Power transmission and distribution system, neutral point grounding control device, and neutral point grounding control method

Abstract

To detect a cable way failure with a simple device configuration and deal with the cable way failure.SOLUTION: A transmission / distribution system 1 comprises: a three-phase first transformer 20 which has first primary winding 21 and first secondary winding 22 that is star-connected; a three-phase second transformer 40 which has second primary winding 41 that is start-connected and second secondary winding 42 that is delta-connected; a three-phase first cable way 34 which connects the first secondary winding 22 with the second primary winding 41; a disconnection detection part 92 which outputs a disconnection detection signal SA when a disconnection failure in the first cable way 34 is detected; and a grounding control part 96 which grounds a first neutral point 22N of the first secondary winding 22 and a second neutral point 41N of the second primary winding 41 when the disconnection detection signal SA is output.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power transmission and distribution system. 、 Neutral grounding control device and neutral point grounding control method Regarding. [Background technology]

[0002] When a single-phase open circuit fault occurs in a three-phase transmission line, an unbalanced voltage appears in the system receiving power from the line via a transformer. At domestic and international power plants, it is common to detect the open circuit fault and issue an alarm or switch power to a healthy system to prevent adverse effects on auxiliary equipment. As an example, claim 1 of Patent Document 1 below describes an electric circuit fault detection device comprising: a current sensor for measuring a primary current flowing in an electric circuit connected between a primary winding of a three-phase transformer and a power source; a voltage sensor for measuring a secondary voltage of the transformer; and a control unit for determining the presence or absence of an open circuit fault in the electric circuit based on a phase relationship of the primary current and the secondary voltage, and outputting the determination result, wherein the control unit outputs a determination signal indicating the occurrence of an open circuit fault when a ratio between the amplitude values ​​of each phase of the secondary voltage of the transformer is equal to or exceeds a predetermined phase voltage deviation detection rate. The description of this document is incorporated herein by reference. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6927892 Summary of the Invention [Problem to be solved by the invention]

[0004] The configuration shown in Patent Document 1 is capable of detecting faults and switching power to a healthy system effectively, but depending on the configuration of the electrical circuit, it is thought that electrical circuit faults can be detected and responded to with a simpler device configuration. The present invention has been made in view of the above-mentioned circumstances, and provides a power transmission and distribution system that can detect and respond to electrical circuit faults with a simple device configuration. 、 Neutral grounding control device and neutral point grounding control method The purpose is to provide the following. [Means for solving the problem]

[0005] In order to solve the above problems, the power transmission and distribution system of the present invention includes a three-phase first transformer having a first primary winding and a star-connected first secondary winding, a three-phase second transformer having a star-connected second primary winding and a delta-connected second secondary winding, a three-phase first electric circuit connecting the first secondary winding and the second primary winding, a control unit, When a wire breakage fault in the first electrical path is detected, a wire breakage detection signal is output. death, The first neutral point of the first secondary winding and the second neutral point of the second primary winding are grounded. [Effects of the Invention]

[0006] According to the present invention, an electrical circuit fault can be detected and dealt with using a simple device configuration. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a block diagram of a power transmission and distribution system according to a first embodiment. [Figure 2] FIG. 3 is a vector diagram of voltages in the first embodiment. [Figure 3] 3A to 3C are examples of various waveform diagrams according to the first embodiment. [Figure 4] FIG. 1 is a block diagram of a power transmission and distribution system according to Comparative Example #1. [Figure 5] FIG. 10 is a voltage vector diagram in Comparative Example #1. [Figure 6] 10A and 10B are examples of waveform diagrams in Comparative Example #1. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Outline of the embodiment] While it is conceivable to apply the content of the aforementioned Patent Document 1 to all power receiving circuits, it is believed that, depending on the configuration of the electrical circuit, it is possible to detect and respond to electrical circuit faults with a simpler device configuration. For example, in an ungrounded electrical circuit, if one phase of a three-phase electrical circuit breaks, a large voltage drop is generally expected, so it is conceivable to detect the open circuit fault using a general low-voltage relay. On the other hand, if one phase breaks when an electric motor is connected as a load to the three-phase electrical circuit, it may be difficult to detect the open circuit fault using a low-voltage relay. The reason for this is that if the electric motor continues to rotate, it generates an induced voltage, and although the voltage of the broken line drops slightly compared to the voltage before the break, it does not change significantly.

[0009] Furthermore, when a motor is operating at a constant power output, a decrease in the voltage applied to the motor increases the current flowing through the motor. If this current increase is large, there is a concern that thermal damage to the motor may occur. Furthermore, even if a phase break is detected, disconnecting the external power transmission system from the power receiving circuit reduces the number of power supply lines that can supply power to the power receiving circuit, leading to a decrease in the reliability of the power supply system. Therefore, in the embodiment described below, the neutral point of the transformer connected to the power receiving circuit is ungrounded under normal conditions. By ungrounding the neutral point, it becomes easier to detect a wire break fault. Furthermore, when a wire break fault is detected, the neutral point of the transformer is forcibly grounded, and the voltage applied to the power receiving circuit is made equal to that when the transformer is operating normally. This suppresses thermal damage to the motor and allows the power to continue to be received from the power transmission system.

[0010] [First embodiment] <Configuration of the first embodiment> FIG. 1 is a block diagram of a power transmission and distribution system 1 according to the first embodiment. In Figure 1, the power transmission and distribution system 1 includes three-phase electric circuits 32, 34 (first electric circuit), 36 (second electric circuit), 38, a transformer 20 (first transformer) having a primary winding 21 (first primary winding) and a secondary winding 22 (first secondary winding), a transformer 40 (second transformer) having a primary winding 41 (second primary winding) and a secondary winding 42 (second secondary winding), a low-voltage relay 50 (low-voltage detection unit), load equipment 60, sensor units 74, 76, switches 82, 84, and a control unit 90 (neutral grounding control device).

[0011] The secondary winding 22 of the transformer 20 is star-connected, and the primary winding 21 may be star-connected or delta-connected. The primary winding 41 of the transformer 40 is star-connected, and the secondary winding 42 is delta-connected. The electric circuit 32 is connected to the power grid 200 and the primary winding 21 of the transformer 20. The electric circuit 34 is connected to the secondary winding 22 of the transformer 20 and the primary winding 41 of the transformer 40. That is, the transformer 20 (first transformer) has the primary winding 21 and a star-connected secondary winding 22 (first secondary winding), and the transformer 40 (second transformer) has the star-connected primary winding 41 (second primary winding) and a delta-connected secondary winding 42 (second secondary winding).

[0012] The electric circuit 36 ​​is connected to the secondary winding 42 of the transformer 40 and the low-voltage relay 50. The electric circuit 38 is connected to the low-voltage relay 50 and a load equipment 60. The load equipment 60 is, for example, an auxiliary machine of a power plant, and includes an electric motor 62 and various other devices (not shown). The sensor units 74, 76 measure the voltages in the primary winding 41 and the secondary winding 42 of the transformer 40. The sensor units 74, 76 may also measure the currents flowing through the primary winding 41 and the secondary winding 42.

[0013] The low-voltage relay 50 monitors the voltage in the electric circuit 36, and if the voltage is equal to or greater than a predetermined operational setting, it connects the electric circuits 36, 38. On the other hand, if the voltage is less than the operational setting, the low-voltage relay 50 disconnects the electric circuits 36, 38. In this case, the low-voltage relay 50 outputs a low-voltage signal SL to the control unit 90 to notify the occurrence of a low voltage. The switch 82 opens and closes the connection between the neutral point 22N (first neutral point) of the secondary winding 22 of the transformer 20 and the ground point E based on a control signal from the control unit 90. Similarly, the switch 84 opens and closes the connection between the neutral point 41N (second neutral point) of the primary winding 41 of the transformer 40 and the ground point E based on a control signal from the control unit 90.

[0014] The control unit 90 includes a wire break detection unit 92, a holding circuit 94, and a ground control unit 96. The wire break detection unit 92 detects whether a wire break has occurred in the electrical circuit 34 based on the detection signals from the sensors 74 and 76, and outputs a wire break detection signal SA if a wire break is detected. The wire break detection unit 92 can be implemented using various known circuits, such as the device described in Patent Document 1, or a more simply configured device. The wire break detection unit 92 also outputs the wire break detection signal SA when the low-voltage relay 50 outputs the low-voltage signal SL. This allows the wire break detection unit 92 to output the wire break detection signal SA even if the detection signal from the sensor 76 fails to detect a wire break, such as when the electrical circuit 36 ​​is broken.

[0015] When the disconnection detection signal SA is output, the hold circuit 94 continues to output the signal as a detection result hold signal SB until a predetermined reset operation is performed by the user, even if the disconnection detection signal SA is subsequently turned off. A latching relay, for example, can be used for the hold circuit 94. When the hold circuit 94 is outputting the detection result hold signal SB, the ground control unit 96 sets the switches 82 and 84 to a closed state, and otherwise sets the switches 82 and 84 to an open state.

[0016] <Operation of the First Embodiment> Next, the operation of this embodiment will be described. If a wire breakage occurs in one phase of the electric circuit 34, the wire breakage detection unit 92 detects this and outputs a wire breakage detection signal SA. As a result, the holding circuit 94 continues to output the detection result holding signal SB thereafter. When the holding circuit 94 outputs the detection result holding signal SB, the grounding control unit 96 sets the switches 82, 84 to a closed state. As a result, the neutral points 22N, 41N are grounded, and the detection results by the sensor units 74, 76 become closer to those in a normal state (this will be described later with reference to FIG. 2).

[0017] When the detection results of the sensors 74, 76 approach those of the normal state, the open circuit detection unit 92 may determine that the electric circuit 34 is not open and turn off the open circuit detection signal SA. However, even in this case, the holding circuit 94 continues to output the detection result holding signal SB, and the grounding control unit 96 keeps the neutral points 22N, 41N grounded.

[0018] FIG. 2 is a vector diagram of voltages in the first embodiment. 2 are voltage vectors of the R-phase, S-phase, and T-phase that appear in the primary winding 41 of the transformer 40 when the electric circuit 34 is normal. Also, voltage vectors V20RS, V20ST, and V20TR are voltage vectors of the line voltages that appear in the secondary winding 42 of the transformer 40 when the electric circuit 34 is normal.

[0019] Furthermore, voltage vectors V11R, V11S, and V11T are voltage vectors of the R phase, S phase, and T phase that appear in the primary winding 41 of the transformer 40 when the T phase of the electric circuit 34 is broken. Furthermore, voltage vectors V21RS, V21ST, and V21TR are voltage vectors of the line voltage that appear in the secondary winding 42 of the transformer 40 when the T phase of the electric circuit 34 is broken.

[0020] If an open circuit fault occurs in the T-phase of the electric circuit 34 (see FIG. 1), the voltage vector V11T is momentarily lost. The open circuit detection unit 92 of the control unit 90 (see FIG. 1) then detects that an open circuit fault has occurred in the T-phase of the electric circuit 34, and the grounding control unit 96 grounds the neutral points 22N and 41N. Since the phase relationship between the voltage vectors V10R and V10S is maintained, the voltage vectors V21RS, V21ST, and V21TR appearing in the secondary winding 42 become similar to the voltage vectors V20RS, V20ST, and V20TR under normal conditions. This voltage in the secondary winding 42 induces the voltage vector V11T, shown by the dashed line.

[0021] As a result, the voltage vectors V10R, V10S, V10T, V20RS, V20ST, and V20TR before the wire-breaking accident and the voltage vectors V11R, V11S, V11T, V21RS, V21ST, and V21TR after the wire-breaking accident occurs and neutral points 22N and 41N are grounded become similar to each other. This allows the load equipment 60 (see FIG. 1) to continue operating in the same way as before the wire-breaking accident.

[0022] Thereafter, the user repairs the electric circuit 34 and then resets the holding circuit 94. When the holding circuit 94 is reset, the grounding control unit 96 sets the switches 82 and 84 to the open state, so that the neutral points 22N and 41N are again returned to the ungrounded state. When the neutral points 22N and 41N are in the ungrounded state, the control unit 90 will be able to detect the occurrence of another open circuit fault in the electric circuit 34.

[0023] FIG. 3 is an example of various waveform diagrams in the first embodiment. Voltages V2RS, V2ST, and V2TR are the line voltages between the RS phase, the ST phase, and the TR phase in the secondary winding 42, respectively. Currents I2R, I2S, and I2T are the output currents of the R phase, the S phase, and the T phase of the secondary winding 42, respectively. In each waveform diagram, the horizontal axis represents time, and the vertical axis represents voltage or current. The fault occurrence time tf is the time when an open circuit fault occurs in the T phase of the electric circuit 34 connected to the primary winding 41. The illustrated example shows a case in which the control unit 90 immediately detects the open circuit fault at the fault occurrence time tf and grounds the neutral points 22N and 41N. Therefore, there is no significant change in the voltage and current waveforms before and after the fault occurrence time tf.

[0024] [Comparative Example] Comparative Example #1 In order to clarify the effects of this embodiment, various comparative examples will be described below. 4 is a block diagram of a power transmission and distribution system 2 according to Comparative Example #1. In the following description, parts corresponding to those in the first embodiment described above are given the same reference numerals, and their description may be omitted. Similar to the power transmission and distribution system 1 of the first embodiment (see FIG. 1), the power transmission and distribution system 2 includes three-phase electric circuits 32, 34, 36, and 38, a transformer 20, a transformer 40, a low-voltage relay 50, and a load facility 60. However, the power transmission and distribution system 2 does not include the sensor units 74 and 76, the switches 82 and 84, and the control unit 90 of the power transmission and distribution system 1 of the first embodiment (see FIG. 1).

[0025] FIG. 5 is a vector diagram of voltages in Comparative Example #1. The voltage vectors V10R, V10S, and V10T and the voltage vectors V20RS, V20ST, and V20TR shown in Figure 5 are the voltages that appear in the primary winding 41 and secondary winding 42 of the transformer 40 when the electrical circuit 34 is normal, similar to those shown in Figure 2.

[0026] Furthermore, voltage vectors V15R, V15S, and V15T are examples of voltage vectors of the R phase, S phase, and T phase that appear in the primary winding 41 of the transformer 40 when the T phase of the electric circuit 34 is broken. Note that the voltage vector V15T is a zero vector. Furthermore, voltage vectors V25RS, V25ST, and V25TR are examples of voltage vectors of line voltages that appear in the secondary winding 42 of the transformer 40 when the T phase of the electric circuit 34 is broken. In Comparative Example 1, the neutral points 22N and 41N are not grounded, and therefore the potentials of the neutral points 22N and 41N fluctuate greatly due to a wire breakage accident, causing each voltage vector to change significantly, for example as shown in the figure.

[0027] However, the example shown in Fig. 5 is an example in which the electric motor 62 (see Fig. 4) was not operating. If the electric motor 62 continued to operate before and after the wire breakage accident, it is possible that the voltage vectors would not change as much as in the example shown in Fig. 5. This is because the electric motor 62 functions to maintain the line voltages of the secondary winding 42 as much as possible.

[0028] FIG. 6 is an example of various waveform diagrams in Comparative Example #1. However, the example shown in FIG. 6 assumes that the motor 62 continues to operate before and after the wire breakage accident, and functions to maintain the line voltages of the secondary winding 42 as much as possible. 6, similar to Fig. 3, voltages V2RS, V2ST, and V2TR are line voltages in the secondary winding 42, and currents I2R, I2S, and I2T are output currents of the R phase, S phase, and T phase of the secondary winding 42. Furthermore, the fault occurrence time tf is the time when an open circuit fault occurs in the T phase of the electric circuit 34 connected to the primary winding 41.

[0029] In the illustrated example, voltages V2RS and V2ST have decreased slightly since the fault occurrence time tf, and voltage V2TR has increased slightly since the fault occurrence time tf. However, because the motor 62 functions to maintain the line voltages of the secondary winding 42 as much as possible, the changes in these voltages are not very large. In this way, when the decrease in each line voltage is small, these line voltages are maintained at values ​​higher than the operating setting values ​​of the low voltage relay 50, and the low voltage relay 50 remains in a state where it does not interrupt the electrical circuits 36, 38.

[0030] Here, when the motor 62 is operating at a constant output, the current increases as the voltage drops. In particular, in the illustrated example, the T-phase current I2T increases after the fault occurrence time tf. To prevent thermal damage to the motor 62 due to an increase in current, the motor 62 is often equipped with a thermal relay. However, for a thermal relay to operate, a current greater than the set value and a certain amount of time for current flow are required. If only the T-phase current I2T increases, as in the illustrated case, it may become difficult for the thermal relay to detect the current. If this condition continues for a long period of time, there is a risk of damage to equipment such as the motor 62.

[0031] Comparative Example #2 Next, comparative example #2 will be described. Although illustration of comparative example #2 is omitted, it has the same configuration as the first embodiment (see FIG. 1) except for the following points: In comparative example #2, neutral points 22N, 41N are always grounded, and switches 82, 84, holding circuit 94, and grounding control unit 96 of the first embodiment are not provided. In comparative example #2, since neutral points 22N, 41N are always grounded, the waveforms and vectors of each part are the same as those of the first embodiment (see FIGS. 2 and 3).

[0032] However, if the neutral points 22N, 41N are always grounded, it becomes difficult to detect a wire breakage in the electric circuit 34. In order to detect a wire breakage in this state, it is necessary to use an expensive device such as that shown in Patent Document 1 as the wire breakage detection unit 92, which makes it difficult to simplify the wire breakage detection unit 92 and reduce costs.

[0033] [Effects of the embodiment] As described above, according to the embodiment, the power transmission and distribution system 1 includes a three-phase first transformer (20) having a first primary winding (21) and a star-connected first secondary winding (22), a three-phase second transformer (40) having a star-connected second primary winding (41) and a delta-connected second secondary winding (42), a three-phase first electric circuit (34) connecting the first secondary winding (22) and the second primary winding (41), a wire break detection unit 92 that outputs a wire break detection signal SA when it detects a wire break fault in the first electric circuit (34), and a grounding control unit 96 that grounds the first neutral point (22N) of the first secondary winding (22) and the second neutral point (41N) of the second primary winding (41) when the wire break detection signal SA is output. As a result, when the first neutral point (22N) of the first secondary winding (22) and the second neutral point (41N) of the second primary winding (41) are not grounded, the open circuit detection unit 92 detects an open circuit fault, making it possible to detect an electric circuit fault with a simple device configuration. Furthermore, the grounding control unit 96 can respond to an electric circuit fault by grounding the first neutral point (22N) and the second neutral point (41N).

[0034] Furthermore, it is more preferable that the power transmission and distribution system 1 further includes a holding circuit 94 that, when the disconnection detection signal SA is output, continues to output a detection result holding signal SB regardless of the state of the disconnection detection signal SA thereafter, and that the grounding control unit 96 grounds the first neutral point (22N) and the second neutral point (41N) when the detection result holding signal SB is being output. This allows the first neutral point (22N) and the second neutral point (41N) to be continuously grounded, and allows power to be continuously supplied from the second transformer (40) to the load equipment (60).

[0035] Furthermore, the power transmission and distribution system 1 further includes a second electric circuit (36) connected to the second secondary winding (42), and a low voltage detection unit (50) that outputs a low voltage signal SL when the voltage of the second electric circuit (36) is less than a predetermined operating set value, and more preferably, the open circuit detection unit 92 further outputs an open circuit detection signal SA when the low voltage signal SL is output. This allows the open circuit detection unit 92 to output the open circuit detection signal SA even if a wire breakage accident or the like occurs in the second electric circuit (36).

[0036] [Variations] The present invention is not limited to the above-described embodiment, and various modifications are possible. The above-described embodiment is provided as an example to facilitate understanding of the present invention, and is not necessarily limited to a configuration including all of the described configurations. Furthermore, other configurations may be added to the configurations of the above-described embodiment, and some of the configurations may be replaced with other configurations. Furthermore, the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all control lines and information lines necessary for the product. In reality, it can be assumed that almost all of the configurations are interconnected. [Explanation of symbols]

[0037] 1. Power transmission and distribution system 20 Transformer (first transformer) 21 Primary winding (first primary winding) 22 Secondary Winding (First Secondary Winding) 22N Neutral point (first neutral point) 34 Electrical Circuit (First Electrical Circuit) 36 Electrical Circuit (Second Electrical Circuit) 40 Transformer (Second Transformer) 41 Primary winding (second primary winding) 41N Neutral point (second neutral point) 42 Secondary Winding (Second Secondary Winding) 50 Low voltage relay (low voltage detection unit) 90 Control unit (neutral point grounding control device) 92 Disconnection detection unit 94 Holding circuit 96 Ground control section SA disconnection detection signal SB Detection result hold signal SL Low voltage signal

Claims

1. a three-phase first transformer having a first primary winding and a star-connected first secondary winding; a three-phase second transformer having a star-connected second primary winding and a delta-connected second secondary winding; a three-phase first electric circuit connecting the first secondary winding and the second primary winding; a control unit, The control unit When an open circuit fault in the first electric path is detected, an open circuit detection signal is output, and a first neutral point of the first secondary winding and a second neutral point of the second primary winding are grounded. A power transmission and distribution system characterized by:

2. A three-phase first transformer having a first primary winding and a star-connected first secondary winding; a three-phase second transformer having a star-connected second primary winding and a delta-connected second secondary winding; a three-phase first electric circuit connecting the first secondary winding and the second primary winding; a control unit, The control unit When a wire breakage fault in the first electric path is detected, a wire breakage detection signal is outputted; A first neutral point of the first secondary winding and a second neutral point of the second primary winding are grounded, a phase relationship of the voltage vector of the second primary winding is maintained, and the voltage vector of the second secondary winding is made to approximate that of the second primary winding in a normal state, thereby inducing a voltage vector of the second primary winding in the electric path in which the open circuit fault is detected. A power transmission and distribution system characterized by:

3. A holding circuit for holding a signal is provided, When the disconnection detection signal is output, the holding circuit outputs a detection result holding signal regardless of the state of the disconnection detection signal thereafter; The control unit grounds the first neutral point and the second neutral point when the detection result holding signal is output. The power transmission and distribution system according to claim 1 .

4. a second electrical path connected to the second secondary winding; a low voltage detection unit, the low voltage detection unit outputs a low voltage signal when the voltage of the second electrical path is less than a predetermined operation set value; The control unit outputs the disconnection detection signal when the low voltage signal is output. The power transmission and distribution system according to any one of claims 1 to 3.

5. A neutral grounding control device for controlling an electric power transmission and distribution system including: a three-phase first transformer having a first primary winding and a star-connected first secondary winding; a three-phase second transformer having a star-connected second primary winding and a delta-connected second secondary winding; and a three-phase first current path connecting the first secondary winding and the second primary winding, The neutral point grounding control device includes a disconnection detection unit, a holding circuit, and a grounding control unit, the disconnection detection unit outputs a disconnection detection signal when detecting a disconnection fault in the first electrical path; When the disconnection detection signal is output, the holding circuit outputs a detection result holding signal regardless of the state of the disconnection detection signal thereafter; When the disconnection detection signal is output, the ground control unit grounds a first neutral point of the first secondary winding and a second neutral point of the second primary winding. A neutral point grounding control device characterized by the above.

6. A method for controlling neutral grounding in a power transmission and distribution system comprising: a three-phase first transformer having a first primary winding and a star-connected first secondary winding; a three-phase second transformer having a star-connected second primary winding and a delta-connected second secondary winding; a three-phase first electric circuit connecting the first secondary winding and the second primary winding; and a control unit, comprising: The control unit When an open circuit fault is detected in the first electric path, a first neutral point of the first secondary winding and a second neutral point of the second primary winding are grounded, the phase relationship of the voltage vector of the second primary winding is maintained, and the voltage vector of the second secondary winding is made to approximate that in a normal state, thereby inducing a voltage vector of the second primary winding in the electric path in which the open circuit fault is detected. A neutral point grounding control method characterized by the above.

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