JPS6358230A - Fatigue detecting method for power cable - Google Patents

Abstract

PURPOSE:To know the fatigue degree and rest life of a metallic sheath and to attain preventive maintenance for a power cable by installing a detection pipe covering the laid power cable. CONSTITUTION:The power cable 1 which has the metallic sheath of Al, Pb, etc., is laid to a radius R of curvature. The detection pipe 2 is installed covering the power cable 1, its external diameter r2 is larger than the external diameter r1 of the metallic sheath of the power cable 1, and its material is the same metal with the metallic sheath of the power cable 1. The detection pipes 2 are so coupled by coupling device 3 like clamping bands so that the pipes deform integrally with the power cable 1. Inert gas 5 is pressurized properly and charged in the detection pipes 2 and this gas pressure is detected by a monometer 4, so that a warning is generated when the pressure drops below a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application-1f) The present invention relates to a method for detecting the degree of damage due to fatigue of a metal sheath of a power cable having a metal sheath made of aluminum, lead, etc., for example.

(Prior art and problem to be solved) Power cables are usually laid in underground conduits or troughs on old roads, and recently they are laid on bridges, but in both cases, the cables have their own The cable laying shape changes due to thermal expansion and contraction due to temperature changes and various expansion and contraction of the bridge girder, and the bending radius (
Fatigue occurs in the metal north due to the change in R).

In addition, especially when installed on a bridge -1-, constant vibration occurs due to the running of the vehicle, and this is transmitted to the cable, causing slight vertical and horizontal deformation of the cable, causing distortion in the metal sheath. It turns out.

By the way, if the metal sheath suffers fatigue failure during its use, OF cables will suffer from sagging, and plastic insulated cables will have air leakage inside, leading to a decline in electrical insulation performance in either case. We pay close attention to measures to prevent sheath fatigue from occurring.

One of the countermeasures is to perform theoretical studies and experiments on the cable installation shape, support method, etc. at the design stage, and to reduce the strain change occurring in the metal sheath by 30% due to expected expansion/contraction, vibration conditions, etc. The shape and supporting methods (t, y) are determined so that the metal sheath will not break even if the metal sheath is repeatedly applied over a year.

However, there is no problem with this method as long as the expansion/contraction, vibration conditions, etc. applied to the cable are the same as or less than the expected values at the time of design, but if they exceed the expected values, sudden fatigue failure may occur within the required chisel life period. 1 may occur.

Since the above-mentioned problems arise with the above-mentioned measures alone, measurement cables of the same size are laid several meters to more than ten meters along with the cable in areas that are likely to cause particular problems during the cable installation route. The sheath strain of this cable can be indirectly changed by peeling off the anti-corrosion layer on the surface of this measurement cable locally to expose the metal sheath, attaching a strain gauge to the surface of the metal sheath in this area, and measuring the strain change. Knowing, setting 3
We understand the difference between 1 value and 1 value.

According to this method, it is possible to know the strain change of 1° when actual expansion/contraction, vibration conditions, etc. are applied to the cable laid with the actual installation shape and support method, so the difference between the design value and the actual value can be determined. However, the problem of discrepancies in estimation of the fatigue period due to the difference in timing can be solved, but ■It takes a lot of effort and cost to install a measurement cable.

- Due to expansion/contraction and vibration, the position and direction where the maximum strain occurs is 5° (5°), so the number of co-gauges to be attached increases, and the effort and cost of attaching strain gauges is large.

■The measurement period is limited (usually several years), making it impossible to continue measuring strain changes for 30 years after cable installation. Therefore, after d111 regular time 1);i and subsequent distortion changes cannot be grasped.

There was a problem.

(Means for Solving the Problems) The present invention provides a method for detecting fatigue of a power cable that eliminates the problems mentioned above. A detection pipe made of the same material as the metal sheath is installed along the power cable, a pressure gas is sealed in the detection pipe, and changes in the pressure of the pressure gas are detected. be.

FIG. 1 is an explanatory diagram of a specific example of the fatigue detection method of the present invention, and FIG.
The figure is an explanatory diagram of the connection status of the detection pipe and power cable.
The same figure (A) shows the case where the detection pipe is installed in the horizontal direction, and the same figure (1J) shows the case where the detection pipe is installed in the vertical direction.

In the drawings, (1) is a power cable that penetrates a metal sheath made of aluminum, lead, etc. and is laid with a bending radius R. ■ is the detection pipe installed along with the above-mentioned type cable (+), and its outer diameter (r2) is the power cable (
+), and is made of the same metal as the metal sheath of the power cable (1). This detection pipe ■ is connected to the power cable (1
) are connected by a coupling device (3), such as a tightening band, so as to deform as one unit. In addition, an appropriately pressurized inert gas (5) is sealed inside the detection pipe (2), and this gas pressure is detected by a pressure gauge (4), and an alarm is issued when the pressure falls below a specified value.

Is the detection pipe ■ above flat even with corrugations? Q may also be used, and if the cable is tied and bent in advance, the strain (εC) in the pipe is greater than the strain (εC) generated in the cable.
εp) is set as r+>rl, and εp/
The ratio of εC is also kept constant in a separate laboratory.

In addition, the location where the detection pipe ■ is tied together does not have to be the entire length of the cable, and is particularly suitable for locations where there is insufficient room for the installation shape or support method, or where there is a risk of being subjected to a lot of expansion/contraction, vibration, etc. Just set it up.

(Function) In Fig. 1, if the bending radius (R) in the cable changes to RR' due to the expansion and contraction of the left and right cables, then the strain change in the cable metal sheath and detection pipe is εp/ εc=r2/r+, and εp is ε
. This results in a strain that is r2/r+ times larger than that of the cable, and the detection pipe always breaks faster than the metal sheath of the cable.

Therefore, the degree of fatigue and remaining life of the cable at that point can be accurately known. That is, εp of 1111
/εC ratio and the strain (ε) to fracture number (tJ) characteristics of the sheath material metal shown in Figure 3 to predict the expected failure of the cable sheath [1
The number (Nc) is known. Note that in the drawings, Np is the number of pipes until the detection pipe (3) is destroyed.

Therefore, if the remaining life of the metal sheath at the point in time is insufficient, preventive maintenance such as reinforcing the cable or replacing it becomes possible.

(Effects of the Invention) According to the series of the present invention, since the detection pipe is installed tied to the installed power cable, the metal sheath of the cable and the detection pipe are subjected to the same expansion and contraction and vibration, and the metal Detection/Iip is always destroyed faster than the sheath.

Therefore, the degree of fatigue and remaining life of the metal sheath at that point in time can be known, and preventive maintenance of the cable can be performed.

3. There is no need to use measurement cables like in the past.・1y It is labor-saving and economical because it does not require strain measurement.Furthermore, the destruction of the detection pipe causes the gas pressure to drop and an alarm to be emitted. It has advantages such as being able to know the timing accurately.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a specific example of the fatigue detection method of the present invention, and FIG.
Figures (A) and (IJ) are explanatory diagrams of the connection state of the power cable and the detection pipe, and Fig. 3 is an explanatory diagram of how to grasp the remaining life of the metal north in the present invention. 1... Power cable, 2... Detection pipe, 3...
Coupling device, 4...pressure gauge, 5...pressure gas. N two -

Claims (1)

[Claims] (1) A detection pipe having an outer diameter larger than the outer diameter of the metal sheath of the power cable and made of the same material as the metal sheath is installed along the power cable, and a pressure gas is sealed in the detection pipe. A method for detecting fatigue in a power cable, comprising detecting a pressure change in the pressure gas.