JP2008216141A - Method of locating occurrence of partial discharge in electric power cable, and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately locate the occurrence of a partial discharge at a plurality of locations. <P>SOLUTION: In S1, a partial discharge signal is detected at the time of day t1 in A end of CV cable, in B end at the time of day t2, the partial discharge signal is detected, in S2, whether the condition of ¾t2-t1¾≤L/C(L:length of cable, C:propagation speed) is fulfilled is discriminated. Then, in S4, the next signal is detected at the time of day t3 in A end and the signal is detected at the time of day t4 in B end, in S5, whether the condition of ¾t4-t3¾≤L/C is fulfilled is discriminated. And when each condition is fulfilled, in S7, whether both conditions (t3-t1)>L/C and (t4-t2)>L/C are fulfilled is discriminated, if both conditions are not fulfilled, the occurrence location is not performed (S8), if both conditions are fulfilled, the occurrence location is performed in S9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for locating a partial discharge occurrence position caused by water tree degradation or the like generated in a power cable, and an apparatus for performing the method.

As a power cable, a crosslinked polyethylene insulated cable (hereinafter referred to as “CV cable”) has been put into practical use for underground power transmission. However, in this CV cable, when it is used for a long time under wet conditions such as a pipe where water has accumulated, an AC electric field is applied to minute foreign matters and voids (minute voids) in the insulator, and the “water tree” ( It is known that an insulation deterioration phenomenon called a dendritic crack filled with water occurs. If this water tree is generated and grows, it may cause a decrease in insulation performance and eventually cause a dielectric breakdown called an electric tree. Need to diagnose by condition.
On the other hand, in the CV cable before embedment, if there is a damage or the like, there is a risk of causing insulation deterioration, and therefore, a quality test for detecting these in advance is performed.

FIG. 9 shows a measurement circuit of a direct current leakage current method which is an example of a water tree deterioration diagnosis method for the CV cable 20. Reference numeral 24 denotes a direct current power source. The negative electrode side is connected to the core conductor 21 of the CV cable 20 via the protective resistor 25, while the positive electrode side is connected to the guard electrode 26 covered with the insulator 22 of the CV cable 20. Then, the other of the positive electrode side is connected to the ground line connected to the shielding layer 23 of the CV cable 20 via the current detection resistor 27 and the ammeter 28. Reference numeral 29 denotes a recorder.
In this measurement circuit, after disconnecting the CV cable 20 from the power system, a predetermined DC high voltage is applied to the core conductor 21 side. At this time, if a water tree that bridges between the inner peripheral surface and the outer peripheral surface of the insulator 22 exists in the insulator 22, a direct current flows on the ground line side. As shown in FIG. 10, this current shows a tendency to increase as water tree deterioration progresses, and when the deterioration state further deteriorates, a sudden change (kick phenomenon) in current is observed (FIG. 10). K section).

However, with this DC leakage current method, the presence or absence of water tree deterioration can be diagnosed, but the location cannot be specified, and if water tree deterioration is confirmed, the entire CV cable must be replaced.
On the other hand, in Patent Documents 1 to 4, sensors are arranged at both ends of a CV cable, a DC high voltage is applied to the conductor of the cable, and the time when each sensor detects the generated partial discharge signal is measured. A method for detecting a position where a partial discharge has occurred is disclosed. It is known that the current increase tendency and kick phenomenon at the time of DC leakage current measurement are caused by partial discharge inside the water tree. It will be possible.

JP-A-6-294839 JP-A-4-320977 JP 2001-183410 A Japanese Patent Laid-Open No. 2-10274

However, in the method for detecting the occurrence point of the partial discharge, when the partial discharge occurs only at one location of the cable, the occurrence location can be detected. If partial discharges are occurring at the same time, it is difficult to determine the position of each occurrence, and eventually the entire cable needs to be replaced.
Further, in such a detection device, noise is likely to enter from the detection ends at both ends of the cable that are not sufficiently shielded from noise, and if the noise enters, it cannot be distinguished from the partial discharge signal, and the accuracy of orientation is reduced. There was also a problem.

  Therefore, the present invention has an object to provide a method for locating a partial discharge occurrence position of a power cable capable of accurately locating occurrence positions of a plurality of partial discharges, and an apparatus for carrying out the method. .

In order to achieve the above object, the invention described in claim 1 applies a DC voltage to the power cable, detects a partial discharge signal generated in the power cable at both ends of the power cable, and the partial discharge signal is A partial discharge occurrence position locating method for a power cable that determines a position where a partial discharge signal is generated based on a time difference between propagation times arriving at both detection ends of the power cable, wherein the partial discharge is detected at both detection ends of the power cable. The detection time difference between the partial discharge signals at both detection ends is less than the time required for the partial discharge signal to propagate through the entire length of the power cable, and the repeated detection time interval at each detection end is The generation position is determined for a partial discharge signal that is longer than the time required for the partial discharge signal to propagate through the entire length of the power cable.
In order to achieve the above-mentioned object, the invention described in claim 2 applies a DC voltage to two power cables that are folded back with one end connected, and the partial discharge signals generated in the power cable are both detected. Partial discharge occurrence position determination of the power cable, which is detected at the other end side of the power cable and determines the generation position of the partial discharge signal based on the time difference between the propagation times when the partial discharge signal reaches the detection ends of both power cables, respectively. In this method, the partial discharge signal is repeatedly detected at both detection ends of the power cable, and the difference in detection time between the partial discharge signals at both detection ends propagates the total length of the two power cables. For partial discharge signals that are less than or equal to the time required for the detection, and the repeated detection time interval at each detection end is greater than the time required for the partial discharge signal to propagate through the total length of the two power cables It is characterized in carrying out the orientation of the raw position.
In order to achieve the above object, the invention described in claim 3 applies a DC voltage to two power cables that are connected with one end and turned back to generate both partial discharge signals generated in the power cable. Partial discharge occurrence position determination of the power cable, which is detected at the other end side of the power cable and determines the generation position of the partial discharge signal based on the time difference between the propagation times when the partial discharge signal reaches the detection ends of both power cables, respectively. A method in which an amplifier is connected between two power cables to amplify a partial discharge signal propagating through the folded power cable, and the partial discharge signal is repeatedly detected at both detection ends of the power cable. The delay time generated by amplification is Δt, the length of the power cable is L, the propagation speed of the partial discharge signal is C, and the difference in detection time between the partial discharge signals at both detection ends is Δt or more and Δt + 2L / C or less. And the occurrence position is determined for a partial discharge signal whose repetition detection time interval at each detection end is longer than the time required for the partial discharge signal to propagate through the total length of two power cables. To do.
In addition to the object of any one of claims 1 to 3, the invention described in claim 4 is characterized in that the location of the partial discharge signal generation position is 100 kHz to The configuration is based on the time difference in the propagation time of the partial discharge signal in the 10 MHz band.

In order to achieve the above object, the invention as set forth in claim 5 is characterized in that a power applying means for applying a DC voltage to the power cable and a partial discharge signal generated in the power cable by the power application are respectively applied to both ends of the power cable. A partial discharge occurrence position locating device for a power cable, comprising: detection means for detecting; and locating means for locating the generation position of the partial discharge signal based on a time difference between propagation times at which the partial discharge signals reach each detection means. The detection means repeatedly detects the partial discharge signal, and the orientation means detects the difference in detection time of the partial discharge signals at both detection ends to be less than the time required for the partial discharge signal to propagate through the entire length of the power cable. In addition, the location of the occurrence of the partial discharge signal is determined with respect to the partial discharge signal whose repetition detection time interval at each detection end is longer than the time required for the partial discharge signal to propagate through the entire length of the power cable. It is an feature.
In order to achieve the above-mentioned object, the invention described in claim 6 is characterized in that an electric power applying means for applying a direct current voltage to two electric power cables which are connected with one end and turned back, and the electric power is applied in the electric power cable. Standardization for locating the partial discharge signal generation position based on the time difference between the detection means for detecting the generated partial discharge signal at the other end of each power cable and the propagation time at which the partial discharge signal reaches the detection means. A partial discharge generation position locating device for a power cable comprising: a detecting means that repeatedly detects a partial discharge signal; and the locating means has a detection time difference between the two partial discharge signals at both detection ends. The total length of the power cable is less than the time required for the partial discharge signal to propagate, and the repeated detection time interval at each detection end is required for the partial discharge signal to propagate the total length of the two power cables. It is characterized in carrying out the orientation of the generation position for greater partial discharge signal than during.
In order to achieve the above-mentioned object, the invention according to claim 7 is characterized in that the power supply means for applying a DC voltage to the two power cables that are folded back with one end connected thereto, Standardization for locating the partial discharge signal generation position based on the time difference between the detection means for detecting the generated partial discharge signal at the other end of each power cable and the propagation time at which the partial discharge signal reaches the detection means. A partial discharge generation position locating device for a power cable comprising means for amplifying a partial discharge signal propagating through the power cable on the folded side by connecting an amplifier between the two power cables. By repeatedly detecting the partial discharge signal at both detection ends of the cable, the locator means that the delay time generated by amplification is Δt, the length of the power cable is L, and the propagation speed of the partial discharge signal is C. The difference in detection time between the partial discharge signals at both detection ends is Δt or more and Δt + 2 L / C or less, and the repetition detection time interval at each detection end propagates the total length of the two power cables. The generation position is determined for a partial discharge signal that is longer than the time required for.
In addition to the object of any one of claims 5 to 7, the invention according to claim 8 is characterized in that the location of the partial discharge signal generation position is 100 kHz to The configuration is based on the time difference in the propagation time of the partial discharge signal in the 10 MHz band.

According to the present invention, even when partial discharges are generated from a plurality of water tree degradation positions, etc., by repeatedly detecting partial discharges generated in the insulator of the CV cable during DC voltage application, The occurrence position of the partial discharge can be accurately determined. Therefore, the replacement of the entire cable length in a certain section as in the prior art can be replaced with a partial cable replacement in a certain section, and the cost required for the replacement can be reduced.
According to the inventions of claims 3 and 7, in addition to the above effects, the occurrence position is determined only when the arrival time difference between the partial discharge signals is not less than Δt and not more than Δt + 2 L / C, so that the partial discharge It is possible to distinguish between a signal and noise. Therefore, improvement in orientation accuracy can be expected.
Furthermore, according to the fourth and eighth aspects of the invention, since the determination is made based on the time difference between the propagation times of the partial discharge signals in the specific band, the generation position can be more accurately determined.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Form 1]
FIG. 1 is an explanatory view showing an example of a partial discharge occurrence position locating apparatus (hereinafter simply referred to as “positioning apparatus”) of the present invention. In the figure, reference numeral 1 denotes a CV cable to be measured, which has a known configuration in which a core conductor is covered in the order of an insulator, a shielding layer, and an insulating sheath. Among the detection ends (hereinafter referred to as “A end” and “B end”) of the core conductor of the CV cable 1, a DC power source 3 serving as a power application means is provided at the A end via the protective resistor 2. A resistor 4 for current detection and an ammeter 5 are connected in series to the ground side. 6 is a pen recorder. Further, the shielding layers at both ends of the CV cable 1 are grounded via the coupling capacitor 7 and the signal detection impedance 8 serving as detection means, and the partial discharge signals (hereinafter simply referred to as “ "Signal") can be input to the digital oscilloscope 9 as an orientation means.

  In this orientation device, when a DC high voltage is applied to the core conductor of the CV cable 1, if the CV cable 1 has a defect such as water tree deterioration, the signal generated at that location propagates through the CV cable 1. Each reaches the AB end, is detected by the signal detection impedances 8 and 8, and is input to the digital oscilloscope 9 via CH1 and 2, respectively. The digital oscilloscope 9 measures the propagation time difference of the signals detected by the signal detection impedances 8 and 8, and calculates the position where the partial discharge has occurred by a well-known calculation based on the time difference, the length of the CV cable, and the propagation speed. To do.

To give a specific example, 10 m of CV cable used for 20 years was removed, and partial discharge measurement was performed using the orientation device shown in FIG. 1. As the DC leakage current increased, the frequency was increased several times per second. A discharge was detected. FIG. 2 shows the detected partial discharge waveform (PD part). As a result of examining the frequency spectrum of the partial discharge waveform, it was found that the frequency spectrum spread to 100 MHz or more as shown in FIG. Furthermore, when the kick phenomenon occurred, partial discharge was detected with a higher occurrence frequency than when the DC leakage current increased. From this test result, it was confirmed that the increase tendency of DC leakage current and the kick phenomenon at the time of measuring DC leakage current were caused by partial discharge inside the water tree.
Further, a defect was artificially produced in the center of a 300 m CV cable, and a partial discharge was generated by applying a DC high voltage using the orientation device of FIG. At this time, when the signal propagation time difference in the 100 kHz to 10 MHz band was measured at the both end positions of the CV cable and the position of the defect where the partial discharge occurred was determined, the error was 1% with respect to the cable length. The orientation was possible.

  From these test results, by measuring the signal propagation time difference in the 100 kHz to 10 MHz band due to the increase in DC leakage current detected during DC high voltage application and the kick phenomenon, the position where the water tree degradation occurred with high accuracy It became clear that it can be standardized.

Next, a partial discharge occurrence position locating method (hereinafter simply referred to as “orientation method”) implemented in the above-described orientation apparatus will be described based on the flowchart of FIG.
First, when a partial discharge occurs, the signal waveform from the A end and the signal waveform from the B end are digitized (captured) and recorded in the memory for each partial discharge. Here, in S1, when the signal is detected at the A end at time t1 and the signal is detected at the B end at time t2, in S2, the cable length is L, and the signal speed in the 100 kHz to 10 MHz band in the cable is C. In this case, it is determined whether or not the condition of | t2-t1 | ≦ L / C is satisfied. If this condition is not satisfied, it is determined that the signals are not from the same position, and the position is not determined (S3).

If this condition is satisfied, in S4, the next signal is detected at the A end at time t3 (t3> t1), and the next signal is detected at the B end at time t4 (t4> t2). Then, similarly to S2, it is determined whether or not the condition of | t4-t3 | ≦ L / C is satisfied. If this condition is not satisfied, it is determined that the signals are not from the same position, and the position is not determined (S6).
In S7, it is determined whether or not both (t3-t1)> L / C and (t4-t2)> L / C are satisfied. Here, if both conditions are not satisfied, position location is not performed (S8), and if both conditions are satisfied, it is assumed that partial discharge has occurred at different positions X1 and X2, and in S9, Perform location.
When the next signal is not detected at the A end or the B end, the position is determined only by the equation 1 in S9, and the position determination is terminated.

Position X1 = (L−C × | t2−t1 |) / 2 Formula 1
Position X2 = (LC- || t4-t3 |) / 2 .. Formula 2
If the orientation is continuously performed in the determination of S10, the process returns to S4 as t3 → t1 and t4 → t2 in S11, and the same processing is repeated.

In S7, the time difference at which the signal is detected at each AB end is compared with L / C to determine whether or not position determination is possible, and the position determination is performed only for those determined to be possible. For the following reasons.
For example, if a partial discharge first occurs at a distance X1 (0 ≦ X1 ≦ L) from the A end, the difference in propagation distance when propagating from the X1 to the A end and the B end is | L−2X1 |. Therefore, the arrival time difference is | L−2X1 | / C. The difference in arrival time is greatest when partial discharge occurs near the A and B ends, and the value is close to L / C.
Next, it is assumed that another partial discharge occurs at a distance X2 from the A end (X1 <X2). When the time delay t until the partial discharge occurs at X2 after the partial discharge occurs at X1, the waveform measured first at the B end is the discharge at X2 when the time delay t is shorter than (X2-X1) / C. If the partial discharge point is calculated based on the time difference between the wave fronts, correct positioning cannot be performed. Therefore, when the partial discharge delay time t becomes smaller than L / C which is the maximum value of (X2−X1) / C, it is excluded because there is a possibility of mislocation.
In order to prevent such mislocation cases from occurring frequently, the voltage to be applied should be adjusted so that the frequency of occurrence of partial discharge over the entire length of the cable is sufficiently lower than L / C. is there.

  If the position determination results obtained in this way are plotted with the position of the position on the horizontal axis and the cumulative number of partial discharge occurrences on the vertical axis as shown in FIG. 5, it is possible to grasp the discharge occurrence state in the cable longitudinal direction. In the example of FIG. 5, since the cumulative partial discharge occurrence number suddenly increases at the points a, b, and c and in the vicinity thereof, it will occur near the points a, b, and c. It is determined that partial discharge has occurred from the water tree.

  Thus, according to the orientation method and orientation device of form 1 above, the partial discharge generated in the insulator of the CV cable 1 at the time of DC voltage application is repeatedly detected, and the detection time difference of the signal at each end of AB is Occurs due to arrival time difference in propagation time at the AB end for signals that are less than the time L / C required for signal propagation through the entire length of the CV cable and the repeated detection time interval at each end of AB is greater than the time L / C Since the location is determined, even when partial discharges are generated from a plurality of water tree deterioration positions, all the partial discharge generation positions can be accurately determined. Therefore, the replacement of the entire cable length in a certain section as in the prior art can be replaced with a partial cable replacement in a certain section, and the cost required for the replacement can be reduced.

[Form 2]
Next, another embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same structure part as previous form 1, and the overlapping description is abbreviate | omitted.
In an actual CV cable having a length of several kilometers, a signal detected at one end is sent back to the other end, which is a measurement end, and measurement is performed with the orientation device shown in FIG. In other words, the signal detection impedance 8 on the B end side is connected to the C end of the core conductor of the signal return cable (one of the remaining two phases of the three-phase cable) 11 via the amplifier 10. The D end serving as the detection end is connected to the measuring instrument 12 as the orientation means.
Therefore, the signal detected by the signal detection impedance 8 on the B end side is amplified by the amplifier 10. Since the signal propagating in the cable is attenuated more on the high frequency side, the amplifier 10 uses a signal that is amplified more greatly on the high frequency side as shown in the lower side of FIG. The signal that has passed through the amplifier 10 propagates through the signal return cable 11 and is sent back to the D end. Therefore, in the measuring instrument 12, the position of the partial discharge occurrence position (water tree deterioration position) is determined according to the time difference between the signals reaching the A end and the D end according to the flowchart of FIG.

However, in the orientation apparatus of FIG. 6, the signal sent back from the B end to the D end of the signal sending back cable 11 always arrives at the measuring instrument after a delay from the signal obtained at the A end. This delay time includes a delay time Δt generated by amplifying the signal obtained at the B end by the amplifier 10. The delay time of the signal sent back to the D end with respect to the signal obtained at the A end is minimized when a partial discharge occurs in the vicinity of the B end, and connects the signal detection impedance 8 on the B end side and the amplifier 10. If the time delay due to the line or the line for connecting the amplifier 10 and the signal return cable 11 is ignored, Δt is obtained.
In addition, the delay time of the signal sent back to the D end with respect to the signal obtained at the A end becomes the maximum when a partial discharge occurs in the vicinity of the A end, the cable length is L, and in the band of 100 kHz to 10 MHz in the cable. When the signal propagation speed is C, Δt + 2L / C. This relationship is shown in (1) of FIG. That is, when the signal obtained at the D end is compared with the signal obtained at the A end, it always has a delay time of Δt or more and Δt + 2 L / C or less.

  On the other hand, this orientation device is shielded by a coaxial structure except for the ends (including the detection impedance portion) of the CV cable 1 and the signal sending back cable 11 to be measured, so that noise from the outside hardly penetrates. Can not. In other words, external noise penetrates at the A end and D end or B end and C end simultaneously from the location where the shield at the end of the cable is not sufficiently shielded (the location surrounded by the dotted line and the two-dot chain line in FIG. 6). Therefore, there is almost no time difference between the signals obtained by CH1 and CH2 of the measuring instrument 12 as shown in (2) of FIG. From this, it can be seen that the signal and the noise can be distinguished. Here, if the amplifier 10 does not exist, the difference in arrival time between the A end and the D end of the signal generated in the vicinity of the B end is 0, and it is impossible to distinguish it from noise.

Here, the time delay Δt of the amplifier 10 can be obtained as follows.
First, the measurement circuit is calibrated by injecting a known discharge pulse from the A end before the positioning. That is, when a discharge pulse is injected from the A end, a reflected wave and a transmitted wave are generated at the B end. By measuring the arrival time Δt1 of the reflected wave at the A end, the signal speed C in the band of 100 kHz to 10 MHz in the cable can be obtained by C = 2L / Δt1, where L is the cable length. The time delay Δt of the amplifier 10 can be obtained from Δt = Δt2−Δt1, where Δt2 is the arrival time of the signal detected at the D end of the signal return cable 11.

  Accordingly, in the flowchart of FIG. 7, first, at S21, when signals are detected at the A end at time t1 and at the D end at time t2, respectively, at S22, from the arrival time t2 of the signal detected at the D end, Δt + Δt1 / 2 (= Δt + L / C) is subtracted to obtain a time t2 ′ calibrated in consideration of the time delay Δt by the amplifier 10 and the propagation time L / C of the signal return cable 11. Therefore, in S23, the time difference between t2 'and t1 is compared with L / C, and if it exceeds L / C, it is excluded from the positioning in S24. Further, when the equation t2 ′ = t2− (Δt + L / C) of S22 is substituted into the equation | t2′−t1 | ≦ L / C of S23 and transformed, Δt ≦ t2−t1 ≦ Δt + 2L / C is obtained as shown in FIG. In order to satisfy the signal relationship (1), it can be distinguished from noise.

In S25, when the next signal is detected at the A end at time t3 and at the D end at time t4, in S26, Δt + Δt1 / 2 (= Δt + L) from the arrival time t4 of the signal detected at the D end. / C) is subtracted, and a time t4 ′ calibrated in consideration of the time delay Δt by the amplifier 10 and the propagation time L / C of the signal return cable 11 is obtained. In S27, the time difference between the times t4 ′ and t3 is calculated. If it is compared with L / C and exceeds L / C, it is excluded from the positioning in S28. Further, when the equation t4 ′ = t4− (Δt + L / C) of S26 is substituted into the equation | t4′−t3 | ≦ L / C of S27 and transformed, Δt ≦ t4−t3 ≦ Δt + 2L / C is obtained. In order to satisfy the signal relationship (1), it can be distinguished from noise.
The subsequent processing of S29 to S33 is the same as the processing of S7 to S11 described in FIG. 4, but here, the times t2 ′ and t4 ′ calibrated in S22 and S26 are replaced with the times t2 and t4, respectively. Will be used.

As described above, also in the orientation method and orientation device of the above-described form 2, even when partial discharges are generated from a plurality of water tree deterioration positions, etc., all partial discharge occurrence positions can be accurately determined. . Therefore, the replacement of the entire cable length in a certain section as in the prior art can be replaced with a partial cable replacement in a certain section, and the cost required for the replacement can be reduced.
In particular, since the occurrence position is determined only when the arrival time difference of the signal is not less than Δt and not more than Δt + 2L / C, it is possible to determine the position by discriminating between the signal and the noise, and the improvement of the localization accuracy can be expected. .

The specific configuration of the orientation device is not limited to the first and second embodiments. For example, in the above embodiment, the location of the partial discharge occurrence position is determined together with the DC leakage current measurement, but it is natural that only the location of the partial discharge occurrence position may be determined, and in this case, an ammeter, a pen recorder, etc. are omitted. it can.
In the second embodiment, the signal propagating through the folded-back CV cable is amplified by the amplifier, but the amplifier may be omitted.

Using a 11 km VCV cable line for electric power with a total length of 1.2 km that has been used for 20 years, the location of the occurrence of water tree deterioration was measured by partial discharge measurement while measuring DC leakage current. When a DC voltage of 16 kV was applied, an increasing tendency of the DC leakage current was observed, and ten kick phenomena were detected in 7 minutes of the application time. When a DC voltage of 16 kV is applied, a signal in a band of 100 kHz to 10 MHz having a magnitude of about 10 to 20 mV is detected at a frequency of several times per second at both ends of the line, and when a kick phenomenon occurs, 10 to 20 mV. A signal in a band of about 100 kHz to 10 MHz was detected with a frequency of several tens of times per second.
The detected signal is taken into the computer for a maximum of 300 pulses during the charging time of 7 minutes, the partial discharge occurrence position is calculated from the taken pulse from the propagation time difference according to the flowchart of FIG. When the frequency distribution of the occurrence positions of the partial discharges divided into two is obtained, the distribution in the range from 540 m to 570 m with the maximum position at 560 m from the end of the cable where the DC voltage was applied, and the position at 1070 m were maximized. There was a distribution ranging from 1060m to 1100m. The signal detected when the kick phenomenon occurred was standardized at a position of 550 to 570 m from the end of the cable where the DC voltage was applied 10 times as a partial discharge occurrence position.

A DC high voltage was applied, and a dielectric breakdown test was performed on the CV cable subjected to the test. When the position where the insulation breakdown occurred was investigated, the breakdown occurred at a position of 556 m from the end of the cable where the DC voltage was applied when measuring the DC leakage current.
In addition, when the state of generation of water trees was confirmed for the insulator of the CV cable having a longitudinal direction of 50 mm in the vicinity of the breaking point, a water tree in which eight insulators were bridged was found.
Furthermore, among the CV cable lines used for the test, the cable in the range of 1060 m to 1100 m was removed from the end of the cable on which the DC voltage was applied, and a precursor interruption test (with a precursor of dielectric breakdown using a partial discharge comparator) When a test was conducted to monitor a partial discharge and shut off the power supply just before breakdown, the precursor cutoff point was 1066 m.

  And when the generation | occurrence | production condition of the water tree was confirmed about the insulator of the CV cable of the longitudinal direction 50mm vicinity near a precursor interception point, the water tree which bridged five insulators was discovered. One of them was an electric tree that was a precursor of dielectric breakdown from the inside of the water tree. The partial discharge observed at the time of measuring the DC leakage current was generated during the progress of this electric tree.

In addition, in the said form and Example, although this invention is applied to the orientation of the water tree degradation position which generate | occur | produced in the CV cable, it is not restricted to water tree degradation, Other internal factors (mechanical stress, heat shrink, Even contamination of impurities) or trauma can be found by locating the partial discharge occurrence position. Therefore, the present invention can be applied not only to cables buried underground but also to quality tests at a factory before being buried.

It is explanatory drawing of the orientation apparatus of form 1. It is an example of the partial discharge waveform measured when the leakage current increased in the DC leakage current measurement. It is the frequency spectrum of the partial discharge waveform measured at the time of the leakage current increase of DC leakage current measurement. It is a flowchart of the orientation method. It is a graph which shows the discharge generation condition of a CV cable longitudinal direction. It is explanatory drawing of the orientation apparatus of form 2. It is a flowchart of the orientation method. The relationship of the input time of the signal input into the orientation apparatus is shown. It is explanatory drawing which shows the example of a measurement circuit of DC leakage current. It is an example of the direct current leakage current waveform measured with the high voltage | pressure power cable in which a bridge water tree exists.

Explanation of symbols

  1 .... CV cable, 2 .... Protection resistance, 3 .... DC power supply, 8 .... Signal detection impedance, 9 .... Digital oscilloscope, 10 .... Amplifier, 11 .... Signal return cable, 12 .... Measurement device .

Claims (8)

A direct current voltage is applied to the power cable, a partial discharge signal generated in the power cable is detected at both ends of the power cable, and a propagation time of the partial discharge signal reaching both detection ends of the power cable, respectively. Based on a time difference, a partial discharge occurrence position locating method of a power cable for locating the generation position of the partial discharge signal,
The partial discharge signals are repeatedly detected at both detection ends of the power cable, and the difference in detection time of the partial discharge signals at both detection ends is required for the partial discharge signal to propagate the entire length of the power cable. It is characterized in that the occurrence position is determined for a partial discharge signal that is equal to or shorter than the time and has a repeated detection time interval at each detection end longer than the time required for the partial discharge signal to propagate through the entire length of the power cable. A method for locating the partial discharge occurrence of a power cable. A DC voltage is applied to two power cables that are folded back with one end connected, and the partial discharge signals generated in the power cables are detected on the other end sides of the two power cables, respectively. Is a partial discharge occurrence position locating method for a power cable that locates the generation position of the partial discharge signal based on the time difference between the propagation times respectively reaching the detection ends of the both power cables,
The partial discharge signal is repeatedly detected at both detection ends of the power cable, and the partial discharge signal propagates the total length of the two power cables by the difference in detection time between the partial discharge signals at both detection ends. The occurrence position of the partial discharge signal that is less than the time required for the detection and the repetition detection time interval at each detection end is greater than the time required for the partial discharge signal to propagate the total length of the two power cables. A method for locating a partial discharge occurrence position of a power cable, characterized in that A DC voltage is applied to two power cables that are folded back with one end connected, and the partial discharge signals generated in the power cables are detected on the other end sides of the two power cables, respectively. Is a partial discharge occurrence position locating method for a power cable that locates the generation position of the partial discharge signal based on the time difference between the propagation times respectively reaching the detection ends of the both power cables,
An amplifier is connected between the two power cables to amplify a partial discharge signal propagating through the folded power cable, and the partial discharge signal is repeatedly detected at both detection ends of the power cable, The delay time generated by amplification is Δt, the length of the power cable is L, the propagation speed of the partial discharge signal is C, and the difference in detection time of the partial discharge signal at both detection ends is Δt or more and Δt + 2L / C or less And the position of the occurrence of the partial discharge signal is determined for a repetition discharge time interval at each detection end larger than the time required for the partial discharge signal to propagate through the total length of the two power cables. A method for locating a partial discharge occurrence position of a power cable.   The power cable according to any one of claims 1 to 3, wherein the location of the partial discharge signal is determined based on a time difference in propagation time of the partial discharge signal in a band of 100 kHz to 10 MHz. Partial discharge occurrence location method. A power applying means for applying a DC voltage to the power cable; a detecting means for detecting a partial discharge signal generated in the power cable by the power application at both ends of the power cable; and the partial discharge for each detecting means. A partial discharge occurrence position locating device for a power cable, comprising a locating means for locating the generation position of the partial discharge signal, based on a time difference between propagation times at which the signals arrive respectively.
The detection means repeatedly detects the partial discharge signal, and the orientation means detects the difference in detection time between the partial discharge signals at the two detection ends, while the partial discharge signal propagates the entire length of the power cable. The occurrence position is determined for a partial discharge signal that is equal to or shorter than the time required and the repetition detection time interval at each detection end is longer than the time required for the partial discharge signal to propagate through the entire length of the power cable. A partial discharge occurrence position locating device for power cables. An electric power applying means for applying a DC voltage to two power cables that are folded back by connecting one end thereof, and a partial discharge signal generated in the electric power cable by the electric power application at the other end sides of the two electric power cables, respectively. A partial discharge occurrence position locating device for a power cable, comprising: detection means for detecting; and locating means for locating the generation position of the partial discharge signal based on a time difference between propagation times at which the partial discharge signals reach the detection means. Because
The detection means repeatedly detects the partial discharge signal, and the orientation means detects the difference between detection times of the partial discharge signals at the two detection ends, and the partial discharge signal indicates the total length of the two power cables. Occurs for partial discharge signals that are less than or equal to the time required for propagation and that have a repeated detection time interval at each detection end that is greater than the time required for the partial discharge signal to propagate the total length of the two power cables. An electric power cable partial discharge generation position locating device characterized by performing position locating. An electric power applying means for applying a DC voltage to two power cables that are folded back by connecting one end thereof, and a partial discharge signal generated in the electric power cable by the electric power application at the other end sides of the two electric power cables, respectively. A partial discharge occurrence position locating device for a power cable, comprising: detection means for detecting; and locating means for locating the generation position of the partial discharge signal based on a time difference between propagation times at which the partial discharge signals reach the detection means. Because
An amplifier is connected between the two power cables to amplify the partial discharge signal propagating through the folded power cable, and the detection means repeatedly detects the partial discharge signal at both detection ends of the power cable. Then, the locating means detects the partial discharge signal at both detection ends, where Δt is a delay time generated by the amplification, L is a length of the power cable, and C is a propagation speed of the partial discharge signal. A partial discharge signal whose time difference is greater than or equal to Δt and less than or equal to Δt + 2 L / C and whose repeated detection time interval at each detection end is greater than the time required for the partial discharge signal to propagate through the total length of the two power cables A power cable partial discharge generation position locating apparatus characterized by performing generation position locating.   The power cable according to any one of claims 5 to 7, wherein the location of the partial discharge signal is determined based on a time difference in propagation time of the partial discharge signal in a band of 100 kHz to 10 MHz. Partial discharge generation position locator.

Images