JP2005085711A - Automatic electric power control device of arc furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic electric power control device of an arc furnace in which a desired furnace injection electric power can be maintained always even if a power supply voltage fluctuates greatly. <P>SOLUTION: This device is provided with an instrument transformer 52 to detect an electrode voltage V<SB>FB</SB>of the arc furnace 3, a voltage control circuit to change the electrode voltage V<SB>FB</SB>by selecting alternatively a plurality of taps of the transformer 2 for a furnace, and a judgment part to actuate the voltage control circuit so as to return the electrode voltage V<SB>FB</SB>back within a prescribed range in the case the electrode voltage V<SB>FB</SB>exceeds downward or upward a prescribed range under the selected tap. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an automatic power control apparatus for an arc furnace, and more particularly to an automatic power control apparatus that can always supply desired arc power regardless of fluctuations in power supply voltage.

  In the arc furnace, it is necessary to supply desired arc power into the furnace in accordance with each furnace period such as an ignition period, a boring period, a puddle formation period, and a melting period. Therefore, in the past, the electrode current (furnace current) was maintained at a constant set value by an electrode lifting device and the like, and the tap of the furnace transformer was switched and selected in each furnace period, so that it corresponded to each furnace period. Desired arc power is supplied into the furnace.

Patent Document 1 discloses a technique in which the electrode current is reduced by switching the tap of the furnace transformer so as to reduce the voltage fluctuation when the fluctuation of the power supply voltage at the power receiving point increases. ing.
JP-A-9-106886

  However, in the above-described conventional automatic power control apparatus, since taps selected in each furnace period are determined in advance, if there is a fluctuation in the power supply voltage exceeding the expectation during the furnace period, for example, a desired electrode voltage is As a result, there was a problem that arc power (furnace input power) was insufficient and the time for melting and refining became longer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an automatic power control apparatus for an arc furnace that can always maintain a desired furnace input power even if the power supply voltage fluctuates greatly.

In order to achieve the above object, according to the first aspect of the present invention, voltage detection means (52) for detecting the electrode voltage (V _FB ) of the arc furnace (3) and a plurality of taps of the furnace transformer (2) are selected. Selection means (46) for changing the electrode voltage (V _FB ) by selective selection, and the electrode voltage when the electrode voltage (V _FB ) exceeds a predetermined range below or above the selected tap. And a control means (42) for operating the tap selection means (46) to return (V _FB ) to a predetermined range.

  In the first invention, when the power source fluctuates and the detected electrode voltage exceeds a predetermined range under the tap selected at that time, the tap selection means is activated to reduce the electrode voltage to the predetermined range. A new tap is selected that returns to the inside. Thereby, even if the power supply voltage fluctuates greatly, a desired furnace input power is always supplied.

In the present second invention, a current detecting means for detecting an electrode current (I _FB) (51), the current changing means (45) for changing the set value of the electrode current (I _FB) and further comprising a control means (42 ) Activates the tap selection means (46) when the electrode voltage (V _FB ) falls below or above a predetermined range under the selected tap, and the electrode under the newly selected tap. The current changing means (45) is operated so that the furnace input power calculated from the voltage (V _FB ) and the electrode current (I _FB ) matches the furnace input power set in the furnace period at this time. Is set. The tap selection means (46) may be operated when the electrode voltage (V _FB ) exceeds the predetermined range downward or upward for a predetermined time or more. In this case, the predetermined range or the predetermined time may be determined according to the selected tap. According to the second aspect of the present invention, the furnace power can be maintained at a desired value even more satisfactorily with respect to fluctuations in the power supply voltage.

  In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

  According to the automatic power control apparatus for an arc furnace of the present invention, desired arc power can always be supplied even if the power supply voltage fluctuates greatly.

FIG. 1 shows the overall configuration of the automatic power control apparatus. The main circuit 1 leading to the commercial power source is provided with a furnace transformer 2 provided with a tap changer, and the secondary side circuit 11 reaches the electrode 31 of the arc furnace 3. The furnace transformer 2 outputs a signal 2a of the currently selected tap position to the control unit 4, while the control unit 4 taps to select a required tap position for the furnace transformer 2. A selection command signal 4a is output. The secondary side circuit 11 is provided with an instrument current transformer 51 and an instrument transformer 52, and the current (electrode current) I _FB and voltage (electrode voltage) V _{FB of the} secondary side circuit 11 are respectively sent to the control unit 4. Has been fed back. The main circuit 1 is actually three-phase.

  The electrode 31 is held by an electrode lifting mechanism 61 and can be lifted and lowered. The electrode lifting / lowering device 62 receives the current command signal 4b from the control unit 4 and appropriately raises or lowers the electrode 31 by the electrode lifting / lowering device via the electrode lifting / lowering driving device 63 to the molten raw material 32 in the furnace. A predetermined arc current (electrode current) is always supplied.

  FIG. 2 shows the configuration of the control unit 4. The control unit 4 includes a power calculation unit 41, a determination unit 42, a power input matrix 43, and a control table 44, which are realized by a computer. The control unit 4 is provided with a current control circuit 45 and a voltage control circuit 46, and the current control circuit 45 outputs a current command signal 4b to the electrode lifting device 62 (FIG. 1). The voltage control circuit 46 outputs a tap selection signal 4a to the furnace transformer 2 (FIG. 1).

  Power control by the control unit 4 is performed as follows. That is, in the power matrix 43, tap numbers (set tap numbers that are preset and set in each furnace period corresponding to each furnace period indicated by “STEP” of 1, 2, 3,... And the set current value (I) of the furnace period is stored, and the control unit 4 determines the set voltage value and the set current value of the furnace period as the current control circuit 45 and the voltage control circuit, respectively, as the furnace period progresses. 46. The voltage control circuit 46 issues a tap selection command signal 4a to the furnace transformer 2 in order to make the electrode voltage coincide with the set voltage value. The current control circuit 45 issues a current command signal 4b to the electrode lifting device 62 so that the electrode current matches the set current value.

The control table 44 stores a tap number, a time (T), and an upper limit value (VU) and a lower limit value (VL) of the deviation corresponding to each tap number. The determination unit 42 determines that the electrode voltage V _FB fed back exceeds the upper limit value (VU) corresponding to the tap number selected at this time or falls below the lower limit value (VL) due to fluctuations in commercial power. If it is determined that this time exceeds the time (T) corresponding to the tap number, the voltage control circuit 46 returns the electrode voltage V _FB to the range between the upper limit value (VU) and the lower limit value (VL). Such a new tap number is instructed to be sequentially switched and selected. The voltage control circuit 46 issues a tap selection command signal 4a in accordance with this command. When the electrode voltage V _FB returns to the range between the upper limit value (VU) and the lower limit value (VL), the selected tap number is also returned to the forward dimension.

In the present embodiment, while a new tap number is selected, a power calculation unit 41 for the set arc power (that is, the product of the set voltage value (set tap number) and the set current value) in the furnace period. The arc power is calculated from the fed back electrode voltage V _FB and the electrode current I _FB, and a current correction value is calculated from the difference between the arc power and the set arc power, and this is supplied to the current control circuit 45. Thereby, the fluctuation | variation of the arc electric power supplied to the arc furnace 3 is suppressed further smaller.

It is a systematic diagram which shows the structure of the electric power automatic control apparatus in one Embodiment of this invention. It is a block diagram which shows the structure of a control part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Main circuit, 2 ... Furnace transformer, 3 ... Arc furnace, 4 ... Control part, 42 ... Determination part, 45 ... Current control circuit, 46 ... Voltage control circuit, 52 ... Instrument transformer, 51 ... Instrument Current transformer.

Claims (5)

Voltage detection means for detecting the electrode voltage of the arc furnace, tap selection means for changing the electrode voltage by selectively selecting a plurality of taps of the furnace transformer, and the electrode voltage under the selected tap An automatic electric power control apparatus for an arc furnace, comprising: a control unit that operates a tap selection unit to return the electrode voltage to a predetermined range when a predetermined range is exceeded downward or upward. A current detecting means for detecting an electrode current; and a current changing means for changing a set value of the electrode current, wherein the control means causes the electrode voltage to exceed the predetermined range downward or upward under the selected tap. In this case, the tap selection means is operated, and the furnace charging power calculated from the electrode voltage and electrode current under the newly selected tap matches the furnace charging power set in the furnace period at that time. The electric power control apparatus for an arc furnace according to claim 1, wherein the electric current changing means is set to operate as described above. The electric power control of the arc furnace according to claim 1 or 2, wherein the control means is set to activate a tap selection means when the electrode voltage exceeds the predetermined range downward or upward for a predetermined time or more. apparatus. The electric power control apparatus for an arc furnace according to any one of claims 1 to 3, wherein the predetermined range is determined according to a selected tap. The arc furnace power automatic control device according to claim 3 or 4, wherein the predetermined time is determined in accordance with a selected tap.

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