JPH01232693A - Automatic adjustment of height of electrode in arc furnace - Google Patents

Abstract

PURPOSE:To secure a proper height of an electrode without receiving effects of current control by a thyrister of a power source to prevent reduction of productivity by providing separate control systems for control of arc current and adjustment of the height of the electrode. CONSTITUTION:A source AC voltage-reduced at a transformer Tr is changed into DC at a thyrister THY to go through a DC reactor DCL, while an arc current between electrodes E1 and E2 is controlled to be constant. In the meanwhile, a voltage between the furnace bottom of an electric furnace F and the upper electrode E2 goes through a voltage converter VT to be compared with a set voltage at a voltage setter VR, and a motor control device D for a drive motor M for the electrode E2 is controlled to eliminate the deviation to zero at an adjuster C. The height of the electrode between the electrode and the furnace bottom is kept proper by this voltage control separately from control of an arc current, so incompliance of molten pool to component specifications, damage to the lining of furnace walls, reduction of an electric power consumption rate, and other reduction of productivity caused by an excessive temperature rise can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for automatically adjusting the electrode height of an arc furnace for controlling arc current in an arc furnace for smelting.

[Prior Art] When melting ferroalloys such as ferromanganese and ferrochrome, a three-phase L-furnace is usually used, and the arc is controlled by constant current control or constant impedance control by adjusting the height of the electrodes. It controls the current. On the other hand, when refractory substances are produced, for example in the case of smelting ferroboron, a DC arc furnace with a bottom electrode is used. The furnace is heat intensive, which avoids the accumulation of refractory materials on the bottom of the furnace and improves product yield.

[Problems to be Solved by the Invention] However, the DC arc furnace uses a thyristor as a power source and controls the current by controlling the firing angle. On the other hand, when automatic electrode height adjustment is performed by arc current control,
Thyristor control takes priority over electrode height control, so if the arc current is constant near the thyristor control set value, electrode height control will no longer function and the electrode height will stop at that position. In a DC arc furnace, it is important to control the current and ensure an appropriate height of the electrode.

For example, if the current suddenly increases due to the unloading of raw materials or the molten metal level rises as the smelting reaction progresses, only the constant current control function will work and if the electrode stops as described above, all the power consumed will be It will be consumed only for heating and smelting will not progress. As a result, there is a significant drop in productivity, such as a drop in power consumption, an excessive rise in temperature that causes the molten metal to fall outside of specifications, and damage to the furnace wall lining.

The present invention was made to solve such problems,
The present invention aims to provide an automatic electrode adjustment method for an arc furnace that ensures normal arc current control function and electrode height control function of a DC arc furnace and improves productivity.

[Means and effects for solving the yA problem] The method for automatically adjusting the electrode height of an arc furnace according to the present invention provides a method for automatically adjusting the height of an electrode in an arc furnace in which a constant current control is performed using a thyristor. The height of 1 & is adjusted by voltage control that keeps the voltage constant.

With this method, the control of the arc current and the adjustment of the electrode height become independent control systems, and are not affected by the current control by the thyristor of the power supply, so that the appropriate height of the electrode is always ensured.

[Examples] Examples of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a circuit diagram according to the present invention.

First, to explain the power supply, the power supply is a 3-phase 330
The power is received at 0V, passes through the circuit breaker CB, AC, and Tuttle ACL, enters the transformer Tr, where the voltage is stepped down from 3300V to 90V, and is rectified by the thyristor THY to become DC. This DC passes through the DC reactor DCL, from the bottom electrode E1 which is the anode, through the electric furnace F, becomes an arc current, reaches the upper electrode E2, and returns to the transformer Tr.

This current is controlled to be constant by the thyristor THY.

Next, the height control of the Earth Dragon iE2 will be explained.

The voltage between the bottom of the electric furnace F and the top tiE2 is determined by the voltage converter VT.
The voltage is compared with the voltage set by the voltage setting device VR,
The regulator C inputs the deviation to the motor control device of the drive motor M of the electrode E2. The motor control device controls the current from the motor drive power source to drive the upper electrode E2 so that the deviation becomes zero. The upper electrode E2 is driven by the winch WT winding up or down the wire W by driving the motor ML:y).

Thus, the arc current is controlled by thyristor control, while the electrode height is controlled to an appropriate position by voltage control that keeps the voltage between the electrode and the furnace bottom constant.

[Effects of the invention] The control of the core current and the adjustment of the electrode height are independent control systems, and are not affected by the current control by the thyristor of the power supply, so the appropriate height of the electrode is always ensured.
A decline in productivity is prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram according to the present invention. CB...Breaker CB, ACL...AC reactor,
Tr...Transformer Tr, THY...Thyristor, D
CL... DC reactor, El... Hearth bottom electrode, E2
...Upper electrode, F...Electric furnace, VT...Voltage converter, VR...Voltage setter, C...Adjuster, D...Motor control device,

Claims (1)

[Claims] An electrode for an arc furnace in which the height of the electrode is adjusted by voltage control that keeps the voltage between the electrode and the bottom of the arc furnace constant, in a direct current arc furnace for smelting in which constant current control is performed using a thyristor. Automatic height adjustment method.