JPS638570A - Constant monitoring of corrosion preventing layer of cable - Google Patents

Abstract

PURPOSE:To simplify the measurement, by connecting a parallel circuit of an electrostatic capacitance and an inductance between a cable shielding layer and the ground when a high frequency power source is used to measure a dielec tric loss tangent of a cable corrosion-proof layer. CONSTITUTION:A dielectric loss tangent measuring device 4 an a high frequency power source 5 on the order of kHz are connected in parallel between a hot cable shielding layer 1 and the ground. A parallel circuit 7 of an electrostatic capacitance C3 and an inductance L2 to arranged as to provide a parallel resonance for the high frequency power source 5 while doing a low impedance for a commercial frequency power source are parallel-connected. Then, when a dielectric loss tangent measuring device 4 is balanced with the high frequency power source 5, the dielectric loss tangent to be measured coincides with that of a cable corrosion-proof layer alone as the parallel circuit 7 provides a parallel resonance for the high frequency power source 5. Depending on the value thereof, deterioration in the cable corrosion-roof layer can be always monitored easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for constantly monitoring a cable anti-corrosion layer.

(Technical background of the invention and its problems) Generally, the presence or absence of abnormalities such as deterioration of the cable anti-corrosion layer and external damage is determined by
As shown in Figure 2,
This is determined by measuring the DC insulation resistance of the i-layer.

That is, in a circuit in which a parallel resonant circuit of a coiled capacitor C2 is connected between a cable shielding layer 1 grounded by a capacitor C1 and the earth, by applying a DC power supply 3 of several volts between the parallel resonant circuit and the earth. The insulation resistance of the cable anti-corrosion layer is calculated by measuring the current value flowing through the defective part of the cable anti-corrosion layer (not shown) on the coil L1 and the insulation layer 1 and the DC voltage at the time of application. The degree of deterioration of the anti-corrosion layer can be determined from the value.

However, this method of measuring the insulation resistance of the cable anti-corrosion layer has the disadvantage that it cannot be detected unless there is a hole in the anti-corrosion layer and the insulation resistance is considerably reduced due to the infiltration of water or the like.

For this purpose, a dielectric loss tangent measuring device and a high frequency power source are connected in parallel between the cable shielding layer grounded by an inductance and the earth, and the tan δ of the cable corrosion protection layer on the cable shielding layer is measured from the equilibrium condition of the dielectric loss tangent measuring device. A method has been proposed.

Here, the above method for constantly monitoring the cable anti-corrosion layer will be explained based on FIG. 3. That is, a dielectric loss tangent measuring device 4 and a high frequency power source 5 on the order of kilohertz are connected in parallel between the live cable insulation layer 1 grounded through an inductance L2 and the ground.

Therefore, the connection between the cable shielding layer 1 and the ground can be equivalently considered as a parallel circuit of the equivalent capacitance Cx and the equivalent resistance R, as shown by the dotted line. Then, the apparent dielectric loss tangent to be measured, which is the dielectric loss tangent tan δ' of the cable anti-corrosion layer including the inductance L2, is expressed as the following equation.

tan δ- = 1/(ωC-1/ωL2) Rx (
1) However, ω is the angular frequency. However, the so-called true value of the dielectric loss tangent tan δ of only the cable anti-corrosion layer that does not include the inductance L2 is 1/ωC
Since it is R, the apparent t××andδ− is as shown in the following equation.

tan δ' Here, since the angular frequency ω and the inductance L2 are known, and the equivalent capacitance Cx is a measurable value, the true tan δ can be determined from equation (2).

However, in the method for constantly monitoring the cable anti-corrosion layer described above, the apparent tan δ′ must be measured and then corrected to the true tan δ value.
There is a drawback that the and[delta] measurement becomes complicated.

(Objective of the Invention) The present invention has been made with attention to these points, and therefore, it is an object of the present invention to provide a method for constantly monitoring a cable anti-corrosion layer, which more easily measures the jan δ of the cable anti-corrosion layer using a high-frequency power source. It is something.

(Embodiment of the Invention) The present invention will be described below based on the drawings of one embodiment. In FIG. 1, where the same parts as in FIG. 3 are given the same numbers, a parallel circuit 7 consisting of a capacitance C3 and an inductance L2 is grounded, which has parallel resonance with the high frequency power source and low impedance with respect to the commercial frequency power source. A dielectric loss tangent measuring device 4 and a kilohertz-order high frequency power source 5 are connected in parallel between the live cable shielding layer 1 and the ground.

Therefore, between the cable shield lff11 and the ground, the equivalent capacitance Cx and the equivalent resistance R are equivalently shown by the dotted line.
Since it can be considered as a parallel circuit of The dielectric loss tangent tan δ- of the anti-corrosion layer is expressed by the following formula.

tan δ- = 1/(ωC+ωC-1/ωL2) Rx×3 (3) However, ω is the angular frequency.However, since the parallel circuit 7 resonates in parallel with the high-frequency power supply 5, that is, ωC3=1 /ωL2, so (
3) The formula is 1/ωCxRx, which is the so-called true value of the dielectric loss tangent tanδ of only the cable anti-corrosion layer that does not include parallel circuits.
matches.

However, in reality, the charged current flowing from the cable conductor 6 into the shielding layer 1 flows into the parallel circuit 7, so a commercial frequency potential difference occurs between the ground and the shielding layer 1, but the parallel circuit 7 Since the impedance is small relative to the commercial frequency, almost no potential difference occurs. Even if a small potential difference occurs, no problem will occur if a detector that selectively amplifies only high frequency components is used.

In addition, in the figure, A is an ammeter, G is a galvanometer, C4 is a variable capacitor,
R is a fixed resistance, R3 is a variable resistance, and C8 is a standard capacitance.

(Effects of the Invention) As described above, in the present invention, since the tan δ of the cable anti-corrosion layer is measured using a high-frequency power source, there are problems such as minute defects that could not be measured conventionally and deterioration due to water absorption in the cable anti-corrosion layer. can also be detected more easily.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing how the insulation resistance of a cable anti-corrosion layer is measured according to the present invention, and FIGS. 2 and 3 are circuit diagrams showing how tan δ of a cable anti-corrosion layer is measured using a conventional method. 1...Cable shielding layer 4...
...Dielectric loss tangent measuring device 5 ...... High frequency power supply 6 ...... Cable conductor 7 ...... Parallel circuit C8 ... ...Cable equivalent capacitance Rx...
・・・・・・Cable equivalent resistance L2・・・・・・・・・
・Inductance C3......Second capacitance. Figure 3

Claims (1)

[Claims] A dielectric loss tangent measuring device and a high-frequency power source are connected in parallel between the ground and the cable layer, which is grounded with a parallel circuit of inductance and capacitance that has parallel resonance with the high-frequency power source and low impedance with respect to the commercial frequency power source. connect to
A method for constantly monitoring a cable anti-corrosion layer, characterized in that tan δ of the cable anti-corrosion layer on the cable shielding layer is measured from the equilibrium condition of the dielectric loss tangent measuring device.