阅读说明：本技术 压板 (Pressing plate ) 是由 C·皮托伊斯 E·蒙蒂邦 F·萨伦 L·施密特 O·吉尔兰达 T·布拉特伯格 L·瓦格博 于 2015-10-16 设计创作，主要内容包括：本发明涉及用于电功率变压器中的绝缘的纤维素基压板。压板以压板的重量的0.01％与20％之间的组合量包括聚乙烯胺(PVAm)和聚丙烯酰胺(PAM)。本发明还涉及这样的压板作为功率变压器中的绝缘的使用、包括这样的压板的功率变压器以及生产压板的方法。(The present invention relates to a cellulose-based laminate for insulation in electrical power transformers. The press plates include polyvinyl amine (PVAm) and Polyacrylamide (PAM) in a combined amount between 0.01% and 20% of the weight of the press plate. The invention also relates to the use of such a press plate as insulation in a power transformer, a power transformer comprising such a press plate and a method of producing a press plate.)

1. An insulated cellulose-based press plate for use in an electrical apparatus (100), wherein the press plate is made of cellulose pulp mixed with a quantity of cationic polyvinylamine, PVAm, and a quantity of anionic polyacrylamide, PAM;

wherein the platen comprises PVAm and PAM in a combined amount between 0.01% and 20% of the weight of the platen;

wherein the platen has at least 1g/cm³And in the form of a solid insulator for the load of the electrical apparatus; and

wherein the weight ratio of PVAm to PAM is between 1:1 and 2: 1.

2. The platen of claim 1, wherein the combined amount of PVAm and PAM in the platen is between 0.01 wt% and 5 wt%, for example between 0.02 wt% and 2 wt%, such as between 0.02 wt% and 1 wt% or between 0.03 wt% and 0.5 wt%.

3. The platen of claim 1 or 2, wherein the amount of PVAm in the platen is between 0.01 wt% and 5 wt%, for example between 0.01 wt% and 1 wt%, such as between 0.02 wt% and 0.3 wt%.

4. The platen according to any of the preceding claims, wherein the amount of PAM in the platen is between 0.01 wt% and 5 wt%, for example between 0.01 wt% and 1 wt%, such as between 0.01 wt% and 0.2 wt%.

5. The platen of any preceding claim wherein the weight ratio of PVAm to PAM is 3: 2.

6. The platen of any of the preceding claims, wherein the cellulose of the platen is from sulfite pulp.

7. The platen according to any of the preceding claims, wherein the platen is in the form of a spacer (105), an axial rod (106) or a winding table (107), such as a spacer for a winding (101) in an electrical power transformer (100).

8. The hold down of any of the preceding claims, wherein the PVAm and PAM are formed layer by layer.

9. Use of a press plate according to any of the preceding claims as an insulating material in an electrical apparatus, such as a transformer (100).

10. An electrical device (100) comprising a solid insulating material made of a press plate according to any of claims 1 to 8.

11. The electrical device of claim 10, wherein the device is a transformer (100), the transformer (100) comprising:

a transformer winding (101); and

an insulating fluid filling the transformer.

12. The transformer according to claim 11, wherein the solid insulating material is in the form of a plurality of spacers (105) integral with the winding (101).

13. The transformer according to claim 11 or 12, wherein the insulating fluid is a liquid.

14. The transformer of any of claims 11 to 13, wherein the transformer is a power transformer configured for high voltage operation.

15. A method for producing a cellulose-based press plate in the form of a solid load-bearing insulator for an electrical apparatus, the method comprising:

providing a cellulose pulp;

mixing an amount of cationic PVAm into the slurry;

mixing a quantity of anionic PAM into the slurry; and

applying pressure to the slurry comprising PVAm and PAM to form a slurry having at least 1g/cm³A platen of apparent density of (a); and

forming the platen into the form of a solid insulator for an electrical device;

wherein the combined amount of PVAm and PAM in the platen is between 0.01% and 20% of the weight of the platen; and

wherein the weight ratio of PVAm to PAM is between 1:1 and 2: 1.

16. The method of claim 15 wherein the PVAm is mixed into the slurry prior to mixing the PAM into the slurry.

Technical Field

The present disclosure relates to a cellulose-based press plate for insulation in an electrical power transformer as well as such a transformer and a method for producing the press plate.

Background

In different parts of electrical transformers, insulating materials are used to avoid flashovers and the like. The insulation material is typically cellulose based, as such paper or board materials are cheap and easy to handle while giving good insulation and having suitable mechanical, electrical and thermal properties. Examples of insulators in oil filled transformers are:

-spacers positioned between the turns/discs of the winding allowing oil to circulate between them.

-axial bars positioned between the windings and the core, or between different windings.

A cylinder positioned around the winding between the winding and its core, or between different windings.

-a winding table positioned above and below the plurality of windings, supporting them.

-an insulating coating of the conductor of the winding.

Press boards are a type of cellulose-based material, typically consisting of one or several layers (plies) of paper that when compressed using a combination of heat and pressure form a stiff, dense material within a certain range of weight.

Press plates have been used as insulating materials in power transformers for many years. The composition and manufacturing process of the press plates has remained essentially unchanged for many years. This lack of innovation has many reasons. The press plates provide good mechanical and electrical properties, mainly at a relatively cheap price. In addition, the ease of machining and versatility in the shop floor increases the value of the material.

However, there are several aspects in which platen materials that can be improved are desired. These aspects are mainly related to the mechanical properties of the material. One challenge is to improve the in-plane and out-of-plane mechanical properties of the platen without degrading its dielectric properties. The improved in-plane stiffness and strength will result in higher bending stiffness for both the individual sheets and the laminate. The out-of-plane higher stiffness helps during both the manufacturing process and the transformer lifetime.

It is important to remember that the improvement of the first does not necessarily lead to the improvement of the second and vice versa, in the sense that the in-plane and out-of-plane properties are not directly linked.

US 6,736,933 discloses a multi-ply paperboard comprising at least one ply of conventional cellulosic fibers with from about 0.1 to about 6 weight percent of an aqueous binder, and at least one ply of chemical fiber inter-crosslinked cellulosic high-volume fibers with from about 0.1 to about 6 weight percent of an aqueous binder. The aqueous binder may be starch, modified starch, polyvinyl alcohol, polyvinyl acetate, polyethylene/acrylic acid copolymer, acrylic acid polymer, polyacrylate, polyacrylamide, polyamine, guar gum, oxidized polyethylene, polyvinyl chloride/acrylic acid copolymer, acrylonitrile/butadiene/styrene copolymer, or polyacrylonitrile.

Disclosure of Invention

It is an object of the present disclosure to provide a platen having improved mechanical properties.

According to an aspect of the present invention, there is provided an insulated cellulose-based laminate for use in an electrical apparatus. The press plates include polyvinyl amine (PVAm) and Polyacrylamide (PAM) in a combined amount between 0.01% and 20% of the weight of the press plate.

According to another aspect of the invention, there is provided the use of an embodiment of the inventive press plate as an insulating material in an electrical device, such as a transformer.

According to another aspect of the present invention, there is provided an electrical apparatus comprising a solid insulating material made from an embodiment of the platen of the present invention. In some embodiments, the electrical device is an electrical transformer (e.g., a power transformer or a distribution transformer) that includes transformer windings, an insulating fluid filling the transformer, and a solid insulating material made from embodiments of the platens of the present invention.

According to another aspect of the present invention, there is provided a method for producing a cellulose substrate. The method includes providing cellulose pulp, mixing a quantity of cationic PVAm into the pulp, mixing a quantity of anionic PAM into the pulp, and applying pressure to the pulp containing PVAm and PAM to form a pressboard. The combined amount of PVAm and PAM in the press plate is between 0.01% and 20% of the weight of the press plate.

By using a combination of PVAm and PAM as additives in the press plate, an increase in-plane tensile strength and a decrease in out-of-plane compressibility is achieved. For example, cationic PVAm can bind to negatively charged cellulose, rendering the surface positive. The addition of anionic PAM made the surface slightly negative. With this layer-by-layer formation of the polyelectrolytes PVAm and PAM, the cellulose fibers become stronger and stiffer and may also repair weaker regions along the fibers. The additives may also strengthen the fiber-fiber bond, giving overall better mechanical properties.

In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, device, component, means, step, etc" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first," "second," etc. for different features/components of the disclosure is intended only to distinguish the features/components from other similar features/components, and not to impart any order or hierarchy to the features/components.

Drawings

Examples will be described by way of example with reference to the accompanying drawings, in which:

fig. 1 is a schematic cross-section of an embodiment of a transformer having an insulator made from the platens of the present invention.

Fig. 2 is a schematic flow diagram of an embodiment of the method of the present invention.

Detailed Description

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, many different forms of other embodiments are possible within the scope of this disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout.

Fig. 1 schematically illustrates an embodiment of an electrical device in the form of an electrical transformer 100. Other examples of electrical devices in which the insulating platen may be beneficially used include, for example, motors, generators, and switches. The transformer of fig. 1 is at least partially filled with oil (schematically illustrated by the wave oil-air interface indicated in the figure), for example with mineral oil or ester-based oil. It is noted that this figure is merely schematic and is provided to particularly illustrate some of the different kinds of insulators that may be made by the platen of the present invention.

Two adjacent windings 101(a & b) are shown, each comprising a coil of electrical conductor 102(a & b) surrounding a core 103(a & b), e.g. a metal core. The cores 103a and 103b are connected and fixed to each other by top and bottom yokes 104. This is thus one example arrangement of a transformer, but any other transformer arrangement may alternatively be used with the present invention, as will be appreciated by those skilled in the art.

The conductors 102 are insulated from each other and from other components of the transformer 100 by the fluid (i.e., oil in the embodiment of fig. 1) contained by the transformer. However, a solid insulator is also required to structurally hold the conductors and other components of the transformer in place in their intended locations. Today, such solid phase insulators are typically made of cellulose-based laminates or Nomex impregnated with insulating fluids^TMAnd (4) preparing. In contrast, according to the present invention, a pressboard comprising additives in the form of PVAm and PAM is used to prepare at least some of the solid insulators. The insulation may for example be in the form of spacers 105 separating the turns or discs of the winding 101 from each other, axial rods 106 separating the winding 101 from its core 103 or from another winding 101, for example, of the conductor 102, winding tables 107 separating the winding from other parts of the transformer 100, for example, forming supports or tables on which the winding, core, yoke, etc. rest, and an insulating coating (not shown) of the conductor 102 forming the winding 101. In the drawings, only a few different example insulators are shown for clarity. For example, a cylinder made of an insulating composite material surrounding the windings between the windings and their cores or between different windings (e.g., between high and low voltage windings) may be used in some embodiments. Such a barrel may provide mechanical stability to the windings when the conductor is, for example, wound on/to the barrel, and it may block a large oil gap between two windings (e.g., low and high voltage windings), which improves the overall dielectric strength of the gap between the two windings. In some embodiments, concentric cylinders around the core may be used to separate and insulate different conductor layers of the winding from each other.

Spacers 105 are positioned between the turns or disks of the conductor 103, separating the turns or disks from each other. To avoid the spacer from being compressed during manufacture or use, it is advantageous to use a substantially rigid and non-porous material for the spacer 105. A problem with cellulose pressboards is that they are compressed over time, resulting in a change in the height of the windings, which causes an axial imbalance between the windings 101. An axial imbalance between the two windings results in a higher axial short-circuit force. In addition, the spacer needs to withstand the stresses imposed thereon. The axial bars 106 are positioned along the windings 101, for example between the conductor 102 of the winding and its core 103 or between two windings 101, insulating them from each other and spaced apart. The winding rod should also be able to withstand stress so as not to break or deform. The winding table 107 should be able to support a relatively heavy winding/core assembly. As discussed herein, by using a press plate with additives according to the present invention, the compressibility as well as tensile strength are improved compared to conventional press plates.

Fig. 2 is a schematic flow diagram of an embodiment of the method of the present invention. The method is used to produce a cellulose substrate having improved properties as discussed herein. Cellulose pulp, e.g. sulfite pulp, is provided in S1. An amount of PVAm, typically a cation, is mixed S2 into the slurry. Similarly, a quantity of PAM, typically an anion, is mixed S3 into the slurry. PVAm and PAM can be mixed into the slurry simultaneously or one after the other. For example, cationic PVAm may be first mixed S2 into the slurry, possibly followed by some additional agitation, and then anionic PAM mixed S3 into the slurry, or PAM may be mixed S3 into the slurry and then PVAm mixed S2 into it. Alternatively, PVAm and PAM may be mixed with each other first and then the combined additives mixed into the slurry S2 and S3. An advantage of first mixing the cationic additive (e.g. cationic PVAm) with the pulp is that the cellulose fibres of the pulp are generally anionic, allowing the cationic additive to bind to the cellulose of the pulp, after which mixing the anionic additive (e.g. anionic PAM) with the pulp allows the anionic additive to bind to the cationic additive already bound to the cellulose. The additives PVAm and PAM may be in the form of an aqueous solution, suspension or slurry or powder when mixing the S2 and S3 into the slurry. Next, the pulp is made into a pressboard from one or more plies in a conventional manner, including applying pressure and typically heat S4 to the pulp/paper plies containing PVAm and PAM to form the pressboard. The press plates were produced with an additive amount (PVAm + PAM) between 0.01% and 20% of the weight of the press plate.

Experiments (see, e.g., the examples below) were performed to determine more appropriate amounts of additives. The amount should be large enough to obtain improved properties, but it is not necessary to use more additives than necessary. A combined amount of PVAm and PAM of between 0.01% and 20% of the weight (wt%) of the press plate is found to be suitable, preferably between 0.01 wt% and 5 wt%, for example between 0.02 wt% and 2 wt%, such as between 0.02 wt% and 1 wt% or between 0.03 wt% and 0.5 wt%. It was also found that the ratio between the PVAm and PAM additives can affect the properties of the press plates, allowing the additives to cooperate properly with each other. A weight ratio of PVAm to PAM between 1:1 and 2:1, for example about 3:2, is suitable. Typically, the amount of PVAm in the press plate is between 0.01wt and 5 wt%, for example between 0.01wt and 1 wt%, such as between 0.02wt and 0.3 wt%. Similarly, typically the amount of PAM in the press plate is between 0.01 wt% and 5 wt%, for example between 0.01 wt% and 1 wt%, such as between 0.01 wt% and 0.2 wt%. It is noted that the amounts discussed herein are amounts in the board produced, and not amounts added to the slurry prior to producing the board thereof. At least some of the additive mixed with the pulp will leave with the moisture of the pulp during production, typically during pressing. For example, the retention of the additive may be between 20 wt% and 90 wt% of the amount mixed with the slurry.

In some embodiments of the invention, the platen is of at least 1g/cm as measured in accordance with IEC 641-2 at 23 ℃ and standard atmosphere³The apparent density of (a), but in other embodiments of the invention the platen is a low density platen. A high density platen may be suitable to obtain the appropriate strength and rigidity of the platen, especially if it is a carrier, and the high density is then combined with additives to obtain improved mechanical properties, especially reduced out-of-plane compressibility (i.e., compression of the platen thickness) and improved in-plane tensile strength to handle tensile stresses along the paper sheet of the platen but not between them.

In some embodiments of the invention, the pressure plates are in the form of spacers 105, axial bars 106 or winding tables 107 or any other type of solid insulator in a transformer, such as spacers for windings 101 in an electrical power transformer 100. For example, the platen solid insulation material may be in the form of a plurality of spacers 105 integral with the windings 101.

The transformer may be a power transformer, typically filled with an electrically insulating liquid such as a mineral oil or an ester-based liquid or oil. In some embodiments, the transformer is configured for high voltage applications.

Examples of the invention

The following press plate samples with different combined amounts of PVAm and PAM in a weight ratio of 3:2 were used and compared to a reference plate without PVAm and PAM. It is noted that the following amounts of additives for the different samples are the amounts added to the slurry. Depending on the retention, the amount in the produced board may be lower. In some other experiments, retention was estimated to be about 50%, but may vary between 20% and 90%.

1. Reference to

PVAm and PAM 0.15 wt%

PVAm and PAM 0.3 wt%

PVAm and PAM 0.75 wt%

PVAm and PAM 1.5 wt%

Weight percentages are calculated based on the weight of the additive rather than the weight of the additive suspension/slurry/solution, and the dry weight of the slurry excluding the moisture in the slurry. The base slurry is a sulfite slurry without additives to ensure good dielectric properties. The PVAm and PAM were separately dosed to the aqueous solution. The cation PVAm is available from BASF under the trade name Luredur VM and has a concentration of approximately 15 wt%. Solutions of anionic Polyacrylamide (PAM) are also available from BASF under the trade name Luredur AM and have a concentration of approximately 15 wt%.

PVAm and PAM were added to the stock in a 3:2 ratio. The cation PVAm was added first and the material was stirred for 10 minutes. Followed by the addition of anionic PAM.

Tensile testing was performed according to IEC standard 60641-2. The experiments were performed at room temperature and 110 ℃ in the Machine Direction (MD) of the paper machine and in the Cross Direction (CD) of the paper machine. The data included strength and stiffness values.

The compressibility test was performed according to IEC standard 60641-2. The values of compressibility and reversible compressibility are specified by IEC standard 60641. These properties are associated with the platens used in the spacers, typically non-laminated High Density (HD) platens having a thickness ranging from 1mm to 3 mm. The practical reason for this requirement is the necessity to define the winding height at different stages of transformer production. A stiffer material in the thickness direction causes less deformation and thus reduces the need to include adjustment spacers.

Tests were performed on both dry material at room temperature and hot and dry material at 110 ℃. The option of running the compressibility test at high temperatures is intended to understand how much the increased temperature reduces the out-of-plane mechanical properties of the modified material. Some additives are known to have lower mechanical properties at high temperatures. The equipment for the compressibility test, i.e. the plate and the connection to the piston, was inserted into the oven. The temperature was monitored with two sensors. One sensor measures the air temperature. A second sensor is inserted into the stack of platens having the same test specimen height. The dummy stack is used as a temperature reference for the middle of the test stack. The test pieces tested at 110 ℃ were stored in a hot air oven prior to testing. After transfer from the hot air oven to the tensile tester, the compressibility test was started when the temperature of the replica reached the 110 ℃ mark.

Tensile test

A summary of the results for the tensile strength and modulus of elasticity values for the reference and modified platens is shown in table 1 (below).

Most test pieces showed an improvement in tensile strength at Room Temperature (RT). The improvement also remains for tests performed at 110 ℃.

Table 1: values of tensile Strength and elastic modulus at RT and 110 ℃

Compressibility test

A general summary of the results of the compressibility tests performed according to the IEC standard is given in table 2 (below). Low compressibility and high reversible compressibility are sought. The value of 10% of the combined PVAm + PAM was not available due to insufficient material.

Table 2: summary of compressibility and reversible compressibility values for test sample materials

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the disclosure, as defined by the appended claims.