JPH0429294B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a reactive power compensator.

Voltage fluctuations occur in electrical systems connected to loads such as arc furnaces that generate irregularly fluctuating reactive power, which causes flicker. To avoid this, reactive power compensators (hereinafter referred to as compensation equipment) is installed.

FIG. 1 shows the configuration of a conventional compensation device of this type.
1 is an AC power supply, 2 is a power supply impedance, 3 is an electrical system, 4 is a load, and 5 is a furnace transformer. The compensation device (within the dashed line in the figure) 100 includes a transformer 11,
A lagging reactive power adjusting device 10 consisting of a thyristor circuit 13 formed by connecting a reactor 12 and a thyristor in antiparallel, and a phase advancing capacitor/filter device 2 consisting of a capacitor 21 and a reactor 22.
It is mainly composed of 0 and 0. In addition, 30, 40
are a fluctuation detection circuit and an ignition pulse generation circuit, respectively. Further, PT is provided to detect the power supply voltage, and CT is provided to detect the load current, and the respective detected voltages and currents are input to the fluctuation detection circuit 30.

Now, the conventional device configured as described above is
It has the characteristics shown in the figure. That is, load 4
When the reactive current I _QL of reactor 12 increases,
When the reactive current I _QL of load 4 _becomes smaller, the so-called reactor current I _Re flowing through the load 4 is reduced, and when the reactive current I
The thyristor circuit 13
As a result, fluctuations in reactive power in the electrical system 3 are reduced, and the occurrence of flicker is reduced.

Therefore, from the viewpoint of countermeasures against frizz, it is better to control the reactor current I _Re up and down around 50% of the rated value to compensate for the reactive power of load 4.
Conventionally, a 50% shift circuit and an automatic dead zone circuit have been installed because they are advantageous in terms of flicker reduction effect and effective use of equipment.

For example, a 50% shift circuit uses the reactor current
It detects I _Re and constantly performs feedback control with a certain time constant so that this current I _Re becomes 50% of the rated value. Therefore, regardless of the magnitude of the reactive current I _QL of load 4, the reactor current I _Re is
It exhibits a characteristic that compensates for the reactive power of the load 4 around 50% of the rating.

Further, the automatic dead band circuit is a circuit that provides a dead band according to the base amount so as not to be sensitive to the base portion (reactive power that does not fluctuate) of the reactive power of the load 4. As a result, the reactor current I _Re exhibits a characteristic that compensates for the reactive power of the load 4 around 50% of the rated value, as described above. Due to such characteristics, the average reactive power generated by the reactor 12 can be considered to be about 50% of the rated value.

By the way, the phase advancing capacity of the phase advancing power device 20 in FIG.
It is often selected to be equal to the lagging phase capacity of the reactor 12 at 0. Therefore, in this case, the leading phase capacitor/filter device 20 and the slow phase reactive power adjusting device 1
The average reactive power of the so-called compensation device 100 as a whole, including the reactive power generated by 0 and 0, is:
The phase leading reactive power is 50% of the rated capacity.

That is, although the compensator 100 is installed to prevent flicker, it can also be used to improve the power factor.

Now, the frizz caused by fluctuating loads, especially the frit caused by arc furnaces, includes high-level frizz that occurs during the melting stage and low-level frizz that occurs during the refining stage. This difference in flicker level is the fluctuation range of reactive power (△
This is caused by Q), and is caused by the fact that the fluctuation range of reactive power is large during the melting period, and is small during the refining period. Although there is a difference in the fluctuation range of reactive power between the melting period and the refining period, the average reactive power is about the same.
In particular, in direct reduced iron furnaces, the period during which frizz occurs is about the first 10 minutes of 1 charge (2 hours), and after this time the frittle level drops to about 1/3 of the peak value. Most of the driving time is spent with low levels of flicker.

Therefore, the main purpose of anti-flicker measures is to suppress high-level flicker, and there is no particular need to suppress low-level flicker. Therefore, it is better to use the compensator mainly as a phase advance capacitor device, even if it sacrifices some of the anti-flicker effect, during the melting period when the flicker level is high, and as a flicker suppressing device during the refining period when the flicker level is low. improves operating efficiency. Regarding anti-flicker measures, high-level anti-flicker effects can be considered to be on the same level as conventional anti-flicker effects.

The present invention was proposed based on the above-mentioned circumstances, and its purpose is to cause a compensator to function as a conventional flicker suppressing device when the flicker level is high, and on the other hand, when the flicker level is low. It mainly functions as a phase advance capacitor device, improving the operating power factor of the load more than before, and reducing the reactor current.
The objective is to reduce the operating loss of this type of compensator by reducing I _Re .

In order to achieve the above object, the present invention includes a control circuit that detects any one of flicker, reactive power fluctuation, and voltage fluctuation based on load fluctuation and compares the detected signal with a reference value of a reference setting circuit. established,
When the detection signal is smaller than a preset reference value, the operation of the compensator is switched so that it primarily functions as a phase advance capacitor device.

Hereinafter, this invention will be explained in detail with reference to the drawings.
FIG. 3 shows an embodiment of the present invention.
In the figure, the same or corresponding parts as in FIG. 1 are given the same reference numerals. The major difference from the conventional example shown in FIG. 1 is that a control circuit 50 is provided. This control circuit 50 is configured to be able to detect at least one of flicker detection, reactive power fluctuation detection, and voltage fluctuation detection. Figure 4 shows
2 is a block diagram showing a specific configuration of this control circuit 50. FIG. 51 is an input terminal into which a signal is input; 52
is a detection unit, and includes at least one of a flicker detection circuit, a reactive power fluctuation detection circuit, and a voltage fluctuation detection circuit. Reference numeral 53 denotes an average value circuit that calculates the average value of the detection signal obtained by the detection section 52, and is composed of a first-order lag type integrating circuit having a time constant of, for example, several tens of seconds to several minutes. 54 is a constant circuit, and 55 is a comparison circuit, which compares the reference value from the reference value setting circuit 56 and the detection signal. 57 is a relay circuit. Note that 31 is an input terminal to which a bus voltage value and a load current value are input.

For convenience, a case will be described below in which the flicker level is determined and the operation of the compensator 100 is switched based on this determination.

In this case, a flicker level signal f from a flicker meter (not shown) is applied to the input terminal 51.
Therefore, the detection section 52 is omitted. A reference flicker level fs, which is a switching level for device functions, is set in the reference value setting circuit 56. Input terminal 5
1, the flicker level signal f is sent to the average value circuit 53.
are input and averaged (take that value).
This flicker level is compared with a reference flicker level fs in a comparison circuit 55, and when f>fs, the compensation device 100 is used to improve flicker.
acts as a flicker suppressor. On the other hand, f
<fs, the compensation device 100 mainly functions as a phase-advance capacitor device, as shown in FIGS. 5a, b, and c, respectively.

In FIG. 5, is the characteristic line of the reactive power generated by the reactor 12 when the compensator 100 functions as a flicker suppressor, and is the characteristic line of the compensator 10.
The line representing the average reactive power generated by the reactor 12 when the compensator 100 functions as a flicker suppressor is the straight line representing the average reactive power generated by the reactor 12 when the compensator 100 primarily functions as a phase advance capacitor device. is a straight line representing the average reactive power generated by the reactor 12 when it mainly functions as a phase advance capacitor device.

FIG. 5a shows a case where the flicker level is low and the ignition pulse to the thyristor circuit 13 is stopped so that the reactor current I _Re becomes zero. In this case, compensator 1
The phase-advanced reactive power of the phase-advanced capacitor/filter device 20 of 00 is directly directed to power factor improvement. Therefore, compared to the past, the electrical system 3 is 50% more rated than before.
Contributes to improving the power factor of

FIG. 5b shows a case where the flicker level is low, the firing pulse to the thyristor circuit 13 is throttled to a certain fixed phase, and the reactor 12 is supplied with the rated q.
% (<50%) when a constant reactor current I _Re is passed. In this case, the phase-advanced reactive power generated by the compensator 100 will be increased by (50-q)% of the rated value compared to the conventional one, and this amount will contribute to improving the power factor of the electrical system 3. .

FIG. 5c shows a case where the flicker level is low and the firing pulse to the thyristor circuit 13 is not fixed or stopped. in this case,
The characteristics when the compensating device 100 functions as a flicker suppressing device are transferred as they are to the smaller reactor current I _Re , and the characteristics are made such that the reactive power generated by the load 4 can be compensated to some extent. However, by reducing the average reactive power to q% (<50%), on average, as in the case of FIG. (50-q)% of the power is generated, and this amount contributes to improving the power factor.

On the other hand, when the flicker level is high, the compensating device 100 functions as a flicker suppressing device as in the prior art, so the flicker improvement effect remains the same as in the prior art.

FIG. 6 shows the flicker improvement effect of the compensation device according to the present invention in comparison with that of a conventional compensation device. Figure 6a shows the temporal transition of the load flicker generation level, Figure 6b shows the flicker level after countermeasures using a conventional compensator, and Figure 6c shows the fluctuation of the flicker generation level over time. 3 shows the flicker level caused by the compensation device according to the invention.

In general, the fritska level evaluation is 95 for a normal distribution.
Since it is evaluated as a percentage value, the evaluation of flicker countermeasures does not change even if only the areas with high flicker levels are improved. As can be understood from Fig. 6, even if flicker countermeasures are taken for all time periods as in the past, and even when flicker countermeasures are taken only for high flicker time periods as in the present invention, the flicker level remains the same. I can say that.

From the above, according to this invention, The flicker suppression effect is the same as before.

The operating power factor of the load is improved compared to the conventional method.

Therefore, it may be possible to reduce the capacitance of the power factor correction capacitor that was conventionally provided on the load side for power factor correction. Furthermore, in the case of a newly installed load, the capacity of the power factor improvement phase advancing capacitor may be small.

The capacity of the compensator itself remains the same as before.

In addition to achieving the following effects, the control circuit 50 of the present invention
It also has the feature that it can be easily added to conventional compensation devices of this type.

In the above description, a case has been described in which operation switching is performed based on flicker level determination, but the following signals other than flicker can be considered as signals for switching determination.

○B The average level of the load's reactive power fluctuation (△Q) is used as the operation switching signal. Generally, the flicker level is proportional to the reactive power fluctuation (ΔQ) of the load.
In other words, since the flicker level increases as the reactive power fluctuation increases, the average level of the reactive power fluctuation is detected, and this is compared with a reference level. The compensation device functions as a device. In this case, part of the configuration of the control circuit 50 shown in FIG. 4 is changed as follows. That is, the system bus voltage and load current are input to the input terminal 51,
A reactive power detection circuit that outputs a DC signal is used as the detection unit 52, and a reactive power fluctuation level is set in the reference value setting circuit 56.

○B Use the average level of instantaneous voltage fluctuations (△V) as the operation switching signal. Similarly to the above, the flicker is proportional to the instantaneous voltage fluctuation (ΔV), so this fluctuation (ΔV) is detected and the operation is switched. In this case, part of the configuration of the control circuit 50 shown in FIG. 4 is changed as follows. That is, the bus voltage of the system is input to the input terminal 51, a voltage fluctuation detection circuit that outputs a DC signal is used as the detection section 52, and a voltage fluctuation level is set to the reference value setting circuit 56.
Alternatively, the voltage fluctuation output signal of the flicker meter is inputted to the input terminal 51, the detection section 52 is omitted, and the voltage fluctuation level is set in the reference value setting circuit 56.

[Brief explanation of drawings]

Fig. 1 is a single line diagram showing a conventional device, Fig. 2 is an operating characteristic diagram of the conventional device, Fig. 3 is a single line diagram of a device according to the present invention, Fig. 4 is a block diagram showing the configuration of the main parts, 5 and 6 are operational characteristic diagrams. 4...load, 100...reactive power compensator.

Claims (1)

[Claims] 1 A reactive power system in which a slow-phase reactive power adjustment device consisting of a reactor and a thyristor circuit and a phase-advanced capacitor/filter device are installed in parallel, and the phase of the current flowing through the reactor is controlled by the thyristor to compensate for reactive power due to load fluctuations. In the compensator,
A control circuit is provided that detects any one of flicker, reactive power fluctuation, and voltage fluctuation based on the load fluctuation and compares the detection signal with a reference value of a reference setting circuit, and the detection signal is set in advance. A reactive power compensator characterized in that the reactive power compensator mainly functions as a phase advance capacitor device when the value is smaller than the reference value.