JPS602855B2 - Unbalanced load correction control device - Google Patents

Description

[Detailed Description of the Invention] The invention described in this) is an unbalanced load in order to reduce the negative influence on the power supply when a three-phase load becomes an unbalanced load state, especially a single-phase load state during operation. The present invention relates to an unbalanced load correction control device that connects a dummy load for load correction to a power supply bus.

A three-phase load, for example a three-phase electric furnace, that was in an equilibrium operating state
If a single-phase negative state occurs due to hot water blowing up near the electrode, depending on the type of electric furnace power supply, the operator may judge the degree of unbalance and lower the tap of the crab furnace transformer. By controlling the power supplied to the fin furnace, we aim to reduce the negative impact on crab sources.

In this conventional method that relies on manual intervention, the response time is delayed and inconsistent, so that an adverse effect on the power source is unavoidable.

Also, it goes without saying that a major or medium decline in capacity utilization is unavoidable. Furthermore, since the frequency of occurrence of the unbalanced state is not small, there is a drawback that the life of the electric furnace transformer is significantly shortened due to repeated tap operations. The invention described in (a) was made with the aim of solving the above-mentioned drawbacks of the secondary system. The occurrence of an unbalanced load state and an abnormal phase are determined based on the difference in the amount of fluctuation of each phase, and a resistive dummy load is automatically applied between specific phases of a predetermined power supply bus line in response to an abnormality in the gutter phase. According to
It is an object of the present invention to provide an unbalanced load correction control device that can automatically and effectively correct the degree of unbalance of the three-phase load as seen from the power source, and without waste only when measures are required.

The basic invention will be explained below based on the illustrated embodiments.

In the figure, ~ i is a power supply bus; 2 is a three-phase electric furnace connected to the fin source bus 1 via an electric furnace shield switch 3; 4, H and 6 are current transformers for each phase, respectively. A current converter such as a rectifier that converts the R-phase, S-phase and T-phase currents of the electric furnace supply current taken out through 4', 5' and 6' into scalar quantities,
Both outputs are supplied to a current combining/averaging device 71 (V).

The current combining averager 7 is configured to add and average the inputs. The outputs of the current converters 4, 5 and 6 are also supplied to abnormal phase detectors, ie comparators 8, 9 and 01, respectively, and are compared with the output of the current combining averager 7. Comparators 8, 9 and 101
Well, the deviation of the two inputs is determined by the respective deviation setters 8', 9' and G.
The output is output when the value is equal to or higher than the set value given by O', but the output disappears when a reset signal is received from the dummy load injection preventer, that is, the addition multiplier 11. The adder intensifier 1 sends out an output when any two of the comparators 8, 9 and IQ output (in this case, the electric furnace is not in an unbalanced load state). Therefore, only when the above-mentioned abnormal phase detector, that is, the comparator in No. 1, outputs an output, the output of the comparator is sent to the subsequent stage, and an unbalanced load condition occurs and abnormality that requires the measures specified by the set values of each of the above-mentioned comparators. phase is detected. Comparator 8? The outputs of 9 and 0 are supplied to dummy load input signals 6, 16 and 17 via delay elements or timers 12, 13 and 14, respectively. These timers are
This is a dummy load prevention confirmation timer installed to prevent dummy loads from being turned on during momentary unbalanced load states of the ant furnace 2. ) is also stipulated. Only when the outputs of comparators 8, 9 and 10 are still present even after the timer 2s 13 and 4', the dummy load transfer signal 5; 1 is activated, respectively.
6 and 171 outputs are sent out. Reference numerals 18 and 19 indicate dummy load switching devices constituted by three-phase switches for connecting dummy load power sources. The switch is closed and the corresponding two-phase electrodes of the water resistor 20 and two three-phase electrodes A and B constituting the dummy load are connected to the power supply bus 1.

For example, when the R-phase dummy load input signal blade outputs,
The R-phase and S-phase switches of the opening/closing bag layer 8 for electrode A are closed, and the R-phase and T-phase switches of the switchgear turtle 9 for electrode B are closed, and a connection is made between the R-phase of the power bus and the other two phases. 〜That is, dummy charge of the V connection electrode is applied centering on the R phase.Similarly, when the dummy load immersion signal device 16 or the force 7 outputs, the V connection electrode centering on the S or T phase of the power supply bus 1 A dummy load of connection electrodes is applied.The power consumption of the dummy load is adjusted in consideration of the power consumption in an unbalanced load state that requires measures for the electric furnace.
Note that the dummy load switching devices 18 and 19 can of course be constructed using semiconductor switching elements.

The operation of this embodiment will be explained below.If a hot water blow-up phenomenon occurs near the R-phase electrode in the electric furnace 2 in equilibrium operation, and a single-phase load state occurs, It is rumored that the R-phase current of the air furnace supply current will decrease during the course of the year.

This phenomenon becomes more pronounced as the hot water blows up. When this phenomenon occurs, the output of the R-phase current converter 4 decreases.
On the other hand, the output of the current combining averager 7 also decreases, but since this decrease is smaller than the decrease in the output of the current converter, a deviation occurs between the two outputs. In the event of the above phenomenon that adversely affects the power supply, the above deviation exceeds the value set by the deviation setting device 8',
An output is generated in the R-phase comparator 8. This causes timer 12
starts operating, and if the scratch blow-up phenomenon is not instantaneous, after the timer 12 has expired, the dummy load input signal 15 receives the timer output. In this way, the electric furnace 2 has an abnormality in the R phase and is in an unbalanced load state, and it is detected that the degree of unbalance is large and persistent enough to require measures, and the dummy load input signal device 15 outputs an output. . This output closes the switches of the dummy load switching devices 18 and 19 as described above, and closes the switches of the dummy load switching devices 18 and 19 as described above, and closes the switches between the S and T phases of the power supply bus 1 (the electric furnace is in a single rotation state between these phases). Dummy loads 20 and 21 are connected to the terminals. Therefore, the total load seen from the power supply is corrected to a three-phase balanced load state, and if the KW of the dummy load is appropriately adjusted, the negative sequence current flowing to the power supply is greatly reduced, and the load relative to the power supply is The negative effects are virtually eliminated. When the electric furnace 2 restores equilibrium, the output of the comparator 8 disappears, and the electrodes A and B connected to the power supply bus 1 are disconnected from the bus. Even when a hot water blow-up phenomenon occurs near the S-phase and T-phase electrodes of the electric furnace 2, resulting in a single-phase load state, the load imbalance correction is automatically realized in the same manner as in the above case. As described above, according to the present invention, the amount of variation in each phase of the three-phase load supply current is detected relative to the amount of variation in the composite average value of each phase current, and the relative amount of variation in one phase is detected. Since a resistive dummy load is turned on when the voltage exceeds a certain value, even if it is a 3-phase load such as an electric furnace where the power supply fluctuates widely, it will only be detected when an unsanitary load condition that requires countermeasures occurs. Abnormal phases are constantly and reliably detected. Therefore, it is possible to specify in advance the source bus phase to which a dummy load should be applied in response to an abnormality in that phase. , only when an unbalanced load condition that adversely affects the power supply occurs, an optimal dummy load is immediately and automatically connected to the power supply bus, and the unbalanced load seen from the power supply is virtually completely corrected. In addition, ``For non-sustainable unsanitary conditions mentioned above, it is possible to prevent the input of dummy loads by simply providing a delay element.It is possible to avoid unnecessary input of dummy loads, but it is possible to input the dummy loads at the optimum timing. Therefore, according to the present invention, even if an unsanitary load condition occurs, operation can be continued, thereby avoiding the large or medium decrease in operating efficiency that would occur in the past. In addition, the dummy load is automatically turned on under certain conditions without requiring the tap operation of the transformer as in the case of a secondary transformer, which reduces the workload of the operator and prevents the life of the transformer from being shortened. I can do it.

In addition, in the embodiment shown in Fig. 1, the amount of decrease in each phase of the three-phase load is
Although the detection is performed relative to the phase composite value, it is clear that it is also possible to detect the absolute amount of variation for each phase independently.

Fig. 2 shows an embodiment of another invention in which the amount of fluctuation in the supplied power is used as a dummy load input condition, and the same or corresponding parts as in Fig. 2 are denoted by the same symbols.
The input opening/closing registers 18 and 19 are not shown for convenience of explanation.

Reference numeral 23 denotes a power detector for detecting the power supplied to the electric furnace, which is connected to the power supply bus shown in FIG. The signal is supplied to an intensifier 25 and a memory element, ie, a memory timer 26, via the signal.

The memory timer 26 has a structure in which its output gradually decreases in response to a sudden decrease in the input. When the input to the crab force detector 23 suddenly decreases, as shown in FIG. occurs. 2? is a comparator, memory timer 26 and multiplier 2
5 is compared, and if the deviation between the two is greater than the set value given by the deviation setter 27', an output is generated.

This set value defines the degree of power fluctuation caused by electric furnace hot water blowing up, etc., which appears in the electric furnace supply power. The power fluctuation detection system has been established as a result of the above, and its output month. Comparator 27
The outputs of the comparators 28, 29 and 331 are supplied as operating conditions. These comparators have comparator fins shown in Figure 1,
9 and 101 correspond to each other, and the difference is that the former is configured to generate an output when receiving the output of the comparator 27 as an operating condition. Of course, comparator 27
The outputs of the AND elements and the outputs of the comparators 8, 9, and 10 shown in FIG. It may be supplied to the signal generators 15, 16 and 17, respectively.The reset output of the adder intensifier 1 is supplied to the comparator 27, which is configured to reset the output of the comparator 27, but of course the above-mentioned IJ Set output to each comparator 28, 29
and may be given to 30. In this configuration, when the electric furnace 2 in FIG. 1 enters the unbalanced load state explained in FIG.
When the R-phase V supply current decreases and the deviation between the output of the R-phase current converter 4 and the output of the composite averager 7 is greater than the set value, an abnormal phase is detected and comparator 2 can generate an output. state.

On the other hand, at the same time, the supplied power also decreases significantly, so if the degree of decrease exceeds the set value (Figure 3), the comparator 27
An output is supplied from the comparator 8, and in addition to an abnormal phase, the occurrence of an uneven load condition requiring action is detected and the latter outputs. As a result, the dummy load 288 shown in the map is connected to the power supply bus 1, and the unsanitary degree of the load as seen from the power supply is corrected. Since the amount of variation is specified as the dummy load application condition, the power consumption of the dummy load can be adjusted based on this specified amount, and it is easily possible to apply the optimal dummy load. is more noticeable than a single change in the V supply current (in this sense, the same applies to the amount of change in the sum of the three phases of the supply current). Even though the selection range of the dummy load application conditions is widened, the dummy load can be applied even when the power supply is good and the magnitude of the adverse effect on the generator is substantially outside the allowable range.In the case of the present invention, , each abnormal phase detector does not function as an abnormal phase detection and unsanitary detection element as shown in FIG.
It functions only as an abnormal phase detection element that determines the magnitude of the input.

The degree of power fluctuation, which is a dummy load application condition, is detected by a power fluctuation detection device. Note that an absolute value synthesizer (not shown) of the three-phase load V supply current taken out via a current transformer may be used in place of the power detector.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing embodiments of the unbalanced negative correction control device according to each invention, and FIG. 3 is a diagram showing the input time relationship of the comparator 27 in FIG. 2. In the figure, 1 is a three-phase power supply bus, 2 is an electric furnace, 4, 8, and a current converter, and 4', wealth', and 6' are current transformers.
Sama current synthesis averager `` 臥 g, 10'ma comparator, honey'
, 9' and pupil' are deviation setting devices, and turtle 1 is an addition intensifier.
200 and 200 are dummy loads, 1 is the blind period, dummy load switching device, 23 is the power detector, 2 is the power amplifier, 2 is the memory element ÷ 27, 2 is false, 9 and 3 are the dummy loads. The skin level comparator, 27' is a deviation setting device. In the figure, the same symbols t indicate the same or equivalent parts.
Figure 1 Figure 2

Claims (1)

[Claims] 1. An abnormal phase detector for each phase that outputs when the amount of decrease in one phase of the three-phase load supply current is equal to or greater than a certain value, and when at least two of the abnormal phase detectors output The present invention is characterized in that it is equipped with a dummy load prevention device that prevents erroneous application of dummy loads, and applies resistive dummy loads between specific phases of respective predetermined power supply buses in response to the outputs of the respective abnormal phase detectors. Unbalanced load correction control device. 2. A dummy load erroneous application prevention device is supplied with the output of each abnormal phase detector, and includes a summing amplifier that sends a reset signal to each of the abnormal phase detectors when receiving at least two of the outputs, and each of the above abnormalities. and a delay element supplied with the respective outputs of the phase detectors.
The unbalanced load correction control device described in . 3 Power fluctuation detection device that outputs when the degree of power fluctuation of 3-phase load is above a certain value, abnormal phase detection for each phase that outputs when the amount of decrease in 1 phase of 3-phase load supply current is above a certain value a dummy load prevention device that prevents erroneous input of dummy loads when at least two of the abnormal phase detectors output, and a dummy load prevention device that prevents erroneous input of the dummy load when at least two of the abnormal phase detectors output, Correspondingly, an unbalanced load correction control device characterized in that a resistive dummy load is inserted between specific phases of respective predetermined power supply buses. 4. A patent characterized in that the power fluctuation detection device comprises a power detector and a comparator that outputs an output when the amount of decrease in the three-phase load supply power extracted via the power detector is less than or equal to a set value. An unbalanced load correction control device according to claim 3. 5. Claim No. 5, characterized in that the power fluctuation detection device includes a comparator that outputs an output when the amount of fluctuation in the composite value of the three-phase load supply current taken out via the current transformer is greater than or equal to a set value. The unbalanced load correction control device according to item 3. 6 The operating condition is that the abnormal phase detector receives the output of the power fluctuation detection device that determines that the 1-phase scalar value extracted via the current transformer is smaller than the average value of the 3-phase scalar values. 4. The unbalanced load correction control device according to claim 3, wherein the unbalanced load correction control device is a comparator. 7. The dummy load erroneous application prevention device is supplied with the output of each abnormal phase detector, and a summing amplifier that sends a reset signal to the power fluctuation detection device when receiving at least two of the outputs, and each of the above abnormal phase detectors. 4. The unbalanced load correction control device according to claim 3, further comprising a delay element supplied with the respective outputs of the control device.