RU2170651C1 - Ventilated transformer - Google Patents

Abstract

FIELD: equipment for electric welding or electric steel melting in different branches of metallurgical industry and machine engineering. SUBSTANCE: transformer includes primary winding 1, magnetic circuit 2, secondary winding having winding 4 for initially exciting electric arc and winding 3 for sustaining electric arc burning. Cooling system is in the form of ventilating electric motor 8. One circuit 6 of two circuits for full-wave rectifying is connected with winding 4 and other circuit 5 - with winding 3 respectively. Winding of electric motor 8 is connected in series with winding 4 before or after respective full-wave rectifying circuit. Such design of transformer allows to decrease energy losses, mass and dimension of transformer and also cost price of furnace and welding transformers. EFFECT: improved design. 3 dwg

Description

 The invention relates to the field of electrical engineering, namely, electric steelmaking and electric welding equipment, allows to reduce unproductive losses, weight and size indicators and the cost of furnace and welding transformers.

 Known furnace and welding transformers with blowing to reduce the thermal stress of the windings (see, for example, N.V. Okorokov. Arc steel-smelting furnaces. Metallurgy Publishing House, Moscow, 1971, pp. 17-19, l. 1). But for the electric drive fans blowing well-known transformers need additional energy consumption from an external source. The efficiency of such transformers does not exceed 50%.

 It is also known that the operation of furnace and welding transformers requires the so-called “falling” current-voltage characteristic (CVC), since the initial arc excitation requires a voltage several times higher than for the arc maintenance process, i.e. actually melting metal. This is achieved by the use of chokes, additional resistances, magnetic systems with increased magnetic flux scattering, etc., which is 2–3 times higher than the power required for melting and electric welding (see, for example, Titov OI, Manual Manual Electric Welder. Novosibirsk Book Publishing House, 1939, p. 2).

 There is also the principle of forming a “falling” I – V characteristic by controlling the cutoff angle of the sinusoidal voltage (see, for example, V. Baranov Low-power electric welding machine, Radio N 7, 1996, p. 3).

 According to the principle of operation, this is an adjustable rectifier that requires a complex elemental base, therefore it is unacceptable for more powerful transformers.

 A prototype can be a furnace transformer containing a housing with a cooling system, a high-voltage primary winding, a rod-type or armor-type magnetic circuit, a low-voltage secondary winding, as well as related equipment: a disconnector, a high-voltage switch, a choke, a high-voltage switch for shunting the inductor, low busbars voltage, control devices and systems for electric power regulation (l-1, p. 17-19).

The prototype has the following disadvantages:
low efficiency, complexity, metal consumption, high cost and unsatisfactory performance.

 The technical task is to reduce the metal consumption and cost of steelmaking and welding equipment, increase efficiency and improve their performance.

This is achieved:
- rejection of complex systems for regulating electric power from the side of the high voltage winding (primary winding);
- dividing the secondary winding of each phase into two parts, connected to one electrode through a locking diode current isolation, one of which is designed for full electric power and low voltage for maintaining the arc burning, and the other, which is a continuation of the first and giving the arc ignition voltage with it in all real modes, the minimum power is made;
- the use of a magnetic circuit with minimal magnetic scattering, for example, in the form of a torus and the refusal to use chokes;
- serial connection of the coil of the initial excitation of the arc with the winding of the blower motor (EDF) of the transformer and, in the limit, the refusal and the use of additional resistance to equalize the voltage of the two parts of the secondary winding and obtain a "falling" CVC.

 The essence of the invention is to use the new principle of obtaining a "falling" I-V characteristic. In this case, the slope of the I – V characteristic for the stabilization of the arc burning is regulated automatically due to the counter-EMF of the blower motor as it accelerates with the fan load while performing the function of decreasing the thermal stress of the windings.

 A patent search showed the absence of furnace and welding transformers with the proposed set of features.

 Thus, in this case, the known elements are combined with new bonds, give the furnace and welding transformers new properties, manifested in positive effects, as a result of which the solution can be recognized as having an inventive step.

The invention is illustrated in the drawing, where in FIG. 1 shows a schematic diagram of a single-phase welding transformer with an AC blower motor; in FIG. 2 shows a variant of a transformer with a lightweight secondary winding, its half-period separation of current at zero point (with a - sign) and a DC blowing motor; in FIG. 3 shows a three-phase version of the furnace or welding transformer circuit with the legend:
1 - primary winding of the transformer;
2 - magnetic circuit;
3 - part of the secondary winding-winding maintain the arc;
4 - part of the secondary winding-winding of the initial excitation of the arc;
5 - two-half-wave rectification circuit of the arc burning current;
6 is a two-half-wave rectification circuit of the arc excitation current;
7 - adjustable additional resistance;
8 - blower motor (EDO);
9 - electrodes;
10 - welded part.

 As can be seen from FIG. 1, the windings 1, 3, 4 and their connection schemes are made similarly to those specified in l-4, but instead of the additional adjustable resistance 7, the winding of the blowing motor 8 is connected in series with the initial excitation coil of the arc.

 In the general case, in order to reduce the rated power of the blowing motor 8, it is possible to completely or partially bypass its windings with resistance 7, as shown in FIG. 2 and 3.

 In this case, the winding of the blower motor 8 can be made in the form of a collector machine of direct (Fig. 2) or alternating current, and such a contactless machine of alternating single-phase (Fig. 1) or three-phase (Fig. 3) current.

 Depending on this, sequentially the winding of the initial excitation of the arc 4, the blower motor 8 is turned on before (for alternating current) or after (for direct current) the rectification circuit of the excitation current of the arc 6.

 For powerful furnace transformers, not one, but several blowing motors 8 connected in parallel to each other can be used.

 All circuits are designed in such a way that in the absence of a current arc in parts 3, 4 of the secondary winding of the transformer and the blower motor 8 there is no blowing, and the electrode ignition voltage 9 is suitable for the total arc ignition voltage in all real operating modes of the transformer, equal to the sum of the voltages of the two parts 3 and 4 of the secondary windings.

 This is possible due to the use of a locking diode current isolation, consisting of two-half-wave rectification of the current of the initial excitation of the arc 6 and two-half-wave rectification of the current to maintain the burning of the arc 5.

 When the arc is ignited, a current flows through the arc excitation winding 4 and the winding of the blowing motor 8, which is directly proportional to the applied total voltage of the secondary winding 3, 4 and inversely proportional to the sum of the internal resistances of the secondary winding 3, 4, the windings of the blowing motor 8 and the transition resistance in the arc.

 This current will provide ionization of the interelectrode medium and the conducting channel of the plasma, which directly includes part 3 of the secondary winding, which supports arc burning and metal melting.

 As the blowing motor 8 accelerates in accordance with the property of self-regulation of electric machines, the voltage applied to the electric motor 8 will decrease due to the counter-EMF, automatically ensuring a “drop” of the I – V characteristic and stabilization of the arc burning in the presence of magnetic circuit 2 with minimal magnetic scattering, for example, in the form of a torus .

 The mechanical energy of the electric motor 8 is transmitted to the fan, which intensively cools the working windings of the transformer without additional energy consumption.

 This allows you to significantly reduce the thermal stress of the windings, to allow a greater current density, and therefore less weight and dimensions at the maximum efficiency of the transformer, because the internal resistance of its secondary winding and the magnetic flux of scattering are always less in comparison with the resistance and flux of scattering of known transformers.

Claims (1)

 A blow transformer for an arc melting furnace or electric welding, comprising a primary winding, a magnetic circuit, a secondary winding consisting of an initial arc excitation winding and an arc supporting winding, and a cooling system made in the form of an electric blowing motor, characterized in that two half-wave circuits are introduced into it rectifications, one of which is connected to the winding of the initial excitation of the arc, and the second, respectively, to the winding of maintaining the combustion of the arc, while the winding of the electric motor blowing pos is connected to the winding of the initial arc excitation before or after the corresponding two-half-wave rectification circuit.

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