RU2404032C2 - Two-phase induction welding generator - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed invention can be used in hand-held electric arc welding devices. Induction welding generator has two-winding stator. Three-phase excitation winding 2 has terminals for excitation capacitors 3 to be connected thereto. Working winding 4 is a two-phase winding. Circuit of said winding each phase 4, 5, shifted through 90 degrees, incorporates compound capacitor 6, 7 and single-phase bridge rectifier 8, 9 shunted by shunting capacitors 10, 11. Output terminals of rectifiers 8, 9 are connected in parallel and welding electrode 12 is connected thereto.

EFFECT: increased welding current.

3 dwg

Description

The invention relates to electrical engineering, in particular to asynchronous electric machines with capacitor self-excitation, and can be used in devices for manual arc electric welding.

A known design of an asynchronous welding generator with two multiphase windings on a stator, one of which is an excitation winding has terminals for connecting a capacitor bank, the other is working and has terminals for connecting to a welding device [1]. The working winding is offset by an angle α el. hail. relative to the field winding in the direction of rotation of the rotor. The primary windings of the compounding transformer are connected to the phases of the field winding, and the secondary windings of this transformer are connected to the phases of the working winding of the same name.

One of the disadvantages of this generator is the presence of a compounding transformer, which leads to an increase in the mass of the entire welding installation and a decrease in the total efficiency. Another disadvantage can be considered that the circuit resistance “generator excitation winding - primary winding of the compounding transformer - capacitor bank” depends on the operating mode of the generator. In the absence of load (idle), the resistance of the primary winding of the compound transformer is very large, and in the short circuit mode (short circuit) or rated load it is very small. Because of this, self-excitation, as well as the operation of the generator in the mode of low loads and idle (XX), becomes problematic. In manual arc welding, the generator at first starts in XX mode, then, after the electrode touches the welded part, it switches to short-circuit mode, and after ignition of the arc, it starts to work in nominal mode. Thus, the difficulties encountered in XX mode make this generator unsuitable for manual arc welding. The presence of switches that in XX mode bypass the primary winding of the compounding transformer does not improve the situation, because switches not only complicate the design of the generator, but must also close and open their contacts with each welding cycle. It should be noted that the external characteristics of the generator do not cross the voltage axis [1]. This is an indirect confirmation of the above.

A known design of a non-contact welding generator [2], which has a squirrel-cage rotor and two three-phase windings on the stator. A load (arc) is connected to the first winding through a rectifier device and a choke. Excitation capacitors are connected to the second winding, and the terminals of this winding can be used to power consumers of an alternating three-phase voltage.

The disadvantage of this generator is that in idle mode the magnetizing current exceeds the nominal current several times.

This is due to the fact that to ensure nominal induction in the gap of the generator in mode XX, one value of the capacitance of the capacitors is required, and in short-circuit or load mode, another, and more. Therefore, with a fixed capacitance of the capacitors, which is selected for operation with rated load, the transition to mode XX is accompanied by an increase in the magnetizing current and a significant saturation of the generator magnetic system.

It should be noted that this disadvantage is inherent in the asynchronous generator of conventional design. The use of a high-speed reactive power regulator that can solve this problem will lead to a significant complication of the generator set, reduce its reliability and increase mass.

The prototype of the invention is a non-contact asynchronous welding generator [3]. This generator has two three-phase windings on the stator. One winding is an excitation winding. Excitation capacitors are connected to its terminals, which ensure the generator is idling and under load. The other winding is working. The phases of the working winding have terminals for connecting shunt capacitors and a rectifier to the output of which a welding electrode is connected, and the ends of the phases of this winding have terminals for connecting compounding capacitors connected in a triangle.

The presence of compounding capacitors can reduce losses and increase efficiency by reducing the demagnetizing effect of the welding current of the working winding.

. В свою очередь, наименьшее номинальное напряжение современных силовых полипропиленовых конденсаторов, например, серии К78-17, при частоте 50 Гц равно 250 B, а при частоте 200 Гц - 165 B. Поскольку реактивная мощность конденсаторов пропорциональна квадрату напряжения, то в первом случае серийные конденсаторы будут развивать 9,5% от номинальной реактивной мощности, а во втором - 22%.The disadvantage of this generator is the low voltage on the compounding capacitors and, as a consequence, the low efficiency of their use. This is because the allowable open circuit voltage of the welding current source for arc welding should not exceed U _dXX <100 V [4, _p . ₂₈ ]. Correspondingly, the open-circuit phase voltage of the working winding of the generator is limited, which, for example, at U _dXX = 80 V will be U _2XX = U _dXX / 2.34 = 34.19 V. The highest voltage on the compounding capacitors occurs when a short circuit occurs in the load circuit. In this mode, the prototype compounding capacitors connected in a triangle fall under a linear voltage, which increases due to the additional reactive power of these capacitors. Suppose that the growth was 30% compared with the open circuit voltage of the working winding. Under this assumption, the voltage supplied to the compounding capacitors of the prototype will be equal to

. In turn, the lowest rated voltage of modern power polypropylene capacitors, for example, K78-17 series, at a frequency of 50 Hz is 250 V, and at a frequency of 200 Hz is 165 V. Since the reactive power of the capacitors is proportional to the square of the voltage, then in the first case, serial capacitors will develop 9.5% of the nominal reactive power, and in the second - 22%.

The technical result that the claimed invention provides is to increase the welding current due to the more efficient use of serial capacitors designed to compound the generator.

The specified technical result is achieved in that an asynchronous welding generator with two windings on the stator, one of which is a three-phase field winding has terminals for connecting field capacitors, the other is a working winding, and the working winding is two-phase, in the circuit of each phase of this winding, shifted 90 email degrees, compounding capacitors and a single-phase bridge rectifier shunted by shunt capacitors are connected in series, the rectifier leads are connected in parallel and a welding electrode is connected to them.

The electrical circuit of an asynchronous welding generator is shown in figure 1. Figure 2 shows the external characteristics and the operating voltage at the compounding capacitors of the claimed generator and prototype. Short-circuit transient curves are shown in FIG. 3.

The generator has a squirrel-cage rotor 1 of conventional designs (figure 1). A three-phase field winding 2 and a working winding, which has two phases 4, 5, are laid in the stator slots of the asynchronous welding generator. The number of turns of the field winding 2 is selected so as to ensure optimal use of the voltage of the field capacitors 3. In series of the first phase of the working winding 4 in series compounding capacitors 6 are included, a single-phase bridge rectifier 8, shunted by shunting capacitors 10. Compounding conductors are respectively connected to the second phase of the working winding 5 nsatory 7, the rectifier 9 and shunt capacitors 11. The DC Conclusions rectifiers 8 and 9 are connected in parallel. Phases 4, 5 of the working winding have the same number of turns. Capacitors capacitors in phases 4 and 5 are also equal. The rectifiers 8, 9 have the same parameters. The number of turns in the phases of the working winding depends on the required open circuit voltage on the welding electrode 12.

The generator operates as follows. When the rotor 1 is rotated by a drive motor (internal combustion engine, electric motor), the residual flow induces an EMF in the stator windings. Under the influence of this EMF in capacitors 3, a capacitive current arises, which, flowing along the excitation winding 2, increases the field in the gap, which, in turn, leads to an increase in EMF, etc. The avalanche-like process of increasing EMF (the process of asynchronous self-excitation) is completed when the generator is saturated, when it starts to work in steady state with capacitor self-excitation. In the windings of the generator, voltages are established that are proportional to the number of turns of the corresponding windings and the value of the capacitance of the field capacitors. 3. With a decrease in load resistance, the current of the working winding increases. In this case, the reactive power of the compounding capacitors 6, 7 increases, and therefore the generator does not lose excitation and operates stably even during short circuit. When the load is dropped, the energy of the compounding capacitors is dissipated along the circuit created by the shunting capacitors 10, 11. In addition, these capacitors allow you to adjust the open circuit voltage and generate the dynamic characteristics of the generator. So, with an increase in their capacitance, the idle voltage at the welding electrode decreases, and when the electrode of the welded part is touched (short circuit), the peak current value increases.

[5, с.58]. Здесь U_d - среднее выпрямленное напряжение, U_1ф - однофазное переменное напряжение, подводимое к выпрямителю. К каждому из параллельно соединенных мостовых выпрямителей 8, 9 подводятся напряжения, которые сдвинуты по фазе на 90 гр. Для такой схемы можно записать:

, где U_2ф - фазное напряжение двухфазной системы. Трехфазный мостовой выпрямитель, который используется в прототипе, имеет:

[5, с.67]. Здесь U_3ф - фазное напряжение трехфазной системы. Сравнение двух последних формул показывает, что при одинаковом значении среднего выпрямленного напряжения переменное напряжение, подводимое к выпрямителям двухфазного асинхронного сварочного генератора, в U_2ф/U_3ф=1,3 раза больше, чем у прототипа. Соответственно у предлагаемого генератора больше фазное напряжение рабочей обмотки, а следовательно, больше постоянная составляющая выпрямленного тока. Это подтверждают результаты расчета внешних характеристик заявленного генератора (кривая 13) и прототипа (кривая 14), представленные на фиг.2. При расчете предполагалось, что генераторы имеют одинаковые магнитные системы, плотности тока в обмотках, магнитные индукции в воздушных зазорах и соответствующие суммарные емкости конденсаторов всех фаз (возбуждения, компаундирующих, шунтирующих), т.е. ΣC_возб.3ф=ΣC_возб.2ф, ΣC_комп.3ф=ΣC_комп.2ф, ΣC_шунт.3ф=ΣC_шунт.2ф. Зависимости напряжения на компаундирующих конденсаторах от сварочного тока представлены на фиг.2 в виде кривых 15 и 16. Эти кривые показывают, что при одинаковых значениях напряжений сварочный ток у заявленного генератора больше.For single-phase bridge rectification, the following formula is valid:

[5, p. 58]. Here U _d is the average rectified voltage, U _1ph is a single-phase alternating voltage supplied to the rectifier. Each of the parallel-connected bridge rectifiers 8, 9 is supplied with voltages that are phase shifted by 90 g. For such a scheme, you can write:

where U _2f is the phase voltage of the two-phase system. The three-phase bridge rectifier, which is used in the prototype, has:

[5, p. 67]. Here U _3ph is the phase voltage of a three-phase system. A comparison of the last two formulas shows that with the same value of the average rectified voltage, the alternating voltage supplied to the rectifiers of the two-phase asynchronous welding generator is U _2f / U _3f = 1.3 times more than that of the prototype. Accordingly, the proposed generator has more phase voltage of the working winding, and therefore, more than the DC component of the rectified current. This is confirmed by the results of calculating the external characteristics of the claimed generator (curve 13) and the prototype (curve 14), presented in figure 2. In the calculation, it was assumed that the generators have the same magnetic systems, current densities in the windings, magnetic inductions in the air gaps and the corresponding total capacitances of the capacitors of all phases (excitation, compounding, shunting), i.e. ΣC _exc.3f = ΣC _exc.2f , ΣC _comp.3f = ΣC _comp.2f , ΣC _shunt.3f = ΣC _shunt.2f . The dependences of the voltage on the compounding capacitors on the welding current are shown in Fig. 2 in the form of curves 15 and 16. These curves show that at the same voltage values the welding current of the claimed generator is greater.

This pattern with currents is preserved both during operation in the steady-state welding mode and during a short circuit. Suppose that the operating voltage of the arc and the welding current are related by the relation: U _p = 20 + 0.04I _d [4, p.342, p.531] (line 17), then in the steady state the current of the two-phase generator will be I _d.2f = 132 A (point a), and the prototype has I _d.3ph = 112 A (point b). In the _{event of a} short circuit, respectively, we have the following currents: I _d . _KZ.2f = 159 A (c) I _d . _KZ.3f = 127 A (point d). The current growth in the first case amounted to 17.85%, and in the second - 25%. When working in these modes, the voltage at the compounding capacitors of the two-phase generator is greater than that of the prototype (points ef, gh). The voltage increase on the compounding capacitors is not so significant compared with the preliminary calculation, since in this case the influence of saturation and voltage drop in the generator circuits is taken into account.

Thus, with the same magnetic systems, current densities in the windings, the same voltages at the compounding capacitors and other things being equal, the welding current of a two-phase generator is greater than that of a three-phase prototype. Therefore, the claimed generator uses serial capacitors more efficiently when they operate as compounding capacitors.

Figure 3 shows the voltage curves 18, 19 and current 20, 21 in the welding circuit and on compounding capacitors 22, 23 with a short circuit with a resistance of R _d = 0.01 Ohms. Curves 19, 21, 23 refer to a two-phase generator, and 18, 20, 22 to a prototype. The voltage at the compounding capacitors 23 and the current 21 of the two-phase generator is greater than that of the prototype (curves 22, 20). The dynamic characteristics of the generators differ slightly.

The disadvantages of this solution include the greater value of the ripple factor k _{P. 2f} = 13.3%, versus k _{P. 3.3} = 5.7% of the prototype [5, _p . ₇₅ ], which may slightly impair the quality of welding.

INFORMATION SOURCES

1. A.S. 1798863 USSR, H02K 17/00. Asynchronous welding generator / P.I. Kostrauskas, V.-Yu. A.Zhalis, A.K. Kulakauskas, L.P. Lemezhenene, S.Yu. Marazas, S.A. Dirzhas, A.I. .V. Pashtukas. - No. 4845636/07; Application. 23.04.90; Publ. 02/28/93. Bull. No. 8.

2. Pat. No. 237406, GDR, H02K 47/10. Burstenljser schweib generator / Julke Edmund, Dassel Jurgen; VEB Mansfeld - Kombinat Wilhelm Pick. ¹ 2763853; Claim 05.16.85, publ. 07/09/86.

3. Patent RU No. 2211519, H02K 17/00, H02P 9/46, B23K 9/00. Asynchronous welding generator. / A-Z.R. Dzhendubaev. - No. 2001124752/09; Publ. 08/27/03. Bull. Number 24.

4. Equipment for arc welding: Reference manual / Ed. V.V.Smirnova. - L .: Energoatomizdat. 1986.

5. Rozanov Yu.K. The basics of power electronics. - M .: Energoatomizdat, 1992.

Claims (1)

An asynchronous welding generator containing two windings on a stator, one of which in the form of a three-phase field winding has terminals for connecting field capacitors, and the other is a working winding, characterized in that the working winding is made of two-phase, each phase of which is shifted by 90 °, compounding capacitors and a single-phase bridge rectifier shunted by shunt capacitors are connected in series, while the terminals of the rectifiers are connected in parallel and a welding elec ctrod.

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