Aluminum winding wires. Electrical networks, equipment, documentation, instructions What kind of wiring is used for winding transformers

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 at 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 relative thickness of the wire insulation, 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.

A. P. Kashkarov, St. Petersburg

For the manufacture of transformers and chokes, special winding wires are used. The main types of such wires of domestic and foreign production are described in this article.

Domestic winding wires

Winding wires in enamel insulation based on high-strength synthetic varnishes with a temperature index (TI) in the range of 105 ... 200 are most widely used. TI is understood as the temperature of the wire at which its useful life is at least 20,000 hours.

Copper enameled wires with insulation based on oil varnishes (PEL) are produced with a core diameter of 0.002 ... 2.5 mm. Such wires have high electrical insulation characteristics, which are practically independent of the external influence of elevated temperatures and humidity.

PEL type wires are characterized by a greater dependence on the external influence of solvents, compared to wires with insulation based on synthetic varnishes. The PEL winding wire can be distinguished from others even by its external sign - the enamel coating is close to black in color.

Copper wires of types PEV-1 and PEV-2 (produced with a core diameter of 0.02 ... 2.5 mm) have polyvinyl acetate insulation and are distinguished by a golden color. Copper wires of types PEM-1 and PEM-2 (with the same diameter as PEV) and rectangular copper conductors PEMP (section 1.4 ... 20 mm2) have varnished insulation on polyvinylformal varnish. Index "2" in the corresponding designation of PEV and PEM wires characterizes two-layer insulation (increased thickness).

PEVT-1 and PEVT-2 are enameled wires with a temperature index of 120 (diameter 0.05 ... 1.6 mm), they have insulation based on polyurethane varnish. These wires are easy to install. When soldering, it is not necessary to strip the varnished insulation and apply fluxes. Enough ordinary solder brand POS-61 (or similar) and rosin.

Enamelled wires with insulation based on polyesteramide PET-155 have a TI equal to 155. They are produced with conductors not only of a round cross section (diameter), but also of a rectangular (PETP) type with a conductor diameter of 1.6-1 1.2 mm2. In terms of their parameters, PET wires are close to the PEVT type wires discussed above, but have a higher resistance to heat and thermal shock. Therefore, winding wires of types PEVT and PET, PETP can be especially often found in powerful transformers, including transformers for welding.

Domestic high-frequency winding wires

At high frequencies, stranded enameled winding wires (litz wires) of the LESHO type in silk single-layer insulation or LESHD - fv double silk insulation are used. Such wires consist of a bundle of copper enameled wires with a diameter of 0.05 ... 0.1 mm and are used for inductors (and chokes). In high-frequency wires of the LESHO, LESHD, PELO, LELD, DEP, LEPKO types, the cores are twisted from individual enameled wires to reduce losses from the surface effect (proximity effect). Table No. 1 shows the diameters of widely used high-frequency winding wires of domestic production. For odd numbers, the wire diameter is approximately equal to half the sum of the diameters of two adjacent (even) numbers.


Designation of popular foreign winding wires

In the US and UK, the designation of the diameters of the winding wires is written with the words wire size (wire size).

For example, in the USA the system

American Wire Gauge (AWG). Also sometimes in the USA they use the B&S system, and in the UK they use the Standard Wire Gauge (SWG). Table 2 and Table 3 show the diameters of widely used types of winding wires according to AWG and SWG standards.
Permissible load on conductors


The maximum allowable current that can be passed through the wires without worrying about fire or contact failure is determined in accordance with Table 4. The maximum heating of rubber or plastic (as well as their combinations or derivatives) insulation of wires should not exceed +50 degrees. The duration of safe exposure depends on this temperature parameter.
on the conductor of the maximum allowable current (I max A in Table 4)
Magazine "Electrician"

In transformers, windings are used to convert electrical energy. By changing the voltage and current, they save the transmitted power. Together with the windings, a set of metal plates is involved in the energy conversion, which plays the role of a magnetic circuit.

Transformer windings are made of conductors covered with a layer of insulation, which also holds the wires in position and creates a cooling channel. Various winding designs provide neutral and linear taps as well as adjustment taps. During work related to the design of windings, the following parameters are calculated:

• allowable temperature rise at rated power and operating load;
• electrical strength at high voltage;
• mechanical strength during short circuit.

For the manufacture of windings of converters, copper wire is most often used. This is due to the fact that copper has low electrical resistance and high electrical conductivity. Due to its flexibility and mechanical strength, it is well machined and resistant to corrosion.

However, copper is a fairly valuable and scarce metal. The high cost of copper is associated with small world reserves of its ore. Because of this, the cost of the metal is constantly increasing, so transformer manufacturers are forced to look for a replacement for it. Aluminum is by far the best alternative to copper. Its reserves far exceed those of copper, and it is much more common in nature.

However, aluminum has a lower electrical conductivity. It is also less flexible and inferior to copper in terms of strength. It is rarely used in the windings of powerful transformers. In addition, it is technically difficult to make internal connections of the windings by welding. The performance of this operation requires the workers connecting the windings to have the relevant knowledge and skills, extensive experience and certain skills. In the case when copper conductors are connected, everything is much simpler.

Comparative characteristics of metals

The debate about which metal is better to use for transformer windings has not stopped for many years. Opponents, bringing different technical arguments in favor of different metals, are constantly changing their views. Most of all the arguments are not so significant, and some of the so-called facts are outright misinformation.

In order to choose the right material for the converter winding, a comparative analysis of the operating parameters of aluminum and copper should be made, and the degree of their difference should be determined. Attention is paid to those parameters that cause the greatest concern, since they are the most important in the operation of the converting device.

Characteristic differences between copper and aluminum

Expansion factor

When aluminum is heated, it has 30% more expansion than copper. If aluminum lugs are connected with a bolt and nut, a spring washer must be placed under the clamping nut. In this case, the contact connection will not loosen while the voltage is off and the tips cool down, thus reducing their size.

Conclusion: To ensure that the quality of the connection of aluminum cables is not inferior to the quality of copper contacts, it is necessary to use proper fittings.

Thermal conductivity

Copper conducts heat much better than aluminum. Therefore, if different metals of the windings in transformers have the same cross section, then a copper product is cooled much better than aluminum. To achieve the same electrical conductivity, and hence the same heat transfer, the aluminum wire in the converter must have a cross section of 60% more than copper.

Designers, developing a package of documents for the production of transformers, take into account the characteristics of the material, design, as well as the total area of ​​the cooling surface of the winding.

Conclusion: All transformers, regardless of what metal their windings are made of, have very similar thermal characteristics. .

Electrical conductivity

Due to the fact that aluminum has an electrical conductivity 60% less than copper, aluminum windings have higher losses. The developers of converters with aluminum windings in the design documentation lay down the cross-sections of conductors that exceed the values ​​for similar products made of copper. This equalizes the energy loss in products with different materials in the windings.

However, manufacturers have certain limits that limit the choice of wire section. Therefore, sometimes it turns out that the copper winding in the transformer has more significant losses than a similar product made of aluminum. This is due to the fact that manufacturers, for one reason or another, used copper wire as a winding, the cross section of which does not correspond to the design norm.

As for dry transformers, regardless of the metal of the winding, they have losses in the core, recruited from metal plates, remain unchanged. A higher efficiency of the converter can be achieved only by changing the cross section of the winding wire. This is the main criterion that indicates a higher degree of effectiveness of a particular device.

Conclusion: Due to the fact that aluminum wire is much cheaper, for the same money they can wind a winding with a larger cross section. This will lead to a significant reduction in energy losses during the operation of the converter. In some cases, such windings are much more efficient than copper ones.

Tensile strength of metals

Aluminum requires 40% less force to break than copper. For manufacturers of electrical products, this fact is of some concern, since most of their products are often subjected to cyclic loads. This is due to the large starting currents that occur when starting some electrical power devices. Powerful electromagnetic forces arising from such currents cause an increased movement of molecules in the conductors, which leads to a displacement of the windings in the products.

A comparative analysis of the technical indicators of various conductors is done based on their cross-sectional area. Based on the analysis data, the same electrical conductivity in transformers with different windings is ensured as follows. In products with an aluminum winding, the cross-sectional area of ​​\u200b\u200bthe wire should be 60% larger than in a similar device with a copper winding. In this case, the technical indicators of products made from different materials will be approximately the same.

Conclusion: The transformer cannot receive mechanical damage due to a sudden change in load, since the winding section is selected in such a way that there is a necessary safety margin. Damage can only occur due to unreliable fastening at the junction of the wires.

External connections of transformers

Currently, the use of copper in transformer windings is caused by the desire to produce better and more reliable converting devices. Both aluminum and copper are known to be susceptible to environmental damage. Because of this, corrosion, oxidation and other chemical changes occur in metals.

The surface of the aluminum wire coated with oxide becomes an insulator and does not allow electric current to pass through. Because of this, the timely cleaning of aluminum contacts is of great importance and should be carried out regularly, in strict accordance with the schedule of preventive maintenance.

Oxidized copper, on the other hand, loses its electrical conductivity much less, since the sulfides and oxides that appear on it, of course, are not to the extent that we would like, but still have some electrical conductivity. All this is well known to the personnel who maintain transformer substations. Therefore, a specially trained team of electricians regularly performs a scheduled inspection of the bolted connections of working equipment.

In addition, there is a problem of connecting the aluminum windings of the converter to the copper wires of the external electrical network. Directly connect aluminum and copper tips with bolts. The fact is that metals have different electrical conductivity, because of which the joints are constantly overheated, and the connected surfaces are destroyed. Welding technologies developed specifically for this turned out to be ineffective, therefore they are not used for welding cables from different metals.

To connect copper and aluminum cables, tinned lugs coated with a thin layer of tin or silver are now used. When connecting aluminum windings of transformers with copper network cables, the lugs are covered with tin. Silver is used in electronics where a higher quality connection of parts is required. The practice of such connections is generally accepted. The reliability of the connections is confirmed by the long periods of uninterrupted operation of the equipment.

Various wires are also often connected using special metal terminals. Such a terminal is made in the form of a rectangular frame into which two connected conductors are inserted. There are threaded holes on one plane of the terminal. After the conductors are inserted into the frame, they are fixed with screws that are screwed into the thread.

Internal connection of transformer windings

The copper windings of the converters are connected by soldering. The refractory solder used in this case somewhat reduces the electrical conductivity of the soldered area. In this area, copper oxide is constantly released, due to which the outer layer exfoliates, which leads to damage to the entire conductor. This is a significant disadvantage of this connection method.

In aluminum joints, the method of welding wires using an inert gas is used. In them, aluminum oxide forms a resistant protective coating that protects contact from the negative effects of the environment. In addition, in this method of connecting conductors, a great advantage is that during operation of the device there is no loss of electrical conductivity in the welded areas.

The operating time of transformers is to some extent related to the conditions in which they operate. This includes negative environmental influences, extreme loads and other adverse conditions. However, people using electricity should not worry about this. As practice has shown, converters with different windings can work for many years without any problems.

CONCLUSION

A transformer with one or another winding is mainly selected based on personal preferences. The higher cost of a product with a copper winding requires a technical justification for those additional material costs that will arise during its purchase. Today, all reviews based on the experience of practical use of equipment do not indicate any clear advantages in the operation of certain devices.

The only advantage of the copper winding can be considered that the coil wound with copper wire has a much smaller size. This allows transformers with such a winding to be made more compact, which saves some space in which they are located.

However, the vast majority of enclosed transducers are available in standard package sizes that fit both copper and aluminum coils. So here the advantage of copper does not matter. Therefore, the demand for transformers with aluminum winding is now much higher.

The cost of metals is constantly increasing, and since the price of copper is several times higher than the price of aluminum, the cost of a product with a copper winding is much more expensive. Because of this, many buyers prefer not to overpay for copper, but to buy products with aluminum windings. In the future, they try to monitor the reliability of electrical connections, and pay due attention to preventive maintenance of equipment.

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Over the past two decades, the concept of equipment maintenance has taken on different dimensions and has changed to a great extent, perhaps more than any other management discipline. Electrical equipment, which has a rather complex design, requires new methods of maintenance, and a change in views on the organization of maintenance and the responsibility associated with it.

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The principle of operation of most electrical machines is based on the interaction of magnetic fields that are created using coil windings. Coils are an indispensable part of generators and transformers, almost all electronic devices.

To create them, use a winding wire. Let's talk about its types and brands, features and application of different types.

Many make repairs with their own hands, or assemble home-made structures. Often, a burned-out electric motor is rewound on its own, electromagnets (solenoids), transformers, magnetic antennas and inductors for electronic devices are wound. In this case, only the diameter of the wire and the number of turns are taken into account (these characteristics can be found in reference books, repair manuals or calculated).

• But often not only they are important, but also the type of wire - and it may not be indicated. For example, the required number of turns due to the choice of a brand with a thicker layer of insulation may simply not fit into the dimensions of the coil.
• The type of wire is also important for the reliability of the device, and even its safety, if you choose it with insufficient insulation resistance or not intended for operation at such a temperature, an interturn short circuit or breakdown may occur.
• If the first will only lead to the failure of the device, then the second, if safety measures (grounding, zeroing, etc.) are not observed, can be life-threatening.

In addition to the above, the price of wires with the same electrical characteristics, but different types, can vary significantly. Knowing this, you can save on material.

Why overpay for a wire designed to operate at elevated temperatures and humidity for a transformer in which a widely used PEV brand can work perfectly.

Wire classification

Wires are classified according to several criteria.

Conductor material

This is:

1. Copper- the most widespread.
2. Aluminum- because of the greater resistivity than that of copper, they are used less often. But, recently, their use is expanding, as aluminum is cheaper.
3. From resistance alloys (nichrome and the like)- used for some devices.

Section geometry

Wire cross-sections are round and rectangular. The latter are used when it is necessary to pass a large current through a conductor, for conductors with a large cross-sectional area. For cooled coils, hollow wire is used.

Insulation material

Various materials are used - from paper and natural fibers to glass. Often several layers are used, for example: paper and enamel.

For insulation, not only dielectric properties are important, but also mechanical strength, as well as thickness. The smaller it is, the more turns can be placed in the coil for a given wire diameter.

Wire marking

They are marked with several letters and numbers, after the brand they usually indicate the diameter of the section.

Attention. The diameter of the wire section is determined by copper, so if you want to know it by measuring, for example, with a micrometer, first remove the insulation.

Copper wires have the letter P (wire) first, aluminum wires are designated AP, resistance alloys have their own designations. Then comes the designation of the insulation, usually by the initial letters of the materials of its constituents and the number of layers. For rectangular wires, the letter P (rectangular) is placed at the end, then a number that distinguishes the types can follow through a hyphen.

For example PELSHKO - Wire Enamel Lacquer Silk Nylon Single, copper wire covered with lacquer enamel and additionally insulated with one layer of nylon silk. If there were two layers, then the letter D (double) would stand.

Attention. We give the markings generally accepted in our country. For imported wire, it may differ, to the extent that each company has its own designation system. Therefore, when buying material from foreign manufacturers, it is necessary to study the passport characteristics and select analogues according to operating conditions.

paper insulation

Such wires, due to low dielectric properties, are usually used in low-voltage devices, combined with other materials. Paper for their production is used special: cable or telephone.

Winding wire in paper insulation is widely used for oil-filled transformers. In them, the oil not only cools the windings, but increases the breakdown resistance. An example of APB marking is aluminum winding wires in paper insulation.