SU1192033A1 - Electric power supply system for steel melting arc furnace - Google Patents

Abstract

1. POWER SUPPLY SYSTEM OF THE ARC STEEL MELT, containing a furnace transformer, high-harmonic filters connected to the primary windings of the furnace transformer, counter-parallel thyristors with a system of pulse-phase phase control, current measuring organs, different from that, with the aim of extending the limits and Due to the accuracy of balancing the currents in the power supply system, it additionally contains converters of the effective current value and the unit for selecting the least loaded phase, with primary The furnace transformer windings are connected in a triangle pattern, the indicated anti-parallel thyristors are included in the dissection of the furnace transformer primary windings, and the current measuring units are connected to the output windings of the current measuring units, the outputs of which are connected to the selector unit least connected to the primary windings of the furnace transformer. the loaded phase, and the outputs of the block of the least loaded phase are connected to the system inputs of the pulse-phase ofaznogo control. 2. The power supply system according to claim 1, wherein the selection unit of the least loaded phase comprises memory devices, a reference signal adder, a comparison unit, an inverter unit, an adder unit, a block of Signal matching schemes, electronic keys, In this case, the outputs of the transducers of the effective current value are connected to the inputs of memory devices whose outputs are connected to one of the inputs of the comparator unit and to the inputs of the adder of the reference signal, and the output of the adder of the reference signal; vneny, you are a. Comparison block moves are connected to one of the adder block inputs and to 9 inputs of the inverter block, block outputs: А9 inverters are connected to other inputs of the adder block, the outputs of which are connected to the first inputs of electronic keys and the signals block outputs the coincidence of the signs of the signals is connected to the second inputs of the electronic switches, and the outputs of the electronic switches are connected to the inputs of the impulse-phase pah control.

Description

The invention relates to electrical engineering, in particular to the power supply systems of arc steel-smelting furnaces. The aim of the invention is to expand the limits of balancing and varying the accuracy of balancing. in the power supply system of arc steel-smelting furnaces. Fig. 1 shows a block diagram of a power supply system for an electric steel-smelting furnace, Fig. 2 is a block diagram of a selection of the least loaded phase; Fig. 3 is a vector diagram of currents. The power supply system of the steel-making arc furnace (Fig. 1) contains the power supply system 1, from which the arc steel-smelting furnace 2 is fed through a furnace transformer 3, the counter-parallel thyrisers 4 are included in the dissection of the primary windings 4, in series with the primary windings of the furnace transformer 3 are transformers current 5, in the secondary circuit of which shunts 6 are connected, to which the anti-parallel thyristor protection unit 7 and effective current converters 8 are connected, and the outputs of block 8 are connected to the input m of the least loaded phase selection unit 9 whose outputs are connected to the pulse phase-phase control system 10, and the outputs of the pulse phase-phase control system are connected to the control electrodes anti-parallel to the thyristors 4, in addition, filters are connected to the electrical supply system 1 higher harmonics 11. Block 9 choice of the least loaded phase (figure 2) contains memory 12, the inputs of which are connected to the outputs of the transducers effective values of currents 8, and the outputs of the storage devices 12 are connected They are connected to one of the inputs of the comparison unit 13 and to the inputs of the adder of the reference signal 14, the output of which is connected to the upstream inputs of the comparison unit 13, and the codes of the comparison unit 13 are connected to one of the inputs of the block of adders 15 and to the inputs of the inverter unit 16, the outputs of which are connected to the second inputs of the block of adders 15, the outputs of block 16 are connected to the inputs of the matching circuit signs of the signals 17 and to one of the inputs of the electronic switches 18, and the outputs of the matching circuits of the signals of the signals 17, the outputs of the electronic switches 18 are connected to the second inputs of the electronic switches enes to the system per phase pulse-phase control system 10. The power electric arc furnace operates sleduyupschm manner. The inequality of the load resistances of an arc steel-smelting furnace 2, connected according to a star, causes a skew and phase shift of the linear currents 1e „, 1-96 (Figure 1). When this occurs, the phase currents Iflii imbalance occur in the secondary windings of the furnace transformer 3 and, accordingly, currents 1d0, IBC 1c in the primary windings connected in a triangle pattern. Asymmetrical 1dc currents, IRC sd forming an irregular triangle (Fig. 3), will create direct and reverse currents in linear currents 1d, 1, power supply system, since the power supply of arc steelmaking furnaces is carried out from a three-phase voltage system without a neutral wire. In order to achieve the symmetry of the linear currents 1d, Ig, IP systems are electro-. supplies from shunts 6 are removed signals proportional to the instantaneous values of the phase currents, IRC-CA and fed to the transducers of the effective current value 8, forming signals proportional to the effective values of the phase currents 1dd, Igc CAJ after which these signals are sent to the memory of the device 12, where they are remembered on the interval from one to several periods of the industrial frequency. From memory devices 12, signals 1dr, Igp, 1dd are fed to adder 14, the output of which is the sum of signals of all phases (1dr + 1d. + 1 (.d) with the opposite sign, the module of which is greater than the modules of signals of any short-circuit phases. This sum is the reference signal IQ and is fed to one of the inputs of the comparison unit 13, to the second inputs of which signals are fed directly from the inputs of the storage devices. 12. As a result of the comparison, the differences between the reference signal 1, n, and the signals of the corresponding phases are obtained at the outputs of the comparison unit 13 i.e. (A1d5, ulftc-CA reverse Signs of the corresponding differences depend on the values of the signals proportional to the current values of the phase outflows. For a larger current, the difference will be smaller, and for a smaller one, greater. On the inverters 16, the signal differences change signs, and in the block of adders 15 the difference of signals is compared (l1dd, --cfl among themselves so that the differences of the other phases are subtracted from each difference, and the output of the block of adders 15 results in the difference of the differences of signals with opposite signs, with each phase having o two signals, signals (ltdc41 gp) and () to phase bc are signals (ltvs-l ae,) and (l1rc), and phase cc - signals (l1rd-d1dv) and (xyd d1). the smaller differences from the larger one are subtracted, then two signals — a with negative signs — that correspond to the phase with the lowest current are obtained, and these signals are fed to the inputs of the coincidence sign of the signals of this phase 17, and from the subtractions between the other differences, signals with different or positive signs, which correspond to phases with large currents, and these signals are sent to the rest of the Signs matching symbols of the signals 17. A matching circuit of the signs of the signals of the phase with the lowest current at the output causes a signal that is fed to the input of electronic switches of the same phase, and the electronic switches 18 feed signals to the controllers of the pulse-phase-phase control system 10 of the other two phases, reducing The currents in these phases of the CHO of the magnitude of the smallest current with the help of anti-parallel thyristors4 included in the corresponding phases. After alignment of the phase currents, the moduli of the DHdv - ls L1sd modulate, resulting in comparison of which the blocks of adders 16 at the outputs of this block get zeros, therefore the signals acting on the controllers of the pulse phase-phase control system are not generated and all the thyristors return to the open state tion ,.

For example, the smallest current in the phase AB, the largest in the phase SA and the average in magnitude between the highest and the lowest. In the phase BC. From shunts 6 signals are received that are proportional to the instantaneous discharge of phase currents 1dv. ps 1cd, to the effective current value converters 8, on the outputs of which receive analog signals 1dv ac 1 (d proportional to the effective values of the corresponding phase currents that are fed to the inputs of the storage devices 12, where they are stored for one to several periods. devices 12, the signals with positive signs are fed to one of the inputs of the comparator unit 13 and to the three inputs, according to the number of phases, adder 14, which forms the reference signal IOH -AB - BS SI ° module larger from the signals, phases, and from the reference signal with a negative sign enters the other inputs of the comparator block 14. At the outputs of this block, the differences between the reference signal and the signals of individual phases with positive signs are obtained, for phase AB - d 1; q -1dr + 1 dts Largest in modulus, for phase BC - l1v (.- 1op vs smaller in magnitude from yHdts and for the phase SA - D 1 (.d -1 (50 sf the smallest in modulus that fall on one of the inputs of the block of adders 15 and the inputs of the inverters 16. At the outputs of the processor, the difference L1dts, D1diHs with negative signs, which are received at the second inputs b eye adders 15 in the following order: to adders phase signals supplied ulgc AB and BC phase - and signals UIpiB y1sd, SA phase - yHdts signals and A.,. The outputs of the block of adders 15 receive signals for the phase .AB with the lowest current - () AB --- CA are both with negative signs, for the BC phase with a high current + (and - (Л1) different signs and for the phase SA with the highest current + (S (, dy1dv) and + (positive signs. These signals go to the inputs of the sign matching circuit of the signals 17 and one of the inputs of the electronic switches 18. The sign matching circuit of the signals of the signals of phase 17 AB will work because its inputs are given two signals negative signs, i.e. - (and - (d1dd-s (; d) and - (the signal to turn on the electron x keys 18 included in the phase AB, which served signals

Phase-phase and phase-phase phase control systems 10. The signals of these controllers, which are proportional to the signals (, A1) and (1db-A1sl), change the unlocking angles of the counter-parallel thyristors 4 in the phases VS and CA, thus that the currents of the phases BC and SA decrease to the magnitude of the current of the phase AB, which will lead to equalization modulo 1dr, Igc cd, therefore, to the disappearance of negative sequence currents in the currents of the power supply system 1d, 10, (;.

The proposed power supply system for an electric arc furnace can be used for balancing current in three-phase power supply systems for electric arc furnaces, workshops with electric welding equipment and other consumers with asymmetrical, non-linear and rapidly changing loads. In addition, the power supply system of the method automatically balances the currents of the power supply system in 0.04-0.06 s, without the need to change the position of the electrodes of the electric steel-arc furnace, if the value of the arc phase current with the lowest

 current not less than a given. In the event of an arc breaking and current disappearing, the device will turn off the currents of the remaining phases using thyristors, thereby greatly facilitating the operating conditions of the main electrical equipment and switching equipment of the power supply system. In addition, in high-power arc steel-smelting furnaces, the inequality of arc power in phases can reach large values.

(0.5-0.7) (1.3-1.5) P,

which leads to asymmetry of the currents in the power supply system of electric arc furnaces, reaching 4.5%. The use of the proposed power supply system makes it possible to reduce the asymmetry of the currents in the power supply systems of arc steel-smelting furnaces to 1.52% per. account phase control and high speed power system.

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Claims (2)

1. The power supply system of the arc furnace, containing the furnace transformer, filters of higher harmonics connected to the primary windings of the furnace transformer, counter-parallel thyristors with a pulse-phase phase-phase control system, measuring currents, characterized in that, in order to expand the limits and increase the accuracy of balancing currents in the power supply system, it additionally contains converters of the effective current value and a unit for selecting the least loaded phase, while the primary windings the furnace transformer is connected according to a triangle circuit, the indicated counter-parallel thyristors are included in the cut-out of the primary windings of the furnace transformer, and the current measuring elements are connected in series with the primary windings of the furnace transformer, the converters of the effective current values are connected to the outputs of the measuring currents, the outputs of which are connected to the least the loaded phase, and the outputs of the unit for selecting the least loaded phase are connected to the inputs of the pulse-phase phase-by-phase control system eniya. 2. The power system according to claim 1, characterized in that the unit for selecting the least loaded phase contains. memory devices, the reference signal adder, comparator unit, the unit inverters block summa- _e tori block diagrams coincidence signal S of signs, electronic keys, wherein the transducer outputs effective current value are connected to inputs of memory devices, the outputs of which are connected to one input of block comparison to the inputs of the adder of the reference signal, and the output of the adder of the reference signal is connected to other inputs of the unit of comparison, you-. the strokes of the comparison block are connected to one of the inputs of the adder block and to the inputs of the inverter block, the outputs of the inverter block are connected to other inputs of the adder block, the outputs of which are connected to the first inputs of electronic keys and to the inputs of the block of signal sign matching circuits, the outputs of the block of signal sign matching to the second inputs of the electronic keys, and the outputs of the electronic keys are connected to the inputs of the pulse-phase control system. and ,, 1192033 1 1192033 2