Connection Phase Determination Device and Program

Abstract

To reduce voltage unbalance and a frequency of switches of connection phases.SOLUTION: A connection phase determination device includes: an estimation unit for estimating which phase of three phases a high voltage distribution line has a transformer connected to the high voltage distribution line is connected at present; an unbalance index calculation unit for calculating an unbalance index indicating a degree that electric energy used in each phase is unbalance mutually, in a phase to which the transformer is estimated to be connected at present, and the unbalance index at the time of being connected to a different phase; a comparison unit for comparing the unbalance indexes; a determination unit for determining that a connection phase switch is performed to a phase different from the phase which the transformer is estimated to be connected at present, when the unbalance index is improved even if the connection phase switch is performed to any phase different from the phase which the transformer is estimated to be connected at present from the phase which the transformer is estimated to be connected at present; and an output unit for outputting a result determined by the determination unit.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a connection phase determination device and a program.

Background Art

[0002] In recent years, the installation of distributed power sources such as solar panels has been increasing. In a three-phase three-wire distribution line, each facility is connected so that the currents of the first phase, the second phase, and the third phase are balanced with each other. Such a state is called three-phase balance. However, when the distributed power source is biased and connected to a specific one of these three phases, and forward power flow to the load or reverse power flow from the distributed power source to the distribution line occurs, etc., the three-phase balance may be lost. Also, due to fluctuations in the load of consumers, the three-phase balance may be lost. Such a state is called three-phase unbalance with respect to three-phase balance. When three-phase unbalance occurs, it may cause problems in the equipment of consumers receiving power supply from the distribution line.

[0003] Conventionally, in order to avoid a situation where three-phase unbalance occurs, among a plurality of loads connected to a distribution line, it is known to move a specific load so that the three-phase unbalance is eliminated. In particular, there has been a technique for calculating the amount of load movement required to eliminate three-phase unbalance. As an example of such a technique, for example, the unbalance elimination support device described in Patent Document 1 can be cited.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the imbalance elimination support device as described above, although it may be possible to calculate the load transfer amount that can reduce the voltage imbalance, it is not easy to actually transfer the calculated load. For example, when changing the connection phase of a transformer connected to a distribution line, it is preferable to have a smaller number of transformers for which the connection phase is changed from the perspective of reducing the labor, time, cost, or risk required for the work.

[0006] The present invention has been made in view of such a situation, and an object thereof is to provide a connection phase determination device and a program that can reduce voltage imbalance and can reduce the number of times of connection phase change.

Means for Solving the Problems

[0007] A connection phase determination device according to an aspect of the present invention includes an estimation unit that estimates to which phase among the three phases of a high-voltage distribution line that transmits power in a three-phase three-wire system a transformer connected to the high-voltage distribution line is currently connected, and an imbalance index indicating the degree to which the amounts of power used in each of the three phases of the high-voltage distribution line are unbalanced with each other. The imbalance index in the phase where the transformer is estimated to be currently connected and the imbalance index when the transformer is connected to a phase different from the phase where the transformer is estimated to be currently connected are calculated by an imbalance index calculation unit, a comparison unit that compares the imbalance index in the phase where the transformer is estimated to be currently connected with the imbalance index when the transformer is connected to a phase different from the phase where the transformer is estimated to be currently connected, and a determination unit that determines to perform a connection phase change to a phase different from the phase where the transformer is estimated to be currently connected when the imbalance index improves even if the transformer is connected to any phase different from the phase where the transformer is estimated to be currently connected, and an output unit that outputs the result determined by the determination unit.

[0008] Further, in the connection phase determination device according to an aspect of the present invention, the determination unit determines to perform a connection phase change to the phase in which the imbalance index is more improved.

[0009] Also, in the connection phase determination device according to one aspect of the present invention, the imbalance index calculation unit calculates, in order, for a plurality of the transformers connected to the high-voltage distribution line based on a predetermined priority order, and the comparison unit compares the imbalance indices for the plurality of the transformers connected to the high-voltage distribution line.

[0010] Also, in the connection phase determination device according to one aspect of the present invention, for the transformer determined by the determination unit to perform connection phase switching, the imbalance index calculation unit calculates the imbalance index assuming that the connection phase switching has been performed.

[0011] Also, in the connection phase determination device according to one aspect of the present invention, the predetermined priority order is in descending order of average power consumption.

[0012] Also, in the connection phase determination device according to one aspect of the present invention, the imbalance index indicates the degree to which the power amounts are unbalanced with each other in a predetermined period including a plurality of unit periods, and the imbalance index calculation unit calculates the imbalance index based on the imbalance index in the unit period in which the imbalance index was the maximum among the plurality of unit periods.

[0013] Also, in the connection phase determination device according to one aspect of the present invention, the predetermined period includes the period in which the power consumption is the smallest and the period in which the power consumption is the largest within one year.

[0014] Also, in the connection phase determination device according to one aspect of the present invention, for the transformer determined by the determination unit to perform connection phase switching, the imbalance index calculation unit calculates the imbalance index while alternately assuming that the connection phase switching has been performed and assuming that the connection phase switching has not been performed.

[0015] Also, a program according to an aspect of the present invention causes a computer to perform an estimation step of estimating to which phase among the three phases of a high-voltage distribution line that transmits power in a three-phase three-wire system the transformer connected to the high-voltage distribution line is currently connected; an unbalance index calculation step of calculating an unbalance index indicating the degree to which the amounts of power used in the respective phases of the three phases of the high-voltage distribution line are unbalanced with each other, the unbalance index in the phase estimated to be currently connected to the transformer, and the unbalance index when the transformer is connected to a phase different from the phase estimated to be currently connected; a comparison step of comparing the unbalance index in the phase estimated to be currently connected to the transformer with the unbalance index when the transformer is connected to a phase different from the phase estimated to be currently connected; a determination step of determining to perform a connection phase change to a phase different from the phase estimated to be currently connected to the transformer when the unbalance index improves even if the connection phase change is made to any phase different from the phase estimated to be currently connected to the transformer; and an output step of outputting the result determined by the determination step.

Effect of the Invention

[0016] According to the present invention, it is possible to provide a connection phase determination device and a program that can reduce voltage unbalance and reduce the number of times of connection phase change.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

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Figure 8

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Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0018] [First Embodiment] First, with reference to FIGS. 1 to 8, the connection phase determination device 10 according to the first embodiment will be described. The connection phase determination device 10 determines a connection phase change of a connection phase that reduces the voltage imbalance of the single-phase transformer group 4 connected to the distribution line 3 in the distribution network 1. As a premise of this embodiment, the distribution network 1 will be described.

[0019] FIG. 1 is a diagram showing an example of a distribution network according to the first embodiment. As shown in FIG. 1, the distribution network 1 includes a substation 2, a distribution line 3, a single-phase transformer group 4, a low-voltage consumer group 5, a high-voltage consumer group 6, a power generation company group 7, and a switch 8.

[0020] The substation 2 is a facility that converts the three-phase alternating current voltage transmitted from the power plant via the transmission line into a predetermined voltage, for example, 6600V, and provides three-phase alternating current to the distribution line (high-voltage distribution line) 3.

[0021] The distribution line 3 includes a first distribution line 31, a second distribution line 32, and a third distribution line 33, and transmits electric power in a three-phase three-wire system. The first distribution line 31, the second distribution line 32, and the third distribution line 33 may be, for example, overhead distribution lines strung on utility poles or underground distribution lines buried underground. The first distribution line 31 conducts the current of the first phase of the three-phase alternating current power supplied by the substation 2. Similarly, the second distribution line 32 conducts the current of the second phase of the three-phase alternating current power supplied by the substation 2. Also, the third distribution line 33 conducts the current of the third phase of the three-phase alternating current power supplied by the substation 2. In the following description, the first phase, the second phase, and the third phase may be described as the U phase, the V phase, and the W phase, respectively.

[0022] The single-phase transformer group 4 includes a plurality of single-phase transformers (hereinafter, may be simply referred to as transformers), that is, single-phase transformers 41,..., single-phase transformers 4k (k: a natural number of 2 or more). In the following description, when the single-phase transformers 41,..., single-phase transformers 4k are not distinguished, they may be described as the single-phase transformer 41. The single-phase transformer 41 is, for example, a pole-mounted transformer that converts 6600V three-phase power into 200V single-phase power or 100V single-phase power. Also, the single-phase transformer 41 is connected to any two of the first phase, the second phase, and the third phase of the three-phase alternating current power supplied by the substation 2.

[0023] The low-voltage consumer group 5 includes low-voltage consumers 51,..., low-voltage consumers 5k. In the following description, when the low-voltage consumers 51,..., low-voltage consumers 5k are not distinguished, they may be described as the low-voltage consumer 51. The low-voltage consumer 51 has equipment connected to the single-phase transformer 41, and is a consumer that uses the electric power obtained by converting 6600V three-phase electric power into 200V single-phase electric power or 100V single-phase electric power by the single-phase transformer 41. Similarly, the low-voltage consumers 52, …, 5k each have equipment connected to the single-phase transformers 42, …, 4k, and are consumers that use the electric power obtained by converting 6600V three-phase electric power into 200V single-phase electric power or 100V single-phase electric power by the single-phase transformers 41, …, 4k. As an example of the low-voltage consumers 51, …, 5k, for example, ordinary households can be cited.

[0024] Also, as shown in FIG. 1, the low-voltage consumer 51 includes a smart meter 511, a distributed power source 521, and a load 531. Similarly, the low-voltage consumers 52, …, 5k each include smart meters 512, …, 51k, distributed power sources 522, …, 52k, and loads 532, …, 53k. Note that the low-voltage consumers 51, …, 5k only need to include at least one of the distributed power sources 521, …, 52k or the loads 531, …, 53k.

[0025] The smart meter 511 may have a communication function. For example, the smart meter 511 measures the line voltage on the secondary side of the single-phase transformer 41 that supplies power to the low-voltage consumer 51, and generates transformer voltage data indicating the line voltage. Then, the smart meter 511 stores the transformer voltage data in a storage device provided inside or outside the smart meter 51k.

[0026] For example, the line voltages indicated by the transformer voltage data generated by the smart meter 511 may all be average values of the line voltages over a predetermined period. The predetermined period may be, for example, 1 minute, 10 minutes, 30 minutes, or the like.

[0027] Note that the smart meter 511 may be a next-generation smart meter that can store not only the amount of electric power but also the average value of the voltage over a predetermined period (for example, 30 minutes).

[0028] The distributed power sources 521, …, 52k are, for example, distributed power sources such as solar panels, and reverse power flow the power they generate into two of the first distribution line 31, the second distribution line 32, and the third distribution line 33. Note that at least one of the low-voltage consumers 51, …, 5k does not necessarily have the distributed power sources 521, …, 52k respectively. The low-voltage consumers 51, …, 5k that do not have the distributed power sources 521, …, 52k have loads 531, …, 53k.

[0029] The high-voltage consumer group 6 includes high-voltage consumers 61, …, 6m (m: a natural number of 2 or more). The high-voltage consumers 61, …, 6m have equipment connected to the first distribution line 31, the second distribution line 32, and the third distribution line 33, and are consumers that convert the three-phase power received at 6600V into a desired voltage for use. As an example of the high-voltage consumers 61, …, 6m, for example, factories, large-scale condominiums, etc. can be mentioned. Also, each of the high-voltage consumers 61, …, 6m operates a load such as a motor using three-phase power.

[0030] The power generation business operator group 7 includes power generation business operators 71, …, 7n (n: a natural number of 2 or more). The power generation business operators 71, …, 7n generate power using renewable energy and reverse power flow into the distribution line 3. Examples of renewable energy include, for example, sunlight, wind power, geothermal energy, hydropower, biomass, etc.

[0031] The switch 8 is a switch that switches between the case of flowing three-phase alternating current through the first distribution line 31, the second distribution line 32, and the third distribution line 33 and the case of not flowing three-phase alternating current through the first distribution line 31, the second distribution line 32, and the third distribution line 33.

[0032] In addition, the switch 8 includes a voltmeter (not shown) that measures the line voltage between the first phase and the second phase, the line voltage between the second phase and the third phase, and the line voltage between the third phase and the first phase of the three-phase alternating current flowing through the substation 2. This voltmeter measures, for example, the line voltage between the first phase and the second phase and generates first line voltage data indicating the line voltage. Further, this voltmeter measures the line voltage between the second phase and the third phase and generates second line voltage data indicating the line voltage. Further, this voltmeter measures the line voltage between the third phase and the first phase and generates third line voltage data indicating the line voltage. The first line voltage data, the second line voltage data, and the third line voltage data are stored, for example, in a storage device (not shown) provided inside or outside the switch 8.

[0033] In addition, the line voltage indicated by the first line voltage data, the line voltage indicated by the second line voltage data, and the line voltage indicated by the third line voltage data are all the average of the line voltages over a predetermined period. The predetermined period may be, for example, 10 minutes, 30 minutes, etc. Note that the predetermined period is the same length as the predetermined period for the transformer voltage data, and it is preferable that the start period and the end period coincide with the start period and the end period of the predetermined period for the transformer voltage data described above.

[0034] In addition, the switch 8 may include an instrument current transformer (CT: Current Transformer) and an instrument voltage transformer (VT: Voltage Transformer) (not shown). The instrument current transformer is a device used to expand the range of currents that can be measured by the ammeter included in the switch 8. The instrument voltage transformer is a device that steps down a high voltage to a voltage that can be used by the above-described voltmeter, etc. The instrument current transformer and the instrument voltage transformer may be attached to the side of the switch 8 on the substation 2 side.

[0035] FIG. 2 is a diagram for explaining a connection phase change pattern according to the first embodiment. With reference to this figure, an example of changing the connection phase of the single-phase transformer 41 will be described. FIG. 2(A) shows an example when the single-phase transformer 41 is connected between the U-V phases, FIG. 2(B) shows an example when the single-phase transformer 41 is connected between the W-U phases, and FIG. 2(C) shows an example when the single-phase transformer 41 is connected between the V-W phases, respectively.

[0036] In the example shown in FIG. 2, the single-phase transformer 41 includes a secondary winding 411. The single-phase transformer 41 supplies 100V single-phase power to the loads P1 and P2 and supplies 200V single-phase power to the load P3.

[0037] As shown in FIG. 2(A), when the single-phase transformer 41 is connected between the U-V phases, the secondary winding 411 of the single-phase transformer 41 is connected between the U-V phases. When changing the connection phase from the state where the secondary winding 411 is connected between the U-V phases to the W-U phases, as shown in FIG. 2(B), while maintaining one end connected to the U phase, the other end connected to the V phase is changed to be connected to the W phase. In this case, since the loads 1, 2, and 3 supplied with power by the single-phase transformer 41 are all single-phase loads, there is no influence due to the connection phase change.

[0038] Also, when changing the connection phase from the state where the secondary winding 411 is connected between the U-V phases to the V-W phases, as shown in FIG. 2(C), while maintaining one end connected to the V phase, the other end connected to the U phase is changed to be connected to the W phase. In this case, since the loads 1, 2, and 3 supplied with power by the single-phase transformer 41 are all single-phase loads, there is no influence due to the connection phase change.

[0039] In the following embodiments, when the single-phase transformer 41 is currently connected between the U-V phases, when maintaining the connection between the U-V phases from the state of being connected between the U-V phases, when changing the connection phase from the state of being connected between the U-V phases to the W-U phases, and when changing the connection phase from the state of being connected between the U-V phases to the V-W phases, the unbalanced state is calculated for each case, and a suitable connection phase change is determined.

[0040] FIG. 3 is a diagram for explaining a series of operations of the connection phase determination device according to the first embodiment. With reference to this figure, a series of operations of the connection phase determination device 10 will be described. (Step S110) First, the connection phase determination device 10 performs input data processing. As input data processing, the connection phase determination device 10 acquires a plurality of data used for connection phase determination, such as power distribution facility data, IT switchgear data, and smart meter data. The power distribution facility data includes information regarding the single-phase transformer group 4 connected to the power distribution line 3. The IT switchgear data includes information regarding the three-phase voltage and current acquired by the switchgear 8. The smart meter data includes, for example, the line-to-line voltage on the secondary side of the single-phase transformer 41 acquired by the smart meter 511.

[0041] (Step S120) The connection phase determination device 10 performs transformer connection phase determination. For example, it is performed by the VV method, the PI method, or the like. The VV method is a method for discriminating the connection phase from the correlation between the voltage acquired by the IT switchgear and the line-to-line voltage of the smart meter 511. The PI method is a method for discriminating the connection phase from the correlation between the current acquired by the IT switchgear and the power consumption of the smart meter 511.

[0042] (Step S130) The connection phase determination device 10 creates a list of connection phase change transformer candidates. The list of connection phase change transformer candidates is a list in which the single-phase transformers 41,..., 4k connected to the power distribution line 3 are rearranged in a predetermined order. The predetermined order may be, for example, the order of decreasing average power consumption during the target period. Here, the target period may be, for example, one year. The target period preferably includes the period with the lowest power consumption and the period with the highest power consumption within one year. Also, the average power consumption used for the rearrangement is preferably data acquired after all of the single-phase transformers 41,..., 4k that are the targets of connection phase change are installed.

[0043] (Step S140) The connection phase determination device 10 sets the change pattern of the connection phase of the single-phase transformer to be the object of connection phase replacement. Specifically, three patterns of U-V phase, W-U phase, and V-W phase are set.

[0044] (Step S150) The connection phase determination device 10 calculates the maximum value of the unbalance index (unbalance index maximum value U) during the target period for each single-phase transformer. The maximum value of the unbalance index is the maximum unbalance index in the pattern (U-V phase, W-U phase, V-W phase) set in Step S140. Specifically, the maximum unbalance index is the maximum among the unbalance indices when the target single-phase transformer is connected in the U-V phase, the unbalance index when connected in the W-U phase, and the unbalance index when connected in the V-W phase. Here, the unbalance index is an index indicating the degree to which the amounts of power used in the U-V phase, the amounts of power used in the W-U phase, and the amounts of power used in the V-W phase are unbalanced with each other. More specifically, the period for calculating the maximum unbalance index may be the period in which the unbalance index is the maximum among the unbalance indices for each unit period during the target period.

[0045] (Step S160) If the unbalance index of the currently connected connection phase (existing connection phase) is the maximum value U among the unbalance indices of the three patterns connected in Step S150, the connection phase determination device 10 changes the connection phase. The case where the maximum value U of the unbalance index of the existing connection phase is the maximum means that, that is, even if the connection phase is changed from the currently connected connection phase to any connection phase that is not currently connected, the unbalance index decreases.

[0046] (Step S170) The connection phase determination device 10 determines whether or not the maximum unbalance index value U is equal to or greater than a predetermined value as a result of performing the connection phase change. The predetermined value is, that is, the target value of the unbalance index. When the maximum unbalance index value U is equal to or greater than the predetermined value (that is, Step S170; YES), the connection phase determination device 10 ends the process. When the maximum unbalance index value U is less than the predetermined value (that is, Step S170; NO), the connection phase determination device 10 advances the process to Step S180.

[0047] (Step S180) The connection phase determination device 10 then determines whether or not there is a candidate for a single-phase transformer to be determined next. The case where there is no candidate for a single-phase transformer to be determined next means, that is, the case where the determination for all the single-phase transformers connected to the distribution line 3 has been completed. In this case, the connection phase determination device 10 may not be able to achieve the target value of the unbalance index. When there is a candidate for a single-phase transformer to be determined next (that is, Step S180; YES), the connection phase determination device 10 advances the process to Step S140. When there is no candidate for a single-phase transformer to be determined next (that is, Step S180; NO), the connection phase determination device 10 ends the process.

[0048] FIG. 4 is a diagram for explaining an example of the connection of the transformer load to be phase-changed according to the first embodiment. An example of the connection phase change will be described with reference to this figure. In this figure, it shows to which of the U-V phase interval, the W-U phase interval, and the V-W phase interval a plurality of single-phase transformers connected to the distribution line 3 are connected. In this example, an example in the case where nine single-phase transformers from single-phase transformer T1 to single-phase transformer T9 are connected to the distribution line 3 will be described. FIG. 4(A) shows the state before the connection phase change, and FIG. 4(B) shows the state after the connection phase change.

[0049] As shown in FIG. 4(A), the single-phase transformer T1 is connected to the W-U phase interval. Also, the single-phase transformers T2, T3, and T4 are connected to the U-V phase interval. Also, the single-phase transformers T5, T6, T7, T8, and T9 are connected to the V-W phase interval.

[0050] Here, the connection-phase determination device 10 determines about the connection-phase replacement of the single-phase transformer so as to eliminate the imbalance. For example, the connection-phase determination device 10 makes the determination in the order from the single-phase transformer T1 to the single-phase transformer T9. As a result of the determination, when it is determined that the imbalance is eliminated by performing the connection-phase replacement of the single-phase transformers T5 and T6 from the V-W phase interval to the W-U phase interval, the connection-phase replacement is performed as shown in FIG. 4(B). However, in order to actually eliminate the imbalance, it is necessary to perform the connection-phase replacement of the single-phase transformer at the site.

[0051] FIG. 5 is a block diagram showing an example of the functional configuration of the connection-phase determination device according to the first embodiment. With reference to this figure, an example of the functional configuration of the connection-phase determination device 10 will be described. The connection-phase determination device 10 includes an estimation unit 11, an imbalance index calculation unit 12, a comparison unit 13, a determination unit 14, an output unit 15, and a storage unit 16.

[0052] The estimation unit 11 estimates which phase among the three phases of the distribution line (high-voltage distribution line) 3 to which power is transmitted in a three-phase three-wire system the single-phase transformers 41 to 4k, which are transformers connected to the distribution line 3, are currently connected to. Specifically, the estimation unit 11 determines whether the single-phase transformers 41 to 4k are connected to any of the U-V phase interval, the W-U phase interval, and the V-W phase interval, respectively. For example, the estimation unit 11 estimates by a method such as the VV method or the PI method. The estimation unit 11 outputs the determined result to the imbalance index calculation unit 12 as estimation information ESI.

[0053] The imbalance index calculation unit 12 calculates the imbalance index for each single-phase transformer. Specifically, the imbalance index calculation unit 12 calculates the imbalance index in the phase in which the single-phase transformer 41 is estimated to be currently connected and the imbalance index when the single-phase transformer 41 is connected to a phase different from the phase in which it is estimated to be currently connected. Here, the unbalance index indicates the degree to which the amounts of power used in each of the three phases of the distribution line (high-voltage distribution line) 3 are unbalanced with respect to each other. The unbalance index calculation unit 12 outputs the determined result to the comparison unit 13 as calculation information CAI.

[0054] The comparison unit 13 compares the unbalance index in the phase estimated to be currently connected to the single-phase transformer 41 with the unbalance index when connected to a phase different from the phase estimated to be currently connected to the single-phase transformer 41. For example, when it is estimated that the single-phase transformer 41 is connected between the U-V phases, the comparison unit 13 compares the unbalance index between the U-V phases, which is the phase estimated to be currently connected to the single-phase transformer 41, with the unbalance indices when connected between the W-U phases and the V-W phases, which are phases different from the phase estimated to be currently connected to the single-phase transformer 41. The comparison unit 13 outputs the comparison result to the determination unit 14 as comparison information COI.

[0055] The determination unit 14 determines to perform a connection changeover to a phase different from the phase estimated to be currently connected to the single-phase transformer 41 when the unbalance index improves even if the single-phase transformer 41 is connection-changed to any phase different from the phase estimated to be currently connected to the single-phase transformer 41. For example, when it is estimated that the single-phase transformer 41 is connected between the U-V phases, the determination unit 14 determines to perform a connection changeover to the W-U phase or the V-W phase, which is a phase different from the U-V phase, which is the phase estimated to be currently connected to the single-phase transformer 41, when the unbalance index improves even if the single-phase transformer 41 is connection-changed to the W-U phase or the V-W phase, which are phases different from the U-V phase, which is the phase estimated to be currently connected to the single-phase transformer 41. The determination unit 14 outputs the determined result to the output unit 15 as determination information JUI.

[0056] Further, the determination unit 14 determines to perform a connection changeover to the phase in which the unbalance index is further improved. In this case, when it is estimated that, for example, the single-phase transformer 41 is connected between the U-V phases, and the unbalance index improves regardless of which phase between the W-U phases and the V-W phases is reconnected, the determination unit 14 determines to perform the reconnection to the phase in which the unbalance index is more improved among the W-U phases and the V-W phases. That is, the determination unit 14 determines to perform the reconnection to the phase with a more effective connection.

[0057] Here, the determination unit 14 also outputs the determination information JUI, which is the result of the determination, to the unbalance index calculation unit 12. For the transformer determined by the determination unit 14 to perform the reconnection, the unbalance index calculation unit 12 calculates the unbalance index of the other transformers assuming that the reconnection has been performed.

[0058] The unbalance index calculation unit 12 acquires a predetermined default value based on the stored information MEI stored in the storage unit 16. The predetermined default value is the target value of the unbalance index. When the unbalance index has not reached the predetermined default value, the unbalance index calculation unit 12 calculates the unbalance index for the next transformer according to the list of reconnection transformer candidates. When the unbalance index has reached the predetermined default value, the unbalance index calculation unit 12 may end the process.

[0059] The output unit 15 outputs the result determined by the determination unit 14.

[0060] FIG. 6 is a diagram for explaining the method of calculating the unbalance index according to the first embodiment. The method of calculating the unbalance index will be described with reference to this figure. In this figure, with the unbalance index on the vertical axis and time on the horizontal axis, the change in the unbalance index for each time is shown. Here, when the unbalance index calculation unit 12 calculates the unbalance index, a calculation target cell to be evaluated is set. With reference to this figure, the selection of the calculation target cell to be evaluated will be described. The calculation target cell may be, for example, 30 minutes.

[0061] In selecting the calculation target command to be evaluated, first, the unbalance index is calculated for each calculation target command for a predetermined period (for example, one year). Here, specifically, the unbalance index is a value obtained by dividing the value obtained by subtracting the minimum current value from the maximum current value in the calculation target command by the three-phase average current value. That is, the unbalance index indicates the degree to which the power amounts are unbalanced with each other in a predetermined period including a plurality of unit periods (calculation target commands). The connection phase determination device 10 calculates the unbalance index for each calculation target command in this way, and selects the calculation target command with the maximum value as the evaluation target period. The unbalance index calculation unit 12 calculates the unbalance index for the calculation target command that becomes the selected evaluation target period. That is, the unbalance index calculation unit 12 calculates the unbalance index based on the unbalance index in the unit period (calculation target command) in which the unbalance index is the largest among the plurality of unit periods (calculation target commands).

[0062] Note that the predetermined period may be any period that includes the period with the smallest power consumption and the period with the largest power consumption within one year, and is not limited to the example of one year described above.

[0063] FIG. 7 is a diagram showing an example of a list of transformer candidates to be replaced according to the first embodiment. With reference to this figure, the candidates for the transformer to be replaced and the priorities will be described. This figure shows the average power consumption per 30 minutes [kWh / 30min], the connection phase determination result, and the presence or absence of an on-site inspection result for each single-phase transformer connected to the distribution line 3. The average power consumption is the average power consumption in the calculation target command to be evaluated. The connection phase determination result is the result estimated by the estimation unit 11. The presence or absence of an on-site inspection result indicates whether the connection phase of the transformer has been actually inspected on-site by an operator or the like.

[0064] The on-site inspection of the connection phase refers to, for example, following the distribution line 3 from the substation to identify to which phase the single-phase transformer is connected. If the connection phase has been inspected on-site, the connection phase determination by the estimation unit 11 may not be performed. That is, in this embodiment, single-phase transformers with investigation results and single-phase transformers without investigation results may be mixed.

[0065] In an example shown in FIG. 7, specifically, transformers T1 to T5 are shown as candidates for single-phase transformers to be phase-changed. The average power consumption of transformer T1 is "7.1 [kWh / 30 min]", and the connection phase determination result is "W-U phase". The average power consumption of transformer T2 is "4.5 [kWh / 30 min]", and the connection phase determination result is "U-V phase". The average power consumption of transformer T3 is "3.3 [kWh / 30 min]", and the connection phase determination result is "U-V phase". The average power consumption of transformer T4 is "2.5 [kWh / 30 min]", and the connection phase determination result is "U-V phase". The average power consumption of transformer T5 is "2.2 [kWh / 30 min]", and the connection phase determination result is "V-W phase". Among transformers T1 to T5, only transformer T5 has an on-site investigation result of "yes".

[0066] In an example shown in FIG. 7, the priority is determined in the order of transformers T1 to T5. This priority may be, for example, in the order of decreasing average power consumption. In this case, the unbalance index calculation unit 12 calculates for a plurality of transformers connected to the distribution line 3 in the order of decreasing average power consumption, which is a predetermined priority. The comparison unit 13 compares the unbalance indices for a plurality of transformers connected to the distribution line 3 in the order of decreasing average power consumption. The priority is not limited to this example and may be determined considering, for example, the ease of construction.

[0067] FIG. 8 is a diagram for explaining the presence or absence of phase change performed by the connection phase determination device according to the first embodiment. With reference to this figure, an example of the phase change performed by the connection phase determination device 10 will be described. The diagrams shown in FIG. 8 each correspond to a single-phase transformer. Each diagram shows the unbalance index for each connection phase. Also, each diagram shows the presence or absence of connection phase change determined from the unbalance index.

[0068] FIG. 8(A) shows an example of the determination for transformer T1, FIG. 8(B) shows an example of the determination for transformer T2, FIG. 8(C) shows an example of the determination for transformer T3, and FIG. 8(D) shows an example of the determination for transformer T4. The priority order will be described assuming that it is from transformer T1 to transformer T4 in order.

[0069] As shown in FIG. 8(A), transformer T1 is currently connected to the W-U phase. The unbalance index when assuming connection to the U-V phase is 0.35, the unbalance index when assuming connection to the W-U phase is 0.37, and the unbalance index when assuming connection to the V-W phase is 0.39. In this case, if the connection phase is changed from the currently connected W-U phase to the U-V phase, the unbalance index improves from 0.37 to 0.35. However, if the connection phase is changed to the V-W phase, the unbalance index changes from 0.37 to 0.39 and does not improve. Therefore, since the unbalance index does not improve when the connection phase of transformer T1 is changed to the V-W phase, the connection phase determination device 10 determines not to change the connection phase of transformer T1.

[0070] As shown in FIG. 8(B), transformer T2 is currently connected to the U-V phase. The unbalance index when assuming connection to the U-V phase is 0.37, the unbalance index when assuming connection to the W-U phase is 0.35, and the unbalance index when assuming connection to the V-W phase is 0.34. In this case, if the connection phase is changed from the currently connected U-V phase to the W-U phase, the unbalance index improves from 0.37 to 0.35. Further, if the connection phase is changed to the V-W phase, the unbalance index also improves from 0.37 to 0.34. Therefore, since the unbalance index improves regardless of which phase the connection phase is changed to, the connection phase determination device 10 determines to change the connection phase of transformer T2. Specifically, the connection phase determination device 10 determines to change the connection phase to the V-W phase where the unbalance index improves more.

[0071] Here, since it was determined that the phase connection of transformer T2 is to be changed to the V-W phase, the phase connection determination device 10 calculates the unbalance index assuming that the phase connection of transformer T2 has been changed to the V-W phase in subsequent determinations.

[0072] As shown in FIG. 8(C), transformer T3 is currently connected to the U-V phase. The unbalance index when assuming connection to the U-V phase is 0.34, the unbalance index when assuming connection to the W-U phase is 0.33, and the unbalance index when assuming connection to the V-W phase is 0.32. In this case, when the phase connection is changed from the currently connected U-V phase to the W-U phase, the unbalance index improves from 0.34 to 0.33, and when the phase connection is further changed to the V-W phase, the unbalance index also improves from 0.34 to 0.32. Therefore, since the unbalance index improves regardless of which phase the phase connection is changed to, the phase connection determination device 10 determines to perform the phase connection change of transformer T3. Specifically, the phase connection determination device 10 determines to perform the phase connection change to the V-W phase where the unbalance index improves more.

[0073] Here, since it was determined that the phase connection of transformer T3 is to be changed to the V-W phase, the phase connection determination device 10 calculates the unbalance index assuming that the phase connection of transformer T3 has been changed to the V-W phase in subsequent determinations.

[0074] As shown in FIG. 8(D), transformer T4 is currently connected to the U-V phase. The unbalance index when assuming connection to the U-V phase is 0.32, the unbalance index when assuming connection to the W-U phase is 0.29, and the unbalance index when assuming connection to the V-W phase is 0.31. In this case, when the phase connection is changed from the currently connected U-V phase to the W-U phase, the unbalance index improves from 0.32 to 0.29, and when the phase connection is further changed to the V-W phase, the unbalance index also improves from 0.32 to 0.31. Therefore, the connection phase determination device 10 determines that the connection phase of the transformer T4 should be changed because the unbalance index will improve regardless of which phase the connection phase is changed to. Specifically, the connection phase determination device 10 determines that the connection phase should be changed to the W-U phase where the unbalance index improves more.

[0075] Here, since it is determined that the connection phase of the transformer T4 should be changed to the W-U phase, the connection phase determination device 10 calculates the unbalance index assuming that the connection phase of the transformer T4 has been changed to the W-U phase in subsequent determinations.

[0076] Note that when the determination of the transformer T4 is completed, the unbalance index is less than 0.3. For example, if the connection phase determination device 10 sets the condition that the unbalance index is less than 0.3 as the termination condition, the process can be terminated when the determination of the transformer T4 is completed, and it is not necessary to make a determination for the remaining transformers. The predetermined termination condition may be stored in the storage unit 16, for example, and acquired by the unbalance index calculation unit 12.

[0077] [Summary of the First Embodiment] According to the embodiment described above, the connection phase determination device 10 includes an unbalance index calculation unit 12 to calculate the unbalance index when the single-phase transformer is assumed to be connected between each of the U-V phase, W-U phase, and V-W phases, includes a comparison unit 13 to compare the unbalance index in the currently connected phase with the unbalance index when the connection phase is changed to a different phase, includes a determination unit 14 to determine that the connection phase should be changed when the unbalance index improves regardless of which phase the connection phase is changed to, and includes an output unit 15 to output the determined result. Therefore, according to the connection phase determination device 10, it is possible to determine the connection phase change of the single-phase transformer that can reduce the voltage unbalance, and if the connection phase of the single-phase transformer is changed based on the result determined by the connection phase determination device 10, the voltage unbalance can be reduced.

[0078] Here, according to the prior art, when performing connection phase change on one connection phase, even if the unbalance index deteriorates, if it is determined that the unbalance index improves when performing connection phase change on the other connection phase, the connection phase change was performed. In this case, there was a problem that the number of times of performing connection phase change increased. FIG. 11 is a diagram for explaining an example of the connection of a transformer load to be changed according to the prior art. An example of the prior art will be described with reference to this figure. In this figure, it shows to which of the U-V phase interval, W-U phase interval, and V-W phase interval a plurality of single-phase transformers connected to the distribution line 3 are connected. In this example, an example will be described in the case where nine single-phase transformers from single-phase transformer T1 to single-phase transformer T9 are connected to the distribution line 3. FIG. 11(A) shows the state before the connection phase change, and FIG. 11(B) shows the state after the connection phase change.

[0079] As shown in FIG. 11(A), the single-phase transformer T1 is connected to the W-U phase interval. Also, the single-phase transformers T2, T3, and T4 are connected to the U-V phase interval. Further, the single-phase transformers T5, T6, T7, T8, and T9 are connected to the V-W phase interval. According to the prior art, for example, as shown in FIG. 11(B), the connection phase change is performed. As a result of performing the connection change of the single-phase transformers in the three connection phase intervals in this way, the number of times of connection increase and replacement increases. Thus, according to the prior art, there was a problem that the number of times of performing connection phase change increased.

[0080] According to the present embodiment, since the connection phase change is performed when it improves regardless of which phase the connection phase change is made to, the number of times of performing the connection phase change can be reduced.

[0081] In addition, according to the present embodiment, since voltage imbalance can be reduced, power quality can be maintained and improved. Furthermore, by reducing voltage imbalance, the imbalance in equipment utilization is improved, and the power supply capacity can be enhanced. As a result, the power supply cost can be reduced by effectively utilizing the equipment.

[0082] In addition, according to the present embodiment, since the number of connection phase changes can be reduced, the workload of the operator can be decreased. Here, in order to change the connection phase of the single-phase transformer, it may be necessary to temporarily stop the power supply to the low-voltage consumers. Therefore, according to the present embodiment, since the number of connection phase changes can be reduced, the burden on the low-voltage consumers to which the single-phase transformer supplies power can be decreased. Furthermore, an increase in the number of connection phase changes also leads to an increase in the risk of accidents. Therefore, according to the present embodiment, since the number of connection phase changes can be reduced, the risk of accidents can also be reduced.

[0083] In addition, according to the embodiment described above, the determination unit 14 determines that the connection phase change is to be performed to a phase in which the imbalance index is further improved. Therefore, according to the present embodiment, voltage imbalance can be efficiently improved.

[0084] In addition, according to the embodiment described above, the imbalance index calculation unit 12 calculates the imbalance indices for a plurality of transformers connected to the distribution line 3 in order based on a predetermined priority order, and the comparison unit 13 compares the imbalance indices for the plurality of transformers connected to the distribution line 3. That is, the connection phase determination device 10 makes a determination for a plurality of transformers connected to the distribution line 3. Therefore, according to the present embodiment, voltage imbalance can be efficiently improved.

[0085] Further, according to the embodiment described above, for the transformer determined by the determination unit 14 to perform connection phase change, the unbalance index calculation unit 12 calculates the unbalance index assuming that the connection phase change has been performed. That is, according to this embodiment, for the transformer after determination, the unbalance index of the next transformer is calculated in a state where the connection phase change has been performed. Therefore, according to this embodiment, the unbalance of the plurality of transformers connected to the distribution line 3 can be reduced.

[0086] Further, according to the embodiment described above, the connection phase determination device 10 determines the connection phases of the plurality of transformers in descending order of the average power consumption. That is, according to this embodiment, the connection phase change is performed in order from the transformer having a greater effect when the connection phase change is performed. Therefore, according to this embodiment, the number of times of performing the connection phase change can be reduced, and the voltage unbalance can be efficiently reduced.

[0087] Further, according to the embodiment described above, the unbalance index is calculated based on the unbalance index in the unit period in which the unbalance index is the largest among the plurality of unit periods. Therefore, according to this embodiment, the voltage unbalance can be reduced even during the period when the unbalance index becomes large.

[0088] Further, according to the embodiment described above, the period for calculating the unbalance index is specified based on the period including the period with the smallest power consumption and the period with the largest power consumption in a year. Therefore, according to this embodiment, the voltage unbalance can be reduced even during the period when the unbalance index becomes large.

[0089] [Second Embodiment] Next, with reference to FIGS. 9, 10, and 12, the connection phase determination device 10A according to the second embodiment will be described. FIG. 9 is a diagram for explaining the problem to be solved by the connection phase determination device according to the second embodiment. First, with reference to this figure, the problem to be solved by the connection phase determination device 10A according to the second embodiment will be described.

[0090] FIG. 9(A) shows the connection phase to which the transformer T2 is currently connected. Currently, the transformer T2 is connected between the U-V phases. FIG. 9(B) shows the connection phases that are candidates for changing the connection phase. Here, an operator who performs the connection phase change of the single-phase transformer can determine that the transformer T2 is connected between the U-V phases, but it may not be easy to determine which of the distribution lines 3 is the U phase or the V phase. Therefore, the connection phase will be changed from either the U phase or the V phase to the W phase. When the connection phase of the U phase is changed to the W phase, the transformer T2 is connected between the V-W phases. When the connection phase of the V phase is changed to the W phase, the transformer T2 is connected between the W-U phases.

[0091] FIG. 9(C) shows the connection phase to which the transformer T2 is connected after the connection phase change. Since it is not easy for the operator to determine which of the distribution lines 3 is the U phase or the V phase, it is not clear whether the transformer T2 has been changed to be connected between the V-W phases or the W-U phases as a result of the connection phase change. That is, as a result of the connection phase change, the probability of being connected between the V-W phases is 50%, and the probability of being connected between the W-U phases is 50%.

[0092] Therefore, even when the connection phase change of the single-phase transformer is performed based on the result determined by the connection phase determination device 10 by the determination method described in the first embodiment, the operator may not be able to identify the phase for performing the connection phase change of the single-phase transformer, and thus may not be able to achieve the target unbalance index. Therefore, in the present embodiment, it is an object to be able to achieve the target unbalance index even when the operator does not identify the phase for performing the connection phase change of the single-phase transformer.

[0093] Here, even when the operator does not identify the phase for performing the connection phase change of the single-phase transformer, according to the prior art, to some extent, estimation can be made based on the information in the adjacent transformer. FIG. 12 is a diagram for explaining the estimation of the connected phase by an adjacent transformer according to the prior art. With reference to this figure, the estimation of the connected phase based on the information in the adjacent transformer will be described. FIG. 12(A) shows the phase to which the transformer is actually connected, and FIG. 12(B) shows the prediction result.

[0094] Regarding the transformer targeted for the work of changing the connected phase as transformer B, the transformers adjacent to both ends of transformer B are described as transformer A and transformer C. As shown in FIG. 12(A), transformer A is connected between the U-V phases, transformer B is connected between the W-U phases, and transformer C is connected between the V-W phases. At the site, it is not easy to determine which phase each distribution line is. Conventionally, the distribution lines existing on the building side are distinguished as "home", the distribution lines existing on the road side are distinguished as "road", and the distribution lines existing between the distribution lines on the building side and the distribution lines on the road side are distinguished as "middle".

[0095] Here, it is assumed that as a result of the estimation of the connected phase, a result as shown in FIG. 12(B) is obtained. Specifically, it is assumed that the result is that transformer A is connected between the U-V phases, transformer B is connected between the W-U phases, and transformer C is estimated to be between the V-W phases. Since transformer A is connected between "road" and "middle", it can be estimated that either "road" or "middle" is the U phase and the other is the V phase. Also, since transformer B is connected between "home" and "road", it can be estimated that either "home" or "road" is the U phase and the other is the W phase. Also, since transformer C is connected between "home" and "middle", it can be estimated that either "home" or "middle" is the V phase and the other is the W phase. Taking these results into comprehensive consideration, it can be seen that "home" is the W phase, "middle" is the V phase, and "road" is the U phase.

[0096] Thus, even in the prior art, when there are multiple adjacent transformers, by combining the transformer to be worked on, which is the target of connection phase change, with the connection phases (phase A, phase B, phase C) of the adjacent transformers and the connection phase determination results (U-V phase, V-W phase, W-U phase), it was possible to determine the breakdown of the connection phases of the transformer to be worked on. Also, in the case of overhead lines, it was also referred to that the probability of "phase B" being the V phase is high. However, when there are no adjacent transformers, there was a problem that the method according to the prior art could not be used.

[0097] FIG. 10 is a diagram for explaining a connection example of the transformer load to be phase-changed according to the second embodiment. With reference to this figure, a connection example of the transformer to be phase-changed determined by the connection phase determination device 10A according to the second embodiment will be described. The end condition when the connection phase determination device 10A makes a determination will be described as the unbalance index falling below 0.3, similar to the connection phase determination device 10. The connection phase determination device 10A ends the process when the unbalance index falls below 0.3 and does not make a determination for the remaining transformers.

[0098] FIG. 10(A) shows an example of the determination for the transformer T5, FIG. 10(B) shows an example of the determination for the transformer T6, and FIG. 10(C) shows an example of the determination for the transformer T7. The priority order will be described as being the transformer T5 to the transformer T7 in order.

[0099] As shown in FIG. 10(A), the transformer T5 is currently connected to the U-V phase. The unbalance index when assuming connection to the U-V phase is 0.34, the unbalance index when assuming connection to the W-U phase is 0.33, and the unbalance index when assuming connection to the V-W phase is 0.31. In this case, when changing the connection phase from the currently connected U-V phase to the W-U phase, the unbalance index changes from 0.34 to 0.33 and improves, and when further changing the connection phase to the V-W phase, the unbalance index also changes from 0.34 to 0.31 and improves.

[0100] Since the unbalance index improves regardless of which phase is subjected to connection phase change, the connection phase determination device 10A determines to perform connection phase change. Here, the connection phase determination device 10A is common with the connection phase determination device 10 in that it determines to perform connection phase change when the unbalance index improves regardless of which phase is subjected to connection phase change. However, the connection phase determination device 10A is different from the connection phase determination device 10 in that it does not necessarily perform connection phase change to the connection phase with a more improved unbalance index. For example, the connection phase determination device 10A alternately repeats the case of performing connection phase change to the connection phase with a more improved unbalance index and the case of performing connection phase change to the connection phase that is not the connection phase with a more improved unbalance index.

[0101] That is, the unbalance index calculation unit 12 according to the second embodiment calculates the unbalance index while alternately adopting the assumption that the connection change has been performed and the assumption that the connection change has not been performed for the transformer determined by the determination unit 14 to perform connection change.

[0102] Specifically, compared with the case where the connection phase is changed from the currently connected U-V phase to the W-U phase, the unbalance index is more improved when the connection phase is changed to the V-W phase. However, the connection phase determination device 10A performs connection phase change to the W-U phase, which is not the connection phase with a more improved unbalance index. Since it is determined that the connection phase of the transformer T5 is to be changed to the W-U phase, the connection phase determination device 10A calculates the unbalance index assuming that the connection phase of the transformer T5 has been changed to the W-U phase in the subsequent determination.

[0103] As shown in FIG. 10(B), the transformer T6 is currently connected to the U-V phase. The unbalance index when assumed to be connected to the U-V phase is 0.33, the unbalance index when assumed to be connected to the W-U phase is 0.31, and the unbalance index when assumed to be connected to the V-W phase is 0.32. In this case, when the connection phase is switched from the currently connected U-V phase to the W-U phase, the unbalance index improves from 0.33 to 0.31. Further, when the connection phase is switched to the V-W phase, the unbalance index also improves from 0.33 to 0.32.

[0104] Since the unbalance index improves regardless of which phase the connection phase is switched to, the connection phase determination device 10A determines that the connection phase should be switched. Here, in the previous determination (the determination of transformer T5), the connection phase was switched to a connection phase that did not result in a greater improvement in the unbalance index. Therefore, in this determination (the determination of transformer T6), the connection phase will be switched to a connection phase that results in a greater improvement in the unbalance index.

[0105] Specifically, compared to the case where the connection phase is switched from the currently connected U-V phase to the V-W phase, the unbalance index improves more when the connection phase is switched to the W-U phase. However, the connection phase determination device 10A switches the connection phase to the W-U phase, which is the connection phase that results in a greater improvement in the unbalance index. Since it was determined that the connection phase of transformer T6 should be switched to the W-U phase, the connection phase determination device 10A calculates the unbalance index assuming that the connection phase of transformer T6 has been switched to the W-U phase in subsequent determinations.

[0106] As shown in FIG. 10(C), transformer T7 is currently connected to the U-V phase. The unbalance index when assuming connection to the U-V phase is 0.31, the unbalance index when assuming connection to the W-U phase is 0.29, and the unbalance index when assuming connection to the V-W phase is 0.28. In this case, when the connection phase is switched from the currently connected U-V phase to the W-U phase, the unbalance index improves from 0.31 to 0.29. Further, when the connection phase is switched to the V-W phase, the unbalance index also improves from 0.31 to 0.28.

[0107] Since the unbalance index improves regardless of which phase the connection phase is switched to, the connection phase determination device 10A determines that the connection phase should be switched. Here, the connection-phase determination device 10A performed a connection-phase change to a connection phase with a more improved unbalance index in the previous determination (the determination of transformer T6). Therefore, in this determination (the determination of transformer T7), a connection-phase change is performed to a connection phase that is not a connection phase with a more improved unbalance index.

[0108] Specifically, compared with the case where a connection-phase change is made from the currently connected U-V phase to the W-U phase, the unbalance index is more improved when a connection-phase change is made to the V-W phase. However, the connection-phase determination device 10A performs a connection-phase change to the W-U phase, which is not a connection phase with a more improved unbalance index. Since it is determined that a connection-phase change is to be made to the W-U phase for transformer T7, the connection-phase determination device 10A calculates the unbalance index assuming that a connection-phase change has been made to the W-U phase for transformer T7 in subsequent determinations.

[0109] Note that when the determination of transformer T7 is completed, the unbalance index, which is the termination condition, is less than 0.3. Therefore, the connection-phase determination device 10A terminates the process when the determination of transformer T7 is completed, and it is not necessary to perform determinations for the remaining transformers.

[0110] In this embodiment, by alternately repeating the case of performing a connection-phase change to a connection phase with a more improved unbalance index and the case of performing a connection-phase change to a connection phase that is not a connection phase with a more improved unbalance index, even when the operator cannot specify the phase for performing a connection-phase change of the single-phase transformer, the target unbalance index can be achieved. Instead of the above-described embodiment, the object may be achieved by setting the unbalance index as the termination condition to a value smaller than the target value. In this case, for example, when the target value of the unbalance index is 0.3, it may be set to 0.28, which is smaller than 0.3. Also, the object may be achieved by setting the unbalance index after the connection-phase change to the intermediate value of the unbalance indices of the two connection phases.

[0111] [Summary of the Second Embodiment] According to the embodiment described above, the unbalance index calculation unit 12 calculates the unbalance index while alternately assuming that the connection change has been made and that the connection change has not been made for the transformer determined by the determination unit 14 to perform the connection change. Therefore, according to the present embodiment, it is possible to determine whether or not the target value of the final unbalance index is achieved while considering the case where the connection phase change is made to the target connection phase by the operator and the case where the connection phase change is made to a connection phase different from the target. Therefore, according to the present embodiment, even when it is not known which connection phase the operator will change the connection phase to, the target value of the unbalance index can be achieved.

[0112] Note that all or part of the functions of each unit included in the connection phase determination device 10 in the above-described embodiment may be realized by recording a program for realizing these functions on a computer-readable recording medium, reading the program recorded on this recording medium into a computer system, and executing it. Here, the "computer system" is assumed to include hardware such as an OS and peripheral devices.

[0113] In addition, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, etc., and a storage unit such as a hard disk built in a computer system. Further, the "computer-readable recording medium" also includes a communication line such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, which dynamically holds the program for a short time, and a volatile memory inside a computer system that becomes a server or a client in that case, which holds the program for a certain period of time. Also, the above program may be for realizing a part of the above-described functions, and may further be realized in combination with a program already recorded in the computer system for realizing the above-described functions.

[0114] As described above, the embodiments of the present invention have been described with reference to the drawings. However, the specific configuration is not limited to the above-described embodiments, and design changes and the like within the scope not departing from the gist of the present invention are also included.

Description of Reference Numerals

[0115] 1... power distribution network, 10... connection phase determination device, 11... estimation unit, 12... unbalance index calculation unit, 13... comparison unit, 14... determination unit, 15... output unit, 16... storage unit, 2... substation, 3... distribution line, 31... first distribution line, 32... second distribution line, 33... third distribution line, 41... single-phase transformer, 5... low-voltage customer group, 51... low-voltage customer, 6... high-voltage customer group, 61... high-voltage customer, 7... power generation business operator group, 71... power generation business operator, 8... switch

Claims

1. A transformer connected to a high-voltage distribution line that transmits power in a three-phase three-wire system includes an estimation unit that estimates to which of the three phases of the high-voltage distribution line the transformer is currently connected, an unbalance index that indicates the degree to which the amounts of power used in each of the three phases of the high-voltage distribution line are unbalanced with respect to each other, and an unbalance index calculation unit that calculates the unbalance index in the phase in which the transformer is estimated to be currently connected and the unbalance index when the transformer is connected to a phase different from the phase in which the transformer is estimated to be currently connected, a comparison unit that compares the unbalance index in the phase in which the transformer is estimated to be currently connected with the unbalance index when the transformer is connected to a phase different from the phase in which the transformer is estimated to be currently connected, a determination unit that determines to perform a connection phase change to a phase different from the phase in which the transformer is estimated to be currently connected when the unbalance index improves even if the transformer is connected to any phase different from the phase in which the transformer is estimated to be currently connected, and an output unit that outputs the result determined by the determination unit A connection phase determination device comprising:

2. The determination unit determines to perform a connection phase change to a phase in which the unbalance index is further improved. The connection phase determination device according to Claim 1.

3. The unbalance index calculation unit calculates, in order, for a plurality of the transformers connected to the high-voltage distribution line, based on a predetermined priority order, and the comparison unit compares the unbalance indexes for a plurality of the transformers connected to the high-voltage distribution line. The connection phase determination device according to Claim 1 or Claim 2.

4. For the transformer determined by the determination unit to perform a connection phase change, the unbalance index calculation unit calculates the unbalance index assuming that the connection phase change has been performed. The connection phase determination device according to Claim 3.

5. The predetermined priority order is in descending order of average power consumption. The connection phase determination device according to Claim 3 or Claim 4.

6. The unbalance index indicates the degree to which the amounts of power are unbalanced with respect to each other in a predetermined period including a plurality of unit periods, and the unbalance index calculation unit calculates the unbalance index based on the unbalance index in the unit period in which the unbalance index was maximum among the plurality of unit periods. The connection phase determination device according to any one of Claims 1 to 5.

7. The predetermined period includes the period in which the power consumption is the smallest within one year and the period in which the power consumption is the largest. The connection phase determination device according to claim 6.

8. The unbalance index calculation unit calculates the unbalance index while alternately assuming that the connection phase has been changed and that the connection phase has not been changed for the transformer determined by the determination unit to perform connection phase change. The connection phase determination device according to any one of claims 1 to 3.

9. A computer, An estimation step of estimating to which phase of the three phases of the high-voltage distribution line, a transformer connected to the high-voltage distribution line for transmitting power in a three-phase three-wire system, is currently connected; An unbalance index indicating the degree to which the amounts of power used in the respective phases of the three phases of the high-voltage distribution line are unbalanced with each other, the unbalance index in the phase in which the transformer is estimated to be currently connected, and the unbalance index when the transformer is connected to a phase different from the phase in which the transformer is estimated to be currently connected. An unbalance index calculation step for calculating; A comparison step of comparing the unbalance index in the phase in which the transformer is estimated to be currently connected with the unbalance index when the transformer is connected to a phase different from the phase in which the transformer is estimated to be currently connected; A determination step of determining to perform a connection phase change to a phase different from the phase in which the transformer is estimated to be currently connected when the unbalance index improves even if the transformer is connected to any phase different from the phase in which the transformer is estimated to be currently connected; An output step of outputting the result determined by the determination step A program for causing the above to be executed.

Images