DC insulation resistance monitoring device, and DC insulation resistance monitoring method

Abstract

To provide a DC insulation resistance monitoring device capable of monitoring DC insulation resistance in a live power distribution system while minimizing current measurement errors requiring no highly sensitive current measuring means.SOLUTION: The DC insulation resistance monitoring device for a high-voltage power distribution system includes: a neutral switch 11 that is connected to a grounded potential transformer 10; an insulation capacitor 12 that is opened / closed by the neutral switch 11; a DC power supply 13 for charging the insulation capacitor 12; a DC power supply switchgear 14 that opens / closes the connection between the DC power supply 13 and the insulation capacitor 12; a voltage measurement unit 15 that measures the voltage of the insulation capacitor 12 depending on the opening / closing of the DC power supply switchgear 14; and a control unit 17 that controls the open / close operation of the neutral switch 11 and the DC power supply switchgear 14. The voltage measurement unit 15 resist-divides the voltage of the insulation capacitor 12 and inputs the resist-divided voltage to measure the voltage change of the insulation capacitor 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a DC insulation resistance monitoring device and a DC insulation resistance monitoring method for measuring the DC insulation resistance of, for example, an ungrounded high-voltage distribution system. [Background technology]

[0002] Conventionally, the method for measuring the DC insulation resistance of a high-voltage power distribution system has generally been to shut down the power distribution system, connect a high-voltage DC power supply, and measure the leakage current. In addition, for example, Patent Document 1 discloses a DC insulation resistance monitoring device. Patent Document 1 discloses a configuration in which the primary neutral point of a grounded instrument transformer connected to the power distribution system is DC-insulated by a capacitor, a DC power supply is connected to the neutral point, and the leakage current is measured. This makes it possible to measure the DC insulation resistance of the power distribution system in a live line state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 58-55870 Summary of the Invention [Problem to be solved by the invention]

[0004] The DC insulation resistance monitoring device described in Patent Document 1 has the problem that it requires a highly sensitive current measuring means to measure minute leakage currents and is susceptible to the effects of external noise during measurement, making it prone to measurement errors.

[0005] The present invention has been made in view of the above background, and has as its object to provide a DC insulation resistance monitoring device and a DC insulation resistance monitoring method that are capable of monitoring the DC insulation resistance of a high-voltage distribution system using a live line while minimizing current measurement errors, without the need for a highly sensitive current measurement means for measuring minute currents. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the above-mentioned object, one embodiment of the present invention is a DC insulation resistance monitoring device for a high-voltage distribution system equipped with a grounded instrument transformer, comprising: a neutral point switch connected to the grounded instrument transformer, an insulating capacitor opened and closed by the neutral point switch, a DC power source for charging the insulating capacitor, a DC power supply switch for opening and closing a connection between the DC power source and the insulating capacitor, a voltage measuring unit for measuring a voltage of the insulating capacitor in response to opening and closing of the DC power supply switch, and a control unit for controlling the opening and closing operations of the neutral point switch and the DC power supply switch, wherein the voltage measuring unit performs resistance division to divide the voltage of the insulating capacitor, inputs the resistance-divided voltage, and measures a voltage change of the insulating capacitor.

[0007] Another embodiment of the present invention is a method for monitoring DC insulation resistance in a high-voltage distribution system equipped with a grounded instrument transformer, the high-voltage distribution system comprising: a neutral point switch connected to the grounded instrument transformer; an insulating capacitor opened and closed by the neutral point switch; a DC power source for charging the insulating capacitor; a DC power source switch for opening and closing a connection between the DC power source and the insulating capacitor; a voltage measuring unit for measuring a voltage of the insulating capacitor in response to opening and closing of the DC power source switch; and a control unit for controlling the opening and closing operations of the neutral point switch and the DC power source switch, the high-voltage distribution system being characterized in that the neutral point switch in a closed state is opened under the control of the control unit, the DC power source switch in an open state is closed, and the insulating capacitor is charged to a predetermined voltage by the DC power source, and after charging to the predetermined voltage, the DC power source switch is returned to an open circuit and then the neutral point switch is returned to a closed circuit. Effect of the Invention

[0008] According to the present invention, it is possible to provide a DC insulation resistance monitoring device and a DC insulation resistance monitoring method that do not require a highly sensitive current measuring means, and that are capable of monitoring the DC insulation resistance of a high-voltage distribution system using a live line while minimizing current measurement errors. [Brief description of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing an example of a high-voltage power distribution system including a DC insulation resistance monitoring device according to a first embodiment of the present invention. [Diagram 2] 2 is a configuration diagram showing an example of a circuit configuration of a voltage measuring unit according to the first embodiment of the present invention. FIG. [Diagram 3] FIG. 2 is an explanatory diagram showing a time chart of the DC insulation resistance monitoring device according to the first embodiment of the present invention. [Figure 4] FIG. 3 is an explanatory diagram showing an example of a voltage waveform of the insulating capacitor according to the first embodiment of the present invention. [Diagram 5] FIG. 11 is an explanatory diagram showing another example of a voltage waveform of the insulating capacitor according to the first embodiment of the present invention. [Figure 6] FIG. 4 is an explanatory diagram showing an example of a voltage waveform of an insulating capacitor when a single-line ground fault occurs in a high-voltage power distribution system during monitoring according to the first embodiment of the present invention. [Figure 7] FIG. 2 is an explanatory diagram showing an example of phase voltage waveforms when a single-line ground fault occurs in a high-voltage distribution system during monitoring according to the first embodiment of the present invention. [Figure 8] FIG. 2 is an explanatory diagram showing an example of a zero-phase voltage waveform of a system voltage measured by a grounded potential transformer when a single-line ground fault occurs in a power distribution system during monitoring according to the first embodiment of the present invention. [Figure 9] FIG. 11 is a configuration diagram showing an example of a voltage measurement unit according to a second embodiment of the present invention. [Figure 10] FIG. 11 is a configuration diagram showing an example of a voltage measurement unit according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following description and drawings are merely examples for explaining the present invention, and appropriate omissions and simplifications have been made in order to clarify the explanation. The present invention can also be implemented in various other forms. Furthermore, unless otherwise specified, each component may be singular or plural.

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the following are merely examples of the present invention, and the contents of the present invention are not limited to the specific embodiments described below. The present invention can of course be modified into various embodiments, including the embodiments described below.

[0012] <Embodiment 1> First, the configuration of the first embodiment of the present invention will be described. Fig. 1 is a configuration diagram showing an example of a high-voltage distribution system including a DC insulation resistance monitoring device of the first embodiment. The high-voltage distribution system in which DC insulation resistance is measured is composed of an extra-high voltage transformer (hereinafter referred to as extra-high voltage transformer) 1, a high-voltage distribution panel 2, a high-voltage incoming panel 3, a low-voltage panel 4, and a high-voltage transformer 5, for example, as shown in Fig. 1.

[0013] Extra-high voltage transformer 1 converts the extra-high voltage received voltage, for example 66 kV, to a voltage of 6.6 kV, high-voltage distribution panel 2 measures voltage and current and detects ground faults, high-voltage receiving panel 3 receives electricity, low-voltage panel 4 drops the voltage of 6.6 kV to, for example, 400 V, and high-voltage transformer 5 transforms the voltage and supplies it to motors and the like not shown.

[0014] In the first embodiment, the measurement of DC insulation resistance, i.e., the function of monitoring DC insulation resistance, is provided in a high-voltage distribution board 2. The high-voltage distribution board 2 includes a grounded instrument transformer 10, a neutral point switch 11, an insulating capacitor 12, a DC power supply 13, a DC power supply switch 14, a voltage measurement unit 15, and a control unit 17. Here, the control unit 17 is configured using a timer relay and a microcomputer, and is responsible for controlling the entire DC insulation resistance monitoring device.

[0015] In the high-voltage distribution board 2 of the first embodiment, an insulating capacitor 12 is inserted between the neutral point of a grounded instrument transformer 10 and ground, and a neutral point switch 11 is connected to the insulating capacitor 12. A DC power supply 13 is connected to the insulating capacitor 12 via a DC power supply switch 14. Furthermore, a voltage measuring unit 15 is provided to measure the insulating capacitor voltage of the insulating capacitor 12.

[0016] In the first embodiment, the DC insulation resistance monitoring device is provided in a high-voltage distribution panel 2, and is composed of a neutral point switch 11, an insulating capacitor 12, a DC power supply 13, a DC power supply switch 14, a voltage measurement unit 15, and a control unit 17. This DC insulation resistance monitoring device measures leakage resistance in the high-voltage distribution system of FIG.

[0017] The high-voltage switchboard 2 is provided with a grounded potential transformer 10. For this reason, adding the configuration from the neutral switch 11 to the control unit 17 to the grounded potential transformer 10 is suitable for leakage resistance measurement, and satisfies conditions such as meeting the requirements for grounding and minimizing the number of parts required. Of course, it goes without saying that the DC insulation resistance monitoring device can be incorporated in any configuration that satisfies these conditions, and is not limited to the high-voltage switchboard 2.

[0018] Next, the main configuration for measuring leakage current, i.e., leakage resistance, will be described with reference to Fig. 2. Fig. 2 is a configuration diagram showing an example of the circuit configuration of the voltage measurement unit of the present embodiment 1. As shown in Fig. 2, the voltage measurement unit 15 includes a resistive voltage divider 20 composed of a resistive voltage divider high-side resistor 21A and a resistive voltage divider low-side resistor 21B, a voltage follower circuit 22, a measuring device 23, and the like.

[0019] In voltage measurement section 15, the insulating capacitor voltage output from insulating capacitor 12 is divided by resistive voltage divider high-side resistor 21A and resistive voltage divider low-side resistor 21B of resistive voltage divider 20. The divided voltage is input to voltage follower circuit 22 and further input to an A / D converter (not shown) or the like, and a measuring device 23 measures the change over time of the insulating capacitor voltage stored in insulating capacitor 12.

[0020] Although not shown, the resistive voltage divider 20 is connected in parallel with the main circuit resistance to be measured, which may cause measurement errors. Therefore, the high-side resistor 21A of the resistive voltage divider is set to a value larger than the main circuit resistance to be measured, thereby reducing the error.

[0021] Next, a change in the insulation capacitor voltage will be described with reference to Fig. 3. Fig. 3 is an explanatory diagram showing a time chart of the DC insulation resistance monitoring device according to the first embodiment. Fig. 3 shows, on the time axis, the insulation capacitor voltage that changes in response to the opening and closing of the neutral point switch 11 and the DC power switch 14 under the control of the control unit 17. Here, t1, t2, t3, and t4 indicate the times when the control unit 17 controls the opening and closing of the neutral point switch 11 and the DC power switch 14.

[0022] In the time chart of FIG. 3, the control unit 17 opens the neutral point switch 11 (normally closed contact) at time t1, and closes the DC power switch 14 at time t2. As a result, the insulating capacitor 12 is charged to a predetermined voltage from the DC power source 13 via the DC power switch 14. When the control unit 17 opens the DC power switch 14 at time t3, the voltage of the insulating capacitor 12 leaks due to leakage resistance in the main circuit and gradually decreases. When the control unit 17 closes the neutral point switch 11 at time t4, the insulating capacitor 12 is short-circuited. The period from when the DC power switch 14 is returned to an open circuit to when the neutral point switch 11 is closed is set based on the period during which the voltage of the insulating capacitor 12 leaks due to leakage resistance in the main circuit and gradually decreases. The insulating capacitor voltage shown here indicates a value measured by a measuring device 23.

[0023] Next, measurement of leakage resistance in a live line state will be described with reference to Fig. 4 to Fig. 8. First, voltage waveforms when no line-to-ground fault occurs in the power distribution system during monitoring will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is an explanatory diagram showing an example of a voltage waveform of an insulating capacitor in the DC insulation resistance monitoring device of the present embodiment 1, and Fig. 5 is an explanatory diagram showing another example of a voltage waveform of an insulating capacitor in the DC insulation resistance monitoring device of the present embodiment 1.

[0024] 4 and 5, the vertical axis represents the measured insulating capacitor voltage (V) and the horizontal axis represents time (t). The voltage waveforms shown in the graphs of FIGS. 4 and 5 are measured by voltage measuring unit 15.

[0025] The graph in Fig. 4 shows the voltage waveform of the insulating capacitor 12 when the neutral point switch 11 is opened, the insulating capacitor 12 is charged to a certain voltage from the DC power source 13 via the DC power switch 14, and then the DC power switch 14 is opened in the DC insulation resistance monitoring device in Fig. 1. Here, the graph allows confirmation of voltage attenuation, which corresponds to a case where the leakage resistance is small (insulation resistance is low).

[0026] An induced voltage of commercial frequency is superimposed on the voltage waveform of insulating capacitor 12, but by setting an appropriate interval and taking a moving average or passing the signal through a low-pass filter, it is possible to extract the voltage component that changes with a time constant determined by the product of the leakage resistance of insulating capacitor 12 and the leakage resistance of the high-voltage distribution system.

[0027] The graph shown in Fig. 5 shows the voltage waveform of the insulating capacitor 12 when the leakage resistance of the high-voltage distribution system is large. In the graph of Fig. 5, since the discharge time constant is large, the voltage waveform of the insulating capacitor 12 shows a substantially constant value.

[0028] Next, voltage waveforms when a single line-to-ground fault occurs in a high-voltage distribution system during monitoring will be described with reference to Fig. 6, Fig. 7, and Fig. 8. Fig. 6 is an explanatory diagram showing an example of a voltage waveform of an insulating capacitor when a single line-to-ground fault occurs in a high-voltage distribution system during monitoring by the DC insulation resistance monitoring device of the first embodiment, and Fig. 7 is an explanatory diagram showing an example of a phase voltage waveform when a single line-to-ground fault occurs in a high-voltage distribution system during monitoring by the DC insulation resistance monitoring device of the first embodiment.

[0029] Furthermore, Fig. 8 is an explanatory diagram showing an example of a zero-phase voltage waveform of a system voltage measured by a grounded potential transformer when a single-line ground fault occurs in a power distribution system during monitoring by the DC insulation resistance monitoring device of the present embodiment 1. In the graphs shown in Figs. 6, 7 and 8, the vertical axis represents the measured insulating capacitor voltage (V) and the horizontal axis represents time (t).

[0030] The graph shown in Fig. 6 shows the voltage waveform of the insulating capacitor 12 when a single line-to-ground fault occurs in the high-voltage distribution system at 2 seconds while measuring the DC insulation resistance. When a single line-to-ground fault occurs in the high-voltage distribution system, as shown in Fig. 6, the voltage of the insulating capacitor 12 drops to -700 V, for example.

[0031] The graph in Figure 7 shows that between 2 seconds and 2.1 seconds when a line-to-ground fault occurs in the phase voltage waveform of a high-voltage distribution system, the voltage of the faulty phase drops and the voltage of the healthy phase increases by approximately 1.7 times.

[0032] The graph in Fig. 8 shows a zero-phase voltage waveform measured by the grounded potential transformer 10. The zero-phase voltage has the same waveform as that in the normal state where the insulating capacitor 12 is short-circuited, and even if a single-line ground fault occurs in the high-voltage distribution system while measuring the DC insulation resistance, the fault can be detected. This state can be achieved by setting the capacitance of the insulating capacitor 12 to, for example, 1 to 10 μF.

[0033] Furthermore, if the charging voltage of the insulating capacitor 12 is set to about 10 V, the influence on other systems, including bias magnetism of the grounded potential transformer 10, can be ignored.

[0034] Although not shown, if the voltage measuring unit 15 is connected to an output device such as a display device via an external output interface, it becomes possible to display the voltage waveform data outside the high voltage distribution system as shown in FIGS.

[0035] As described above, according to the first embodiment, it is possible to monitor the DC insulation resistance of a high-voltage distribution system with a live line while minimizing errors in current measurement without requiring a highly sensitive current measuring means.

[0036] <Embodiment 2> Next, a second embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 is a configuration diagram showing an example of a voltage measurement unit according to the second embodiment. In the second embodiment, in a high-voltage distribution system similar to that of the first embodiment, the internal configuration of the voltage measurement unit is different, so a description of the common parts will be omitted and only the different parts will be described below.

[0037] In the second embodiment, as shown in FIG. 9, a configuration is shown in which a Zener diode 24 for limiting an input signal to a voltage follower circuit 22 is connected in parallel to a low-voltage side resistor 21B of the resistive voltage divider.

[0038] With this configuration, it is possible to reduce measurement errors as in the first embodiment described above, and also to prevent failure of the voltage follower circuit 22 even if an excessive voltage is input to the resistive voltage divider 20. In addition, since the Zener diode 24 is connected to the insulating capacitor 12 via the high-voltage side resistor 21A of the resistive voltage divider, it is possible to prevent an excessive current from flowing through the Zener diode 24, which has the effect of reducing the withstand current capacity of the Zener diode 24.

[0039] <Embodiment 3> Next, a third embodiment of the present invention will be described with reference to Fig. 10. Fig. 10 is a configuration diagram showing an example of a voltage measurement unit according to the third embodiment. In the third embodiment, in a high-voltage distribution system similar to that of the first embodiment, the internal configuration of the voltage measurement unit is different, so a description of the common parts will be omitted and only the different parts will be described below.

[0040] In the third embodiment, a configuration is shown in which an overvoltage suppression circuit 25 such as a zinc oxide element is connected in parallel to a resistive voltage divider. With such a configuration, it is possible to reduce measurement errors as in the first and second embodiments described above, and also to protect the voltage follower circuit 22 from an excessively large signal even in the case of an overvoltage suppression circuit 25 with a high operating voltage.

[0041] Today, with the decline in the working population, there is an increasing need to reduce maintenance, improve the operation rate of production facilities, and reduce downtime. The ability to measure the DC insulation resistance of extra-high voltage consumers' power receiving and distribution equipment and distribution lines while they are in a live state is beneficial in meeting these needs.

[0042] Furthermore, in a high-voltage distribution system, the DC insulation resistance monitoring device can be simply connected to the grounded instrument transformer 10 and incorporated into the high-voltage distribution panel 2, so the number of parts required to introduce the DC insulation resistance monitoring device into the high-voltage distribution system is small, thereby reducing parts costs. [Explanation of symbols]

[0043] 1. Extra-high voltage transformer 2 High voltage switchboard 3 High voltage receiving panel 4 Low voltage board 5. High-voltage transformer 10. Earthed potential transformers 11 Neutral switch 12 Insulating capacitors 13 DC power supply 14 DC power switch 15 Voltage measurement section 17 Control section 20 Resistor Divider 21A resistor divider high side resistor 21B Resistor divider low-side resistor 22 Voltage follower circuit 23 Measuring instruments 24 Zener Diode 25 Overvoltage Suppression Circuit

Claims

1. A DC insulation resistance monitoring device for a high-voltage distribution system equipped with a grounded instrument transformer, comprising: a neutral switch connected to the grounded potential transformer; an insulating capacitor connected to the neutral point switch; a DC power source for charging the insulating capacitor; a DC power supply switch that opens and closes a connection between the DC power supply and the insulating capacitor; a voltage measuring unit that measures a voltage of the insulating capacitor in response to opening and closing of the DC power switch; A control unit for controlling the opening and closing operations of the neutral point switch and the DC power switch; Equipped with the voltage measuring unit performs resistance division to divide the voltage of the insulating capacitor, inputs the resistance-divided voltage, and measures a change in the voltage of the insulating capacitor.

2. 2. The DC insulation resistance monitoring device according to claim 1, wherein the control unit controls the DC power supply switch in an open state to close during a period in which the neutral point switch in a closed state is open-circuited, until the insulating capacitor reaches a predetermined voltage at the DC power supply.

3. 2. The DC insulation resistance monitoring device according to claim 1, wherein the voltage measuring unit has a resistive voltage divider consisting of a high-voltage side resistor and a low-voltage side resistor for dividing the voltage of the insulating capacitor.

4. 2. The DC insulation resistance monitoring device according to claim 1, wherein said voltage measuring section has a voltage follower circuit to which said resistor-divided voltage is input.

5. 4. The DC insulation resistance monitoring device according to claim 3, further comprising a Zener diode connected in parallel with the low-voltage side resistor of the resistive voltage divider.

6. 4. The DC insulation resistance monitoring apparatus according to claim 3, further comprising an overvoltage control circuit connected in parallel with said resistive voltage divider.

7. 4. The DC insulation resistance monitoring device according to claim 3, wherein the high-voltage side resistance of said resistive voltage divider is set to a value larger than the resistance of the main circuit to be measured.

8. A method for monitoring DC insulation resistance in a high-voltage power distribution system equipped with a grounded instrument transformer, comprising the steps of: The high-voltage distribution system includes: a neutral switch connected to the grounded potential transformer; an insulating capacitor connected to the neutral point switch; a DC power source for charging the insulating capacitor; a DC power supply switch that opens and closes a connection between the DC power supply and the insulating capacitor; a voltage measuring unit that measures a voltage of the insulating capacitor in response to opening and closing of the DC power switch; A control unit for controlling the opening and closing operations of the neutral point switch and the DC power switch; Equipped with a control unit for controlling the control of the insulation capacitor to charge the insulation capacitor to a predetermined voltage by opening the neutral point switch in a closed state and closing the DC power supply switch in an open state in the high-voltage distribution system, and then returning the DC power supply switch to an open state and then returning the neutral point switch to a closed state.

9. 9. The DC insulation resistance monitoring method according to claim 8, wherein a period from when the DC power supply switch is returned to an open circuit to when the neutral point switch is returned to a closed circuit is set as a period for allowing a gradual decrease in the voltage of the insulating capacitor due to leakage resistance.

10. 9. The DC insulation resistance monitoring method according to claim 8, wherein the voltage measuring unit has a resistive voltage divider consisting of a high-voltage side resistor and a low-voltage side resistor for dividing the voltage of the insulation capacitor, and the high-voltage side resistor of the resistive voltage divider is set to a value larger than the resistance of the main circuit to be measured.

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