JPH06283264A - Steel mill arc furnace device - Google Patents

Abstract

PURPOSE:To increase safety and reliability of operation by providing a variable voltage and variable frequency inverter control device to reduce the generation of a voltage flicker and at the sane time to supply the three-phase alternating current of the most suitable frequency for the inside state of a furnace. CONSTITUTION:A variable voltage and variable frequency (VVVF) control device 8 selectively controls the frequency of a three-phase alternating current to be supplied to a three-phase alternating current arc furnace (AC furnace) so as to be the most suitable frequency in accordance with the inside state of the furnace at the initial melting period of a material, the main melting period, the final melting period, the refining period and the like. Thereby, the operation of high efficiency of the AC furnace 1 can be achieved. Also, in the case where a fluctuating current to exceed the set-up current of the AC furnace 1 is generated due to the irregular approach and contiguity between a melted and refined material and a three-phase graphite electrode 2, an electrode control device 7 controls a current and at the same time the VVVF inverter control device 7 instantaneously controls a voltage supplied to the arc furnace to control the current of the AC furnace to a set-up value, thereby reducing the generation of a voltage flicker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc furnace apparatus for steelmaking.

[0002]

2. Description of the Related Art A conventional steelmaking arc furnace apparatus is provided with a three-phase AC arc furnace (hereinafter referred to as an AC furnace), and a current supplied to the three-phase AC arc furnace is controlled by an electrode controller. There is something. Further, there are those equipped with a direct current type arc furnace (hereinafter referred to as a DC furnace). In this case, due to the breakthrough of the power thyristor, the furnace lead electrode of the arc furnace for steelmaking is used as the cathode ((-) electrode), and The bottom electrode is the anode ((+)
A DC furnace which has been made into a pole has been put into practical use in recent years.

[0003]

In a steelmaking arc furnace apparatus provided with a conventional three-phase AC arc furnace (hereinafter referred to as an AC furnace), fluctuations in arc current due to irregular changes in melting and refining raw materials are caused by an electrode controller. In the melting period, short-circuit flow-through occurs between the electrodes for the furnace, the reactive power (Mvar) fluctuation is large, and it depends on the power supply capacity, but voltage flicker occurs. This greatly limits the power supply capacity of the arc furnace, which is one of the major obstacles to the ultra-high power (UHP) large arc furnace replacement business. Therefore, as a countermeasure against this, a large amount of capital investment is made in the flicker suppressing facility.

Further, in the steelmaking arc furnace apparatus provided with the conventional AC furnace, it is necessary to keep the reactance on the upper furnace side in order to keep the arc stable during the melting period because of the basic characteristics of the arc. Is optimal between 30 and 60Hz (depending on the capacity of the furnace and the capacity of the transformer for the furnace). On the other hand, the arc between the furnace electrode (artificial graphite) and the molten steel is stable and stable during the main melting period, the final melting period, and the refining period when molten steel is formed in the hearth. (It depends on the transformer capacity) is optimal for the arc / energy thermal efficiency. However, the power supply frequency is limited to 50Hz or 60Hz depending on the region, and it is impossible to adjust the optimum frequency for the situation inside the reactor. Even if the frequency can be adjusted by private power generation, etc., it has not been put to practical use due to lack of quick response.

On the other hand, in the conventional steelmaking arc furnace apparatus equipped with DC, the arc current is controlled at a high speed by the adjustment control of the arc current and voltage by the SCR, resulting in a reactive power fluctuation (ΔQm [Mvar]). The voltage flicker value can also be suppressed to about 50% of that of the AC furnace because it can be limited to about 50% of that of the AC furnace. Therefore, the DC reactor is rapidly becoming popular for new installation of a large ultra high power (UHP) reactor in an area where the capacity of the power receiving system is relatively small. However, in the steelmaking arc furnace device equipped with this DC furnace, because the anode electrode is installed on the furnace bottom, this furnace bottom electrode is the greatest obstacle to safety, reliability, life, and maintenance of operation. The solution is the biggest issue.

In view of the above problems, the present invention requires less generation of voltage flicker, can supply a three-phase alternating current having a frequency most suitable for the in-furnace conditions, has good operational safety and reliability, and has a long service life. It is also designed to be excellent in maintenance management.

[0007]

[Means for Solving the Problems] The technical means of the present invention for solving this technical problem is a three-phase AC arc furnace 1 and an electrode control device for controlling the supply current to the outer three-phase AC arc furnace 1.
In the arc furnace for steelmaking equipped with 7 and 7, select the frequency of the three-phase AC to be supplied to the three-phase AC arc furnace 1 according to the furnace conditions such as raw material melting stage, main melting period, final melting period, refining period, etc. In addition to controlling, the supply voltage to the three-phase AC arc furnace 1 is selectively controlled, and when the current to the three-phase AC arc furnace 1 exceeds the set current, the three-phase AC current is controlled simultaneously with the current control by the electrode control device 7. The point is that a variable voltage variable frequency inverter controller 8 for instantaneously controlling the arc furnace supply voltage to suppress the current to the arc furnace 1 is provided.

[0008]

[Operation] The variable voltage variable frequency inverter control device 8
Depending on the furnace conditions of the raw material melting stage, main melting period, melting end period, and refining period, the frequency of the three-phase AC supplied to the three-phase AC arc furnace 1 is selectively controlled to be the optimum frequency.
The supply voltage to the three-phase AC arc furnace 1 is selectively controlled to be the optimum voltage. As a result, highly efficient operation of the three-phase AC arc furnace 1 is achieved. In addition, the three-phase AC arc furnace may be formed by irregular approach or contact between the melting and refining raw material and the three-phase graphite electrode 2.
If a fluctuating current exceeding the set current of 1 occurs, the electrode control device 7 performs current control, and at the same time, the variable voltage variable frequency inverter control device 7 instantaneously controls the arc furnace supply voltage to The current of AC arc furnace 1 is suppressed to the set value. Thereby, the fluctuation of the reactive power (Mvar) is limited to the minimum, and the voltage flicker value is reduced to 50% or less of the voltage flicker value generated in the three-phase AC arc furnace of the conventional steelmaking arc furnace apparatus.

Regarding a large VHP furnace, a steelmaking arc furnace device of the present invention, a conventional steelmaking arc furnace device using a normal three-phase AC arc furnace (conventional example 1), and a conventional DC furnace. Table 1 shows a comparison of the basic characteristics with the steelmaking arc furnace device (conventional example 2).

[0010]

[Table 1]

The following are the clear points in the quantitative comparison of the basic characteristics between the present invention and the conventional example shown in Table 1. (1) The operating impedance is as low as about 60% of that of an ordinary AC furnace,
Therefore, it is possible to apply to a larger UHP furnace as a measure for insulation on the furnace side. (2) The arc input (Pa [Mw]) is larger than that of the AC furnace and the DC furnace, and the input in the furnace is the maximum at the same power source capacity, which is excellent in productivity.

(3) The amount of splash due to arc and jet is the lowest, which is the most advantageous in terms of steelmaking yield. (4) The stirring index (F) of the steel bath by arc plasma is more than twice that of the AC furnace, which is almost comparable to that of the DC furnace. This means uniform rapid dissolution and good refining property.

(5) The point that the arc voltage is the lowest means that the UHP arc in the flat bath can be easily covered with slag and the maximum electric power can be supplied during the refining period, and it is extremely effective in the refining furnace. (6) The flicker level is equivalent to that of the DC furnace and about half that of the AC furnace. In Table 1, the operating impedance is the impedance of the entire arc furnace apparatus including the reactor transformer when actually operating.

[0014]

EXAMPLE The present invention will be described below with reference to the illustrated example. In FIG. 1, 1 is a three-phase AC arc furnace and 2 is its three-phase graphite electrode. 3 is the power switch, 4 is the circuit breaker,
5 is a transformer for the furnace, 6 is a current transformer, and 7 is an electrode control device, for example, when a fluctuating current exceeding the set current is generated due to irregular approach or contact between the melting and refining raw material and the three-phase graphite electrode 2. In addition, the current to the three-phase AC arc furnace 1 is controlled.

Reference numeral 8 is a variable voltage variable frequency (VVVF) inverter control device, which is a three-phase AC depending on the internal conditions of the three-phase AC arc furnace 1, that is, the initial melting stage of the raw material, the main melting stage, the final melting stage, the refining stage, etc. The three-phase alternating current supplied to the arc furnace 1 is selectively controlled so that it has an optimum frequency, and the supply voltage to the three-phase alternating current arc furnace 1 is also selectively controlled to the optimum voltage according to the above-mentioned in-furnace conditions. It is designed to achieve high-efficiency operation of the phase AC arc furnace 1. Further, when a fluctuating current exceeding the set current of the three-phase AC arc furnace 1 is generated due to irregular approach or contact between the smelting and refining raw material and the three-phase graphite electrode 2, the current is controlled by the electrode control device 7 at the same time. The arc furnace supply voltage is instantaneously controlled in order to suppress the current to the three-phase AC arc furnace 1 to the set current value.

The arc furnace apparatus of the present invention can of course be applied to an arc furnace apparatus having a three-phase AC arc heating furnace refining furnace.

[0017]

According to the present invention, the AC according to the situation in the furnace
Optimum frequency control of the arc furnace is possible, maximum efficiency of the arc heat source is obtained, productivity (ton / hr person) is dramatically improved, and operating cost can be minimized. In addition, the inverter control enables voltage control that responds quickly to the load disturbance of the arc furnace, and the voltage flicker value, which is the biggest problem of the UHP large-scale AC furnace, can be reduced to about 50% of that of a normal AC furnace like a DC furnace.

Further, the bottom electrode, which is the maximum neck of the DC furnace, is unnecessary because it is a three-phase AC furnace, and the fundamental problems in operation and maintenance are solved. Furthermore, the low power factor operation and the generation of harmonics due to the characteristics of the DC furnace in terms of SCR control are also caused by the AC furnace V
It is solved by VVF inverter power supply control. The DC furnace has a limitation on the large capacity due to the basic characteristics of the power supply and the arc, but the arc furnace apparatus of the present invention has no capacity limitation, and can be applied to a continuous charging arc furnace which is expected to develop in the future due to the basic characteristics of the arc. The suitability is also sufficient and it has the basic characteristics of the optimum melting and refining furnace.

[Brief description of drawings]

FIG. 1 is a single line system diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 Three-phase AC arc furnace 7 Electrode controller 8 Variable voltage variable frequency inverter

[Procedure amendment]

[Submission date] April 21, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

[0003]

In a steelmaking arc furnace apparatus provided with a conventional three-phase AC arc furnace (hereinafter referred to as an AC furnace), fluctuations in arc current due to irregular changes in melting and refining raw materials are caused by an electrode controller. slow time response, particularly in soluble phase, occurs a short circuit circulating between the furnace electrodes, large reactive power (Mvar) variation, is also dependent on power supply integration capacitance, the voltage flicker occurs , The power supply capacity of the arc furnace is greatly limited, which is one of the major obstacles for the ultra high power (UHP) large arc furnace replacement business. Therefore, as a countermeasure against this, a large amount of capital investment is made in the flicker suppressing facility.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

[Operation] The variable voltage variable frequency inverter control device 8
Raw material Initial mainly lytic phase, dissolving the end, depending on furnace condition of refining Quito, with selectively controlled to be optimum frequency the frequency of the three-phase alternating current supplied to the three-phase AC arc furnace 1,
The supply voltage to the three-phase AC arc furnace 1 is selectively controlled to be the optimum voltage. As a result, highly efficient operation of the three-phase AC arc furnace 1 is achieved. In addition, the three-phase AC arc furnace may be formed by irregular approach or contact between the melting and refining raw material and the three-phase graphite electrode 2.
If a fluctuating current exceeding the set current of 1 occurs, the electrode control device 7 performs current control, and at the same time, the variable voltage variable frequency inverter control device 7 instantaneously controls the arc furnace supply voltage to The current of AC arc furnace 1 is suppressed to the set value. Thereby, the fluctuation of the reactive power (Mvar) is limited to the minimum, and the voltage flicker value is reduced to 50% or less of the voltage flicker value generated in the three-phase AC arc furnace of the conventional steelmaking arc furnace apparatus.

Claims (1)

[Claims] 1. A steelmaking arc furnace apparatus comprising a three-phase AC arc furnace 1 and an electrode control device 7 for controlling a current supplied to the three-phase AC arc furnace 1, wherein a raw material melting stage and a main melting stage are set. The frequency of the three-phase AC supplied to the three-phase AC arc furnace 1 is selectively controlled according to the internal conditions of the melting stage, the refining period, etc., and the supply voltage to the three-phase AC arc furnace 1 is selectively controlled, and When the current to the three-phase AC arc furnace 1 exceeds a set current, the current is controlled by the electrode control device 7 and at the same time, the arc furnace supply voltage is instantaneously controlled to suppress the current to the three-phase AC arc furnace 1. An arc furnace apparatus for steelmaking, which is provided with a voltage variable frequency inverter controller 8.