Partial discharge diagnostic device

Abstract

The present invention improves the SN ratio of a partial discharge measurement device. The partial discharge measurement device has a first metal plate (2) and a second metal plate (1) disposed inside a panel (101) and electrically connected to the first metal plate (2) via a cable (3), and measures a current in the first metal plate (2) to measure partial discharges inside the panel (101).

Description

Partial Discharge Diagnosis Device

[0001] The present invention relates to a partial discharge diagnosis device.

[0002] High-voltage equipment such as switchboards, switchgears, and switching devices is used for a long time after installation, and over-time deterioration such as a decrease in insulation performance may occur accordingly. It is generally known that partial discharge occurs when the insulation performance of power equipment deteriorates. When discharge (hereinafter also referred to as partial discharge) repeatedly occurs inside power equipment, it may lead to insulation breakdown and potentially cause disasters such as fires. Therefore, in order to safely operate power equipment, it is important to detect partial discharge of the equipment.

[0003] An example of a method for detecting partial discharge is disclosed in Patent Document 1.

[0004] Patent Document 2 also discloses a partial discharge detection technique using a transient earth voltage sensor (TEV sensor). The current induced in the metal wall inside the switchboard by the electromagnetic wave generated by the partial discharge inside the switchboard leaks from the openings such as bushings to the metal wall outside the switchboard, and this leakage current is voltage-converted by the TEV sensor. In this method, the signal-to-noise ratio (SN ratio) is determined by the amount of current induced in the internal metal wall that leaks to the external metal wall.

[0005] Japanese Patent Application Laid-Open No. 2006-234602 WO2024 / 127682

[0006] In the method of Patent Document 2, since the signal-to-noise ratio (SN ratio) is determined by the amount of current induced in the internal metal wall that leaks to the external metal wall, there is a problem that the SN ratio is low.

[0007] Therefore, an object of the present invention is to provide a partial discharge diagnosis device with a high SN ratio and high detection sensitivity.

[0008] A partial discharge measurement device that measures the current of the first metal plate to perform measurement inside the board for an object having a first metal plate and a second metal plate that is electrically connected to the first metal plate by a cable and disposed inside the board.

[0009] According to the present invention, it is possible to provide a partial discharge diagnostic device with a high signal-to-noise ratio and high detection sensitivity. Further means and effects of the present invention will become clear throughout the entire specification below.

[0010] This is a schematic diagram of one embodiment. This is an explanatory diagram of a discharge test. These are the test results. This is a schematic diagram of another embodiment. This is an explanatory diagram of the switch operation. This is an explanatory diagram of the switch operation. This is an explanatory diagram of the switch operation. This is an explanatory diagram of the switch IC operation. This is a schematic diagram of another embodiment. This is a schematic diagram of another embodiment. This is an example of an oblique view of the shape of a metal plate. This is an example of a plan view of the shape of a metal plate. This is a schematic diagram of a partial discharge monitoring system.

[0011] The embodiments of the present invention will be described below, with reference to drawings as necessary.

[0012] Figure 1 is a conceptual diagram illustrating this embodiment. 101 is a panel, which houses electrical equipment within a metal casing. One example is a power receiving panel.

[0013] An internal metal plate 1 is positioned inside the panel 101. This internal metal plate 1 is positioned so that it does not directly make electrical contact with the internal wall surface of the panel 101. This can also be described as a floating arrangement.

[0014] One example of a configuration that avoids direct contact is to insert a thin insulating material between the inner wall surface of the panel 101 and the inner metal plate 1.

[0015] When a partial discharge occurs inside the panel 101, an induced current is generated on the surface of the internal metal plate 1 by the electromagnetic field generated from the power supply 401. This induced current flows into the core wire of the coaxial cable 3 attached to the end of the internal metal plate 1. While not limited to a coaxial cable, a coaxial cable is preferable from the viewpoint of signal-to-noise ratio.

[0016] The coaxial cable 3 is led out of the panel 101 through a cable exit hole (not shown) in the panel 101. The other end of the coaxial cable 3 is connected to one end of the external metal plate 2. Then, the induced current generated in the internal metal plate 1 flows through the external metal plate 2.

[0017] A transient ground voltage sensor (TEV sensor) 6 is attached to the external metal plate 2. The TEV sensor 6 detects the transient voltage generated by the impedance of the external metal plate 2 due to the induced current flowing through the external metal plate 2 as a voltage signal.

[0018] The current that flows into the outer metal plate 2 is returned to the panel 101 via the shield wire of the coaxial cable 3 attached to the other end of the outer metal plate 2, and flows to the ground of the panel 101. With the above configuration, the inner metal plate 1 is ultimately grounded at the grounding point of the panel 101.

[0019] The voltage signal from the TEV sensor 6 is input to the signal processing circuit 8. Then, the presence or absence of a partial discharge signal is determined and recorded by the signal storage and comparison calculation unit 9.

[0020] In this state, the shield box 5 and the external metal plate 2 are not electrically connected. The external metal plate 2 can also be said to be electrically floating relative to the shield box 5. The shield box 5 is made of metal, and external noise is shielded by the shield box 5.

[0021] The coaxial cable 3 can use the shield wire as a signal return. Therefore, to further enhance resistance to external noise, the shield wire may be constructed in a multi-layer or multi-layer structure. In that case, even greater noise immunity can be achieved.

[0022] Figure 2A is an explanatory diagram of the discharge test. This is a test that simulates the conditions when a partial discharge occurs inside the panel.

[0023] The test specimen 52 is placed in the metal box 51. A voltage generator 50 generates a test voltage, which causes a discharge 54 between the test specimen 52 and the discharge needle 53. This corresponds to a partial discharge in the actual device. The discharge generates electromagnetic waves 55 on the inner wall side of the metal box 51. This induces a surface current 56 on the outer surface of the metal box 51.

[0024] Figure 2B shows the test results. It is the result of analyzing the induced currents generated inside and outside the panel when a discharge occurs. The external current 81 generated outside the metal box as an induced current (56) is the induced current generated inside the metal box that leaks out through openings such as bushings. Therefore, it is a minute current with an intensity reduced to a fraction of that of the internal current 80 generated inside the metal box. In Figure 2B, the external current 81 is shown multiplied by 10, so in reality, it is a current with an amplitude of one-tenth.

[0025] In actual machine applications, since the control panel is constructed from a large metal casing, the distance from the partial discharge generation point to the metal wall of the panel is also large, and consequently, the induced current induced in the outer wall of the panel becomes small. Furthermore, the current value detected by the external TEV sensor described in Patent Document 2 becomes even smaller.

[0026] The technical concept disclosed in Figure 1 involves installing an internal metal plate 1 inside the panel and an external metal plate 2 outside the panel, connecting them with a cable, thereby directly extracting the strong induced current inside the panel to the outside. Therefore, the internal current shown in Figure 2B can ideally be detected directly at the location of the external metal plate 2. As a result, the signal-to-noise ratio can be easily and significantly improved, theoretically by more than ten times.

[0027] Furthermore, because the internal metal plate 1 is smaller in size than the metal wall of the panel, it becomes possible to implement more proactive sensitivity improvement measures, such as arranging multiple plates or installing them near equipment with a high risk of partial discharge. This further improves the signal-to-noise ratio.

[0028] As described above, this embodiment provides a partial discharge diagnostic device with a high signal-to-noise ratio and high detection sensitivity.

[0029] Figure 3 is a conceptual diagram illustrating this embodiment. The first difference from Figure 1 is that, in addition to board 101, it also has boards 102 and 103. While the number of boards is explained using three as an example, it also includes cases with two or four or more boards.

[0030] In environments requiring partial discharge diagnosis, such as factories, multiple panels are often used. For example, power receiving panels, distribution panels, and switchboards. In such cases, diagnosing and detecting partial discharge in each panel traditionally required installing a separate partial discharge diagnostic device for each panel. This presented a significant problem in terms of cost. This is largely because TEV sensors, in particular, are expensive due to their need for the ability to detect minute currents.

[0031] On the other hand, from the perspective of preventive maintenance and ensuring operational efficiency, partial discharge diagnosis is required for a large number of control panels.

[0032] Figure 3 shows the technological concept that enables the provision of a low-cost partial discharge diagnostic device for a large number of panels. Compared to Figure 1, it newly includes a signal switching switch 4 and a grounding switching switch 7.

[0033] The signal changeover switch 4 is connected to the internal metal plate 1 of panel 101 by coaxial cable 3, to the internal metal plate 201 of panel 102 by coaxial cable 202, and to the internal metal plate 301 of panel 103 by coaxial cable 302. The signal changeover switch 4 also has a switch inside the shield box to switch the connection destination.

[0034] The grounding switch 7 is electrically connected to the ground of panel 101 via the shield wire of coaxial cable 3. Similarly, it is connected to the ground of panel 102 via the shield wire of coaxial cable 202, and to the ground of panel 103 via the shield wire of coaxial cable 302. The grounding switch 7 also has a switch inside the shield box to switch the connection destination.

[0035] The output of the signal changeover switch 4 is connected to one end of the external metal plate 2 via the core wire of the coaxial cable 3. The output of the ground changeover switch 7 is connected to the other end of the external metal plate 2 via the shield wire of the coaxial cable 3.

[0036] The signal changeover switch 4 and the ground changeover switch 7 are switched simultaneously to connect to at least the same panel.

[0037] The signal switching switch 4 and the grounding switching switch 7 receive a switch switching instruction 60 from the signal storage and comparison calculation unit 9 as needed. This also includes cases where the instruction for the switching destination is issued by other parts, units, or circuits.

[0038] Figure 4A is an illustrative diagram of the switching circuit for the signal changeover switch 4 and the ground changeover switch 7. It is possible to select whether to connect or not connect each of the multiple systems. Figure 4B shows an example where only the left side is connected, and Figure 4C shows an example where all connections are selected. Figure 4D shows a desirable configuration example of this switching circuit, in which it is constructed using a switch IC. By using a switch IC, the switching time is shortened. This reduces the monitoring time lag for the control panel (the state in which it is not connected to the internal metal plate 1). In addition, since a large number of switches corresponding to a large number of control panels can be realized with a single IC, cost reduction is also achieved.

[0039] The configuration shown in Figure 3 allows the TEV sensor 6 to diagnose or detect partial discharge in a panel selected by the switch. In other words, it becomes possible to diagnose and detect partial discharge in multiple panels using a single TEV sensor. For example, conventionally, five TEV sensors were required for five panels, whereas in this embodiment, only one TEV sensor and two switch ICs are needed. Therefore, it becomes possible to provide a low-cost partial discharge diagnostic device that can handle multiple panels.

[0040] For example, even if the number of units to be diagnosed increases to 10 or more, in this embodiment, the increase in cost is essentially limited to the cost of the coaxial cable. Therefore, partial discharge diagnostic equipment can be introduced in factories and areas where it was previously impossible to implement due to cost constraints, thus making a significant contribution to power safety for society as a whole.

[0041] Figure 5 is a conceptual diagram illustrating this embodiment. In this embodiment, the signal storage and comparison calculation unit 9 includes a partial discharge signal detection and storage unit 311, a discharge signal magnitude determination unit 312, and a switch control unit 313.

[0042] The difference between this embodiment and Embodiment 2 mainly lies in the measurement sequence. Therefore, even if the internal units of the signal storage and comparison operation unit 9 are different, as long as the technical idea described below is used, it falls within the scope of the disclosure of this embodiment.

[0043] The measurement sequence of this embodiment will be described below.

[0044] (STEP 1) Partial discharge detection mode: In this state, the signal switching switch 4 and the ground switching switch 7 turn on all the switches. For example, as shown in FIG. 4C, all the switches are connected simultaneously. This enables simultaneous measurement and monitoring of all the boards to be connected. The partial discharge signal detection and storage unit 311 and the discharge signal magnitude determination unit 312 determine whether the value of the detected signal is less than or equal to a preset threshold. If it is less than or equal to the threshold, the measurement continues as it is.

[0045] (STEP 2) Board identification mode: When the discharge signal magnitude determination unit 312 determines that the value of the detected signal exceeds the preset threshold, it is determined that partial discharge has occurred in one of the boards. Then, the operation of identifying the board where partial discharge actually occurred is performed. According to the switch switching instruction 60 from the switch control unit 313, the signal switching switch 4 and the ground switching switch 7 switch from the fully selected state as shown in FIG. 4C to the state of obtaining signals from only one board as shown in FIG. 4B, and sequentially switch the connection destination board. Then, it is sequentially determined whether the value of the detected signal of each board is less than or equal to the preset threshold, and the board showing a value exceeding the threshold is identified as the board where partial discharge has occurred.

[0046] With the above measurement sequence, even when one TEV sensor handles a plurality of boards, a configuration can be achieved in which there is no monitoring time lag (state not connected to the internal metal plate 1) for the boards. As a result, the certainty of constant monitoring can be improved. And it is possible to eliminate the time loss during the switching of the power receiving board and to eliminate the oversight of the initial occurrence of partial discharge.

[0047] FIG. 6 shows a diagram corresponding to FIG. 3.

[0048] This embodiment is characterized in that a plurality of internal metal plates 1 are provided inside the board in any one of Embodiments 1 to 3.

[0049] As a result, improvement in the detection sensitivity of partial discharge or improvement in the signal-to-noise ratio is achieved.

[0050] The number of the internal metal plates 1 may be different among a plurality of boards. This is because the number of built-in devices where partial discharge is likely to occur differs depending on the function of the board.

[0051] Examples of devices where partial discharge is likely to occur include circuit breakers, disconnectors, power converters, transformers, etc.

[0052] Therefore, by arranging the internal metal plates 1 in the vicinity of a plurality of devices where partial discharge is likely to occur, the signal-to-noise ratio in partial discharge detection can be improved. This is not only the effect of simply increasing the number of the internal metal plates 1, but also has the effect of reducing the spatial distance from the partial discharge source.

[0053] Also, the internal metal plates 1 may be arranged at a plurality of positions with respect to a device where partial discharge is likely to occur. As a result, improvement in the detection sensitivity of partial discharge from the device is achieved.

[0054] The mutual connection of the plurality of internal metal plates 1 includes any of series connection, parallel connection, or series-parallel connection.

[0055] As a result, it becomes possible to receive a partial discharge signal near the discharge source, and it becomes possible to increase the signal-to-noise ratio of the signal.

[0056] This embodiment is an embodiment in which the shape of the internal metal plate 1 has a feature in any of Embodiments 1 to 4.

[0057] FIG. 7A is a perspective view of the internal metal plate 1 in this embodiment, and FIG. 7B is a plan view. It is characterized by having a hexagonal shape.

[0058] As a result, the induced current 501 flowing on the metal plate surface is concentrated at the end, and it becomes possible to efficiently capture the induced current 501 without loss at the coaxial cable connection part.

[0059] More preferably, the shape of the hexagonal end is determined so that the impedance determined by the shape is equivalent to the impedance of the coaxial cable. This achieves impedance matching, eliminates signal reflection with the coaxial cable, and further improves the signal-to-noise ratio.

[0060] Furthermore, even when the internal metal plate 1 has a shape that tapers at both ends relative to the center, it is still included in the category of a hexagon in this implementation.

[0061] This embodiment is an example in which the shape of the internal metal plate 1 from Embodiment 5 is applied to the external metal plate 2. As a result, the effects similar to those of Embodiment 5 can be achieved with the external metal plate 2.

[0062] Furthermore, both the internal metal plate 1 and the external metal plate 2 may be structured as shown in Figures 7A and 7B. This is because both configurations produce the same effects as described in Example 5.

[0063] This embodiment is an example that can be applied in combination with any of Examples 1 to 6. In this embodiment, the size of the internal metal plate 1 is larger than the size of the external metal plate 2.

[0064] The internal metal plate 1 is preferable to be larger in order to induce a greater induced current. On the other hand, if the external metal plate 2 is larger than necessary for the TEV sensor, its sensitivity will actually decrease. Therefore, by making the size of the internal metal plate 1 larger than the size of the external metal plate 2, an improvement in the signal-to-noise ratio can be achieved.

[0065] This embodiment is an example that can be applied in combination with any of Examples 1 to 7. Figure 8 is a diagram illustrating the partial discharge monitoring system based on Figure 3.

[0066] The signal storage and comparison calculation unit 9 transmits the measurement results 73 to the monitoring device 71 via the communication network 70. The monitoring device 71 includes various examples, such as a user's monitoring terminal or a management server of a monitoring contractor.

[0067] The monitoring device 71 continues monitoring if no partial discharge is detected. When a partial discharge is detected, it transmits an instruction 72 to the signal storage and comparison calculation unit 9 via the communication network 70, instructing it to perform a more detailed analysis or to transition to the panel identification mode shown in STEP 2 of Embodiment 3.

[0068] 75 is a display unit. This includes various examples such as monitoring terminals, user management terminals, and the control panel itself. When the monitoring device 71 detects a partial discharge, it notifies the display unit 75 of the occurrence of the partial discharge and the control panel in which the partial discharge occurred. This enables quick confirmation of the actual control panel status and recovery work.

[0069] As a monitoring system for partial discharge, having only one TEV sensor compared to having a number of TEV sensors corresponding to the control panel reduces the amount of information transmitted via the communication network 70, thus lowering monitoring costs. Furthermore, it also reduces the risk of failure of the insulation monitoring device itself, resulting in a decrease in overall monitoring and operation costs.

[0070] The idea and concept of the present invention have been described above using various embodiments. Of course, examples realized by combining these embodiments are also included within the scope of the present invention. Furthermore, modifications and similar examples thereof, as long as they utilize the disclosed ideas and concepts, are also included within the scope of the present invention.

[0071] Furthermore, an example of the present invention described using the above embodiments can also be expressed as follows.

[0072] <Part 1> A partial discharge measuring device for an object having a first metal plate and a second metal plate electrically connected to the first metal plate by a cable and placed inside the panel, which measures the current of the first metal plate to measure the inside of the panel. <Part 2> The partial discharge measuring device according to <Part 1>, wherein a TEV sensor is installed on the first metal plate and the current of the first metal plate is measured as a voltage signal from the TEV sensor. <Part 3> The partial discharge measuring device according to <Part 2>, wherein the cable is a coaxial cable, the core wire of the coaxial cable electrically connects one end of the second metal plate and the first metal plate, and the shield wire of the coaxial cable electrically connects the other end of the first metal plate to the metal housing of the panel. <Part 4> The partial discharge measuring device according to <Part 3>, which has a plurality of panels, each of which has the second metal plate, and has a switch to switch whether the first metal plate is connected to any of the second metal plates individually or simultaneously. <5> The partial discharge measuring device according to <4>, wherein the switch normally connects the first metal plate and a plurality of the second metal plates simultaneously, and when a partial discharge is detected, it sequentially connects the first metal plate and the second metal plates individually to detect the partial discharge. <6> The partial discharge measuring device according to <5>, further comprising a partial discharge detection unit for detecting a partial discharge, a partial discharge storage unit for storing the partial discharge, a determination unit for determining the magnitude of the discharge signal, and a control unit for instructing the switching of connections based on the determination result. <7> The partial discharge measuring device according to any one of <1> to <6>, wherein a plurality of the second metal plates are provided in a single panel. <8> The partial discharge measuring device according to <7>, wherein the second metal plates are installed in correspondence with a circuit breaker, disconnector, power converter, or transformer. <9> The partial discharge measuring device according to <8>, wherein the second metal plates are installed in correspondence with a plurality of circuit breakers, disconnectors, power converters, or transformers. <10> The partial discharge measuring device described in <8>, wherein the second metal plate is installed in multiple locations on any of the circuit breakers, disconnectors, power converters, or transformers. <11> The partial discharge measuring device described in any one of <1>1 to <6>, wherein the second metal plate is hexagonal in shape. <12> The partial discharge measuring device described in <11>, wherein the first metal plate is hexagonal in shape.<13> The partial discharge measuring device according to any one of <1> to <6>, wherein the second metal plate is larger than the first metal plate. <14> A partial discharge monitoring system having the partial discharge measuring device according to any one of <1> to <6>, and monitoring the presence or absence of partial discharge via a communication line with the partial discharge measuring device.

Claims

1. A partial discharge measuring device for an object having a first metal plate and a second metal plate electrically connected to the first metal plate by a cable and placed inside the panel, which measures the current of the first metal plate and measures the inside of the panel.

2. The partial discharge measuring device according to claim 1, wherein a TEV sensor is installed on the first metal plate, and the current of the first metal plate is measured as a voltage signal from the TEV sensor.

3. The partial discharge measuring device according to claim 2, wherein the cable is a coaxial cable, the core wire of the coaxial cable electrically connects one end of the second metal plate and the first metal plate, and the shield wire of the coaxial cable electrically connects the other end of the first metal plate to the metal housing of the panel.

4. The partial discharge measuring device according to claim 3, which has a plurality of plates, each of which has the second metal plate, and a switch for switching whether the first metal plate is connected to any of the second metal plates individually or simultaneously.

5. The partial discharge measuring device according to claim 4, wherein the switch normally connects the first metal plate and a plurality of the second metal plates simultaneously, and when a partial discharge is detected, it sequentially connects the first metal plate and the second metal plates individually to detect the partial discharge.

6. The partial discharge measuring device according to claim 5, comprising: a partial discharge detection unit for detecting partial discharge; a partial discharge storage unit for storing partial discharge; a determination unit for determining the magnitude of the discharge signal; and a control unit for instructing a connection switch based on the determination result.

7. The partial discharge measuring device according to any one of claims 1 to 6, wherein the second metal plate is provided in multiple locations within a single panel.

8. The partial discharge measuring device according to claim 7, wherein the second metal plate is installed in accordance with any of the circuit breakers, disconnectors, power converters, or transformers.

9. The partial discharge measuring device according to claim 8, wherein the second metal plate is installed in accordance with a plurality of circuit breakers, disconnectors, power converters, and transformers.

10. The partial discharge measuring device according to claim 8, wherein multiple second metal plates are installed on any of the circuit breakers, disconnectors, power converters, or transformers.

11. The partial discharge measuring device according to any one of claims 1 to 6, wherein the second metal plate has a hexagonal shape.

12. The partial discharge measuring device according to claim 11, wherein the first metal plate has a hexagonal shape.

13. The partial discharge measuring device according to any one of claims 1 to 6, wherein the second metal plate is larger than the first metal plate.

14. A partial discharge monitoring system having a partial discharge measuring device according to any one of claims 1 to 6, and monitoring the presence or absence of partial discharge via a communication line with the partial discharge measuring device.

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