阅读说明：本技术 用于中压和高压电气开关设备的低环境影响的电气绝缘系统 (Low environmental impact electrical insulation system for medium and high voltage electrical switchgear ) 是由 杰稣·伊斯卡拉·祖罗 哈维尔·拉里塔·苏比亚 于 2020-02-26 设计创作，主要内容包括：本发明涉及一种电气绝缘系统,包括两个基本要素：a)由i)一种或多种具有至少4个碳原子的不易燃的氢氟烯烃和ii)一种、两种或三种选自N-(2)、O-(2)、干燥空气、氦气、CO-(2)或其混合物的载气形成的气态介质；和b)一种或多种干燥剂。(The invention relates to an electrical insulation system comprising two basic elements: a) from i) one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms and ii) one, two or three members selected from N 2 、O 2 Dry air, helium, CO 2 Or mixtures thereof; and b) one or more desiccants.)

1. A low environmental impact electrical insulation system for medium or high voltage electrical switchgear comprising:

a) a gaseous medium formed from a mixture of:

i. one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms; and

one or more selected from N₂、O₂Dry air, helium, CO₂Or a mixture thereof;

b) one or more desiccants.

2. The electrical insulation system according to claim 1, wherein the gaseous medium further comprises at least one hydrofluoroolefin having 3 carbon atoms.

3. The system of claim 1 or 2 wherein the hydrofluoroolefin having at least 4 carbon atoms is HFO-1336mzzZ, HFO-1336mzzE, or a combination of both.

4. The system of claim 2 wherein the hydrofluoroolefin having 3 carbon atoms is HFO-1234 zeE.

5. The system of claims 2-4 wherein the percentage of hydrofluoroolefin having 3 carbon atoms in the mixture is outside the flammability limit of the hydrofluoroolefin having 3 carbon atoms.

6. The system according to any of the preceding claims, wherein the carrier gas is selected from dry air, N₂And O₂。

7. The system of claims 1 to 6, wherein the desiccant can be calcium oxide, calcium sulfide, calcium sulfate, calcium carbonate, calcium hydride, montmorillonite clay, silica gel, activated alumina and pore size from 3 to 3 pore sizeAnd molecular sieves having polar surfaces and combinations thereof.

8. The system of claims 1-7, wherein the desiccant is calcium oxide.

9. The system of claims 1-7, wherein the desiccant is of pore size 3 to 3 And a molecular sieve having a polar surface.

10. The system of claims 1-7, wherein the desiccant is calcium oxide and has a pore size of 3 to 3 aAnd a molecular sieve having a polar surface.

11. The system of any one of claims 9 or 10, wherein the molecular sieve has a pore size of from 3 to 3

12. The system of claim 1 wherein the mole fraction of hydrofluoroolefin having at least 4 carbon atoms is at least 1% or at least 2% or at least 5% or at least 10% or at least 15%.

13. Use of an electrical insulation system according to any of the preceding claims for electrical insulation and/or arc extinguishing in a medium or high voltage electrical switchgear.

14. Method for electrical insulation and/or arc extinguishing in a medium or high voltage electrical switchgear, comprising introducing an electrical insulation system according to any of claims 1 to 12 into a closed and sealed container in which the element to be insulated of the medium or high voltage electrical switchgear is located.

15. Medium or high voltage electrical switchgear comprising a closed vessel inside which there are energized electrical components and an electrical insulation system according to any one of claims 1 to 12.

16. An electrical switching apparatus according to claim 15 wherein the switching apparatus may be a switching apparatus for distributing electrical energy in a network of up to 72 kV.

Technical Field

The present invention belongs to the field of electrical insulation systems for medium and high voltage electrical switchgear. More particularly, the invention relates to an electrical insulation system comprising two basic elements:

a) from i) one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms and ii) oneOne or more selected from N₂、O₂Dry air, helium, CO₂Or mixtures thereof; and

b) one or more desiccants.

Similarly, the invention relates to the use of said electrical insulation system and to a medium or high voltage electrical switchgear comprising an enclosed area in which there are energized electrical components and an electrical insulation system according to the invention.

Background

Electrical insulation in medium and high voltage installations is generally ensured by using a dielectric gas, which is introduced into a closed and sealed container, in which the voltage components of the electrical installation can be found.

In recent years, the most widely used dielectric gas is SF₆Gas, which is due to its excellent dielectric properties, and in particular because it is non-toxic to humans, among many other advantages. However, this gas exhibits a significant environmental impact due to its high global warming potential (GWP of 22,800).

Therefore, in recent years, alternative gases have been sought that can replace such gases in these types of equipment. SF having good dielectric properties has been considered₆But for some reason (unacceptable toxicity, high global warming potential, flammability, etc.) they have not been implemented in the end.

Similarly, only more environmentally friendly gases (e.g. dry air, N) are used in these devices₂、O₂Or CO₂) As a dielectric, a significant increase in the size of these devices for a given voltage level will be involved, due to the SF₆In contrast, these gases have a lower dielectric strength. In this case, an additional option is to increase the filling pressure of the device to be greater than with SF₆The filling pressure value of (about 1300 mbar), but this would involve adapting the design to meet the requirements of different existing countries for containers with pressures greater than 1500 mbar, with consequent increase in the cost of the equipment.

An alternative option is to use fluoroketones, not only because they have good dielectric strength, but also because some of them are non-toxic to humans and have much less environmental impact than SF₆A gas. In fact, documents WO 2010/1460022 and WO 2010/142346 have described the use of fluoroketones for the electrical insulation of medium and high voltage equipment.

Other documents (e.g. WO 2012/160158 and WO 2012/160155) describe fluoroketones with carrier gases (e.g. CO)₂、N₂、O₂Or air or mixtures thereof).

Another problem that negatively affects the dielectric capacity of gas-insulated systems is the presence of water molecules from the materials used to manufacture certain electrical components of the switchgear. Water can occur in closed and watertight areas where insulating gases can be found in switchgear, as some thermoplastics (e.g., polyamides) used to make electrical components can contain water. For example, in the case of a polyamide, it may have absorbed 4.5 to 7.5% by weight of water.

The presence of water in the gaseous medium leads to a reduction of the dielectric properties of the gaseous medium and the presence of water should therefore be avoided. To address the problem of water present inside electrical switching apparatus, desiccants and molecular sieves have been used. Molecular sieves are materials containing small pores of precise, uniform size that are used as adsorbents for gases and liquids. Molecules small enough to pass through the pores are adsorbed, while larger molecules do not. Unlike filters, this process is performed at the molecular level. For example, water molecules may be small enough to pass through, while other larger molecules do not.

In the presence of SF₆In insulation systems in which the gas is the only insulating gas, due to SF₆The size of the molecules is much larger than the size of water molecules, so it is relatively simple to isolate water using molecular sieves, and thus selection by molecular size does not represent a significant problem.

However, in molecules of a size comparable to that of water molecules (e.g. carrier gases such as N)₂、CO₂Dry air) together with an insulator (e.g. fluoroketone), in a gas-insulated system, in which the insulator is present in a gas-insulated systemThe problem is not easily solved. In these types of dielectric insulators, a gas (CO) acts as a carrier₂、N₂Air, O₂Etc.) are similar in size to water molecules, molecular sieves can adsorb a portion of these gases instead of water molecules.

In document WO 2016/116637, the authors of the invention have solved this problem by means of a gaseous medium formed from one or more fluoroketones, another dielectric gas (in particular fluoronitrile) and one or more carrier gases, and a molecular sieve having certain properties.

There is still a need to develop insulation systems for medium and high voltage electrical switchgears based on gas or gaseous mixtures which, in addition to performing the main electrical insulation function, allow to provide improved characteristics in terms of safety, environmental impact or durability, which increase the versatility of the existing insulation systems and increase the adaptability of the insulation systems to as many operating conditions as the systems or medium and high voltage switchgears can withstand.

Another alternative is based on fluoroketones and hydrofluoroolefins, both of which have high dielectric strength, in combination with a carrier gas (e.g. N)₂、CO₂Or dry air) combined mixture. The document WO 2013/041695 describes a process for the preparation of a fluoroolefin having 3 carbon atoms (for example HFO-1234ze or HFO-1234yf) based on a mixture of a hydrofluoroolefin having 5 carbon atoms and a fluoroketone having 5 carbon atoms (for example N)₂) The electrically insulating gaseous medium of the mixture of constituents. The document WO 2013/004796 describes a process for the preparation of a catalyst based on a mixture of a hydrofluoroolefin having 3 carbon atoms (for example HFO-1234ze or HFO-1234yf) and a carrier gas (for example N)₂) The electrically insulating gaseous medium of the mixture of constituents.

However, a problem with hydrofluoroolefins having 3 carbon atoms (HFO-1234ze or HFO-1234yf) is that they can be flammable at certain operating concentrations and temperatures of medium and high voltage electrical switching apparatus for which the insulation systems described herein are intended.

In addition, there is another problem associated with the use of fluoroketones in these electrical insulation systems. When fluoroketones are used in combination with molecular sieves with the aim of minimizing the amount of residual water in the gaseous medium, there is a risk that part of the water adsorbed in the molecular sieve will not migrate to the interior of the molecular sieve material, but will remain adsorbed on its outer surface, as indicated in document WO 2016/113292. This water adsorbed on the outer surface of the molecular sieve can react with the fluorone and cause a cascade of reactions, resulting in the degradation of part of the fluorone, the occurrence of undesirable decomposition products and a reduction in the insulating properties or the arc extinction of the initial gaseous medium.

The authors of the present invention have developed an electrical insulation system for medium and high voltage switchgear based on a mixture which is free of fluoroketones and which consists of one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms and one or more carrier gases (for example N)₂、O₂、CO₂Helium or dry air) and at least one or more desiccants.

The electrical insulation system for medium and high voltage switchgears of the invention increases the dielectric strength of the aforementioned system and also makes the dielectric insulation capacity unaffected by the presence of water that may be present inside the closed container of the electrical switchgear in which the electrical components insulated with dielectric gas can be found. Furthermore, the system of the present invention has excellent environmental characteristics, high safety (because it is not flammable) and very low toxicity.

Disclosure of Invention

It is therefore an object of the present invention a low environmental impact electrical insulation system for medium or high voltage electrical switchgear, which represents a solution to the above mentioned problems. More particularly, the main object of the present invention is an electrical insulation system for medium or high voltage electrical switchgear, comprising:

a) a gaseous medium formed from a mixture of:

i. one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms; and

one or more selected from N₂、O₂Dry air, helium, CO₂Or a mixture thereof;

b) one or more desiccants.

Another object of the invention is the use of the electrical insulation system of the invention for electrical insulation and/or arc extinguishing in medium or high voltage electrical switchgear.

A further object of the present invention is a method for electrical insulation and/or arc extinguishing in a medium or high voltage electrical switchgear, comprising introducing the electrical insulation system in a closed and sealed container in which energized electrical components of the medium or high voltage electrical switchgear are located.

A final object of the invention is a medium or high voltage electrical switchgear comprising a closed container inside which there are energized electrical components and an electrical insulation system according to the invention.

Drawings

FIG. 1: schematic of the structure of zeolite a.

FIG. 2: schematic representation of the position of sodium cations in zeolite structure a.

FIG. 3: BAUR DTA-100E apparatus for determining the dielectric strength of an electrically insulating gas system.

Detailed Description

A first object of the present invention relates to an electrical insulation system for a medium or high voltage electrical switchgear, comprising:

a) a gaseous medium formed from a mixture of:

i. one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms; and

one or more selected from N₂、O₂Dry air, helium, CO₂Or a mixture thereof;

b) one or more desiccants.

The first element of the electrical insulation system of the present invention is a gaseous medium.

The essential element of the gaseous medium will be a hydrofluoroolefin having at least 4 carbon atoms. In particular, the hydrofluoroolefin having at least 4 carbon atoms is preferably trans-1, 1,1,4,4, 4-hexafluoro-2-butene (HFO-1336mzzE) and cis-1, 1,1,4,4, 4-hexafluoro-2-butene (HFO-1336 mzzZ).

These two hydrofluoroolefins have the property of very low global warming potential, in particular, the GWP of HFO-1336mzzZ is 2, the GWP of HFO-1336mzzE is 18, and their toxicity level is sufficiently low to be safely applicable to medium and high voltage electrical equipment. For example, the hydrofluoroolefin HFO-1336mzzZ has an occupational contact limit OEL (8 hours) of 500ppmv and the hydrofluoroolefin HFO-1336mzzE has an occupational contact limit OEL (8 hours) of 400 ppmv.

Moreover, one particularly relevant advantage of hydrofluoroolefins having at least 4 carbon atoms, in particular of the hydrofluoroolefins HFO-1336mzzZ and HFO-1336mzzE, is that they are not flammable, that is to say that they do not exhibit the flammability limit at the normal operating temperatures of medium-and high-voltage electrical equipment. Unlike hydrofluoroolefins having 3 carbon atoms, hydrofluoroolefins having 3 carbon atoms exhibit a flammability limit at the temperatures described. Thus, for example, the hydrofluoroolefin HFO-1234yf having 3 carbon atoms exhibits a lower flammability limit of 6.2% (volume in air) and an upper flammability limit of 12.3% (volume in air) s/ASTM E681-01 at 21 ℃. Hydrofluoroolefins HFO-1234zeE having 3 carbon atoms do not exhibit any flammability limit at 21 deg.C, but do exhibit flammability limits above 30 deg.C, for example, a lower flammability limit of 5.7% (volume in air) at 60 deg.C and an upper flammability limit of 11.3% (volume in air) s/ASTM E681-01. This means that systems based on mixtures of hydrofluoroolefins having 3 carbon atoms, such as the systems mentioned above, are not safe under certain operating conditions. For example, using the above data, it can be concluded that a mixture formed from 8% HFO-1234zeE in dry air would be flammable at 60℃, whereas a mixture formed from 8% HFO-1336mzzE in dry air would not be flammable at 60℃.

Thus, the use of hydrofluoroolefins having at least 4 carbon atoms allows the system of the invention to be safer to a greater extent than those described in WO 2013/004796.

Nevertheless, in a particular embodiment of the invention, the gaseous mixture of the system of the invention may comprise one or more hydrofluoroolefins having 3 carbon atoms, the percentage of which is outside its flammability range. The introduction of these hydrofluoroolefins having 3 carbon atoms at a percentage outside their flammability range does not affect the safety of the mixture, but it has been observed that it results in an increase in dielectric strength. Preferably, the hydrofluoroolefin having 3 carbon atoms that may be added to the gaseous mixture of the present invention is HFO-1234 zeE.

The last element of the gaseous mixture of the electrical insulation system of the present invention is a carrier gas. Carrier gases are those gases used to dilute the hydrofluoroolefins, which, despite having a lower dielectric strength, cause the gaseous medium to exhibit such behavior at low temperatures. They are therefore generally completely harmless (non-toxic) gases and generally have a reduced environmental impact. The carrier gas may vary, e.g. N₂、O₂Dry air, helium, CO₂Or mixtures thereof. In particular and preferably, in the system of the invention the carrier gas is selected from N₂、O₂Dry air or mixtures thereof.

A particular and preferred embodiment of the present invention relates to an electrical insulation system wherein the gaseous mixture comprises one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms and one or more carrier gases. In this embodiment, the carrier gas is preferably selected from N₂、O₂Dry air or mixtures thereof.

The overall dielectric strength of the gaseous mixture will be affected by the amount of hydrofluoroolefin having at least 4 carbon atoms (and optionally 3 carbon atoms) such that the more hydrofluoroolefin present in the gaseous mixture, the higher its dielectric strength will be.

However, the amount of hydrofluoroolefin having at least 4 carbon atoms in the gaseous mixture is dictated by the minimum operating temperature of the switchgear in which it is to be used. Generally, the lower the minimum operating temperature of the electrical switchgear, the less amount of hydrofluoroolefin having at least 4 carbon atoms that can be added to the gaseous mixture, since it is desirable to avoid its partial condensation at low temperatures.

In addition to the gaseous medium, another essential element of the electrical insulation system of the invention is a desiccant.

The desiccant can be of two types: an absorbent or adsorbent. Absorption is caused when one substance, in this case water, is chemically incorporated into another substance, the absorbent. On the other hand, when one substance (in this case, water) is held in another substance due to relatively weak intermolecular physical bonds (e.g., van der waals forces, electrostatic interactions), adsorption is caused. In a particular embodiment of the invention, the desiccant is selected from the group consisting of calcium oxide, calcium sulfide, calcium sulfate, montmorillonite clay, silica gel, activated alumina, and molecular sieves.

The use of desiccants in the electrical insulation system of the present invention is based on the need to retain water molecules present in the materials forming certain parts of the electrical switchgear, since the presence of said molecules negatively affects the dielectric strength and therefore the ability to use gaseous mixtures of hydrofluoroolefins as insulators.

One preferred embodiment of the present invention uses calcium oxide in view of its high water adsorption capacity (not less than 28.5% of its weight). Calcium oxide (also known as quicklime) has the unique property that it absorbs a large amount of water vapor at very low relative humidity compared to other types of sorbents. That is, this is particularly effective when very low relative humidity is required (as is the case in enclosed areas of medium and high voltage electrical switching apparatus).

In another preferred embodiment, the desiccant may also be of a pore size of 3 to 3(preferably 3 to) And a molecular sieve having a polar surface. As mentioned above, molecular sieves are materials containing small pores of precise, uniform size that are useful as adsorbents for gases and liquids. Molecular sieves are capable of distinguishing at the molecular level so that molecules small enough to pass through the pores are adsorbed while larger moleculesThen it will not.

Molecular sieves also have a high water adsorption capacity, in some cases up to 22% of their own weight in water. However, the carrier gas (N) of the gaseous mixture due to the insulation system₂、O₂Dry air or helium) have a molecular size similar to that of water molecules and molecular sieves must have the ability to selectively separate water molecules from the molecules of these gases. Using pore sizes of 3 to(preferably 3 to) And molecular sieves with polar surfaces are capable of such discrimination and with respect to N₂、O₂Dry air, CO₂Or helium gas molecules selectively adsorb water molecules, which means that the dielectric strength of the electrical insulation system of the present invention is not altered or deteriorated.

This water selectivity of the molecular sieve results not only from the size of the pores, but also (particularly for molecules having a size similar to the size of water molecules) from the polar surface of the molecular sieve. The fact that the surface is polar means that it attracts those more polar molecules with greater strength in preference to less polar molecules.

Table 1 describes the size and polarity of the molecules determined:

TABLE 1

Based on these data it is easy to understand, e.g. by size distinguishing water molecules with respect to e.g. SF₆Adsorption of molecules of fluoroketones or hydrofluoroolefins can be easy. However, relative to size similarityCarrier gas (e.g. helium, O)₂、N₂、CO₂Or air) molecules are not as easy. For these molecules, the polarity of water is much more relevant than the polarity of other carrier gases. When the surface of the molecular sieve is polar, this property of the water molecule causes it to be adsorbed in a preferred manner relative to the rest of the molecule.

There are molecular sieves of different nature, such as zeolites (which are aluminosilicates), porous glasses, clays, microporous carbon, activated carbon, etc. First, any molecular sieve is suitable for use in the electrical insulation system of the present invention, as long as the pore size is in the range of 3 toPreferably between 3 andand have a polar surface.

In a particular embodiment, the molecular sieve is a zeolitic molecular sieve. The zeolite may be natural and is preferably a synthetic zeolite. The zeolite is an aluminosilicate, which may exhibit different structures (e.g., zeolite a, zeolite X, zeolite Y, etc.).

Preferred zeolites have structure a. In fig. 1, the structure of zeolite a can be observed. The aluminum, silicon and oxygen atoms are joined to form truncated octahedra, which are called sodalite cages. Said sodalite cages are combined in the form of simple cubes to form zeolite a, leaving an internal space called cage α with a diameter ofIs accessible from the six-sided opening of the cube. These inlets are surrounded by 8 oxygen atoms and one or more exchangeable cationic moieties block the front region. When the cation is sodium (Na)⁺) When (see FIG. 2), the ring of oxygen atoms is provided with a diameter ofTo gain access to the interior of the structure (cage a). Sodium cationMay be partially substituted by other cations in the synthetic zeolite, e.g. potassium (K)⁺) Or calcium (Ca)²⁺) Respectively result inAndis provided.

In addition to helping to determine the pore opening diameter (which is undoubtedly related to the molecular differentiation of the gas adsorbed by the zeolite), they help to establish strictly positive and negative charges in the crystal structure of the zeolite, which causes the charge to be unevenly distributed, resulting in the surface having polarity. This property of the zeolite is precisely such that water molecules are in relation to other carrier gases (e.g. N)₂、O₂Dry air or helium) molecules are preferably adsorbed.

Another object of the invention is represented by the use of an electrical insulation system, such as the above-mentioned use for electrical insulation and/or arc extinguishing in medium or high voltage electrical switchgear.

The gaseous medium, which comprises a mixture of one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms and one or more carrier gases (and optionally one or more hydrofluoroolefins having 3 carbon atoms, the percentage of use of which is outside of its flammability limit), provides the system with dielectric strength, while the desiccant is responsible for maintaining this dielectric strength due to its ability to adsorb water molecules that may be present in said gaseous medium, said water molecules coming from certain elements of medium-voltage and high-voltage electrical switchgear that can be found in the closed and sealed containers of said switchgear. It is for this reason that the system of the invention is very useful in electrical insulation and is capable of extinguishing arcs in electrical switching apparatus of this type.

Another object of the invention is related to the use of the electrical insulation system of the invention in part, relating to a method for electrical insulation and/or arc extinguishing in high and medium voltage electrical switchgear, the method comprising introducing an electrical insulation system comprising:

a) a gaseous medium formed from a mixture of:

i. one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms; and

one or more selected from N₂、O₂Dry air, helium, CO₂Or a mixture thereof;

b) one or more desiccants.

The elements to be insulated of the medium or high voltage electrical switchgear are located in a closed and sealed container.

In a particular embodiment of the foregoing process, the gaseous mixture may comprise one or more hydrofluoroolefins having 3 carbon atoms in a percentage outside the range of their flammability.

To carry out the process, one or more gas-permeable and desiccant-containing sachets are first placed within a container. The container is then closed to make it completely sealed and evacuated. Subsequently, a gaseous mixture of a non-flammable hydrofluoroolefin having at least 4 carbon atoms (and optionally one or more hydrofluoroolefins having 3 carbon atoms, which are used in percentages above their flammability limit) and a carrier gas is introduced until the desired pressure is reached.

A final object of the present invention relates to a medium or high voltage electrical switchgear comprising a closed container in which there are energized electrical components and an electrical insulation system comprising:

a) a gaseous medium formed from a mixture of:

i. one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms (and optionally one or more hydrofluoroolefins having 3 carbon atoms, the percentage of which is outside of its flammability limit); and

one or more selected from N₂、O₂Dry air, helium, CO₂Or a mixture thereof;

b) one or more desiccants.

In a particular embodimentIn one embodiment, the desiccant may also be calcium oxide or have a pore size of 3 to 3 angstroms(preferably 3 to) And a molecular sieve having a polar surface or a mixture of both.

Fig. 3 is a test system for experimentally determining the dielectric strength of a gas insulation system.

In a particular embodiment of the invention, the switchgear may be a secondary distribution cabinet for a distribution network of up to 72 kV.

The following are examples for understanding possible embodiments of the present invention:

example 1: detailed description of embodiments of the invention

As a preferred embodiment of the invention, an electrical insulation system in a closed and sealed container forming part of a medium or high voltage electrical switchgear is proposed, comprising one or more desiccants, preferably calcium oxide, of size between 3 and 3Preferably betweenAndof zeolite molecular sieves or a mixture of both, and a further gaseous mixture comprising:

a) at least one non-flammable hydrofluoroolefin having four carbon atoms, such as HFO-1336mzzE or HFO-1336 mzzZ;

b) in addition, another carrier gas or gases, e.g. N₂Dry air, O₂、CO₂Or helium or any combination thereof.

The presence of one or more non-flammable hydrofluoroolefins having at least 4 carbon atoms (e.g., HFO-1336mzzE or HFO-1336mzzZ) in the gaseous mixture results in a significant increase in the dielectric strength of the mixture without negatively affecting other operating parameters.

In addition to the improved dielectric strength of the insulation system due to the reduction of water therein by the presence of one or more desiccants, the dielectric strength of the insulation system will also be affected by the percentage of hydrofluoroolefin having at least 4 carbon atoms used in the gaseous mixture. In this manner, the more hydrofluoroolefin in the gaseous mixture that has at least 4 carbon atoms, the greater its dielectric strength for a given final fill pressure. However, as previously mentioned, if condensation at low temperatures is to be avoided, which would involve a reduction in the dielectric properties of the gaseous mixture at these low temperatures, the amount of hydrofluoroolefin having at least 4 carbon atoms in the gaseous mixture is limited by the minimum operating temperature of the switchgear.

In the table below, the mole fraction values of hydrofluoroolefins HFO-1336mzzZ and HFO-1336mzzE are shown which can be used in gaseous mixtures without condensation at different minimum operating temperatures of the switchgear, assuming a filling temperature of the switchgear of 20 ℃ and a total filling pressure of the mixture of 1400 mbar.

TABLE 2 mixtures using HFO-1336mzzZ

Temperature (. degree.C.)	Pvs, HFOZ (Bar)	P, HFOZ (Bar)	X,HFOZ
				-40	0.023	0.029	0.0211
-35	0.033	0.041	0.0292
				-30	0.046	0.056	0.0398
-25	0.063	0.075	0.0534
				-20	0.085	0.099	0.0706
-15	0.114	0.129	0.0921
				-10	0.149	0.166	0.1186
-5	0.193	0.211	0.1508
				0	0.247	0.266	0.1897

TABLE 3 mixtures using HFO-1336mzzE

Wherein:

pvs, HFOZ and Pvs, HFOE are hydrofluoroolefins HFO-1336mzzZ and HFO-1336mzzE at different temperature values of saturated vapor pressure,

p, HFOZ and P, HFOE are the pressure values of hydrofluoroolefins HFO-1336mzzZ and HFO-1336mzzZ in switchgear at a filling temperature of 20 ℃ (P, HFOZ ═ Pvs, HFOZ x 293.15/Tmin (K)),

x, HFOZ and X, HFOE are the mole fractions of hydrofluoroolefins HFO-1336mzzZ and HFO-1336mzzE in the final mixture (final fill pressure 1400 mbar), which can be used without condensation even at the lowest operating temperature of the switchgear.

For example, for medium-voltage switchgear with a filling pressure of 1.40 bar at 20 ℃ and a minimum operating temperature of-10 ℃, the following mixtures can be used:

a)N₂(or dry air or O)₂Or helium or a mixture thereof) with 11.86% HFO-1336mzzZ,

b) or, N₂(or dry air or O)₂Or helium or a mixture thereof) with 38.99% HFO-1336mzzE,

c) or, N₂(or dry air or O)₂Or helium or mixtures thereof)With 38.99% HFO-1336mzzE and 11.86% HFO-1336mzzZ,

condensation of the hydrofluoroolefin does not occur until-10 deg.C.

Below this temperature of-10 c, the hydrofluoroolefin will start to partially condense, its percentage in the gaseous mixture being reduced, thus reducing the initial dielectric strength of the insulation system.

Likewise, for medium-voltage switchgear with a filling pressure of 1.40 bar at 20 ℃ and a minimum operating temperature of-20 ℃, the following mixtures can be used:

a)N₂(or dry air or O)₂Or helium or a mixture thereof) with 7.06% HFO-1336mzzZ,

b) or, N₂(or dry air or O)₂Or helium or a mixture thereof) with 23.99% HFO-1336mzzE,

c) or, N₂(or dry air or O)₂Or helium gas or mixtures thereof) with 23.99% HFO-1336mzzE and 7.06% HFO-1336mzzZ,

condensation of the hydrofluoroolefin does not occur until-20 deg.C.

Below this temperature of-20 c, the hydrofluoroolefin will start to partially condense, its percentage in the gaseous mixture being reduced, thus reducing the initial dielectric strength of the insulation system.

And so on for other minimum operating temperatures of the switchgear.

If the final pressure of the mixture in the switchgear differs from 1.40 bar, the percentages of HFO-1336mzzZ and HFO-1336mzzE will also be modified accordingly according to the following formula:

X,HFOZ＝P,HFOZ/P_{total mixture}

X,HFOE＝P,HFOE/P_{Total mixture}

P_{Total mixture}(Ptotal mix) is the final pressure of the mixture. If the percentage of hydrofluoroolefin used in the mixture is higher than the percentage indicated for the respective temperature when filling the switchgear, the dielectric strength will be logically greater, but it must be taken into account that, at the mostAt low operating temperatures, the dielectric strength of the insulation system will be reduced due to condensation of part of the hydrofluoroolefin and will be lower than if the hydrofluoroolefin percentages indicated in tables 2 and 3 for the respective temperatures were used.

Example 2: dielectric Strength testing of gaseous mixtures

The dielectric strength of the different gaseous mixtures was evaluated, and the "dielectric breakdown voltage" was measured according to the standard ASTM D2477, with a BAUR DTA-100E apparatus equipped with a chamber for the test gas, with two electrodes (one of the 5 electrodes being a wafer with a plane of diameter 1.50 inches, the other electrode being a spherical sphere of diameter 0.75 inches) and the distance between the electrodes being 8 mm.

The gaseous mixtures tested were as follows:

a)1.4 bar of dry air

b)1.4 Bar Dry air + 4.0% HFO-1336mzzZ mixture

c)1.4 Bar Dry air + 5.4% HFO-1336mzzZ mixture

d)1.4 Bar Dry air + 7.0% HFO-1336mzzZ mixture

e)1.4 Bar Dry air + 13.7% HFO-1336mzzE mixture

f)1.4 Bar Dry air + 17.3% HFO-1336mzzE mixture

g)1.4 Bar Dry air + 23.1% HFO-1336mzzE mixture

h)1.4 bar of dry air + 13.7% HFO-1336mzzE + 15.2% HFO-1234zeE the results of these tests are shown in Table 4:

table 4: dielectric breakdown voltage value of gaseous mixture

From the penultimate item of table 4 it can be seen that the mixture of dry air with 23.1% of hydrofluoroolefin HFO-1336mzzE makes the dielectric breakdown voltage of the dry air almost double at the same pressure of 1.4 bar, which means that the application of a gaseous mixture with these characteristics for electrical insulation in medium or high voltage electrical switchgear is a desirable choice. Similarly, it was observed that the addition of 15.2% HFO-1234zeE to 13.7% HFO-1336mzzE + dry air mixture also increased the dielectric strength by about 8.5%.

Example 3: environmental impact of examples of gaseous mixtures (greenhouse effect)

The Global Warming Potential (GWP) of a gaseous mixture is calculated according to european regulations on fluorinated greenhouse gases, which is a weighted average obtained by multiplying the weight fraction of each substance by the sum of its GWP values.

This is done:

a) the Global Warming Potential (GWP) of a mixture containing 17% HFO-1336mzzE and 83% dry air will be 9.66, that is, SF₆0.0424% of the global warming potential (GWP, 22,800) of gas (considering that HFO-1336mzzE has a GWP of 18, HFO-1336mzzE has a molecular weight of 164, and dry air has a molecular weight of 29).

b) The Global Warming Potential (GWP) of a mixture containing 6% HFO-1336mzzZ and 94% dry air will be 0.53, that is, SF₆0.0023% of the global warming potential (GWP, 22,800) of gas (considering that the GWP of HFO-1336mzzZ is 2, the molecular weight of HFO-1336mzzZ is 164, and the molecular weight of dry air is 29).