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.
The most widespread are winding wires in enamel insulation based on high-strength synthetic varnishes with a temperature index (TI) in the range of 105 ... 200. TI means the temperature of the wire at which its useful resource 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 insulating characteristics, which are practically independent of the external influence of high temperatures and humidity.
PEL-type wires are characterized by a great dependence on the external influence of solvents, relative to wires with insulation based on synthetic varnishes. The PEL winding wire can be distinguished from others even by its appearance - the enamel coating is close to black in color.
Copper wires of the types PEV-1 and PEV-2 (produced with a core diameter of 0.02 ... 2.5 mm) have polyvinyl acetate insulation and are golden in color. Copper wires of the FEM-1 and FEM-2 types (with the same diameter as PEV) and rectangular copper conductors FEMP (section 1.4 ... 20 mm2) have lacquered insulation on polyvinyl formaldehyde varnish. Index "2" in the corresponding designation of PEV and FEM 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. It is convenient to mount such wires. When brazing, you do not need to strip varnished insulation and use fluxes. The usual POS-61 grade solder (or similar) and rosin are enough.
Enameled wires with PET-155 insulation on a polyester amide base have a TI equal to 155. They are produced with conductors not only of a circular cross-section (diameter), but also of 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 above-considered wires of the PEVT type, but they have a higher resistance to heating and thermal shock. Therefore, winding wires of the types PEVT and PET, PETP can be especially often found in high-power transformers, including transformers for welding.
At high frequencies, multi-core enameled winding wires (litz wires) of the LESHO type in silk single-layer insulation or LESHD - fw double silk insulation are used. Such wires consist of a bundle of enameled copper 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 separate enameled wires to reduce losses from the surface effect (Proximity effect). Table 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 USA and Great Britain, the designation of the diameters of the winding wires is written in the words wire size (wire size).
For example, in the USA the system is used
American Wire Gauge (AWG). Also sometimes in the USA they use the B&S system, and in the UK they use the Standar 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 permissible 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 a temperature of + 50 degrees. The duration of safe exposure depends on this temperature parameter.
on the conductor of the maximum permissible current (Imax A in Table 4)
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