WO2018032269A1

WO2018032269A1 - Electrically insulating composite material and electrical product

Info

Publication number: WO2018032269A1
Application number: PCT/CN2016/095350
Authority: WO
Inventors: Maoshan NIU; Jiansheng Chen; Delun MENG; Orlando Girlanda; Cuicui SU; Fredrik Sahlen; Torbjorn Brattberg; Sufeng Zhang
Original assignee: Abb Schweiz Ag
Priority date: 2016-08-15
Filing date: 2016-08-15
Publication date: 2018-02-22

Abstract

An electrically insulating composite material is disclosed. The material includes a first portion of a fiber and a second portion of a fibrid, the fiber including a pre-oxidized polyacrylonitrile (PAN) fiber and the fibrid including an aromatic polyamide fibrid. An electrical product including the electrically insulating composite material is also disclosed. A method and an apparatus for producing an electrically insulating composite material are also disclosed. The produced material provides decent electrical properties while keeping the cost low, and thus enabling its use in various electrical applications.

Description

ELECTRICALLY INSULATING COMPOSITE MATERIAL AND ELECTRICAL PRODUCT

TECHNOLOGY

Example embodiments disclosed herein generally relate to a composite material， more specifically， to an electrically insulating composite material， an electrical product incorporating such a composite material， and a method and an apparatus for producing such a composite material.

BACKGROUND

In various applications， electrically insulating materials are in need to be used in components such as transformers. Some examples of the electrically insulating materials include electrically insulating papers， pressboards and laminates， which are all used for electrical insulation in different applications due to their outstanding electrical and mechanical properties. For example， insulating materials in oil-filled transformers endure high electrical and physical stresses around cores and windings.

Currently， cellulose materials or polymer materials are used to form the electrically insulating materials in transformers. The former can be used in a less demanding environment in terms of thermal stability， while the latter can be used in a harsher environment but the current products are less cost effective. Thus， there is a need in the art for providing a more cost effective electrically insulating material.

SUMMARY

Example embodiments disclosed herein propose an electrically insulating composite material and an electrical product， a method and an apparatus for producing an electrically insulating composite material.

In one aspect， example embodiments disclosed herein provide an electrically insulating composite material. The electrically insulating composite material include a first portion of a fiber and a second portion of a fibrid， the fiber including a pre-oxidized polyacrylonitrile (PAN) fiber and the fibrid including an aromatic polyamide fibrid.

In another aspect， example embodiments disclosed herein provide an electrical product comprising the electrically insulating composite material described above.

In yet another aspect， example embodiments disclosed herein provide a method of producing an electrically insulating composite material. The method includes： mixing a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber with a second portion of an aromatic polyamide fibrid in a liquid to form a mixture， wherein the pre-oxidized PAN fiber is obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber， and heat-pressing the mixture to form sheets of the electrically insulating composite material.

In still another aspect， example embodiments disclosed herein provide an apparatus for producing an electrically insulating composite material. The apparatus includes： a mixer configured to mix a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber with a second portion of an aromatic polyamide fibrid in a liquid to form a mixture， wherein the pre-oxidized PAN fiber is obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber， and a sheet producer configured to heat-press the mixture to form sheets of the electrically insulating composite material.

Through the following description， it would be appreciated that the electrically insulating composite material produced according to the present disclosure has a desirable dielectric strength and permittivity compared with traditional cellulose products， and a better cost effectiveness compared with high performance products available on the market. As a result， such a prepared electrically insulating composite material has a potential to be used in various electric devices requiring a decent dielectric performance that is otherwise expensive to achieve by existing products.

DESCRIPTION OF DRAWINGS

Through the following detailed descriptions with reference to the accompanying drawings， the above and other objectives， features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings， several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner， wherein：

Figure 1 illustrates a process of producing an electrically insulating composite material in accordance with an example embodiment； and

Figure 2 illustrates an apparatus for producing an electrically insulating composite material in accordance with an example embodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The subject matter described herein will now be discussed with reference to several example embodiments. These embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the subject matter described herein， rather than suggesting any limitations on the scope of the subject matter.

The term “includes” and its variants are to be read as open terms that mean “includes， but is not limited to. ” The term “or” is to be read as “and/or” unless the context clearly indicates otherwise. The term “based on” is to be read as “based at least in part on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” Unless specified or limited otherwise， the terms ″mounted， ″ ″connected， ″ ″supported， ″ and ″coupled″ and variations thereof are used broadly and encompass direct and indirect mountings， connections， supports， and couplings. Further， ″connected″ and ″coupled″ are not restricted to physical or mechanical connections or couplings.

Figure 1 illustrates a process 100 of producing an electrically insulating composite material in accordance with an example embodiment. In step 101， a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber is mixed with a second portion of an aromatic polyamide fibrid in a liquid. As a result， a mixture is formed in the liquid form. Prior to the mixing step， PAN fibers are treated by a thermal process with a temperature ranging from approximately 200 to 320 degrees Celsius， which results in an oxidation and a stabilization of the PAN fiber. After the thermal process， the PAN filers are turned into the so-called pre-oxidized (or oxidized) PAN fibers ready to be used in the mixing step.

Aromatic polyamide may be either a poly-p-phenylene terephthamide (PPTA) or a poly (metaphenylene isophthamide) (PMIA) ， whose chemical formulae are illustrated below， in which formula (1) is for poly-p-phenylene terephthamide while formula (2) is for poly (metaphenylene isophthamide) . The inventors have discovered that it is especially effective to improve the performance of the final product if the pre-oxidized PAN fiber is mixed with the fibrid including phenylene and phthamide components (which constitute the aromatic polyamide) ， which will be illustrated in later paragraphs. Although aromatic polyamides also include other forms except poly-p-phenylene terephthamide and poly (metaphenylene isophthamide) ， it is used especially for one of the two illustrated forms. As other aromatic polyamides including phenylene and phthamide components are expected to perform similarly with the two illustrated forms but less common， only poly-p-phenylene terephthamide and poly (metaphenylene isophthamide) are to be explained in details in the context.

In one embodiment， the mixing step 101 may include beating and dispersing the first portion of the pre-oxidized PAN fiber and the second portion of the aromatic polyamide fibrid for a period from 10 to 80 minutes. In some situations， the period for this beating and dispersing process can range from 20 to 40 minutes. Such a process is to better mix the two ingredients in the solution. Although water is used as the liquid or solution for the mixing step， other agents may also be used for the sake of desired effects.

In step 102， the mixture is heat-pressed in order to form sheets of the electrically insulating composite material. In one embodiment， the heat-pressing step 102 may include applying a pressing temperature from approximately 200 to 400 degrees Celsius. In some situations， the pressing temperature for this heat-pressing process can range from 250 to 350 degrees Celsius. After the step 102， a paper or multi-layer pressboard can be formed with a certain thickness.

Although the step 102 is to be carried out after the step 101， this does not mean that the step 102 immediately follows the step 101. In other words， additional steps may be incorporated prior to the heat-pressing process. For example， the mixture can be formed into sheets and then the liquid can be removed.

Figure 2 illustrates an apparatus 200 for producing an electrically insulating composite material in accordance with an example embodiment. A mixer 201 is configured to mix a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber with a second portion of an aromatic polyamide fibrid in a liquid to form a mixture. As discussed above with the method 100， the pre-oxidized PAN fiber can be obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber. A sheet producer 201 is configured to heat-press the mixture to form sheets of the electrically insulating composite material.

In one embodiment， the mixer 201 may be further configured to beat and disperse the first portion of the pre-oxidized PAN fiber and the second portion of the aromatic polyamide fibrid for a period ranging from 10 minutes to 80 minutes， preferably from 20 minutes to 40 minutes. In another embodiment， the sheet producer 202 is further configured to apply a pressing temperature ranging from 200 degrees Celsius to 400 degrees Celsius， preferably from 250 degrees Celsius to 350 degrees Celsius.

Because the pre-oxidized PAN fiber and the aromatic polyamide fibrid both provide excellent thermal stabilities as well as electrical properties， the mixture of the pre-oxidized PAN fiber and the aromatic polyamide fibrid is able to improve the thermal and electrical performances of the resulting sheets after the step 102 or after being produced by the sheet producer 202. In the meantime， the cost is not significantly higher than that of the cellulose insulating material. In addition， mechanical properties can be improved by adding some additives or other ingredients.

In various embodiments of the present disclosure， the electrically insulating composite material includes at least a first portion of a fiber and a second portion of fibrid. The fiber includes the pre-oxidized PAN fiber. In some other examples， the fiber can also include one or more other kinds of fibers. For example， at least one of a polyacrylonitrile fiber， a poly-p-phenylene terephthamide fiber， a poly (metaphenylene isophthamide) fiber， a polysulfonamide fiber， a polyphenylene sulfide fiber， or a polyoxadiazole fiber can be added into the liquid in the course of the mixing step 101. The formulation of the fibers affects mechanical or electrical properties of the resulting material. The fibers may have a length ranging from lmm to 20mm， and many of the fibers may be in a range from 3mm to 6mm to get better dispersion in the composites and compatibility with fibrids.

The fibrid includes the aromatic polyamide fibrid so that the resulting material include both the pre-oxidized PAN fiber and the aromatic polyamide fibrid. As discussed above， aromatic polyamide has different forms such as a poly (metaphenylene isophthamide) fibrid and a poly-p-phenylene terephthamide. In some other examples， the fibrid can also include one or more other kinds of fibrids. For example， at least one of a polyacrylonitrile fibrid， a polysulfonamide fibrid， a polyphenylene sulfide fibrid， or a polyoxadiazole fibrid can be added into the liquid in the course of the mixing step 101. The fibrid may have a specific surface area from 3 m²/g to 80 m²/g， and many of the fibrids may be in a range from 5 m²/g to 40 m²/g to improve mechanical properties of the composites. The specific surface area refers to a total surface area of the fibrid per unit of mass.

In one embodiment， the formulation of the mixture can be represented by a weight percentage of an ingredient over the total weight. In the context， water is removed from each of the ingredients and thus the weight percentage is obtained from dry weights of the ingredients. For example， a weight percentage of the pre-oxidized PAN fiber by dry weight ranges from 1 wt％to 99 wt％. This range can be further specified as from 30 wt％to 70 wt％for obtaining improved cost effectiveness or so-called price-quality ratio. Accordingly， a weight percentage of the aromatic polyamide fibrid by dry weight ranges from lwt％to 99 wt％. This range can be further specified as from 30 wt％to 70 wt％. In case that no other ingredient is provided， the pre-oxidized PAN fibers and the aromatic polyamide fibrids constitute 100％of the total weight.

In one embodiment， in case that other fiber is also provided， as discussed above， its weight percentage is to be specified as well based on the compatibility with mixture and the cost. A weight percentage of the polyacrylonitrile fiber by dry weight can range from 0 wt％to 20 wt％. A weight percentage of the poly-p-phenylene terephthamide fiber by dry weight can range from 0 wt％to 30 wt％. A weight percentage of the poly (metaphenylene isophthamide) fiber by dry weight can range from 0 wt％to 10 wt％. A weight percentage of the polysulfonamide fiber by dry weight can range from 0 wt％to 40 wt％. A weight percentage of the polyphenylene sulfide fiber by dry weight can range from 0 wt％to 20 wt％. A weight percentage of the polyoxadiazole fiber by dry weight can range from 0 wt％to 20 wt％.

In one embodiment， in case that other fibrid is also provided， as discussed above， its weight percentage is to be specified as well based on the compatibility with mixture and the cost. A weight percentage of the polyacrylonitrile fibrid by dry weight can range from 0 wt％to 40 wt％， or more specifically from 5 wt％to 20 wt％. A weight percentage of the polysulfonamide fibrid by dry weight can range from 0 wt％to 40 wt％. A weight percentage of the polyphenylene sulfide fibrid by dry weight can range from 0 wt％to 20 wt％. A weight percentage of the polyoxadiazole fibrid by dry weight can range from 0 wt％to 10 wt％.

In one embodiment， the electrically insulating composite material may include an inorganic micro-filler or an inorganic nano-filler. Preferably， the weight percentage of the fillers range from 0 wt％to 20 wt％based on the total weight of the electrically insulating composite material. The fillers can improve dielectric strength and electrical creepage resistance. Some examples of the fillers that can be used include silica， alumina and/or their mixture.

In order to test the electrical properties of the resulting electrically insulating composite material， the material is shaped in a form of a pressboard with a thickness of about lmm. The pressboard is a multi-layer structure， although single-layer papers can also be formed in some other situations. The resulting pressboard has a relatively high oil absorption ratio (from 30％to 40％) and a very low moisture absorption ratio (smaller than 1％) ， which is much lower than that of IEC (International Electrotechnical Commission) requirements， dramatically lowering the drying cost of the same. The pressboard also has a good compressibility as low as 5％， which is much lower than the requirement of 10％specified in the IEC standard.

One of the metrics measured for the electrical properties is dielectric strength. Dielectric strength is a physical quantity used to measure how strong the pressboard is to resist electrical impact such as impulses so that the pressboard with high dielectric strength will not be broken down. Therefore， sometimes it can be called “breakdown strength. ” In the context， dielectric strength or breakdown strength is measured in “kV/mm， ” indicating that how much voltage in kilovolts the pressboard is able to sustain for a given thickness in millimeter. The higher the value for the breakdown strength， the better the pressboard can avoid being broken down during operation.

Another metric measured for the electrical properties is permittivity. Permittivity is the measure of resistance that is encountered when forming an electric field in a medium. Therefore， permittivity of a medium describes how much electric field (more correctly， flux) is generated per unit charge in that medium. For an electrically insulating material， it is desired that the permittivity has a closer value compared with a working medium to obtain uniform electric field in the final product. For example， when the pressboard is immersed in oil used for an oil immersed transformer， a permittivity of the pressboard close to the permittivity of oil (3.1) is desired. Some experimental results are provided in Table 1 below， showing the measured values of breakdown strength and permittivity of the pressboard formed by different formulations. In Table 1， as one embodiment， a poly-p-phenylene terephthamide fibrid is used to be mixed with a pre-oxidized PAN fiber， while additionally a PAN fibrid can be included as a third component in the mixure.

Table 1

The experimental results were aimed to showcase the improvements on the electrical properties of prepared pressboards in accordance with the subject matter described herein， especially used as the component in an electrical product such as an electrical transformer or an electrical motor. The value of breakdown strength exceeding 30 kV/mm is desirable and all of the above samples satisfy this requirement. In addition， the value of permittivity in a dry environment below 4 is desirable， while the value of permittivity in an oil environment below 9.0 is desirable. Therefore， the inclusion of the pre-oxidized PAN fiber as well as the poly-p-phenylene terephthamide fibrid allows for desirable electrical properties， and the inclusion of the PAN fibrid is able to further alter the electrical properties slightly.

It should be understood that the form of pressboard is merely an example for demonstrating the electrical properties of the electrically insulating composite material， and the material can exist in other electrical applications， for example， it can be manufactured to a spacer， a barrier， a paper wrapped conductor or a press ring， for functioning as an insulating material of high quality.

In addition， the poly-p-phenylene terephthamide fibrid is merely an example of aromatic polyamide fibrid. In another experiment carried out separately， a pre-oxidized PAN fiber of 40 wt％in percentage was mixed with a poly (metaphenylene isophthamide) fibrid of 60 wt％in percentage. By this combination， the breakdown strength was measured to be 32.5 kV/mm. The permittivity value in a dry environment was 4.6 while the permittivity value in an oil environment was 6.2. These results indicate that poly (metaphenylene isophthamide) fibrids result in a similar performance to that of poly-p-phenylene terephthamide fibrids. Other forms of aromatic polyamide fibrids are in line with the above results and are thus not illustrated in details.

It is also to be understood that Table 1 only shows results from a relatively effective range， i.e.， from 30 to 70 wt％of the pre-oxidized PAN fiber， as tested previously. As discussed above by reference to Table 1， all the tested pressboard exhibited a considerable improvement over the control sample prepared with only one ingredient， especially reflected in the mechanical properties. Therefore， even a very small fraction of the pre-oxidized PAN fiber or aromatic polyamide fibrid (e.g.， poly-p-phenylene terephthamide fibrid) in the mixture (for example， only 1％for each material) is able to improve the electrical properties as well as the mechanical properties.

Moreover， the present disclosure also relates to an electrical product formed by the electrical insulating composite material described above， and use of the material described above as an insulating sheet in a transformer or a motor. Because of the improved electrical properties as well as the relatively high cost effectiveness， the insulating composite material is especially suitable for replacing some existing costly insulating products such as the

from DuPont which exhibits no better electrical properties but cost significantly more than the prepared material in accordance with the present disclosure.

While operations are depicted in a particular order in the above descriptions， this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order， or that all illustrated operations be performed， to achieve desirable results. In certain circumstances， multitasking and parallel processing may be advantageous. Likewise， while several details are contained in the above discussions， these should not be construed as limitations on the scope of the subject matter described herein， but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. On the other hand， various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the subject matter has been described in language specific to structural features and/or methodological acts， it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather， the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

An electrically insulating composite material comprising a first portion of a fiber and a second portion of a fibrid， the fiber including a pre-oxidized polyacrylonitrile (PAN) fiber and the fibrid including an aromatic polyamide fibrid.
The electrically insulating composite material according to Claim 1， wherein the aromatic polyamide fibrid is a poly-p-phenylene terephthamide fibrid or a poly (metaphenylene isophthamide) fibrid.
The electrically insulating composite material according to Claim 1， wherein the pre-oxidized PAN fiber is obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber.
The electrically insulating composite material according to Claim 1， wherein the first portion of the fiber further comprises at least one of a polyacrylonitrile fiber， a poly-p-phenylene terephthamide fiber， a poly (metaphenylene isophthamide) fiber， a polysulfonamide fiber， a polyphenylene sulfide fiber， or a polyoxadiazole fiber.
The electrically insulating composite material according to any of Claims 1 to 3， wherein a plurality of fibers from the first portion of the fiber have a length ranging from 1mm to 20mm， preferably from 3mm to 6mm.
The electrically insulating composite material according to Claim 1， wherein the second portion of the fibrid further comprises at least one of a polyacrylonitrile fibrid， a polysulfonamide fibrid， a polyphenylene sulfide fibrid， or a polyoxadiazole fibrid.
The electrically insulating composite material according to Claim 1 or 6， wherein a plurality of fibrids from the second portion of the fibrid have a specific surface area ranging from 3 m²/g to 80 m²/g， preferably from 5 m²/g to 40 m²/g， the specific surface area being a total surface area of the fibrid per unit of mass.
The electrically insulating composite material according to Claim 1， wherein a weight percentage of the pre-oxidized PAN fiber by dry weight ranges from 1 wt％ to 99 wt％， preferably from 30 wt％ to 70 wt％.
The electrically insulating composite material according to Claim 1， wherein a weight percentage of the aromatic polyamide fibrid by dry weight ranges from 1wt％ to 99 wt％， preferably from 30 wt％ to 70 wt％.
The electrically insulating composite material according to Claim 4， wherein a weight percentage of the polyacrylonitrile fiber by dry weight ranges from 0 wt％ to 20 wt％， a weight percentage of the poly-p-phenylene terephthamide fiber by dry weight ranges from 0 wt％ to 30 wt％， a weight percentage of the poly (metaphenylene isophthamide) fiber by dry weight ranges from 0 wt％ to 10 wt％， a weight percentage of the polysulfonamide fiber by dry weight ranges from 0 wt％ to 40 wt％， a weight percentage of the polyphenylene sulfide fiber by dry weight ranges from 0 wt％ to 20 wt％， and a weight percentage of the polyoxadiazole fiber by dry weight ranges from 0 wt％ to 20 wt％.
The electrically insulating composite material of Claim 6， wherein a weight percentage of the polyacrylonitrile fibrid by dry weight ranges from 0 wt％ to 40 wt％， preferably from 5 wt％ to 20 wt％， a weight percentage of the polysulfonamide fibrid by dry weight ranges from 0 wt％ to 40 wt％， a weight percentage of the polyphenylene sulfide fibrid by dry weight ranges from 0 wt％ to 20 wt％， and a weight percentage of the polyoxadiazole fibrid by dry weight ranges from 0 wt％ to 10 wt％.
The electrically insulating composite material according to Claim 1， wherein the electrically insulating composite material further comprises an inorganic micro-filler or an inorganic nano-filler selected from at least one of silica or alumina.
The electrically insulating composite material of Claim 12， wherein a weight percentage of the silica ranges from 0 wt％ to 20 wt％， and a weight percentage of the alumina ranges from 0 wt％ to 20 wt％， the weight percentage being based on a total weight of the electrically insulating composite material.
The electrically insulating composite material according to Claim 1， wherein the electrically insulating composite material is in the form of a paper or a pressboard.
The electrically insulating composite material according to Claim 1， wherein the first portion of the fiber and the second portion of the fibrid are mixed to form a mixture by being beaten and dispersed for a period ranging from 10 minutes to 80 minutes， preferably from 20 minutes to 40 minutes.
The electrically insulating composite material according to Claim 15， wherein the mixture is heat-pressed by applying a pressing temperature ranging from 200℃to 400℃， preferably from 250℃ to 350℃.
An electrical product comprising the electrically insulating composite material according to any of Claims 1 to 16.
The electrical product according to Claim 17， wherein the electrical product is an electrical transformer or an electrical motor.
The electrical product according to Claim 17 or 18， wherein the electrically insulating composite material is manufactured to a spacer， a barrier， a paper wrapped conductor or a press ring， for insulation.
A method of producing an electrically insulating composite material， comprising：

mixing a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber with a second portion of an aromatic polyamide fibrid in a liquid to form a mixture， wherein the pre-oxidized PAN fiber is obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber； and

heat-pressing the mixture to form sheets of the electrically insulating composite material.
The method according to Claim 20， wherein the mixing comprises beating and dispersing the first portion of the pre-oxidized PAN fiber and the second portion of the aromatic polyamide fibrid for a period ranging from 10 minutes to 80 minutes， preferably from 20 minutes to 40 minutes.
The method according to Claim 20 or 21， wherein the heat-pressing comprises applying a pressing temperature ranging from 200℃ to 400℃， preferably from 250℃ to 350℃.
An apparatus for producing an electrically insulating composite material， comprising：

a mixer configured to mix a first portion of a pre-oxidized polyacrylonitrile (PAN) fiber with a second portion of an aromatic polyamide fibrid in a liquid to form a mixture， wherein the pre-oxidized PAN fiber is obtained by a thermal process resulting in an oxidation and a stabilization of the PAN fiber； and

a sheet producer configured to heat-press the mixture to form sheets of the electrically insulating composite material.
The apparatus according to Claim 23， wherein the mixer is further configured to beat and disperse the first portion of the pre-oxidized PAN fiber and the second portion of the aromatic polyamide fibrid for a period ranging from 10 minutes to 80 minutes， preferably from 20 minutes to 40 minutes.
The apparatus according to Claim 23 or 24， wherein the sheet producer is further configured to apply a pressing temperature ranging from 200℃ to 400℃， preferably from 250℃ to 350℃.