RU2216883C2 - Power supply for dc arc furnace - Google Patents

Abstract

FIELD: electrical engineering; dc power supply for electrical metal-working installations. SUBSTANCE: power supply has diode groups of three- phase bridge rectifiers connected in series and in parallel by means of controllable diodes whose anodes are connected to ac leads of one bridge set and cathodes, to like-phase leads of other rectifier set. Connected to opposite secondary-winding leads of respective transformer phases are ac leads of sets being connected. Number of bridge sets being connected is unlimited. EFFECT: simplified design, enhanced reliability, enlarged capability of matching power supply and load parameters. 7 cl, 8 dwg

Description

 The invention relates to electrical engineering, in particular to power supplies of an electric arc or other load, requiring deep regulation of voltage and current (electrometallurgical installations), for example, direct current arc furnaces.

 Arc melting furnaces are characterized by a significant decrease in the arc voltage during the melting process due to a decrease in the potential gradient in the arc column as the charge is heated and melted and the working space of the furnace is heated. At a certain stage of the process, the arc voltage decreases so that special measures are required (changing the arc length, increasing the current) to maintain the level of power introduced into the furnace.

 Widely known (Semiconductor rectifiers. / Under the editorship of F.I. Kovalev, G.P. Mostkova. M .: Energy, 1979), series and parallel connection of rectifier devices, providing the necessary coordination with the load parameters at constant power supply. The disadvantage of this source in relation to arc furnaces is the impossibility of promptly switching the power circuit from a serial connection to a parallel one, which leads to the need for a serious disruption of the process with the aim of this switch.

 A device is known for powering an arc direct current furnace (A.S. USSR 1702546), which allows for prompt transition from a serial to a parallel circuit for connecting two three-phase bridge rectifiers. The device contains a three-phase supply transformer with two groups of secondary windings, each of which is connected to a three-phase controlled bridge valve group with a control unit, as well as a three-phase zero controlled valve group and an uncontrolled single-phase valve group. The first of them is connected by AC terminals to the AC terminals of one of the bridge valve groups, and by a direct current output to the furnace electrode not connected to the DC terminals of the same bridge valve group, and the second is connected between the DC terminals of one bridge valve group according to its gates. A disadvantage of the known device is the presence of additional valve groups and the complexity of the control circuit, which reduces the reliability of the device as a whole.

 The closest technical solution, selected as a prototype, is a direct current source for supplying an arc furnace (Russian Patent 1790321), containing the first and second three-phase bridge valve sets with smoothing reactors in DC circuits, each consisting of the first and second three-phase zero groups of valves whose DC outputs of the same name are intended to be connected to the electrode and the hearth of the furnace, respectively, and the AC terminals of each of them are intended to be connected to the terminal the corresponding secondary windings of the supply transformer, the third and fourth three-phase zero groups of valves, the opposite DC terminals of which are interconnected, and the alternating current leads are connected respectively to the alternating current terminals of the first and second three-phase bridge sets, as well as a control system and a switching device. One of the three-phase zero groups of valves of each bridge set is made uncontrolled, a smoothing reactor is included in its DC circuit, and the third and fourth three-phase zero groups of valves are made controlled, and the third, fourth controlled three-phase zero groups of valves of the bridge valve sets are installed so that the conclusions alternating current, designed to connect to the terminals of the corresponding secondary windings of the specified transformer, connected the same terminals of the controlled valve lei of the indicated groups, and smoothing reactors are connected in series in the DC circuit of uncontrolled valve groups of the corresponding bridge valve sets.

 The disadvantage of this device is the presence of additional controlled three-phase zero groups of valves, which leads to an increase in the cost of the power source and a decrease in its reliability.

 The technical task of the invention is the creation of a simpler and more reliable source of direct current for powering the arc furnace with advanced possibilities of matching the source and load parameters, increasing the power factor and efficiency of the installation, providing more complete compensation of magnetic fields in the converter, reducing its weight and dimensions, increasing speed charge melting at a lower specific energy consumption.

 The problem is solved in that in the power source of the DC arc furnace, containing two three-phase bridge valve sets, the unipolar DC terminals of which are designed to connect respectively to the arch and hearth electrodes of the furnace, and between the AC terminals designed to connect the corresponding secondary windings of the three-phase supply transformer, connecting elements are included, controlled by a switching device connected to the control system, Nogo current bridge rectifier sets are attached to opposite ends of the secondary windings of the respective phases, and each of the coupling elements is in the form of at least one regulation valve, which is connected to the anode terminal of the first set, and the cathode - to the phase terminal of the same name of the second set.

 The problem is also solved by the fact that the power source is equipped with at least one additional three-phase bridge valve set, the AC terminals of which are connected to the terminals of the previous set by similar additional connecting elements and connected to the ends of the additional secondary windings of the corresponding phases of the transformer, opposite to the ends, to which connected the findings of the previous bridge valve kit.

 The problem is also solved by the fact that the power supply is equipped with another additional three-phase bridge valve set, which is connected to the additional secondary windings of the transformer and connected to the previous set by two three-phase zero groups of controlled valves connected between the alternating current terminals of the indicated sets and interconnected by multipolar terminals direct current, and the valves of these groups are included in accordance with the valves of the bridge valve sets.

 The problem is also solved by the fact that the power source is equipped with at least two additional three-phase bridge valve sets, the AC terminals of which are connected to the opposite ends of the additional secondary windings of the corresponding phases and interconnected by similar additional connecting elements, and at least one of the additional sets is connected to one of the previous ones by means of two three-phase zero groups of controlled gates connected between the terminals of the variables first current and said sets of interconnected DC terminals of different polarities, and the gates of these groups included accordance with valves connecting the AC terminals of bridge rectifier remaining sets.

 The problem is solved by the fact that the first and last three-phase bridge valve sets can be made semi-controllable.

 In addition, the problem is solved in that in at least one pair of three-phase zero groups, one of the groups is made of uncontrolled valves.

 The problem is also solved by the fact that reactors with pairs of counter-connected magnetically connected parts of the windings are alternately connected to the bipolar DC terminals of three-phase bridge valve sets, and the counter-connected parts of the windings of each reactor are connected to the unipolar DC terminals of the bridge valve sets.

 The invention is illustrated by drawings.

 Figure 1 shows a diagram of a power source with connection to the electrodes of the furnace.

 In FIG. Figure 2 shows a simplified diagram of a power supply with two additional three-phase bridge valve sets.

 In FIG. 3 shows the connection of bridge valve sets (not shown) by means of two three-phase zero groups of controlled gates.

- вентиль выключен, значок

- вентиль включен.Figure 4-6 shows a diagram of the inclusion of the source shown in figure 2. Icon

- valve is off, icon

- the valve is on.

 Figure 7 shows an embodiment of the connecting elements.

 In FIG. Figure 8 shows the connection diagram of the reactors with the terminals of the power source and with the load.

 The power source of the arc furnace (Fig. 1) according to the invention comprises a three-phase supply transformer with secondary windings 1 and 2, to which three-phase bridge valve sets 3 and 4 are connected, assembled from controlled valves, for example thyristors. In the anode group of valves of one of the sets and the cathode group of valves of the other set, uncontrolled valves, for example diodes, i.e. bridge valve kits can be semi-controlled, which helps simplify and reduce the cost of the power source. Inductors (reactors) 5 and 6 can be installed in the DC circuit of uncontrolled valve groups, which provide voltage equalization of bridge valve sets when they are connected in parallel and increase the stability of arc burning. Unipolar DC leads of two bridge valve sets are interconnected and connected to the vault 7 and hearth 8 electrodes of the furnace 9 (or other load requiring deep regulation of voltage and current, for example, for DC welding and in other applications). The AC terminals of the bridge valve set 3 are connected to the beginnings of the secondary windings 1 of the transformer, and the AC terminals of the set 4 are connected to the ends of the secondary windings 2. Between the AC terminals of the bridge valve sets connected to the secondary windings of the same phases, the connecting elements 10 made in at least one controlled valve, for example, a thyristor, which is connected to the output of set 3 by the anode and by the cathode to the output of set 4. Vent control electrodes or bridge sets 3, 4 and connecting elements 10 are connected to the control unit 11 through a switching device 12, which enables the on and off switching of valve groups.

 The device according to the invention uses a smaller number of controllable valves in the connecting elements in comparison with the prototype, which, in addition to simplifying and reducing the cost, makes the claimed power supply more reliable and economical - it increases its efficiency.

 The above-described power supply can be supplemented by at least one more three-phase bridge valve set, the AC terminals of which are connected to the terminals of the previous set by similar additional connecting elements and connected to the ends of the additional secondary windings of the corresponding phases of the transformer, opposite to the ends to which the terminals are connected previous bridge valve kit. The use of this source is possible to power a single-electrode, as well as a multi-electrode direct current furnace. By switching the controlled valve groups of the bridge sets and connecting elements, the following operating modes can be realized: 1) parallel connection of three bridge sets connected to one electrode or each to the corresponding electrode of the furnace; 2) the sequential inclusion of three bridge sets connected to one electrode with tripling the rectified voltage; 3) series connection of two bridge sets connected to one electrode with doubling the rectified voltage.

 The power source shown in figure 2, it is advisable to use to power an arc furnace with one arch electrode, as well as with an even number of them. This source is equipped with two additional three-phase bridge valve sets 13 and 14, the AC terminals of which are connected to the opposite ends of the additional secondary windings 15 and 16 of the corresponding transformer phases (an additional three-phase transformer can be installed) and interconnected by additional connecting elements 17 similar to elements 10 An additional bridge kit 13 is connected to the kit 4 by means of connecting elements 18, which can be performed to the elements 10 or according to the circuit of Fig. 3, formed by two three-phase zero controlled valve groups 19 and 20, which are connected between the AC terminals of sets 4, 13 and interconnected by bipolar DC terminals, and the valves of these groups are connected in accordance with the valves connecting AC terminals of the remaining bridge valve sets. When such a circuit is implemented (Fig. 3, 7), the voltage requirements for thyristors 19, 20 and diodes 21 of the connecting elements 10, 17, 18 are reduced. In addition, more complete compensation of magnetic fields in the design of the converter unit and a reduction in electromagnetic losses are provided, which helps to reduce the mass and dimensions of the rectifier.

 The inclusion of reactors (chokes) 22 (23), in which the magnetically connected parts 24 and 25 (respectively 26 and 27) of the windings are made on the same magnetic circuit and are turned on in accordance with Fig. 8, allows to reduce their mass and dimensions, as well as improve the current distribution along the valve sets when connected in parallel to the load 28.

 The operation of the above-described power source is carried out according to the following modes, implemented by switching the controlled groups of valves of the bridge sets and connecting elements by switching, using a switching device, control pulses generated by the control unit.

 Figure 4 shows the parallel connection of four bridge valve sets with a nominal rectified voltage on each. The valves of the connecting elements 10, 17 and 18 in this mode are switched by the switching device to the off state.

 Figure 5 shows the series connection of the valve groups of each pair of bridge valve sets with doubling the rectified voltage, which can be connected to one or to a pair of vault electrodes of the furnace. In this mode, using the connecting elements 10 (and 17), the anode groups of kit 3 (13) are cascaded to the cathode groups of kit 4 (14).

 In FIG. 6 shows the series connection of the valve groups of the first and last bridge valve sets and all connecting elements. The anode group of kit 3 is cascaded to the cathode group of kit 14 via connecting elements 10, 18, 17. In this case, a quadruple rectified voltage at a rated rectified current can be applied to one electrode.

 The possibility of stepwise changing the rectified voltage allows in some cases to significantly simplify the design of the supply transformer by eliminating the device for switching the turns of the primary winding, which favorably affects the cost of the power source and reliability.

 In addition, reducing the number of valves turned on allows you to increase the efficiency of the power source. The use of deep control of the furnace voltage by switching valve groups creates the conditions for increasing the power factor of the power source and, as a result, allows to increase the rate of charge melting and reduce the specific energy consumption in the arc furnace.

Claims (7)

 1. The power source of the DC arc furnace, containing two three-phase bridge valve sets, the unipolar DC terminals of which are designed to connect respectively to the arch and hearth electrodes of the furnace, and between the AC terminals designed to connect the corresponding secondary windings of the three-phase supply transformer are connected elements controlled by a switching device associated with the control system, characterized in that the AC terminals of the bridges x valve sets are attached to opposite ends of the secondary windings of the respective phases, and each of the coupling elements is in the form of at least one regulation valve, which is connected to the anode terminal of the first set, and the cathode - to the phase terminal of the same name of the second set.  2. The power supply according to claim 1, characterized in that it is equipped with at least one additional three-phase bridge valve set, the AC terminals of which are connected to the terminals of the previous set by similar additional connecting elements and connected to the ends of the additional secondary windings of the corresponding phases of the transformer opposite to the ends to which the leads of the previous bridge valve kit are connected.  3. The power supply according to claim 1 or 2, characterized in that it is equipped with an additional three-phase bridge valve set, which is connected to additional secondary windings of the transformer and connected to the previous set by two three-phase zero groups of controlled valves connected between the alternating current terminals of these sets and interconnected by bipolar DC terminals, and the valves of these groups are included in accordance with the valves of the bridge valve sets.  4. The power supply according to claim 1, characterized in that it is equipped with at least two additional three-phase bridge valve sets, the AC terminals of which are connected to the opposite ends of the additional secondary windings of the corresponding phases and interconnected by similar additional connecting elements, and at least one of the additional sets is connected to one of the previous ones by means of two three-phase zero groups of controlled gates connected between the terminals of the ennogo current and said sets of interconnected DC terminals of different polarities, and the gates of these groups included accordance with valves connecting the AC terminals of bridge rectifier remaining sets.  5. The power supply according to claim 3 or 4, characterized in that, in at least one pair of three-phase zero groups, one of the groups is made of uncontrolled valves.  6. The power supply according to claim 1, or 2, or 3, or 4, characterized in that the first and last three-phase bridge valve sets are made semi-controlled, the first having an uncontrolled cathode group of valves, and the last with an anode one.  7. The power source according to any one of paragraphs. 1-6, characterized in that reactors with pairs of counter-connected magnetically connected parts of the windings are alternately connected to bipolar DC terminals of three-phase bridge valve sets, and the counter-connected parts of the windings of each reactor are connected to unipolar DC terminals of the bridge valve sets.

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