RU1612961C - Power supply for steel-melting dc arc furnace - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: power supply has transformers 1, 2 with valve groups 3-8 connected to their secondary windings. Power supply has also two control units, each having series-connected load current sensor 18, comparison assembly 19, current regulator 20, pulse-phase control system 21, and switching unit 22. Power supply enables sequential supply of voltage to electrode from two bridge circuits which limits transformer voltage and holds it at minimum level so as to prevent change-over of primary winding turns and connection groups of primary windings. EFFECT: improved mass-size and power characteristics of power supply. 1 dwg

Description

 The invention relates to electrical engineering and can be used in AC to DC converters, designed to supply DC electric arc furnaces with an even number of movable electrodes.

 The purpose of the invention is the improvement of mass and energy parameters of the source.

The drawing shows a circuit diagram of the proposed source. It contains transformers 1,2, to the secondary windings of which valve groups 3-8 are connected. At the same time, valve groups 3.4 form the first controllable valve set included in a three-phase bridge circuit, and valve groups 6.7 form a second similar set. Both valve sets are connected through the first smoothing reactors 9.10 with direct current leads to two movable electrodes 11,12, and through the second smoothing reactors 13,14 - to two stationary electrodes 15,16 of the furnace hearth 17. Fixed electrodes 15,16 can be connected between themselves. Valve groups 5 and 8 form the third and fourth valve sets included in a three-phase zero circuit. The source also contains two control units, each of which contains in series a load current sensor 18, a comparison unit 19, a current regulator 20, a pulse-phase control system 21 and a switching unit 22. The first three-channel terminal groups of the pulse-phase control system 21 are connected respectively to the control inputs of the valve groups 4 and 7, respectively, and the second three-channel groups of outputs through the switching blocks 22 are connected to the control inputs of the valve groups 3 and 5 in the first case and the valve groups n 6 and 8 in the second case. At the second input of each comparison node 19, a current reference signal U _{3 is} connected, and at the inputs of the switching blocks 22, the switching signal is U _{input 1} and U _{input 2,} respectively.

The source also contains a unit 23 for setting the current frequency common to both control units, the first and second outputs of which are connected to the second input of the pulse-phase control system 21 of each control unit. At the input of block 23, a permission signal U _{in3 is connected} .

 The source works as follows.

 An alternating voltage of the mains frequency is supplied to the primary windings of transformers 1,2.

 The voltage from the secondary winding of the transformers 1 is supplied to the valve groups 3,4,5, and from the secondary winding of the transformer 2 to the valve groups 6,7,8.

In the initial melting period, when a high (double) voltage is required, one of the two electrodes, for example 13, is put into operation, and the second electrode is raised, and an algorithm for controlling valve groups is provided, in which unlocking pulses are applied to the vertical groups 4-7. The specified algorithm is provided by applying to the inputs of blocks 22 signals U _in1 "1" and U _in2 "0". Thus, a double voltage is applied to the electrode 13 relative to the electrodes 15, 16 due to the series connection of two three-phase bridges formed by groups 4-7.

 Block 23 sets the current frequency in this mode does not work, its input is a logical signal "0". The output signal of the block 23 "1" allows the operation of blocks 21.

After penetration of the well under the electrode 22, it rises and the control algorithm is changed so that the unlocking pulses are supplied to valve groups 3.4 and 7.8. For this, signals U _in1 = 0 and U _in2 = 1 are _supplied . Now a double voltage is already applied to the electrode 14, in this mode, the block 23 also does not work. After penetration of the well under the electrode 12 and provided that the voltage on the arc can be reduced by half, the control algorithm is changed for the third time.

Set U _in1 = 1 and U _in2 = 0, i.e., valve groups 3.4 and 6.7 are _turned on and both electrodes 11, 12 are put into operation, each of which is applied relative to the electrodes 15.16 the voltage of one valve set, and the main part of the heat is in this mode until the formation of a liquid bath.

In this case, the voltage on the arc of the electrode continues to decrease. After the introduction of alloying additives, a fourth control algorithm is implemented when all three input signals U _in1 , U _in2 , U _in3 are logical "1". In this mode, unlocking pulses are applied to valve groups 4.5 and 7.8 at the command of block 23, which provides variable operation of groups 4.5 and 7.8 with a given low frequency, for example 5 Hz. Moreover, during the operation of three-phase bridges formed by groups 4.5 and 7.8, their output voltage is applied between two electrodes to two arc gaps, which contributes to the better use of transformers 1,2. A low-frequency current passing through a liquid bath from one electrode to another provides mixing of the liquid metal.

 The current regulators 20 provide stabilization of the arc current in all modes of operation of the source except for the fourth low frequency mode, when the current sensors 18 are not surrounded by the arc current. In the first three modes, at least one of the current sensors 18 is surrounded by current. The stabilization of the arc current of the valves in this case is carried out by changing the phase (angle) of unlocking one or two valve sets. Moreover, in the serial connection of bridges, one of them works with a fixed angle of unlocking the valves. Changing the phase of the pulses for unlocking the valves is carried out by the block 21 at the signal of the regulator 20.

The output signals of block 23 with an input signal U _in3 = 1 are rectangular pulses that follow at a given frequency. The duration of the pulses is equal to half the period of the low frequency, and the pulses at its two outputs are shifted in time by half a period of low frequency.

With U _in3 = 0, the operation of block 23 is blocked and signals of a unit level appear at its outputs.

This mode of operation of block 23 is easy to implement by introducing into its composition the logical elements AND and NAND, the outputs of which are interconnected and are one of the outputs of the block, their second inputs are also connected and connected to the signal U ₃ , and the first inputs are connected respectively to pulses setting the frequency and the logic signal "1".

 Due to the introduction of two zero valve sets, it becomes possible, with their respective switching, to supply the voltage of two bridge systems to the electrodes in turn, which allows to limit the transformer power at a minimum level and to exclude switching devices of the primary winding turns and primary connection groups, which improves the energy performance of the device and simplifies his. (56) Electric industrial furnaces. Arc furnaces and special heating installations. Ed. A. D. Svenchansky, M., Energoatomizdat, 1981, p. 262, 263.

 French patent N 2588434, cl. H 02 M 7/155, 1984.

Claims (1)

 POWER SOURCE OF A DC STEEL ARC FURNACE with two movable electrodes and a conductive hearth, containing the first and second controlled valve sets included in a three-phase bridge circuit, the first DC outputs of the same name are intended for connection through the first smoothing reactors to the furnace electrodes, the second of the same name of each set are designed to be connected through the second smoothing reactors to the hearth of the furnace, and the alternating current leads of each set are black h the first and second transformers - to the supply network, characterized in that, in order to improve the weight and size and energy parameters of the source, the third and fourth controlled valve sets are included in it, included in a three-phase zero circuit, the AC terminals of the third valve set are connected to the terminals alternating current of the first valve set, and the valves in the branches of the third valve set are turned on counter to the valves in the branches of the first valve set, For connecting to the furnace electrode, the AC terminals of the fourth valve set are connected to the AC terminals of the second valve set, and the valves in the branches of the fourth valve set are turned in opposite to the valves in the branches of the second valve set designed to connect to the furnace electrode, the current of the third valve set is connected to the first terminal of the second valve set, and the DC terminal of the fourth valve set is connected to the first Displayed first valve kit.