JPH06289094A - Cable shielding layer and method for monitoring abnormality of sheath - Google Patents

Abstract

PURPOSE:To detect the breaking of a shielding layer and abnormality in insulation by grounding the shielding layer at both ends of cable line through capacitors, applying a DC voltage to the shielding layer all the time from one end, measuring the leaking current from a sheath, and always measuring the sheath potential at the other end. CONSTITUTION:A cable shielding layer 2 at both ends of a cable line 10 without grounding at the intermediate part is grounded through capacitors C2 and C3. The potential at a point D at one end side always becomes a value which is divided by the total capacitance of a cable insulator and the parallel capacitances of C2 and C3. When the shielding layer 2 is cut at a point F, the potential becomes the value, which is divided by the capacitance between the points D and F and the capacitor C2. A shield- layer-potential measuring part 21 is connected to the point D, and the change is detected. Then, an alarm and the like are issue. A sheath-leak-current measuring power supply 22 is connected to a point E at the other end side. A DC voltage is always applied in this way. Measurement of deteriorated insulation is performed with a sheath-leak-current measuring part 23. When abnormality is judged even in the measuring part 23, the alarm is issued. The part corresponding to the capacitor C can be grounded through high resistance.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art It is necessary to constantly monitor the breakage of a shielding layer and the remarkable drop in MEG of a sheath while using a cable line. As a conventional technique for this purpose, there is a method described in Japanese Patent Laid-Open No. 54-23987 for detecting breakage of a shielding layer. As shown in FIG. 3, in the cable line consisting of the cable conductor 1, the cable shield layer 2 and the cable sheath 3, the cable shield layer 2 at both ends is grounded, and the voltage measuring unit 5 is installed on the ground wire 4 at this end. To detect. In the present invention, only the detection of disconnection of the shield layer is targeted, and the shield layer is directly grounded at one end for measurement.

Regarding the detection of an abnormality in the sheath meg, conventionally,
The ground line of the cable line is removed and a DC voltage is applied to the shielding layer for measurement.

[0004]

By the way, regarding the detection of cutting of the shielding layer, according to the method disclosed in the above-mentioned Japanese Patent Laid-Open No. 54-23987, even if the shielding layer is cut at point B in FIG. C on the A side of the measurement end from the same point or B point
If there is a hole in the sheath at the point and the sheath is submerged, the voltage at the measuring end A does not rise and cannot be detected. If the shielding layer is cut and the sheath is pierced or there is a hole in the sheath,
After that, a phenomenon in which abnormalities such as disconnection of the shielding layer are overlapped is actually occurring, and a countermeasure for this point has been demanded.

Regarding the detection of an abnormality in the sheath meg, conventionally,
The sheathmeg measurement is carried out as needed, but by constantly and continuously measuring this, it is possible to quickly find an abnormality and prevent a serious trouble from occurring. Further, since the sheath meg changes significantly due to water absorption and deterioration of the sheath, it is desired to know the change with time unless a hole is apparently opened somewhere and it is judged that it is in a grounded state. Further, even if the sheath has a hole, if there is no water immersion, the Meg is not likely to decrease, and it may be difficult to determine that there is no abnormality with only one measurement. Therefore, constant monitoring is desired.

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 the disconnection of the cable shielding layer and the MEG abnormality of the sheath to confirm the soundness of the cable line. To aim.

[0007]

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

[0008]

The invention of the present application has the same principle of detection as the invention described in the above publication, but differs in that the shielding layer is grounded at both ends of the capacitor in order to detect the sheathmeg lowering at the same time. . That is, by applying a DC voltage to the shield layer, the sheathmeg abnormality is detected from the current flowing through the DC power supply section, and the disconnection of the shield layer is detected from the rise in the potential of the capacitor at the opposite end, to confirm the integrity of the cable line. Can be surely confirmed.

[0009]

EXAMPLE The principle of the invention of the present application is shown in FIG. That is,
At both ends of the cable line 10, the cable shield layer 2 is grounded by capacitors C2 and C3. The total capacitance of the cable insulator is C1, and D 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 divided by the parallel capacitance of C1, C2, and C3 {C1 / (C2, C3 / C2 + C3) + C1}. When the shielding layer is cut at the point F, the value obtained by dividing the voltage by C4 and C2 is (C2 / C4) .V. The shield layer potential measuring unit 21 is connected to the point D on one end side to detect this change, and an alarm or the like is issued.

Next, in the case where the sheath meg is abnormally lowered, both ends of the cable line are connected to the capacitor ground. Therefore, as shown in FIG. 2, the sheath leak current measuring DC power source 22 is connected to the E point on one end side. Therefore, the DC voltage can be constantly applied, and the sheath leakage current measuring unit 23 can perform the MEG measurement. This sheath leakage current measuring unit 23
Also in (1), if an abnormality is determined, an alarm or the like is issued. The portion corresponding to the capacitor C2 may be grounded with high resistance, or may be divided by capacitance or divided by resistance.

Next, a circuit diagram of the cable shielding layer / sheath abnormality monitoring method of the present invention is shown in FIG. 1, and a specific embodiment thereof will be described. That is, in FIG. 1, the target cable 10
Is a 3300 VCV cable 1 × 250 mm ² and has a pipe length of 1 km. Since the capacitance of the cable insulator is about 0.4 μF and the capacitance between the shield layer and the ground is 60 μF, the shield layer voltage is about 12 V at all times, and when the shield layer 2 is cut off, the potential at point D is on the side of point D. Since the electrostatic capacity between the shielding layer and the ground is several μF or less, it rises to several hundred V or more. This voltage is divided by 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 voltage of DC 10V is constantly applied to the shielding layer 2 from the DC power source 9, and the leak current is continuously measured by the meter relay 8 '. The sheath resistance of the cable line 10 is 5 MΩ or more at the initial stage, and there is no practical problem even if the sheath resistance is reduced to 1 MΩ due to water absorption or the like. Therefore, an alarm is issued when the meter relay 8 ′ drops below 10 μA. In addition, an arrester 11 and choke coil 12 are incorporated for safety measures in the measurement system.

[0013]

As described above, according to the cable shielding layer / sheath abnormality monitoring method of the present invention, the shielding layer cutting,
By constantly and continuously detecting the sheathmeg abnormality, the soundness of the cable line can be confirmed at all times, and when an abnormality occurs, it can be detected immediately after the occurrence, so it is possible to prevent a major trouble. . Further, it is possible to detect the abnormality even when the abnormality such as the cutting of the shielding layer and the through hole in the sheath occur at the same point. Furthermore, by continuously measuring and recording the sheath meg, it is possible to grasp the relationship between the change in the meg with time and external conditions (for example, season, weather, power transmission capacity, etc.), which facilitates accurate sheath abnormality determination.

[Brief description of drawings]

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

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

FIG. 3 is a circuit diagram of a conventional shield layer disconnection detection method.

[Explanation of symbols]

 1 Cable Conductor 2 Cable Shielding Layer 3 Cable Sheath 4 Ground Wire 5 Voltage Measuring Section 6,7 Voltage Dividing Resistance 8,8 'Meter Relay 9 DC Power Supply 10 Measured Cable Line 11 Arrester 12 Choke Coil 21 Shielding Layer Potential Measuring Section 22 Leakage DC power supply for current measurement 23 Sheath leakage current measurement unit

Claims (1)

[Claims] 1. A sheath leakage current is measured by connecting one end of a non-grounded cable line to a capacitor ground and the other end to a capacitor or high resistance ground, and applying a DC voltage from the capacitor ground end to the shielding layer at all times. A cable shielding layer and a sheath abnormality monitoring method, which is configured to detect an abnormality in the sheath meg and detect the disconnection of the shielding layer by constantly measuring the sheath potential at the other end.