JPS61198312A - Operation controller of low frequency induction furnace - Google Patents

Abstract

PURPOSE:To operate efficiently a low frequency induction furnace by performing the control to keep an impressed power at a rated power in accordance with the deviation between the impressed power of the induction furnace and the rated power. CONSTITUTION:The adjustment of the output voltage of a transformer 12, the adjustment of the capacity of parallel capacitors, or the combinational adjustment of both of them is used to perform such power control in accordance with the deviation between the output voltage of the transformer 12 and the rated power of an induction coil 10 that the deviation is suppressed to zero. Thus, the output power of the transformer 12 is allowed to approach the rated power in a short time, and the output power of the transformer 12 is kept at the rated power. Consequently, the time required for melting is shortened to improve the melting capability, and the loss of the energy required for cooling of the furnace wall or the like and a melting electric energy unit are reduced.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to an operation control device for a low frequency induction furnace.

In particular, the present invention relates to an operation control device for a low-frequency induction furnace suitable for controlling the power of a crucible-type low-frequency induction furnace for melting cast iron, nonferrous metals, and the like.

[Conventional technology]

When melting cast iron, non-ferrous metals, etc. in a crucible-type low-frequency induction furnace, it takes a long time to melt only the phase-resistant material, so the molten metal is left at 1/2 to 2/3 of the furnace capacity, and the phase-resistant metal is melted several times. A commonly used method is to charge the material separately into a furnace and melt it. As a device for operating a low frequency induction furnace using such a melting cycle, the device shown in FIG. 7 has been employed.

In FIG. 7, an induction coil 10 wound around a crucible-type low-frequency induction furnace is supplied with output power from a step-down transformer 12, and the induction coil 10 uses the power to maintain phase resistance in the furnace. Can be dissolved.

Three-phase AC power is supplied to the step-down transformer 12 via a switch 14 and a circuit breaker 16, and the output of the transformer 12 is supplied to an induction coil via a balancer 18 and a water-cooled cable 20.

Further, on the secondary side of the transformer 12, a power factor adjustment capacitor CI...Cn and a switch S1...S
n are connected and inserted in series, respectively, and the power factor on the secondary side is controlled to be 1 by turning on the switches SI...Sn. The power factor on the secondary side is detected by the reactive wattmeter 22, and the turning on of the switches S1...Sn is controlled by a command from the power factor control section 24. Note that the current, voltage, and power on the secondary side are detected by an ammeter 26, a voltmeter 28, and a wattmeter 30, respectively.

Further, the transformer 12 has a plurality of taps that vary the output voltage, and is configured such that the output voltage of the transformer 12 can be varied by operating the tap operating section of the tap control section 32.

Incidentally, since the amount of molten metal melted in the low frequency induction furnace increases sequentially during the melting cycle, the relationship between the amount of molten metal and the power coefficient n has a characteristic as shown in FIG. Therefore, as shown in Figure 9, 1/3 of the dissolution cycle
In the ~1/2 recycle, the induction coil 10 is not supplied with rated power. Therefore, in the apparatus shown in Fig. 7, in the first half a of the melting cycle, a tap position that provides a higher output than the tap position at the rated output is selected, and the furnace power approaches the rated power A in the shortest possible time. In the latter half of the melting cycle, power control was performed in which the transformer 12 was sequentially tapped down to the tap at which the transformer 12 reached its rated output. Since the change in the output power of the transformer 12 is about 10 degrees of the rated power, it is difficult to maintain the output power of the transformer 12 at the rated power A by just adjusting the tag. Furnaces were operated using electricity (Characteristic B)
. For this reason, the melting time becomes longer to the extent that the furnace power is lower than the rated power, and melting capacity (tons/H) and melting power consumption (K
There was a problem that the WH/ton) was worse than the rating.

In addition, in conventional equipment, the tap of the transformer 12 was manually adjusted, so if the tap was not adjusted properly by the operator, more power than the rated power was supplied to the furnace, which could cause abnormal wear on the furnace wall, etc. There was a risk that trouble would occur.

[Problem that the invention seeks to solve]

Therefore, in order to solve these drawbacks of the conventional technology,
Japanese Patent Application No. 59-89932, which is not yet publicly known, proposes an operation control device for a low frequency induction furnace.

This operation control device is equipped with a control device consisting of a microcomputer, and this control device can be used to adjust the tap position of the induction furnace transformer, adjust the capacity of the power factor adjustment capacitor, or adjust a combination of these. The electric power applied to the induction furnace is automatically maintained at the rated power by adjusting the electric power.

However, the conventional device shown in FIG.
In the device according to No. 89932, a balancer 18 is inserted on the output side of the three-phase transformer 12 to adjust the current balance in order to supply current from the three-phase AC power supply to the single-phase induction coil 10. This balancer 18 is current parannu vI! It has a 18A capacitor for adjustment, and this current balance adjustment capacitor 18 is adjusted according to the load of the induction furnace.
The capacity of A is adjusted to maintain the current balance between each phase within an allowable value. However, this balancer 18
Even if the balancer 18 is not properly adjusted or the balancer 18 is working properly, the current balance on the transformer output side will collapse when the induction furnace wall is about to be replaced, and the induction furnace power may fall below the rated value. However, the current value of either the R phase or the T phase may become excessive.

In the device according to Japanese Patent Application No. 59-89932, the current of each phase is taken into the control device via the ammeter 26, and the R
, S, and T phases are below the allowable value, the transformer tap position is controlled by commands from this control device.
Parallel capacitor C!・・・・・・It is possible to perform power-up processing by controlling the supply of Cn, but the current value of either the R phase or T phase becomes excessive and the conditions for power-up are not met. If the current exceeds a certain allowable current value, the power of the induction furnace is lower than the rated value and power-up processing is not possible even though power-up processing is possible, and the power of the induction furnace cannot be temporarily controlled. A new problem has been raised:

In particular, when trying to automatically control the applied power to an induction furnace as in Japanese Patent Application No. 59-89932, not only the power-up process described above cannot be performed, but also the three-phase current on the output side of the transformer exceeds the allowable value. This has led to the problem that power down processing is performed even though the electric power of the induction furnace is lower than the rated value.

The present invention was devised in view of the problems of the prior art and the device proposed in Japanese Patent Application No. 59-89932, and its purpose is to enable efficient operation of a low-frequency induction furnace and to increase the melting capacity. An object of the present invention is to provide an operation control device for a low frequency induction furnace that can improve the operation of a low frequency induction furnace.

[Means for solving problems]

The operation control device for a low frequency induction furnace according to the present invention includes an output voltage regulator that adjusts the output voltage of a three-phase transformer for an induction furnace that supplies power to a single-phase induction coil of the low frequency induction furnace, and an output voltage of the transformer. an applied power regulator that adjusts the applied power to the induction furnace according to a capacitance value of a parallel capacitor connected in parallel to the side; and a control device that monitors the power of the induction furnace and gives a power adjustment command to the regulator. comprising: the control device;
Determine the deviation between the applied power of the induction furnace and the rated power of the induction furnace, and according to this deviation, adjust the output voltage of the transformer, adjust the capacity of the parallel capacitor, or combine both as a power adjustment command to suppress the deviation to zero. An operation control device for a low frequency induction furnace that performs control to maintain applied power to the induction furnace at the rated power of the induction furnace according to the selected power adjustment command, the control device comprising: , when the power of the induction furnace is below the rated power and the three-phase current on the output side of the transformer exceeds the allowable current value due to the balance ratio being collapsed, the balance ratio of the three-phase current is adjusted by adjusting the capacity of the parallel capacitor. It is characterized by performing stabilizing control.

[Function] As described above, in the present invention, the control device selects three types of adjustment means: adjustment of the output voltage of the transformer, adjustment of the applied power to the induction furnace by adjusting the capacity of the parallel capacitor, and adjustment of a combination of both, and adjusts the output voltage. Since the output of the induction furnace is adjusted using a regulator and an applied voltage regulator, accurate control suitable for the operating conditions can be performed.

In addition, if the power of the induction furnace is below the rated value and the three-phase current on the output side of the transformer exceeds the allowable value due to the imbalance ratio, the control device will control the capacity of the parallel capacitor for power factor adjustment of the induction furnace. The three-phase current balance ratio is adjusted to an appropriate range by adjusting the three-phase current balance ratio, so if the output side current of the three-phase transformer for induction furnace is out of balance, the output side current will be within the allowable range. The value will not be exceeded, and problems such as being forced to power down or not being able to perform power up processing are eliminated.

〔Example〕

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 shows the overall configuration of an apparatus according to an embodiment of the present invention. In this figure, the device according to this example is
In order to automatically adjust the output voltage of the transformer 12 according to the power of the induction furnace, a tap control unit 40 as an output voltage regulator that adjusts the output voltage of the transformer 12 and an applied power regulator that adjusts the power of the induction furnace. a power factor control section 24 as;
It has a control device 42 that controls each regulator. This control device 42 includes a circuit breaker 16 , an ammeter 46 , a tap control section 40 , an ammeter 26 , a voltmeter 28 , a wattmeter 30 . Output signals from the power factor meter 48 and the power factor control unit 24 are supplied.

One control device 42 is composed of a microcomputer including a CPU, ROM, RAM, etc., and includes an ammeter 26,
It is configured to output a power adjustment command based on an output signal from the wattmeter 30 or the like.

When a power adjustment command is given to the tap control section 40 and the power factor control section 24, the applied power to the induction furnace is controlled in accordance with this command.

The control to maintain the induction coil 10 at the rated power is to find the deviation between the applied power to the induction furnace and the rated power of the induction furnace, and to control the output voltage of the transformer 12 according to this deviation to suppress the deviation to zero. This can be done either by adjustment, by adjusting the capacitance of a parallel capacitor, or by a combination of both.

In addition, in this embodiment, in order to finely adjust the power applied to the induction furnace, a power factor adjustment capacitor CO...Cn
A capacitor C with a smaller capacity than the switch Sx is connected in series and inserted into the secondary side of the transformer 12. That is, the transformer 1 is turned on or off by turning on or off the switch Sx according to a command from the power factor control section 24.
It is possible to finely adjust the output power of 2.

In addition, in this example, when the electric power of the induction furnace is below the rated value,
In addition, when the secondary current of the three-phase transformer is greater than the allowable value and the current unbalance ratio is greater than a predetermined value, the capacitance of the power factor adjustment capacitor co...Cn, C, is adjusted. Furthermore, in this embodiment, after adjusting the capacitor capacity to reduce the current unbalance ratio, or when the current amparanne ratio is not higher than a predetermined value, the secondary current After performing the tap-down adjustment of the transformer tap when is above the allowable value, an overload flag is set that prohibits further adjustment. For example, after adjusting the capacitor capacity to optimize the three-phase current imbalance, if you perform power-up processing that exceeds the capacitor capacity adjustment amount, the secondary current etc. will exceed the allowable value and power-down processing will be performed again. Since this is unavoidable, such duplication of control is avoided by setting an overload flag.

In this embodiment, the same parts as those in the conventional apparatus shown in FIG. 7 are given the same reference numerals, and their explanation will be omitted.

The apparatus according to this embodiment has the above configuration, and the operation of the apparatus according to this embodiment will be explained below.

First, in step 100 in FIG. 2, the control device 42 and peripheral interfaces are initialized, the reference power Po of the transformer 120, and the output power of the transformer predicted when the tap position of the transformer is increased (or decreased) by one tap. The change value △Pd is the predicted change in the output power of the transformer when the tap position of the transformer is turned up (or down) by one tap and one of the capacitors C1...Cx is cut off (on). Value Δptc l capacitor C!・・・・・・CX1
A set value such as a change value ΔPc in the output power of the transformer predicted when one capacitor is turned on (cut off) is loaded, and the process moves to step 110. In step 110, the control is manual.
It is determined whether it is FF or not, and if it is manual ON, in step 120, analog values such as induction furnace power, transformer secondary current, secondary voltage, secondary power factor, reactive power, etc. and the main circuit breaker 16 are determined.
Digital values such as the ON and OFF states of the transformer 12, the tap position of the transformer 12, and the closing state of the capacitor are captured and displayed, and the process returns to step 110. If the control is manually OFF in step 110, the process moves to step 130, and it is determined whether the control is automatically ON. If the control is automatically ON in step 130, the process moves to step 140. In step 140, it is determined whether the main circuit on the primary side of the transformer is ON or not, and YES is determined.
If so, the process moves to step 150, where it is determined whether or not the transformer tap has automatically returned, and if the automatic return has been completed, the process moves to step 160. In step 160, it is determined whether the transformer tap is number 11 or higher, and if YES, the process moves to step 170. If NO in each step of 130, 140, 150°160, step 110
Return to In step 170, data such as the transformer output power, secondary voltage, primary (secondary) current, reactive power, capacitor closing state, transformer tap position, etc. are taken in, and among this data, the analog value is approximately 5 Q. Qms
Take the moving average for each ec. Next, proceed to step 180,
In step 170, it is determined whether the average value of each piece of data taken in is below the respective allowable value. If YES, the process moves to step 190, and the output power P of the transformer 12 is determined as the rated power of the induction coil 10. It is determined whether the power is lower than the reference power Po, and if YES, the process moves to step 200. In step 200, p<p continues for more than 120 seconds.
Determine whether it is in the o state, and if YES, step 2
After the power-up process in step 10, step 110
Return to If NO is determined in steps 190 and 200, the process returns to step 110 without going through the power-up process in step 210. If the determination in step 180 is NO, that is, if any one of the average values of the data acquired in step 170 exceeds the allowable value, the process moves to step 220, where content-based power down processing is performed, and then step 1] Return to 0.

As shown in FIG. 3, the power down process in step 220 first determines whether the output power P of the transformer 12 exceeds the allowable power Pmax of the induction coil 10 in step 300. If YES, step 310
After performing power down processing, the process returns to step 110 shown in FIG. If No in step 300, the process moves to step 400, and the secondary voltage Vz reaches the allowable value V2.
It is determined whether or not it exceeds max. If YES in step 400, the process moves to step 410, and in step 41.0, it is determined whether or not the state in which the secondary voltage exceeds the allowable value continues for 5 seconds or more, and if YES, the process moves to step 420 to tap down. Perform processing. Thereafter, the process moves to step 430, and it is determined whether the transformer tap exceeds number 10. If YES, the process returns to step 110 shown in FIG. 2. On the other hand, if NO in step 430, an alarm process is performed in step 440, and then the process returns to step 110. If NO in step 410, the process returns to step 110 without performing the tap-down process.

If NO in step 400, the process moves to step 500, in which it is determined whether the secondary current exceeds the allowable value, and if YES, in step 51
On the other hand, if the answer is NO, the process returns to step 110 shown in FIG. 2 without performing power-down control until this time. In step 510, the secondary current (work 2) is adjusted to the allowable value (I, ma
x) It is determined whether or not it is 110% or more, and if YES, the process moves to step 520, and if step 2≧1. It is determined whether the state of I11max continues for 5 seconds or more, and if YES in step 520, the process moves to step 530, and step 53
At 0, the current unbalance ratio (maximum phase current/minimum phase current)
It is determined whether or not is greater than or equal to 1.1. If NO in step 510, the process moves to step 515, and I 2) I 2
Determine whether the state of max continues for 20 seconds or more, and select YE.
If S, the process moves to step 530, while if NO, the process returns to step 110 shown in FIG. 2 without performing any control. If the determination in step 520 is No, the process also returns to step 110 shown in FIG. death,
If YES, the process moves to step 550 and the capacitor (C
It is determined whether the reactive power after turning on or cutting off control of r...C,) is closer to 0 than the current reactive power value, and if YES, the process moves to step 560 and the reactive power is set to O. The power factor control unit 24 turns on or off the capacitors (CI...C,) so that the power factor approaches .

This improves the unbalance of the three-phase currents, and when either the R phase or the T phase exceeds the allowable value, the current value can be suppressed to within the allowable value. After performing unbalanced current ratio control by adjusting the capacity of the capacitor in step 560, the process moves to step 570.

In step 570, an overload flag is set, and the overload flag is set as shown in FIG.
1) and (2), the prohibition indicator light is turned on to display control contents that should not be continued. In Figure 4, ○ indicates the prohibition indicator light is on,
The mark indicates the prohibition indicator light is off, and the ○ mark (lit)
Some controls are no longer possible. For example, if the capacitor control shown in step 560 is performed, overload flags as shown in FIG. 4 (1) and (2) will be set. In other words, tap control, whether the capacitor is turned on or off is adjusted.
This indicates that neither tap capacitor control nor capacitor control can be performed successively.

In step 560, the capacitor (CI...
・If adjustment is made to suppress the unbalanced current by cutting off Cx), then if tap-up control is performed to increase the output of the induction furnace, the secondary current will exceed the allowable value and the current unbalance ratio will increase. Then, the process goes through step 530 again and the capacitor (C1...) in step 5'60 is
Current unbalance ratio control due to CX>S disconnection must be performed, and the previously performed current unbalance ratio control is wasted. Therefore, an overload flag indicating prohibition control that should not be continued is set, and a prohibition indicator light as shown in FIG. 4 is turned on to efficiently operate the induction furnace.

After setting the overload flag in step 570, the process returns to step 110 shown in FIG. Also step 530.54
0.550, that is, if the current unbalance ratio < 1.1, if the reactive power is outside the hunting prevention range with power factor control, or if the capacitor CI...Cx If the reactive power is not within the range approaching O due to the continuous application control, the process moves to step 535, where a power down process is performed to lower the transformer tap position by one tap, and then the process moves to step 545.

In step 545, it is determined whether or not the tap is number 10 or higher. If YES, the process moves to step 570, as shown in FIG.
) and lights up the corresponding prohibition indicator light. With the overload flag shown in Fig. 4 (3), power up by transformer tap up and capacitor capacity reduction control and power up process by capacitor capacity increase control may be performed, but power up by transformer tap up may be performed. Processing is no longer possible. In addition, after setting the overload flag as shown in Figure 4 (3), power-up processing is performed by transformer tap-up - capacitor capacity reduction control or capacitor capacity increase control, and as a result, the secondary current returns to the allowable value again. If the overload flag is exceeded and tap-down is performed in step 535, the overload flags shown in FIG. It has become. The overload flag shown in Figure 4 (1) to (5) is cleared when the secondary current reaches a value that is lower than the current value immediately after power-down processing by an amount that exceeds the allowable current value. It is now possible to do so.

If NO is determined in step 545, step 55
After performing the alarm processing in step 5, the process returns to step 110 shown in FIG.

Details of the power-up process in step 210 shown in FIG. 2 are shown in FIG. 5. First, in step 600, the output power P of the transformer and the reference power P of the induction coil are
Calculate the deviation ΔP from o.

Next, in step 610, it is determined whether the transformer tap is smaller than number 17. If YES (smaller than number 17), the process moves to step 620. Stellar ΔPT is a predicted change in the output power of the transformer 12 when the tap position of the transformer 12 is increased by one tap. step 620
If YES in step 630, the secondary voltage V2' of the transformer when the tap position of the transformer 12 is turned up by one tap is calculated, and the process moves to step 640. Stella 7'640 determines V2' (V2max).

Here, V2max is the permissible value of the transformer secondary voltage v2.

If YES in this step 640, step 6
50, it is determined whether the overload flag for increasing the transformer tap is OFF. YES (OF
If F), the process moves to step 660, where a signal for increasing the tap position of the transformer 12 by one tap is output from the control device 42 to the tap control unit, and the tap position of the transformer 12 is increased by one tap, and then the process shown in FIG. Return to step 110.

If the determination in step 610 is No, that is, if the transformer tap position is No. 17, the process moves to step 615. In step 615, it is determined whether the power factor PF is within a predetermined range. If YES, the process moves to step 625.

In step 625, P F (PFLead is determined).

Here, P F L ead indicates the leading reference power factor, and if it is determined YES in step 625, the process proceeds to step 63.
Move on to 5. In step 635, it is determined whether the capacitance of the capacitor is within a range in which the capacitance can be increased. That is, capacitor C! If all Cx are in the closed state, the capacitor loading process will be difficult, so it is determined whether or not a new capacitor can be loaded based on the current capacitor loaded state. If YB2 is determined in step 635, the process moves to step 645, where it is determined whether the overload flag for increasing the capacitance of the capacitor is OFF'. YES in step 645
In other words, if it is OFF, the process moves to step 655, and a signal for injecting one stage of capacitor ft into the secondary circuit of the transformer 12 is output to the power factor control section 24, thereby increasing the capacitance of the capacitor and reducing the applied power to the induction coil 10. increases. After step 655, step 110 shown in FIG.
Return to When the determination is No in any of steps 625, 635, and 645, the process returns to step 110 without performing the capacitor capacitance increase adjustment in step 655.

In any of steps 620, 640, 650
If it is determined to be O, the process moves to step 627. In step 627, it is determined whether the power factor PF is within a predetermined range,
If YB2, the process moves to step 637, while if NO, the process returns to step 110 shown in FIG. Step 637
Then, it is determined that PF>PFlag. Here, PFLag is the reference power factor of delay, and in step 637, YB2
If the determination is NO, the process moves to step 647, while if the determination is NO, the process moves to step 625. In step 647, it is determined whether the capacitance is within a range in which the capacitance of the capacitor can be reduced. In other words, if all of the capacitors C1...Cx are in the cutoff state, it will be difficult to cut off the capacitors, so it is important to check whether it is possible to cut off a new capacitor based on the current capacitor cutoff state. It is to determine. If YES is determined in this step 647, step 65
Move on to 7. In step 657, it is determined whether the overload flag for reducing the capacitor capacity and the overload flag for increasing the transformer tap are both OFF. If YES, that is, the overload flag is OFF, the process moves to step 667, and a signal is output to the power factor control section 24 to shut off any of the switches (Sl...aX). Further, the process moves to step 677 and the control device 40
A signal is output to increase the tap position of the transformer 12 by one tap.

Since the amount of increase in the output power of the transformer 12 when the tap position of the transformer is tapped up is greater than the amount of decrease in the output power of the transformer 12 when one stage of the capacitor is cut off, the transformer consists of steps 667 and 677. The induction furnace is powered up by the tap-up-capacitor OFF adjustment. After passing through step 677, the process returns to step 110 shown in FIG. If it is determined No in either step 647 or 657, the process moves to step 625.

Details of the power down process in step 310 shown in FIG. 3 are shown in FIG.
At 00, the output power P of the transformer 12 and the induction coil 1
The deviation ΔPH of the allowable power Pmax of 0 is determined. Next, the process moves to step 710, and it is determined whether the power factor PF is within a predetermined range. If YES, the process moves to step 720. In step 720, ΔPH(PC is determined. Here, ΔPc is the predicted output power of the transformer 12 when one of the capacitors C1...Cx is inserted or cut off on the secondary side of the transformer 12. It is a change value.

If YES is determined in this step 720, the stem 73
0, PF) Determine PFLag. Note that here P
FLag is the reference power factor of delay. If YES is determined in step 730, the process moves to step 740, and in step 740, similarly to step 647 shown in FIG.
It is determined whether the capacitance of the capacitor is within a range where the capacitance can be reduced. If YES is determined in step 740,
Moving to step 750, a signal for cutting off one stage of the capacitor in the secondary circuit of the transformer 12 is output to the power factor control section 24, thereby reducing the capacitance of the capacitor and the power applied to the induction coil 10. After passing through the capacitor charging process of step 750, the process returns to step 110 shown in FIG.

In any of steps 720, 730, 740
If it is determined to be O, the process moves to step 760, and ΔPH(ΔPT
Determine C. Note that ΔPTc taps down the tap position 1&:1 of the transformer 12, and switches S!・・・・・・
- It is the change value of the output power of the transformer 12 predicted when one switch of Sx is turned on. Step 76
If YES is determined at 0, the process moves to step 770.
Power factor PF (advanced power factor PFLead 2 determined, YES
If so, the process moves to step 780. In step 780,
Similar to step 635 shown in FIG. 5, it is determined whether the capacitance of the capacitor is within a range in which the capacitance can be increased. If YES is determined in step 780, step 790
The transformer tap-down process in step 800 and the capacitor input process in step 800 are performed, and the process moves to step 810. In step 810, it is determined whether or not the transformer tap position exceeds number 10. If the transformer tap position is greater than number 10, the process returns to step 110 shown in FIG. After doing step 110
Return to Further, if the determination in step 710 is NO, the process moves to step 830 to perform alarm processing, and then moves to step 840. If the determination in step 7.60 is No, the process moves to step 840. Step 840 performs transformer tap-down processing, and then step 81
Move to 0. If NO is determined in either step 770 or 780, the process moves to step 850 to perform transformer tap-down processing, then to step 860 to perform alarm processing, and then moves to step 810.

As described above, in this embodiment, when operating the induction furnace, the output power of the transformer 12 and the induction coil 1 are
Determine the deviation from the rated power of 0, and according to this deviation, perform power control to suppress the deviation to zero by adjusting the output voltage of the transformer 12, adjusting the capacity of the parallel capacitor, or adjusting the combination of the two. Since the power is adjusted to suppress the deviation to zero according to the deviation, the output power of the transformer 12 can be brought close to the rated power in a short time, as shown by the characteristic C shown by the broken line in FIG. Further, the output power of the transformer 12 can be maintained at the rated power. Therefore, according to this example, the time required for melting is shortened, the melting capacity can be improved, and the loss of energy required to cool the furnace wall etc. is reduced, resulting in a reduction in the melting power consumption rate. can be achieved.

In addition, in this embodiment, since the adjustment of the output power of the transformer 12 can be automated, the induction furnace will not be operated with power exceeding the allowable value due to the operator forgetting to operate the tap, etc., and the furnace wall will be abnormal. It is possible to prevent wear and the like from occurring.

In addition, on the real side, when the power of the induction furnace is below the rated power and the balance ratio of the secondary current collapses and the secondary current exceeds the allowable value, the capacity of the parallel capacitor is adjusted. Since the unbalance ratio of the secondary current is stabilized, continuous operation at high power close to the rated power is possible. Furthermore, in this embodiment, step 570
By setting the overload flags shown in FIG. 4 (1) to (5), redundant control is omitted, allowing efficient operation of the induction furnace.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the induction furnace can be operated efficiently, the melting capacity can be improved, and as a result, the productivity can be improved.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Fig. 2, Fig. 3
5 and 6 are respectively 70 charts for explaining the operation of the device according to the present invention, and FIG. FIG. 7 is a diagram showing the configuration of a conventional device, FIG. 8 is a diagram showing the relationship between the amount of molten metal and the power coefficient, and FIG. 9 is a power transition characteristic diagram of the melting cycle of the conventional device and the device according to the present invention. 10... Induction coil, 12... Step-down transformer,
24...Power factor control unit, 26.46...Ammeter, 2
8... Voltmeter, 30... Wattmeter, 40... Tap control unit, 42... Control device, 48... Power factor meter.

Claims (1)

[Claims] (1) An output voltage regulator that adjusts the output voltage of a three-phase transformer for induction furnaces that supplies power to the single-phase induction coil of a low-frequency induction furnace, and the capacitance value of a parallel capacitor connected in parallel to the output side of the transformer. an applied power regulator that adjusts the applied power of the induction furnace according to The deviation between the applied power and the rated power of the induction furnace is determined, and according to this deviation, the output voltage of the transformer is adjusted as a power adjustment command to suppress the deviation to zero.
Operation control of a low frequency induction furnace that selects either capacity adjustment of a parallel capacitor or adjustment that combines both, and performs control to maintain the applied power of the induction furnace at the rated power of the induction furnace according to the selected power adjustment command. The control device controls the capacitance of the parallel capacitor when the power of the induction furnace is below the rated power and the three-phase current on the output side of the transformer exceeds an allowable current value due to a loss of balance ratio. An operation control device for a low frequency induction furnace characterized by performing control to stabilize the balance ratio of three-phase currents through adjustment.