JP2024075327A - Determination method and voltage regulating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a determination method and a voltage regulating device capable of determining power transmission direction with greater accuracy.

SOLUTION: A determination method includes: determining in a computer provided in an automatic voltage regulating device whether or not a tap of a tapped regulating transformer provided in the automatic voltage regulator is, among a plurality of taps, an upper limit tap that increases the voltage from the primary side to the secondary side of the automatic voltage regulating device the most, or a lower limit tap that decreases the voltage from the primary side to the secondary side the most; and determining the transmission direction based on the comparison of the amount of change between the voltages on the primary side and the secondary side in the automatic voltage regulating device when the tap is switched to a tap closer to a straight-through tap that passes the voltage directly from the primary side to the secondary side in the automatic voltage regulating device without transformation if it is determined that the tap is the upper limit tap or the lower limit tap.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for determining the direction of power transmission in a voltage regulator, and to a voltage regulator.

It is necessary to keep the system voltage of a power distribution system within a set range. The main cause of fluctuations in the voltage of a power distribution system is load fluctuations at consumers. Other factors include fluctuations due to the power generation status of distributed power sources such as solar power generation. To suppress these fluctuations and keep the voltage within a set range, voltage adjustment devices that switch taps (SVR: Step Voltage Regulator) and devices that adjust the system voltage by adjusting reactive power (SVC: Static Var Compensator) are used.

In recent years, private power generation facilities such as solar power generation facilities have been installed, and such private power generation facilities are beginning to be linked to the power distribution system. As a result, the power distribution system may need to switch systems, i.e., change the connections of substations, due to accidents or other reasons. In such cases, the load side of the SVR may also be switched, resulting in reverse power transmission. Accordingly, thyristor type automatic voltage regulators (TVRs), which use thyristors to improve the responsiveness of tap switching, are also being used.

For this reason, SVRs and TVRs have been developed that have the function of autonomously determining the power transmission direction and controlling the load side voltage by comparing the amount of change in the primary and secondary voltages, impedance, reactive power, etc., as described in Patent Document 1. The power transmission direction (substation direction) indicates which of the primary and secondary sides is the substation side and which is the load side. In addition, an SVR has been proposed that assumes that the load side voltage will rise due to power generation by the distributed power source when reverse current flow occurs, and performs control to fix the load side voltage to a lower tap (fixed tap control during reverse current flow).

These SVRs and TVRs, which have different operating methods, are dotted at various points along the power distribution lines connected to the power distribution system and work in conjunction with each other.

JP 2018-133982 A

The determination of the power transmission direction in a voltage regulator is subject to a non-zero probability of error due to a complex combination of factors such as the power generation status of distributed power sources and inconsistencies in coordination with other voltage regulators. If the power transmission direction is determined incorrectly, the voltage regulator may attach the tap to the limit tap, which is the tap for the greatest voltage increase or decrease to the greatest voltage on the load side, and this may cause problems such as overvoltage or undervoltage on the load side. For this reason, as shown in Patent Document 1, a more accurate method of determining the power transmission direction is required.

The present invention aims to provide a method and voltage regulator that can more accurately determine the direction of power transmission.

In one embodiment of the present disclosure, the determination method is such that a computer provided in an automatic voltage regulator determines whether the tap of a tapped regulating transformer provided in the automatic voltage regulator is, among multiple taps, an upper limit tap that increases the voltage the most from the primary side to the secondary side in the automatic voltage regulator, or a lower limit tap that decreases the voltage the most from the primary side to the secondary side in the automatic voltage regulator, and if it is determined that the tap is the upper limit tap or the lower limit tap, the tap is switched to a tap closer to a straight-through tap that passes the voltage directly from the primary side to the secondary side in the automatic voltage regulator without transformation, and the power transmission direction is determined based on a comparison of the amount of change in voltage between the primary side and the secondary side in the automatic voltage regulator when the tap is switched.

A voltage regulator according to an embodiment of the present disclosure includes a regulating transformer with a tap, a voltage meter for measuring the voltages on the primary and secondary sides, a tap changer for switching the tap of the regulating transformer, and a control unit for controlling the tap changer. The control unit determines whether the tap of the regulating transformer is an upper limit tap that increases the voltage from the primary side to the secondary side the most, or a lower limit tap that decreases the voltage from the primary side to the secondary side the most, and if it is determined that the tap is the upper limit tap or the lower limit tap, instructs the tap changer to switch the tap to a tap closer to a straight-through tap that passes the voltage from the primary side to the secondary side without transforming it, determines the direction of power transmission based on a comparison of the amount of change in the voltage on the primary side and the secondary side when the tap is switched, and controls the voltage value on the load side to a target voltage value based on the determination result.

The determination method and voltage regulation device disclosed herein can forcibly switch taps even when the tap is stuck to the limit tap, and can determine the substation direction during the switch.

According to the present disclosure, even if a system switchover is performed, the power transmission direction can be determined autonomously and more accurately, and the responsiveness to connection changes by the power distribution system can be improved.

1 is a diagram showing a configuration of a voltage regulating device according to an embodiment of the present invention; 5 is a flowchart showing an example of a determination procedure in the voltage regulating device of the present embodiment. 5 is a flowchart showing an example of a determination procedure in the voltage regulating device of the present embodiment. FIG. 11 is a diagram illustrating a configuration of a voltage regulating device according to a second modified example. 4 shows an example of the contents of a table for determining whether a system voltage is abnormal. 11 is a flowchart showing an example of a processing procedure performed by a voltage regulating device in Modification 2.

The present disclosure will be described in detail with reference to the drawings showing the embodiments. In the following embodiment, a voltage regulator to which the determination method of the present disclosure is applied will be described.

Figure 1 is a diagram showing the configuration of a voltage regulator 1 of this embodiment. The voltage regulator 1 of this embodiment includes a series transformer 10, a regulating transformer (tapped transformer) 11, a tap changer 12, a primary voltage meter 13, a secondary voltage meter 14, and a control unit 15.

The series transformer 10 includes a primary winding 101 connected in series to the distribution line L1 of the distribution lines L1 and L2, and a corresponding secondary winding 102.

The regulating transformer 11 includes a tap winding 111 connected in parallel to the distribution lines L1 and L2, and a corresponding control winding 112. The tap winding 111 is provided with a plurality of contacts (switch elements) 113 for selecting a portion (tap) of the tap winding to be used. The taps are, for example, a first tap to a ninth tap. The first tap is a tap for most greatly reducing the voltage on the primary side and outputting it to the secondary side. The fifth tap is a tap for directly outputting the voltage on the primary side to the secondary side without transforming it. The ninth tap is a tap for most greatly increasing the voltage on the primary side and outputting it to the secondary side.

The tap changer 12 switches the tap of the regulating transformer 11 in response to a tap switching command output from the control unit 15. The tap changer 12 is connected to the secondary winding 102 of the series transformer 10, and switches the connection switch between the secondary winding 102 of the series transformer 10 and the contacts 113 corresponding to each tap (the first tap to the ninth tap) of the regulating transformer 11 by driving a motor based on a tap switching command signal. The tap changer 12 may use a thyristor (switch) to switch the connection with the contacts 113 based on a control signal. Note that although the tap changer 12 in FIG. 1 is an indirect switching type, it is of course not limited to this and may be a direct switching type.

The primary voltage meter 13 uses a measurement transformer 131 connected to the primary side of the distribution lines L1 and L2, a digital-to-analog converter (not shown), a moving average processing circuit, etc., to measure and output the primary voltage value. The secondary voltage meter 14 uses a measurement transformer 131 connected to the secondary side of the distribution lines L1 and L2, a digital-to-analog converter (not shown), a moving average processing circuit, etc., to measure and output the secondary voltage value.

The control unit 15 is configured, for example, by a microcomputer, and includes a CPU (Central Processing Unit) 150. The control unit 15 includes a memory 151, such as a ROM (Read Only Memory), a RAM (Random Access Memory), or a flash memory. The control unit 15 includes a timer 152 for measuring elapsed time. The control unit 15 executes the control process described below according to a control program (program product) P1 prestored in the memory 151. A table (not shown) showing the relationship between voltage values and tap positions is stored in the non-volatile storage area of the memory 151.

The control unit 15 includes a voltage regulating relay (90 relay) and a line drop compensator (LDC) to which the output from a current transformer CT that detects the load current flowing through the secondary side of the distribution line is input (neither shown).

The control unit 15 is connected to the control winding 112 of the regulating transformer 11, the tap changer 12, the primary voltage meter 13, and the secondary voltage meter 14. The control unit 15 can recognize which tap has been switched to from the control winding 112 and the tap changer 12. The control unit 15 can obtain the primary voltage value and the secondary voltage value at any timing based on the signals obtained from the primary voltage meter 13 and the secondary voltage meter 14.

The control unit 15 controls the tap changer 12 based on the primary voltage value and the secondary voltage value. By switching the tap, the control unit 15 can gradually adjust the single-phase AC from the primary side from a stepped-down voltage to a stepped-up voltage and distribute it to the secondary side. The control unit 15 basically controls the tap changer 12 to keep the secondary side voltage of the regulating transformer 11 at the target voltage (forward mode). For example, when the voltage detected by the secondary side voltage meter 14 deviates from the allowable range (dead band) of the target voltage, the control unit 15 attempts to adjust the voltage by switching the tap.

In addition, the distribution system to which the voltage regulator 1 is connected may switch systems due to accidents or other reasons, i.e., the connection of the substation may be changed. In response to this, the control unit 15 of the voltage regulator 1 can autonomously determine whether the substation direction is the primary side or the secondary side, and adjust the load side voltage to the target voltage according to the direction. When autonomously controlling according to the substation direction, the control unit 15 determines the substation direction by utilizing the relationship that the voltage change amount on the substation side is smaller than the voltage change amount on the load side when the above-mentioned tap is changed. If the control unit 15 determines that the substation direction is the primary side, it operates in a "forward transmission mode" in which the secondary side is the load side and voltage is adjusted. Conversely, if the control unit 15 determines that the substation direction is the secondary side, it operates in a "reverse transmission mode" in which the primary side is the load side and voltage is adjusted.

The method of determining the substation direction by the voltage regulator 1 of this embodiment will be described below with reference to a flowchart. Figures 2 and 3 are flowcharts showing an example of a determination procedure in the voltage regulator 1 of this embodiment. The control unit 15 executes this process according to the control program P1 stored in the memory 151 when the voltage detected by the primary voltage meter 13 or the secondary voltage meter 14 on the load side deviates from the dead zone of the target voltage.

The control unit 15 refers to the signal from the tap changer 12 (step S101) and determines whether the tap at that time is the upper limit tap (9th tap) or the lower limit tap (1st tap) (step S102).

If it is determined in step S102 that the tap is an upper limit tap or a lower limit tap (S102: YES), the control unit 15 determines whether the operation time limit (extreme operation time limit) for the limit tap (upper limit tap, lower limit tap) is being counted up (step S103). In step S103, the control unit 15 determines whether the count value of the extreme operation time limit, which starts counting (S113) when it is determined in step S103 that the tap is an extreme limit tap (upper limit tap or lower limit tap), is invalid (or zero).

If it is determined that the limit operation time is being counted up (S103: YES), the control unit 15 determines whether the count value of the limit operation time has reached a predetermined upper limit value (step S104).

If it is determined in step S103 that count-up is not in progress (S103: NO), the control unit 15 starts counting the limit operation time using the timer 152 (step S113) and proceeds to step S104.

If it is determined that the count value of the extreme operating time limit has reached a predetermined upper limit value (S104: YES), the timer 152 stops counting the extreme operating time limit (step S105), clears the count value (step S106), and the process proceeds to step S107.

The control unit 15 outputs a tap switching instruction to the tap changer 12 to switch the tap to the through direction (step S107). In step S107, if the tap at that time is the upper limit tap (9th tap), the control unit 15 outputs a tap switching instruction to switch to the 8th tap, and if the tap is the lower limit tap (1st tap), the control unit 15 outputs a tap switching instruction to switch to the 2nd tap.

The control unit 15 determines the substation direction based on the voltage values measured by the primary side voltage meter 13 and the secondary side voltage meter 14 at a predetermined time after the tap switching instruction is output in step S107 (step S108). In step S108, the control unit 15 compares the absolute value of the voltage change amount obtained from the primary side voltage meter 13 with the absolute value of the voltage change amount obtained from the secondary side voltage meter 14. If the difference exceeds a first predetermined value, the control unit 15 determines that the primary side is in the substation direction, and if the difference is less than a second predetermined value that is lower than the first predetermined value, the control unit 15 determines that the secondary side is in the substation direction. If the difference is equal to or greater than the second predetermined value and equal to or less than the first predetermined value, the control unit 15 determines to reserve the determination of the substation direction.

The control unit 15 determines whether or not the determination of the substation direction was reserved in step S108 (step S109). If it is determined that the determination of the substation direction is reserved (S109: YES), the process ends.

When it is determined that the determination of the substation direction is not to be reserved (S109: NO), the control unit 15 determines whether or not it has been determined that the primary side is in the substation direction (step S110). When it is determined that the primary side is in the substation direction (S110: YES), the control unit 15 determines that the control mode is the "forward transmission mode" (step S111) and ends the determination process. In step S111, if the original mode is the "forward transmission mode", the control unit 15 leaves it as it is, and if the original mode is the "reverse transmission mode", the control unit 15 switches the mode to the "forward transmission mode".

If the control unit 15 determines in step S110 that the primary side is not in the direction of the substation (S110: NO), it determines that the secondary side is in the direction of the substation, and the control unit 15 determines that the control mode is "reverse transmission mode" (step S112) and ends the determination process. In step S112, if the original mode is "forward transmission mode", the control unit switches the mode to "reverse transmission mode", and if the original mode is "reverse transmission mode", it leaves it as it is.

In step S104, if it is determined that the count value of the limit operation time has not reached the predetermined upper limit value (S104: NO), the control unit 15 ends the process as is. Note that, if the load side voltage returns to the dead zone of the target voltage outside the process shown in Figures 2 and 3, the count value of the limit operation time during counting up is decremented by the time the load side voltage has returned to the dead zone of the target voltage.

If it is determined in step S102 that the tap is not the upper limit tap or the lower limit tap (S102: NO), the control unit 15 determines whether or not the operation time limit in steady operation is being counted up (step S114). In step S114, the control unit 15 determines whether or not the count value of the operation time limit at which counting is started (S119) when it is determined that the voltage has deviated from the target voltage value and is not being counted up, is invalid (or zero).

If it is determined in step S114 that count-up is not in progress (S114: NO), the control unit 15 starts counting the operation time limit by the timer 152 (step S119) and proceeds to step S115. If it is determined in step S114 that count-up is in progress (S114: YES), the control unit 15 proceeds to step S115.

The control unit 15 determines whether the count value of the operation time limit has reached a predetermined upper limit value (step S115). Note that, if the load side voltage returns to the dead zone of the target voltage outside the processing shown in FIG. 2 and FIG. 3, the count value of the operation time limit being counted up is decremented by the time the load side voltage has returned to the dead zone of the target voltage.

If it is determined that the count value of the operation time limit has reached a predetermined upper limit value (S115: YES), the timer 152 stops counting the operation time limit (step S116), clears the count value (step S117), and the process proceeds to step S118.

The control unit 15 outputs a tap switching instruction to the tap changer 12 to switch the tap to the target voltage side (to increase or decrease the target voltage side) (step S118). In step S118, for example, if the tap at that time is the second tap and needs to be lowered, the control unit 15 outputs a tap switching instruction to switch to the first tap.

When the control unit 15 switches the tap in step S118, it proceeds to step S108, executes the process of determining the substation direction and setting the mode in steps S108 to S112 during the tap switching period, and ends the process.

If it is determined in step S115 that the count value of the operation time limit has not reached the predetermined upper limit value (S115: NO), the control unit 15 ends the process as is. In this case, too, if the load side voltage returns to the dead zone of the target voltage outside the process shown in Figures 2 and 3, the count value of the operation time limit being counted up is decremented by the time the load side voltage has returned to the dead zone of the target voltage.

In this way, even if the voltage on the secondary side needs to be increased further but the tap is already at the ninth tap and cannot be increased any further, the voltage regulator 1 performs a process to switch the tap to the pass-through side (the side closer to the fifth tap, which is neither higher nor lower). Conversely, the voltage regulator also performs the same process even if the tap needs to be lowered further but the tap is already at the first tap and cannot be decreased any further. This makes it possible to re-determine the substation direction even if the tap is stuck at the limit tap, improving responsiveness to connection changes by the distribution system.

In this way, if the voltage on the controlled side deviates from the dead zone and the limit operation time count reaches the upper limit, tap switching can be performed almost forcibly, and a situation in which the voltage regulator 1 stops with the tap stuck at the limit tap can be avoided.

The tap switching process based on the "operation time limit count" and "ultimate operation time limit count" in the processes shown in Figures 2 and 3 can be applied to both fixed-time type voltage regulation control and integral type voltage regulation control.

(Variation 1)
The configuration of the voltage regulator 1 of this embodiment and the process described with reference to Figures 2 and 3 can improve the responsiveness of the substation to system switching and more accurately determine the substation direction. A state in which the secondary side needs to be further boosted even though the tap is the ninth tap, or a state in which the secondary side needs to be further lowered even though the tap is the first tap, can also occur when the system voltage of the distribution system is extremely high or low. In the modified example, the voltage regulator 1 performs control by distinguishing between a case in which the tap is stuck to the limit tap because the substation direction is erroneously determined, and a case in which the tap is stuck to the limit tap because the system voltage is abnormal.

In the process shown in FIG. 2 and FIG. 3, the control unit 15 of the voltage regulator 1 determines that the count value of the limit operation time limit has reached the upper limit and stores the fact that the limit count has been reached together with time information in the non-volatile storage area of the memory 151 each time the process of switching the tap is executed (S104: YES, S107). The control unit 15 may then store the substation direction (forward/reverse) determined in S111 or S112. In this case, the control unit 15 periodically derives the frequency at which the limit count has been reached, or the frequency at which the determination of the substation direction is switched, based on these memories, and compares it with a predetermined frequency. If the derived frequency is higher than the predetermined frequency, the control unit 15 determines that a change in the connection of the distribution system has occurred, making it easy for an erroneous determination to occur, and continues to make highly responsive determinations based on the flowcharts of FIG. 2 and FIG. 3.

When the derived frequency is equal to or lower than a predetermined frequency, the control unit 15 determines that the distribution system connection has not been changed, but that the system voltage has increased or decreased excessively. In this case, the control unit 15 stores the system abnormality in the memory 151, and may output a control signal for turning on a warning light or the like (not shown) provided in the voltage regulator 1 in a predetermined pattern, or a notification signal to an external device.

(Variation 2)
The control unit 15 of the voltage regulating device 1 may be configured to function as an undervoltage relay and an overvoltage relay in addition to the components shown in Fig. 1. In the second modification, the control unit 15 uses the detection results of these functions to distinguish whether the tap is stuck at the limit tap because the substation direction is erroneously determined, or the tap is stuck at the limit tap because the system voltage is abnormal. In the second modification, the control unit 15 also stores a table 154 for determination, which will be described later, in the memory 151. Fig. 4 is a diagram showing the configuration of the voltage regulating device 1 in the second modification.

The voltage regulator 1 in the second modification basically executes the processing steps shown in the flowcharts of FIG. 2 and FIG. 3, but also executes a determination of system voltage abnormality using table 154, which will be described later.

Figure 5 shows an example of the contents of table 154 for determining system voltage abnormality. Table 154 shown in Figure 5 shows a pattern in which the substation direction may be incorrect. Table 154 includes items such as the determination result of the substation direction, the voltage values of the primary and secondary sides, and the output of the undervoltage relay function and the overvoltage relay function of digital relay 153. For example, if the determined substation direction is the primary side, neither undervoltage nor overvoltage is detected, and the tap is the first tap or the ninth tap, the control unit 15 can determine that there is a possibility of an erroneous determination. If the determined substation direction is the primary side, and an undervoltage or overvoltage is detected in the primary side voltage, the control unit 15 can determine that there is a possibility of an erroneous determination. Also, if the determined substation direction is the secondary side, neither undervoltage nor overvoltage is detected, and the tap is the first tap or the ninth tap, the control unit 15 can determine that there is a possibility of an erroneous determination. If the determined substation direction is the secondary side and an undervoltage or overvoltage is detected in the secondary voltage, the control unit 15 can determine that an erroneous judgment may have occurred.

In a situation that is included in the pattern of table 154 shown in FIG. 5, the tap can be switched in the straight-through direction and the substation direction can be determined by the processing procedure shown in the flowcharts of FIG. 2 and FIG. 3, improving responsiveness to switching of the substation direction. And, if the situation is not included in the pattern of table 154 shown in FIG. 5 and the tap position remains stuck at the first tap or the ninth tap, it can be determined that there is a possibility of a system voltage abnormality.

Figure 6 is a flowchart showing an example of a processing procedure by the voltage regulator 1 in Modification 2. The control unit 15 of the voltage regulator 1 executes the processing procedure in Figure 6 each time a predetermined time has elapsed, when the dead zone of the target voltage has been exceeded, or when an undervoltage or overvoltage is detected.

The control unit 15 refers to the signal from the tap changer 12 (step S121) and determines whether the tap at that time is the upper limit tap (first tap) or the lower limit tap (ninth tap) (step S122).

If it is determined to be an upper limit tap or a lower limit tap (S122: YES), the control unit 15 determines whether the substation direction, tap position, and detection results by the undervoltage relay or overvoltage relay function that can be determined based on the control mode match the patterns in table 154 (step S123). In step S123, the control unit 15 can determine that in the "forward transmission mode", the substation direction has most recently been determined to be the primary side, and that in the "reverse transmission mode", the substation direction has most recently been determined to be the secondary side.

When the control unit 15 determines that the substation direction, tap position, and detection result match the pattern in table 154 (S123: YES), it executes a process of determining the substation direction by tap switching (step S124) and ends one processing cycle. In step S124, the control unit 15 executes the process equivalent to steps S103 to S112 shown in the flowcharts of Figures 2 and 3.

When the control unit 15 determines that the substation direction, tap position, and detection result do not match the pattern in table 154 (S123: NO), it determines that there is a system voltage abnormality, notifies this (step S125), and ends one processing round. As in the first modification, the notification of the system voltage abnormality may be sent to a warning light or the like (not shown) or an external device. Depending on the settings, the control unit 15 may at least temporarily stop the operation of the voltage adjustment device 1.

The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not by the above meaning, and is intended to include all modifications within the meaning and scope of the claims.

Regarding multiple claims described in the claims, they may be combined with each other regardless of the form of reference. The claims describe multiple dependent claims that depend on multiple claims. The claims do not describe multiple dependent claims that depend on multiple dependent claims, but multiple dependent claims that depend on multiple dependent claims may be described.

REFERENCE SIGNS LIST 1 Voltage regulator 10 Series transformer 11 Regulating transformer 12 Tap changer 13 Primary voltage meter 14 Secondary voltage meter 15 Control unit (computer)
150 CPU

Claims (5)

A computer provided in the automatic voltage regulator,
determining whether or not a tap of a tapped regulating transformer included in the automatic voltage regulator is an upper limit tap among a plurality of taps that most greatly increases voltage from the primary side to the secondary side in the automatic voltage regulator, or a lower limit tap that most greatly decreases voltage from the primary side to the secondary side;
When it is determined that the tap is the upper limit tap or the lower limit tap, the tap is switched to a tap closer to a plain tap that passes voltage directly from the primary side to the secondary side in the automatic voltage regulator without transformation;
A method for determining a power transmission direction based on a comparison of changes in primary and secondary voltages in the automatic voltage regulator when a tap is changed. The computer includes:
2. The method according to claim 1, further comprising the steps of: switching the tap to a tap closer to the through tap and determining the power transmission direction when the load-side voltage value of the automatic voltage regulator deviates from an allowable range of the target voltage value and an extreme tap state in which the tap remains at the upper limit tap or the lower limit tap continues for a predetermined count upper limit value or more. The computer includes:
The method according to claim 2 , further comprising the steps of: switching the tap to a tap closer to the plain tap and determining a power transmission direction based on a frequency of the extreme tap state. The computer includes:
The method according to claim 1, further comprising: switching the tap to a tap closer to the through tap and determining the power transmission direction when an undervoltage or an overvoltage is detected only for the voltage on the power transmission source side based on a result of a previous power transmission direction determination. A regulating transformer with taps;
A voltage measuring instrument for measuring the voltage on the primary side and the voltage on the secondary side,
a tap changer for changing a tap of the regulating transformer;
A control unit for controlling the tap changer,
The control unit is
determining whether the tap of the regulating transformer is an upper limit tap that most greatly increases the voltage from the primary side to the secondary side or a lower limit tap that most greatly decreases the voltage from the primary side to the secondary side among a plurality of taps;
When it is determined that the tap is the upper limit tap or the lower limit tap, instruct the tap changer to switch the tap to a tap closer to a plain tap that passes the voltage directly from the primary side to the secondary side without transformation;
determining a power transmission direction based on a comparison of changes in the primary and secondary voltages when a tap is changed;
A voltage regulator that controls the load side voltage value to reach a target voltage value based on the judgment result.

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