JP7791020B2 - voltage regulator - Google Patents

Description

This disclosure relates to a voltage regulator.

Patent Document 1 discloses a voltage regulator that adjusts the effective value of the AC voltage between two of three distribution lines. This voltage regulator has three series transformers. Each series transformer has a primary winding and a secondary winding. The secondary winding of each of the three series transformers is located midway between the three distribution lines. Various AC voltages are applied to the primary windings of the three series transformers. This adjusts the effective value of the AC voltage on the output side.

Japanese Patent Application Laid-Open No. 2017-85715

In Patent Document 1, the three primary windings of the three series transformers are connected in a Y-connection. The three secondary windings are also connected in a Y-connection. The neutral point to which one terminal of the three secondary windings is connected is not grounded. In this case, if a third harmonic component, whose frequency is three times the fundamental wave, is induced in each secondary winding, a zero-phase voltage, which is the voltage at the neutral point, is generated. If a zero-phase voltage with a large effective value is generated, various problems arise. One method for suppressing the zero-phase voltage is to use a three-phase, three-legged core as the common core used by the three series transformers.

When a three-phase, three-legged core is used, the width direction length is small and the height direction length is large. When a three-phase, five-legged core is used, the width direction length is large and the height direction length is small. When a three-phase, five-legged core is used in the configuration of Patent Document 1, an additional winding is required to suppress the effective value of the zero-phase voltage. For this reason, it is difficult to use a three-phase, five-legged core in the configuration of Patent Document 1. As a result, the configuration of Patent Document 1 requires the use of a three-phase, three-legged core, which poses the problem of limited flexibility in terms of placement.

The present invention was made in consideration of these circumstances, and its purpose is to provide a voltage regulator that allows for a high degree of freedom in terms of placement.

A voltage adjustment device according to one aspect of the present invention is a voltage adjustment device that adjusts the effective value of the AC voltage between two of a first distribution line, a second distribution line, and a third distribution line, and includes: a first tap transformer having a primary winding connected between the first distribution line and the second distribution line and a secondary winding to which multiple taps are connected; a second tap transformer having a primary winding connected between the second distribution line and the third distribution line and a secondary winding to which multiple taps are connected; a first series transformer having a secondary winding located midway between the primary winding and the first distribution line; a second series transformer having a secondary winding located midway between the primary winding and the second distribution line; and a second series transformer having a secondary winding located midway between the primary winding and the third distribution line. and a selector for selecting a tap, among the multiple taps connected to the secondary windings of the first and second tap transformers, to which the terminals of the three primary windings of the first, second, and third series transformers are electrically connected. One terminal of the primary winding of the first series transformer is connected to one terminal of the primary winding of the second series transformer, the other terminal of the primary winding of the second series transformer is connected to one terminal of the primary winding of the third series transformer, and the other terminal of the primary winding of the third series transformer is connected to the other terminal of the primary winding of the first series transformer.

The above aspect allows for a great degree of freedom in terms of placement.

1 is a circuit diagram of a voltage regulator according to an embodiment of the present invention. FIG. 2 is a block diagram showing the main configuration of a switch; FIG. 10 is a circuit diagram of the upper switch circuit of the assembly. 10 is a diagram showing combinations of upper and lower switch circuits in a conducting state; FIG. 1 is a side view of a core around which three primary windings are wound. FIG. 10 is an illustration of the AC voltage across the three secondary windings. FIG. 2 is an explanatory diagram of an increase and decrease in line voltage.

The present invention will be described in detail below with reference to the drawings showing embodiments thereof.
1 is a circuit diagram of a voltage adjustment device 1 according to the present embodiment. Three distribution lines U, V, and W are connected to an AC power source 2. The AC power source 2 outputs an AC voltage via the distribution lines U and V, outputs an AC voltage via the distribution lines V and W, and outputs an AC voltage via the distribution lines W and U. The AC power source 2 is, for example, a substation. Hereinafter, the effective value of the AC voltage between two of the three distribution lines U, V, and W will be referred to as the line voltage. The line voltage between the distribution lines U and V is common to the line voltage between the distribution lines V and W, and is also common to the line voltage between the distribution lines W and U.

The distribution lines U, V, and W function as the first distribution line, second distribution line, and third distribution line, respectively. Note that "common" between two line voltages indicates that they are substantially the same. Therefore, if the difference between the two line voltages is within the design error range, the two line voltages are common.

The voltage regulator 1 is placed midway between the three distribution lines U, V, and W. The voltage regulator 1 receives three AC voltages from the AC power source 2 and outputs three AC voltages. The voltage regulator 1 simultaneously adjusts the line voltage between the output distribution lines U and V, the line voltage between the output distribution lines V and W, and the line voltage between the output distribution lines W and U.

The voltage regulator 1 has three series transformers 3u, 3v, and 3w, two regulating transformers 4a and 4b, and a switch 5. Each of the series transformers 3u, 3v, and 3w has a primary winding 31 and a secondary winding 32. The three primary windings 31 and the three secondary windings 32 are wound around a common iron core 33 (see Figure 5). The iron core 33 is a magnetic material. One terminal of each of the three secondary windings 32 is connected to the input distribution lines U, V, and W. The other terminal of each of the three secondary windings 32 is connected to the output distribution lines U, V, and W. The series transformers 3u, 3v, and 3w function as the first, second, and third series transformers, respectively.

One terminal of the primary winding 31 of the series transformer 3u is connected to one terminal of the primary winding 31 of the series transformer 3v. The other terminal of the primary winding 31 of the series transformer 3v is connected to one terminal of the primary winding 31 of the series transformer 3w. The other terminal of the primary winding 31 of the series transformer 3w is connected to the other terminal of the primary winding 31 of the series transformer 3u. Therefore, the three primary windings 31 are connected in a delta configuration. The three secondary windings 32 are connected in a wye configuration.

Each of the regulating transformers 4a and 4b has a primary winding 41 and a secondary winding 42. The primary winding 41 and secondary winding 42 are wound around an iron core (not shown). This iron core is also made of magnetic material. The primary winding 41 of the regulating transformer 4a is connected between two distribution lines U and V. The primary winding 41 of the regulating transformer 4b is connected between two distribution lines V and W. The two primary windings 41 are V-connected. The AC voltage between the output distribution lines U and V is applied to the primary winding 41 of the regulating transformer 4a. The AC voltage between the output distribution lines V and W is applied to the primary winding 41 of the regulating transformer 4b.

Three taps T1, T2, and T3 are connected to the secondary windings of each of the regulating transformers 4a and 4b. Regulating transformers 4a and 4b function as a first tap transformer and a second tap transformer, respectively. The two primary windings 41 have the same number of turns. For the two secondary windings 42, the number of turns between taps T1 and T2 is the same. The number of turns between taps T2 and T3 is also the same. The number of turns between taps T1 and T2 is smaller than the number of turns between taps T2 and T3. The secondary winding 42 outputs an AC voltage from two of the three taps T1, T2, and T3. The effective value of the output AC voltage is expressed as the product of the effective value (line voltage) of the AC voltage applied to the primary winding 41 and the turns ratio. The turns ratio is obtained by dividing the number of turns between the two taps by the number of turns of the primary winding 41.

Figure 2 is a block diagram showing the main components of the switch 5. The switch 5 has two assemblies 50a and 50b and a control unit 51. Each of the assemblies 50a and 50b has three upper switch circuits A1, A2, and A3, three lower switch circuits B1, B2, and B3, a fault correction switch circuit C, and a bridging resistor R. The control unit 51 is configured using a logic circuit or an FPGA (Field Programmable Gate Array), etc.

Hereinafter, the connection node between the two primary windings 31 of the series transformers 3u and 3v will be referred to as the first node N1. The connection node between the two primary windings 31 of the series transformers 3v and 3w will be referred to as the second node N2. The connection node between the two primary windings 31 of the series transformers 3u and 3w will be referred to as the third node N3. The first node N1 is grounded.

The first terminals of the upper switch circuits A1, A2, and A3 in the assembly 50a and the first terminals of the lower switch circuits B1, B2, and B3 in the assembly 50b are connected to a first node N1. The first terminals of the upper switch circuits A1, A2, and A3 in the assembly 50b are connected to a second node N2. The first terminals of the lower switch circuits B1, B2, and B3 in the assembly 50a are connected to a third node N3.

In each of the assemblies 50a and 50b, the fault correction switch circuit C is connected in series with the bridging resistor R. The series circuit of the assembly 50a, including the fault correction switch circuit C and the bridging resistor R, is connected between the first node N1 and the third node N3. The series circuit of the assembly 50b, including the fault correction switch circuit C and the bridging resistor R, is connected between the first node N1 and the second node N2.

For assembly 50a, the second terminals of the upper switch circuits A1, A2, and A3 are connected to taps T1, T2, and T3, respectively, which are connected to the secondary winding 42 of the regulating transformer 4a. The second terminals of the lower switch circuits B1, B2, and B3 are also connected to taps T1, T2, and T3, respectively, which are connected to the secondary winding 42 of the regulating transformer 4a.

Similarly, for assembly 50b, the second terminals of the upper switch circuits A1, A2, and A3 are connected to taps T1, T2, and T3, respectively, which are connected to the secondary winding 42 of the regulating transformer 4b. The second terminals of the lower switch circuits B1, B2, and B3 are also connected to taps T1, T2, and T3, respectively, which are connected to the secondary winding 42 of the regulating transformer 4b.

The control unit 51 switches the state of each of the six upper switch circuits A1, A2, A3, the six lower switch circuits B1, B2, B3, and the two fault correction switch circuits C between a conducting state in which current can flow and a blocking state in which current flow is blocked.

Figure 3 is a circuit diagram of the upper switch circuit A1 of assembly 50a. The upper switch circuit A1, four upper switch circuits A2 and A3, six lower switch circuits B1, B2, and B3, and two fault correction switch circuits C of assembly 50b are each configured in the same way as the upper switch circuit A1 of assembly 50a.

Each of the six upper switch circuits A1, A2, A3, the six lower switch circuits B1, B2, B3, and the two fault correction switch circuits C has a first thyristor 61 and a second thyristor 62. The cathode of the first thyristor 61 is connected to the anode of the second thyristor 62. The cathode of the second thyristor 62 is connected to the anode of the first thyristor 61. The connection node between the cathode of the first thyristor 61 and the anode of the second thyristor 62 functions as the first terminal described above. The connection node between the cathode of the second thyristor 62 and the anode of the first thyristor 61 functions as the second terminal described above.

The gates of the first thyristor 61 and the second thyristor 62 are connected to the control unit 51. The control unit 51 adjusts the gate voltages of the first thyristor 61 and the second thyristor 62 to switch their states between conductive and cut-off. When the upper switch circuit A1 is in the conductive state, AC current can flow through the upper switch circuit A1. Current flowing from the second terminal to the first terminal flows through the first thyristor 61, as indicated by the solid arrow. Current flowing from the first terminal to the second terminal flows through the second thyristor 62, as indicated by the dashed arrow. When the upper switch circuit A1 is in the cut-off state, no current flows through the upper switch circuit A1.

The current-related functions of the upper switch circuit A1, the four upper switch circuits A2 and A3, the six lower switch circuits B1, B2, and B3, and the two fault correction switch circuits C of assembly 50b are similar to the current-related functions of the upper switch circuit A1 of assembly 50a.

For each of assemblies 50a and 50b shown in FIG. 2, normally, one of the three upper switch circuits A1, A2, and A3 is in a conducting state, and the remaining two upper switch circuits are in a blocking state. For each of assemblies 50a and 50b, normally, one of the three lower switch circuits B1, B2, and B3 is in a conducting state, and the remaining two lower switch circuits are in a blocking state.

The first node N1 is electrically connected to one of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a, which is connected to the upper switch circuit of the assembly 50a in a conducting state. The first node N1 is electrically connected to one of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b, which is connected to the lower switch circuit of the assembly 50b in a conducting state.

The second node N2 is electrically connected to one of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b, which is connected to the upper switch circuit of the assembly 50b in a conducting state. The third node N3 is electrically connected to one of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a, which is connected to the lower switch circuit of the assembly 50a in a conducting state. The two secondary windings 42 are connected in a V-connection.

The control unit 51 switches the tap electrically connected to the first node N1 among the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a by changing the conducting state of the upper switch circuit for the assembly 50a. The control unit 51 switches the tap electrically connected to the third node N3 among the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4a by changing the conducting state of the lower switch circuit for the assembly 50a.

Similarly, the control unit 51 switches which of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b is electrically connected to the second node N2 by changing the conducting state of the upper switch circuit for the assembly 50b. The control unit 51 switches which of the three taps T1, T2, and T3 connected to the secondary winding 42 of the regulating transformer 4b is electrically connected to the first node N1 by changing the conducting state of the lower switch circuit for the assembly 50b.

The two fault correction switch circuits C are normally in a cutoff state. The control unit 51 switches the state of the fault correction switch circuit C to a conduction state in the process of changing the conduction state of the upper switch circuit or the lower switch circuit. In the assembly 50a, when the control unit 51 changes the conduction state of the upper switch circuit from upper switch circuit A1 to upper switch circuit A2, it first switches the state of the fault correction switch circuit C from a cutoff state to a conduction state. Next, the control unit 51 switches the state of upper switch circuit A1 from a conduction state to a cutoff state. At this time, the states of the three upper switch circuits A1, A2, and A3 are in a cutoff state.

Next, the control unit 51 switches the state of the upper switch circuit A2 from a cut-off state to a conduction state. Thereafter, the control unit 51 switches the state of the fault correction switch circuit C from a conduction state to a cut-off state. As described above, when changing the conduction state of the upper switch circuit or the lower switch circuit in one of the assemblies 50a, 50b, the control unit 51 switches the state of the fault correction switch circuit C from a cut-off state to a conduction state and then to a cut-off state.

An AC voltage is applied to each of the three primary windings 31 of the series transformers 3u, 3v, and 3w from at least one of the two secondary windings 42 via the switch 5. When an AC voltage is applied to the three primary windings 31, the two secondary windings 32 of the series transformers 3u and 3v either increase or decrease the line voltage between the output distribution lines U and V. The two secondary windings 32 of the series transformers 3v and 3w either increase or decrease the line voltage between the output distribution lines V and W. The two secondary windings 32 of the series transformers 3u and 3w either increase or decrease the line voltage between the output distribution lines U and W.

When the control unit 51 of the switch 5 switches the electrically connected tap for at least one of the first node N1, second node N2, and third node N3, the AC voltage applied to at least one primary winding 41 changes. This changes at least one of the line voltage between the output side distribution lines U and V, the line voltage between the output side distribution lines V and W, and the line voltage between the output side distribution lines W and U.

Figure 4 is a diagram showing combinations of upper and lower switch circuits in a conducting state. The same combinations of upper and lower switch circuits in a conducting state are selected for each of assemblies 50a and 50b. Figure 4 also shows the primary tap voltages and secondary rated voltages in addition to the combinations of upper and lower switch circuits in a conducting state.

Let k denote any integer. Integer k may be 1, 2, or 3. In each of assemblies 50a and 50b, when the combination of upper and lower switch circuits in a conducting state is upper switch circuit Ak and lower switch circuit Bk, the voltages of the first node N1, second node N2, and third node N3 are the same. Therefore, no voltage is applied to the three primary windings 31. As a result, the three line voltages are not regulated.

The primary tap voltage is the effective value of the AC voltage applied to each of the two primary windings 41 of the regulating transformers 4a and 4b when the three line voltages are not regulated. The secondary rated voltage is a predetermined constant effective value for each of the AC voltage between distribution lines U and V, the AC voltage between distribution lines V and W, and the AC voltage between distribution lines W and U. In the example of Figure 4, the secondary rated voltage is 6600 V. The secondary rated voltage corresponds to the rated effective value.

As mentioned above, the line voltage between distribution lines U and V is common to the line voltage between distribution lines V and W, and is also common to the line voltage between distribution lines W and U. The line voltage between distribution lines U and V, the line voltage between distribution lines V and W, and the line voltage between distribution lines W and U are regulated collectively.

In each of assemblies 50a and 50b, when the combination of the upper switch circuit and downstream switch circuit in the conducting state is upper switch circuit A1 and lower switch circuit B3, the three line voltages increase. The increase in the line voltages is the largest. The primary tap voltage at which the three line voltages are adjusted to the secondary rated voltage, i.e., 6600V, is 6300V.

In each of assemblies 50a and 50b, when the combination of the upper and downstream switch circuits in a conducting state is upper switch circuit A2 and lower switch circuit B3, or upper switch circuit A1 and lower switch circuit B2, the three line voltages increase. Figure 4 shows the primary tap voltages at which the three line voltages are regulated to the secondary rated voltage for each of the two combinations.

When the combination of upper and lower switch circuits in a conducting state is upper switch circuit Ak and lower switch circuit Bk, the primary tap voltage at which the three line voltages are adjusted to the secondary rated voltage, i.e., 6600V, is 6600V.

In each of assemblies 50a and 50b, when the combination of the upper switch circuit and downstream switch circuit in the conducting state is upper switch circuit A3 and lower switch circuit B1, the three line voltages decrease. The decrease in line voltage is the largest. The primary tap voltage at which the three line voltages are adjusted to the secondary rated voltage, i.e., 6600V, is 6900V.

In each of the assemblies 50a and 50b, when the combination of the upper and lower switch circuits in the conducting state is the upper switch circuit A3 and the lower switch circuit B2, or the upper switch circuit A2 and the lower switch circuit B1, the three line voltages are reduced. Figure 4 shows the primary tap voltages at which the three line voltages are regulated to the secondary rated voltage for each of the two combinations.
As shown in FIG. 4, the minimum and maximum values of the primary tap voltage at which the line voltage on the output side is adjusted to the secondary rated voltage are 6300V and 6900V, respectively.

In the following, the line voltage between output side distribution lines U and V, the line voltage between output side distribution lines V and W, and the line voltage between output side distribution lines W and U will be represented by Vuv, Vvw, and Vwu, respectively. The control unit 51 of the switch 5 acquires the three line voltages Vuv, Vvw, and Vwu. Each of the three line voltages Vuv, Vvw, and Vwu is measured, for example, using a voltage sensor (not shown).

The control unit 51 calculates the deviation from a fixed target value for each of the seven tap switching combinations (patterns). The control unit 51 functions as a deviation calculation unit. When the target value is represented by Vg, the deviation Du is expressed by the following equation (1).

The control unit 51 switches the combination of current-carrying upper and lower switch circuits in each of the assemblies 50a and 50b to the combination (pattern) that corresponds to the smallest deviation among the seven calculated deviations. As a result, the three line voltages are adjusted by the three secondary windings 32 to target values or values close to the target values. The target values may match the secondary rated voltage or may differ from the secondary rated voltage.

As shown in Figure 1, the three secondary windings 32 are connected in a Y-connection. When a third harmonic component, whose frequency is three times that of the fundamental wave, is induced in each secondary winding 32, a zero-phase sequence voltage, which is the voltage at the neutral point, is generated. When the AC power source 2 is a substation and a zero-phase sequence voltage with a large effective value is generated, the substation's ground fault relay may operate unnecessarily. In a similar case, when a zero-phase sequence voltage carrier method is used in the remote control method for automatic section switches in an automated distribution system, communication failures may occur between the device and the switch. If communication failures occur, system operation may be hindered in the event of an accident.

When the three secondary windings 32 are connected in a Y-connection and the three primary windings 31 are also connected in a Y-connection, measures must be taken to prevent the generation of zero-phase voltages with large effective values. The first measure is to use a three-phase, three-legged core as the common core 33 around which the three primary windings 31 and three secondary windings 32 are wound. The second measure is to add a winding to create a path for the third harmonic excitation current flowing through the primary winding 31 to return.

However, as mentioned above, in the voltage regulator 1, the three primary windings 31 are delta-connected, forming a path for the third harmonic excitation current to return. This results in a small effective value for the zero-phase voltage. Therefore, no additional windings are required, and a core other than a three-phase, three-legged core, such as a three-phase, five-legged core, can be used as the core 33.

Figure 5 is a side view of an iron core 33 around which three primary windings 31 are wound. The upper part of Figure 5 shows an example in which a three-phase, three-legged iron core is used as the iron core 33. In this case, the iron core 33 has three rod-shaped legs extending vertically and aligned horizontally. The upper ends of the three legs are connected to a rod-shaped upper column extending horizontally. The lower ends of the three legs are connected to a rod-shaped lower column extending horizontally. For example, three secondary windings 32 of three series transformers 3u, 3v, and 3w are wound around each of the three legs. For example, a primary winding 31 is wound around each of the three legs from the outside of the secondary winding 32.

The lower part of Figure 5 shows an example in which a three-phase, five-legged core is used as the core 33. In this case, the core 33 has five rod-shaped legs extending vertically and aligned horizontally. The upper ends of the five legs are connected to a rod-shaped upper column extending horizontally. The lower ends of the five legs are connected to a rod-shaped lower column extending horizontally. For example, three secondary windings 32 of the three series transformers 3u, 3v, and 3w are wound around each of the three central legs. For example, a primary winding 31 is wound around each of the three central legs from the outside of the secondary winding 32.

When a three-phase, three-legged core is used as the iron core 33, the width of the iron core 33 is small and the height of the iron core 33 is large. When a three-phase, five-legged core is used as the iron core 33, the width of the iron core 33 is large and the height of the iron core 33 is small. As the iron core 33, it is possible to use, from among three-phase, three-legged cores and three-phase, five-legged cores, an iron core that is suitable for the installation location of the voltage regulator 1. As a result, there is a great degree of freedom in the placement of the voltage regulator 1.

In the following, the effective value of the AC voltage between the secondary windings 42 will be referred to as the secondary winding voltage. The three secondary winding voltages for the three secondary windings 42 of the three series transformers 3u, 3v, and 3w are common. The secondary winding voltage corresponds to the first effective value. Note that "common" for the three secondary winding voltages means that they are substantially the same. Therefore, if the difference between the maximum and minimum values for the three secondary winding voltages is within the error range, the three secondary winding voltages are common.

When the tap changer 5 changes the taps to adjust the three line voltages from the minimum value of the primary tap voltage, e.g., 6300 V, to the secondary rated voltage, e.g., 6600 V, the ratio obtained by dividing the secondary winding voltage by the line voltage between distribution lines U and V or between distribution lines V and W is referred to as the first ratio. Here, the secondary winding voltage and line voltage are the values after the change. When the tap changer 5 changes the taps to adjust the three line voltages from the maximum value of the primary tap voltage, e.g., 6900 V, to the secondary rated voltage, e.g., 6600 V, the ratio obtained by dividing the secondary winding voltage by the line voltage between distribution lines U and V or between distribution lines V and W is referred to as the second ratio. Here, the secondary winding voltage and line voltage are the values after the change. The ranges satisfied by the first ratio and second ratio in the voltage regulator 1 are described below. The line voltage between distribution lines U and V or between distribution lines V and W corresponds to the second effective value.

Figure 6 is an explanatory diagram of the AC voltage between both ends of the three secondary windings 32. As mentioned above, the two primary windings 41 of the two regulating transformers 4a and 4b are connected in a V-connection. The AC voltage between the distribution lines U and V is represented by vector 70. The AC voltage between the distribution lines V and W is represented by vector 71. The magnitude of vector 70 indicates the line voltage between the distribution lines U and V. The magnitude of vector 71 indicates the line voltage between the distribution lines V and W. The angle between the two vectors indicates the phase difference between the two AC voltages corresponding to the two vectors.

As mentioned above, the two secondary windings 42 of the two regulating transformers 4a and 4b are connected in a V-connection. The two AC voltages output from the two secondary windings 42 are represented by vectors 80 and 81. The slopes of vectors 80 and 81 match the slopes of vectors 70 and 71. The magnitudes of vectors 80 and 81 are represented by the product of the magnitudes of vectors 70 and 71 and the turns ratio described above. Because the turns ratio is adjusted to a value less than 1, the magnitudes of vectors 80 and 81 are smaller than the magnitudes of vectors 70 and 71.

As mentioned above, the three primary windings 31 of the three series transformers 3u, 3v, and 3w are delta-connected. The two AC voltages corresponding to vectors 80 and 81 are applied directly to the three primary windings 31. The three AC voltages applied to the three primary windings 31 are represented by vectors 90, 91, and 92. Vectors 90, 91, and 92 form a triangle. The magnitude of each of vectors 90, 91, and 92 is the effective value of the AC voltage applied to the three primary windings 31.

As mentioned above, the three secondary windings 32 of the three series transformers 3u, 3v, and 3w are connected in a Y-connection. The AC voltages between both ends of the three secondary windings 32 are represented by three vectors. The starting points of the three vectors are the same. The slopes of the three vectors are the same as those of vectors 90, 91, and 92. When the control unit 51 of the switch 5 performs switching, the magnitudes of vectors 80 and 81 are changed. When the magnitudes of vectors 80 and 81 are changed, the magnitudes of the three vectors representing the AC voltages between both ends of the three secondary windings 32 are also changed.

Figure 7 is an explanatory diagram of the rise and fall of line voltages. The AC voltages of the input distribution lines U, V, and W are represented by vectors Eu1, Ev1, and Ew1. The AC voltages of the output distribution lines U, V, and W are represented by vectors Eu2, Ev2, and Ew2. The AC voltages across the secondary windings 32 of the series transformers 3u, 3v, and 3w are represented by vectors ΔEu, ΔEv, and ΔEw.

When increasing the line voltage, vector Eu2 is expressed as the sum of vectors Eu1 and ΔEu. Similarly, vector Ev2 is expressed as the sum of vectors Ev1 and ΔEv. Vector Ew2 is expressed as the sum of vectors Ew1 and ΔEw. The distance between the end points of the two vectors Eu2 and Ev2 indicates the line voltage Vuv between the output distribution lines U and V. The end points of the vectors are the tips of the arrows. The distance between the end points of the two vectors Ev2 and Ew2 indicates the line voltage Vvw between the output distribution lines V and W. The distance between the end points of the two vectors Ew2 and Eu2 indicates the line voltage Vwu between the output distribution lines W and U. The three line voltages Vuv, Vvw, and Vwu are the same.

The AC voltages of the distribution lines U, V, and W are three-phase balanced voltages. Furthermore, the magnitudes of the vectors ΔEu, ΔEv, and ΔEw are the same. Therefore, the triangle formed by vectors Eu1, Eu2, and ΔEu is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv, and is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv.

As mentioned above, for series transformers 3u, 3v, and 3w, the primary winding 31 is delta-connected and the secondary winding 32 is wye-connected. Therefore, the angle between vectors Eu2 and ΔEu, the angle between vectors Ev2 and ΔEv, and the angle between vectors Ew2 and ΔEw are 30 degrees.

In the following, the magnitude of vectors Eu1, Ev1, and Ew1 will be represented by E1. The magnitude of vectors Eu2, Ev2, and Ew2 will be represented by E2. The magnitude of vectors ΔEu, ΔEv, and ΔEw will be represented by ΔE. The magnitude of the input line voltages Vuv, Vvw, and Vwu will be represented by V1. The magnitude of the output line voltages Vuv, Vvw, and Vwu will be represented by V2. The ratio obtained by dividing ΔE by V2 will be represented by K.

When the line voltage is increased, the following equation (2) holds true according to the cosine law.
E1 ² =E2 ² +ΔE ² -2・E2・ΔE・cos30°…(2)
"·" indicates a product. ΔE = K·V2 holds. By substituting K·V2 for ΔE in equation (2), the following equation (3) is obtained.
E1 ² = E2 ² + (K・V2) ² −E2・K・V2・√3…(3)

As mentioned above, the AC voltages of the distribution lines U, V, and W are three-phase balanced voltages. Therefore, E1 = V1/√3 and E2 = V2/√3 hold. By using these equations and deleting E1 and E2 from equation (3), the following equation (4) is obtained.
3・K ²・V2 ² −3・K・V2 ² +V2 ² −V1 ² =0…(4)

Equation (4) is a quadratic equation with respect to K. By using the solution formula, K can be expressed as equation (5) below.

Normally, V2 is sufficiently larger than ΔE. Therefore, K will never exceed 0.5. Therefore, solutions in equation (5) where K is 0.5 or greater are eliminated. As a result, K can be expressed as equation (6).

If the minimum value of the primary tap voltage at which the output line voltage is adjusted to the secondary rated voltage is represented by Vmin, and the secondary rated voltage is represented by Vc, the first ratio K1 is expressed by the following equation (7).

When a deviation of r% is allowed for the transformation ratio (= V1/V2) of the line voltages on the input and output sides, the transformation ratio should be greater than or equal to (1 - (r/100)) V1/V2 and less than or equal to (1 + (r/100)) V1/V2. Therefore, when a deviation of r% is allowed for the transformation ratio (= V1/V2) of the line voltages on the input and output sides, the first ratio K1 satisfies the following equation (8). Here, r is a real number greater than or equal to 0 and less than or equal to 100.

In the voltage regulator 1, ΔE and V2 are designed so that the first ratio K1 satisfies equation (8). This allows for accurate voltage regulation with minimal error when the primary tap voltage is at its minimum value. The allowable deviation, r, is determined by standards and is, for example, 0.4.

In the example of Figure 4, the minimum value Vmin of the primary tap voltage is 6300V. The secondary rated voltage Vc is 6600V. When r is 0.4, ΔE and V2 are designed to satisfy 0.0280≦K1≦0.00331. When the first ratio K1 is 0.03055, the angle between vectors Eu1 and Eu2, the angle between vectors Ev1 and Ev2, and the angle between vectors Ew1 and Ew2 are approximately 1.6 degrees, which is sufficiently small. Therefore, the phase fluctuation of the AC voltages of the distribution lines U, V, and W that occurs when the line voltage is increased is small.

When lowering the line voltage, as shown in the lower part of Figure 7, vector Eu2 is obtained by subtracting vector ΔEu from vector Eu1. Similarly, vector Ev2 is obtained by subtracting vector ΔEv from vector Ev1. Vector Ew2 is obtained by subtracting vector ΔEw from vector Ew1. In this case, too, the magnitudes of the three line voltages Vuv, Vvw, and Vwu are the same.

The triangle formed by vectors Eu1, Eu2, and ΔEu is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv, and is the same as the triangle formed by vectors Ev1, Ev2, and ΔEv. The angle between vectors Eu2 and ΔEu, the angle between vectors Ev2 and ΔEv, and the angle between vectors Ew2 and ΔEw are all 30 degrees.

When the line voltage is reduced, the following equation (9) holds true according to the cosine law.
E1 ² =E2 ² +ΔE ² -2・E2・ΔE・cos150°…(9)
Since ΔE=K·V2 holds, by substituting K·V2 for ΔE in equation (9), the following equation (10) is obtained.
E1 ² = E2 ² + (K・V2) ² +E2・K・V2・√3…(10)

As described above, E1=V1/√3 and E2=V2/√3 hold. By using these equations to delete E1 and E2 from equation (10), the following equation (11) is obtained.
3・K ²・V2 ² +3・K・V2 ² +V2 ² −V1 ² =0…(11)

Equation (11) is a quadratic equation with respect to K. By using the solution formula, K can be expressed as the following equation (12).

K is a ratio, so it cannot be a negative value. Therefore, we eliminate solutions in equation (12) where K is a negative value. This allows K to be expressed as equation (13).

If the maximum value of the primary tap voltage at which the output line voltage is adjusted to the secondary rated voltage is represented by Vmax, and the secondary rated voltage is represented by Vc, the second ratio K2 is expressed by the following equation (14).

When a deviation of r% is allowed for the transformation ratio (= V2/V1) of the line voltages on the input and output sides, the second ratio K2 satisfies the following equation (15). As mentioned above, r is a real number greater than or equal to 0 and less than or equal to 100.

In the voltage regulator 1, ΔE and V2 are designed so that the second ratio K2 satisfies equation (15). Therefore, when the primary tap voltage is at its maximum value, accurate voltage regulation with small error is achieved. As mentioned above, r is, for example, 0.4.

When the first ratio K1 satisfies equation (8) and the second ratio K2 satisfies equation (15), even if the primary tap voltage has values different from the minimum and maximum values, the deviation in the transformation ratio between the line voltages on the input and output sides is r% or less.

In the example of Figure 4, the maximum value Vmax of the primary tap voltage is 6900V. The secondary rated voltage Vc is 6600V. When the error tolerance ratio r is 0.004, ΔE and V2 are designed to satisfy 0.0273≦K2≦0.00328. When the second ratio K2 is 0.03086, the angle between vectors Eu1 and Eu2, the angle between vectors Ev1 and Ev2, and the angle between vectors Ew1 and Ew2 are approximately 1.4 degrees, which is sufficiently small. Therefore, the phase fluctuation of the AC voltages of the distribution lines U, V, and W that occurs when the line voltage is reduced is small.

Furthermore, in a voltage regulator in which the primary winding 41 and the secondary winding 42 are connected in a V-connection and the primary winding 31 and the secondary winding 32 are connected in a Y-connection, direct adjustment of one of the three line voltages is impossible. However, in voltage regulator 1, the primary winding 31 is connected in a delta-connection, so the angle between vectors Eu1 and Eu2, the angle between vectors Ev1 and Ev2, and the angle between vectors Ew1 and Ew2 exceed zero. Therefore, the three line voltages can be directly adjusted.

For the regulating transformers 4a and 4b, the number of taps connected to the two secondary windings 42 is not limited to three and may be two, four, or more. The selector 5 switches between the taps electrically connected to the first node N1, the second node N2, and the third node N3, respectively, among the multiple taps. For each of the assemblies 50a and 50b, the number of upper switch circuits is the same as the number of taps connected to one secondary winding 42. The number of lower switch circuits is also the same as the number of taps connected to one secondary winding 42.

The upper switch circuits A1, A2, A3, the lower switch circuits B1, B2, B3, and the fault correction switch circuit C can be any circuit that transitions between a conducting state and a blocking state. Therefore, each of these switch circuits is not limited to circuits using the first thyristor 61 and the second thyristor 62, and may be, for example, circuits using semiconductor switches other than thyristors. The aforementioned switch circuits may also use triacs, for example.

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

1: Voltage regulator, 3u: Series transformer (first series transformer), 3v: Series transformer (second series transformer), 3w: Series transformer (third series transformer), 4a: Regulating transformer (first tap transformer), 4b: Regulating transformer (second tap transformer), 5: Switch, 51: Control unit (deviation calculation unit), 31, 41: Primary winding, 32, 42: Secondary winding, T1, T2, T3: Tap, U: Distribution line (first distribution line), V: Distribution line (second distribution line), W: Distribution line (third distribution line)

Claims (8)

A voltage regulator that adjusts an effective value of an AC voltage between two of a first distribution line, a second distribution line, and a third distribution line,
a first tap transformer having a primary winding connected between the first distribution line and the second distribution line and a plurality of taps connected to a secondary winding;
a second tap transformer having a primary winding connected between the second distribution line and the third distribution line and a plurality of taps connected to a secondary winding;
a first series transformer having a primary winding and a secondary winding disposed midway along the first distribution line;
a second series transformer having a primary winding and a secondary winding disposed midway along the second distribution line;
a third series transformer having a primary winding and a secondary winding disposed midway along the third distribution line;
a selector for selecting a tap to which terminals of three primary windings of the first series transformer, the second series transformer, and the third series transformer are electrically connected, among a plurality of taps connected to the secondary windings of the first tap transformer and the second tap transformer;
Equipped with
One terminal of the primary winding of the first series transformer is connected to one terminal of the primary winding of the second series transformer;
The other terminal of the primary winding of the second series transformer is connected to one terminal of the primary winding of the third series transformer,
the other terminal of the primary winding of the third series transformer is connected to the other terminal of the primary winding of the first series transformer;
two of the three secondary windings of the first series transformer, the second series transformer, and the third series transformer adjust an effective value of an AC voltage on an output side between two of the first distribution line, the second distribution line, and the third distribution line;
When the switch performs tap switching, the effective value of the AC voltage on the output side changes,
a first effective value of AC voltages between both ends of three secondary windings of the first series transformer, the second series transformer, and the third series transformer is common;
a second effective value of the AC voltage applied to the primary windings of the first tap transformer and the second tap transformer is common;
When a constant rated effective value of the AC voltage between two of the first distribution line, the second distribution line, and the third distribution line is represented by Vc, the minimum value of the second effective value at which the effective value of the AC voltage on the output side is adjusted to the rated effective value is represented by Vmin, and a deviation of r % is allowed in a transformation ratio of the effective values of the AC voltages on the input side and the output side, when the switch performs switching so that the effective value of the AC voltage on the output side is adjusted from the minimum value to the rated effective value, a first ratio obtained by dividing the first effective value by the second effective value satisfies the following formula:
r is a real number greater than or equal to 0 and less than or equal to 100
Voltage regulator.
However, K1: the first ratio two of the three secondary windings of the first series transformer, the second series transformer, and the third series transformer adjust an effective value of an AC voltage on an output side between two of the first distribution line, the second distribution line, and the third distribution line;
When the switch performs tap switching, the effective value of the AC voltage on the output side changes,
a first effective value of the AC voltage between both ends of three secondary windings of the first series transformer, the second series transformer, and the third series transformer is common;
a second effective value of the AC voltage applied to the primary windings of the first tap transformer and the second tap transformer is common;
When a constant rated effective value of the AC voltage between two of the first distribution line, the second distribution line, and the third distribution line is represented by Vc, the maximum value of the second effective value at which the effective value of the AC voltage on the output side is adjusted to the rated effective value is represented by Vmax, and a deviation of r % is allowed in a transformation ratio of the effective values of the AC voltages on the input side and the output side, when the switch performs switching so that the effective value of the AC voltage on the output side is adjusted from the maximum value to the rated effective value, a second ratio obtained by dividing the first effective value by the second effective value satisfies the following formula:
r is a real number greater than or equal to 0 and less than or equal to 100
The voltage regulator of claim 1 .
However, K2: the second ratio r is 0.4
The voltage regulator according to claim 1 or 2 . a deviation calculation unit that calculates a deviation from a certain target value for each of a plurality of switching patterns performed by the switch;
the switcher switches to a pattern with the smallest deviation among the plurality of deviations calculated by the deviation calculation unit,
The deviation is expressed by the following formula:
The voltage regulator according to any one of claims 1 to 3 .
however,
Vg: the target value V12: the effective value of the AC voltage between the first distribution line and the second distribution line V23: the effective value of the AC voltage between the second distribution line and the third distribution line V31: the effective value of the AC voltage between the third distribution line and the first distribution line A voltage regulator that adjusts an effective value of an AC voltage between two of a first distribution line, a second distribution line, and a third distribution line,
a first tap transformer having a primary winding connected between the first distribution line and the second distribution line and a plurality of taps connected to a secondary winding;
a second tap transformer having a primary winding connected between the second distribution line and the third distribution line and a plurality of taps connected to a secondary winding;
a first series transformer having a primary winding and a secondary winding disposed midway along the first distribution line;
a second series transformer having a primary winding and a secondary winding disposed midway along the second distribution line;
a third series transformer having a primary winding and a secondary winding disposed midway along the third distribution line;
a selector for selecting a tap to which terminals of three primary windings of the first series transformer, the second series transformer, and the third series transformer are electrically connected, among a plurality of taps connected to the secondary windings of the first tap transformer and the second tap transformer;
Equipped with
One terminal of the primary winding of the first series transformer is connected to one terminal of the primary winding of the second series transformer;
The other terminal of the primary winding of the second series transformer is connected to one terminal of the primary winding of the third series transformer,
the other terminal of the primary winding of the third series transformer is connected to the other terminal of the primary winding of the first series transformer;
two of the three secondary windings of the first series transformer, the second series transformer, and the third series transformer adjust an effective value of an AC voltage on an output side between two of the first distribution line, the second distribution line, and the third distribution line;
When the switch performs tap switching, the effective value of the AC voltage on the output side changes,
a first effective value of AC voltages between both ends of three secondary windings of the first series transformer, the second series transformer, and the third series transformer is common;
a second effective value of the AC voltage applied to the primary windings of the first tap transformer and the second tap transformer is common;
When a constant rated effective value of the AC voltage between two of the first distribution line, the second distribution line, and the third distribution line is represented by Vc, the maximum value of the second effective value at which the effective value of the AC voltage on the output side is adjusted to the rated effective value is represented by Vmax, and a deviation of r % is allowed in a transformation ratio of the effective values of the AC voltages on the input side and the output side, when the switch performs switching so that the effective value of the AC voltage on the output side is adjusted from the maximum value to the rated effective value, a second ratio obtained by dividing the first effective value by the second effective value satisfies the following formula:
r is a real number greater than or equal to 0 and less than or equal to 100
Voltage regulator.
However, K2: the second ratio r is 0.4
The voltage regulator according to claim 5 . a deviation calculation unit that calculates a deviation from a certain target value for each of a plurality of switching patterns performed by the switch;
the switcher switches to a pattern with the smallest deviation among the plurality of deviations calculated by the deviation calculation unit,
The deviation is expressed by the following formula:
The voltage regulator according to claim 5 or 6.
however,
Vg: the target value
V12: Effective value of AC voltage between the first distribution line and the second distribution line
V23: Effective value of AC voltage between the second distribution line and the third distribution line
V31: Effective value of AC voltage between the third distribution line and the first distribution line A voltage regulator that adjusts an effective value of an AC voltage between two of a first distribution line, a second distribution line, and a third distribution line,
a first tap transformer having a primary winding connected between the first distribution line and the second distribution line and a plurality of taps connected to a secondary winding;
a second tap transformer having a primary winding connected between the second distribution line and the third distribution line and a plurality of taps connected to a secondary winding;
a first series transformer having a primary winding and a secondary winding disposed midway along the first distribution line;
a second series transformer having a primary winding and a secondary winding disposed midway along the second distribution line;
a third series transformer having a primary winding and a secondary winding disposed midway along the third distribution line;
a selector for selecting a tap to which terminals of three primary windings of the first series transformer, the second series transformer, and the third series transformer are electrically connected, among a plurality of taps connected to the secondary windings of the first tap transformer and the second tap transformer;
Equipped with
one terminal of the primary winding of the first series transformer is connected to one terminal of the primary winding of the second series transformer;
The other terminal of the primary winding of the second series transformer is connected to one terminal of the primary winding of the third series transformer,
the other terminal of the primary winding of the third series transformer is connected to the other terminal of the primary winding of the first series transformer;
a deviation calculation unit that calculates a deviation from a certain target value for each of a plurality of switching patterns performed by the switch;
the switcher switches to a pattern with the smallest deviation among the plurality of deviations calculated by the deviation calculation unit,
The deviation is expressed by the following formula:
Voltage regulator.
however,
Vg: the target value
V12: Effective value of AC voltage between the first distribution line and the second distribution line
V23: Effective value of AC voltage between the second distribution line and the third distribution line
V31: Effective value of AC voltage between the third distribution line and the first distribution line