JPH06331278A - Monitoring method of insulation of dc arc furnace - Google Patents

Abstract

PURPOSE:To ensure insulation of a conductor of a furnace bottom electrode part and measuring equipment and to minimize the damage of a measuring apparatus die to a spark current by a method wherein the voltage characteristic of a measured value and that of an abnormality set value for the same current value are compared with each other, it is determined that the measured value is present in the abnormal range, and thereby the abnormality is detected and outputted. CONSTITUTION:A furnace bottom electrode 6 and furnace body steel shell 3 positioned on the opposite side of an insulator 7 disposed on the circumference of the furnace bottom electrode 6 are connected to insulation monitoring equipment 18 by conductors 17. This equipment is constructed of a voltage detector 24 detecting a voltage between the conductors 17, a current detector 23 detecting a current flowing through a resistor 22 for grounding, a determination circuit 28 storing a voltage characteristic for the current on the occasion when an insulation resistance is normal and comparing the range of abnormality of the voltage value for a current value set by an alarm setting unit 29 with a voltage measured value for the current value obtained by computing the measured value, and others. Abnormality is detected by determining that the voltage measured value for the same current value is present in the set abnormal range of the voltage value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to insulation monitoring of a bottom electrode of a DC arc furnace for melting and heating a melted material such as scrap by forming an arc between an upper electrode and a bottom electrode. Regarding the method.

[0002]

2. Description of the Related Art With the recent increase in capacity of power semiconductor devices such as thyristors, a DC arc furnace has come into general use as an arc furnace for steelmaking. A DC arc furnace does not require three movable electrodes like an AC arc furnace, and an arc is formed between at least one movable electrode and a furnace bottom electrode to melt and heat molten metal such as scrap. However, it has an advantage that the structure is simple.

However, unlike the AC arc furnace, since it has an electrode on the bottom of the furnace, it is necessary to provide an insulator between the bottom electrode and the furnace shell to ensure insulation between the bottom electrode and the furnace shell. There is. However, the metals to be melted such as scrap in the arc furnace contain impurities, and among them, metals having a higher specific gravity than iron, especially heavy metals such as lead, are deposited on the hearth during the melting process, and Part of the reaches the hearth iron skin.
In addition, part of it reaches the insulator provided between the hearth bottom electrode and the hearth iron shell, which in turn electrically connects the hearth bottom electrode and the furnace body iron shell, making the insulator meaningless. Disappear.

In this state, the current flows from the bottom electrode to the furnace shell →
It is often found that the furnace wall → scrap → upper electrode flow, sparks occur in the insulation part between the furnace bottom electrode and the furnace body skin, and the furnace body skin part is damaged. It takes time and effort. Therefore, in order to avoid this phenomenon, the furnace shell is provided with an opening hole for discharging the above impurities, mainly lead outside the furnace, but the above impurities cannot be completely removed. Therefore, Japanese Patent Laid-Open No. 4-165
In JP-A-289, there is proposed an insulation monitoring device for a DC arc furnace, which is characterized in that a furnace bottom electrode and a furnace shell are respectively connected to the insulation monitoring device by a conductive wire.

However, in order to measure the insulation resistance by the insulation monitoring device, a voltage drop method for measuring the insulation resistance by measuring the voltage and current of the measurement section, and a bridge circuit composed of three reference resistors and the measurement section. In order to constantly monitor the insulation resistance of the bottom electrode using the bridge method, which measures the insulation resistance, the voltage at the bottom electrode part fluctuates according to the change in current due to the fluctuation of the arc during operation. There is a problem that it is not possible to determine whether the applied voltage is due to a change in insulation resistance or due to a voltage fluctuation at the bottom electrode part of the furnace, and there is a problem in that This is an expensive device because it requires safety measures such as ensuring insulation and installing a limiting resistor to prevent damage to the measuring device due to spark current.

[0006]

In view of the problems of the prior art, the main object of the present invention is to monitor the insulation resistance between the bottom electrode and the furnace shell of the furnace due to impurities deposited on the furnace floor. ,
In order to achieve a means to minimize the damage to the furnace shell due to sparks, it was measured by eliminating the effect of voltage fluctuations in the bottom electrode part caused by changes in current due to arc fluctuations during operation. An abnormality in insulation resistance is detected by determining whether the voltage is due to a change in insulation resistance or due to a voltage change in the furnace bottom electrode, and the insulation between the conductor wire of the furnace bottom electrode and the measuring device is detected. Another object of the present invention is to provide a method for monitoring the insulation of a DC arc furnace, which is equipped with safety measures to secure and prevent damage to measuring equipment due to spark current.

[0007]

According to the invention, such an object occurs between the bottom electrode of a DC arc furnace and one or more conductors or bottom shells separated by an insulator. The voltage is measured through the voltage detector, and the current flowing from the furnace bottom electrode to the grounding resistor is measured through the current detector,
Each measured value is calculated to obtain the voltage characteristic with respect to the current value, the voltage characteristic when the insulation resistance is normal is stored in advance, and the abnormal range of the voltage characteristic is set for the normal voltage characteristic. Insulation monitoring of a DC arc furnace characterized by comparing the voltage characteristic of the measured value with the voltage characteristic of the same current value of the abnormal set value, determining that the measured value is within the abnormal range and detecting and outputting the abnormality. This is accomplished by providing a method.

[0008]

The insulation monitoring method of the present invention uses the fact that the current flowing through the grounding resistor changes according to the fluctuation of the voltage of the bottom electrode due to the fluctuation of the arc. By grasping the relationship between voltage values as the relationship between the current value flowing through the grounding resistor and the voltage value of the insulator, whether the voltage change of the insulator is due to the voltage change of the bottom electrode, or It is possible to determine whether it is due to a decrease in the insulation resistance of the furnace bottom electrode and the furnace bottom iron shell are connected to the voltage detectors with conductors respectively, and Voltage between the voltage detector and the current flowing from the furnace bottom electrode to the grounding resistor via the current detector, and the voltage change amount calculator and the current to calculate the respective measured values. Change amount calculation unit and voltage characteristic calculation unit and insulation resistance are positive By storing the voltage characteristics for various current values, the judgment circuit for comparing the voltage measurement value for the current value obtained by calculating the abnormal range of the voltage value for the current value set by the alarm setting device and the measurement value, It is determined that the voltage measurement value for the same current value has entered the abnormal range of the set voltage value, and the abnormality is detected and output.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic block diagram showing the overall structure of an embodiment of the present invention. The DC arc furnace 1 shown in FIG. 1 includes a hearth 2 made of a refractory material, a furnace wall 4 covering the outer periphery of the upper part thereof, a furnace body 2 and a furnace shell 3 for mechanically holding the furnace wall 2. , The furnace lid 5 covering the upper part of the
The upper electrode 8 which can vertically move from the center of the furnace and the hearth 2
Arc 1 formed between the molten metal 14 such as scrap stored in the hearth 2 and the tip of the upper electrode 8 by the direct current supplied to the hearth bottom electrode 6 provided in the central part of the
3, the molten metal 14 such as scrap is melted and heated.

The negative (-) terminal of the thyristor converter 10 for converting AC power supplied from a transformer (not shown) into controlled DC power is connected to the upper electrode 8 via the reactor 9 and the power feeding body 12. Has been done. Thyristor converter 10
The positive (+) terminal of the furnace bottom electrode 6 via the power supply body 11.
It is connected to the. The bottom electrode 6 is composed of the grounding conductors 20, 2
1. Grounded via a grounding resistor 22.

In FIG. 1, when there is no influence of impurities such as lead accumulated on the hearth 2 and when the electric conduction between the furnace bottom electrode 6 and the molten metal 14 is sufficient, a direct current is applied to the furnace bottom. The electrode 6 → melted metal 14 → arc 13 → upper electrode 8 flows (shown in FIG. 15), and normal operation is performed.

However, due to impurities such as lead accumulated on the hearth 2, the insulator 7 arranged on the circumference of the bottom electrode 6
Is not functioning normally, and the electrical conduction between the furnace bottom electrode 6 and the metal to be melted 14 is not sufficient, a direct current is applied to the furnace bottom electrode 6 → insulator 7 → furnace shell 3 → furnace Flowing from wall 4 → molten metal 14 → arc 13 → upper electrode 8 (Fig. 1
6) Sparks are generated on the insulator 7 and damage the furnace shell.

In this embodiment, as shown in FIG.
The furnace bottom electrode 6 and the furnace shell 3 located on both sides of the insulator 7 arranged on the circumference of the furnace bottom electrode 6 are connected to an insulation monitoring device 18 by a conductor 17. A voltage detector 24 that detects the voltage between the conductors, a voltage change amount calculation unit 26 that calculates the detected voltage, a current detector 23 that detects the current flowing through the grounding resistor 22, and a current change that calculates the detected current. Quantity calculation unit 25, a voltage characteristic calculation unit 27 that calculates a voltage characteristic with respect to a current value from a voltage value and a current value, a voltage characteristic with respect to a current whose insulation resistance is normal, and stores the voltage characteristic with respect to the current value set by the alarm setter 29. It is composed of a judgment circuit 28 that compares the abnormal range of the voltage value with the measured voltage value for the current value obtained by calculating the measured value, and the measured voltage value for the same current value falls within the abnormal range of the set voltage value. It is determined that the abnormality is detected.

Further detailed description will be made with reference to FIG. FIG. 4 shows a voltage characteristic diagram with respect to the current value calculated by the voltage characteristic calculation unit 27 of the present invention. The measured current value is plotted on the horizontal axis and the measured voltage value is plotted on the vertical axis.The voltage characteristics for a current value where the insulation resistance of the insulator is normal are the characteristics of a straight line rising to the right as shown by the solid line. The voltage characteristic with respect to the current value when the insulation resistance is reduced is a straight-line upward characteristic shown by the dotted line.
It is set in the range from a straight line with a small slope to the right and a horizontal straight line with a slope of 0.

(1) Voltage characteristic and alarm setting device 29 for a current value whose insulation resistance stored in the judgment circuit 28 is normal
Set the abnormal range of the voltage value with respect to the current value with the value set in.

(2) The voltage change amount calculation unit 26 calculates the measured values of the voltage value between the furnace bottom electrode and the furnace bottom shell separated by the insulator and the current value flowing from the furnace bottom electrode to the grounding resistor. Then, the current change amount calculation unit 25 and the voltage characteristic calculation unit 27 perform calculation to obtain the voltage characteristic with respect to the current value. Fig. 4 shows the voltage characteristics with respect to the current value obtained when the insulation resistance of the insulator decreases.
As shown by the dotted line in (1), the characteristic is located between a normal straight line and an upper limit straight line set as an abnormal value.

(3) The voltage characteristic with respect to the current value obtained when the insulation resistance of the insulator is further reduced is a characteristic that falls within the abnormal range shown by the diagonal lines in FIG. In the decision circuit 28,
The abnormal range of the voltage value for the current value set by the alarm setter 29 is compared with the voltage measurement value for the current value obtained by calculating the measurement value, and the voltage measurement value for the same current value It judges that the abnormality has entered the abnormal range, detects the abnormality, outputs an abnormality signal to the outside, and automatically shuts off the operation of the DC arc furnace.

As described above, when an abnormality in the insulation resistance is detected, an abnormality signal is output to the outside to automatically shut off the operation of the DC arc furnace, thereby preventing damage to the furnace shell part due to sparks. It becomes possible to prevent it.

FIG. 2 shows a case where a plurality of (two in FIG. 2) annular insulators 7 are arranged on the circumference of the furnace bottom electrode 6 shown in FIG. It is a partially expanded view which shows a 2nd Example. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted. The voltage detector 24-1 shown in FIG.
And 24-2 by storing the current-voltage characteristics from the respective voltage values and the current value flowing in the grounding resistor 22, two current-voltage characteristics are stored, and the voltage characteristics for each current value are described in (1) to When an abnormality in insulation resistance is detected as in (3), an abnormality signal is output to the outside, and the operation of the DC arc furnace is automatically shut off to prevent damage to the furnace shell part due to sparks. Is possible. By providing and partitioning a plurality of insulators, even if the insulation at one place is destroyed, the remaining insulators ensure the insulation, so that the life is extended.

FIG. 3 shows another embodiment of the present invention and is a partially enlarged view of the third embodiment of the present invention. Two detection conductors 19-1 and 19-2 are arranged on the circumference so as to surround the furnace bottom electrode 6 on the insulator 7 which is arranged on the circumference so as to surround the furnace bottom electrode 6. Bottom electrode 6, detection conductors 19-1 and 1
9-2 and the voltage between the conductors connected to the furnace body iron shell 3 from the respective voltage values and the current value flowing through the grounding resistor 22 via the voltage detectors 24-1, 24-2, 24-3. By calculating the voltage characteristic with respect to the current value, when an abnormality in the insulation resistance is detected as in the above (1) to (3) with respect to the voltage characteristic with respect to each current value, an abnormality signal is output to the outside and the DC arc furnace By automatically shutting down the operation, it is possible to prevent damage to the furnace shell part due to sparks. By providing the detection conductors 19-1 and 19-2, the state of impurities such as lead accumulated on the hearth can be known before the actual insulation is destroyed.

Regarding the safety of the apparatus, since it is connected to the measuring section via the voltage detectors 24 to 24-3 and the current detector 23, it is easy to secure the insulation, and the measuring equipment is damaged by the spark current. It is possible to construct an extremely safe device without the danger of.

[0022]

As described above, according to the present invention, the influence of the voltage fluctuation at the measurement site due to the fluctuation of the arc during energization is eliminated to prevent the spark accident due to the impurities such as lead in the furnace bottom electrode portion. In addition, it is possible to minimize damage to the iron shell of the furnace body, improve the operating efficiency of the DC arc furnace and improve the durability of the DC arc furnace, prevent damage to the equipment due to abnormalities, and inexpensive equipment Can be configured. The effect is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an overall configuration according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG. 1 and is a schematic block diagram showing a second embodiment of the present invention when a plurality of insulators are arranged on the circumference of the furnace bottom electrode.

FIG. 3 is a partially enlarged view of FIG. 1 showing a third embodiment of the present invention, which is a schematic block diagram showing an example in which a conductor for detection is arranged on an insulating plate arranged on the circumference of a furnace bottom electrode. It is a figure.

FIG. 4 is a characteristic diagram of voltage with respect to current value according to the present invention.

[Explanation of symbols]

 1 DC arc furnace 2 Hearth 3 Furnace shell 4 Furnace wall 5 Furnace lid 6 Furnace bottom electrode 7 Insulator 8 Upper electrode 9 Reactor 10 Thyristor converter 11, 12 Feed conductor 13 Arc 14 Molten metal 15 Normal operation Current flow 16 Current flow during abnormal operation 17 Conductor 18 Insulation monitoring device 19 Detection conductor 20, 21 Grounding conductor 22 Grounding resistor 23 Current detector 24-24-3 Voltage detector 25 Current change amount calculator 26 Voltage change amount calculation unit 27 Voltage characteristic calculation unit 28 Judgment circuit 29 Alarm setting device

Claims (1)

[Claims] The voltage generated between the bottom electrode of a DC arc furnace and one or more conductors isolated by an insulator or the bottom iron shell is measured via a voltage detector, and from the bottom electrode to a grounding resistor. The flowing current is measured through a current detector, each measured value is calculated to obtain the voltage characteristic with respect to the current value, and the voltage characteristic when the insulation resistance is normal is stored in advance. Set the abnormal range of the voltage characteristic for the characteristic, compare the voltage characteristic of the measured value with the voltage characteristic for the same current value of the abnormal set value, judge that the measured value is in the abnormal range, and detect the abnormality. A method for monitoring insulation of a DC arc furnace, which is characterized by outputting.