition products of SF ₆ gas, such as SO ₂ F ₂ , SOF ₂ , SF ₄ , SF ₂ , H ₂ S, SOF ₄ etc., are all highly toxic substances, which pose a great threat to personnel health; in addition, the greenhouse effect of SF ₆ gas is very large, and its global warming potential (GWP) is about 23900 times that of CO ₂ gas, and its life in the atmosphere About 3200 years, therefore, in the "Kyoto Protocol" signed by the parties to the United Nations Convention on Climate Change in 1997, SF ₆ gas was listed as one of the six restricted greenhouse gases. Therefore, researchers have conducted a lot of research, hoping to find a new medium that can replace SF ₆ gas for electrical equipment.

At present, it is very difficult to replace SF ₆ gas with a single gas. Therefore, people try to use mixed gas instead of pure SF ₆ gas. At present, there have been reports of using SF ₆ /N _{2 mixed gas} or SF ₆ /CO ₂ mixed gas to replace pure SF ₆ gas. Gas gas insulated transmission pipelines replace the original overhead lines. The use of mixed gas containing _SF6 has the following advantages: reducing the sensitivity to electrode surface defects, lowering the gas liquefaction temperature, and reducing costs, so it has good application prospects, especially _{SF6 /} N ₂ mixed gas.

However, the use of mixed gas containing SF ₆ cannot fundamentally solve the threat to the human body caused by the greenhouse effect of SF ₆ gas and the highly toxic substances contained in its decomposition products. Therefore, it is necessary to find a mixed gas that does not contain SF ₆ for high-voltage power equipment.

"A gas-insulated transformer" is disclosed in 02103455.9. This patent uses an inert gas with a global warming coefficient equal to or less than 1 as the insulating medium. Although the environmental protection effect is greatly improved, the insulating performance of the inert gas is much lower than that of SF ₆ The volume of equipment increases, and the production cost increases.

In 200610084702.8, an "environmentally friendly gas-insulated combined electrical appliance" is disclosed. This patent uses dry low-pressure air as the insulating medium, which reduces the harm to the environment. However, due to the poor insulating ability of air, this patent is mainly suitable for applications below 12kV. of electrical equipment.

In 200710001562.8, a "gas-insulated electrical equipment" is disclosed. This patent uses CF ₃ I with a volume ratio of more than 40% mixed with other non-SF ₆ gases to form an insulating medium, reducing the impact on the environment, but CF ₃ I is relatively stable. Poor, easy to decompose, so it is necessary to increase adsorbent and increase the number of maintenance, which increases the operating cost.

Contents of the invention

The object of the present invention is to provide a mixed gas insulating medium with good environmental protection effect and good insulation performance, which can replace SF ₆ gas for high-voltage power equipment.

The composition of the mixed gas insulating medium provided by the invention is 15%-20% (volume percentage) of octafluorocyclobutane and 80%-85% (volume percentage) of nitrogen.

In the mixed gas insulating medium provided by the present invention, the component octafluorocyclobutane has a chemical molecular formula of C ₄ F ₈ , a molecular weight of 200.0, a boiling point of -8°C, non-toxic, no ozone hazard, and a warming potential value of 8900, about It is 37% of SF ₆ gas, and the partial discharge inception voltage is about 1.2 to 1.4 times that of SF ₆ at the same pressure. The decomposition products of this component under superheated _conditions at 600°C mainly include C ₂ F ₄ , C ₃ F ₆ , 1,3-C 4 F ₆ , cC ₄ F ₆ , 2-C ₄ F ₈ The main decomposition products are C ₂ F ₄ , C ₃ F ₆ , 1,3-C ₄ F ₆ , cC ₄ F ₆ , 2-C ₄ F ₈ , C ₂ F ₆ , C ₃ F ₈ , and these decomposition products belong to Non-toxic or low-toxic substances.

In the mixed gas insulating medium provided by the present invention, the component nitrogen is a buffer gas, and its main function is to lower the boiling point of the mixed gas. The boiling point of the mixed gas of the invention is below -20°C, which can meet the use requirements in winter in most areas.

The mixed gas insulating medium provided by the present invention satisfies the requirements of environmental protection and personal safety well, and has the following advantages compared with the gas insulating medium SF ₆ mainly used in current high-voltage power equipment:

1. Good environmental performance. The overall warming potential value of the mixed gas provided by the invention is lower than 2000, less than 10% of the warming potential value of SF ₆ gas, which can well improve the greenhouse effect caused by SF ₆ gas on the environment.

2. Low personal hazard. The main decomposition products of the mixed gas provided by this invention are non-toxic or low-toxic substances when the power equipment is in operation, unlike most of the decomposition products of SF ₆ gas, which are highly toxic substances, which will cause serious damage to personal safety if handled improperly. threaten.

Description of drawings

Figure 1 is the variation curve of partial discharge initial voltage of pure C ₄ F ₈ gas and SF ₆ gas with pressure;

Fig. 2 is the relationship curve between the liquefaction temperature T _mb of C ₄ F ₈ /N ₂ mixed gas and the mixing ratio k;

Figure 3 is the variation curve of partial discharge initial voltage of C ₄ F ₈ /N ₂ mixed gas with air pressure when the electrode distance is 20mm;

Fig. 4 is the variation curve of partial discharge inception voltage of C ₄ F ₈ /N ₂ mixed gas with pressure when the electrode distance is 30mm.

Detailed ways

The reasons for limiting the contents of the main components constituting the mixed gas of the present invention will be explained below.

First, the component octafluorocyclobutane, the chemical formula is C ₄ F ₈ , the molecular weight is 200.0, the boiling point is -8°C, it is non-toxic, no ozone hazard, and the warming potential value is 8900, which is about 37% of SF ₆ gas, which is the same The partial discharge inception voltage under atmospheric pressure is about 1.2 to 1.4 times that of SF ₆ , as shown in the experimental results in Figure 1. The decomposition products of C ₄ F ₈ under superheated conditions at 600°C mainly include C ₂ F ₄ , C ₃ F ₆ , 1,3-C ₄ F ₆ , cC ₄ F ₆ , and 2-C ₄ F ₈ . The main decomposition products are C ₂ F ₄ , C ₃ F ₆ , 1,3-C ₄ F ₆ , cC ₄ F ₆ , 2-C ₄ F ₈ , C ₂ F ₆ , C ₃ F ₈ , and these decomposition products are It is a non-toxic or low-toxic substance. Therefore, C ₄ F ₈ is an ideal environmental protection and low-hazard insulating medium. The disadvantage is that it has a high liquefaction temperature and is not suitable for cold regions and winter.

Secondly, in order to improve the liquefaction temperature of C ₄ F ₈ gas, N ₂ is added in it as a buffer gas. Power equipment is generally required to operate normally at -20°C. At the same time, the gas insulation medium in power equipment generally exists in a state of 0.4-0.5MPa, so it is required that the liquefaction temperature of the mixed gas is lower than -20 in the state of 0.4-0.5MPa. ℃. Figure 2 shows the variation curve of the liquefaction temperature of the mixed gas with the content of C ₄ F ₈ gas under the condition of 0.4MPa and 0.5MPa of the mixed gas of C ₄ F ₈ /N ₂ . It can be seen from Figure 2 that at 0.4MPa, when the content of C ₄ F ₈ gas in the mixed gas exceeds 20%, the liquefaction temperature of the mixed gas will be higher than -20°C; at 0.5MPa, when the C When the content of ₄ F ₈ gas exceeds 15%, the liquefaction temperature of the mixed gas will be higher than -20°C. Therefore, from the perspective of the liquefaction temperature of the mixed gas, the content of C ₄ F ₈ in the mixed gas should not exceed 20%.

Third, as an insulating medium, the insulating properties of the mixed gas also need to meet certain requirements, otherwise it will cause large-scale power equipment, high material consumption, and high production costs. Figure 4 and Figure 5 show the partial discharge initiation of C ₄ F ₈ /N ₂ mixed gas when the C ₄ F ₈ gas content is below 20%, the electrode distance is 20mm and 30mm, and the gas pressure is 0.1-0.4MPa. The result of the starting voltage test. It can be seen from the results in the figure that when the gas pressure is 0.4MPa, the partial discharge inception voltage of the mixed gas with a C ₄ F ₈ content of 15% to 20% is 22kV at an electrode distance of 20mm, and 26kV at an electrode distance of 30mm, about It is 70% of the initial voltage of partial discharge of SF ₆ gas under the same conditions, which is consistent with the partial discharge performance of SF ₆ /N ₂ mixed gas with SF ₆ content of 20%. Therefore, using a mixed gas with a C ₄ F ₈ gas content of 15% to 20% as the insulation medium of power equipment can meet the insulation requirements only by slightly increasing the insulation distance of the power equipment, and will not increase the production cost. increase. If the content of C ₄ F ₈ in the mixed gas is lower than 15%, the insulation performance of the mixed gas will be reduced more, so that the electrical equipment needs a larger insulation distance, thus consuming more materials. Therefore, the content of C ₄ F ₈ in the mixed gas is required to be 15% to 20%.

The present invention will be further described below in conjunction with accompanying drawings, examples and comparative examples, but the present invention is not limited to these examples.

Embodiment 1: the mixed gas that C ₄ F ₈ content is 20% (volume percentage) and _N content is 80% (volume percentage);

Embodiment 2: _C4F8 content is 19% (volume percentage) and N _The mixed gas that _content is 81% (volume percentage);

Embodiment 3: C ₄ F ₈ content is that 18% (volume percentage) and N ₂ content is the mixed gas of 82% (volume percentage);

Embodiment 4: C ₄ F ₈ content is the mixed gas that 17% (volume percentage) and _N content are 83% (volume percentage);

Embodiment 5: C ₄ F ₈ content is 16% (volume percentage) and N ₂ content is the mixed gas that 84% (volume percentage) forms;

Embodiment 6: C ₄ F ₈ content is 15% (volume percentage) and N ₂ content is the mixed gas that 85% (volume percentage) forms;

Comparative example: the mixed gas that SF _content is 20% (volume percentage) and N _content is 80% (volume percentage);

The composition and relevant properties of embodiment 1, 2 and comparative examples are shown in the following table:

It can be seen from the comparison results that under the same conditions, the partial discharge inception voltage of the embodiment is not lower than that of the comparison example, that is, the insulation performance is better than that of the comparison example, and the warming coefficient is 37.5%, 35.2%, 33.3%, 31.4% of the comparison example. %, 29.5% and 27.8%, that is, the greenhouse effect is weaker than that of the comparison.

Claims (1)

1. A mixed gas insulating medium, characterized in that: the volume percentage of the mixed gas insulating medium components is: 15% to 20% of octafluorocyclobutane, and 80% to 85% of nitrogen.

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