JP5529300B1 - High voltage insulation monitoring method and high voltage insulation monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively monitor an insulation deterioration state of a high-voltage power facility with a simple means.
A zero-phase current transformer ZCT15 installed in a power cable 13 of a high-piezoelectric circuit 12 connected to a non-grounded electric circuit causes a zero to flow through the power cable 13 due to the occurrence of a ground fault in the power cable 13. A high-voltage insulation monitoring method for detecting a phase current I ₀ and determining that a ground fault is a ground fault on the premises, wherein a clamp-type current transformer 18 is connected to a shield wire 17 of a power cable 13 installed in a high-voltage path 12. Are connected, and a zero-phase current I _0S flowing through the shield wire 17 when a ground fault occurs is detected by a clamp-type current transformer 18, and the phase difference of the zero-phase current I ₀ with reference to the phase of the zero-phase current I _0S is detected. To determine that the ground fault is a ground fault on the premises.
[Selection] Figure 1

Description

The present invention relates to a high voltage insulation monitoring method and a high voltage insulation monitoring method for monitoring an insulation deterioration state of a high piezoelectric path by detecting a zero-phase current I ₀ generated in a high piezoelectric path connected to an ungrounded circuit due to a ground fault. Relates to the device.

Various electrical devices (for example, transformers, phase-advancing capacitors, instrument transformers, current transformers, etc.) are connected to the high-voltage path connected to the ungrounded circuit, and installed on the high-voltage path. The zero-phase current transformer ZCT detects the zero-phase current I ₀ flowing in the high-voltage path when a ground fault occurs, thereby monitoring the insulation deterioration state of the high-voltage path. In general, the load side from the power receiving point, which is a connection point with the high piezoelectric path, is referred to as a premise, and the protection range is called, and the system side from the power receiving point is called the premise, and is outside the protection range.

In this way, by detecting the zero-phase current I ₀ flowing in the high piezoelectric path at the time of occurrence of the ground fault with the zero-phase current transformer ZCT, it is determined whether or not the ground fault is a campus ground fault. Therefore, the insulation deterioration state of the high piezoelectric path is monitored. Conventionally, as means for monitoring an insulation deterioration state of an electric circuit, for example, one disclosed in Patent Document 1 has been proposed.

In this patent document, a zero-phase current transformer ZCT, a zero-phase transformer, and a grounding transformer are installed in an electric circuit, and zero-phase current I ₀ , zero-phase voltage V ₀ and phase voltage V generated in the electric circuit are detected. This is an insulation deterioration measuring device which monitors the insulation deterioration state of the electric circuit by calculating with a complex number.

Japanese Patent No. 4121979

By the way, in Patent Document 1, as described above, the insulation deterioration state of the electric circuit is monitored by detecting the zero-phase current I ₀ , the zero-phase voltage V ₀ and the phase voltage V generated in the electric circuit. When this monitoring method is adopted, there is no need to measure or input the ground-to-ground constant in advance. However, in order to obtain the ground fault current Ig due to the ground fault, the zero phase current I ₀ , the zero phase voltage V _0, and the phase voltage V must be measured in complex numbers and vector-calculated. Therefore, the insulation deterioration measuring device becomes expensive, and there has been a problem that an expensive insulation deterioration measuring device has to be used for periodically monitoring the insulation deterioration state of the electric circuit.

  Accordingly, the present invention has been proposed in view of the above-described problems, and the object of the present invention is to provide a high voltage insulation monitoring method and high voltage insulation which can monitor the insulation deterioration state of a high piezoelectric path at a low cost with simple means. It is to provide a monitoring device.

The present invention, by ground fault ungrounded system path, detects a zero-phase current I ₀ flowing through the high-pressure path, and a zero-phase current I _0S flowing through the shield wire of the power cable installed in a high-pressure path, ground A high-voltage insulation monitoring method and a high-voltage insulation monitoring device for determining that an accident is a ground fault on the premises.

As a technical means for achieving the above-mentioned purpose of ground fault detection, the high voltage insulation monitoring method according to the present invention detects a zero-phase current I ₀ flowing in a high-voltage circuit connected to a non-grounded circuit, and A zero-phase current I flowing in the shield line when a ground fault occurs by connecting a current transformer to the shield line of the power cable installed on the high-voltage road. _0S is detected by a current transformer, and it is determined that the ground fault is a ground fault from the phase difference of the zero phase current I _{0 based on} the phase of the zero phase current I _0S. . The high-voltage insulation monitoring device according to the present invention is a device that detects a zero-phase current I ₀ flowing through a high-voltage circuit connected to a non-grounded circuit and determines that a ground fault is a ground fault on the premises. And a current transformer that is detachably connected to the shield wire of the power cable installed on the high-voltage path and detects the zero-phase current I _0S flowing through the shield wire in the event of a ground fault, and is detected by the current transformer. zero-phase current I and the gain adjusting unit to 1 _0S by the gain adjusting the size of the zero-phase voltage V _0S converted to the zero-phase voltage V _0S phase by which the zero-phase voltage V _0S 1 by gain adjust And a calculation unit that calculates a ground fault current Ig by multiplying the zero phase voltage V _0S that is the reference by a vector multiplication of the zero phase current I ₀ .

In the high voltage insulation monitoring method and the high voltage insulation monitoring device of the present invention, the zero-phase current I _0S flowing through the shield wire at the time of occurrence of the ground fault is detected by a current transformer, and the zero-phase current I _0S flows through the terminal resistance. The voltage across the terminal resistor is a zero-phase voltage V _0S based on the zero-phase current I _0S , the magnitude of this zero-phase voltage V _0S is set to 1 by gain adjustment, and the zero-phase voltage V _{0S is set} to 1 by gain adjustment. Thus, the phase of the zero-phase voltage V _0S is used as a reference, and the zero-phase voltage V _{0S used} as a reference is multiplied by the vector of the zero-phase current I ₀ , so that it is determined that the ground fault is a ground fault. Therefore, unlike the conventional insulation monitoring method (Patent Document 1), a complicated vector calculation based on measuring the zero-phase current I ₀ , the zero-phase voltage V _0, and the phase voltage V as complex numbers becomes unnecessary. The ground capacitance between the core wire of the power cable 13 and the ground varies depending on the diameter and length of the power cable 13. Therefore, in order to measure the zero-phase voltage V ₀ , a circuit for correcting an error due to the current flowing through the ground capacitance is required. However, in the present invention, by setting the zero-phase voltage V _0S to 1 by gain adjustment, the above-described correction circuit becomes unnecessary and a high voltage insulation monitoring device can be realized with a simple circuit configuration. As described above, the ground fault current Ig can be easily obtained by a simple and inexpensive high voltage insulation monitoring device for constantly monitoring the insulation deterioration state of the high piezoelectric path.

In the high voltage insulation monitoring method of the present invention, the zero phase current transformer ZCT installed in the high piezoelectric path can detect the zero phase current I ₀ flowing in the power cable when a ground fault occurs. As a means, it is desirable to connect a current transformer to the secondary side of the zero-phase current transformer ZCT, and to detect the zero-phase current I ₀ flowing through the power cable when a ground fault occurs. In the high voltage insulation monitoring device of the present invention, a current transformer is detachably connected to the secondary side of the zero-phase current transformer ZCT and detects the zero-phase current I ₀ flowing through the high-voltage path when a ground fault occurs. It is desirable to have it. In this way, insulation monitoring can be performed simply by attaching a current transformer to the secondary side of the zero-phase current transformer ZCT already installed for ground fault protection relays. Even when an overvoltage such as the above is applied, insulation is performed by the zero-phase current transformer ZCT, so that the protection against the overvoltage is ensured and the reliability can be improved.

In the high voltage insulation monitoring method of the present invention, a current transformer is connected to each of a plurality of feeder lines branched from a high piezoelectric path, and zero-phase currents I ₀₁ to I flowing in the feeder lines when a ground fault occurs due to the current transformers. It is desirable to detect I _0N . In the high voltage insulation monitoring device of the present invention, the zero-phase currents I _{01 to} I _0N flowing through the feeder lines are detected by being detachably connected to each of the plurality of feeder lines branched from the high piezoelectric path. It is desirable to have a current transformer that In this way, insulation monitoring can be easily performed for a plurality of feeder lines branched from the high piezoelectric path.

According to the present invention, by a zero-phase voltage V _0S obtained based on the zero-phase current I _0S by gain adjustment and 1, the zero-phase current I ₀ relative to the phase of the zero-phase voltage V _0S Since it is determined from the phase difference that the ground fault is a premise ground fault, the zero-phase current I ₀ , zero-phase voltage V _0, and phase voltage as in the conventional insulation monitoring method (Patent Document 1). A complicated vector operation based on measuring V as a complex number is not necessary. The zero-phase voltage V _0S obtained on the basis of the zero-phase current I _0S is determined by using the power cable diameter and length that determine the ground capacitance between the core of the power cable and the ground as parameters. A circuit for correcting an error due to the current flowing in the circuit becomes unnecessary. For this reason, an inexpensive high voltage insulation monitoring device can be used with a simple circuit configuration for constantly monitoring the insulation deterioration state of the high piezoelectric path, and its practical value is great.

It is a block diagram which shows schematic structure of the high voltage | pressure insulation monitoring apparatus connected to the high piezoelectric path at the time of a one-line ground fault in embodiment of this invention. In other embodiment of this invention, it is a block diagram which shows schematic structure of the high voltage | pressure insulation monitoring apparatus connected to the high piezoelectric path at the time of a one-line ground fault. It is an equivalent circuit diagram at the time of occurrence of a one-line ground fault. It is a vector diagram at the time of occurrence of a one-line ground fault. It is a block diagram which shows the state which the off-ground ground fault generate | occur | produced in the high piezoelectric road. It is a block diagram which shows the state which the local ground fault generate | occur | produced in the high piezoelectric road. Is a waveform diagram showing a zero-phase current I ₀ at the time of the actual ground fault.

  Embodiments of the present invention are described in detail below. In the following embodiments, a high voltage insulation monitoring method and a high voltage insulation monitoring device for monitoring the insulation deterioration state of a high piezoelectric path by detecting a zero phase current Io generated in the high piezoelectric path due to a ground fault will be described.

FIG. 1 shows one embodiment of the present invention, and FIG. 2 shows another embodiment of the present invention. In the 6.6 kV ungrounded electric circuit (three-phase circuit) shown in FIGS. 1 and 2, various electric devices (for example, a transformer, a phase advancement) are connected to the power cable 13 installed in the high-voltage circuit 12 extending from the substation 11. Capacitors, instrument transformers, current transformers, etc.) are connected, and the insulation deterioration state of the high-voltage path 12 is monitored by detecting the zero-phase current I ₀ that flows when a ground fault occurs. . 1 and 2 exemplify a case where a one-line ground fault has occurred in the A phase of the power cable 13, and let the ground fault current at that time be Ig.

The load side from the power receiving point that is the connection point of the high piezoelectric path 12 and the power cable 13 is referred to as a premise, and the protection side is referred to as the premise, and the system side from the power receiving point is referred to as the premise, and is outside the protective range. _Reference numerals C _A1 , C _B1 , and C _C1 in FIGS. 1 and 2 are external ground capacitances existing between the high piezoelectric path 12 and the ground, and C _A2 , C _B2 , and C _C2 are power cables 13 and various types. This is the ground capacitance on the premises that exists between the electrical equipment and the ground. The current I _0S flowing through the shield wire 17 of the power cable 13 is a current flowing through the ground capacitances C _AS , C _BS , C _CS (not shown) between the core wire and the ground of the power cable 13 due to the zero-phase voltage V _0. (I _0S = ω · C _0S · V ₀ , where ω = 2 · π · power frequency (Hz), C _0S = C _AS + C _BS + C _CS ).

  In the non-grounded electric circuit, a grounding transformer (EVT) is installed at the neutral pole of the main transformer of the power company supplying the power or the special high voltage substation equipment. The secondary (tertiary) winding of the grounding transformer has an open delta connection, and a limiting resistor is connected to the output terminal. The limiting resistance Rn obtained by converting the limiting resistance to the primary (high voltage) side is about 10 kΩ to 40 kΩ (see FIGS. 1 and 2). When a one-line ground fault occurs in the ungrounded circuit shown in FIGS. 1 and 2, an equivalent circuit as shown in FIG. 3 is obtained.

Here, in the ground fault monitoring method and apparatus previously proposed by the present applicant (see Japanese Patent No. 2774443), the ground constant (ground capacitance) between the terminals of the limiting resistor Rn and the high piezoelectric path 12 is parallel. Thus, a zero-phase voltage Vot is generated between the terminals of the limiting resistor Rn. In addition, a zero-phase voltage Vor is generated due to an unbalanced ground-to-ground constant (ground capacitance) of the ungrounded circuit. The zero-phase voltage Vor due to the unbalance of the ground constant of the high piezoelectric path 12 is 5% or less of the zero-phase voltage [line voltage / √3 = 6600V / √3 = 3810V (typical value)] at the time of one line complete ground fault. It always arises and fluctuates in value. The zero-phase voltage V ₀ generated in the high piezoelectric path 12 is composed of a zero-phase voltage Vot caused by insulation deterioration and a (residual) zero-phase voltage Vor due to an unbalanced ground constant. In the present invention, the zero phase voltage Vor due to the unbalance of the ground constant cannot be predicted and is not handled, and only the zero phase voltage Vot caused by the insulation deterioration is handled.

As shown in FIG. 4, in the power cable 13 and various electric devices of the high piezoelectric path 12, the zero-phase current I _{0C that} flows due to the zero-phase voltage V ₀ and the electrostatic capacitance of the power cable 13 and various electric devices (see FIGS. 2) is 90 degrees advance with respect to the zero-phase voltage V ₀ (Vot) generated in the high piezoelectric path 12, but when viewed from the zero-phase current transformer 15, the phase is reversed and the delay is 90 degrees. In particular, the zero phase current I _0C and the ground fault current Ig can be distinguished by using the zero phase current I _0S flowing through the shield wire 17 of the power cable 13 as a reference phase. On the other hand, the ground fault current Ig due to the insulation deterioration of the high piezoelectric path 12 is in phase with the ground voltage Vrg (see FIGS. 1 and 2).

In the case of the embodiment shown in FIG. 1, the high-voltage insulation monitoring device 14 that determines whether or not the ground fault is a premises ground fault by detecting the zero-phase current I ₀ that flows when the ground fault occurs is A configuration is adopted in which the zero-phase current transformer ZCT15 already installed for the ground fault protection relay detects the zero phase current I ₀ that flows when a ground fault occurs. On the other hand, in the case of the embodiment shown in FIG. 2, a clamp-type current transformer 16 is connected to the secondary side of the installed zero-phase current transformer ZCT15, and this clamp-type current transformer 16 causes a ground fault to occur. A configuration for detecting a flowing zero-phase current I ₀ is employed. The current transformer connected to the secondary side of the zero-phase current transformer ZCT15 may be, for example, a through-type current transformer other than the clamp-type current transformer 16 described above.

As in the embodiment shown in FIG. 2, a clamp-type current transformer 16 is connected to the secondary side of the zero-phase current transformer ZCT15, and this clamp-type current transformer 16 causes a zero-phase current I flowing when a ground fault occurs. By detecting ₀ , insulation monitoring can be performed simply by attaching the clamp type current transformer 16 to the secondary side of the existing zero-phase current transformer ZCT15 to which the ground fault protection relay 31 is connected. Even if an overvoltage such as a lightning surge is applied to the power cable 13, the overvoltage is not directly applied to the high voltage insulation monitoring device 14, so that protection against the overvoltage is ensured and reliability can be improved.

  The clamp-type current transformer 16 described above has a structure in which a ring-shaped portion that forms a magnetic circuit and detects current is provided at the front end of the main body so as to be opened and closed. The clamp-type current transformer 16 is attached to the secondary side of the zero-phase current transformer ZCT15 by opening the ring-shaped part by manual operation and closing it after taking the connection line with the ground fault protection relay inside. The connection is made to penetrate the ring-shaped portion constituting the magnetic circuit. Since the attachment work is easy by such a simple operation, the work in the field can be carried out efficiently and its practical value is great.

The high voltage insulation monitoring device 14 includes a zero-phase current transformer ZCT15 (see FIG. 1) installed in the high piezoelectric path 12 or a clamp-type current transformer 16 (see FIG. 1) connected to the secondary side of the zero-phase current transformer ZCT15. 2), the zero-phase current I ₀ flowing at the time of the ground fault occurring in the power cable 13 and various electric devices is detected, and it is determined that the ground fault is a ground fault on the premises.

As shown in FIGS. 1 and 2, the high-voltage insulation monitoring device 14 is detachably connected to the shield wire 17 of the power cable 13, and detects a zero-phase current I _0S flowing through the shield wire 17 when a ground fault occurs. And the voltage across the terminal resistor 21 when the zero-phase current I _0S detected by the clamp-type current transformer 18 flows through the terminal resistor 21 is the zero-phase voltage based on the zero-phase current I _0S. V _0S , the gain adjusting unit 19 that _sets the magnitude of the zero-phase voltage V _0S to 1 by gain adjustment, and the zero-phase voltage V _{0S is set} to 1 by gain adjustment, and the phase of the zero-phase voltage V _0S is used as a reference. A calculation unit 20 for calculating a ground fault current Ig by multiplying the zero-phase voltage V _0S as a reference by the zero-phase current I ₀ detected by the zero-phase current transformer ZCT or the clamp-type current transformer 16 The main part is composed of. The current transformer attached to the shield wire 17 of the power cable 13 described above may be, for example, a through-type current transformer in addition to the clamp current transformer 18 described above. In addition, terminal resistors 21 and 22 for converting current into voltage and low-pass filters 23 and 24 for removing harmonic noise are provided in front of the gain adjustment unit 19 and the calculation unit 20. .

In this high voltage insulation monitoring device, a zero-phase current I _0S that flows through the shield wire 17 of the power cable 13 when a ground fault occurs is caused by a clamp-type current transformer 18 that is detachably connected to the shield wire 17 of the power cable 13. To detect. When the zero-phase current I _0S detected on the secondary side of the clamp type current transformer 18 flows through the terminal resistor 21, the zero-phase voltage V _0S obtained at both ends of the terminal resistor 21 is the zero-phase voltage V ₀ and the power It is in phase with the zero-phase current I _0S (= −jωCV ₀ , where C = capacitance between the power cable 13 and ground), which is the vector product of the capacitance between the cable 13 and ground. Furthermore, in order to standardize the parameter part (variable C) of the capacitance between the power cable 13 and the ground, the magnitude of the zero-phase current I _0S is set to 1 (| −jωC | = 1) by gain adjustment. The zero-phase voltage V _0S indicates a phase (reference) delayed by 90 degrees from the phase of the zero-phase voltage V ₀ .

Accordingly, the zero fault voltage V _0S and the zero phase current I ₀ detected by the zero phase current transformer ZCT are vector-multiplied (power calculation) by the arithmetic unit 20 to determine that the ground fault is a ground fault on the premises. Judgment was made. Therefore, unlike the conventional insulation monitoring method (Patent Document 1), a complicated vector calculation based on measuring the zero-phase current I ₀ , the zero-phase voltage V _0, and the phase voltage V as complex numbers becomes unnecessary. Further, the zero-phase voltage V _0S obtained based on the zero-phase current I _0S is _{measured using} the diameter and length of the power cable 13 that determines the ground capacitance between the core wire and the ground of the power cable 13 as parameters. A circuit for correcting an error due to the current flowing in the capacitance is not necessary. Thus, in order to constantly monitor the insulation deterioration state of the high piezoelectric path 12, the inexpensive high voltage insulation monitoring device 14 can be used with a simple circuit configuration.

The vector calculation of the multiplication operation in the arithmetic unit 20 applies a commonly used power measurement arithmetic element (W = V · I · cosφ), and this power measurement arithmetic element is widely supplied to the general market. It is an element that can be obtained at low cost. The current and voltage input of the calculation unit 20 using this power measurement calculation element are obtained by using the zero-phase current I ₀ detected by the zero-phase current transformer 15 or the clamp-type current transformer 16 and the clamp-type current transformer 18. The voltage across the terminal resistor 21 when the zero-phase current I _0S detected on the secondary side flows through the terminal resistor 21 is _defined as a zero-phase voltage V _{0S obtained} by adjusting the gain. The zero-phase voltage V _0S obtained by adjusting the first automatic reference value the size of the zero-phase voltage V _0S as a reference phase, the zero-phase current transformer ZCT in the zero-phase voltage V _0S which was the reference When the sign of the ground fault current Ig of the calculation result is negative by vector multiplication (Ig = I ₀ · V _0S · cosφ) of the zero-phase current I ₀ detected by the Can be determined.

  FIG. 5 illustrates an off-site ground fault when a ground fault occurs on the high-voltage road 12, and FIG. 6 illustrates a pre-ground when a ground fault occurs on a plurality of feeder lines 25 to 27 branched from the power cable 13. It explains the ground fault. 5 and 6 exemplify the three feeder lines 25 to 27 branched from the power cable 13 as described above, but the number thereof is arbitrary. Various electric devices (for example, a transformer, a phase advance capacitor, an instrument transformer, a current transformer, etc.) are connected to the feeder lines 25 to 27.

  Note that the feeder lines 25 to 27 branched from the power cable 13 are not shown in FIGS. 1 and 2. 5 and 6 illustrate a case where the zero-phase current Io is detected by the zero-phase current transformer ZCT15 installed in the power cable 13 (the embodiment in FIG. 1). Although not shown, the following description is the same when the clamp type current transformer 16 is connected to the secondary side of the zero-phase current transformer ZCT15 installed in the power cable 13 (embodiment of FIG. 2).

As shown in FIGS. 5 and 6, the high-voltage insulation monitoring device 14 is detachably connected to each of a plurality of feeder wires 25 to 27 branched from the power cable 13, and a ground fault (external ground fault or internal ground fault is detected). ), Clamp-type current transformers 28 to 30 for detecting zero-phase currents I _{01 to} I ₀₃ flowing in the feeder lines 25 to 27 are provided. Thus, by connecting the clamp type current transformers 28 to 30 to the feeder lines 25 to 27 branched from the power cable 13, it is possible to easily monitor the insulation of the feeder lines 25 to 27.

When the ground fault is an off-premise ground fault, as shown by the arrows in FIG. 5, the zero-phase current I ₀ flowing through the power cable 13, the zero-phase current I _0S flowing through the shield wire 17 of the power cable 13, and each feeder line 25 all zero-phase current of the zero-phase current I ₀₁ ~I ₀₃ flowing in to 27 has a delay of 90 ° phase with respect to the zero-phase voltage V _0. On the other hand, if the ground fault is a ground fault in the feeder line 27, for example, as shown by the arrow in FIG. 6, the zero-phase current I ₀₃ flowing through the feeder line 27 and the zero-phase current I ₀ flowing through the power cable 13 are shown. Is advanced with respect to the zero-phase voltage V ₀ and has a phase of 90 °. Conversely, the zero-phase currents I ₀₁ and I ₀₂ flowing through the remaining feeder lines 25 and 26 and the zero-phase current I _0S flowing through the shield line 17 of the power cable have a phase of 90 ° behind. That is, the zero-phase current I ₀ flowing through the power cable 13 is I ₀ = −I _0S −I ₀₁ −I ₀₂ + I ₀₃ .

  FIG. 7 shows a measurement example of the zero-phase current waveform when a ground fault occurs in an actual high-voltage multi-circuit branch facility. In FIG. 7, Main is the measurement result for the power cable 13, CH1 to CH5 are the five feeder lines branched from the power cable 13, and CH6 is the measurement result for the shield line 17 of the power cable 13. Since the ground fault current Ig at the time of the ground fault was large (about 2 A), it exceeds the zero phase current waveform measurement range of the measuring device. Therefore, although the four waveforms of Main, CH1, CH3, and CH6 of the current waveform are recorded like a rectangular wave, it is considered that the actual ground fault current Ig has a waveform close to a sine wave of the commercial frequency. The current value and phase are measured by different means, and the results are shown below.

From the current waveform shown in FIG. 7, Main is a zero-phase current I ₀ (= 2000 mA, phase 262 degrees) flowing through the power cable 13, CH1 is a zero-phase current I ₀₁ (= 336 mA, phase 82 degrees) flowing through the feeder line, CH2 Is a zero-phase current I ₀₂ (= 41 mA, phase 84 degrees) flowing through the feeder line, CH3 is a zero-phase current I ₀₃ (= 2620 mA, phase 262 degrees) flowing through the feeder line, and CH4 is a zero-phase current I ₀₄ flowing through the feeder line. (= 62 mA, phase 84 degrees), CH5 is a zero-phase current I ₀₅ (= 33 mA, phase 84 degrees) flowing in the feeder line, and CH6 is a zero-phase current I ₀₆ (= 149 mA, phase) flowing in the shield line 17 of the power cable 13. 82 degrees).

Zero-phase current measurement:
I ₀ = −I ₀₁ −I ₀₂ + I ₀₃ −I ₀₄ −I ₀₅ −I _0S
2000 = −336−41 + 2619−62−33−149 Unit [mA]
Phase calculation: (based on the phase of the zero-phase current I _0S flowing through the shield wire 17 of the power cable 13)
I ₀ φ−I _0S φ = 262−82 = 180 degrees I ₀₁ φ−I _0S φ = 82−82 = 0 degrees I ₀₂ φ−I _0S φ = 84−82 = 2 degrees I ₀₃ φ−I _0S φ = 262-82 = 180 degrees I ₀₄ φ-I _0S φ = 84-82 = 2 degrees I ₀₅ φ-I _0S φ = 84-82 = 2 degrees

As a result of this phase calculation, the zero-phase current I ₀ φ that detects the ground fault of the power cable 13 and various electric devices and the I ₀₃ φ of the feeder line CH ₃ are 180 degrees when the zero-phase current I _0S is the reference phase. The phase of is detected. Therefore, the vector calculation result of the zero-phase current I ₀ φ and the feeder line I ₀₃ φ is in reverse phase (180 degrees). The zero-phase current phases I ₀₁ φ, I ₀₂ φ, I ₀₄ φ, and I ₀₅ φ of the healthy feeder lines CH1, CH2, CH4, and CH5 are substantially equal to 0 degrees when the zero-phase current I _0S is a reference phase. The phase is detected. Therefore, the vector calculation results of zero phase current I ₀ φ and I ₀₁ φ, I ₀₂ φ, I ₀₄ φ, and I ₀₅ φ of feeder lines CH1, CH2, CH4, and CH5 are all positive phase (0 degree, 2 degrees). Become.

It can be understood from this ground fault case that the voltage across the terminal resistor 21 when the zero-phase current I _0S detected on the secondary side of the clamp type current transformer 18 flows to the terminal resistor 21 is the zero-phase current I _0S. a zero-phase voltage V _0S based on the zero-phase voltage V _0S obtained by adjusting the first automatic reference value the size of a reference phase, zero-phase zero-phase voltage V _0S which was the reference When the sign of the ground fault current Ig as a result of the calculation is obtained by vector multiplication (Ig = I ₀ · V _0S · cosφ) of the zero-phase current I ₀ detected by the current ZCT, the ground fault current Ig Can be determined to have occurred in the campus accident.

Here, regarding the zero-phase voltage V _0S , the zero-phase current I _0S flowing through the shield wire 17 of the power cable 13 at the time of occurrence of the ground fault is detected by the clamp type current transformer 18, and the zero-phase current I _0S is the terminal. When the voltage across the terminal resistor 21 when flowing through the resistor 21 is used as a reference as the zero-phase voltage V _0S , the diameter and length of the power cable 13 that determines the ground capacitance between the core wire and the ground of the power cable 13 are used as parameters. The error due to the current flowing through the ground capacitance must be corrected. Therefore, in the high voltage insulation monitoring device 14 of this embodiment, the voltage across the terminal resistor 21 when the zero-phase current I _0S detected on the secondary side of the clamp type current transformer 18 flows through the terminal resistor 21 is gained. It is set to 1 by adjustment, and this is set as a reference zero-phase voltage V _0S .

It is determined from the phase difference of the zero-phase current I _{0 based on} the phase of the zero-phase voltage V _{0S that} the ground fault is a campus ground fault. That is, as shown in FIGS. 1 and 2, the zero-phase current I ₀ flowing through the power cable 13 is converted into a zero-phase current transformer ZCT15 (in the case of the embodiment of FIG. 1) or a clamp-type current transformer 16 (implementation of FIG. 2). The zero-phase current I _0S flowing through the shield wire 17 of the power cable 13 is detected by the clamp type current transformer 18. The power zero-phase current I _0S flowing through the shield wire 17 of the cable, converted to zero-phase voltage V _0S obtained based on the zero-phase current I _0S at the terminal resistor 21, the gain adjusting unit that zero-phase voltage V _0S 19 is adjusted to 1 by gain adjustment.

As a result, the arithmetic unit 20 multiplies the zero-phase current I ₀ flowing through the power cable 13 by the phase difference cosφ of the zero-phase current I _{0 based on} the phase of the zero-phase current I _0S flowing through the shield wire 17 (I ₀ · cosφ). That is, by setting the zero-phase voltage V _0S obtained based on the zero-phase current I _0S by gain adjustment to 1, and using only the phase information of the zero-phase current I _0S , the ground fault is caused by the ground fault on the premises. It is determined whether or not. If ground fault premises ground fault (see FIG. 6), the power zero-phase current I ₀ flowing through the power cable 13 with respect to the zero-phase current I _0S flowing through the shield wire 17 of the cable 13 opposite phase (180 °) from becoming, vector outputted from the arithmetic unit 20 calculates _{(Ig = I 0 · V 0S} · cosφ: However, since the zero-phase voltage V _0S obtained based on the zero-phase current I _0S is 1, I ₀ · cosφ) corresponds to the ground fault current Ig. When the sign of the result of vector calculation (Ig = I ₀ · V _{0 S} · cosφ) of the zero phase current I ₀ and the zero phase voltage V _0S is negative, it is determined that the ground fault is in the premises.

Thus, by setting the zero phase voltage V _0S obtained based on the zero phase current I _0S by gain adjustment to 1, the phase difference cosφ of the zero phase current I _{0 with} the phase of the zero phase current I _0S as a reference. Therefore, the zero-phase current I ₀ , the zero-phase voltage V _0, and the phase voltage V are determined as in the conventional insulation monitoring method (Patent Document 1). Complex vector operations based on measurement with complex numbers become unnecessary. Further, the zero-phase voltage V _0S obtained based on the zero-phase current I _0S is _measured by using the diameter and length of the power cable that determines the ground capacitance between the core wire and the ground of the power cable 13 as parameters. A circuit for correcting an error due to the current flowing through the capacitor is not necessary. Therefore, in order to periodically monitor the insulation deterioration state of the high piezoelectric path 12, an inexpensive high voltage insulation monitoring device 14 can be used with a simple circuit configuration.

As shown in FIG. 7, many ground faults are observed for several cycles. The ground fault current Ig of the present invention is calculated by multiplying the zero phase voltage I ₀ detected by the zero phase current transformer ZCT by the zero phase voltage V _0S (Ig = I ₀ · V _0S · cosφ). The sign of the resulting ground fault current Ig is determined for each waveform cycle. A detection level of the ground fault current Ig is set in advance, and when the ground fault current Ig exceeds this set value and exceeds a preset duration, a ground fault is determined and an alarm is output. be able to.

The ground fault current Ig of the present invention is a vector of the harmonic component (nth order) of the commercial frequency (first order) of the zero phase current I ₀ and zero phase voltage V _0S detected by the zero phase current transformer ZCT. It is also possible to measure the ground fault current Ign by multiplication (Ign = I _0n · V _0Sn · cosφ).

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

12 High Voltage Path 13 Power Cable 14 High Voltage Insulation Monitoring Device 15 Zero Phase Current Transformer ZCT
16 Current transformer (clamp type current transformer)
17 Shield wire of power cable 18 Current transformer (clamp type current transformer)
19 Gain Adjustment Unit 20 Calculation Unit 25-27 Feeder Line 28-30 Current Transformer (Clamp Type Current Transformer)
I ₀ Zero-phase current flowing in high piezoelectric path I _0S Current flowing in shielded cable of power cable Reference phase obtained based on I _0S φ I _0S

Claims (7)

A high-voltage insulation monitoring method for detecting a zero-phase current I ₀ flowing in a high-piezoelectric path connected to a non-grounded electric circuit and determining that the ground fault is a ground fault on the premises,
A current transformer is connected to the shield line of the power cable installed in the high piezoelectric path, and the zero-phase current I _0S flowing through the shield line at the occurrence of the ground fault is detected by the current transformer. A high voltage insulation monitoring method, wherein a ground fault is determined as a ground fault from a phase difference of the zero phase current I _{0 based on} the phase of I _0S . The high-voltage insulation monitoring method according to claim 1, wherein a zero-phase current I ₀ flowing in the high-voltage path is detected by a zero-phase current transformer ZCT installed in the high-voltage path when a ground fault occurs. A current transformer is connected to the secondary side of the zero-phase current transformer ZCT installed in the high-voltage path, and the zero-phase current I ₀ flowing in the high-voltage path is detected by the current transformer when a ground fault occurs. The high voltage insulation monitoring method according to claim 1. A current transformer is connected to each of a plurality of feeder lines branched from the high piezoelectric path, and zero-phase currents I _{01 to} I _0N flowing through the feeder lines when a ground fault occurs are detected by the current _transformer . The high voltage | pressure insulation monitoring method as described in any one of Claims 1-3. A high-voltage insulation monitoring device that detects a zero-phase current I ₀ that flows in a high-voltage circuit connected to a non-grounded circuit, and determines that the ground fault is a ground fault on the premises,
A current transformer that is detachably connected to a shield line of a power cable installed on the high-voltage path, and that detects a zero-phase current I _0S that flows through the shield line when the ground fault occurs, and is detected by the current transformer The zero-phase current I _0S is detected, and a gain adjustment unit that _sets the magnitude of the zero-phase voltage V _0S obtained by converting the zero-phase current I _0S to 1 by gain adjustment, and the zero-phase voltage V _0S by gain adjustment. with respect to the phase of the zero-phase voltage V _0S by 1 and the configuration of the zero-phase current I ₀ to the zero-phase voltage V _0S which was the reference in a calculation unit for calculating the ground fault current Ig by vector multiplication A high voltage insulation monitoring device characterized by A current transformer is provided which is detachably connected to a secondary side of a zero-phase current transformer ZCT installed in the high-voltage path and detects a zero-phase current I ₀ flowing in the high-voltage path when a ground fault occurs. Item 6. The high voltage insulation monitoring apparatus according to Item 5. 6. A current transformer is provided that is detachably connected to each of a plurality of feeder lines branched from the high-voltage path and detects zero-phase currents I _{01 to} I _0N flowing through the feeder lines when a ground fault occurs. Or the high voltage | pressure insulation monitoring apparatus of 6.

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