JP3077446B2 - Cable shielding layer, sheath abnormality monitoring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a 3 to 6 kV C
In a V cable line and a CVT cable line, a cable shielding layer in a line without a sheath ground at an intermediate portion of the line,
This is a sheath abnormality monitoring method.

[0002]

2. Description of the Related Art During the use of a cable line, it is necessary to constantly monitor the cutting of a shielding layer and a remarkable drop of a Meg in a sheath. As a conventional technique for this purpose, there is a method described in Japanese Patent Application Laid-Open No. 54-23987 regarding the detection of cutting of the shielding layer. As shown in FIG. 3, in a cable line composed of a cable conductor 1, a cable shielding layer 2 and a cable sheath 3, the cable shielding layers 2 at both ends are grounded, and a voltage measuring unit 5 is installed on a ground wire 4 at one end. To detect it. In the present invention, only the detection of the cutting of the shielding layer is targeted, and the measurement is performed by directly grounding the shielding layer at one end.

[0003] Conventionally, regarding the detection of abnormality of sheath meg,
The measurement is performed by removing the ground wire of the cable line and applying a DC voltage to the shielding layer.

[0004]

By the way, regarding the detection of cutting of the shielding layer, the method described in the above-mentioned Japanese Patent Application Laid-Open No. 54-23987 discloses a method in which even if the shielding layer is cut at the point B in FIG. C on the A side of the measuring end from the same point or B point
If there is a hole in the sheath at the point and it is submerged, the voltage at the measuring end A does not rise and cannot be detected. A hole in one or sheath holes in the sheath lye and shielding layer is cut, then the phenomenon of abnormal overlap like shielding layer is cut has just occurring in reality, have measures sought for this point Was.

[0005] Conventionally, regarding the detection of an abnormality of a sheath meg,
Although sheathmeg measurement is performed as needed, continuous measurement is performed continuously, so that an abnormality can be found quickly and a major trouble can be prevented from occurring. In addition, since the sheath meg changes significantly due to water absorption and deterioration of the sheath, it is desired to know the change over time except when it is apparent that a hole is opened somewhere and it is determined that the sheath is in a ground contact state. Further, even if a hole is formed in the sheath, the MEG is unlikely to be reduced unless it is immersed in water, and it may be difficult to determine that there is no abnormality with only one measurement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an improved method for simultaneously detecting a disconnection of a cable shielding layer and a meg abnormality of a sheath to confirm soundness of a cable line. Aim.

[0007]

According to the present invention, one end of a shielding layer in a cable line having no ground in the middle is grounded by a capacitor, and the other end of the shielding layer in the cable line is grounded by a capacitor or a high resistance. A DC voltage is always applied to the shielding layer, and at one end, the sheath leakage current is continuously measured by the sheath leakage current measuring unit to detect an abnormality in the sheath meg, and at the other end, the shielding layer voltage is measured by the shielding layer potential measuring unit. > This is a cable shielding and sheath abnormality monitoring method characterized in that the position is constantly measured to detect the shielding layer breakage.

[0008]

The principle of detection of the invention of the present application is the same as that of the invention described in the above-mentioned publication, but is different in that the shielding layers are grounded at both ends with a capacitor in order to simultaneously detect sheath-meg drop. . That is, by applying a DC voltage to the shielding layer, the sheath-meg abnormality is detected from the current flowing through the DC power supply unit, and the disconnection of the shielding layer is detected from the rise in the potential of the capacitor at the opposite end. Can be surely confirmed.

[0009]

FIG. 2 shows the principle of the invention of the present application. That is,
At both ends of the cable line 10, the cable shielding layer 2 is grounded by capacitors C2 and C3. C1 is the total capacitance of the cable insulator, and D is the value when the shielding layer is cut at point F.
Assuming that the capacitance between F is C4 and the applied voltage is V, the potential at point D is always a value obtained by dividing the parallel capacitance of C1, C2 and C3.

(Equation 1) When the shielding layer is cut at point F, the value divided by C4 and C2

(Equation 2) Becomes This change is applied to a point D on one end side of the shielding layer potential measuring unit 2.
1 is connected and detected, and an alarm or the like is issued.

Next, when the sheath meg is abnormally lowered, the both ends of the cable line are connected to the capacitor ground, so that a DC power supply 22 for measuring the sheath leakage current is connected to the point E at one end as shown in FIG. Thus, a DC voltage is constantly applied, and the MEG measurement can be performed by the sheath leakage current measurement unit 23. This sheath leakage current measuring unit 23
Is configured to issue an alarm or the like if an abnormality is determined. The portion corresponding to the capacitor C2 may be grounded with high resistance, or may be divided by a capacitor or a resistor.

Next, a circuit diagram of a method for monitoring a cable shielding layer and a sheath abnormality of the present invention is shown in FIG. 1, and a specific embodiment thereof will be described. That is, in FIG.
Is a 3300VCV cable of 1 × 250 mm ² , having a pipe length of 1 km. Since the capacitance of the cable insulator is about 0.4 μF and the capacitance between the shielding layer and the ground is 60 μF, the voltage of the shielding layer is about 12 V at all times. , The capacitance between the shielding layer and the ground becomes several μF or less, so that it rises to several hundred volts or more. This voltage is divided by the resistors 6 and 7 and measured by the meter relay 8, and an alarm is issued when the potential rises significantly.

On the other hand, a DC voltage of 10 V is always applied from the DC power supply 9 to the shielding layer 2, and the leakage current is continuously measured by the meter relay 8 '. The sheath resistance of the cable line 10 is initially 5 MΩ or more, and there is no practical problem even if the resistance is reduced to 1 MΩ due to water absorption. Therefore, an alarm is issued when the resistance becomes 10 μA or less by the meter relay 8 ′. In addition, an arrester 11, a choke coil 12, and the like are incorporated for safety measures in the measurement system.

[0013]

As described above, according to the cable shielding layer and the sheath abnormality monitoring method of the present invention, cutting of the shielding layer,
By performing continuous detection of sheathmeg abnormality at all times, the soundness of the cable line can always be checked, and when an abnormality occurs, it can be detected immediately after the occurrence, thus preventing a major trouble. . Further, even if an abnormality such as a through hole in the shielding layer and the sheath occurs at the same point, the abnormality can be detected. Further, by continuous measurement and recording of the sheath meg, it is possible to ascertain the relationship between the meg over time and external conditions (for example, season, weather, power transmission capacity, and the like), and it is easy to accurately determine the sheath abnormality.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a method for monitoring a cable shielding layer and a sheath abnormality according to an embodiment of the present invention;

FIG. 2 is a circuit diagram for explaining the principle of FIG. 1,

FIG. 3 is a circuit diagram of a conventional shielding layer cut detection method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cable conductor 2 Cable shielding layer 3 Cable sheath 4 Grounding wire 5 Voltage measuring part 6, 7 Voltage dividing resistance 8, 8 'Meter relay 9 DC power supply 10 Cable line to be measured 11 Arrester 12 Choke coil 21 Shielding layer potential measuring part 22 Leakage DC power supply for current measurement 23 Sheath leakage current measurement unit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 31/12 G01R 31/02

Claims (1)

(57) [Claims] An end of a shield layer in a cable line having no ground in the middle is grounded by a capacitor, and the other end of the shield layer in the cable line is grounded by a capacitor or a high resistance.
A DC voltage is constantly applied to the shielding layer from the one end, the sheath leakage current is continuously measured by the sheath leakage current measuring unit at the one end to detect an abnormality in the sheath meg, and the shielding layer potential is measured by the shielding layer potential measuring unit at the other end. A method for monitoring cable shielding and sheath abnormalities, characterized in that the measurement of the shielding layer is detected by constantly measuring the temperature.