JP5418219B2 - High voltage insulation monitoring device - Google Patents

Description

  The present invention relates to a zero-phase current detecting means for detecting a zero-phase current on a load side of a high-voltage cable in the electric circuit, and a ground fault based on detection information of the zero-phase current detecting means in the electrical equipment of the non-grounded electric circuit. The present invention relates to a high voltage insulation monitoring apparatus provided with a ground fault current detecting means for detecting current.

Such a high-voltage insulation monitoring device is a device for detecting a ground fault that occurs in an electrical facility of a non-grounded electric circuit.
As a method for detecting the ground fault current of the non-grounded circuit, as described in Patent Document 1 below, the zero-phase current and zero-phase voltage of the circuit are detected, and the ground fault is detected from the detected information. A method for obtaining a current is often used.

JP-A-11-271384

However, in the conventional method for detecting the zero-phase voltage and the zero-phase current, the zero-phase current can be detected by a relatively inexpensive zero-phase current transformer, and the installation work can be performed by a simple operation. The zero-phase transformer for detecting the fault is an expensive device, and installation and removal of the transformer requires a large-scale construction with a power failure, and the overall cost for detecting the ground fault current is very large. It was a thing. In the case of an intermittent ground fault, it may be difficult to determine whether the ground fault is on-site or off-site.
The present invention has been made in view of such circumstances, and its purpose is to reduce the cost required for detecting a ground fault current as much as possible, and to accurately determine whether a ground fault is on-site or off-site. There is in point to do.

  According to a first aspect of the present application, there is provided a zero-phase current detecting means for detecting a zero-phase current on the load side of the high-voltage cable in the electric circuit, and detection information of the zero-phase current detecting means. In the high voltage insulation monitoring device provided with the ground fault current detecting means for detecting the ground fault current based on the ground line current flowing in the ground line connected to the line of each phase of the electric circuit via the capacitive member A ground line current detecting means for detecting the ground line current detecting means, wherein the ground fault current detecting means includes a value of the ground line current and a value of the zero-phase current on the load side when no ground fault occurs in the electric circuit. Is obtained in advance and stored in the storage means, and from the value of the zero-phase current on the load side at the time of measurement, the value of the ground line current at the time of measurement and the ratio stored in the storage means The obtained zero-phase current on the load side It is configured to detect the current value of the ground fault current by subtracting the estimated value.

That is, as a basic idea for detecting the ground fault current, the load side zero when the load side zero phase current at the time of measurement is normal (that is, no ground fault has occurred). The ground fault current is obtained by subtracting the phase current.
However, the zero-phase current on the load side fluctuates over time due to various environmental conditions even when there is no ground fault at the location subject to insulation monitoring. If the stored value is subtracted from the zero-phase current on the load side at the time of measurement, the ground fault current is not accurately obtained.
In other words, assuming that a ground fault has occurred at the time of measurement, if there is no ground fault at the time of measurement, determine the amount of zero-phase current on the load side and measure it. It is necessary to subtract from the zero-phase current on the load side at the time.

This “ground wire that is connected to each phase line of the circuit via a capacitive member” indicates the amount of zero-phase current on the load side if no ground fault has occurred at the time of measurement. It is estimated by detecting the ground line current flowing through
This will be described in detail with reference to FIG. 2 schematically showing a state in which the load 101 is connected to the high-voltage cable 1 drawn from the power source E to the premises and the detecting means such as the zero-phase current transformer 102 is installed.
In FIG. 2, the capacitive members are shown as capacitors Ca ₁₀ , Cb ₁₀ , and Cc ₁₀ , and each line of the electric circuit 2 is connected to the ground line 104 through the capacitive members.
The ground capacitance of the load 101 is indicated by Ca ₂ , Cb ₂ , and Cc ₂ .
What kind of wiring corresponds to the ground line 104 will be described later.

The current flowing through the earth capacity _{Ca 2,} Cb _2, Cc 2 load, the capacitor _{Ca 10,} Cb 10, the relationship between the current through _{Cc 10} flows to the ground line 104, the capacitance to ground _Ca 2, Cb ₂ and Cc _{2 and} the capacitance values of the capacitors Ca ₁₀ , Cb ₁₀ and Cc ₁₀ are in a proportional relationship.
The current flowing through the ground capacitances Ca ₂ , Cb ₂ , and Cc ₂ of the load corresponds to the above-described zero-phase current on the load side and varies with time as described above. The ratio of the current flowing through the ground capacitances Ca ₂ , Cb ₂ , Cc ₂ (that is, the zero-phase current on the load side) and the current flowing through the capacitors Ca ₁₀ , Cb ₁₀ , Cc ₁₀ to the ground line 104 is Since each capacitance value does not change, it is constant.

Therefore, the ground line current (current flowing through the ground line 104) is measured by the zero-phase current transformer 103 or the like while no ground fault has occurred in the monitored electric circuit, and the zero-phase current on the load side is measured. The value is measured by the zero-phase current transformer 102, and the ratio between the two is obtained in advance and stored in the storage means.
Then, from the ratio and the measured value of the ground line current at the time of measurement (measured value by the zero-phase current transformer 103), the “zero-phase current on the load side at normal time” at the time of measurement is estimated, and the load at the time of measurement is estimated. The ground fault current is obtained by subtracting the estimated value from the measured value of the zero-phase current on the side (measured value by the zero-phase current transformer 102).
Specifically, for example, the ratio of the value of the zero-phase current on the load side to the value of the ground line current in a state where no ground fault has occurred in the electric circuit is obtained in advance and stored in the storage means, and at the time of measurement From the measured value of the load-side zero-phase current, the estimated value of the load-side zero-phase current obtained by the product of the measured value of the ground line current at the time of measurement and the ratio stored in the storage means is subtracted.
In FIG. 2, the ground wire 104 is wired so as to pass through the zero-phase current transformer 102 along the high-voltage cable 1 toward the outer side of the construction, but this is because the capacitors Ca ₁₀ , Cb ₁₀ , Cc ₁₀ exemplifies a state of being located closer to the load 101 than the zero-phase current transformer 102. Therefore, the detection ground line 104 is detected so that the zero-phase current transformer 102 detects only the zero-phase current on the load 101 side. This is for subtracting in advance the current flowing through the.
Of course, the load-side zero-phase current can be obtained by subtracting the detection information of the zero-phase current transformer 103 from the detection information of the zero-phase current transformer 102 by the arithmetic processing without performing the wiring arrangement as described above. good.

In addition to the configuration of the first invention, the second invention of the present application provides an unbalanced zero-phase current due to the unbalanced ground capacitance of the load connected to the electric circuit between the phases. Unbalanced zero-phase current detection means is provided, and the ground fault current detection means further subtracts the unbalanced zero-phase current value from the load-side zero-phase current value at the time of measurement. Is configured to detect the current value of the ground fault current.
That is, when the ground capacitances Ca ₂ , Cb ₂ , and Cc _{2 of the} load shown in FIG. 2 are unbalanced between the phases, a zero-phase current caused by the unbalance flows.
Therefore, if the value of the zero-phase current due to the unbalance becomes large and works as a measurement error of the ground fault current, it is removed from the measured value of the zero-phase current on the load side and Improve current measurement accuracy.
Note that the zero-phase current resulting from the unbalance of the ground capacitance of the load is obtained by taking the vector sum of the products of the admittance and voltage obtained for each phase.

According to a third invention of the present application, in addition to the configuration of the first or second invention, the ground fault current detecting means includes the detection information of the zero phase current detecting means and the grounding during a set time. The detection information of the line current detection means is stored in the storage means, and the zero-phase current value on the load side and the ground line current value are obtained by vector calculation including phase information based on the storage information. Has been.
That is, the calculation processing related to the current value in the AC circuit is generally calculated by vector calculation including phase information, and the time series data of the measured current for the time that allows such calculation processing is obtained. Collect and store and calculate the current value with high accuracy.

According to a fourth invention of the present application, in addition to the configuration of the first or second invention, the ground fault current detecting means includes a value of the zero-phase current on the load side and the ground line current at the time of measurement. As the measured value, an instantaneous value at the time of measurement is used.
In other words, in order to detect a ground fault current using a conventional zero phase voltage and zero phase current, an operation using phase information is indispensable, and sudden ground fault currents such as arc ground faults and intermittent ground faults are generated. It is not necessarily suitable for detecting at high speed and taking necessary actions.
On the other hand, the method of subtracting the estimated value of the load-side zero-phase current from the measured value of the load-side zero-phase current enables real-time processing using instantaneous values, such as an arc ground fault or intermittent ground fault. It can effectively cope with detection of sudden ground fault current.

The fifth invention of the present application uses a sheath ground wire of the high-voltage cable as the ground wire in addition to the configuration of any one of the first to fourth inventions.
That is, in the high-voltage cable, a capacitor is equivalently formed by the wire of each phase of the high-voltage cable, the sheath, and the insulating member existing between them, thereby forming a capacitive member.
The sheath ground wire is a ground wire connected to the wire of each phase through this capacitive member.
The sheath ground line is a wiring generally installed in an electric facility (power receiving facility), and the ground line current can be detected using the wiring.

The sixth invention of the present application uses a ground wire of a zero-phase transformer connected to the electric circuit as the ground wire in addition to the configuration of any of the first to fourth inventions.
In other words, it is not preferable to install a zero-phase transformer specially for detecting the ground fault current because it significantly increases the equipment cost, but the zero-phase transformer is installed in the electrical equipment for some other purpose. If it is, ground fault current can be calculated | required using it.
However, the zero-phase voltage output from the zero-phase transformer is not used for the detection of the ground fault current, but the above-described ground line current is detected using the ground line of the zero-phase transformer.
As shown in FIG. 3 showing a state in which the zero-phase transformer is connected to the electric circuit, the zero-phase transformer 105 is provided with capacitors Ca ₁₂ , Cb ₁₂ , and Cc ₁₂ for connecting to the lines of each phase of the electric circuit. Yes.
Therefore, the ground line 106 of the zero-phase transformer 105 is a circuit configuration corresponding to the ground line connected to the lines of each phase of the electric circuit 2 via the capacitive members (capacitors Ca ₁₂ , Cb ₁₂ , Cc ₁₂ ). The current flowing through the ground line 106 can be detected as the ground line current.

According to the first aspect of the invention, since the ground fault current is obtained mainly by current detection that can be easily detected at low cost, the cost required for detecting the ground fault current can be reduced as much as possible. . In addition, the zero-phase current flowing into the ground capacitance of the load is compared with the ground line current flowing into another ground capacitance having the same properties, and the influence of the disturbance is completely canceled by performing a predetermined calculation. it can. Therefore, even if the zero-phase voltage and the zero-phase current are large and irregularly fluctuate due to an off-ground ground fault or induced lightning, a ground fault on the premises can be detected with high accuracy. In other words, it is possible to accurately determine whether the ground fault is on-site or off-site by accurately excluding the off-ground ground fault from the detection target and detecting the ground fault current.
According to the second aspect of the invention, since the ground fault current is obtained in consideration of the fact that the load capacitance to ground is unbalanced between the phases, the ground fault current detection accuracy can be further improved. .
According to the third aspect of the invention, since the calculation for obtaining the ground fault current is performed by the vector calculation including the phase information, the ground fault current can be obtained with high accuracy.

According to the fourth aspect of the invention, since the ground fault current can be obtained in real time, an arc ground fault or an intermittent ground fault can be accurately detected.
Further, according to the fifth aspect, since the ground line current can be detected using a generally installed sheath ground line, the cost of the apparatus configuration can be further reduced.
According to the sixth aspect of the present invention, when a zero-phase transformer is installed for another purpose, the zero-phase current on the load side in the normal state is utilized by using the ground wire of the zero-phase transformer. The ground line current for obtaining the estimated value can be detected.
In this case, the capacitive member interposed between the ground wire and the wire of each phase of the electric circuit is the capacitor itself, and since the capacitance value is known and extremely stable, the detection accuracy of the ground fault current is improved. It will contribute to.

The figure which shows the whole high voltage insulation monitoring apparatus concerning embodiment of this invention Diagram for explaining the basic concept of the present invention The figure which shows the structure of this invention at the time of using a zero phase transformer

Embodiments of the high voltage insulation monitoring apparatus of the present invention will be described below with reference to the drawings.
The high-voltage insulation monitoring apparatus of the present embodiment is a high-voltage power source E (for example, 6.5) supplied from a substation facility of an electric power company, as schematically shown in FIG. 6 kV) is an object to be monitored for electrical equipment of a so-called non-grounded circuit that supplies the load 8 via the circuit 2. In practice, a transformer for lowering to the required voltage of the load is also installed, and a high voltage is drawn to the transformer by the electric circuit 2, but the description is omitted here. Further, “external” in the present invention refers to the power source E side of the power receiving point in FIG. 1, and “premises” refers to the load 8 side of the power receiving point in FIG.

In the above-described equipment, the zero-phase current transformer ZCT2 is a high-voltage as the zero-phase current detection means 3 for detecting the zero-phase current on the load 8 side of the high-voltage cable 1 in order to perform insulation monitoring on the power consumer side. It is attached so as to surround the outer periphery of the cable 1, and a current (ground line current) flowing through the sheath ground line 4 is detected in the sheath ground line 4 (ground line) drawn from the end of the high-voltage cable 1 on the load 8 side. A zero-phase current transformer ZCT1, which is a grounding line current detection means 5 for this purpose, is attached.
The sheath ground wire 4 is drawn from the high-voltage cable 1 and then passed through the zero-phase current transformer ZCT2 toward the outside of the construction along the high-voltage cable 1 (rewinding), whereby a current flowing through the sheath ground wire 4 Are routed so as to cancel each other through the zero-phase current transformer ZCT2. That is, the zero-phase current transformer ZCT2 is wired so as not to detect the cable ground fault of the high-voltage cable 1.

The electric circuit 2 is further connected to a reference voltage detection circuit 6 used for detecting a zero-phase current caused by the unbalanced capacitance of the load 8 to the ground.
The circuit configuration of the reference voltage detection circuit 6 includes two transformers 11 and 12 whose primary side is V-connected to the electric circuit 2, and three resistors that are star-connected to the secondary side of the two transformers 11 and 12. 13, 14, and 15, and the voltages of the respective phases a, b, and c are obtained as reference voltages from the voltages at both ends of the resistors 13, 14, and 15. Although FIG. 1 shows the case where the reference voltage detection circuit 6 is connected to the electric circuit 2, the reference voltage is supplied from the power line after being converted to a low voltage by a transformer not shown. You may comprise so that it may obtain.

The output signals of the zero-phase current transformers ZCT1 and ZCT2 and the reference voltage detected by the reference voltage detection circuit 6 are input to the ground fault detection device 7 which is the main part of the high voltage insulation monitoring device.
The ground fault detection device 7 is constituted by a general-purpose computer (more specifically, a personal computer), and is based on the output signals of the zero-phase current transformers ZCT1 and ZCT2 and the reference voltage detected by the reference voltage detection circuit 6. The ground fault current is obtained by calculation.
Although this calculation is executed as software processing, it is functionally composed of an unbalanced zero-phase current detection unit 7a and a ground fault current calculation unit 7b.
Although not shown, the reference voltage signal input to the unbalanced zero-phase current detection unit 7a and the detection signals of the zero-phase current transformers ZCT1 and ZCT2 input to the ground fault current calculation unit 7b are A / D. An A / D converter for conversion is provided.

Zero-phase current detecting portion 7a disequilibrium (in FIG. 2, the capacitance shown as Ca 2, _{Cb 2,} Cc ₂₎ the earth capacitance of the load 8 connected to the path 2 that is unbalanced between phases Is an unbalanced zero-phase current detection means UC for detecting an unbalanced zero-phase current due to the reference voltage detected by the reference voltage detection circuit 6 and a memory 7c which is a storage means ME provided in the ground fault detection device 7. The unbalanced zero-phase current is obtained from the admittance value of each phase of the load 8 stored in advance. Note that the admittance stored in the memory 7c may be practically regarded as admittance due to only the capacitive component.
The unbalanced zero-phase current is obtained by calculating the product of the reference voltage and the admittance for each phase and taking the vector sum thereof.

The ground fault current calculation unit 7b is a ground fault current detection means GS that detects a ground fault current based on the detection information of the zero phase current transformer ZCT2, and the detection information of the zero phase current transformers ZCT1 and ZCT2 and the unbalanced zero. A ground fault current is obtained by arithmetic processing from the unbalanced zero-phase current obtained by the phase current detector 7a.
The basic idea for detecting the ground fault current by the ground fault current calculation unit 7b is that the zero phase current (measured value at the time of measurement) on the load 8 side at the time of measurement is normal (that is, a ground fault occurs). The ground fault current is obtained by subtracting the zero-phase current on the load 8 side when the current state is not.
The zero-phase current on the load 8 side when no ground fault has occurred is that the zero-phase current fluctuates in time and the zero-phase current on the load 8 side even if the zero-phase current fluctuates. Considering that the ratio between the current and the ground line current flowing through the sheath ground wire 4 is constant, the ratio is obtained in advance and stored in the memory 7c, and the measured value of the ground line current at the time of measurement and the memory Based on the ratio stored in 7c, the zero-phase current on the load 8 side when no ground fault has occurred is estimated.

The "estimated value of the zero-phase current on the load 8 side when no ground fault has occurred" thus obtained is subtracted from the measured value of the zero-phase current on the load 8 side at the time of measurement. Find the fault current.
Further, when the ground capacitance of the load 8 varies between the phases and affects the calculation of the ground fault current as an error, the unbalanced zero-phase obtained by the unbalanced zero-phase current detector 7a is further obtained. Subtract the current value.

The ground fault current calculation unit 7b performs the above processing in parallel with both the vector calculation including the phase information and the calculation using the instantaneous value.
For this execution process, the ground fault current calculation unit 7b sends the measurement signals (detection information) sent from the zero-phase current transformers ZCT1 and ZCT2 during the set time (for at least one cycle) to A / D-convert and store in memory 7c.
Further, the ground fault current calculation unit 7b extracts time-series data of the current value read from the memory 7c as a vector quantity including phase information by performing DFT (Discrete Fourier Transform) by software processing, and performs the above arithmetic processing by vector calculation. Do.

Explaining by the equation, the capital letter “I” represents the vector quantity. First, in the situation where no ground fault has occurred on the premises, the zero phase on the load 8 side is detected from the detection signal of the zero phase current transformer ZCT2. The current value Io0 of the current is obtained, and further, the value Ie0 of the ground line current flowing through the sheath ground wire 4 is obtained from the detection signal of the zero-phase current transformer ZCT1.
Then, the ratio K of the zero-phase current Io0 on the load 8 side to the ground line current Ie0 is obtained as K = Io0 / Ie0 (K is a scalar amount) and stored in the memory 7c.

After making such a preparation in advance, a vector including phase information includes the zero-phase current value Io1 on the load 8 side at the time of measurement at the predetermined measurement timing and the ground line current value Ie1 flowing through the sheath ground wire 4. The amount is obtained from the data stored in the memory 7c.
And ground fault current Ig is calculated | required as Ig = Io1-K * Ie1 (* is an operator which means a product and it is the same in the following).
Furthermore, when the ground capacitance of the load 8 varies between phases and the unbalanced zero-phase current becomes a value that cannot be ignored, the unbalanced value is further calculated from the zero-phase current value Io1 on the load 8 side. The unbalanced zero-phase current value Ix obtained by the zero-phase current detector 7a is subtracted.
That is, the ground fault current Ig is obtained as Ig = Io1-K * Ie1-Ix.

On the other hand, in the process using the instantaneous value of the measurement data of the zero-phase current transformers ZCT1 and ZCT2, the lower-case “i” represents the instantaneous value, and the zero-phase current on the load 8 side at the time of measurement at a predetermined measurement timing. And io of the ground line current flowing in the sheath ground wire 4 are obtained by A / D converting the detection information (output signals) of the zero-phase current transformers ZCT1 and ZCT2, respectively.
Then, the ground fault current ig is obtained as ig = io−K * ie.
Note that even when the ground fault current is obtained from the instantaneous value, the above-described unbalanced zero-phase current may be taken into account, but the target of detection by the instantaneous value is that of an arc ground fault or intermittent ground fault pulse shape. Therefore, the unbalanced zero-phase current need not be particularly considered.

  As described above, when the ground fault current Ig obtained by the vector calculation or the ground fault current Ig obtained by the instantaneous value exceeds the set value for alarm generation set for each, a buzzer or the like is provided. An alarm is output from the alarm unit 7d.

[Another embodiment]
Hereinafter, other embodiments of the present invention will be listed.
(1) In the above embodiment, the current flowing through the sheath ground wire 4 is detected by the zero-phase current transformer ZCT1 in order to obtain the ground line current. However, for other purposes, a zero-phase transformer is provided in the electric circuit. If installed, the above-described ground line current may be obtained using the ground line of the zero-phase transformer.
Specifically, as shown in FIG. 3, the zero-phase transformer 105 is connected to each phase line of the electric circuit 2, and the zero-phase current transformer 103 attached to the ground line 106 of the zero-phase transformer 105 is connected to the ground line. Used as current detection means 5.
Even in this case, the calculation process for obtaining the ground fault current is exactly the same as in the above embodiment, and the output signal of the zero phase current transformer 103 is simply replaced with the output signal of the zero phase current transformer ZCT1 in the above embodiment. Well, the ground fault current can be obtained by the same arithmetic processing.

(2) In the above embodiment, when the ground fault current Ig obtained by vector calculation or the ground fault current Ig obtained by an instantaneous value exceeds a set value for alarm generation set for each, a buzzer or the like Although the case where the alarm is output from the alarm unit 7d having the above is illustrated, the alarm output mode from the ground fault detection device 7 is not the notification from the alarm unit 7d, or the alarm unit 7d In parallel with the notification, a separate communication means may be used to notify the monitoring center or the like that remotely monitors the above-described electrical equipment.

DESCRIPTION OF SYMBOLS 1 High voltage cable 2 Electric circuit 3 Zero phase current detection means 4 Sheath earth wire 5 Ground line current detection means 8 Load 105 Zero phase transformer 106 Ground wire GS Ground fault current detection means ME Storage means UC Unbalanced zero phase current detection means

Claims (6)

In electrical equipment of a non-grounded electric circuit, zero-phase current detecting means for detecting a zero-phase current on the load side of the high-voltage cable in the electric circuit, and detecting a ground fault current based on detection information of the zero-phase current detecting means A high-voltage insulation monitoring device provided with a ground fault current detection means,
A ground line current detecting means for detecting a ground line current flowing in a ground line connected via a capacitive member to each phase line of the electric circuit;
The ground fault current detection means obtains in advance a ratio between the value of the ground line current and the value of the zero-phase current on the load side in a state where no ground fault has occurred in the electric circuit, and stores the ratio in the storage means. Then, an estimated value of the load-side zero-phase current obtained from the value of the load-side zero-phase current at the time of measurement and the value stored in the storage means and the value of the ground line current at the time of measurement is obtained. A high voltage insulation monitoring device configured to detect a current value of a ground fault current by subtraction. An unbalanced zero-phase current detecting means for detecting an unbalanced zero-phase current due to an unbalanced ground capacitance of the load connected to the electric circuit between the phases;
The ground fault current detecting means is configured to detect the current value of the ground fault current by further subtracting the value of the unbalanced zero phase current from the value of the zero phase current on the load side at the time of measurement. The high voltage insulation monitoring apparatus according to claim 1.   The ground fault current detection means stores detection information of the zero-phase current detection means and detection information of the ground line current detection means during a set time in a storage means, and includes phase information based on the storage information. 3. The high voltage insulation monitoring apparatus according to claim 1, wherein the load-side zero-phase current value and the ground line current value are obtained by vector calculation.   3. The high voltage according to claim 1, wherein the ground fault current detecting unit is configured to use an instantaneous value at a measurement time as a value of a zero-phase current on the load side and a value of the ground line current at the time of measurement. Insulation monitoring device.   The high-voltage insulation monitoring apparatus according to claim 1, wherein the grounding wire is a sheath grounding wire of the high-voltage cable.   The high-voltage insulation monitoring device according to any one of claims 1 to 4, wherein the ground line is a ground line of a zero-phase transformer connected to the electric circuit.

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