JP3045262B2 - Current control circuit for DC arc furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control circuit for a DC arc furnace, and more particularly to a current control circuit for a rectifier used in a DC arc furnace.

[0002]

2. Description of the Related Art Generally, a rectifier connected to each of a plurality of bottom electrodes of a DC arc furnace can set a current flowing through each bottom electrode to an individual current set value, but each has a current control circuit independently. However, the total energizing current of all the bottom electrodes is not controlled.

[0003]

In such a conventional current control circuit, if a high-resistance material such as slag or a nonconductor covers the furnace bottom electrode, the current flowing through the furnace bottom electrode becomes larger than a set value. As a result, the total energizing current of all the furnace bottom electrodes decreases, and there is a problem that the melting efficiency decreases.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a DC arc furnace which controls a current supplied to a rectifier connected to each of a plurality of bottom electrodes to an individual current set value. In the control circuit, when a current drop is detected between the current measured value of any one of the rectifiers and the current set value, the set current value and the current measured value of the rectifier in which the current drop is detected DC arc having a circuit for controlling the difference between the current drop and the set current value of a rectifier other than the rectifier in which the current drop is detected and controlling the total current flowing through the plurality of bottom electrodes to be constant. A furnace current control circuit is provided.

[0005]

According to the present invention, when the current flowing through the furnace bottom electrode falls below a set value due to the fact that a high resistance material such as slag or a non-conductor covers the furnace bottom electrode, a decrease in current is detected. In order to control so that the difference between the set current value of the rectifier and the measured current value is added to the set current value of the rectifier other than the rectifier for which the current drop is detected, the total current supplied to all the bottom electrodes is constant. Can be kept.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In FIG. 1, 1a, 1b, 1c..., Furnace bottom electrodes 2a, 2b, 2c. Apparatuses 3a, 3b, 3c Current set values 4a, 4b, 4c DC current detectors 5a, 5b, 5c Limiter circuits 6a, 6b, 6c Comparator 7a, 7b, 7c... Phase control circuit 8a, 8b, 8c... Current drop detecting circuit 9a, 9b, 9c... Operating contacts of current drop detecting circuit 10a, 10b, 10c Dividers 11a, 11b, 11c Sound rectifier calculation circuits 12a, 12b, 12c Adders 13a, 13b, 13c DC reactors 14a, 14b, 14c Transformers 15a, 15b, 15c ... a circuit breaker.

In such a configuration, the currents flowing through the rectifiers 2a, 2b, 2c connected to the furnace bottom electrodes 1a, 1b, 1c are usually set by current setting units 3a, 3a.
b, 3c, the current setting units 3a, 3b, 3
c and the DC current detectors 4a, 4a
b and 4c are different from the current detection values by the comparators 6a and 6b
6c, and the phase control circuit 7a,
By controlling the firing angles of the rectifiers 2a, 2b and 2c, the rectifiers 7b and 7c are controlled to keep the set energizing current constant.

Here, for example, when the current detection value of the DC current detector 4a falls below the threshold value set by the current drop detection circuit 8a, the operating contact 9a of the current drop detection circuit
Is closed, whereby the deviation between the current set value of the current setter 3a detected by the comparator 6a and the current detected value of the DC current detector 4a is calculated by the sound rectification calculation circuit 11 by the divider 10a. The correction amount divided by 2 is the adder 12
The currents b and 12c are added to the set values of the rectifiers 2b and 2c, and are controlled so that the set energizing current is kept constant. The same applies to the case where the current drop detection circuits 8b and 8c operate independently, and the case where two of the current drop detection circuits 8a, 8b and 8c operate simultaneously.

[0009]

As described above, according to the present invention, the current flowing through the furnace bottom electrode can be set to a predetermined value by covering the furnace bottom electrode with a simple circuit having a high resistance such as slag or a non-conductor covering the furnace bottom electrode. Even if the current drops, the insufficient current of the rectifier other than the rectifier for which the current drop was detected can be distributed to keep the total current flowing through all the bottom electrodes constant, so that the total current flowing through all the bottom electrodes can be kept constant. Does not decrease, and the efficiency of dissolution can be maintained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1a, 1b, 1c Furnace bottom electrode 2a, 2b, 2c Rectifier 3a, 3b, 3c Current set value 4a, 4b, 4c DC current detector 5a, 5b, 5c Limiter circuit 6a, 6b, 6c Comparator 7a, 7b, 7c Phase control circuit 8a, 8b, 8c Current drop detection circuit 9a, 9b, 9c Operating contact of current drop detection circuit 10a, 10b, 10c Divider 11a, 11b, 11c Sound rectifier calculation circuit 12a, 12b, 12c Adder 13a , 13b, 13c DC reactor 14a, 14b, 14c Transformer 15a, 15b, 15c Circuit breaker

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-312183 (JP, A) JP-A-2-302581 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 7/148 F27D 19/00

Claims (1)

(57) [Claims] 1. A current control circuit for a DC arc furnace for controlling a current supplied to a rectifier connected to each of a plurality of bottom electrodes to an individual current set value, wherein a current of any one of the rectifiers is controlled. When a current drop is detected between the measured value and the current set value, the difference between the set current value of the rectifier in which the current drop is detected and the current measured value is set in a rectifier other than the rectifier in which the current drop is detected. A current control circuit for a DC arc furnace, comprising: a circuit that distributes and adds current values to control the total current flowing through the plurality of furnace bottoms to be constant.