Method for suppressing voltage flicker in electric furnaces

Abstract

The present invention provides a method for suppressing voltage flicker in an electric furnace, which can suppress voltage flicker while maintaining the operational efficiency of the electric furnace. [Solution] A voltage flicker measurement step ST1 is performed by initializing and measuring the integrated value of voltage flicker every minute using a flicker meter 6 connected to a power transmission and distribution line 2 that supplies power to an electric furnace 3 that uses an arc, and ΔV 10 If the value exceeds a preset reference value, the applied voltage applied to the arc generating electrode 31 is reduced by a set amount in an applied voltage reduction step ST2, and after the applied voltage is reduced, the change in the cumulative value of voltage flicker Δa over a set time Δt shorter than 1 minute is compared with a threshold value Δst that is smaller than the reference value, and a determination step ST3 is performed to determine the relationship between the two.

Description

[Technical Field]

[0001] The present invention relates to a method for suppressing voltage flicker generated by electric furnaces that utilize arcs, such as arc furnaces (arc-type electric melting furnaces) and ladle refining furnaces. In particular, the present invention relates to a method for suppressing voltage flicker in electric furnaces that can suppress voltage flicker while maintaining the operational efficiency of the electric furnace. [Background technology]

[0002] Known electric furnaces that utilize an arc include arc furnaces and ladle smelting furnaces. Arc furnaces operate by supplying electricity received from commercial power distribution facilities to arc generating electrodes via transformers, etc., and heating and melting raw materials such as scrap metal with the arc generated from these electrodes. Ladle smelting furnaces operate by refining molten steel while it is heated by the arc generated from the arc generating electrodes. The applied voltage to the arc generating electrodes of these electric furnaces is preset to a predetermined value according to the operating conditions.

[0003] However, within an electric furnace, the shape and state of the molten raw materials and molten steel change constantly, causing the current flowing through the arc-generating electrodes to fluctuate irregularly. Furthermore, because electric furnaces utilize arcs, they consume a large amount of power and experience significant voltage fluctuations. Consequently, these fluctuations in the current flowing through the arc-generating electrodes cause voltage fluctuations in commercial power distribution facilities, leading to adverse effects such as voltage flicker for other users of commercial power.

[0004] Voltage flicker is an indicator that represents voltage fluctuations while taking into account human visual sensitivity. Voltage flicker is the cumulative value over one minute, which is ΔV 10 It is often evaluated using this ΔV. 10 The power distribution facility requires that operations be conducted in such a way that the number of times the voltage exceeds the standard value (e.g., 0.45V) does not exceed a predetermined number (e.g., 4 times) within a 60-minute period.

[0005] Conventionally, methods for suppressing voltage flicker generated by electric furnaces have been proposed, for example, as described in Patent Documents 1 to 3. The method described in Patent Document 1 involves reducing the applied voltage applied to the arc generating electrode from a predetermined value when the magnitude of the voltage flicker measured by a flicker meter exceeds a reference value, and returning the applied voltage to the predetermined value when the magnitude of the voltage flicker falls below the reference value (for example, paragraphs 0010 to 0012 of Patent Document 1). According to the method described in Patent Document 1, after lowering the applied voltage, if the magnitude of the voltage flicker falls below a standard value (becomes normal), the applied voltage is immediately returned to a predetermined value used during normal operation, thus maintaining the operational efficiency of the electric furnace. However, because the applied voltage is immediately returned to a predetermined value used during normal operation, there is a risk that the voltage flicker may not be sufficiently suppressed. One possible cause of large voltage flicker is the descent of the slag forming position inside the electric furnace. Once the slag forming position descends, that state tends to continue for a while, so if the applied voltage is immediately returned to a predetermined value used during normal operation, there is a risk that the magnitude of the voltage flicker will exceed the standard value again. Similarly, the methods described in Patent Documents 2 and 3 may not adequately suppress voltage flicker. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-106886 [Patent Document 2] Japanese Patent Application Publication No. 10-201101 [Patent Document 3] Japanese Patent Publication No. 52-95343 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention has been made in view of the problems of the prior art described above, and aims to provide a method for suppressing voltage flicker in an electric furnace that can suppress voltage flicker while maintaining the operational efficiency of the electric furnace. [Means for solving the problem]

[0008] To solve the above problem, the present invention provides a voltage flicker measurement step in which a flicker meter connected to a power transmission and distribution line that supplies power to an electric furnace using an arc is used to initialize and measure the integrated value of voltage flicker generated in the power transmission and distribution line every minute, and the measured integrated value of voltage flicker over one minute ΔV 10 The present invention provides a method for suppressing voltage flicker in an electric furnace, comprising: an applied voltage reduction step in which, when the applied voltage exceeds a preset reference value, the applied voltage applied to the arc generating electrode provided in the electric furnace is reduced by a preset set reduction amount; a determination step in which, after reducing the applied voltage by the set reduction amount, the change in the cumulative value of the voltage flicker Δa over a set time Δt shorter than 1 minute is compared with a preset threshold value Δst that is smaller than the reference value, and the relationship between the two is determined; and an applied voltage increase step in which, if it is determined in the determination step that Δa < Δst, the applied voltage is increased by a preset set increase amount that is smaller than the set reduction amount, and if it is determined that Δa ≥ Δst, the applied voltage is not increased.

[0009] In this invention, "initializing and measuring the integrated voltage flicker value every minute" means initializing the integrated voltage flicker value to 0 every minute while measuring the integrated value. It is known that a flicker meter can measure the integrated voltage flicker value that is initialized every minute and can output this integrated value as a measured value. Furthermore, in this invention, "to lower by a set amount" literally means lowering by a set amount, but also includes cases where a lower limit of the applied voltage (set lower limit voltage) is set in advance, and if lowering the applied voltage by a set amount would cause it to fall below the set lower limit voltage, then the applied voltage is lowered to the set lower limit voltage. Furthermore, in the present invention, "raising the applied voltage by the set increase amount" literally means, in addition to the case of raising it by the set increase amount, when the upper limit value (set upper limit voltage) of the applied voltage is preset and raising the applied voltage by the set increase amount would exceed the set upper limit voltage, it also includes the case of raising the applied voltage to the set upper limit voltage.

[0010] According to the present invention, in the voltage flicker measurement step, the integrated value of voltage flicker is measured by a flickermeter, and in the applied voltage drop step, the integrated value ΔV of the measured voltage flicker for one minute 10 if it exceeds a preset reference value, the applied voltage applied to the arc generation electrode is lowered by a preset set drop amount. Therefore, voltage flicker can be suppressed. Next, according to the present invention, in the determination step, after lowering the applied voltage by the set drop amount, the change amount Δa of the integrated value of voltage flicker in a set time Δt shorter than one minute and a preset threshold value Δst smaller than the reference value are compared to determine the magnitude relationship between the two. In other words, the magnitude of the gradient of the change in the integrated value of voltage flicker is evaluated, and if the gradient is large (if Δa≧Δst), it is determined that there is a possibility that ΔV 10 will exceed the reference value again when the applied voltage is raised, and if the gradient is small (if Δa<Δst), it is determined that there is a low possibility that ΔV 10 will exceed the reference value again even if the applied voltage is raised to a certain extent. And according to the present invention, in the applied voltage increase step, when it is determined in the determination step that Δa<Δst (that is, even if the applied voltage is raised to a certain extent, it is determined that there is a low possibility that ΔV 10 will exceed the reference value again), the applied voltage is raised by a preset set increase amount smaller than the set drop amount. That is, since it does not immediately return to the applied voltage before lowering by the set drop amount, there is a low possibility that ΔV 10 will exceed the reference value again, and voltage flicker can be suppressed. Also, when it is determined in the determination step that Δa<Δst, in the applied voltage increase step, the applied voltage is raised in a set time Δt shorter than one minute (ΔV 10Rather than increasing the applied voltage every minute of measurement, it is possible to maintain the operating efficiency of the electric furnace without excessively reducing it by increasing the applied voltage in a shorter time than this. On the other hand, when it is determined in the determination step that Δa≧Δst (that is, when it is determined that there is a possibility that ΔV will exceed the reference value again when the applied voltage is increased), the applied voltage is not increased, so the possibility that ΔV will exceed the reference value again is low, and voltage flicker can be suppressed. 10 When it is determined that there is a possibility that ΔV will exceed the reference value again when the applied voltage is increased), the applied voltage is not increased, so the possibility that ΔV will exceed the reference value again is low, and voltage flicker can be suppressed. 10 is low, and voltage flicker can be suppressed. As described above, according to the present invention, it is possible to suppress voltage flicker while maintaining the operating efficiency of the electric furnace.

[0011] In the present invention, it is preferable that the set time Δt is 30 seconds or less, the threshold value Δst is 1 / 2 or less of the reference value, and the set increase amount is 1 / 2 or less of the set decrease amount. In addition, it is more preferable that the set time Δt is 20 seconds or less, further preferably 15 seconds or less, and particularly preferably 10 seconds or less. Also, it is preferable that the set time Δt is 2 seconds or more, and more preferably 5 seconds or more. Further, it is more preferable that the threshold value Δst is a value obtained by multiplying the reference value by Δt [seconds] / 60 [seconds] and further multiplying this by a coefficient of 0.7 to 0.9 as a safety margin among the values of 1 / 2 or less of the reference value. For example, if the reference value is 0.45V and Δt is 10 seconds, it is more preferable that Δst is 0.05 to 0.07V (about 1 / 9 to 1 / 7 of the reference value). Furthermore, if the furnace transformer for applying voltage to the arc generating electrode has multiple taps and the applied voltage is adjusted by switching between these multiple taps, it is more preferable that the set rise amount be a voltage equivalent to one or two taps, which is less than or equal to half of the set drop amount. For example, if the furnace transformer has five taps, the set drop amount will be a voltage equivalent to five taps, and the set rise amount will be a voltage equivalent to one or two taps, so it is more preferable that the set rise amount be 1 / 5 or 2 / 5 of the set drop amount. Also, if the furnace transformer has six taps, the set drop amount will be a voltage equivalent to six taps, and the set rise amount will be a voltage equivalent to one or two taps, so it is more preferable that the set rise amount be 1 / 6 or 2 / 6 (=1 / 3) of the set drop amount.

[0012] According to the present invention, voltage flicker can be suppressed, so the measured voltage flicker over a 60-minute period can be reduced by ΔV 10 The likelihood of the number of times the threshold value is exceeded reaching a predetermined threshold number (for example, 3 times, one less than the 4 times that the power distribution facility is required to operate so as not to exceed that number) is low. However, if the threshold number is reached, it is preferable to forcibly stop the application of the applied voltage to ensure that the requirements from the power distribution facility are reliably met. In other words, in the present invention, preferably, the measured voltage flicker is the cumulative value ΔV per minute over a period of 60 minutes. 10 If the number of times the voltage flicker exceeds the aforementioned reference value reaches a preset reference number, the measured 1-minute integrated value of voltage flicker ΔV over a 60-minute period will be calculated. 10 The system includes an application stop step, which stops applying the applied voltage to the arc generating electrode until the number of times the number exceeds the reference value falls below the reference number.

[0013] According to the preferred method described above, the 1-minute integrated value of the measured voltage flicker ΔV over a 60-minute period is obtained. 10 If the number of times exceeds the standard value reaches a predetermined standard number, ΔV 10The application of the voltage is stopped until the number of times the threshold value is exceeded falls below the threshold, thus ensuring that the requirements from the power distribution facility are reliably met. [Effects of the Invention]

[0014] According to the present invention, it is possible to suppress voltage flicker while maintaining the operating efficiency of the electric furnace. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram illustrating the configuration of an apparatus for implementing the voltage flicker suppression method according to the first embodiment of the present invention. [Figure 2] This is a schematic flowchart illustrating the steps of a voltage flicker suppression method according to the first embodiment of the present invention. [Figure 3] Figure 1 schematically shows the measured value (output of the flicker meter 6) of the flicker meter 6. [Figure 4] Figure 2 schematically illustrates the applied voltage decrease step ST2, the applied voltage increase step ST4, and the application stop step ST5 shown. [Figure 5] Figure 2 schematically illustrates the determination step ST3 and the applied voltage increase step ST4 shown in Figure 2. [Figure 6] This is a schematic diagram illustrating the configuration of an apparatus for implementing a voltage flicker suppression method according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0016] The following describes a method for suppressing voltage flicker in an electric furnace according to an embodiment of the present invention, with appropriate reference to the attached drawings.

[0017] <First Embodiment> The first embodiment shows a case where the electric furnace to which the voltage flicker suppression method according to the present invention is applied is a single arc furnace. Figure 1 is a schematic diagram illustrating the configuration of an apparatus for implementing the voltage flicker suppression method according to the first embodiment. As shown in Figure 1, power supplied from a power source 1 located in a power distribution facility via a transmission and distribution line 2 is received at the power receiving point 2a of the factory where the arc furnace 3 is installed. In Figure 1, the area below the dashed line AA is the factory. The power received at the power receiving point 2a has its voltage adjusted by a power receiving transformer 4, then further adjusted by a furnace transformer 5, and is applied to the arc generating electrodes 31 provided in the arc furnace 3. The power whose voltage has been adjusted by the power receiving transformer 4 is also supplied to other equipment (not shown) in the factory as needed. The furnace transformer 5 has multiple taps, and by switching between these taps, the output voltage (secondary voltage), i.e., the applied voltage applied to the arc generating electrodes 31, can be adjusted. Note that the arc furnace 3 in the first embodiment is a three-phase AC arc furnace and is equipped with three arc generating electrodes 31. Therefore, the transmission and distribution line 2 in the first embodiment is actually a three-phase AC transmission and distribution line, but for convenience, it is shown as a single line in Figure 1.

[0018] A flicker meter 6 is connected to the power transmission and distribution line 2 (receiving point 2a). The flicker meter 6 is a device that measures the cumulative value of voltage flicker generated in the power transmission and distribution line 2, resetting it every minute (resetting the cumulative value of voltage flicker to 0 every minute while measuring the cumulative value). Since the configuration of the flicker meter 6 is publicly known, further detailed explanation is omitted here. The measurement value from the flicker meter 6 (integrated voltage flicker) is input to the control device 7. The control device 7 switches the taps of the furnace transformer 5 according to the measurement value from the flicker meter 6, thereby controlling the applied voltage applied to the arc generating electrode 31.

[0019] The voltage flicker suppression method according to the first embodiment is performed using the furnace transformer 5, flicker meter 6, and control device 7 described above. Figure 2 is a schematic flowchart showing the steps of the voltage flicker suppression method according to the first embodiment. As shown in Figure 2, the voltage flicker suppression method according to the first embodiment includes a voltage flicker measurement step ST1, an applied voltage reduction step ST2, a determination step ST3, and an applied voltage increase step ST4. In a preferred embodiment, the voltage flicker suppression method according to the first embodiment also includes an application stop step ST5. Steps ST1 to ST5 will be described below.

[0020] <Voltage flicker measurement step ST1> In the voltage flicker measurement step ST1, the flicker meter 6 is used to measure the cumulative value of voltage flicker occurring in the power transmission and distribution line 2, resetting it every minute. Figure 3 schematically shows the measurement value (output of the flicker meter 6) of the flicker meter 6. The flicker meter 6 measures the integrated value of voltage flicker, which is initialized to 0 every minute, and outputs it to the control device 7. Therefore, as shown in Figure 3, the output waveform of the flicker meter 6 is a sawtooth waveform with a period of 1 minute. The measurement value of the flicker meter 6 located at the peak of the output waveform is the integrated value of voltage flicker over 1 minute ΔV. 10 It corresponds to this.

[0021] <Applied voltage drop step ST2> In the applied voltage drop step ST2, as shown in Figure 3, the cumulative value of voltage flicker over one minute, ΔV, is measured by the flicker meter 6. 10 If the value exceeds a preset reference value, the applied voltage applied to the arc generating electrode 31 provided in the arc furnace 3 is reduced by a preset set drop amount. Figure 4 schematically illustrates the applied voltage decrease step ST2, the applied voltage increase step ST4, and the application stop step ST5. Specifically, in the applied voltage drop step ST2, the control device 7 calculates the cumulative value of voltage flicker over one minute ΔV based on the waveform shown in Figure 3, which is input from the flicker meter 6. 10 Detect this ΔV 10 It determines whether the voltage exceeds a preset reference value. For example, 0.45V is set as the reference value. The control device 7 then determines whether the voltage exceeds ΔV 10If it is determined that the value exceeds a preset reference value, a control signal is output to the furnace transformer 5 to switch the tap of the furnace transformer 5. This control signal causes the furnace transformer 5 to adjust the ΔV as shown in Figure 4. 10 When the voltage exceeds a reference value for a certain period of time ta, the applied voltage to the arc generating electrode 31 is reduced by a predetermined set amount (set upper voltage - set lower voltage) by switching from the tap corresponding to the preset upper voltage limit to the tap corresponding to the preset lower voltage limit. The set upper limit voltage is the applied voltage used during normal operation according to the operating conditions of the arc furnace 3. Furthermore, as described later, in the process of increasing (including maintaining) the applied voltage in the applied voltage increase step ST4 (the process from time ta to tb and tb to tc shown in Figure 4), before the applied voltage reaches the set upper limit voltage, ΔV 10 If it is determined that the voltage has exceeded a preset reference value (in the case of time tb shown in Figure 4), the applied voltage cannot be reduced by the set reduction amount (because reducing the applied voltage by the set reduction amount would result in a voltage below the set lower limit). Therefore, the furnace transformer 5 will reduce the applied voltage to the set lower limit voltage based on the control signal from the control device 7.

[0022] <Judgment Step ST3> Figure 5 schematically illustrates the determination step ST3 and the applied voltage increase step ST4. Figure 5(a) illustrates the determination step ST3, and Figure 5(b) illustrates the applied voltage increase step ST4. Figures 5(a) and 5(b) are illustrated so that the horizontal axis, which represents time, coincides. As shown in Figure 5(a), in the determination step ST3, as described above, after the applied voltage is reduced by the set drop amount, the control device 7 compares the change in the integrated value of voltage flicker over a set time Δt shorter than 1 minute (i.e., the change in the measured value of the flicker meter 6 over time Δt) Δa with a preset threshold value Δst that is smaller than the reference value, and determines the relationship between the two. In other words, in the determination step ST3, the control device 7 evaluates the magnitude of the slope of the change in the integrated value of voltage flicker. If the slope is large (Δa ≥ Δst), then increasing the applied voltage will cause ΔV10 If it is determined that there is a possibility of exceeding the standard value, and the slope is small (Δa < Δst), then even if the applied voltage is increased to some extent, ΔV will return to normal. 10 It is determined that the likelihood of exceeding the standard value is low. Preferably, the set time Δt is 30 seconds or less, and in the example shown in Figure 5(a), Δt is set to 10 seconds. Also preferably, the threshold value Δst is 1 / 2 or less of the reference value, and in the example shown in Figure 5(a), it is set to 1 / 8 of the reference value.

[0023] <Applied voltage increase step ST4> In the applied voltage increase step ST4, if the control device 7 determines that Δa < Δst (i.e., even if the applied voltage is increased to a certain extent, ΔV 10 If it is determined that the likelihood of exceeding the standard value is low, a control signal is output to the furnace transformer 5 to switch the tap of the furnace transformer 5. This control signal causes the furnace transformer 5 to increase the applied voltage by a preset rise amount, which is smaller than the set drop amount, as shown in Figure 5(b). Specifically, by switching from the current tap to the tap corresponding to the applied voltage increased by the preset rise amount, the applied voltage applied to the arc generating electrode 31 is increased by the preset rise amount. In this way, the applied voltage is not abruptly returned to the voltage before the set drop amount, so ΔV 10 The likelihood of exceeding the standard value is low, and voltage flicker can be suppressed. Furthermore, if the control device 7 determines that Δa < Δst, the applied voltage will be increased for a set time Δt shorter than 1 minute (ΔV 10 Instead of increasing the applied voltage every minute to measure the voltage, the applied voltage is increased at shorter intervals (making it possible to maintain the operating efficiency of the arc furnace 3 without excessively reducing it). The set voltage increase is preferably 1 / 2 or less of the set voltage decrease, and in the example shown in Figure 5(b), it is set to 2 / 5 of the set voltage decrease. In the example shown in Figure 5(a), Δa < Δst at times t1, t2, and t3, so as shown in Figure 5(b), the applied voltage is increased by the set voltage increase at times t1, t2, and t3. Note that at time t3, if the applied voltage is increased by the set voltage increase, it will exceed the set upper voltage limit, so the applied voltage is increased up to the set upper voltage limit.

[0024] On the other hand, if the control device 7 determines that Δa ≥ Δst (i.e., if the applied voltage is increased, ΔV 10 If it is determined that there is a possibility that the value will exceed the standard value, a control signal to switch the tap of the furnace transformer 5 is not output to the furnace transformer 5. As a result, the furnace transformer 5 does not switch the current tap, and the applied voltage applied to the arc generating electrode 31 is maintained without increasing. Therefore, ΔV again 10 The likelihood of exceeding the standard value is low, and voltage flicker can be suppressed.

[0025] <Application Stop Step ST5> By performing the voltage flicker measurement step ST1, applied voltage drop step ST2, determination step ST3, and applied voltage increase step ST4 described above, voltage flicker can be suppressed, thus reducing ΔV over a 60-minute period. 10 The likelihood of the number of times the voltage exceeds the standard value reaching a predetermined standard number (for example, 3 times, one less than the 4 times that the power distribution facility requires to keep the number of times below this limit) is low. However, if the standard number of times is reached, it is preferable to forcibly stop the application of the applied voltage in order to reliably satisfy the requirements from the power distribution facility. For this reason, the voltage flicker suppression method according to the first embodiment includes an application stop step ST5. In the application stop step ST5, the control device 7 calculates the cumulative value of voltage flicker per minute ΔV over a 60-minute period. 10 It is determined whether the number of times the threshold value is exceeded has reached a predetermined threshold number (for example, 3 times). Then, ΔV 10When the reference number of cycles is reached (in the case of time td shown in Figure 4), a control signal to stop the operation of the furnace transformer 5 is output to the furnace transformer 5. This control signal to stop the operation of the furnace transformer 5 is transmitted over a period of 60 minutes, with a ΔV 10 The output to the furnace transformer 5 continues until the number of times the threshold value is exceeded falls below the threshold value. While this control signal is input, the furnace transformer 5 stops applying the voltage to the arc generating electrode 31. The voltage flicker suppression method according to the first embodiment can reliably satisfy the requirements from power distribution facilities by having a voltage application stop step ST5.

[0026] The voltage flicker measurement step ST1, applied voltage drop step ST2, determination step ST3, applied voltage increase step ST4, and application stop step ST5 described above are repeatedly performed until the operation of the arc furnace 3 is completed (until "Yes" is obtained in step ST6) (if "No" is obtained in step ST6, the process returns to the voltage flicker measurement step ST1).

[0027] According to the voltage flicker suppression method of the first embodiment described above, it is possible to suppress voltage flicker while maintaining the operating efficiency of the arc furnace 3.

[0028] <Second Embodiment> The second embodiment shows a case where there are multiple electric furnaces to which the voltage flicker suppression method according to the present invention is applied. Figure 6 is a schematic diagram illustrating the configuration of an apparatus for implementing the voltage flicker suppression method according to the second embodiment. In Figure 6, the same reference numerals are used for components that are the same as those in the first embodiment shown in Figure 1. As shown in Figure 6, in the second embodiment, unlike the first embodiment, multiple electric furnaces (two in the example shown in Figure 6) (the same arc furnace 3 and electric furnace 3b as in the first embodiment) are installed inside the factory (below the dashed line AA). Electric furnace 3b may be an arc furnace or a ladle smelting furnace, as long as it utilizes an arc. In addition, although power is supplied to the factory from a power source 1 installed in the power distribution facility via a power transmission line 2, equipment 8, 9, etc. are also installed inside the factory that do not utilize an arc, resulting in low power consumption or small voltage fluctuations (and therefore no problem with voltage flicker).

[0029] As shown in Figure 6, in the second embodiment, as in the first embodiment, the power supplied from the power source 1 located in the power distribution facility via the power transmission line 2 is received at the power receiving point 2a of the factory where the arc furnace 3, electric furnace 3b, etc., are installed. Then, as described in the first embodiment, the power received at the power receiving point 2a has its voltage adjusted by the power receiving transformer 4, and then its voltage is further adjusted by the furnace transformer 5 before being applied to the arc generating electrode 31 located in the arc furnace 3. In the second embodiment, the power whose voltage has been adjusted by the power receiving transformer 4 is further adjusted by the furnace transformer 5b before being applied to the arc generating electrode (not shown) located in the electric furnace 3b. Furthermore, the power whose voltage has been adjusted by the power receiving transformer 4 is also supplied to equipment 8, 9, etc.

[0030] As described in the first embodiment, the furnace transformer 5 has multiple taps, and by switching between these taps, the output voltage (secondary voltage), that is, the applied voltage applied to the arc generating electrode 31, can be adjusted. Similarly, the furnace transformer 5b also has multiple taps, and by switching between these taps, the output voltage (secondary voltage), that is, the applied voltage applied to the arc generating electrode provided in the electric furnace 3b, can be adjusted.

[0031] In this second embodiment, unlike the first embodiment, multiple electric furnaces (arc furnace 3 and electric furnace 3b in the example shown in Figure 6) that can cause voltage flicker are installed in the factory. Therefore, as in the first embodiment, ΔV is measured by a flicker meter 6 connected to the power receiving point 2a. 10 Simply controlling the applied voltage to the arc generating electrode 31 provided in the arc furnace 3 when the voltage exceeds a standard value may not be sufficient to suppress voltage flicker. Therefore, in the second embodiment, a configuration is adopted in which the applied voltage to the arc generating electrode 31 provided in the arc furnace 3 is controlled, as well as the applied voltage to the arc generating electrode provided in the electric furnace 3b.

[0032] Specifically, as shown in Figure 6, in the second embodiment, flicker meters 6a and 6b are provided for each electric furnace (arc furnace 3, electric furnace 3b). More specifically, flicker meter 6a is connected to power transmission line 21, which applies the applied voltage to the arc generating electrode 31 of arc furnace 3, and flicker meter 6b is connected to power transmission line 22, which applies the applied voltage to the arc generating electrode of electric furnace 3b. Like flicker meter 6, flicker meters 6a and 6b are devices that initialize and measure the integrated value of voltage flicker generated in power transmission lines 21 and 22, respectively, every minute. The measurement value from the flicker meter 6a (integrated voltage flicker) is input to the control device 7a. The control device 7a switches the taps of the furnace transformer 5 according to the measurement value from the flicker meter 6a, thereby controlling the applied voltage applied to the arc generating electrode 31. Similarly, the measurement value from the flicker meter 6b (integrated voltage flicker) is input to the control device 7b. The control device 7b switches the taps of the furnace transformer 5b according to the measurement value from the flicker meter 6b, thereby controlling the applied voltage applied to the arc generating electrode of the electric furnace 3b.

[0033] In the voltage flicker suppression method according to the second embodiment, the furnace transformer 5, flicker meter 6a, and control device 7a are used to perform the voltage flicker measurement step ST1, the applied voltage reduction step ST2, the determination step ST3, the applied voltage increase step ST4, and, in a preferred embodiment, the application stop step ST5, similar to the first embodiment. Alternatively, the furnace transformer 5b, flicker meter 6b, and control device 7b are used to perform the voltage flicker measurement step ST1, the applied voltage reduction step ST2, the determination step ST3, the applied voltage increase step ST4, and, in a preferred embodiment, the application stop step ST5. The contents of each step ST1 to ST5 are the same as in the first embodiment, so their explanation is omitted here. This makes it possible to suppress voltage flicker even when multiple electric furnaces that could cause voltage flicker are installed in the factory, and to reliably meet the requirements of the power distribution facility. In addition, in the applied voltage reduction step ST2 performed in the second embodiment, a reference value (i.e., ΔV measured in the power transmission and distribution lines 21 and 22) is used as a reference for reducing the applied voltage applied to the arc generating electrodes of the arc furnace 3 and electric furnace 3b. 10 The reference value. Hereinafter referred to as the "reference value for arc furnace 3" and the "reference value for electric furnace 3b," respectively, is the reference value set in the first embodiment (i.e., ΔV measured at the power receiving point 2a). 10 This is a reference value, and it is preferable to set it to a value smaller than, for example, 0.45V. The reference value for arc furnace 3 and the reference value for electric furnace 3b may be the same or different, and should be set appropriately according to the magnitude of their respective power consumption, the magnitude of voltage fluctuations in past operating records, and the conditions of simultaneous operation (whether or not they operate simultaneously and how often).

[0034] In Figure 6, an example is shown in which two control devices 7a and 7b are provided corresponding to two flicker meters 6a and 6b. However, this is not the only configuration. It is also possible to adopt a configuration in which the measured values ​​of flicker meters 6a and 6b are input to a single control device, and this single control device can individually execute voltage flicker suppression methods using the measured values ​​of flicker meters 6a and 6b, respectively. Furthermore, although Figure 6 illustrates an example where two electric furnaces (arc furnace 3 and electric furnace 3b) are installed, the method is not limited to this. Even when three or more electric furnaces are installed, the same voltage flicker suppression method can be implemented by providing a flicker meter for each electric furnace. [Explanation of symbols]

[0035] 2...Power transmission and distribution lines 3. Electric furnace (arc furnace) 3b... Electric furnace 5, 5b... Transformer for furnace 6, 6a, 6b... flicker meters 7, 7a, 7b... Control devices 31. Electrode for arc generation ST1...Voltage flicker measurement step ST2...Applied voltage drop step ST3... Judgment Step ST4...Input voltage rise step ST5... Application stop step

Claims

1. A voltage flicker measurement step involves using a flicker meter connected to a power transmission and distribution line that supplies power to an electric furnace using an arc, to measure the integrated value of voltage flicker generated in the power transmission and distribution line, resetting it every minute; The measured cumulative value of the voltage flicker over one minute, ΔV １０ If the value exceeds a preset reference value, the applied voltage applied to the arc generating electrode provided in the electric furnace is reduced by a preset set drop amount in the applied voltage drop step, After the applied voltage has been reduced by the set drop amount, a determination step is performed to compare the change in the cumulative value of the voltage flicker Δa over a set time Δt shorter than one minute with a preset threshold value Δst that is smaller than the reference value, and to determine the relationship between the two. The determination step includes an applied voltage increase step in which, if it is determined that Δa < Δst, the applied voltage is increased by a preset set increase amount that is smaller than the set drop amount, and if it is determined that Δa ≥ Δst, the applied voltage is not increased. A method for suppressing voltage flicker in electric furnaces.

2. The aforementioned setting time Δt is 30 seconds or less. The threshold value Δst is less than or equal to half of the reference value. The set increase amount is 1 / 2 or less of the set decrease amount. A method for suppressing voltage flicker in an electric furnace according to claim 1.

3. The measured cumulative value of voltage flicker over 1 minute, ΔV, over a 60-minute period. １０ If the number of times the voltage flicker exceeds the aforementioned reference value reaches a predetermined reference number, the measured one-minute integrated value of the voltage flicker ΔV over a 60-minute period will be calculated. １０ The system includes an application stop step which stops applying the applied voltage to the arc generating electrode until the number of times the number exceeds the reference value falls below the reference number. A method for suppressing voltage flicker in an electric furnace according to claim 1 or 2.

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