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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING welding transformer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / welding equipment Many radio amateurs, do-it-yourselfers, innovators and others use electric welding. But it is not easy to purchase a small-sized industrial-made welding machine, and not everyone can afford it. I give a brief description of the manufacture and simplified calculations of the welding transformer (CT). Some theoretical foundations, operation and arrangement of welding transformers are set out in RA 1/98, p.21. A welding transformer can be made by a person who has some experience in winding the windings of electrical machine transformers. First you need to find out the maximum diameter of the electrodes for welding. The power of the ST will depend on the maximum diameter of the electrodes used. Since welding will be on alternating current, electrodes for alternating current will be required. We determine the welding current, i.e. current in the secondary winding of the ST according to the maximum diameter of the electrode used I2 = 30De, where I2 is the current in the secondary winding W2 ST, A; 30 - current density, A/mm2; De is the diameter of the electrode. Wire cross section (mm2) secondary winding CT SW2 = I2/Ipl, where Ipl - current density, A / mm2 (for aluminum 2,5 A / mm2, for copper 5 A / mm2). ST power (W) Рst = I2U2, where U2 is the voltage of the secondary winding W2, B. For a single-phase MT, the optimal voltage is U2 = 50 V. Cross section of the ST magnetic core, cm2 Smag \u1d (Pst) 2/XNUMX. The number of turns per 1 V. N = K/Smag, where K is the coefficient (45). Current in the primary winding W1 ST I1 = Рst/U1, where U1 is the mains voltage (usually 220 V). Cross-section of the wire of the primary winding W1, mm2 SW1 = I1/Ipl. Number of turns of the primary winding W1 n1 = NU1. Number of turns of the secondary winding W2 n2 = 1,05NU2 where U2 is the voltage on the secondary winding W2; 1,05 - an increase in turns, taking into account losses by 5%. As a magnetic circuit, you can use a set of transformer steel plates assembled in a U-shaped form, magnetic circuits wound from a transformer steel tape (toroids), stators of asynchronous motors, from W-shaped transformer steel, etc. But the best characteristics of St are obtained on magnetic cores assembled from transformer steel plates in the shape of a rectangular "window", the so-called double-rod magnetic cores. The location of the halves of the primary and secondary windings on two rods of the magnetic core also contributes to the steeply falling characteristic of the welding current.
The primary winding (see figure) of the ST is wound from two coils, which are placed on two rods of the magnetic circuit and connected in series (they are wound in one direction and connect the beginning to the beginning or the end to the end). Half of the calculated turns of the primary winding are wound on each coil of the primary winding. Since one coil of the primary winding will be sectioned (to increase or decrease the welding current), the number of turns must be calculated from the voltages indicated in the diagram. The secondary winding is also wound on two coils, which contain half the turns of the secondary winding and are connected in series. On one rod of the magnetic core, one coil of the primary winding and one coil of the secondary winding are placed. Coils are also placed on the second rod. When assembling the CT, it is necessary to install the coils in such a way that the winding direction coincides on both rods, then it is easier to make coil connections. Coils of the primary winding can be wound with round or rectangular wire. Coils of the secondary winding are usually wound with rectangular wire. The wire can be either copper or aluminum. The wound coils must be impregnated with impregnating varnish and dried in a special oven. If you are going to wind coils at home and with wire in paper insulation, then each layer of the coil must be painted with nitro-enamel paint or air-drying varnish. If you have a rectangular aluminum wire on the secondary winding in paper insulation, then the paper insulation must be removed. In place of it, wind a new one with the help of escapon, glass mica or, in extreme cases, taffeta or keeper tape. The last two insulations must be impregnated with varnish and paint. The coils must have good body insulation and be well secured to the rods with wooden wedges. The coils on the rods are placed close to one another, and the window of the magnetic circuit must be such that the coils located on opposite rods do not touch each other. The length of the coil wire can be determined by measuring the average coil length and multiplying by the number of turns. Author: B.N. Dubinin
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