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After reading this, you will have a comprehensive understanding of the material and construction of the transformer body

The main materials of the transformer body include magnetic circuit materials, circuit materials, insulating materials, structural materials, etc. 


2022/02/24
After reading this, you will have a comprehensive understanding of the material and construction of the transformer body

The main materials of the transformer body include magnetic circuit materials, circuit materials, insulating materials, structural materials, etc. The specific material uses and categories are:

1. Silicon steel sheet

In the transformer, the requirements for the performance of silicon steel are mainly:

 

①Low iron loss, which is the most important indicator of the quality of silicon steel sheets. All countries divide the grades according to the iron loss value. The lower the iron loss, the higher the grade.

 

②The magnetic induction intensity (magnetic induction) is high under the strong magnetic field, which reduces the volume and weight of the iron core of the motor and the transformer, and saves silicon steel sheets, copper wires and insulating materials.

 

③The surface is smooth, flat and uniform in thickness, which can improve the filling factor of the iron core.

 

④It has good punchability and is easy to process.

 

⑤The adhesion and weldability of the surface insulating film are good, which can prevent corrosion and improve the punching property.

 

⑥ Basically no magnetic aging.

 

Classification and grade definition of silicon steel sheet

 

Transformers usually use cold-rolled grain-oriented silicon steel sheets to ensure their no-load energy efficiency levels. Cold-rolled grain-oriented silicon steel sheet can be divided into ordinary cold-rolled grain-oriented silicon steel sheet, high magnetic permeability silicon steel sheet (or high magnetic induction silicon steel sheet), and laser scoring silicon steel sheet according to the properties and processing methods. Usually, under the alternating magnetic field (peak value) of 50Hz and 800A, the silicon steel sheet with the minimum magnetic polarization B800A=1.78T~1.85T achieved by the iron core is called ordinary silicon steel sheet, denoted as "CGO", and B800A=1.85T or more The main difference between Hi-B steel and conventional silicon steel is: the Gaussian orientation texture of Hi-B steel The degree of silicon steel is very high, that is, the alignment of silicon steel grains in the easy magnetization direction is very high. In industry, the secondary recrystallization process is used to manufacture silicon steel sheets with a silicon content of 3%. The grain orientation of Hi-B steel is very high. The average deviation from the rolling direction is 3°, while that of ordinary silicon steel sheet is 7°, so that Hi-B steel has higher magnetic permeability, usually its B800A can reach more than 1.88T, which improves the Gaussian orientation texture and Magnetic permeability reduces iron loss. Another feature of Hi-B steel is that the elastic tension of the glass film and insulating coating attached to the surface of the steel sheet is 3~5N/mm2, which is better than the 1~2 N/mm2 of ordinary oriented silicon steel sheet. The high tension layer reduces the magnetic domain width and reduces abnormal eddy current losses. Therefore, Hi-B steel has lower iron loss value than conventional grain-oriented silicon steel sheet.

 

The laser-marked silicon steel sheet is based on the Hi-B steel, through the laser beam irradiation technology, the surface is slightly strained, the magnetic axis is further refined, and the lower iron loss is achieved. Laser-marked silicon steel sheets cannot be annealed, because the effect of laser treatment will disappear if the temperature is increased.


It is usually around 1.56T, which is about 20% different from the saturation flux density of conventional silicon steel sheet 1.9T, so the design flux density of the transformer also needs to be reduced by 20%. The design flux density of amorphous alloy oil transformers is usually below 1.35T. The design magnetic density of crystalline alloy dry change is usually below 1.2T.

 

2) Amorphous aggregate core strips are sensitive to stress. After the core strips are stressed, the no-load performance is easy to deteriorate. Therefore, special attention should be paid to the structure. The core should be suspended on the support frame and the coil. Bear its own gravity, and at the same time, special attention should be paid during the assembly process, the iron core cannot be stressed, and the beating and other methods should be reduced.

 

3) Magnetostriction is about 10% larger than that of conventional silicon steel sheets, so its noise is difficult to control, which is also one of the main reasons for limiting the widespread promotion of amorphous alloy transformers. The noise of the transformer puts forward higher requirements, which are divided into sensitive areas and non-sensitive areas, and the sound level requirements are put forward in a targeted manner, which requires further reduction of the magnetic density of the core design.

 

4) The amorphous alloy strip is thin, with a thickness of only 0.03mm, so it cannot be made into a lamination form like a conventional silicon steel sheet, but can only be made into a coiled iron core. Therefore, the iron core structure of conventional transformer manufacturers cannot be processed by themselves. Outsourcing, corresponding to the rectangular section of the coiled iron core strip, the coil of the amorphous alloy transformer is usually also made into a rectangular structure;

 

5) The degree of localization is not enough. At present, it is mainly imported amorphous alloy strips from Hitachi Metals, and localization is gradually being realized. In China, Antai Technology and Qingdao Yunlu have amorphous alloy broadband (213mm, 170mm and 142mm). , and there is still a certain gap between its performance and the stability of imported strips.

 

6) The maximum strip length is limited. The maximum outer peripheral strip length of the amorphous alloy strip in the early stage is also greatly limited due to the limitation of the size of the annealing furnace. However, it has been basically solved at present, and amorphous alloys with a maximum peripheral strip length of 10m can be produced. The iron core frame can be used to manufacture 3150kVA and below amorphous alloy dry change and 10000kVA and below amorphous alloy oil change.

 

Based on the excellent energy-saving effect of amorphous alloy transformers, coupled with the promotion of national energy conservation and emission reduction and a series of policies, the market share of amorphous alloy transformers is increasing, and considering the amorphous alloy strip (currently 26.5 yuan) /kg) The price is about twice that of conventional silicon steel sheets (30Q120 or 30Q130), and the gap with copper is relatively small. Considering the quality of power grid products and bidding requirements, amorphous alloy transformers usually use copper conductors. Compared with conventional silicon steel sheets, the main cost gaps of amorphous alloy transformers are as follows:

 

1) Due to the wound core structure, the three-phase five-column structure should be adopted for the transformer core type, which can reduce the weight of the single-frame core and reduce the difficulty of assembly. The three-phase five-column structure and the three-phase three-column structure have their own advantages and disadvantages in terms of cost. , At present, most manufacturers use a three-phase five-column structure. The purchased single-frame iron core and assembly are shown in Figure 2:

2) Since the cross section of the stem is rectangular, in order to keep the insulation distance consistent, the high and low voltage coils are also made into a corresponding rectangular structure.

 

1) Since the core design magnetic density is about 25% lower than that of conventional silicon steel sheet transformers, and the lamination coefficient of its core is about 0.87, which is much lower than that of conventional silicon steel sheet transformers of 0.97, its design cross-sectional area needs to be larger than that of conventional silicon steel sheet transformers. If it is larger than 25%, the corresponding perimeter of the high and low voltage coils will also increase accordingly. At the same time, it is also necessary to consider the increase in the length of the high and low voltage coil turns. To ensure that the load loss of the coil does not change, the cross-sectional area of the wire needs to be Correspondingly, the copper content of amorphous alloy transformers is about 20% higher than that of conventional transformers.

3. Circuit Materials

Overview

 

The internal circuit of the transformer is mainly composed of windings (also known as coils). It is directly connected to the external power grid and is the core component of the transformer. The internal circuit of the transformer is usually made of wire windings. Copper wires and aluminum wires are divided into round wires, flat wires (which can be further divided into single wires, combined wires and transposed wires), foil conductors, etc. according to the cross-sectional shape of the wires. layers, and finally form the overall coil. Therefore, the main conductor materials of the transformer circuit are copper and aluminum.

 

3.1 Comparison of characteristics of copper and aluminum

 

Both copper and aluminum are metal materials with good electrical conductivity and are commonly used conductors for making transformer coils. The differences in physical properties are shown in the following table:

 

3.2 Performance comparison of copper-aluminum wires in transformer windings

 

The difference of copper-aluminum transformer is also determined by the difference of materials, which is embodied in the following aspects:

 

1) The resistivity of copper conductors is only about 60% of that of aluminum conductors. In order to achieve the same loss and temperature rise requirements, the cross-sectional area of aluminum conductors to be used is more than 60% larger than that of copper conductors, so the same capacity and the same parameters are required. The volume of the aluminum conductor transformer is usually larger than that of the copper conductor transformer, but the heat dissipation area of the transformer is also increased at this time, so the temperature rise of the oil is lower;

 

2) The density of aluminum is only about 30% of that of copper, so aluminum conductor distribution transformers are lighter than copper conductor distribution transformers;

 

3) The melting point of the aluminum conductor is much lower than that of the copper conductor, so the temperature rise limit of the short-circuit current is 250 ℃, which is lower than the 350 ℃ of the copper conductor. Large, so the volume is also larger than the copper conductor transformer;

 

4) The hardness of the aluminum conductor is low, so the surface burr is easier to eliminate, so after the transformer is made, the probability of inter-turn or inter-layer short circuit caused by the burr is reduced;

 

5) Due to the low tensile and compressive strength of aluminum conductors and poor mechanical strength, aluminum conductor transformers are not as capable of short-circuiting as copper conductor transformers. The stress limit of the conductor is 1600kg/cm2, and the bearing capacity is greatly improved;

 

6) The welding process between the aluminum conductor and the copper conductor is poor, and the welding quality of the joint is not easy to guarantee, which affects the reliability of the aluminum conductor to a certain extent.

 

7) The specific heat of the aluminum conductor is 239% of that of the copper conductor, but considering the difference in density and design electrical density between the two, the actual thermal time constant difference between the two is not as large as the specific heat difference. The short-term overload capacity of dry-type transformers has little effect.

4. Insulation material

Overview

 

The reliability and service life of a transformer, however, depend to a large extent on the insulating material used. Insulating materials, also known as dielectrics, are substances with high resistivity and low conductivity. Insulating materials can be used to isolate conductors that are charged or at different potentials, allowing current to flow in a certain direction. In transformer products, insulating materials also play the roles of heat dissipation, cooling, support, fixation, arc extinguishing, potential gradient improvement, moisture resistance, mildew resistance and conductor protection. Under the action of DC voltage, only a very small current flows through the insulating material. Its resistivity (referring to the volume resistivity in the air) is relatively high, generally 108~1020Ω·cm (the resistivity of the conductor is 10-6~10-3Ω·cm, and the resistivity of the semiconductor is 10-3~108Ω cm).

 

The insulating material has a very large resistance to DC current. Due to its high resistivity, under the action of DC voltage, it is practically non-conductive except for a very small surface leakage current; while it has capacitance to AC current. Electric current is also generally considered to be non-conductive. The higher the resistivity of the insulating material, the better its insulating properties.

 

Insulating materials are used in transformers to isolate the conductive parts from each other to the ground (zero potential). When used in various supports, they should also have good mechanical properties. In addition, insulating materials also play other roles, such as cooling, fixing, energy storage, arc extinguishing, improving potential gradient, moisture-proof, mildew-proof and protecting conductors.

 

Typically, insulating materials fall into three categories:

 

1) Gas insulating materials: Under normal temperature and pressure, general dry gases have good insulating properties, such as air, nitrogen, hydrogen, carbon dioxide, sulfur hexafluoride, etc. Among them, air and sulfur hexafluoride are used in transformers. widely;

 

2) Liquid insulating material: Liquid insulating material usually exists in the form of oil, also known as insulating oil. Such as mineral oils, vegetable oils, synthetic esters, etc.;

 

3) Solid insulating materials: such as insulating paint, insulating glue, insulating paper, insulating cardboard, corrugated cardboard, electrical plastics and films, electrical laminates (rods, tubes), cast-molded epoxy resin, electrical porcelain, rubber, mica products, etc. .

 

4.1 Insulating oil

 

The insulating oil is characterized by high electrical strength, high lightning, low freezing point, performance temperature under the action of oxygen, high temperature and strong electric field, non-toxic, non-corrosive, low viscosity, good fluidity and so on. It is widely used in electrical products such as transformers, oil switches, capacitors and cables, and plays the role of insulation, cooling, impregnation and filling. In addition, it also plays the role of arc extinguishing in oil switches and energy storage in capacitors.

 

The insulating oil plays the dual role of insulation and cooling in the transformer at the same time;

 

Insulating oils are currently generally divided into the following categories:

 

1) Mineral oil: such as transformer oil, switch oil, capacitor oil, cable oil;

 

2) Synthetic oil: such as dodecylbenzene, silicone oil, synthetic ester, etc.;

 

3) Vegetable oil;

 

4.2 Epoxy resin

 

Epoxy resin is a polymer compound. Resin is characterized by a solid, semi-solid or quasi-solid organic material with an indeterminate molecular mass (usually high), a tendency to flow when subjected to stress, usually a softening or melting range, and a solid cross-section that often presents a shell-like shape. Has the following basic characteristics:

 

1) The molecular chain is very long, each chain contains hundreds or even tens of thousands of atoms, which are covalently bonded to each other;

 

2) The long molecular chain is composed of the smallest repeating unit, that is, the chain link, and the number of chain links in a molecule is called the degree of polymerization;

 

3) The total intermolecular force of macromolecules often exceeds the chemical bond force between atoms in the molecule, so that polymer compounds have a series of characteristics: for example, there is no gaseous polymer, the polymer dissolution process is very slow, etc. If there is cross-linking between molecules, This feature is even more distinctive.

 

Epoxy resin refers to oligomers containing epoxy functional groups. Epoxy resins began to appear in 1891. After 1947, many companies in the United States and Switzerland successfully synthesized bisphenol A epoxy resins industrially. my country started production in 1956.

 

The electrical insulation properties of epoxy materials are particularly outstanding. When no filler is added, the EB of the cured product is higher than 16MV/m, the pV is higher than 1011Ω·m, the εr is 3 to 4, and the tanδ is about 0.002 under the power frequency. Therefore, 20% ring Oxygen resins are used for electrical and electronic insulation, such as epoxy impregnating paint as B-class insulating paint, impregnating small and medium motor stator windings; epoxy solvent-free paint is used for vacuum impregnation of large motor stator windings; laminates (plates, tubes, Rods) are used as slot wedges and spacers of motors, high-voltage switch operating rods; adhesives are used for bonding of high-voltage electric porcelain bushings; castables are used for disc isolation in sulfur hexafluoride fully enclosed combined electrical appliances (GIS). Components such as insulators, transformers and high-voltage ceramic capacitors. At present, the brand names of epoxy resins or modified epoxy resins produced in China are still not uniform for the time being. The names of different epoxy resin manufacturers around the world are also different and need to be identified by trademark.

 

Epoxy resins are just oligomers and can only be used after curing. The curing agent can react with the epoxy resin to cross-link the resin molecules from a linear structure into a bulk structure. Promoters/catalysts can reduce the activation energy of the reaction and can promote/adjust the gel reaction process of the castable. The curing agent uses the active hydrogen contained in it to carry out a ring-opening addition reaction with the active epoxy group in the resin to achieve curing. Active hydrogen is -NH2, -NH-, -COOH, -OH and -SH in the curing agent or accelerator. in the hydrogen. Commonly used curing agents are amines and acid anhydrides. Some curing agents require accelerators/catalysts, some require high temperature conditions, and some can react violently at low temperatures. Different curing agents will also lead to great differences in the properties of cured products, which have a significant impact on the final properties of the product. Therefore, it is very important to design and select curing agent in epoxy resin formulation system.

 

Epoxy insulation is used in dry-type transformers and is a new development in the past 40 years. The design life of the transformer coil is required to reach 30 years, and the heat resistance grade must reach the F grade. It is difficult for general materials to meet the requirements.

 

To this end, it is necessary to design, optimize, test and verify the materials used and their formulation systems and processes in order to obtain the desired effect. In the resin-insulated dry-type transformer, the epoxy resin system is formed by casting or dipping, and then thermally cured to form coil insulation (ie, longitudinal insulation). During the entire operation of the dry-type transformer, the epoxy resin insulation must also ensure the electrical insulation of the coil and mechanical strength, and dissipate the heat inside the coil through thermal conduction.

 

Its biggest weakness is the irreversibility and irreparability of resin insulation defects and damage (generally defects in the manufacturing process and damage in the operation process). Therefore, avoiding cracking of solid insulation, avoiding casting defects, and avoiding partial discharge (ie, partial discharge) are particularly important, and become the key to solid insulation manufacturing technology, and are the focus of competition among manufacturers.

 

Due to the high temperature rise caused by the loss during the operation of the transformer, the resin insulation works at high temperature for a long time (such as the F-class transformer, the maximum designed working temperature is generally around 140 ℃), and the transformer may be in a high temperature before commissioning and during maintenance. Low temperature (such as -30 ℃), and the transformer will be subject to the huge electric shock of lightning high-voltage shock or short circuit at any time. Resin-insulated coils should be able to adapt to these changes, and be able to withstand or withstand short-circuit electrodynamic shocks at extreme high and low temperatures. Therefore, extremely stringent requirements are placed on the thermal, mechanical and electrical properties of epoxy insulation systems.

 

There are currently two types of insulating material systems for resin cast transformers, one is "pure resin casting + high filling rate glass fiber reinforcement", and the other is "resin quartz powder casting + prepreg glass mesh local reinforcement".

 

The insulation system (that is, the conventional insulation structure) covers a wider field than the insulation material system. It refers to the insulation of electrical equipment (or its independent components) as a whole, including not only insulation materials and their combinations, but also insulation and conductors. Or the relationship between magnets, the relationship with the electric field, the relationship between insulation and the surrounding environment (gas or liquid and its conditions, surface contamination, heat dissipation conditions, mechanical force or radiation, etc.), etc., and its adaptability to the operating parameters of the power system It's insulation. The air flow and heat dissipation in the dry-type transformer, the insulation stress, etc., are all within the scope of the insulation system to be considered.

 

4.3 Insulation paper

 

Plant fiber paper is divided into wood fiber, cotton fiber and hemp fiber, of which the most commonly used is pure sulfate wood pulp fiber paper. Fir and Korean pine and other woods are mainly composed of cellulose, which is a natural polymer compound. The manufacturing method of insulating paper adopts a chemical method, such as the sulfate method. In this method, the main component of the cooking liquid is sodium sulfide (Na2S). The sodium sulfide is hydrolyzed to generate sodium hydrogen sulfide and sodium hydroxide. The cellulose reacts and dissolves it in the lye. The cooking liquid is relatively mild, so the molecular weight of the cellulose decreases very little. The commonly used plant cellulose insulating papers in transformers are: power cable paper, high-voltage cable paper and transformer inter-turn insulating paper.

 

1) Cable paper: The cable paper is made of kraft pulp, the grades are DL08, DL12, DL17, the thicknesses are 0.08mm, 0.12mm and 0.17mm, respectively, and are supplied in rolls. After the cable paper is impregnated with transformer oil, its mechanical strength and The electrical strength will be significantly improved. For example, the electrical strength of the power cable paper in the air is 6~9×103kV/m, and after drying and immersing the transformer oil, the electrical strength reaches 70~90×103kV/m. It has sufficient thermal stability and is usually used as winding insulation and interlayer insulation. Cable paper also includes high-voltage cable paper, low-voltage cable paper, high-density cable paper and insulating crepe paper. High-voltage cable paper is suitable for 110-330kV transformers and transformers, with low dielectric loss tangent; low-voltage cable paper is used for insulation of power cables and transformers or other electrical products of 35kV and below; insulating crepe paper is made of electrical insulating paper. It is made of wrinkle processing, and there are wrinkles along its transverse direction, which are pulled apart when stretched. It is often used for wrapping insulation of oil-immersed transformers, such as the insulation wrapping of coil outlets, leads and electrostatic shielding devices; high-density cable paper is also insulating A kind of crepe paper, the electrical strength is 100% to 150% higher than the general crepe paper, the mechanical strength is 50% higher, the electrical strength is high, the oil resistance is good, the elasticity is good, and it is easy to stretch. It can be used as a lead instead of varnished tape. and insulation of wire connections and bends.

 

2) Telephone paper: Telephone paper is also made of sulfate pulp, which is commonly used in telephone cables. It has poor mechanical strength and is generally used as turn insulation, layer insulation or cover insulation of conductors.

 

3) Capacitor paper: Capacitor paper is divided into Class A and Class B according to the requirements of use. Class A capacitor paper is used for metallized paper dielectric capacitors in the electronic industry. Class B is mainly used as an interpole dielectric for power capacitors. Capacitor paper is characterized by high tightness and thin thickness. Generally, current transformers often use capacitor paper, and transformers are rarely used.

 

4) Coiled insulating paper: The coiled insulating paper is used as the backing paper of the sizing paper, and the sizing paper is used to wind the insulating cylinder (tube) and capacitive sleeve, which is characterized in that the water absorption height is higher than the cable paper and lower than the impregnation Paper. The glued paper is divided into single-sided or double-sided glued (phenolic or epoxy resin), which is cured at low temperature. When the glued paper is used to make a paper tube or press a laminate, the glue is finally cured when heated and pressed. , The roll is generally single-sided tape, and the pressed tape is double-sided tape. In addition, there is also diamond glued paper (mesh glued paper), which is used for the interlayer insulation of oil-immersed foil winding coils. After curing, it ensures the adhesion between insulations and between insulation and foil, enhancing Strength and good oil permeability.

 

Conventional transformer insulating paper is mostly used for cable paper, crepe paper and rhombus dispensing paper, which are used in transformers as inter-turn insulation, inter-layer insulation, lead binding, etc. Usually, the prices of various types of insulating paper are not different. It will be too big, about 20 yuan/kg.

 

4.4 Electrical composite materials

 

Electrical thin films and electrical composite materials have excellent dielectric properties and belong to thin sheet insulating materials. Electrical films include polyester film and polyimide film, which can also be used as wire insulation and interlayer insulation in transformers. Electrical composite material is a composite product made of one side or two sides of the film bonded fiber material, which can be used as interlayer insulation in transformers, especially in dry-transformed foil-wound coils, and low-voltage coils are usually made of composite materials. After impregnation with resin, it is used as interlayer insulation. Commonly used composite materials are DMD, GHG and so on.

 

The full name of DMD is polyester film polyester fiber non-woven soft composite material, which is divided into pre-impregnated resin DMD and non-pre-impregnated DMD. D) The fabricated three-layer soft composite. DMD has excellent electrical insulation, heat resistance and mechanical strength as well as excellent impregnation properties. Non-prepreg DMD can be used as interlayer insulation for oil-immersed transformers, and prepreg DMD can be used as interlayer insulation for low-voltage foil wound coils in Class F dry-type transformers. Its specific performance indicators are shown in the following table:

 

The full name of GHG is polyimide film pre-impregnated H-grade resin glass fiber soft composite material. It is a three-layer soft composite material made of glass fiber cloth (G) pasted on both sides of a polyimide film (H). . Compared with DMD, it has better heat resistance and can be used for interlayer insulation of low-voltage foil wound coils of H-class insulation dry-type transformers.

 

The full name of NHN is polyimide film polyaramid fiber paper soft composite material. NHN is currently the most high-grade thin-layer insulating material, with excellent heat resistance, good dielectric properties, small water absorption and excellent moisture resistance. It belongs to class H insulating material and can be used for interlayer insulation of class H dry-type transformers. Its specific performance parameters are shown in the following table:


4.5 Insulating cardboard

 

Insulating paperboard is made of pure kraft wood pulp papermaking and can be used for oil gap spacers, oil gap stays, separators, cardboard tubes, corrugated paper, iron yoke insulation, clip insulation and end insulation winding pressure plates for pie windings etc., its common thickness is 1.0mm, 1.5mm, 2mm, 3mm, 4mm, 6mm, insulating cardboard is divided into low-density cardboard, medium-density cardboard and high-density cardboard according to density, low-density paper is usually called T3 soft cardboard, the density is in Between 0.75g/cm3 and 0.9g/cm3, the strength is low, and it is often used for bending parts or making stretch parts after wetting, such as forming angle rings, annular parts and soft paper tubes. Low-density cardboard has high oil absorption rate, good formability, but poor mechanical properties; medium-density cardboard is usually called T1 cardboard, with a density between 0.95g/cm3 and 1.15g/cm3, used as a stay pad, etc.; high-density cardboard Cardboard is usually called T4 cardboard, with a density of 1.15g/cm3 to 1.3g/cm3, and is used as an insulating cardboard tube, insulating pressure plate and end ring. In the oil-board spacer structure composed of high-voltage coil multi-layer paper tubes, corrugated cardboard can also be used instead of cardboard struts to form oil gaps, which can save materials on the basis of ensuring insulation performance.

 

4.6 Polypropylene film

 

The polypropylene film is made of polypropylene resin (PP) extruded into a thick sheet and stretched in a direction. 0.92g/cm3. 2) It has good electrical properties and chemical stability, the relative dielectric coefficient is 2 to 2.2, and the breakdown pressure is greater than 150MV/m; 3) It has good mechanical properties, and its tensile strength is greater than 100MPa ; 4) It can be used for a long time at 125 ℃ and belongs to E-class insulation; 5) It has hydrophobicity and strong anti-water absorption ability, and can be used for wire insulation of oil-immersed transformers.

 

4.7 Other insulating materials

 

Transformer oil and insulating paper are the main insulating materials for oil-immersed transformer coils. Resin, insulating paper, and composite materials are the main insulating materials for dry-type transformer coils. In addition to these materials, the following insulating materials are also commonly used in transformers: (Laminated wood, laminate, insulating paint, insulating glue, cotton tape, compression tape, no weft tape, etc.

 

1) Laminate: Electrical laminate is a layered insulating material made of paper, cloth and wooden veneer as the substrate, dipped (or coated) with different adhesives, and hot pressed (or rolled). . According to the requirements of use, the laminated products can be made into products with excellent electrical and mechanical properties, heat resistance, oil resistance, mildew resistance, arc resistance and corona resistance. Laminate products mainly include laminates, laminated wood, laminated tubes, rods, capacitor sleeve cores and other special profiles. The properties of laminates depend on the nature of the substrate and adhesive and the process by which they are formed. According to different raw materials and adhesives, laminates are divided into insulating laminates (paperboard, used for oil change), phenolic laminated paperboard (commonly known as bakelite, paperboard impregnated with phenolic resin, used for oil change), phenolic laminated cloth board (cotton cloth impregnated with phenolic resin, commonly used for oil change), epoxy glass cloth board (glass fiber cloth with epoxy resin as adhesive, can be used for F grade dry change or oil change), modified diphenyl ether glass cloth board (Glass fiber cloth uses modified diphenyl ether resin as adhesive, which can be used for H-level dry change), bismaleimide glass cloth board (glass fiber cloth uses bismaleimide resin as adhesive, Can be used for H-level dry change). Laminates usually have good mechanical strength and insulation properties, and are often used as core clip insulation, external supports, etc. in transformers.

 

2) Insulation cylinder (tube): The insulation cylinder in the transformer is mainly used between the inner and outer coils, between the coil and the iron core, for the coil lining the skeleton, and the wire is directly wound on the insulation cylinder. At the same time, the insulation cylinder can also be used for the main Insulation, increase the number of oil gaps in the main insulation, and strengthen the insulation. According to the different materials, the insulating tube is generally divided into phenolic paper tube (commonly used for oil change), epoxy glass cloth tube (commonly used for oil change or F grade dry change), modified diphenyl ether glass cloth tube (commonly used for oil change) H-level dry change), glass fiber reinforced plastic cylinder (commonly used in H-level dry change), bismaleimide glass cloth cylinder (commonly used in H-level dry change), etc.

 

3) Laminated wood: The electrical laminated wood is made of high-quality hardwoods, such as birch, beech, etc. After being cooked twice at 70°C to 80°C, the lignin acid and grease of the wood itself are removed, and then cut into individual pieces of 1 to 3 mm. After drying, it is coated with resin adhesive. After pre-curing, it is repeatedly assembled and stacked. It has good insulating strength and mechanical strength. It can be used as spacer, angle ring, etc. in oil change. .

 

1) Binding tapes: Transformer binding tapes include cotton tapes, compression tapes, mesh semi-dry non-weft tapes, glass tapes, polyester tapes, etc., which are used for binding and tightening iron cores and coils.

5. Material structure and accessories

In the transformer, there are also structural materials and accessories. The structural materials mainly play the functions of transformer support, magnetic circuit, circuit reinforcement, transformer insulating liquid packaging, etc., including clips, oil tanks, radiators, oil conservators, etc. The main materials are For Q235 steel, non-magnetic steel is often used for the outlet bushing of the fuel tank cover to reduce eddy currents. In addition, non-magnetic steel or high-grade steel is sometimes used inside the transformer body.

 

Transformer accessories mainly have performance monitoring and protection functions. Dry transformers include thermostats, fans, transformers, etc., and oil transformers include gas relays, thermostats, pressure relief valves, tap switches, etc. Some accessories are required by customers. propose.

 

Source: Transformer Circle


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