JP2002040088A - Deterioration diagnostic device for power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely diagnose the insulation deteriorated state of a power cable direct-coupled to an underground apparatus, for example, even a local deterioration by deterioration of water tree. SOLUTION: In this device, the voltage applied to the power cable direct- coupled to an underground apparatus direct-coupled terminal 2 is detected as a voltage signal by the voltage induced in a voltage detection part 11, and an earthing conductor current carried to the earthing conductor 12 of the power cable 1 is detected by a CT 13. A loss current arithmetic part 33 calculates the loss current of the same phase as the detected voltage signal from the voltage signal and current signal, and a deteriorated state diagnostic part 43 diagnoses the deterioration of the power cable 1. Accordingly, since the voltage and earthing conductor current of the power cable are detected without providing any detecting means or the like on the power cable 1 or imparting an external signal or the like, and the loss current is detected on the basis of the voltage and earthing conductor current of the power cable 1, the insulation deteriorated state of the power cable direct-coupled to the underground apparatus, for example, even the local deterioration by deterioration of water tree can be easily and surely diagnosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable deterioration diagnosis device for diagnosing a power cable insulation deterioration state in an underground power distribution system, and more particularly to a power cable insulation current deterioration detection apparatus using a power cable loss current. The present invention relates to a device for diagnosing deterioration of a power cable to be diagnosed.

[0002]

2. Description of the Related Art As a conventional power cable deterioration diagnosis apparatus of this type, there is a low frequency superposition method in which a low frequency voltage is superimposed on a high piezoelectric path in a live state as shown in FIG. The dielectric loss tangent method has been known as a method for measuring insulation loss and diagnosing insulation deterioration. The low-frequency superposition power cable deterioration diagnosis apparatus includes a low-frequency power supply 100 that applies a low-frequency AC voltage to a core wire 110 of a power cable 1 to be measured, and an AC voltage applied from the low-frequency power supply 100. The shielding layer 120 of the power cable 1 according to the voltage
A bridge circuit 200 for detecting a loss current flowing through the bridge circuit 200; a voltage / current characteristic calculation unit 300 for calculating a voltage / current characteristic based on the loss current output from the bridge circuit 200 and the AC voltage applied from the low frequency power supply 100; Controlling the applied voltage value of the frequency power supply 100,
The control section 400 controls switching of the frequency of the output current of 00 and controls the calculation operation of the voltage-current characteristic calculation section 300.
A deterioration judging section 500 for judging the deterioration of the power cable 1 based on the voltage / current characteristics calculated by the voltage / current characteristic calculating section 300; and a harmonic current output from the bridge circuit 200. A harmonic current judging section 600 for judging the deterioration of the power cable 1; and a deterioration state diagnosing section 700 for diagnosing the deterioration state of the power cable 1 based on the judgment results of the deterioration judging section 500 and the harmonic current judging section 600. It is a structure provided with.

As described above, the relational expression of the voltage and current is obtained from the low-frequency AC voltage and the loss current obtained by applying the AC voltage, and the degree of deterioration of the power cable 1 is determined from this relational expression. Regardless of the length, a close correlation with local deterioration is obtained, and an accurate diagnosis of the degree of deterioration can be made. On the other hand, the dielectric loss tangent method is disclosed in JP-A-8-36005 and JP-A-9-26447, in which a voltage phase of an applied commercial frequency is directly connected to an underground equipment. Detected through the power detection terminal (power detection unit) or the auxiliary circuit terminal, the current signal is detected from the measured cable ground wire, the dielectric loss tangent is obtained from the phase difference between the two, and the degree of deterioration is estimated based on the magnitude. There is a way.

[0004]

Since the conventional power cable deterioration diagnosis apparatus is configured as described above,
In the low frequency superposition method, since it is necessary to superimpose a low frequency voltage in a live state and obtain a reference signal via a standard capacitor CS of the bridge circuit 200, the power cable 1 of the high piezoelectric path is used.
Connection is essential, but the underground power cable in the underground distribution system has a structure that always has a shielding layer. .

In the dielectric loss tangent method, since measurement is performed using a commercial frequency voltage during operation, superposition of a signal is unnecessary. However, since the dielectric loss tangent is determined by the ratio of a loss current to a charging current. In addition, even if the power cables have the same degree of deterioration when viewed partially, in a long power cable, the deterioration state cannot be detected because the charging current becomes large even if the loss current is the same. That is, Water tre
e) there is a problem in that the detection performance for local degradation due to e.

In the dielectric loss tangent measurement method disclosed in Japanese Patent Application Laid-Open No. 8-36005, a voltage signal is detected from a power detection terminal (power detection unit) of a terminal, and a voltage phase is corrected. There is a problem that the measurement error cannot be ignored because of insufficient measurement. In contrast, Japanese Patent Laid-Open No. 9-26
No. 477 discloses a method for improving the correction accuracy by obtaining a voltage signal from an auxiliary circuit terminal of a switch tower to which a cable to be measured is connected, in order to improve the correction accuracy of the voltage phase. Actually, there are many switch towers without an auxiliary circuit terminal, and there is a problem that such a case cannot be applied in such a case. Further, the commercial frequency slightly fluctuates, and the fluctuation causes the phase of the voltage signal obtained from the power detection terminal (power detection unit) to fluctuate, causing a problem that a measurement error appears greatly or the value fluctuates. . Note that this voltage phase error causes a decrease in measurement accuracy when measuring not only the dielectric loss tangent but also dielectric loss and loss current.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to solve the problem of insulation deterioration of a power cable directly connected to underground equipment, for example, local deterioration due to deterioration of a water tree. It is an object of the present invention to provide a power cable deterioration diagnosis device capable of performing diagnosis easily and reliably.

[0008]

A power cable deterioration diagnosis apparatus according to the present invention provides a voltage induced in a live state at a detection terminal of a cable terminal in which a power cable to be measured is directly connected to an underground equipment. A voltage detection unit that detects and outputs a voltage signal as a voltage signal, a current detection unit that detects a current signal flowing through the ground line of the power cable, and a ground line current of the detected current signal and the detected voltage signal. A loss current calculation unit that calculates a loss current having the same phase as the phase of the voltage signal; and a deterioration diagnosis unit that diagnoses deterioration of the power cable from the calculated loss current.

As described above, according to the present invention, the voltage applied to the power cable directly connected to the underground equipment is detected by the voltage detection unit as a voltage signal using the voltage induced at the power detection terminal. The current detector detects a ground line current flowing through the ground line, and a loss current calculator calculates a loss current having the same phase as the detected voltage signal from the voltage signal and the current signal. Since the deterioration of the cable is diagnosed, the voltage and the ground line current of the power cable are detected without providing any detection means or the like on the power cable and without giving an external signal or the like. The loss current is detected based on the voltage of the ground wire and the ground wire current. Therefore, the insulation deterioration state of the power cable directly connected to the underground equipment, for example, water tree (Water Tree) Even local deterioration due to deterioration can be easily and reliably diagnosed.

The power cable deterioration diagnosis apparatus according to the present invention uses a correlation between a voltage signal detected at a power detection terminal and a voltage applied to the power cable, as required, in advance. A phase correction unit for correcting the phase is provided, and the voltage signal whose voltage phase has been corrected is output to the loss current calculation unit. As described above, in the present invention, the correlation between the magnitude and the phase of the voltage signal of the power cable is obtained in advance, and the voltage phase detected based on the obtained correlation is corrected by the phase correction unit. Therefore, a more accurate loss current can be calculated, and the accurate loss current allows a more accurate and reliable diagnosis of the insulation deterioration state of the power cable.

In the power cable deterioration diagnosis apparatus according to the present invention, if necessary, the detection unit detects a plurality of voltage signals simultaneously from a plurality of detection terminals in the same phase of the power cables constituting the plurality of power lines. A phase correction unit that corrects the phase of the voltage signal based on the sum of the plurality of detected voltage signals, and outputs the voltage signal whose voltage phase has been corrected to the loss current calculation unit. As described above, in the present invention, the voltage signals are simultaneously detected at the power detection terminals of the terminals of the plurality of power cables for each in-phase component in the plurality of power lines, and the voltage phase is phased based on the detected plurality of voltage signals. Since the correction unit corrects the loss, it is possible to calculate a more accurate loss current than when a voltage signal is detected from a single power detection terminal, and the accurate loss current allows the insulation deterioration state of the power cable to be more accurately and reliably determined. Can be diagnosed.

In the power cable deterioration diagnosis apparatus according to the present invention, if necessary, the detection unit may detect the voltage signal when the voltage applied to the power cable fluctuates. Only to detect.
As described above, according to the present invention, the voltage signal and the current signal of the frequency that fluctuates when applied to the power cable are detected only at a specific frequency. Can be detected, and a more accurate loss current can be calculated. With this accurate loss current, the insulation deterioration state of the power cable can be diagnosed more accurately and reliably.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment of the Present Invention) An apparatus for diagnosing deterioration of a power cable according to a first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is an overall block configuration diagram of a power cable deterioration diagnosis device according to the present embodiment, FIG. 2 is a detailed sectional view of a terminal directly connected to an underground equipment in the power cable deterioration diagnosis device shown in FIG. 1, and FIG. FIG. 2 is an explanatory diagram of a loss current calculation operation in the power cable deterioration diagnosis device described in FIG.

In the figures, the power cable deterioration diagnosis apparatus according to the present embodiment detects the underground equipment directly connected terminal 2 where the power cable 1 to be measured is directly connected to the switchgear tower 14 which is the underground equipment. Power terminal 10 (3.8KV, 60H
z), a voltage detector 11 for detecting the voltage applied and outputting it as a voltage signal S10, and a current detector for detecting a ground line current flowing through the ground line 12 of the power cable 1 and outputting a current signal S20 ( CT) 13 and a loss current calculating means 3 for calculating a loss current having the same phase as the voltage phase of the voltage signal S30 whose phase has been corrected from the ground line current of the detected current signal S20 and the detected voltage signal S10. And a deterioration diagnosis control unit 4 for diagnosing the insulation deterioration state of the power cable 1 from the calculated loss current.

The loss current calculating means 3 includes a voltage / frequency measuring unit 31 for measuring the voltage and frequency of the input voltage signal S 10, and converts the voltage signal S 10 into a correction value output from the deterioration diagnosis control means 4. A phase correction unit 32 that corrects the phase based on the corrected voltage signal S30, outputs the corrected voltage signal S30, the current signal S20 output from the CT 13, and the deterioration diagnosis control unit 4. The configuration includes a loss current calculation unit 33 that calculates a loss current in phase with the voltage signal S30 based on the coincidence signal S42. The voltage / frequency measurement unit 31 filters the voltage signal S10 with a band-pass filter that outputs only a predetermined band to remove noise components such as high-frequency components superimposed on the commercial frequency of 60 Hz. This is a configuration for measuring the frequency.

The deterioration diagnosis control means 4 corrects the voltage value of the voltage measured by the voltage / frequency measuring section 31 with respect to the voltage phase based on a previously obtained phase correlation equation, and corrects the correction value by the phase correction. Correction value calculation unit 4 to be output to the unit 32
1 and a frequency value of the frequency measured by the voltage / frequency measurement unit 31 is a predetermined specific frequency value (for example, 6
0 Hz), and a frequency monitoring unit 42 that outputs a coincidence signal S42 to the loss current calculation unit 33 by monitoring whether or not the power cable 1 matches with the power supply 1 based on the loss current calculated by the loss current calculation unit 33. And a deterioration state diagnosis unit 43 for diagnosing the deterioration state and outputting a diagnosis result. The phase correlation equation in the correction value calculation unit 41 creates a database of the magnitude and phase of the voltage signal obtained from the voltage detection unit 11 including the power detection terminal of the removed product or a new underground equipment directly connected terminal 2 in advance, A relational expression between voltage magnitude and phase is obtained in advance.

The terminal 2 directly connected to the underground equipment has the structure shown in FIG. 2, and the power cable 1 is connected to the switch tower 14 shown in FIG.
Are connected as terminal terminals. The terminal 2 directly connected to the underground equipment includes a compression terminal 11 connected to the core wire 110.
1, an insulating layer 113 outside the inner semiconductive layer 112,
And an external semiconductive layer 114 on the outside. The voltage detection unit 11 of the underground equipment directly connected terminal 2 has a structure in which an electrode electrically insulated from the surrounding external semiconductive layer 114 is embedded in the insulating layer 113 of the underground equipment directly connected terminal 2, In this configuration, an AC voltage is induced by the capacitance generated by the insulating layer 113 between the inner semiconductive layer 112 and the embedded electrode, and the voltage is output as a voltage signal S10. In addition, one switch tower 14 is connected to the power cable 1 to which the underground equipment direct connection terminal 2 of the 3 to 4 power lines is omitted (not shown), and the underground equipment direct connection terminal 2 and The power cable 1 has a structure in which all charged portions are shielded so as not to be exposed. It is desirable that the CT 13 change in characteristics with respect to temperature, current, and external magnetic field as little as possible.

Next, a description will be given of a deterioration diagnosis operation of the power cable deterioration diagnosis apparatus according to the present embodiment based on the above configuration. First, in the switch tower 14 to which the power cable 1 to be measured is connected, for example, the power cable 1
Is a branch high-voltage cable connected to the consumer side, the voltage is applied from the power supply 10 by the voltage detection unit 11 composed of the power detection terminal formed on the terminal 2 directly connected to the underground equipment applied to the power cable 1. The detected voltage is detected as a voltage signal S10, and this voltage signal S10 is input to the voltage input terminal 3a of the loss current calculation means 3.

The input voltage signal S10 is amplified as necessary by the voltage / frequency measuring unit 31, and further removes noise components such as harmonic components contained in the commercial radio wave voltage via a band-pass filter or the like. The magnitude and frequency of the applied voltage are measured and output to the correction value calculation unit 41 and the frequency monitoring unit 42. The correction value calculator 41 calculates a correction value for the voltage value of the measured voltage signal S10 based on a phase correlation equation obtained in advance, and
Output to 2. Further, the frequency monitoring unit 42 monitors whether or not the frequency value of the measured voltage signal S10 matches a preset specific frequency (for example, 60 Hz). The coincidence signal S42 is output to the calculation unit 33. That is, even if a slight fluctuation of the frequency occurs at the power of 3.8 KV (60 Hz) supplied from the power supply 10, the detection operation can always be performed under the same condition.

The phase corrector 32 corrects the phase of the voltage signal S10 detected by the voltage detector 11 based on the input correction value to generate a phase-corrected voltage signal S30.
For example, the voltage phase of the voltage signal S10 can be accurately corrected to a voltage signal S30 having a phase of 0 degrees as shown in FIG.
Along with the corrected voltage signal S30, a current signal S20 of the ground line current detected at CT13 is input to the loss current calculation unit 33 via the current input terminal 3b, and the loss current calculation unit 33 outputs the voltage signal S30 and the current Based on the signal S20, a loss current having the same phase (for example, 0 degree) as the voltage phase of the voltage signal S30 is calculated when the coincidence signal S42 is input.

When the frequency of the voltage signal S10 obtained from the voltage detector 11 matches a predetermined specific frequency, the current signal S20 input in this manner has the same phase as the voltage phase in the loss current calculator 33. The components will be calculated. The measurement result of the loss current is stored in the deterioration state diagnostic section 43.
The deterioration state diagnosing unit 43 diagnoses the insulation deterioration state based on the magnitude of the loss current, and the measurement result and the contents of the diagnosis are displayed on the display unit 5.

As described above, the voltage signal S10 is detected by the voltage detection unit 11 including the power detection terminal of the terminal 2 directly connected to the underground equipment.
The voltage phase is corrected using a phase correlation equation indicating the relationship between the magnitude and phase of the voltage relating to the voltage detection unit 11 of the voltage detection terminal obtained in advance, and further, when the frequency of the voltage signal matches the specific frequency, Since the loss current flowing through the power cable 1 to be measured is measured, it is hardly affected by the voltage phase shift and the frequency fluctuation, and the insulation deterioration state of the power cable 1 can be obtained by the loss current according to the degree. The accuracy of the deterioration determination can be improved.

(Second Embodiment of the Present Invention) An apparatus for diagnosing deterioration of a power cable according to a second embodiment of the present invention will be described below with reference to FIG. FIG. 4 is an overall block configuration diagram of the power cable deterioration diagnosis device according to the second embodiment. In the figure, the power cable deterioration diagnosis apparatus according to the present embodiment includes a loss current calculating means 3 and a deterioration diagnosis control means 4 similarly to the power cable deterioration diagnosis apparatus shown in FIG. In addition to the configuration, the high-voltage power supplied from the power-supply-side high-voltage cable 1A is branched at the switch tower 14 and supplied from the plurality of branch cables 1B to each customer and the like as a plurality of power lines. Voltage detection unit 11 composed of a voltage detection terminal formed on the underground equipment directly connected terminal 2 of the branch cable 1B for each in-phase.
Are applied to the respective voltage signals S11, S12,.
1n, and the respective voltage signals S11, S12,.
Is output to the loss current calculating means 3, and the CT 13 is clamped to the ground wire 12 of one of the plurality of branch cables 1B.
13 outputs the ground line current to the loss current calculating means 3 as a current signal S20.

That is, the voltage detecting terminal forming the voltage detecting section 11 is the branch cable 1B (or the power supply side high voltage cable 1A).
Since the high voltage applied to the core wire 110 is detected by the electrostatic partial pressure via the insulating layer 113, the voltage signals S11, S12,.
, S1n can be added to obtain a large voltage value.

As described above, depending on the type of the terminal 2 directly connected to the underground equipment, the voltage signal S11 (or S12,..., S1n) obtained from the voltage detection unit 11, which is a power detection terminal, is small, and sufficient phase correction cannot be performed. In the case, each voltage signal S obtained by the voltage detection unit 11 of the power detection terminal formed on the in-phase underground equipment directly connected terminal 2 of the same plurality of other power lines in the same switch tower 14.
11, S12,..., S1n are input in parallel, and a voltage is applied from the power detection terminal of the other power line and in-phase underground equipment directly connected terminal 2 in the same switch tower 14 where a large voltage signal is obtained. By obtaining the signals S11,..., S1n, measurement can be performed with a higher correction accuracy of the voltage phase.

The voltage signal S thus determined with high precision
Based on 11,..., S1n, the diagnosis of insulation deterioration of the branch cable 1B can be performed with higher accuracy by the power cable 1, the loss current calculation means 3, and the deterioration diagnosis control means 4 as in the above embodiment. In the above embodiments, the terminal 2 directly connected to the underground equipment has the configuration shown in FIG. 2, but the terminal 2 directly connected to the underground equipment shown in FIG. An insulation deterioration diagnosis can be performed.

[0027]

According to the present invention, a voltage detector detects a voltage applied to a power cable directly connected to an underground equipment as a voltage signal by a voltage induced at a detection terminal, and grounds the power cable. The current detector detects the ground line current flowing through the line, and the loss current calculator calculates the loss current in phase with the detected voltage signal from the voltage signal and the current signal. , So that the power cable voltage and the ground line current are detected without providing any detection means or the like in the power cable, and without giving an external signal or the like,
Since the loss current is detected based on the voltage of the power cable and the ground wire current, the insulation deterioration state of the power cable directly connected to the underground equipment, for example, local deterioration due to deterioration of a water tree (Water Tree). However, there is an effect that diagnosis can be easily and reliably performed.

In the present invention, the correlation between the magnitude and the phase of the voltage signal of the power cable is obtained in advance, and the detected voltage phase is corrected by the phase correction unit based on the obtained correlation. As a result, a more accurate loss current can be calculated, and the accurate loss current has the effect that the insulation deterioration state of the power cable can be more accurately and reliably diagnosed.

Further, in the present invention, voltage signals are simultaneously detected at power detection terminals of terminals of a plurality of power cables for each in-phase component in a plurality of power lines, and a voltage phase is detected based on the detected plurality of voltage signals. Is corrected by the phase correction unit, so that a more accurate loss current can be calculated when a voltage signal is detected from a single power detection terminal, and the accurate loss current makes it possible to more accurately determine the insulation deterioration state of the power cable. In addition, there is an effect that the diagnosis can be made reliably.

Further, since the voltage signal and the current signal of the fluctuating frequency applied to the power cable are detected only at a specific frequency, the voltage signal and the current signal can be detected under uniform conditions for the power cable. Thus, a more accurate loss current can be calculated, and the accurate loss current has an effect that the insulation deterioration state of the power cable can be more accurately and reliably diagnosed.

[Brief description of the drawings]

FIG. 1 is an overall block configuration diagram of a power cable deterioration diagnosis apparatus according to a first embodiment of the present invention.

FIG. 2 is a detailed cross-sectional view of a terminal directly connected to an underground equipment in the power cable deterioration diagnosis device shown in FIG.

FIG. 3 is an explanatory diagram of a loss current calculation operation in the power cable deterioration diagnosis device shown in FIG. 1;

FIG. 4 is an overall block configuration diagram of a power cable deterioration diagnosis device according to a second embodiment of the present invention.

FIG. 5 is an overall block configuration diagram of a power cable deterioration diagnosis device according to a second other embodiment of the present invention.

FIG. 6 is an overall block diagram of a conventional power cable deterioration diagnosis apparatus in a low frequency superposition method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power cable 1A Power supply side high voltage cable 1B Branch cable 2 Underground equipment direct connection terminal 3 Loss current calculation means 4 Deterioration diagnosis control means 5 Display unit 3a Voltage input terminal 3b Current input terminal 11 Voltage detection unit 12 Ground line 13 CT 14 Opening / closing Instrument 31 Voltage / frequency measurement unit 32 Phase correction unit 33 Loss current calculation unit 41 Correction value calculation unit 42 Frequency monitoring unit 43 Deterioration state diagnosis unit 100 Low frequency power supply 110 Core wire 111 Compression terminal 112 Internal semiconductive layer 113 Insulation layer 114 External Semiconductive layer 120 Shielding layer 200 Bridge circuit 210 Differential amplifier 300 Voltage-current characteristic calculation unit 400 Control unit 500 Deterioration determination unit 510 Voltage order determination unit 520 Insulation resistance determination unit 600 Harmonic current determination unit 700 Degradation diagnosis unit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Uesono 2-182 Watanabe-dori, Chuo-ku, Fukuoka City, Fukuoka Prefecture Inside Kyushu Electric Power Company (72) Inventor Hiroaki Kambara 660 Minamicho, Kurume-shi, Fukuoka Prefecture Daiden Stock In-house (72) Inventor Yoshinori Kudo 660 Minamicho, Kurume-shi, Fukuoka F-term (reference) 2D015 AA28 BA04 BA06 CA05 CA20

Claims (4)

[Claims] A voltage detection unit for detecting a voltage induced in a live state at a power detection terminal of a cable terminal to which a power cable to be measured is directly connected to an underground equipment and outputting the voltage as a voltage signal; A current detection unit that detects a current signal flowing through a ground line of the cable; and a loss that calculates a loss current having the same phase as the voltage phase of the voltage signal from the ground line current of the detected current signal and the detected voltage signal. A power cable deterioration diagnosis device, comprising: a current calculation unit; and a deterioration diagnosis unit that diagnoses deterioration of the power cable from the calculated loss current. 2. The deterioration diagnosis apparatus for a power cable according to claim 1, wherein a correlation between a voltage signal detected at the power detection terminal and a voltage applied to the power cable is obtained in advance. A power cable deterioration diagnosis apparatus, comprising: a phase correction unit that corrects a voltage phase by using the phase correction unit, and outputs a voltage signal whose voltage phase has been corrected to a loss current calculation unit. 3. The power cable deterioration diagnosis apparatus according to claim 1, wherein the detection unit simultaneously outputs a plurality of voltage signals by a plurality of power detection terminals in the same phase of the power cables constituting the plurality of power lines. Detecting a voltage phase of the voltage signal from the sum of the detected plurality of voltage signals, and outputting the voltage signal with the corrected voltage phase to the loss current calculation unit. Power cable degradation diagnostic device. 4. The deterioration diagnosis device for a power cable according to claim 1, wherein the detection unit detects the voltage signal when a voltage applied to the power cable has a frequency change. Is detected only at a specific frequency set in advance.