JPH02278317A - Flicker compensation device for dc arc furnace - Google Patents

Abstract

PURPOSE:To reduce a flicker generating quantity by predicting reactive power generated in a DC arc furnace with the use of a phase control angle controlling a DC converter and a DC current, controlling a thyristor based on the reactive power generation predicting quantity and generating the reactive power from a flicker compensation part when the DC converter is controlled. CONSTITUTION:In a phase-control angle control means for DC converter 33, the DC converter 23 is controlled by using the phase-control angle alpha obtained based on the deviation between a detection current from the DC detector 32 and a set current, and a constant current is controlled. At that time, a reactive power generating quantity prediction means 41 fetches the command signal of the phase-control angle alpha and the DC current Id and predicts the reactive power generating quantity of the DC arc furnace 25 by setting a non-load DC voltage E0 to be known. Then, a pulse generated from a pulse generator 42 is made variable based on the reactive power generating quantity predictive value, and the phase-control angle of the thyristor 44 is controlled. Thus, the reactive power can be compensated to the power system with the flicker compensation part 46 simultaneously with the control of the DC converter 23, and the flicker generating quantity can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a DC arc furnace that uses a DC arc to melt materials to be melted, such as iron scraps (hereinafter referred to as scrap), which are melting raw materials. This invention relates to an improvement of a flicker compensation device for a DC arc furnace that reduces the amount of flicker generated due to load fluctuations.

[Conventional technology]

In general, arc discharge involves passing a desired current through an electrode rod to generate an arc between the electrode rod and a metal object to melt the metal object. It is widely used for welding, scrap melting, etc. because it can easily create a high-temperature atmosphere, has high energy density, and can control arc current relatively easily.

By the way, conventionally, three-phase AC arc furnaces have been used for steelmaking to melt scrap, but after that, the demand for improved productivity due to the increase in scrap due to expanded consumption led to larger capacity for a while, and Many large three-phase AC arc furnaces are now in operation. Along with this, the power supply equipment has increased in capacity and has become larger than 500 KVA per furnace capacity. As a result, electric power disturbances caused by arc furnaces.

The so-called flicker disorder has become a major problem.

In other words, in an arc furnace that melts scrap,
An arc occurs between the graphite electrode rod and scrap or molten steel, but when the scrap collapses due to arc heat, the shape and position of the scrap change, and the arc generation position and arc generation direction change accordingly, causing the arc voltage and current fluctuate significantly. In addition, in an AC arc furnace, the current flowing to the electrode rod drops to zero every half cycle, so arc breaks and arc short circuits occur frequently in the furnace, making the arc extremely unstable from the power source's perspective. , or one of the five fluctuations is a large load. Such load fluctuations are
This causes fluctuations in the power supply voltage, which in turn causes fluctuations in the voltages of ordinary homes connected to the same power system, causing flickering in lighting equipment, for example.

As a result of repeated research on the causes of flicker in arc furnaces from various angles, it was announced that the range of fluctuations in reactive power generated by fluctuations in the arc is a major factor that determines the degree of flicker failure. (IEEJ Technical Report (Part 11) No. 72, 1978
(Published December 2016).

Therefore, based on the above research results, recent large arc furnace equipment is often equipped with a flicker compensator as shown in FIG. First, in the arc furnace equipment, AC power from the power system 1 is converted to a predetermined voltage by the furnace transformer 2, and then this power is supplied to the movable electrode 4 inserted into the AC arc furnace 3 to generate an arc. However, since the generation of this arc generates reactive power with a delayed phase, the AC arc furnace 3 and the power system 1
A flicker compensator 10 is provided.

This flicker compensator 10 uses a harmonic and power factor improving capacitor 11 to compensate the power system 1 in advance so that it has a predetermined leading phase, and also to compensate for fluctuations in reactive power width due to fluctuations in AC power. After the amount of reactive power generated in the AC power supply line of the AC arc furnace 3 is detected by the reactive power generation amount detection means 12, the phase control angle control means 13 further controls the phase i'171J according to the amount of reactive power generation. An angle command signal is obtained, and a pulse corresponding to the phase control angle command signal is outputted from the pulse generator 14, and a step-down transformer 15. Thyristor 16 and reactor load 1
The phase control angle of the thyristor 16 among the flicker compensation parts connected to the rear torque compensation section 7 is varied.
By controlling the current flowing through the flicker compensator 10, the reactive power generated on the flicker compensator 10 side is added to the power system 1, and the power system 1 is controlled to always have a constant reactive power level.

However, the reactive power generated by the AC arc furnace 3 is irregular, and it is difficult to predict it appropriately. Therefore, reactive power is detected from the AC power supply line and R;IJ
5 rnsec (half cycle)
A certain degree of control delay occurs, and not only is a sufficient compensation effect not obtained, but in some cases, flicker may be aggravated. Therefore, there is a limit to the compensation effect of the flicker compensation device 10 applied to the AC arc furnace 3. Further, the flicker compensator 10 not only does not contribute much to steel production, but also has the problem of requiring a large amount of equipment cost.

On the other hand, in recent years, advances in power electronics technology have increased the reliability of DC converters that convert alternating current to direct current, and at the same time, large-scale DC arc furnaces using such DC converters have been developed. That is, it has been demonstrated that this DC arc furnace greatly contributes to reducing various basic units and flicker generation amount compared to the AC arc furnace 3. This effect of reducing the amount of flicker generation is due to the fact that the arc current can be controlled to a constant value by the DC converter.

Incidentally, for DC arc furnaces and AC arc furnaces, as is clear from the general P (active power) - Q (reactive power) characteristics in Figure 4, the reactive power fluctuation range △Qd of DC arc furnaces is
It can be seen that c is approximately half of the reactive power fluctuation width ΔQac of the AC arc furnace. In the figure, A is P− of the DC arc furnace.
Q characteristic curve, B shows the P-Q characteristic curve of the AC arc furnace.

, where the reactive power Q of the DC arc furnace can be expressed by the following simple formula.

Q″EO-1d −5in a --(1) However, in the above equation, Eo is the no-load DC voltage, Id is the DC current during operation, and α is the phase control angle of the thyristor that constitutes the DC converter. , the no-load DC voltage E. is uniquely determined by the secondary voltage of the furnace transformer, and the DC current 1d is a constant value due to constant current control during operation, and the smoothing of the DC reactor The effect suppresses sudden changes.Therefore, the instantaneous reactive power is determined by the DC current 1d and the phase control angle α, of which the phase control angle α is a major factor.

On the other hand, in the AC arc furnace 3, the reactive power is 3・Id2・Xr
determined by Here, ■a is arc current, xr
is the furnace circuit reactance. As described above, the reactive power generation mechanisms are different between DC arc furnaces and AC arc furnaces. However, conventionally, the flicker compensator 10 for AC arc furnaces has been used as is for DC arc furnaces, and it has not been devised as a flicker compensator particularly suitable for DC arc furnaces.

[Problem to be solved by the invention]

Therefore, the above-mentioned DC arc furnace can reduce the fluctuation range of reactive power by half compared to AC arc furnaces, and this is due to the fact that the arc current is a constant current.

However, since the flicker generation level may still exceed the regulation value, the flicker compensator 10 becomes necessary.

However, in conventional DC arc furnace equipment, the flicker compensator 10 for AC arc furnaces is used as is in the DC arc furnace, so it takes 5 m to detect and control reactive power.
A delay of about 5 ec occurs, making it particularly difficult to appropriately deal with instantaneous fluctuations in reactive power, resulting in a problem that the compensation function cannot be fully demonstrated.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to appropriately control the reactive power of the power demand system without causing a control delay in response to fluctuations in the reactive power generated in the DC arc furnace, and therefore, the flicker compensation function can be appropriately controlled. The object of the present invention is to provide a flicker compensation device for a DC arc furnace that can be used in a DC arc furnace.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a flicker compensator in which a reactor load is connected via a thyristor to the power system that supplies electric power to a DC arc furnace, and on the other hand, the DC arc furnace A reactive power generation quantum Dj means is provided which predicts and calculates the reactive power generated by the DC arc furnace using the DC current flowing through the furnace and the phase control angle of the DC converter, and the reactive power generation amount prediction means predicts the reactive power generated by the DC arc furnace. By varying the phase control angle of the thyristor based on the reactive power generated in the flicker compensator, the reactive power generated in the flicker compensator is added to the power system.

In addition to the flicker compensation unit and the reactive power generation amount predicting means, another invention provides a combination of the reactive power predicted by Δp1 by the reactive power generation amount predicting means and the reactive power acquired from the AC power supply line on the DC arc furnace side. A deviation calculation means for calculating a deviation is provided, and by varying the phase control angle of the thyristor based on the deviation, reactive power generated in the flicker compensator is added to the power system.

[Effect]

Therefore, by taking the above measures, the present invention uses the phase control angle and the DC current of the DC arc furnace to control the phase control angle of the DC converter on the DC arc furnace side. Predict the amount of reactive power generated on the side,
Since the thyristor of the flicker compensation unit is controlled based on this predicted amount of reactive power generation, the flicker compensation unit can compensate for reactive power in the power system at the same time as controlling the DC converter.
The amount of flicker generated can be reduced.

Further, another invention predicts the amount of reactive power generated on the DC arc furnace side, and calculates the predicted value of the reactive power generation amount and the reactive power generated in the AC power line of the DC arc furnace as a result of control of the DC converter. Since the comparison is made and the phase control angle of the SIRISK is controlled according to the deviation, reactive power can be generated from the flicker compensator by appropriately understanding the state of reactive power in the power system, further reducing the amount of flicker generated. can be achieved.

C Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to FIG. Generally, when melting scrap using a DC arc furnace, AC voltage from the power system 21 is transferred to the furnace transformer 2.
After stepping down the voltage to a predetermined voltage in step 2, it is converted to direct current in a direct current converter 23 using Cyrisk, and then converted to direct current in a direct current reactor 24.
After being smoothed by the process, it is supplied to the arc furnace 25.

It is assumed that the control of raising and lowering the movable electrode 27 and the control of the arc current are performed using techniques similar to those of the prior art. That is, in the former electrode elevation control, scrap 26 is charged into the interior of the arc furnace 25, and after the DC voltage between the movable electrode 27 and the furnace bottom electrode 28 is detected by two voltage detectors during operation, this detected voltage is and the set voltage of the voltage setting device 30, and in response to the deviation, an elevation controller 31 controls the elevation of the movable electrode 27.

On the other hand, in the latter arc current control, after detecting the DC current (arc current) on the output side of the DC converter 23 with the current detector 32, this detected current is introduced into the DC converter phase control angle control means 33, Here, a command signal of phase control angle α is output according to the deviation between the detected current and a predetermined set current, and the phase control angle of the DC converter 23 is varied via the pulse generator 34, thereby controlling the arc current. is under control.

Next, the configuration of the flicker compensation device, which is the gist of the present invention, will be explained. This device has no-load DC voltage E. is known and the detected current 1d from the current detector 32 and the phase control angle α output from the phase control angle control means 33 are used to predict and calculate the reactive power due to arc fluctuation based on the above equation (1). 7Il11 means 41, a pulse generator 42 that outputs pulses according to the output of the reactive power generation amount predicting means 41, and a step-down transformer 43 connected to the same power system 21 as the DC arc furnace equipment. A thyristor 44, a reactor load 45, etc. are connected in series, and reactive power is obtained by controlling the phase control angle of the thyristor 44 based on pulses sent from the pulse generator 42 and varying the current flowing through the axle load 45. It is composed of a flicker compensator 46. This flicker compensation section 4
6 is also provided with a harmonic filter/power factor improving capacitor 47.

Next, we will explain the operation of the apparatus configured as described above, especially the operation of flicker compensation9.Generally, flicker occurs due to fluctuations in reactive power caused by the load of the DC arc furnace 25, as described above. It is the cause. The reactive power generated in this DC arc furnace 25 is the above (1
) can be approximately expressed by the equation. The no-load DC voltage Eo in equation (1) is uniquely determined by the secondary voltage of the furnace transformer 22, and the sudden change in the DC current 1d is suppressed to about I K A / m5ec by the DC reactor 24. Furthermore, since the phase control angle α is the phase control angle of the DC converter 23 of the DC arc furnace 25,
In this case, it is possible to predict the amount of reactive power generated from Id and α.

Therefore, in this device, the DC converter phase control angle control means 33 controls the DC converter 23 using the phase control angle α obtained based on the deviation between the detected current from the current detector 32 and the set current. Constant 7u current control is performed, and at this time, the reactive power generation amount predicting means 41 takes in the command signal of the phase angle control angle α and the DC current 1d, and the no-load DC voltage E is obtained. Assuming that dFj is known, the reactive power generation amount of the DC arc furnace is predetermined using the above equation (1). Then, by varying the pulses generated from the pulse generator 42 and controlling the phase control angle of the thyristor 44 based on this reactive power generation amount predicted value, the current flowing through the reactor load 45 changes and the flicker compensator 46 outputs the desired reactive power can be generated and added to the power system 21. That is, almost simultaneously with the control of the DC converter 23, the flicker compensator 46 generates a fluctuation in the reactive power generated in the DC arc furnace 25, and the power system 21
The reactive power can be controlled to a constant level, and flicker can be significantly reduced.

Next, FIG. 2 is a diagram showing another embodiment of the present invention. This device includes a reactive power generation quantum 7ip1 means 41, a reactive power generation amount detection means 51 for detecting the reactive power of the AC power supply line to the DC arc furnace 25, and a deviation between the predicted reactive power value and the detected reactive power. The phase control angle of the thyristor 44 is determined by varying the phase of the pulse generated from the pulse generator 42 according to the output of the deviation calculation means 52. This is a configuration that controls the

Therefore, according to the above configuration, the reactive power generation quantum ap+ means 41 makes the no-load DC voltage EO known and uses the detected current 1d from the current detector 32 and the phase control angle α to calculate (1) The reactive power generation amount is predicted and calculated using the formula, and then the deviation calculation means 52 calculates the reactive power generation quantum 7il.
Reactive power generation quantum A predicted by lj means 41
11l value and the amount of reactive power generated that appears in the AC power supply line after the phase control of the DC converter 23 is compared, and the pulse width of the pulse generated from the pulse generator 42 is changed according to the deviation, and the thyristor 44 is activated. Since the reactive power of the flicker compensator 46 is controlled and varied, the reactive power of the power system 21 can be controlled to be constant without causing a control delay, and fluctuations in reactive power due to the load of the DC arc furnace 25 can be effectively compensated for. I can do it.

Therefore, according to the configuration of the embodiment as described above, when controlling the phase control angle of the DC converter 23, the reactive power of the DC arc furnace is simultaneously predicted from the phase control angle and the DC current of the DC arc furnace. It is controlled by the phase control angle of the flicker compensation thyristor 46 based on this reactive power generation quantum n1 value or based on the deviation between the predicted value of reactive power generation amount and the reactive power that appears late in the AC power supply line of the DC arc furnace. Since the reactive power is controlled by controlling the reactive power, the reactive power of the power system 21 can be controlled at a constant level without causing a control delay, and the amount of flicker generated is significantly reduced compared to the conventional method while taking advantage of the characteristics of the DC arc furnace. can.

〔Effect of the invention〕

As explained above, according to the present invention, the following various effects can be achieved.

First, in claim 1, when controlling a DC converter, the reactive power generated in the DC arc furnace is predicted using the phase control angle and DC current that control the DC converter, and the reactive power generator Since the thyristor is controlled based on the amount of iDJ and reactive power is generated from the flicker compensation section, reactive power in the power system can be appropriately controlled without delaying control in response to fluctuations in reactive power generated in the DC arc furnace. The amount of flicker generated can be significantly reduced compared to the conventional method.

Further, in claim 2, the thyristor of the flicker compensator is controlled based on the deviation between the reactive power generation predicted value and the reactive power generation amount that appears in the AC power supply line with a delay after the control of the DC converter. It is possible to fully understand the reactive power on the supply side and accurately generate reactive power from the flicker compensator, and it is possible to more appropriately control the reactive power in the power system to a constant level, which greatly contributes to reducing the amount of flicker generation and improves the original Fig. 1 is a block diagram showing one embodiment of the flicker compensation device for a DC arc furnace according to the present invention, Fig. 2 is a block diagram showing another embodiment, Fig. 3 is a block diagram of a conventional device, and Fig. 4 The figure is a P-Q characteristic diagram of an AC arc furnace and a DC arc furnace.

21...Power system, 22...Furnace transformer, 23...
- DC converter, 25... Arc furnace, 32... Current detector, 33... Phase control angle control means for DC converter, 4
DESCRIPTION OF SYMBOLS 1... Reactive power generation amount prediction means, 44... Thyristor, 5... Thyrisk load, 6... Flicker compensation part,... Reactive power generation amount detection means, 2... Deviation l-value calculation means

Claims (2)

[Claims] (1) In a DC arc furnace equipment that converts AC power from a power system into DC power using a DC converter and supplies it to a movable electrode of a DC arc furnace to melt the material to be melted in the DC arc furnace, the power system predicting the reactive power generated in the DC arc furnace using a flicker compensator formed by connecting a reactor load to the DC arc furnace through a thyristor, a DC current flowing through the DC arc furnace, and a phase control angle that controls the DC converter. and a reactive power generation amount predicting means for calculating, based on the reactive power predicted value, the phase control angle of the thyristor of the flicker compensation section is controlled, and the reactive power generated in the flicker compensation section is added to the power system. A flicker compensator for a DC arc furnace, characterized in that: (2) In a DC arc furnace equipment that converts AC power from a power system into DC power using a DC converter and supplies the DC power to a DC arc furnace to melt the material to be melted in the DC arc furnace, a thyristor is installed in the power system. Reactive power generation that predicts and calculates reactive power generated in the DC arc furnace using a flicker compensator formed by connecting a reactor load through the DC arc furnace, an arc current flowing in the DC arc furnace, and a phase control angle of the DC converter. and a deviation calculating means for calculating a deviation between the reactive power predicted by the reactive power generation amount predicting means and the reactive power obtained from the AC power supply line on the DC arc furnace side, and based on this deviation. A flicker compensator for a DC arc furnace, characterized in that the phase control angle of a thyristor of the flicker compensator is controlled so that reactive power generated in the flicker compensator is added to the power system.