JPH01206417A - Method for controlling flicker suppression - Google Patents

Abstract

PURPOSE:To operate a self-exciting type converter only when required and to attain effective flicker suppression and high economy by adding a standby signal generation device. CONSTITUTION:The voltage fluctuation of a system, a flicker which occurs by an arc furnace, an operation elapse time, a charged power quantity, data on an invalid power change rate, and a transformer tap voltage value for furnace are set as judgement elements which the exciting type converter requires or not in the middle of the operation of the arc furnace. The self-exciting type converter 5 automatically stops in one of following cases, which occur when voltage fluctuation is small, when the flicker is small, when the operation of the arc furnace is in a boiling period, and when the tap voltage of the transformer for furnace becomes small. When none of the cases is satisfied, the self-exciting type converter 5 resumes a flicker suppression action. For realizing said action, the standby signal generation device 10 is added.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for controlling a flicker suppression device for suppressing system voltage flicker caused by fluctuations in reactive power of an arc furnace load.

(Prior art) During operation, an arc furnace generates irregular and sudden reactive power,
This leaks into the power system, causing voltage flicker. In order to suppress voltage flicker, it has been conventionally considered to provide a device in parallel with the load to detect lagging reactive power of the load and supplying advanced reactive power to offset this. A reactive power compensator 1 using reactor phase control shown in FIG. 3 is commonly used. In this method, the current flowing through a reactor 3 connected in parallel with a capacitor 2 is controlled by firing a thyristor 4, and arbitrary reactive power is generated. Due to the principle that it can only be compensated once per year, only the fundamental reactive power component can be compensated. Further, since harmonics of various orders generated by the arc furnace cannot be sufficiently compensated for, the flicker suppression effect is not sufficient.

Therefore, by using the self-commutated converter 5, which enables the turn-off thyristor to be turned on and off at high speed by PWM control and to perform reactive power compensation with high responsiveness, the above-mentioned phase control reactor type reactive power compensator A very high flicker compensation effect can be produced by compensating for high-speed reactive power components that cannot be compensated for and arbitrary harmonics. However, self-commutated converters have the drawback that the switching frequency of the semiconductor elements constituting the device is high, resulting in large power losses during operation, making them uneconomical.

That is, although the phase control reactor reactive power compensator has a small power loss and is economical, it does not have a sufficient flicker suppressing effect. Although the unidirectional converter has a large loss and is uneconomical, it has a large flicker suppression effect.

Therefore, in order to effectively suppress voltage flicker and improve economic efficiency, it is necessary to use a phase-controlled reactor type reactive power compensator that has sufficient capacity for reactive power fluctuations in the load. A method is used to compensate for the main wave component and to absorb the remaining high-speed, fine reactive power components and harmonics by installing a self-commutated converter with a low capacity and low intrusion.

(Problems to be Solved by the Invention) As in the above-mentioned conventional technology, if the phase control rick 1-le type reactive power compensator and the self-commutated converter are operated in a jlfi series, both economical efficiency and flicker suppression effect can be achieved. can be satisfied to some extent. However, due to the principle of arc furnace load, reactive power fluctuations are large and rapid in the early stages of scrap melting, so it is necessary to operate a self-commutated converter, but once the scrap has been melted and the refining stage begins, reactive power fluctuations will occur. becomes small and it is no problem to stop the operation of the self-excited converter. Rather than operating a self-commutated converter with a large loss all the time, the overall economic efficiency can be improved by stopping it temporarily depending on the situation and suppressing flicker using only the economically advantageous phase control reactor type reactive power compensator. Further improvement.

The present invention aims to achieve effective flicker suppression and high economic efficiency at the same time, and provides a control method for a flicker suppression device for stopping or restarting a self-excited converter as necessary. be.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention changes several elements that determine whether to stop or operate the self-excited converter during operation of the arc furnace. This controls temporary stop and restart.

(Operation) It is assumed that the phase-controlled reactor type reactive power compensator is always turned on during operation of the arc furnace in the operation described in the above-mentioned conventional technique. The self-commutated converter also operates in the same way as described in the conventional technology, but the loss can be reduced by adding a new function to the start-up and stop sequences to issue a signal to pause and restart the flicker suppression operation. By minimizing the operation of self-excited conversion, which is highly uneconomical, it has the effect of further improving the economic efficiency of the flicker suppression device as a whole.

(Example) An example is shown in FIG.

Components having the same functions as those in FIG. 3 showing the prior art are given the same reference numerals, and their explanation will be omitted. In FIG. 1, 1 is a phase-controlled reactor type reactive power compensator, and 5 is a self-excited converter. 6 is a control circuit for the self-excited converter 5.

The present invention is a method of temporarily stopping the self-excited converter 5 when it is determined that it is unnecessary during operation of the arc furnace. What is important is whether The first determining factor is the voltage fluctuation of the grid. The voltage fluctuation is determined from the system current, and if this becomes sufficiently small, the self-excited converter 5
It is okay to stop. Second, flicker caused by the arc furnace can be calculated using a flicker meter and used as a determining factor. Third, when the operation of the arc furnace shifts from the initial melting stage to the refining stage, rapid fluctuations in reactive power subside, so it is confirmed that the refining stage has entered from the data of elapsed operation time, power input area, and rate of change in reactive power. If possible, the self-excited converter 5 may be stopped. Fourthly, the furnace transformer tap voltage value can be used as a determining factor. The common method of gravity adjustment in an arc furnace is to reduce the tap voltage of the furnace transformer as melting progresses, so the tap voltage corresponding to each melting period is roughly determined.

Therefore, in the present invention, the self-excited converter is automatically temporarily stopped when any of the following cases occurs. (When υ voltage fluctuation is small ■ When flicker is small (3) When the operation of the arc furnace enters the refining period 0) When the tap voltage of the furnace transformer ■ becomes small. Further, when any of the above cases is no longer satisfied, the self-excited converter restarts the flicker suppression operation.

In order to realize the following operations, a standby signal generating mechanism 10 as shown in FIG. 1 is added. Voltage fluctuations, flicker, the melting state in the furnace, and tap signals of the furnace transformer are input here, and soft start and soft stop signals to the control circuit of the self-commutated converter are output. This signal acts on the control circuit 6, and the stars 1 to .
Perform step 1. FIG. 2 illustrates the standby signal generation function 10 of FIG. 1 in more detail. IIA, II
B indicates the state of the manual deblocking switch for normal operation and stopping 6. Each judgment element 12A, 1211.12C, 120 respectively indicates a case where a temporary stop of the self-excited converter is requested II I I
I, otherwise it becomes II OII. Assume that one of the four judgments 1 (quasi) is 111 II.The output of the logical sum 13 is 111 II, and the output of the logical sum 14 is also always "1", so in this case, manual deblocking is required. Regardless of the state of the switch, the self-commutated converter soft-stops and ceases flicker suppression operation.

In addition, if the judgment elements 12A, 12B, 12C, and 12D all become '0'' while the manual deblock switch 5 is turned on, the output of the logical sum 14 becomes 110 II, canceling the soft stop, and further inverting the inverter 15. The output of the logical product 16 becomes 111 II from the output II I 11 of 11B and the output II I II of the state 11B, and the soft start is started, and the self-excited converter restarts the flicker suppression operation.

〔Effect of the invention〕

From the above, by adding a standby signal generation mechanism, we can temporarily stop the operation of the self-excited converter when it is unnecessary, and control it to restart when the number of crabs reaches 8 again. The flicker suppression device is highly economical because the 11 rotations (of the economical self-excited converter) are kept to the necessary minimum.

[Brief explanation of the drawing]

FIG. 1 shows a flicker suppression device and a standby device according to the present invention (1-1).
FIG. 2 is a diagram illustrating the operation of the standby signal generation mechanism, and FIG. 3 is a block diagram of a conventional flicker device. 1...'41 Controlled Reactor System Reactive Power Compensation'A
APi231. Capacitor; 3...Coil 4
...Thyristor 5...Self-excited converter 6...
・Control circuit 7...Arc furnace load transformer 8・
・Arc furnace 9...Power reactance 10・
...Standby signal generation mechanism 118, l]11 = 4-movement debris inch 7f
fi12A, 12I3. +2c, 120... Self-excited converter - time stop judgment element 13... OR 14... OR 15...
・Inverter 16... Logical product agent Patent attorney Ken Chika R7 Ken Daishimaru

Claims (1)

[Claims] A phase advancing capacitor and a reactor are connected in parallel, and the current flowing through the reactor is controlled by a thyristor.The reactive power compensator is operated in parallel with the first reactive power compensator, and the reactive power compensator is operated in parallel with the first reactive power compensator. In the second reactive power compensator consisting of a self-excited converter that compensates for residual reactive power and harmonic current generated by the load, there is a voltage tap value of the furnace transformer during operation of the arc furnace. automatically when one of the following occurs: the system voltage falls below a certain value, the measured flicker falls below a certain value, or the arc furnace enters the refining period. A method for controlling a flicker suppressing device, characterized by a function of stopping the second reactive power compensating device and then automatically restarting the second reactive power compensating device when any of the above conditions is no longer satisfied.