Automatic voltage balancing device and automatic voltage balancing method

Abstract

To provide an automatic voltage balancing device and an automatic voltage balancing method that can improve a three-phase unbalanced voltage in a distribution line.SOLUTION: An automatic voltage balancing device is composed of a transformer portion and a control portion. The transformer portion connects a tap changer composed of a mechanical diverter switch and a tap selector in series with a distribution line, and the tap changer changes the tap while the transformer portion is being operated. When a substation is connected to a primary side, the control portion calculates an average value of a primary voltage of the tap changer, and controls the voltage such that a secondary voltage of each phase approaches the average value. When the substation is connected to a secondary side, the control portion calculates an average value of a secondary voltage of the tap changer, and controls the voltage such that the primary voltage of each phase approaches the average value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an automatic voltage balancing device and an automatic voltage balancing method that can reduce the self-capacitance required for the voltage adjustment function, thereby achieving miniaturization and cost reduction. [Background technology]

[0002] In recent years, it has become clear that there are distribution lines with significant voltage imbalances at the outset of substations, making voltage management more difficult.Conventionally, voltage regulators have been known to be installed along high-voltage distribution lines, and they automatically select taps in response to fluctuations in load current to adjust fluctuations in line voltage.

[0003] For example, an automatic voltage regulator (SVR: Step Voltage Regulator) is known that adjusts the output voltage to a constant level by providing a tap on an autotransformer and switching the tap with an on-load tap changer (see Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2011-55599 [Patent Document 2] Patent Publication No. 2017-85715 [Non-Patent Document 1] Aichi Electric Technical Report No. 38, March 17, 2017, p. 31 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional SVRs are designed so that the on-load tap changer operates on all three phases at once, so they can only adjust the voltage on all three phases at once and cannot correct three-phase unbalanced voltages.

[0006] Apart from SVRs, automatic voltage regulators (TVRs: Thyristor-type step voltage regulators) that use thyristors for tap switching are also known as voltage regulating devices. Recent TVRs include those with a three-phase voltage balancing function (see Patent Document 2 and Non-Patent Document 1 above).

[0007] A TVR with a three-phase voltage balancing function can also improve voltage imbalance.

[0008] However, as mentioned above, TVRs use thyristors for tap switching, and because of the characteristics of semiconductor elements, they have a problem of lower short-circuit current resistance compared to SVRs that use mechanical contacts. This means that if an external short circuit occurs on a distribution line, there is a risk that the thyristors that make up the TVR will fail due to an increase in temperature.

[0009] Therefore, an object of the present invention is to provide an automatic voltage balancing device and an automatic voltage balancing method that can solve the problem of small short-circuit current capacity while reducing the self-capacitance required for the voltage adjustment function, thereby achieving a smaller and less expensive device.

[0010] The invention described in claim 1 is an automatic voltage balancing device that is installed on a three-phase high-voltage distribution line and improves the imbalance of three-phase voltage, and is composed of a transformer section and a control section, and the transformer section has a tap changer consisting of a mechanical diverter switch and a tap selector connected in series to the distribution line, and the tap changer changes the tap while the transformer section is operating, and the control section is characterized in that, when the connection direction of the substation is the primary side, it calculates the average value of the primary voltage of the transformer section and controls the secondary voltage of each phase of the transformer section to approach the average value.

[0011] The invention described in claim 2 is an automatic voltage balancing device that is installed on a three-phase high-voltage distribution line and improves the imbalance of three-phase voltage, and is composed of a transformer section and a control section, and the transformer section has a tap changer consisting of a mechanical diverter switch and a tap selector connected in series to the distribution line, and the tap changer changes the tap while the transformer section is operating, and the control section is characterized in that, when the connection direction of the substation is the secondary side, it calculates the average value of the secondary voltage of the transformer section and controls the voltage so that the primary voltage of each phase of the transformer section approaches the average value.

[0012] The invention described in claim 3 is characterized in that the control unit described in claim 1 is configured to switch the tap of the tap selector when the difference between the average value and the secondary voltage exceeds the dead band width.

[0013] The invention of claim 4 is characterized in that the control unit of claim 2 is configured to switch the tap of the tap selector when the difference between the average value and the primary voltage exceeds the dead band width.

[0014] The invention described in claim 5 is characterized in that the control unit described in claim 1 is configured to switch the tap of the tap selector when the time during which the difference between the average value and the secondary voltage exceeds the dead band width exceeds a certain period of time.

[0015] The invention of claim 6 is characterized in that the control unit of claim 2 is configured to switch the tap of the tap selector when the time during which the difference between the average value and the primary voltage exceeds the dead band width exceeds a certain time.

[0016] The invention as set forth in claim 7 is characterized in that the transformer section as set forth in any one of claims 1 to 6 is a single-winding Y-connection.

[0017] The invention described in claim 8 is characterized by a method for calculating an average value of the primary voltage and controlling the voltage so that the secondary voltage of each phase approaches the average value in the automatic voltage balancing device described in claim 1 that is installed on a three-phase high-voltage distribution line and improves the imbalance of three-phase voltage.

[0018] The invention described in claim 9 is characterized by a method for calculating an average value of secondary voltages and controlling voltages so that the primary voltages of each phase approach the average value in the automatic voltage balancing device described in claim 2 that is installed on a three-phase high-voltage distribution line and improves the imbalance of three-phase voltages. [Effects of the Invention]

[0019] According to the inventions of claims 1 and 2, the use of a mechanical switch for tap switching increases the short-circuit current withstand capability. Also, even if the connection direction of the substation changes due to system switching, the voltage in the load direction can always be made close to the average value of the voltage in the substation connection direction.

[0020] According to the invention of claim 3, it is possible to prevent excessive switching operations from being performed in response to voltage fluctuations in which the difference between the average value of the primary voltage of the transformer section and the secondary voltage of each phase of the transformer section is small.

[0021] According to the invention of claim 4, it is possible to prevent excessive switching operations from being performed in response to voltage fluctuations in which the difference between the average value of the secondary voltage of the transformer section and the primary voltage of each phase of the transformer section is small.

[0022] According to the inventions of claims 5 and 6, it is possible to prevent unnecessary tap changing operations from being performed in response to instantaneous voltage fluctuations.

[0023] According to the invention of claim 7, it is possible to realize the advantages of an autotransformer, such as a smaller device, lighter weight, and lower cost.

[0024] According to the invention described in claim 8, voltage control is performed so that the secondary voltage of each phase approaches the average value of the primary voltage, thereby making it possible to reduce the self-capacity of the automatic voltage balancing device, thereby enabling the device to be made smaller and less expensive.

[0025] According to the invention described in claim 9, voltage control is performed so that the primary voltage of each phase approaches the average value of the secondary voltage, thereby reducing the self-capacity of the automatic voltage balancing device and enabling the device to be made smaller and less expensive. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a circuit diagram of an automatic voltage balancing device according to the present invention; [Figure 2] FIG. 2 is a control block diagram illustrating an automatic voltage balancing method in the present invention when a substation is connected to the primary side. [Figure 3] FIG. 10 is a waveform diagram showing the transition of voltage values ​​during individual control of each phase by the automatic voltage balancing method in the case where a substation is connected to the primary side in the present invention. [Figure 4] FIG. 2 is a control block diagram illustrating an automatic voltage balancing method in the present invention when a substation is connected to the secondary side. [Figure 5] FIG. 10 is a waveform diagram showing the transition of voltage values ​​during individual control of each phase by the automatic voltage balancing method in the case where a substation is connected to the secondary side in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 5. Fig. 1 is an example of a circuit configuration diagram showing an automatic voltage balancing device A according to the present invention. The automatic voltage balancing device A shown in Fig. 1 is generally composed of a transformer section A1 and a control section A2, and reference numeral 1 denotes a mechanical change-over switch connected in series to each phase of a three-phase high-voltage distribution system. The change-over switch can be, for example, a vacuum valve with contacts sealed inside the vacuum valve.

[0028] Reference numeral 2 denotes a tap selector connected to the changeover switch 1 of each phase of the three-phase high-voltage distribution system, and 3 denotes a current-limiting resistor attached to the changeover switch 1 that limits the circulating current that flows when the two taps are bridged when the taps are changed by the tap selector 2.

[0029] The tap changer 4 of the transformer section A1 is composed of the diverter switch 1, current limiting resistor 3, and tap selector 2. This tap changer 4 makes it possible to change the tap while the transformer section A1 is still in operation.

[0030] Reference numeral 5 denotes a primary voltage acquisition VT connected in parallel between the lines of a distribution line to acquire the primary voltage of each phase, and reference numeral 6 denotes a secondary voltage acquisition VT connected in parallel between the lines of a distribution line to acquire the secondary voltage of each phase.

[0031] A2 is a control unit that controls the switching of the taps of the tap selector 2. The voltage adjusted by the tap switching of the tap selector 2 is added to the secondary voltage of the tap changer 4, and adjusts the voltage of the distribution line so that it approaches the reference voltage.

[0032] Next, we will explain the automatic voltage balancing method of the present invention when a substation is connected to the primary side of the automatic voltage balancing device A shown in Fig. 1. The automatic voltage balancing device A shown in Fig. 1 constantly acquires the primary voltage of each phase via the primary voltage acquisition VT5 by the control unit A2. It also acquires the secondary voltage of each phase via the secondary voltage acquisition VT6.

[0033] As shown in FIG. 2, the control unit A2 receives the primary voltage V U1 , V V1 , V W1 to the average value of the primary voltage (input voltage) V AVE Calculate.

[0034] Next, the average value V AVE The secondary voltage V of each phase acquired by VT6 for secondary voltage acquisition U2 , V V2 , V W2 Compared with the difference ΔV U , ΔV V , ΔV W Then, calculate the difference |ΔV U |, |ΔV V |, |ΔV W | is compared with the preset dead band voltage Vd, and the difference |ΔV U |, |ΔV V |, |ΔV WIf | is greater than the dead band voltage Vd, it is determined that a voltage imbalance has occurred in each phase, and a count (time limit count) is started for a preset fixed time.

[0035] In more detail, the difference |ΔV U When | is greater than the dead band voltage Vd, ΔV U is large on the positive side or large on the negative side, and similarly, the difference |ΔV V When | is greater than the dead band voltage Vd, ΔV V is large on the positive side or large on the negative side, and similarly, the difference |ΔV W When | is greater than the dead band voltage Vd, ΔV W may be large on the positive side or large on the negative side.

[0036] And the difference |ΔV U |, |ΔV V |, |ΔV W If the time (time limit count) during which | is greater than the dead band voltage Vd has elapsed, a tap change command for each phase (U phase, V phase, W phase) is output to the tap selector 2 and the changeover switch 1 shown in Figure 1, and the tap of the tap selector 2 is changed. Here, the tap change is performed when the secondary voltage (output voltage) is equal to the average value V of the primary voltage (input voltage). AVE Specifically, the difference ΔV U、 ΔV V , ΔV W is greater than the dead band voltage Vd on the positive side, after a certain time has passed, the secondary voltage AVE Lower the tap so that it approaches the difference ΔV U , and ΔV V , ΔV W is greater than the dead band voltage Vd on the negative side, after a certain time has passed, the secondary voltage AVE Raise the tap so that it approaches

[0037] In this way, the voltage of each phase is calculated as the average value V AVE By controlling the voltage to approach the voltage imbalance of each phase, the voltage imbalance of each phase is improved.

[0038] FIG. 3 shows an example of the voltage adjustment result in the automatic voltage balancing device A of the present invention, where the difference |ΔV UV | is larger than the dead band voltage Vd on the positive side, and the difference |ΔV V 10 is a waveform diagram showing the transition of the secondary voltage adjusted by raising and lowering the tap of the tap selector 2 when | is larger on the negative side than the dead band voltage Vd.

[0039] As shown in Figure 3, the difference |ΔV U If the time period during which | is greater than the dead band voltage Vd on the positive side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to lower the U-phase tap by one tap.

[0040] As a result, the adjustment voltage resulting from lowering one tap is added to the secondary voltage of the tap changer 4 shown in Figure 1, and the secondary voltage (output voltage) V UV2 is lowered, and the average value V AVE approaching.

[0041] In this way, by lowering the tap of the U phase by one tap, the secondary voltage (output voltage) of the U phase, V U falls within the dead zone, so no further tap-down operation is performed.

[0042] On the other hand, the difference |ΔV V If the time period during which | is greater than the dead band voltage Vd on the negative side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to raise the V-phase tap by one tap.

[0043] As a result, the adjustment voltage resulting from raising the secondary voltage by one tap is added to the tap changer 4 shown in Figure 1, and the V-phase secondary voltage (output voltage) V V is raised, and the average value V AVE approaching.

[0044] By raising the V phase tap by one tap, the V phase secondary voltage (output voltage) V V is the average value V AVEHowever, since it is still outside the dead zone, the control unit A2 Again, the difference |ΔV V When it detects that | is greater than the dead band voltage Vd on the negative side, it starts counting a fixed time limit.

[0045] And the difference |ΔV V If the time period during which | is greater than the dead band voltage Vd on the negative side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to raise the V-phase tap by one more tap, and raises the tap of the tap selector 2 by one more tap.

[0046] As a result, the adjustment voltage resulting from raising the secondary voltage of the tap changer 4 shown in Figure 1 by two taps is added, and the V-phase secondary voltage (output voltage) V V is raised, and the average value V AVE Get even closer to.

[0047] As a result, the V-phase secondary voltage (output voltage) V V falls within the dead band, so no further tap-up operation is performed.

[0048] In this way, the automatic voltage balancing device A of the present invention calculates the difference |ΔV U |, |ΔV V | is compared with the preset dead band voltage Vd, and the difference |ΔV U |, |ΔV V If | is greater than the dead band voltage Vd, it is determined that a voltage imbalance has occurred in each phase, but if the voltage imbalance continues for less than a preset time (time limit count), no control is performed to improve the unbalanced voltage. This is to prevent tap changing in response to instantaneous voltage fluctuations.

[0049] In Figure 3, after two taps have been raised, the V-phase primary voltage V V voltage drop, and the secondary voltage V V Although the value deviates from the dead band width, the time is shorter than the preset fixed time (time limit count), so the control to raise the tap is not executed.

[0050] In addition, the automatic voltage balancing device A of the present invention calculates the average value V of the primary voltage (input voltage). AVE is used as the reference voltage, and the secondary voltage is the average value V AVE Since the voltage is controlled to approach the reference voltage, the tap voltage range required for adjustment can be narrowed compared to when an arbitrary reference voltage is set, and the self-capacity of the voltage adjustment function can be reduced, resulting in a smaller device and lower cost.

[0051] Furthermore, since the transformer section of the automatic voltage balancing device A of the present invention is a single-winding Y-connection, the primary and secondary sides use the same windings, which reduces the amount of winding used compared to a compound-winding transformer, thereby achieving a smaller, lighter, and less expensive device.

[0052] Next, we will explain the automatic voltage balancing method of the present invention when a substation is connected to the secondary side of the automatic voltage balancing device A shown in Fig. 1. The automatic voltage balancing device A shown in Fig. 1 constantly acquires the primary voltage of each phase via the primary voltage acquisition VT5 by the control unit A2. It also acquires the secondary voltage of each phase via the secondary voltage acquisition VT6.

[0053] As shown in FIG. 4, the control unit A2 converts the secondary voltage V U , V V , V W to the average value of the secondary voltage (input voltage) V AVE Calculate.

[0054] Next, the average value V AVE The primary voltage V between each line captured by VT5 for primary voltage acquisition U1 , V V1 , V W1 Compared with the difference ΔV U , ΔV V , ΔV W Then, calculate the difference |ΔV U |, |ΔV V |, |ΔV W | is compared with the preset dead band voltage Vd, and the difference |ΔV U |, |ΔV V |, |ΔVW If | is greater than the dead band voltage Vd, it is determined that a voltage imbalance has occurred in each phase, and a count (time limit count) is started for a preset fixed time.

[0055] In more detail, the difference |ΔV U When | is greater than the dead band voltage Vd, ΔV U is large on the positive side or large on the negative side, and similarly, the difference |ΔV V When | is greater than the dead band voltage Vd, ΔV V is large on the positive side or large on the negative side, and similarly, the difference |ΔV W If | is greater than the dead band voltage Vd, ΔV W may be large on the positive side or large on the negative side.

[0056] And the difference |ΔV U |, |ΔV V |, |ΔV W If the time (time limit count) during which | is greater than the dead band voltage Vd has elapsed, a tap change command for each phase (U phase, V phase, W phase) is output to the tap selector 2 and the changeover switch 1 shown in Figure 1, and the tap of the tap selector 2 is changed. Here, the tap change is performed when the primary voltage (output voltage) is equal to the average value V of the secondary voltage (input voltage). AVE Raise and lower it to get closer to .

[0057] Specifically, the difference ΔV U、 ΔV V、 ΔV W is greater than the dead band voltage Vd on the positive side, after a certain time has passed, the primary voltage AVE Lower the tap so that it approaches the difference ΔV U , ΔV V , ΔV W is greater than the dead band voltage Vd on the negative side, after a certain time has passed, the primary voltage AVE Raise the tap so that it approaches

[0058] In this way, the voltage of each phase is calculated as the average value V AVEBy controlling the voltage to approach the voltage imbalance of each phase, the voltage imbalance of each phase is improved.

[0059] FIG. 5 shows an example of the voltage adjustment result in the automatic voltage balancing device A of the present invention, where the difference |ΔV U | is larger than the dead band voltage Vd on the positive side, and the difference |ΔV V 10 is a waveform diagram showing the transition of the secondary voltage adjusted by raising and lowering the tap of the tap selector 2 when | is larger on the negative side than the dead band voltage Vd.

[0060] As shown in Figure 5, the difference |ΔV U If the time period during which | is greater than the dead band voltage Vd on the positive side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to lower the U-phase tap by one tap.

[0061] As a result, the adjustment voltage resulting from lowering one tap is added to the secondary voltage of the tap changer 4 shown in Figure 1, and the primary voltage (output voltage) V U2 is lowered, and the average value V AVE approaching.

[0062] In this way, by lowering the tap of the UV phase by one tap, the primary voltage (output voltage) of the U phase, V U1 falls within the dead zone, so no further tap-down operation is performed.

[0063] On the other hand, the difference |ΔV V If the time period during which | is greater than the dead band voltage Vd on the negative side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to raise the V-phase tap by one tap.

[0064] As a result, the adjustment voltage resulting from raising the secondary voltage by one tap is added to the tap changer 4 shown in Figure 1, and the V-phase primary voltage (output voltage) V V1 is raised, and the average value V AVE approaching.

[0065] By raising the V phase tap by one tap, the V phase primary voltage (output voltage) V VW1 is the average value V AVE However, since it is still outside the dead zone, the control unit A2 Again, the difference |ΔV V When it detects that | is greater than the dead band voltage Vd on the negative side, it starts counting a fixed time limit.

[0066] And the difference |ΔV V If the time period during which | is greater than the dead band voltage Vd on the negative side continues to exceed a certain time set by the time limit count, the control unit A2 outputs a switching command to the tap selector 2 to raise the V-phase tap by one more tap, and raises the tap of the tap selector 2 by one more tap.

[0067] As a result, the adjustment voltage resulting from raising the secondary voltage by two taps is added to the tap changer 4 shown in Figure 1, and the primary voltage (output voltage) V of the VW phase is increased. V1 is raised, and the average value V AVE Get even closer to.

[0068] As a result, the V-phase primary voltage (output voltage) V VW1 falls within the dead band, so no further tap-up operation is performed.

[0069] In this way, the automatic voltage balancing device A of the present invention calculates the difference |ΔV U |, |ΔV V |, |ΔV W | is compared with the preset dead band voltage Vd, and the difference |ΔV U |, |ΔV V |, |ΔV W If | is greater than the dead band voltage Vd, it is determined that a voltage imbalance has occurred in each phase, but if the voltage imbalance continues for less than a preset time (time limit count), no control is performed to improve the unbalanced voltage. This is to prevent tap changing in response to instantaneous voltage fluctuations.

[0070] In Figure 5, after two taps are raised, the V-phase secondary voltage V V2voltage drop, and the primary voltage V V1 Although the value deviates from the dead band width, the time is shorter than the preset fixed time (time limit count), so the control to raise the tap is not executed.

[0071] In addition, the automatic voltage balancing device A calculates the average value of the secondary voltage (input voltage) V AVE is used as the reference voltage, and the primary voltage is the average value V AVE Since the voltage is controlled to approach the reference voltage, the tap voltage range required for adjustment can be narrowed compared to when an arbitrary reference voltage is set, and the self-capacity of the voltage adjustment function can be reduced, resulting in a smaller device and lower cost.

[0072] Furthermore, because the transformer section of the automatic voltage balancing device A is a single-winding Y-connection, the primary and secondary sides use the same windings, which means that less windings are used than in a compound transformer, making it possible to achieve a smaller size, lighter weight, and lower cost.

[0073] As described above, the automatic voltage balancing device of the present invention can be constructed compactly and inexpensively. Furthermore, since a mechanical switch is used for tap changing, the short-circuit capacity can be increased compared to when a thyristor is used. [Industrial Applicability]

[0074] The present invention is applicable to correcting the imbalance of three-phase voltages not only at the sending point of a substation but also at other locations. [Explanation of symbols]

[0075] 1 Switch switch 2 Tap Selector 3 Current limiting resistor 4 Tap Changer 5 VT for primary voltage acquisition 6 VT for secondary voltage acquisition A Automatic Voltage Equalizer A1 Transformer section A2 control section

Claims

1. An automatic voltage balancing device that is installed on a three-phase high-voltage distribution line and improves three-phase voltage imbalance, comprising a transformer section and a control section, wherein the transformer section has a tap changer, consisting of a mechanical diverter switch and a tap selector, connected in series to the distribution line, and the tap changer changes the tap while the transformer section is operating, and the control section, when the connection direction of the substation is the primary side, calculates the average value of the primary voltage of the transformer section and controls the secondary voltage of each phase of the transformer section to approach the average value.

2. An automatic voltage balancing device that is installed on a three-phase high-voltage distribution line and improves three-phase voltage imbalance, comprising a transformer section and a control section, wherein the transformer section has a tap changer, which is composed of a mechanical diverter switch and a tap selector, connected in series to the distribution line, and the tap changer changes the tap while the transformer section is operating, and the control section, when the connection direction of the substation is the secondary side, calculates the average value of the secondary voltage of the transformer section and controls the voltage so that the primary voltage of each phase of the transformer section approaches the average value.

3. 2. The automatic voltage balancing device according to claim 1, wherein the control unit is configured to switch the tap of the tap selector when the difference between the average value and the secondary voltage exceeds a dead band width.

4. 3. The automatic voltage balancing device according to claim 2, wherein the control unit is configured to switch the tap of the tap selector when the difference between the average value and the primary voltage exceeds a dead band width.

5. 2. The automatic voltage balancing device according to claim 1, wherein the control unit is configured to switch the tap of the tap selector when the time during which the difference between the average value and the secondary voltage exceeds a dead band width exceeds a certain time.

6. 3. The automatic voltage balancing device according to claim 2, wherein the control unit is configured to switch the tap of the tap selector when the time period during which the difference between the average value and the primary voltage exceeds a dead band width exceeds a certain period.

7. 7. An automatic voltage balancing apparatus according to claim 1, wherein the transformer section is a single-winding Y-connection.

8. 2. An automatic voltage balancing method for an automatic voltage balancing device according to claim 1, which is installed on a three-phase high-voltage distribution line and corrects unbalance in three-phase voltage, comprising calculating an average value of the primary voltages and controlling the secondary voltages of each phase so as to approach the average value.

9. 3. An automatic voltage balancing method for an automatic voltage balancing device according to claim 2, which is installed on a three-phase high-voltage distribution line and corrects unbalance in three-phase voltage, comprising calculating an average value of the secondary voltages and controlling the primary voltages of each phase so as to approach the average value.

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