JPH0739054A - Detecting method for moved section for cable - Google Patents

Abstract

PURPOSE:To provide a method for detecting the moved section due to the occurrence of bending or increase in size caused by thermal expansion in a cable laid without using a complicated mechanical device. CONSTITUTION:Two optical fibers 11 are wound in a spiral form oppositely each other on the outer periphery of a cable 10 to be measured. And a cable is laid through a tunnel or the like in such a manner that the overlapped portions 12 of said fibers will face the bending (moving) direction. Then, transmission loss characteristics of optical fibers 11 at the lower side are measured with OTDR method, and the distribution of loss characteristics of the whole range of length is determined. Then, position created by microbending to the optical fibers 11 is detected by determining the position where the transmission loss has increased from the distribution of said loss characteristics, and it is judged to be the position where movement has occurred in the cable 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a portion where a laid cable has moved its laying position due to thermal expansion and contraction.

[0002]

2. Description of the Related Art Generally, a cable undergoes thermal expansion and contraction due to a change in load and a temperature change with the season, and a paper-insulated cable having an airtight metal sheath such as a lead cover or an aluminum cover is Thermal expansion and contraction may cause fatigue cracks in the metal sheath, resulting in oil leakage or damage to the protrusions. Also, with rubber and plastic insulated cables such as CV cables (cross-linked polyethylene insulated cables), it is conceivable that the cable arrangement in the manhole may collapse due to the extension of the cable, and when it is laid on a sloping ground. The cable may slip off due to thermal expansion and contraction. These phenomena are particularly noticeable in the case of pipe laying or cave laying where the restraining force due to frictional resistance is small, and have been a problem from the past.

Therefore, when the cable is laid in a cave or the like, the snake is laid so as to meander (snake) in the horizontal direction or the vertical direction, and the thermal expansion and contraction is absorbed by the change in the snake shape. ing. Also, in such snake laying, the inflection point or mountain part of the snake is tied to the receiver with a rope or the like, and fixed.
The extension of the cable to the manhole etc. is eliminated.
Furthermore, when laying in a manhole, etc., the cable is laid in a substantially straight line without snakes, and the cable placed on the insulative receiver can be moved together with the receiver in the horizontal direction orthogonal to the axis. A laying method is employed in which the cable is supported and absorbs thermal expansion and contraction by horizontal displacement of the cable.

As described above, the laying method is appropriately selected depending on the laying place, the type or size of the cable, and in any case, the movement of the cable, that is, the horizontal or vertical direction orthogonal to the axis is selected. Is a major problem in terms of design and characteristics. Therefore, it is necessary to detect and measure the presence or absence of movement of the cable or the amount of movement, and conventionally, the optical encoder type cable behavior amount sensor as shown below has been used.

That is, as shown in FIG. 4, this sensor measures the amount of movement (movement amount) of the cable 1 to be measured by replacing it with the number of revolutions of the winding sheave 2, which is always tensioned by a spring. It is a thing. The optical encoder 3 has a rotary disk 4 at the axial end of the take-up sheave 2
The slit 5 is irradiated with light, the light is returned by the prism 6 and detected by the light receiving element, and each slit 5 is counted as an optical pulse 7, whereby the number of rotations of the winding sheave 2 is obtained. There is. In the figure, reference numeral 8
Indicates a connection wire, and reference numeral 9 indicates an optical connector.

[0006]

However, since such a cable movement amount sensor measures by using an optical signal, it has an advantage that it can be measured without being affected by a surge or the like. Since the amount of movement of the cable is replaced with the number of rotations of the winding sheave 2 which can be easily measured via the mechanical mechanism, a measurement error or a failure is likely to occur in the mechanical mechanism section. In addition, there is a problem that the entire structure is complicated.

The present invention has been made in order to solve these problems. In a cable such as a laid electric power cable, a portion where a bending or bending is caused by the heat expansion or contraction or the bending is increased to move the laying position is performed. , And provide a method for detecting and determining without using a complicated mechanical mechanism.

[0008]

According to the method of detecting a cable moving portion of the present invention, when detecting a portion where a laid cable is moved due to bending due to thermal expansion and contraction, an optical fiber is spiraled around the outer circumference of the cable. Along with winding the optical fiber, each position facing the direction of the bend of the optical fiber, after locking on the outer circumference of the cable, using the optical time domain reflectometry, the entire length of the optical fiber It is characterized in that the position where microbending occurs is detected by measuring the distribution of transmission loss characteristics. Where optical time domain reflectometry (OTDR)
Is a method of measuring the characteristics of the optical fiber by detecting the return light that occurs when an optical pulse is incident from one end of the optical fiber.By using this method, the length of the optical fiber can be measured once. It is possible to measure the distribution of transmission loss characteristics over the entire area.

[0009]

In the detecting method of the present invention, first, one optical fiber is spirally wound around the outer circumference of a cable laid in a pipe or a cave or without being snaked, and , Each position facing the direction of bending or bending of the cable is locked and fixed on the outer circumference of the cable by a method of winding another optical fiber in the opposite direction. Then, in this state, the characteristics of the first wound optical fiber are measured by the OTDR method, and the distribution of the transmission loss over the entire length region is obtained. Generally, when a cable is bent or bent, an external force such as lateral pressure acts on the optical fiber located outside the bend to cause microbending (fine bending), which increases optical transmission loss. Therefore, the OTDR
From the distribution of the transmission loss measured by the method, the part where the microbending occurs in the optical fiber is detected, and by this, the part where the cable has moved to the installation position due to thermal expansion and contraction can be clearly seen.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

In the embodiment, as shown in FIG. 1, two optical fibers 11 (10/125 μm SM fiber) are wound around the outer circumference of the cable to be measured 10 or inside the sheath in a spiral shape opposite to each other. At this time, the optical fiber 11 is slightly tightly wound so as not to cause slack. Then, the cable 10 around which the optical fiber 11 is wound is arranged such that the overlapping portions 12 of the optical fiber face the bending (moving) direction of the cable 10 and are arranged at a predetermined interval, which is well known in a cave or the like. Install by the method. In the case of horizontal laying, as shown in FIG. 2, since the bending direction of the cable 10 is often a horizontal direction, the overlapping portion 12 of the optical fiber 11 should come to the side peripheral portion of the cable 10. . Next, the transmission loss characteristic of the optical fiber 11 wound on the lower side is measured by the OTDR method. That is, an optical pulse is made incident from one end of the optical fiber 9, the return light generated at this time is detected and measured by an OTDR measuring device (not shown), and the optical fiber 11
Calculate the distribution of loss characteristics over the entire length of. By obtaining the position where the transmission loss increases in the distribution of the characteristics thus measured, the site where the microbending occurs in the optical fiber 11 can be detected. More specifically, as shown in FIG. 3, the bending of the cable 10 causes micro-bending at the portions indicated by the arrows A and B of the optical fiber 11. This is detected from the measurement result by the OTDR method, and the micro-bending is detected. The generated portion and the bending or movement portion of the cable 10 that causes the occurrence are accurately detected.

In the above embodiment, the two optical fibers 11 are spirally wound in mutually opposite directions, and the lower optical fiber 11 is locked on the outer circumference of the cable 10 at the overlapping portion 12 thereof. It was done, but
The wire wound around the upper side may be another wire instead of the optical fiber. In addition, one optical fiber is wound in a spiral shape, and by the projections and irregularities provided on the cable surface,
It may be configured to be locked and fixed.

[0013]

As described above, according to the detection method of the present invention, it is possible to detect, from a distant place, a portion where the laid cable is displaced due to thermal expansion or the like with high accuracy. Also,
Since no complicated mechanical mechanism is used for detection, failure is unlikely to occur and reliability is high.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of a method for detecting a cable moving portion according to the present invention.

FIG. 2 is a diagram for explaining an arrangement position of an overlapping portion of two optical fibers in the embodiment of the present invention.

FIG. 3 is a perspective view showing a state in which microbending occurs in an optical fiber due to bending of a cable in the example.

FIG. 4 is a diagram showing a schematic configuration of a conventionally used optical encoder type cable movement amount sensor.

[Explanation of symbols]

 1, 10 ... Cable 2 ... Winding sheave 3 ... Optical encoder 4 ... Rotating disk 5 ... Slit 6 ... Prism 7 ... Optical pulse 8 ... Connection wire 9 ... Optical connector 11 ... Optical fiber 12 ... Overlap

Claims (1)

[Claims] 1. An optical fiber is spirally wound around the outer periphery of the cable when the laid cable is detected by a bend caused by thermal expansion and contraction, and the optical fiber is faced in the direction of the bend. After locking each position on the outer circumference of the cable, by using optical time domain reflectometry, by measuring the distribution of the transmission loss characteristics of the entire length region of the optical fiber,
A method for detecting a cable moving portion, which is characterized by detecting a position where microbending has occurred.