DC insulation resistance monitoring device and DC insulation resistance monitoring method

Abstract

This DC insulation resistance monitoring device for a high-voltage power distribution system comprises: a neutral point switch 11 connected to a transformer 10 for a grounding-type instrument; an insulation capacitor 12 which is opened and closed by the neutral point switch 11; a DC power supply 13 which charges the insulation capacitor 12; a DC power supply switch 14 which opens and closes connection between the DC power supply 13 and the insulation capacitor 12; a voltage measurement unit 15 which measures the voltage of the insulation capacitor 12 in response to opening / closing of the DC power supply switch 14; and a control unit 17 which controls the opening / closing operations of the neutral point switch 11 and the DC power supply switch 14. The voltage measurement unit 15 performs resistive voltage division to divide the voltage of the insulation capacitor 12, inputs the voltage resulting from the resistive voltage division, and measures a voltage change in the insulation capacitor 12.

Description

DC insulation resistance monitoring device and DC insulation resistance monitoring method

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

[0002] A common method for measuring DC insulation resistance in a conventional high-voltage power distribution system is to shut down the system, connect a high-voltage DC power supply, and measure the leakage current. Patent Document 1, for example, discloses a DC insulation resistance monitoring device. This patent document discloses a configuration in which the neutral point on the primary side of a grounded voltage transformer connected to the power distribution system is DC-insulated with a capacitor, a DC power supply is connected to the neutral point, and the leakage current is measured. This allows the DC insulation resistance of the power distribution system to be measured while the line is live.

[0003] Japanese Unexamined Patent Publication No. 58-55870

[0004] The DC insulation resistance monitoring device described in Patent Document 1 has the problem that it requires a highly sensitive current measurement means to measure minute leakage currents and is susceptible to the influence 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 aims 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 live lines while minimizing current measurement errors, without the need for highly sensitive current measurement means for measuring minute currents.

[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 potential transformer, comprising: a neutral point switch connected to the grounded potential transformer; an insulating capacitor switched by the neutral point switch; a DC power supply that charges the insulating capacitor; a DC power supply switch that switches the connection between the DC power supply and the insulating capacitor; a voltage measuring unit that measures the voltage of the insulating capacitor in response to the opening and closing of the DC power supply switch; and a control unit that controls 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 change in voltage 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 potential transformer, the high-voltage distribution system comprising: a neutral point switch connected to the grounded potential transformer; an insulating capacitor switched by the neutral point switch; a DC power supply that charges the insulating capacitor; a DC power supply switch that switches the connection between the DC power supply and the insulating capacitor; a voltage measuring unit that measures the voltage of the insulating capacitor in response to the opening and closing of the DC power supply switch; and a control unit that controls the opening and closing operations of the neutral point switch and the DC power supply switch, wherein in the high-voltage distribution system, under the control of the control unit, the neutral point switch in a closed state is opened and the DC power supply switch in an open state is closed to charge the insulating capacitor to a predetermined voltage with the DC power supply, and after charging to the predetermined voltage, the DC power supply switch is returned to an open circuit and then the neutral point switch is returned to a closed circuit.

[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 measurement 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.

[0009] FIG. 1 is a configuration diagram showing an example of a high-voltage distribution system including a DC insulation resistance monitoring device according to a first embodiment of the present invention; FIG. 1 is a configuration diagram showing an example of a circuit configuration of a voltage measurement unit according to the first embodiment of the present invention; FIG. 2 is an explanatory diagram showing a time chart of a DC insulation resistance monitoring device according to the first embodiment of the present invention; FIG. 2 is an explanatory diagram showing an example of a voltage waveform of an insulating capacitor according to the first embodiment of the present invention; FIG. 3 is an explanatory diagram showing another example of a voltage waveform of an insulating capacitor according to the first embodiment of the present invention; FIG. 3 is an explanatory diagram showing an example of a voltage waveform of an insulating capacitor when a single-line ground fault occurs in the high-voltage distribution system during monitoring according to the first embodiment of the present invention; FIG. 4 is an explanatory diagram showing an example of a phase voltage waveform when a single-line ground fault occurs in the high-voltage distribution system during monitoring according to the first embodiment of the present invention; FIG. 4 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 the distribution system during monitoring according to the first embodiment of the present invention;

[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 some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can also be implemented in various other forms. Furthermore, unless otherwise specified, each component may be singular or plural.

[0011] Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the following are merely examples of the present invention, and the content of the present invention is 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] First Embodiment First, the configuration of a first embodiment of the present invention will be described. Fig. 1 is a configuration diagram showing an example of a high-voltage power distribution system including a DC insulation resistance monitoring device according to the first embodiment. The high-voltage power distribution system in which DC insulation resistance is measured comprises, for example, as shown in Fig. 1, 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.

[0013] An extra-high voltage transformer 1 converts the voltage received at extra-high voltage, for example, 66 kV, to a voltage of 6.6 kV, a high-voltage distribution panel 2 measures voltage and current and detects ground faults, a high-voltage receiving panel 3 receives electricity, a low-voltage panel 4 reduces the voltage of 6.6 kV to, for example, 400 V, and a high-voltage transformer 5 transforms the voltage and supplies it to a motor or 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 within the high-voltage switchboard 2. The high-voltage switchboard 2 includes a grounded potential 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. The control unit 17 is configured using a timer relay and a microcomputer, and controls the entire DC insulation resistance monitoring device.

[0015] In the high-voltage switchboard 2 of the first embodiment, an insulating capacitor 12 is inserted between the neutral point of a grounded voltage 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 the 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 measuring unit 15, and a control unit 17. This DC insulation resistance monitoring device measures leakage resistance in the high-voltage distribution system shown in FIG.

[0017] The high-voltage switchboard 2 is provided with a grounded potential transformer 10. For this reason, adding the configuration from the neutral point 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 grounding requirements and minimizing the number of parts required. Of course, it goes without saying that the DC insulation resistance monitoring device can be incorporated into 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 measuring section 15, the insulating capacitor voltage output from insulating capacitor 12 is divided by resistor 21A on the high-voltage side and resistor 21B on the low-voltage side 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 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 can cause measurement errors. Therefore, the high-side resistor 21A of the resistive voltage divider can be set to a value larger than the main circuit resistance to be measured, thereby reducing the error.

[0021] Next, changes in the insulation capacitor voltage will be described using 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 supply switch 14 under the control of the control unit 17. Here, t1, t2, t3, and t4 indicate times when the control unit 17 controls the opening and closing of the neutral point switch 11 and the DC power supply switch 14.

[0022] In the time chart of Figure 3, the control unit 17 opens the neutral point switch 11 (normally closed contact) at time t1 and closes the DC power supply switch 14 at time t2. As a result, the insulating capacitor 12 is charged to a predetermined voltage from the DC power supply 13 via the DC power supply switch 14. When the control unit 17 opens the DC power supply 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 supply 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 gradually decreases due to leakage resistance in the main circuit. The insulating capacitor voltage shown here is a value measured by the measuring device 23.

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

[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 measurement unit 15.

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

[0026] An induced voltage of commercial frequency is superimposed on the voltage waveform of the 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 a voltage component that changes with a time constant determined by the product of the leakage resistance of the insulating capacitor 12 and the high-voltage distribution system.

[0027] The graph shown in Figure 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 Figure 5, the discharge time constant is large, so the voltage waveform of the insulating capacitor 12 shows an almost constant value.

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

[0029] 8 is an explanatory diagram showing an example of a zero-phase sequence voltage waveform of the system voltage measured by a grounded potential transformer when a single-phase ground fault occurs in the power distribution system during monitoring by the DC insulation resistance monitoring device of this 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 Figure 6 shows the voltage waveform of insulating capacitor 12 when a line-to-ground fault occurs in the high-voltage distribution system at 2 seconds during measurement of DC insulation resistance. When a line-to-ground fault occurs in the high-voltage distribution system, the voltage of insulating capacitor 12 drops to -700 V, for example, as shown in Figure 6.

[0031] The graph shown in Figure 7 shows that during the period from 2 seconds to 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 grounded phase drops and the voltage of the healthy phase increases by approximately 1.7 times.

[0032] The graph in Figure 8 shows the zero-phase voltage waveform measured by the grounded potential transformer 10. The zero-phase voltage has the same waveform as in the normal state when the insulating capacitor 12 is short-circuited, making it possible to detect a single-phase ground fault in the high-voltage distribution system even if it occurs while measuring the DC insulation resistance. 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 the 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 voltage waveform data outside the high-voltage distribution system as shown in FIGS.

[0035] As described above, according to the first embodiment, a highly sensitive current measuring means is not required, and it is possible to monitor the DC insulation resistance of a high-voltage distribution system using a live line while minimizing errors in current measurement.

[0036] <Embodiment 2> Next, embodiment 2 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 embodiment 2. In embodiment 2, the internal configuration of the voltage measurement unit is different in a high-voltage distribution system similar to embodiment 1 described above, 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, and also to avoid failure of the voltage follower circuit 22 even if an excessive voltage is input to the resistive voltage divider 20. Furthermore, 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 current-withstanding capacity of the Zener diode 24.

[0039] <Embodiment 3> Next, embodiment 3 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 embodiment 3. In embodiment 3, the internal configuration of the voltage measurement unit is different in a high-voltage distribution system similar to embodiment 1 described above, 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 this configuration, it is possible to reduce measurement errors as in the first and second embodiments, and also to protect the voltage follower circuit 22 from an excessively large signal being input, even in the case of an overvoltage suppression circuit 25 with a high operating voltage.

[0041] Today, with the decline in the labor force, there is a growing need to reduce maintenance, improve the availability of production facilities, and reduce downtime. Being able to measure the DC insulation resistance of extra-high voltage consumers' power receiving and distribution equipment and distribution lines while they are live 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 voltage transformer 10 and incorporated into the high-voltage switchboard 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 component costs.

[0043] REFERENCE SIGNS LIST 1 Extra-high voltage transformer 2 High-voltage distribution panel 3 High-voltage incoming panel 4 Low-voltage panel 5 High-voltage transformer 10 Grounded instrument transformer 11 Neutral point switch 12 Insulating capacitor 13 DC power supply 14 DC power supply switch 15 Voltage measuring unit 17 Control unit 20 Resistive voltage divider 21A High-voltage side resistor of resistive voltage divider 21B Low-voltage side resistor of resistive voltage divider 22 Voltage follower circuit 23 Measuring instrument 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 potential transformer, comprising: a neutral point switch connected to the grounded potential 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 the connection between the DC power source and the insulating capacitor; a voltage measuring unit for measuring the voltage of the insulating capacitor in response to the 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 resistive voltage division to divide the voltage of the insulating capacitor, inputs the resistively divided voltage, and measures a change in voltage of the insulating capacitor.

2. A DC insulation resistance monitoring device as described in claim 1, characterized in that, during the period in which the neutral point switch in a closed state is open-circuit controlled, the control unit controls the DC power supply switch in an open state to be closed until the insulating capacitor reaches a predetermined voltage at the DC power supply.

3. A DC insulation resistance monitoring device as claimed in claim 1, characterized in that the voltage measuring section 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. A DC insulation resistance monitoring device as claimed in claim 1, characterized in that said voltage measuring section has a voltage follower circuit to which said resistor-divided voltage is input.

5. A DC insulation resistance monitoring device as claimed in claim 3, further comprising a Zener diode connected in parallel with the low-voltage side resistor of said resistive voltage divider.

6. A DC insulation resistance monitoring device as claimed in claim 3, further comprising an overvoltage control circuit connected in parallel with said resistive voltage divider.

7. A DC insulation resistance monitoring device as claimed in claim 3, characterized in that the high-voltage side resistance of said resistive voltage divider is set to a value greater than the resistance of the main circuit to be measured.

8. A method for monitoring DC insulation resistance in a high-voltage distribution system equipped with a grounded voltage transformer, the high-voltage distribution system comprising: a neutral point switch connected to the grounded voltage transformer, an insulating capacitor switched by the neutral point switch, a DC power source for charging the insulating capacitor, a DC power source switch for switching the connection between the DC power source and the insulating capacitor, a voltage measuring unit for measuring the voltage of the insulating capacitor in response to the 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, wherein the method for monitoring DC insulation resistance in the high-voltage distribution system comprises, under the control of the control unit, opening the neutral point switch in a closed state and closing the DC power source switch in an open state to charge the insulating capacitor to a predetermined voltage with the DC power source, and after charging to the predetermined voltage, returning the DC power source switch to an open state and then returning the neutral point switch to a closed state.

9. A DC insulation resistance monitoring method as claimed in claim 8, characterized in that the period from when the DC power supply switch is returned to an open circuit until when the neutral point switch is returned to a closed circuit is set as a period for allowing the voltage of the insulating capacitor to gradually decrease due to leakage resistance.

10. A DC insulation resistance monitoring method as claimed in claim 8, characterized in that the voltage measuring section 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, 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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