RU2111599C1 - Three-phase induction welding generator - Google Patents

Abstract

FIELD: electric welding. SUBSTANCE: generator has three-phase windings 1,2,3 and standard squirrel-cage rotor 4 stator coils are wound on tooth stacks of stator 5 arranged axially; two annular yokes 6,7 are placed at ends of teeth; first capacitor bank 8 is connected to first stator winding 1, second capacitor bank 9, to winding 2; capacitors in first and second banks are connected in star or delta; capacitors of third capacitor bank 8 are inserted in series in same phases of first and second stator windings 1 and 2; DC welding circuit 11 is supplied with power from third winding 3 via semiconductor rectifier 12; in particular case, second winding 2 can be used for connecting 380-V loads 13; third winding 3 has taps for connecting 42-V loads. EFFECT: enlarged functional capabilities. 2 cl, 5 dwg, 1 tbl

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, and, if necessary, in autonomous power supply systems.

 A known design of an asynchronous welding generator, which has a squirrel-cage rotor and two three-phase windings on the stator [1]. 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. In order for the generator not to lose excitation during short-circuit, it must consume significant reactive power, which is several times greater than reactive power when operating in idle mode, i.e. if the reactive current of the capacitors provides a nominal induction in the air gap during short circuit, then at idle the magnetic system will be very saturated. 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.

 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 [2]. The working winding is offset by an angle α el. regarding field winding. 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.

 Another disadvantage can be considered that the circuit resistance "excitation winding of the generator - 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 compounding transformer increases by several orders of magnitude compared to the short circuit mode, so self-excitation and the operation of the generator in low load mode become problematic.

 The presence of switches that, when there is no load, shunts the primary winding of the compounding transformer, complicates the design of the generator, reduces the reliability of the welding installation.

 The prototype of the invention is an asynchronous welding generator described in [3]. The generator has three three-phase windings. The coils of these windings cover the stator tooth packets, which are located axially. At the ends of the teeth two ring yokes are fixed. The first and second stator windings, which are located on different end sides of the squirrel-cage rotor, are connected in series and connected to field capacitors. The DC welding circuit is powered by a rectifier that is connected to a third stator winding located next to the second stator winding.

 This generator has four significant drawbacks. The first drawback is the strong saturation of the magnetic system in idle mode. This is due to the fact that in order to obtain an acceptable value of the welding current, reactive power is required, which is several times higher than the power consumed by the generator in idle mode. The reactive power is not regulated, therefore, when switching from the welding mode to the idle mode, the generator is saturated. The second disadvantage: with increasing load, the voltage decreases almost linearly [3], which is not optimal, since manual arc welding is most preferable using a source that has a “bayonet” external characteristic (current source). The third drawback is the significant mass of capacitors. This is because with the same magnetic system, the number of turns of the stator windings and the same welding current, the prototype requires more reactive power compared to the claimed solution. The fourth drawback is the soft external characteristic, which prevents its use in autonomous power supply systems without additional regulatory devices.

 The technical results that the claimed invention provides are that there is no significant saturation of the generator during the transition from the welding mode to the idle mode, the possibility of forming “bayonet” external characteristics that are optimal for manual arc welding, and the generator mass is reduced. If necessary, the claimed invention provides power to both consumers with a voltage of 380 V, and consumers with a voltage of 42 V.

 These technical results are achieved by the fact that a three-phase asynchronous electric welding generator containing three three-phase windings, the coils of which cover axially arranged stator teeth, made in the form of packets, the ends of which are closed by ring yokes on each end side of the short-circuited rotor, and the field capacitors are connected to the first and the second windings, the coils of which are placed on different end sides of the rotor, a rectifier connected to the third winding, the coils of which are placed next to the coils of the second winding, it has one capacitor bank, which is connected to the first winding, a second capacitor bank, which is connected to the second winding, and a third battery, the capacitors of which are connected in series in the same phase circuit of the first and second windings, and in the particular case the second the winding is designed to connect consumers with a voltage of 380 V, and the third winding is equipped with bends for connecting consumers with a voltage of 42 V.

 The design of a three-phase asynchronous electric welding generator is shown in FIG. 1. The electrical circuit of the generator - in FIG. 2. The curves of changes in reactive power of the claimed generator and prototype as a function of the load current are shown in FIG. 3. In FIG. 4 shows the external characteristics of the generator. In FIG. 5 shows the external characteristics of the generator and prototype when connecting a three-phase load.

 The generator (Fig. 1) has three three-phase windings 1, 2, 3 and a squirrel-cage rotor of conventional design 4. Coils of stator windings cover packets of stator teeth 5, which are located axially. Two annular yokes 6, 7 are located at the ends of the teeth. A first capacitor bank 9 is connected to the first winding of the stator 1 (Fig. 2). A second capacitor bank 9 is connected to the second stator winding 2. The capacitors in the first and second batteries are connected in a star or delta. The capacitors of the third battery of capacitors 10 are connected in series in the circuit of the same phases of the first 1 and second 2 stator windings. The DC welding circuit 11 receives power from the third winding 3 through a semiconductor rectifier 12. If necessary, the second winding 2 is used to connect consumers 13 with a voltage of 380 V, and the third winding 3 is equipped with bends for connecting consumers 14 with a voltage of 42 V.

 The generator operates as follows. When the rotor 4 is rotated by a drive motor (internal combustion engine, electric motor), the residual flow induces an EMF in the stator and excitation generator windings. In windings 1, 2 and 3, voltages are established that are proportional to the number of turns of the corresponding windings, to the magnitude and ratio of capacitance of capacitors in capacitor banks 8,9,10.

 In idle mode, the voltage on the second winding 2, which is located next to the third winding 3, is greater than on the first winding 1, because the capacity of the first capacitor bank 8 is greater than the capacity of the second capacitor bank 9. The voltage across the capacitors of the third capacitor bank 10 is determined by the vector voltage difference across the first 1 and second 2 windings. With a short circuit, a decrease in the magnetic flux occurs, which permeates the second 2 and third 3 windings, because the short circuit current (load) flowing in the winding 3 is demagnetizing. With a short circuit, the flow increases, which penetrates the first winding 1. An increase in flow causes an increase in EMF and voltages on the first winding 1, which leads to an increase in the reactive power of the first capacitor bank 8 (curve 15, Fig. 3). The decrease in voltage and reactive power of the second capacitor bank 9 (curve 16, Fig. 3) does not lead to a decrease in the total reactive power (curve 17, Fig. 3), because the capacity of this capacitor bank is less than the capacity of the first and third capacitor banks. With a short circuit, the vector difference between the voltage vectors of the same phases of the windings 1 and 2 increases, which leads to an increase in the voltage and reactive power of the third capacitor bank 10 (curve 18, Fig. 3). The generator reactive power varies from 19.2 kVAr (short circuit) to 17.4 kVAr (idle), the short circuit current is 170 A, the capacitance of the capacitors of all batteries is 849.6 μF (C1 = 252 μF, C2 = 192 μF, C3 = 405, b μF). Similar indicators in the prototype have the following meanings: 10 kVar (short circuit); 28.4 kVar (idle); short circuit current - 78 A; the capacitance of the capacitors in three phases is 709 μF.

 When switching from a short circuit mode to an idle mode, the total reactive power of the claimed generator decreases (curve 17, Fig. 3), but does not increase, as in the prototype (curve 19, Fig. 3). To obtain the same short circuit currents in the prototype, it is necessary to increase the capacitance of the capacitors by more than two times (1418 μF). In this case, the reactive power in the short circuit mode (20 kVar) and idle speed (56 kVar) will increase.

 In idle mode, the claimed generator consumes half the reactive power. Moreover, it provides the same short circuit current as the prototype.

 Thus, the magnetic system of the generator in idle mode is saturated less than that of the prototype.

 The formation of bayonet external characteristics is carried out by selecting the value of the capacitance of capacitors in capacitor banks. In FIG. 4 shows the external characteristics of the generator at various capacitance values in the batteries. Curve 20 was obtained with the capacitance of the first capacitor bank C1 = 252 μF, the second C2 = 202 μF, and the third C3 = 405.6 μF (in three phases). Curve 21 is obtained at the following capacitor bank capacitance values: C1 = 192 μF; C2 = 144 uF; C3 = 240 μF. Curve 22 was obtained at: C1 = 192 uF; C2 = 144 uF; C3 = 108 μF. All windings of the generator have an inductive coupling with each other, therefore the capacity of each capacitor bank affects the curve of the external characteristics of the generator. However, the voltage of the third winding 3 in idle mode mainly depends on the capacity of the second capacitor bank 9. When the capacity decreases, the voltage increases. The stiffness of the external characteristic from the idle point to the inflection point is most affected by the first capacitor bank 8. With increasing capacity of the first capacitor bank, the stiffness increases. The short-circuit current mainly depends on the capacity of the third capacitor bank 10. With increasing capacity, the short-circuit current increases.

 Thus, the generator provides “bayonet” characteristics by selecting the capacitance value in three capacitor banks.

 For the analysis of weight and size indicators, we use the table in which the main characteristics of serial welding generators of inductor and collector types are presented, as well as indicators of a prototype three-phase asynchronous electric welding generator and indicators of a three-phase asynchronous electric welding generator, obtained as a result of the calculation. When analyzing the generator parameters, it was assumed that the excitation is carried out from K78-17 type capacitors.

 As can be seen from the table, the lowest specific gravity has a three-phase asynchronous electric welding generator (calculation).

 The specific gravity of the prototype three-phase asynchronous electric welding generator is slightly larger than the specific gravity of the induction-type welding generator 14 and less than the specific gravity of the collector generator.

 Compared with the prototype, the mass of the claimed generator is less, because To obtain the same short-circuit currents, the declared generator requires less reactive power, and therefore less excitation capacitors (849.6 μF versus 1418 μF).

 Studies of the dynamic characteristics of a three-phase asynchronous electric welding generator showed that the voltage on the electrode is restored to the arc voltage in less than 0.03 s, i.e. Three-phase asynchronous electric welding generator meets the requirements for dynamic performance of welding generators.

 Experimental studies of the prototype showed that the generator provides high-quality welding and in this regard is not inferior to serial generators.

 In the absence of a welding load, a three-phase asynchronous electric welding generator can be used as a conventional generator of an autonomous power supply system for supplying consumers with voltage of 380 V and 42V. The claimed generator provides both separate and joint power supply to the welding circuit and consumers. When working on a mixed load, it is advisable to limit the power of consumers to 10-15% of the rated power of the generator. This property of the generator provides certain advantages. For example, when welding at night or in a poorly lit place, the generator provides power to incandescent lamps. Experimental studies have shown that such a load (three lamps of 150 W each) does not significantly affect the welding process. This is explained by the fact that, in the "idle" mode, when the welding current is zero, the voltage (phase) on the lamps has a maximum value (250 V), and when the arc is powered, the voltage on the second winding decreases (170 V), respectively, the power decreases that the lamps consume. Thus, when the generator is operating on the welding arc, the load power automatically decreases (it is a small part of the arc power), and when welding is completed, the lamps are set to the maximum voltage and they again work with full light output. The claimed generator (when working on a three-phase load) has a more rigid external characteristic (curve 23, Fig. 5) compared to the prototype (curve 24, Fig. 5). Curve 23 was obtained with a total capacitance of 849.6 μF, and curve 24 at 709 μF. The curve of the external characteristics of the generator 23 is out of the standard voltage range (380 V ± 5%). The voltage value can be changed by appropriate selection of the number of turns in the second winding. The stiffness of the external characteristic depends both on the capacitance of the capacitor banks and on the ratio of capacities of all three capacitor banks.

 When powering hand lamps in rooms with an increased risk of electric shock, low voltage (not higher than 42 V) is used. Welding is often carried out precisely in such rooms, therefore, to supply low-voltage consumers with a voltage of 42 V, taps from the third stator winding are provided.

 Thus, the conducted experimental studies and preliminary calculations showed that the three-phase asynchronous electric welding generator fully meets the basic requirements that apply to the power sources of the welding arc, provides high-quality welding, has good overall dimensions and can be used both for supplying consumers with voltage of 380 V, and for supplying consumers with voltage of 42 V.

Claims (2)

 1. Three-phase asynchronous electric welding generator, containing three three-phase windings, the coils of which cover axially arranged stator teeth, made in the form of packets, the ends of which are closed by ring yokes on each end side of the short-circuited rotor, field capacitors, which are connected to the first and second windings, whose coils placed on different ends of the rotor, a rectifier connected to the third winding, the coils of which are located next to the coils of the second winding, distinguishing I in that it has a battery of capacitors, which is connected to the first winding, a second capacitor bank, which is connected to the second winding and a third battery, capacitors which are connected in series in a circuit similar phases of the first and second windings.  2. The generator according to claim 1, characterized in that the second winding is designed to connect consumers with a voltage of 380 V, and the third winding of the stator is equipped with bends for connecting consumers with a voltage of 42 V.

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