Materials used in winding and insulation production - production of windings and insulation of power transformers. Winding wire for transformers. Proper winding of the transformer with your own hands Lacquered copper winding wire

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Electrical maintenance management 1

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The PROVODNIK company carries out sale of the enameled (winding) wire. We offer high quality wiring products in any volume at the most attractive prices. We always have a high-quality level of service and an individual approach to each client.

Enamelled (winding) wire is designed for windings of electrical machines, devices, as well as measuring, regulating and other devices, ignition coils, primers, low-voltage dry transformers. It is also intended for relays, solenoids, electronic products, micromotors, small and medium power motors, generators, power motors for general use, motors for household electrical appliances and power tools, communication equipment, as well as compressors for refrigeration and air conditioners operating in the environment of freons (freons). ). The exceptional mechanical strength of the insulation allows the use of enamelled (winding) wire for automatic winding. Depending on the temperature index and types of insulation, wires are used for different environmental conditions in the manufacture of explosion-proof equipment for the chemical, gas, oil refining and coal industries.

Wires are manufactured with the following temperature indices:

• temperature index 105 (grades PEL, PEV-1, PEV-2, HDPE, PEVA, PEVAT, PEM-1, PEM-2, PEMP, etc.);
• temperature index 120 (grades PEVTL-1, PEVTL-2, PEVTL, etc.);
• temperature index 130 (grades PETV-1, PETV-2, PETV-2-TS, PETVP, PETVM, etc.);
• temperature index 155 (brands PET-155, PETM, etc.);
• temperature index 180 (brands PNET-imide, etc.);
• temperature index 200 (PET-200, PETP-200, etc.).

Wires are made of aluminum, copper and nickel-plated copper. Nickel-plated copper wire is used to make heat-resistant wires to improve oxidation resistance.

To insulate winding wires with enamel insulation, electrical insulating varnishes are used, which are a solution of high-molecular film-forming compounds in organic volatile liquids. When the lacquer coating on the wire is heated, the molecular weight of the film-forming compounds increases, and the solvent evaporates, resulting in the formation of a hard enamel film on the wire. Its flexibility is ensured by the presence of liquids in the film that do not evaporate when heated and act as plasticizers.

Two-layer enamel wire insulation consists of two different varnishes applied sequentially to the wire. On wires intended for bonding when heated, an adhesive layer of polyvinyl acetate varnish is applied over the main insulation based on polyvinyl acetate or polyester varnish. This varnish at a temperature of 120 - 150 ° C softens, and when the temperature drops, it passes into a solid state. To protect the wire from mechanical damage, coatings based on polyamides (lacquer KL-1) are used - a solution of polycaprolactam in tricresol.

The enamelled (winding) wire is made of a copper conductor (round or rectangular), and it is insulated with an electrical insulating varnish based on modified polyester resins.

Almost the main question for all radio amateurs How can a transformer be wound? We already know the simplest methods for calculating transformers (who has forgotten, you can look here), but the most important thing is where to get wire? Yes, and exactly what kind of wire is needed to wind the transformer?

Where did, for example, wire marks PELSHO, PELBO and others that were sold in Soviet times in sets and reels? The first of the above wires is required for winding loop coils for low-frequency ranges, chokes, transformers on ferrite rings, etc. The second is necessary for winding windings powerful power transformers.
After all, the advantage of such wires over conventional ones (lacquered) is great.
First of all, this is the winding pitch created by the braiding of the wire. In powerful network transformers, the voltage difference in the windings between adjacent conductors is 1 V or more, thin varnish insulation, when heated and vibrated with the network frequency, is gradually erased from friction between vibrating turns and crumbles. As a result, there are interturn short circuits.

For illustration, I will give simple calculation. Let's take transformer iron with core section area S=10 cm2. Based on a simple estimate, Pr=S2, we determine that the overall power of the future transformer will be approximately 100 watts. Number of turns per 1 V:
w1 \u003d 50 / S \u003d 50 / 10 \u003d 5 (vit. / V),
Accordingly, the interturn voltage:
U1=1/5=0.2(V)
If the transformer iron is with a cross-sectional area S=50 cm2, the overall power of the transformer in this case is Pg=2500 W, and w1=50/50=1 (vit./V), which is equal to the interturn voltage in the windings. With a further increase in the overall power, the turn-to-turn voltage increases, the risk of insulation breakdown increases, and the reliability of the transformer naturally decreases.
How to get out of this situation? It should be remembered that the wires are not only winding. To wind the transformer, you can use a mounting wire in fluoroplastic insulation (MGTF) with a cross section corresponding to the required current. Since in such wires it is customary to indicate not the diameter, but the cross section (along the core), then you should use the conversion formula
d=2 (Sp/3.14)^0.5
where Sp - wire section, mm2; d - wire diameter, mm. For example, the MGTF-0.35 wire has d-0.66 mm. The wire diameter, depending on the required current I (A), is determined by the formula:
d = 0.8 I0.5.
Then the current in the winding wire:
I \u003d (d / 0.8) ^ 2 \u003d 0.68 (A)
The excellent quality of the insulation of MGTF wires makes it possible to do without winding interlayer gaskets, and its heat resistance allows winding transformers operating at elevated temperatures (fluoroplastic insulation does not melt or char).

Sometimes for balanced circuits it is required to wind a transformer with strictly identical windings.
This can be done by taking a flat cable as winding wires, for example, used in computer connecting cables. Having separated the required number of conductors from the cable, they wind the winding with them, which is then used as several identical ones, isolated from each other. The insulation of the flat cable is sufficiently thermally stable.

To obtain high currents, the secondary windings of power supply transformers are wound with sufficiently thick wires and tires. This work, it must be said, requires not only material (monetary), but also physical costs, since it is necessary to bend the elastic copper bus (wire) to tightness, trying to lay it coil to coil.

As an alternative to winding wire, I suggest using an acoustic cord, which is usuallyconnect the amplifier to the speakers. The acoustic cord has a large cross section of the core and. being double, ensures that the half-windings are identical for a full-wave rectifier with a mid-point. Little attention is paid to the identity of these half-windings, and this entails an increase in the background to which modern high-quality equipment is so sensitive.

The identity of the windings can be ensured in another way, for example, by winding them microphone cord(with a stereo cord we get three windings). In this way it is possible to wind the winding(s) with an electrostatic screen. To do this, the shielding braid of the microphone cord is connected (on one side) to the common wire.

Coaxial cable, due to the large difference in the cross sections of the inner core and braid, is not very suitable for symmetrical windings, but can be used as a winding wire when the screen and the inner core are interconnected. The inner core of the cable can also be used for measuring purposes.

In all cases, one should not forget about the thermal stability of the wire insulation. The increased thickness of the wire insulation relative to varnish, on the one hand, reduces the number of winding turns that can be placed in the window of the transformer core, on the other hand, it makes the use of interlayer insulation (up to interwinding insulation) unnecessary, which speeds up the manufacture of the transformer, and with heat-resistant wire insulation it increases reliability transformers.

V. BESEDIN, Tyumen.

Currently, in the windings of transformers and reactors, types of winding wires known for more than a decade are mainly used:

Growing requirements for the reliability of transformers and reactors, their technical and economic characteristics, increasing competition from foreign companies dictate new development conditions for wire manufacturers. New modifications of well-known types of wires appear on the market, the development of the production of wires not previously manufactured in Russia begins, and the requirements for the quality of winding wires increase.

Wires with paper insulation are used in oil transformers. The simplest construction of two elements: a conductor and paper insulation. Both copper and aluminum are used as conductors, insulation can be made of cable, high density transformer or micro-crepe paper. High density paper insulation has more dielectric properties. Wires with micro-creped paper insulation have higher elasticity, their use is dictated mainly by the appearance of new technological winding equipment at transformer plants. In recent years, there has been a tendency to expand the size range of used conductors and insulation thicknesses.

Today, paper-insulated wires, including subdivided wires, are the most used types of wires in the manufacture of transformers, their share is more than 50%.

Subdivided wires with paper insulation.

To reduce losses in the winding, the wire core is divided into 2.3 or more elementary conductors, each of which is isolated separately and a common paper insulation is applied on top. Wires are widely used in the windings of transformers and high power reactors. Until now, Russian factories could offer subdivided wires with the number of conductors no more than 3, but with the expected commissioning of new equipment in 2009 at CJSC Moskabel-Electrozavod, the number of conductors can be increased to 6.

Recently, the design of a subdivided wire with enamel insulation of elementary conductors has been developed. The use of oil-resistant enamel instead of paper on elementary conductors is justified by the following factors:

Wires with aramid paper.

Insulation made of synthetic aramid paper "Nomex". This type of wire is widely used for dry-type transformers and oil-filled transformers with combined insulation. The main advantage of replacing ordinary paper insulation with aramid one is the increase in the heat resistance class of wires up to 200°C.

Fiberglass insulated wires.

The wire insulation consists of glass strands impregnated with epoxy, polyester or silicone varnishes. The heat resistance class of wires is from 155 to 200. The advantage of this type of insulation is its high resistance to mechanical stress and good compatibility with impregnating electrical insulating varnishes. Wires are used in the windings of dry transformers of the monolith system and reactors.

Rectangular wires with film insulation.

Today, polyethylene terephthalate films (lavsan, mylar) with a heat resistance class of 130-155°C, polyimide-fluoroplastic (PMF) with a heat resistance class of 200°C are used as insulation.

The combination of polyimide and fluoroplastic makes it possible to create thin, heat-resistant insulation with a high dielectric strength. The presence of fluoroplast allows the insulation to be sintered during the manufacture of the wire.

These wires are mainly used in the manufacture of windings of traction motors, where high dielectric strength of insulation is required under fairly severe temperature conditions. In recent years, Russian enterprises have developed designs of dry-type transformers, where wire with PMF insulation has been successfully used. This wire is used in those conditions where it is impossible to use any other. There is a construction of a transposed wire with elementary conductors with PMF insulation.

The advantages of using PMF films are:

In addition to the usual PMF insulation, corona-resistant PMF films, promoted on the Russian market by Du Pont, are also used. Insulation from this film has the following unique features:

Wires with a corona-resistant PMF film have found application in the manufacture of high-voltage dry-type transformers with forced ventilation. The first 16 MVA transformers were tested in accordance with IEC 60726 back in 2005 and are currently in operation.

Enamel wires.

Widely used in both dry and oil transformers of small and medium power. The core for the wire can be either copper or aluminum. The main types of enamel insulation are presented in the table:

The advantage of enameled wires is good electrical strength with a small thickness of insulation. The breakdown voltage of the insulation is more than 1 kV with a double insulation thickness of 0.08-0.16 mm.

For oil transformers, wires with TI 130-155 are used, for windings of dry transformers, wires with TI above 155 are used. Wires are made in the range of sections from 5 to 60 sq. mm.

Flexible wires of round section.

The wire is based on a copper or aluminum core, twisted from 7, 19 or 37 conductors, depending on the section. The total cross section of the wire can be 25-120mm 2 . The insulation material can be synthetic tapes made of lavsan, cable paper, aramid paper or polymide-fluoroplastic film. Wires with PMF insulation are used in unpackaged dry reactors. Reliability is ensured by film sintering and high electrical characteristics of polyimide. These wires are widely used in dry reactors due to their ease of use and the lightness of aluminum, but they cannot be used in compensating and filter reactors due to large additional losses from eddy currents. In this case, a wire with a core consisting of enameled elementary conductors is used.

Transposed wires.

The wire consists of a large number of enameled rectangular conductors arranged in 2 rows and continuously transposed, i.e. the position of each conductor along the wire cross section is continuously changing. The design of the transposed wire is similar to the design of the Robel rod, well known to manufacturers of electrical machines (Ludwig Robel, the executive director of the Air Force, invented in 1912 a special transposition that can significantly reduce losses in conductors by reducing eddy and circulating currents). For the first time, the manufacture of transposed wires was organized at the end of the 50s of the XX century at the factories of British Insulated Callenders Cables Ltd (BICC) (Great Britain).

Due to the unique arrangement of elementary conductors, the following advantages arise in the manufacture of a winding from transposed wires:

According to studies by foreign companies, the savings in various materials in the manufacture of transformers with windings from transposed wires range from 9.4% to 36.4%.

Along with the advantages, this design has one drawback - the weak values ​​of the electrodynamic strength of the winding during short circuit compared to the design of the winding from a conventional rectangular wire. This disadvantage is successfully eliminated by the use of an additional adhesive epoxy coating in the design of the elementary conductor. Advantages of using epoxy coating:

As a modification, it is possible to use a polyamideimide coating in the insulation of elementary conductors for a heat resistance class of 200 º C for dry transformers.

The range of materials used as top - main insulation is quite wide: insulation can be made both from ordinary electrical insulating paper, and from continuous and perforated tapes of aramid paper, polyester threads in the form of a grid or any other tape materials. Paper insulation is the most widely used. However, when organizing the production of transposed wires, CJSC Moskabel-Electrozavod faced the problem of the lack of domestic papers of sufficient quality for the manufacture of wires of this type. One of the main requirements for wires is the accuracy of observance of overall dimensions. Papers produced in accordance with Russian GOSTs and TUs have insufficient requirements for thickness tolerances and an insufficient margin of mechanical strength, which increases the tolerances for wire size by several millimeters. In this regard, it is necessary to use imported papers made according to international standards.

So far, there has been no production of transposed wires in Russia. In August 2009, it is planned to start production of transposed wires at the ZAO Moskabel-Elektrozavod enterprise in Moscow.

Modern requirements for quality control in the technological process of wire production.

The winding wire production technology and the quality of the materials used largely determine the reliability of transformers or reactors. The manufacturing technology of the wires themselves becomes much more complicated, special solutions are needed, the use of additional equipment to ultimately provide an integrated approach to the issue of the quality of the winding wire. On the example of the technological chain of manufacturing a transposed wire, as the most complex product, the implementation of an integrated approach to the quality of winding wires is shown below. It should be noted that most of the solutions described are valid for all types of winding wires.

1. Copper raw materials enter the plant in the form of electrical cathodes. For the production of winding wires, cathodes should be used, exclusively of grades MO and M00. All incoming raw materials undergo input control with the determination of the chemical composition by spectral analysis. The use of high-quality raw materials in the future is guaranteed to ensure that the electrical resistivity of the wire is not higher than 0.01724 Ohm mm 2 /m. Statistical analysis of electrical resistance confirms the correct choice of suppliers.

2. The production of wire rod is carried out on the continuous casting and rolling line of Southwire » , which is the developer of the wire rod production technology of the same name. The use of this technology makes it possible to obtain clarified wire rod with a fairly good surface quality, which undoubtedly affects the quality during subsequent technological operations. During rolling, 100% of the wire rod is subjected to continuous surface quality control using the “Defectomat” device, in which the wire rod is tested by an electromagnetic field. Guaranteed absence of wire rod defects allows to exclude their further occurrence on the wire and in the wire. After manufacturing, the copper rod is also tested for chemical composition and electrical resistivity, as well as for compliance with mechanical parameters.

3. The processing of copper rod into a rectangular wire for transposed wires is carried out by rolling. It is generally accepted that the best result in the manufacture of rectangular wire is achieved on a rolling mill. In the process chain for the production of transposed wires at CJSC Moskabel-Electrozavod, a five-stand rolling mill from Buhler GmbH is used, which is currently the only rolling mill at Russian cable plants.

The correctness of the choice in favor of the technological process of wire was confirmed from the moment of production of the first batches of wire. The fact is that the traditionally used technology of wire drawing does not allow obtaining a stable smooth surface of the wire, in the process of drawing the wire slides over the draw plate, the forces in the metal that occur when drawing through the die are very high. As a result, the possibility of scratches and scratches on the surface of the wire is not excluded at the output. Rolling allows you to process metal in a more gentle mode. The tests carried out to determine the surface cleanliness gave the following results: - surface roughness of the wire obtained by drawing cf. arithmetic value Ra=1.2 µm; - surface roughness of the wire obtained by rolling cf. arithmetic value Ra=0.11 µm.

Surface cleanliness is very important for applying a uniform layer of enamel on the wire - any microscopic unevenness on the wire leads to a slight decrease or increase in the thickness of the coating within 0.01-0.02 mm, and if this does not matter in the manufacture of ordinary wire, everything is in within tolerances with a large margin, then in the manufacture of a transposed wire, where a large number of conductors are added to a column, this becomes very important, because. deviations in hundredths of a millimeter add up to a significant change in the size of the wire as a whole.

View of the monitor with a graph of continuous control of geometric dimensions, the left vertical axis is the thickness deviation (µm), the right vertical axis is the width deviation (µm).

In addition, the rolling technology itself will make it possible to obtain wire with deviations from the nominal value that are much smaller than during drawing. To ensure such accuracy, a laser measuring device is installed on the rolling mill, which has feedback in the control of the machine. Two graphs of the diagram indicate the discretely measured value of the geometric dimensions of the wire in width and thickness, the measured deviations from the nominal values ​​do not exceed ±0.005 mm in thickness and ±0.015 mm in width, with wire dimensions of 1.50 x 8.00 mm. Today, this technology is used in most industries in the world engaged in the manufacture of transposed or other types of winding wires.

4. The application of enamel insulation is carried out on a modern enameling unit, which ensures accurate and uniform application of enamel, computer control of temperature and air exchange processes in the furnace, which are responsible for the polymerization of the insulation. The application of enamel is combined with the operation of annealing the copper wire.

In order to guarantee the quality of the enameled conductors, continuous insulation voltage control is used, roller electrodes are built into the line, and a computerized system allows the collection of statistical data on the quality of the wire produced. This device allows you to fix in the "online" mode insulation sections with reduced electrical resistance, while electrical breakdown of the insulation does not occur.

To control the geometry of the wire, laser measuring instruments with a computerized system are used, which measure the geometric dimensions of the wire online and, if necessary, allow the operator to make timely adjustments by increasing or decreasing the thickness of the enamel coating.

Any continuous control does not preclude acceptance or periodic testing, but allows you to control and intervene in the process in a timely manner if necessary.

5. Transposition is the main technological operation in the manufacture of a transposed wire. The conductors are bent and laid in accordance with the transposition pattern. Due to the fact that in the process of transposition, quite large forces act on elementary conductors and the conductors are tightly pressed against each other, a high-quality transposed wire can only be obtained from a workpiece that has a huge margin of mechanical and electrical strength, for which special manufacturing technologies and quality control are used, described in paragraphs 1-4. After the transposition on the same line, paper insulation is simultaneously applied to the transposed wire.

To prevent inter-conductor short circuits, the transposing machine has a built-in system for continuous monitoring of low voltage short circuits. Not a single section of the wire on which an inter-conductor short circuit is detected should go to the consumer. The final control of the absence of inter-conductor short circuits is carried out after the manufacture of the wire and winding on the shipping container, and this test is already carried out with an increased voltage of 300 V.

Summarizing the above, we can formulate the main modern requirements that significantly affect the quality and reliability of a transformer or reactor.

The following types of continuous monitoring are carried out:

Most of the above control processes have been successfully introduced into the winding wire production technology at Moskabel-Vobmotochnye Provods LLC, all the experience gained will be used in the production of transposed wires at Moskabel-Electrozavod CJSC.

Literature:

1. Production of transposed wires for windings of powerful transformers. I.B. Peshkov, Yu.N. Hudov, "Cable Technology", issue 7, 1973.

2. Use of Continuously Transposed Cables (CTC) in transformers. R. Hegde, F. Hofmann, G. Prasad, IEEMA Journal, July 2007.

3. Application of CTC in Transformer Industry by D.V. Narke, S.D. Paliwal, R.K. Talwar - 1972 ICC Proceeding Seminar Paper

4. Perspective requirements for winding wires for transformers and reactors. A.N. Panibratets, A.I. Fedotov, "Cables and wires", No. 7, 2008.

and many other mechanisms.

The winding wire, unlike other types of conductors, has the diameter of the conductive core as the main parameter, and not its cross section. There is a very thin wire for windings, and having a negligible layer of insulation. The thinnest winding conductors are made according to a special production technology for especially thin conductors and electrical insulation materials.

For a long time, winding wires were made exclusively of copper. Today, aluminum and other alloys with significant resistance are often used for them. Aluminum saves expensive and scarce copper.

Classification

Winding wires are classified according to the material of insulation, according to the shape of the section and the material of the core.

Insulation material

The winding wire is manufactured with the following types of insulation:

• Fibrous.
• Enamel.
• Combined.

fibrous

Wires with fibrous insulation have increased mechanical strength. The thickness of the fibrous insulation is quite large, and can reach up to 0.4 mm per side. Chemical resistance and moisture resistance of such wires is low.

Fibrous insulation of wires used for the rewinding of electric motors and the production of oil coils may include paper, cotton fabric, glass, as well as asbestos fibers, lavsan, silk. These fibers and fabrics are superimposed in several layers in the likeness of a braided stocking.

enamel insulation

The enameled insulation material is vinylflex, metalvin, organosilicon base, polyether terephthalic acid, polyurethane.

Winding wire coated with a special enamel has electrical strength, resistance to moisture, aggressive chemicals. A feature of enamel winding wires is a very small thickness of the insulated layer (the largest thickness is 0.09 mm). The strength of the enamel of the PEL wire is small, such a wire is used only for windings of coils operating in a stationary state.

High-strength enamel wire PETV, as well as PET-155, is used for windings of electric motors with a power of up to 100 kilowatts. PET-155 enameled wire is used for the production of a new series of electric motors, the strength of its insulation makes it possible to wind the wire on automatic machines. Enamel wires also have high heat resistance, and are able to withstand temperatures up to 155 degrees.

Combined

Winding wire with combined insulation in its parameters is in an intermediate position between the two types of wires considered. The combined type of insulation includes several layers. The outer coating usually consists of fibrous material, while the inner coating is enamel. For example, PELSHO wire means: copper winding wire with silk and lacquer enamel insulation.

If the conductor is impregnated with heat-resistant varnish and covered with fiberglass, then its marking contains the letter "K". This type of wire has become popular due to its high reliability, and is used for electric motors of hoisting and transport mechanisms, including shipbuilding cranes.

Section shape

Winding wires come in two cross-sectional shapes:

1. Round.
2. Rectangular.

The round section of the wire is used in various fields. Such a wire has high strength and electrical characteristics.

The sizes of rectangular sections of wires are standardized. Such a wire is often used for transformer windings. The thickness of rectangular reins reaches up to 5.9 mm, and the width is up to 14.5 mm.

The ratio of these sizes may vary. There are some disadvantages expressed in the use of winding wires of flat section. When it is wound on a coil, there is a high probability of damaging the insulation, and also, with very small wire sections, it is visually difficult to distinguish the smaller side of the section from the larger one.

In any winding, an important element is the coil of the conductor around the core. According to the current power, the required wire cross-section is selected. Round wire is usually used for light loads, while rectangular wire is used for higher loads.

Conductor material

Most winding wires are made from the following materials:

• Copper.
• Aluminum.

Copper winding wires make up the majority of all wires produced. They have low resistivity, significant weight. The cost of copper wires is high.

Recently, instead of copper wires for windings, aluminum wire has been used, which is much lighter in weight, has a lower cost, but has a higher resistivity than a copper conductor.

Marking

To designate a wire, it is marked, which means the material of the core and insulation.

• At the beginning of the designation is the letter "P" for copper wire, and means "wire".
• To distinguish between aluminum and copper wires, there is an “A” at the end of the marking, for example, PEVA.
• If the core is made of an alloy with a high resistivity, then there are additional letters in the designation, for example, HX - nichrome, M - manganin, K - constantan.
• To designate a soft conductor, the symbol "M" is put, for a hard one - "T". For example, PEMT wire is hard wire copper wire, and PEMM wire is soft wire.

Letters for isolation

• EM - high-strength polyvinyl enamel.
• EL - oil base.
• EV - high-strength polyvinyl acetate enamel.
• L - lavsan.
• Sh - natural silk.
• B - cotton yarn.
• Oh, one layer.
• C - fiberglass.
• ShK - capron.
• D - two layers.

If the marking is the 2nd letter "P", this means that the insulation is in the form of a film. The PPF wire is equipped with insulation in the form of a fluoroplastic film.

For marking combined insulation, the symbols are in the order of the layers, starting from the inner one. PELSHO - copper wire, oil-based enamel and a single-layer silk braid.

Requirements

• The winding wire is covered with uniform insulation. Allowed at some thickening points according to the brand and size of the wire.
• The wire is transported in coils, drums and bobbins, depending on the size and brand. The conductor in such packages must be wound evenly and tightly, without confusion of turns. The number of pieces of wire in the coil or coil must correspond to the size and brand of the wire.
• Packages must be packed with paper capable of protecting the wire insulation from damage during transport. The maximum weight of the box with wire must not exceed 80 kg.
• A label is attached to the drum and reel with the designation of the manufacturer, weight, standard size and brand of the wire, as well as other parameters.

How to choose winding wires for the motor

The selection of the necessary wire for rewinding electric motors is carried out taking into account the heat resistance class, the allowable insulation layer and other requirements.

Enamel winding wires have the minimum thickness of the insulation layer. They are used with an increased percentage of groove filling during winding. The smooth surface of the insulation facilitates their installation in the grooves, and its small thickness with increased heat transfer provides protection against overheating.

The use of enamelled wires should be consistent with the specific types of lacquers and solvents used in a particular facility, or with those brands of lacquers that the facility is able to supply. There are solvents and varnishes that can destroy the enamel. And also, when heated to 170 degrees, this insulation becomes plastic, which does not allow it to be used for windings of rotors rotating at high angular speed.

The maximum thickness of the insulated layer has a winding wire with a combined and fibrous layer. Its use is prohibited for windings in an aggressive or humid environment. For such purposes, it is advisable to use winding wires equipped with glass insulation, but the low strength of the insulation imposes certain restrictions on the use of such wires. Although, in terms of heat resistance, glass-insulated wires are suitable for such classes of windings. When purchasing a winding wire, it is necessary to take into account that the cost of a wire of one standard size depends on the brand. When repairing low-voltage electrical machines, the price of the wire will make up a large part of the financial costs of the total cost of the repair. In this regard, it is necessary to take into account the technical and economic factors of choice, that is, the price and technical parameters.