JPH02213084A - Dc arc furnace - Google Patents

Abstract

PURPOSE:To enable the quick and easy restriking of arc without any contact between an electrode and a fusion metal by maintaining the electrically live condition of an SCR rectifier with an activation circuit even if an arc is out. CONSTITUTION:A switching control device 10 compares the current set value of a built-in setting unit with output from a current detector 9. In addition, when arc current is equal to or above a set value, the device 10 opens a contact 8 and closes the contact 8 when the current is less than the set value. An arc current control device 11 makes the phase control of an SCR rectifier 5 and controls the arc current. As the contact 8 is kept closed with the arc current equal to or below the predetermined value even when the arc is out, current flows continuously to the SCR rectifier 5 via an activation circuit 6, and voltage is kept applied between an electrode 2 and a furnace bottom electrode 4. Consequently, it becomes possible to restrike the arc without any contact of the electrode 2 with a fusion metal. When the current detector o detects current exceeding the predetermined value due to an increase in arc current, the device 10 opens the contact 8 and only the arc current flows to the rectifier 5.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a DC arc furnace.

[Conventional technology]

Generally, in a DC arc furnace for steelmaking, the phase of the thyristor rectifier used to supply power to the electrodes is controlled to reduce the arc current to 1i.
At the same time, the electrodes are moved up and down to control the arc voltage, power is input to the furnace, and the scrap is melted and refined.

[Problems to be solved by the invention> However, in the above-mentioned conventional furnace, due to causes such as an excessive arc distance due to a shutdown or rapid burn-through of scrap, the arc disappears and the current flows through the thyristor rectifier. The ignition phase angle, such as no flow! No voltage can be applied between the electrodes even if the Therefore, in order to reignite it, it is necessary to bring the electrode (movable N pole) into contact with the WI steel, but if the graphite electrode comes into contact with the molten steel, even momentarily, there is a risk that carbon components may enter the molten steel. Because of this, I don't like it. Furthermore, it is troublesome to move the electrode up and down each time when igniting, which causes a decrease in the operating efficiency of the furnace.

This invention solves the above-mentioned conventional problems, and the electrode (
without contact between the movable electrode) and the molten metal.
It is an object of the present invention to provide a DC arc furnace that can quickly and easily relight the arc.

[Means to solve the problem]

In order to achieve the above object, the DC arc furnace of the present invention has a DC arc furnace in which an electrode is connected to the output side of a thyristor rectifier connected to an AC power source, and a current limiting resistor and a switching resistor are provided on the output side of the thyristor rectifier. A starting circuit is connected in series with the contacts of the i, connected in parallel to the electrode, and an N current detector for detecting the arc current;
l! The present invention is characterized by comprising an open IWINIO device which receives an output signal from a detector and opens the contact when the arc current is a predetermined value of 11 or more, and closes the contact when the arc current is below a predetermined value.

C) In the DC arc furnace of this invention, when the arc curves, i! When the arc tIi current value detected by the current detector becomes less than a predetermined value, the contact of the starting circuit closes and the thyristor regulator 2I
1 through the startup circuit to the l unit! The flow flows. By selecting the resistance value of the current limiting resistor in the starting circuit, excessive short-circuit current is prevented from flowing through the thyristor rectifier, and the phase I
Since it is possible to flow a current of a degree (for example, several A) through the Sirisk rectifier that allows control of the current, a voltage is subsequently applied between the electrodes, and the electrode (movable electrode) is brought into contact with the molten metal simply by approaching it. The arc can be re-ignited without any trouble. When the arc current increases to a predetermined value or more due to re-ignition, the WU open/close s is activated by the output of the current detector.
The m device opens the contacts of the starting circuit to prevent heat loss from the current limiting resistor during normal operation.

(Example) An embodiment of the present invention will be explained below with reference to FIG.

In the figure, 1 is a furnace transformer connected to an AC power source, and 2 is an electrode (
3 is a furnace body, 4 is a furnace bottom electrode, and 5 is a thyristor rectifier for power supply to the electrode.

Further, reference numeral 6 denotes a starting circuit connected in parallel to the electrode 2 and the furnace bottom 111 and the pole 4, which consists of a current limiting resistor 7 and a normally closed switching contact 8 connected in series. , 9 is a current detector for detecting arc current. Reference numeral 10 denotes an opening/closing W1m device which compares the current setting value of a built-in setting device with the output signal of the current detector 9, and outputs an output when the arc current exceeds the setting value to drive the contact 8 to open. , when the arc flow m becomes less than the set value, the output becomes zero and the contact 8 is returned to the closed state.

Note that the setting value of the 7-hook N51 when the contact 8 is opened and closed may be the same current value or different it current values. Reference numeral 11 denotes an arc current control device, which has a known circuit for controlling the arc II current by setting the phase tiqmt of the silice rectifier B5. Note that the illustration of the lifting mechanism for the electrode 2 and the arc voltage MwJ device is omitted.

In the DC arc furnace 12 having the above configuration, even if the arc is extinguished during operation, the contact 8 is in a closed state as soon as the arc current falls below a predetermined value, so the thyristor rectifier B5 passes through the starting circuit 6. Current flows continuously and voltage remains applied between electrode 2 and furnace bottom electrode 4, so! The arc can be reignited without bringing the F electrode into contact with molten metal. When the output of the current detector 9 exceeds a predetermined value due to an increase in arc current, the opening/closing tUa device 10
opens the contact 8, only arc current flows through the thyristor rectifier 5, and the furnace is operated by normal arc heating.

The present invention is not limited to the embodiments described above; for example, a normally open contact may be used as the contact 8, and a switching device 110 that generates an output signal according to this contact type may be used. The present invention can also be applied to DC arc furnaces and heating devices for m-ray melting of various metals other than those for steel manufacturing.

(Effects of the Invention) As explained above, according to the present invention, even if the arc is extinguished, the thyristor rectifier is kept energized by the starting circuit, so that the thyristor rectifier can be quickly and easily operated without contacting the electrode with the molten metal. The arc can be re-ignited.

[Brief explanation of the drawing]

Figure 1 shows 8B of a DC arc furnace showing one embodiment of the present invention.
It is a connection diagram. 2... Electrode (movable electrode), 4... Hearth bottom electrode, 5...
・Thyristor rectifier, 6... Starting circuit, 7... Current limiting resistor, 8... Contact, 9... Current detector, 10...
Opening request device, 12...DC arc furnace.

Claims (1)

[Claims] 1. In a DC arc furnace in which an electrode is connected to the output side of a thyristor rectifier connected to an AC power source, a starting circuit consisting of a current limiting resistor and a switching contact connected in series on the output side of the thyristor rectifier, a current detector that is connected in parallel to the electrode and detects the arc current; and upon receiving an output signal of the current detector, the contact is opened when the arc current is above a predetermined value, and the contact is opened when the arc current is below the predetermined value. A direct current arc furnace characterized by comprising an opening/closing control device that closes a contact.