JPS6393456A - Control device for tandem molten steel heating equipment - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control device for induction heating of molten steel in a tundish for continuous casting with a groove-type induction heating device, and in particular,
The present invention relates to a control device that detects a precursor phenomenon of the pinch effect that occurs when molten steel decreases in a groove-type induction heating device, and avoids the pinch effect by controlling power supplied to the heating device.

[Conventional technology]

In a tundish molten steel heating device using a groove-type induction heating device, the molten steel in the shallow groove is heated by an induced current,
The electric current of Yuzo is a large current of several thousand to several hundred amperes,
Electromagnetic contraction force acts on the molten steel in the shallow groove. When this electromagnetic contraction force increases, the molten steel in the shallow groove of the current path is partially squeezed,
The current density in that part increases, the part becomes more and more constricted, and finally the molten steel in the shallow groove of the current path shrinks and breaks.

As a result of shrinkage rupture, the current path of the molten steel in the shallow groove is cut off, current no longer flows, and the electromagnetic contraction force disappears, so the molten steel in the shallow groove of the current path is immediately connected, but the current also flows and the current path The molten steel in the shallow groove shrinks and breaks.

This is repeated. This phenomenon of discontinuing the molten steel in the shallow groove due to electromagnetic contraction force is called the pinch effect. The occurrence of the pinch effect has a certain relationship with the static pressure of the molten steel in the molten metal groove.
This is likely to occur when the level of the molten steel in the tundish decreases and the static pressure of the molten steel decreases. In addition, when the supplied power is large, it is more likely to occur.

For this reason, in the tundish molten steel heating device using a groove-type induction heating device, a pinch effect occurs depending on the magnitude of the supplied power at the beginning and end of casting, and this pinch effect frequently causes instantaneous interruptions in the current. However, there is a problem that stable heating power cannot be supplied.

In contrast, the present applicant et al.
No. 60-221404, the occurrence of this pinch effect is detected immediately before the occurrence of the pinch effect, and the input voltage to the induction coil is reduced in the state immediately before the occurrence of the pinch effect, thereby avoiding the occurrence of the pinch effect. We proposed a control percentage position.

The detector for detecting the pinch effect of the device proposed in Japanese Patent Application No. 60-152210 uses a power factor meter of the power supplied to the heating induction coil of the groove type induction heating device. In other words, a power factor meter is used to detect the power factor of the induction coil when power is supplied to the single-phase heating induction coil through a phase balance circuit with three-phase AC current, and the U-phase and W-phase of the three-phase AC voltage are The voltage between them and the load current If are input, and the power factor of the heating induction coil of the load is detected. When the operating power factor detected here changes to a predetermined set value or more, it is assumed that a pinch effect has occurred, and the detector generates a detection output and sends a control signal to the control device.

In addition, the detector for detecting the pinch effect of the device proposed in Japanese Patent Application No. 60-221404 detects the variation in each phase current Iu, Iv, Iw of the three-phase alternating current, and detects the pinch effect. Assuming that, each phase current Iu, Iv, Iw of the three-phase alternating current is inputted by a current transformer, and when the difference between the vector composite value of U phase and W phase and the V phase becomes more than a predetermined setting value, Assuming that a pinch effect occurs, the detector generates a detection output and sends a control signal to the control device.

[Problem that the invention seeks to solve]

When examining the pinch effect generation process in a tanditsu molten steel heating device using a groove-type induction heating device, for example, Fig. 2 shows the respective phase currents and operating load forces on the load side of the tap changer obtained from experiments with the tanditsu heating device. However, as shown in FIG. 2, by the time the load power factor changes during operation, the currents in each phase are already in a hunting state, and the pinch effect has begun. Further, the difference in the change in the load power factor during operation at this point is small.

For this reason, it is difficult to set the detection level of the detection device that uses a load power factor detection circuit to distinguish between normal conditions and when the pinch effect occurs, and it is difficult to set the detection level of the detection device that uses a load power factor detection circuit to detect the pinch effect. There is a problem in that the pinch effect has already occurred at the time the detection signal is output.

In addition, Fig. 3 shows a vector diagram of the three-phase AC current supplied to the groove-type induction heating device under normal conditions, immediately before the occurrence of the pinch effect, and
The cases are shown separately for when the pinch effect occurs, but as shown in the figure, l I'u in the normal state and immediately before the pinch effect occurs.
+ I゛w The variation width of the difference in the magnitude of the vectors I and lI'vl is about 1.5% when compared with the absolute value of the ■ phase, and when a significant difference is detected, it is already considered that the pinch effect has occurred. There is a problem that it is in an initial state.

In this way, the two methods described above are both for controlling the pinch effect at its initial stage rather than for immediately avoiding it, and due to current hunting, transformers, phase balance equipment,
This problem causes a reduction in the lifespan of power factor correction capacitors and induction coils, requires increased strength, and becomes an obstacle when replacing tap changers with stationary equipment for continuous power control. There is a point.

In addition, in these detection methods, the range of change between the normal state and the occurrence of the pinch effect is small, and the detection circuit needs to be highly sensitive, which poses problems such as the risk of false detection and difficult settings. have.

In order to solve the above-mentioned problems, the present invention accurately captures the precursor phenomenon of the pinch effect, performs stable detection, and uses a detection device whose detection level can be easily set to control the voltage applied to the heating induction coil. It is an object of the present invention to provide a control device that controls and avoids the occurrence of the pinch effect.

In a control device for a tanditush molten steel heating device that supplies three-phase alternating current to a single-phase heating induction coil via a phase balance circuit, a first A first detection means for detecting the absolute value of the phase current, a second detection means for detecting the difference in the absolute value between the second phase current and the third phase current supplied to the chanting load, and the absolute value of the first phase current. and a predetermined value, and a control means for reducing the voltage applied to the load in accordance with the output of the calculation means.

[Effect]

As shown in the graph of FIG. 2, as a precursor to the occurrence of the pinch effect, the W-phase current Iw tends to decrease and the U-phase current Iu tends to increase as the pinch effect occurs. However, at this time, the V-phase current Iv hardly changes. This is because, due to the generation of electromagnetic contraction force that causes a pinch effect, contraction force acts on the molten steel in the groove through which the molten steel passes, and the resistance of the molten steel in the groove changes in an increasing direction, which increases the load power factor. This is because a constant power factor correction capacitor compensates for this, and the balanced currents of each phase change.

However, they are vector-balanced, and the V-phase current Iv of the phase-balanced current hardly changes due to the phase-balanced circuit.

Detection of a precursor phenomenon to the occurrence of the pinch effect in the present invention utilizes changes in the phase currents Iw and Iu in opposite directions. Phase current Iu by current transformer.

Iv and Iw are detected, and as the pinch effect approaches, the phase current Iu shows an increasing tendency as a precursor phenomenon.
Focusing on the fact that the difference in the absolute value between the phase current Iw and the phase current Iw, which shows a decreasing tendency, increases in ratio with respect to the absolute value of the phase current Iv, which does not increase or decrease, The moment when the pinch effect occurs is detected as a precursor to the occurrence of the pinch effect.

Then, based on a signal from the detection device that detects this, the voltage applied to the induction coil is lowered to avoid the occurrence of the pinch effect.

As shown in the vector diagram in Figure 3, by taking the difference in the absolute values of phase currents that change in opposite directions, even if the change in each phase current is small or the change in one composite vector is small, The difference in absolute values can be interpreted as a large change, and it is possible to easily grasp the precursor phenomenon of the occurrence of the pinch effect. Detection of this pinch effect is based on the fact that the second phase current supplied to a single-phase load and the third phase This is performed by comparing the ratio of the difference between the absolute value and the current with a predetermined set value. Therefore, even if the groove-type induction heating device is operated at a low voltage and the current value of each phase is small and the difference in increase/decrease changes becomes small, the ratio of the difference does not change. Therefore, by detecting the ratio, the set sensitivity of the detection device for detecting a precursor phenomenon to the occurrence of the pinch effect can be kept constant regardless of the operating state of the heating device.

〔Example〕

FIG. 1 is a block diagram showing the general configuration of a control device for a tundish molten steel heating device using a groove-type induction heating device for implementing the present invention.

Power from the 3-phase AC power source is transferred to a 3-phase transformer 1. It is supplied via the tap changer 2 to the single-phase heating induction coil 3 of the groove-type induction heating device. A tap changer 2 is connected to the secondary side of the three-phase transformer 1, and the U phase on the load side of this tap changer 2,
A single-phase heating induction coil 3 and a power factor improving capacitor 4 are connected in parallel to the W phase. In addition, in the ■phase, there is a phase balance reactor 5 and a phase balance capacitor 6 necessary for supplying power from the three-phase circuit to the heating induction coil 3 of the phase load.
are connected. When the pinch detection device 8 detects the occurrence of the pinch effect, detects the current of each of the three phases using the current transformer 7, and detects a precursor phenomenon of the occurrence of the pinch effect from the current detection signal of each phase, this pinch detection signal is detected. The pinch prediction signal and the pinch occurrence signal are input to the control V4 device 9, and the control device 9 drives the tap changer 2 according to this signal to reduce the input voltage supplied to the heating induction coil 3, thereby reducing the pinch effect. avoid the occurrence of

FIG. 4 shows an example of a circuit diagram of the configuration of the pinch detection device 8 in FIG. 1.

In FIG. 4, three current transformers 7 installed in the U-phase, ■-phase, and W-phase power supply lines have phase currents Iu and Iv, respectively.
, Iw are detected, and these signal currents are connected to the level adjustment resistor 1.
1, the rectifier circuit 12 converts the input current into a DC voltage corresponding to the magnitude of the input current. The DC output voltage of this rectifier circuit 12 is adjusted to voltage values Vu, Vv, V by a level adjustment resistor 13.
It becomes a signal of w.

Here, Vu and Vw are input to the differential amplifier 14, and the differential amplifier 14 outputs a difference signal of Vu-Vw, which is input to one input terminal 15a of the divider 15. on the other hand,
Vv is input to the other input terminal 15b of the divider 15. Output of divider 15 (V u - V w )/V
v is input to the comparison input terminal 16a of the comparator 16. A voltage VR1 determined by a level setting resistor 17 for pinch prediction detection is inputted to a reference input terminal 16b of the comparator 16 via an amplifier 18. Further, the output (V u −V w)/V v of the divider 15 is input to the comparison input terminal 19 a of the comparator 19 . A level setting resistor 21 for pinch occurrence detection is connected to the reference input terminal 19b of the comparator 19.
A voltage v82 determined by is inputted via the amplifier 20. The comparison voltage level vFt2 is the comparison voltage level v
It is set slightly larger than PTI, and detects the moment immediately before the pinch effect occurs. From the comparators 16 and 19, the pinch prediction 43 is output according to the comparison level of the detection to be detected.
Pinch occurrence signal PB is output.

In the circuit shown in FIG. 4, the signals Vu and Vw input to the differential amplifier 14 each correspond to a phase current Iu.

It is a value corresponding to Tw, and the magnitude of the output V u -V w is proportional to Iu - Iw. Furthermore, the output of the divider 15 (V
u-Vw)/Vv is proportional to (Iu-Iw)/Iv.

Therefore, by comparing the magnitude of (V u - V w)/V v with the magnitude of the arbitrarily set reference signals vR1 and vR2, the phase currents Iu and Iv
This makes it possible to know the extent of the change in the amount of change, and to detect the occurrence of the pinch effect in advance at multiple stages. As a result, detection can be made 15 to 20 seconds before the occurrence of the pinch effect, and control that takes into account the delay time of transformer tap switching becomes fully possible.

Although the magnitude of Vu-Vw, which is the absolute value difference of the phase currents, changes due to changes in the main circuit voltage of the groove-type induction heating device, Vv
also changes depending on the main circuit voltage. For this reason, V u
- Perform the operation of dividing the absolute value of V w by the absolute value of Vv,
By using that ratio as the comparison value, the pinch effect detection level can be set at a constant value over the entire heating power control range of the groove-type induction heating device, making it possible to detect the pinch effect with high sensitivity and easily. I'm trying to detect it.

FIG. 5 is a block diagram showing an example of the configuration of the control device 9 shown in FIG. 1. In FIG. 5, 22 is the tap changer 2
positioning driver that drives the tap-switching drive motor of
24 is a microprocessor that performs control processing, and 23 is an interface that inputs and outputs data to and from the microprocessor 23. The tap changer 2 includes a switching drive motor with a reducer that switches the tap position, and a position sensor that generates an electric signal corresponding to the tap position to which the tap is currently connected. It is rotated and a detection signal from the position sensor is given to the positioning driver 22 . The positioning driver 22 converts the connection position data corresponding to the applied voltage instruction data to be supplied to the load from the microprocessor 24 into analog (i), compares this with the detection signal of the position sensor, and determines the tap position specified. The switching drive motor is rotated and energized so as to reach the specified tap position, and the tap position is set to the position of the specified applied voltage value.

Target value data of applied voltage supplied to the load, pinch prediction signal P A + from pinch detection device i'28 (Fig. 4)
A pinch generation signal PR is provided to the microprocessor 24 via the interface 23, and the microprocessor 24 provides tap connection position data corresponding to the applied voltage supplied to the load to the positioning driver 22 via the interface 23.

FIG. 6 shows an overview of the control operation of the microprocessor 24. When the power is turned on, the microprocessor 24
Initialize the input/output ports and clear internal registers, timers, etc. (Step 1: The word step will be omitted in parentheses below).

After completing the initialization (1), the microprocessor 24 performs power-on control to start supplying power to the heating induction heating coil 3 (2), and then the microprocessor 24 determines the current tap connection position and applied voltage. The data of the target value, the pinch prediction signal PA from the pinch detection device 8, and the pinch occurrence signal PB are read (3). In a normal case, since no pinch effect occurs, the data of the pinch prediction signal P A r and the pinch occurrence signal PB are not inputted from the pinch detection device 8 . If the generation of the pinch prediction signal PA and the pinch occurrence signal pa is not determined in steps 4 and 6, the process proceeds to step 8, where target value data is input into an output register that holds voltage setting data of the applied voltage to be supplied to the load; Switching control of the tap changer 2 is performed so that the voltage applied to the load is set to this target value. If the data of the pinch occurrence signal P11 or the pinch prediction signal PA is input from the pinch detection device 8, they are determined in steps 4 and 6, and the contents of the output register are divided into two stages in steps 5 and 7, respectively. , and process a one-step decrease.
That is, when the presence of the pinch generation signal PB is determined in step 4, the content of the output register is set as the content of the output register for setting the applied voltage by subtracting 2 from the current content5), and the pinch generation signal PB is determined in step 6. When the presence of the prediction signal PA is determined, 1 is subtracted from the current content of the output register to set the content of the output register for setting the applied voltage (7). Then, tap switching control of the tap changer 2 is performed based on the data contents of these output registers. That is, compare the data contents of the output register that sets the applied voltage set in step 5.7.8 with the current tap connection position data of the tap changer 2 (9), and if they do not match, the data is sent via the interface 23. The contents of the output register are set from the output port to the positioning driver 22, and the tap connection position is switched according to the contents of the output register (1o). and.

Set a T-timer that measures enough time for the tap changer 2 to operate and the voltage applied to the heating induction coil to decrease (11), and wait until the T-timer exceeds the timer 11. (12), return to step 3. In step 9, the current tap connection position data of the tap changer 2 is compared, and if they match, it is sufficient and the process returns to step 3. Repeat these processes.

Through these processes, in a tundish molten steel heating device using a groove-type induction heating device, the applied voltage can be controlled to capture the precursor phenomenon of the occurrence of the pinch effect and reduce the voltage applied to the induction coil for heating the load in advance. Because we do
Power can be supplied to the induction heating device without the occurrence of a pinch effect.6 In the description of the above embodiment, the pinch detection bag c18 in the circuit example shown in FIG. Although it is a processing circuit, it is also possible to perform the signal processing therein as digital signal processing. In that case, this digital signal processing is performed within the microprocessor 24 of the control device 9 shown in FIG. It turns out. At that time, the microprocessor 24 has an interface 2.
Voltage values Vu, which directly correspond to the values of each phase current Iu, Iv, and Iw, through the analog/digital conversion port No. 3.
Vv and Vw are input to the microprocessor 24. That is, in that case, the part surrounded by the one-dot chain line shown in FIG. 4 is not necessary, and the processing of this part replaces the processing steps in the microprocessor 24.

In addition, in FIG. 4, the output of the comparator 16 is outputted via a relay driven by a variable timer, so that the pinch detection device 8 detects the precursor phenomenon of the pinch effect and then outputs the output to the induction coil at an arbitrary time. The applied voltage control can be started. Therefore, by setting the detection level of the pinch detection device 8 and setting the time of the variable timer, it is possible to appropriately perform control to avoid occurrence of the pinch effect.

〔Effect of the invention〕

As explained above, according to the present invention, as a precursor phenomenon to the occurrence of the pinch effect, the change in each phase current gradually increases in one phase, gradually decreases in the other phase, and in the remaining one phase. By using a clear precursor phenomenon that does not change, it is possible to detect the occurrence of the pinch effect in advance, rather than detecting the occurrence of the pinch effect at the initial stage. Depending on the setting of the detection level, it is possible to detect the pinch effect 15 to 20 seconds before it occurs, making it possible to control the transformer tap switching in anticipation of the delay time. In the apparatus, by detecting the occurrence of the pinch effect in advance and controlling the power supply to the heating device, the occurrence of the pinch effect can be reliably avoided, and a decrease in the life of the electrical equipment can be prevented.

Therefore, there is no need to increase the strength of unnecessary electrical equipment, and it becomes possible to employ stationary equipment that is essential for continuous power control of the heating device. Furthermore, compared to the power factor change detection method and the current vector comparison method, the detection resolution is ten times or more, and the detection level can be easily set. This improves the G reliability of the detection device, avoids the pinch effect, and enables stable supply of heating power.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the general configuration of a control device for a tundish molten steel heating device using a groove-type induction heating device in which the present invention is implemented in the kitchen, and Fig. 2 shows each phase current and load during the pinch effect generation process. A graph showing the power factor, Figure 3 is a vector diagram of three-phase alternating current in a predetermined state during the pinch effect generation process,
FIG. 4 is a circuit diagram showing an example of the configuration of the pinch detection device shown in FIG. 1. FIG. 5 is a block diagram showing an outline of the configuration of the control device 9 shown in FIG. 1, and FIG. 6 is a flowchart showing an outline of the control operation of the control device 9 shown in FIG. 1: Three-phase transformer 2: Tap changer 3: Heating induction coil 4: Power factor improvement capacitor 5: Phase balance reactor 6: Wahei street corner capacitor 7: Current transformer 8: Pinch detection device 9: Control device U , t:S Two-level adjustment resistor 12: Rectifier circuit 14: Differential amplifier 15: Divider 16
, 19: Comparator 17.21: Detection level setting resistor 18.20: Amplifier shoulder 1 anti-Fig.

Claims (1)

[Claims] (1) In a control device for a tundish molten steel heating device that supplies three-phase alternating current to a single-phase heating induction coil via a phase-balanced circuit, the phase-balanced circuit does not increase or decrease with respect to the single-phase load. The first detection means detects the absolute value of the first phase current for the single phase load, the second phase current supplied to the single phase load and the third
a second detection means for detecting the difference in absolute value from the phase current; a calculation means for comparing the ratio between the absolute value of the first phase current and the difference in the absolute value with a predetermined value; and a calculation means according to the output of the calculation means. 1. A control device for a tundish molten steel heating device, comprising a control means for reducing a voltage applied to a load.