JPH0793054B2 - Humidity detection method for power cable lines - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a humidity detection method for a power cable line, and more particularly to a humidity detection method suitable for detecting humidity in a CV cable line.

[Prior Art] Generally, power cables are widely used and have social functions indispensable to modern life, but in the current power cables with advanced high voltage, particularly high performance stability and reliability Is required. One of the causes of the performance deterioration and the failure of the power cable having such an important function is the intrusion of water into the cable. In order to prevent this moisture from entering, the power cable is usually covered with a strong coating.However, if moisture should enter the cable, it may be detected or performance may deteriorate due to the intrusion of minute moisture for a long time. I couldn't make a prediction.

By the way, as a so-called humidity sensor for detecting the amount of water and humidity, an electric resistance type humidity sensor using ceramics or the like has been put into practical use.

Further, in a humidity sensor using an optical fiber, the optical fiber is wound around the absorbent material, and a microbend is caused in the optical fiber by pressure measurement due to expansion of the water absorbent material during absorption.
A method has been developed in which this increase in loss is detected by OTDR along the longitudinal direction to detect inundation.

Therefore, there has been a proposal to arrange such a humidity sensor in the power cable or in the cable connection box to monitor the moisture absorption state of the power cable line.

[Problems to be Solved by the Invention] However, in any case, the conventional humidity detection method and device have the following problems.

(1) In the method of incorporating an electric humidity sensor in a power cable to detect its moisture absorption state, it is necessary to draw a metal lead wire from the cable for supplying power to the humidity sensor and extracting a signal. Therefore, it is easily affected by electromagnetic noise, and stable detection is difficult. When applied to a long cable line, a large number of humidity sensors and signal lead lines are required, which causes problems in installation space and cost. Further, in a power cable, a voltage is also induced in the grounding system, so that if a metal lead wire pulled out from the cable accidentally contacts, a circulating current may be generated and the entire power cable line may be destroyed.

(2) Next, a method of providing a water immersion detection sensor using an optical fiber in the cable and detecting the water immersion from the loss change thereof can detect the water intrusion, but can detect minute water and humidity in the cable with good responsiveness. It is impossible to detect a signal change even after a few years have passed even if water enters.

(3) Furthermore, in the method of obtaining a large number of sensor information from the backscattered light distribution using the OTDR, the signal is attenuated when the loss of the neighboring sensor becomes large, and the information from the rear sensor cannot be obtained.

An object of the present invention is to provide a humidity detecting method for a power cable line, which can eliminate the above-mentioned drawbacks of the prior art and can safely and reliably detect a moisture absorption state.

[Means for Solving the Problems] The gist of the present invention is to provide an optical humidity sensor at each connection portion of a power cable and to dispose two transmission optical fibers along the longitudinal direction of the power cable. The optical fiber for transmission is connected to each of the optical humidity sensors through an optical branching coupler and a sensor optical fiber, and the branching ratio of branching into the sensor optical fiber and the transmission optical fiber in the optical branching coupler is determined by the transmission optical fiber It is selected so as to be remarkably large, and an optical pulse is sent to the first transmission optical fiber from one end to be branched by an optical branching / coupling device at a location corresponding to each of the above-mentioned connecting portions, and the optical pulses for inputting through the sensor optical fibers. The optical pulse, which is incident on the optical humidity sensor and has undergone a change in optical loss due to humidity emitted from the optical humidity sensor, is output to the second optical fiber by the optical branching / coupling device via the optical fiber for the sensor for output. The optical pulse signal that is coupled to the optical fiber is emitted from one end of the first transmission optical fiber, and the optical pulse signal returned to the one end of the second transmission optical fiber is averaged each time. This is to obtain the humidity of each connection part by taking into consideration the temporal change of the optical pulse sent from one end of the fiber and returning to the one end of the second optical fiber.

[Operation] When an optical pulse is sent from one end to the first optical fiber, the optical pulse is sequentially branched at branch portions provided at respective locations corresponding to the connection portion of the power cable, and the humidity of each connection portion is increased. The light enters the sensor, undergoes a change in optical loss, and is emitted. The light pulse emitted from these humidity sensors is guided to the branch portion of the second optical fiber corresponding to the connection portion of the power cable, and returns to one end of the second optical fiber. First
Since the location of the branch portion provided on the second optical fiber corresponds to the location of the connection portion of the power cable, the time of the optical pulse that exits from one end of the first optical fiber and returns to the one end of the second optical fiber. The humidity of each connection can be obtained from the dynamic change. Therefore, it is possible to collectively measure the humidity at multiple points by the optical method, and the compactness and safety of the device are significantly improved.

[Examples] Hereinafter, the present invention will be described based on illustrated examples.

FIG. 1 is a block diagram of a measurement system for detecting humidity in a power cable line.

The electric power cables 1 are arranged so as to be connected at predetermined intervals by connecting portions 2, and one optical humidity sensor 3 is installed at each connecting portion 2 of these electric power cables. The optical humidity sensor 3 is of a light transmission type, in which light loss changes depending on humidity.

Two transmission optical fibers 6a and 6b are arranged in the longitudinal direction along the power cable line, and these transmission optical fibers 6a and 6b are provided at respective locations corresponding to the connection portion 2 of the power cable 1. A branching coupler 4 as an optical branching unit is connected to each. Therefore, when viewed in the arrangement direction of the power cable 1, the branch couplers 4 and 4 of the two transmission optical fibers 6a and 6b correspond to the same power cable connecting portion 2 in place. The optical fiber 5a for the sensor, which is branched from one of the two branch couplers 4 and 4 which form a pair in terms of location, is an optical humidity sensor installed in the power cable connection section 2. 3 is connected to one side and the other branch coupler 4
The branched sensor optical fiber 5b is connected to the other side of the same optical humidity sensor 3.

In the optical fiber and humidity sensor system configured as described above, the laser light source 8 driven by the pulse drive circuit 7 is connected to one end side of one transmission optical fiber 6a and the other transmission optical fiber 6b is connected. One end is connected to the light receiver 9. Therefore, the transmission optical fiber 6a functions as a first optical fiber for transmitting an optical pulse, and the transmission optical fiber 6b functions as a second optical fiber for receiving an optical pulse. An averaging processor 10 for removing random noise is connected to the subsequent stage of the light receiver 9, and the signal processed here is sent to the signal processor 11.

The operation of this embodiment in such a system configuration will be described.

The optical pulse emitted from the laser light source 8 driven by the pulse driving circuit 7 propagates through the first optical fiber 6a and is branched to the sensor optical fiber 5a through the branching coupler 4 and the optical humidity sensor 3 It is incident on one side, receives a change in optical loss according to humidity, and is emitted from the other side. The optical pulse whose intensity has been changed by the optical humidity sensor 3 propagates again through the sensor optical fiber 5b, the branch coupler 4 and the second optical fiber 6b, enters the light receiver 9 and is converted into an electrical signal. It

The pulsed light emitted from the laser light source 8 is branched by the branching / coupling unit 4 at each position of the connecting portion 2 distributed in the longitudinal direction, so that the signal detected by the light receiving unit 9 is the second signal. As shown in the figure, it is detected as a pulse train signal 12 with a delay time corresponding to the distance at which the humidity sensor 3 is installed. Therefore, each pulse of the pulse train signal 12 has a value of 1 to the signal of the humidity sensor 3 installed in each connection 2.
Corresponding to the pair 1, the pulse intensity changes depending on the humidity, and many sensor signals can be separated and detected at one place.

It should be noted that since branching makes it difficult to detect a signal from a distant humidity sensor, in the optical branching / coupling device 4, the branching ratio for branching to the sensor optical fibers 5a, 5b and the transmission optical fibers 6a, 6b is This can be dealt with by selecting the transmission optical fibers 6a and 6b to be significantly larger. In this case, the light intensity branched to the sensor optical fibers 5a and 5b becomes small, and the light receiver 9
Although the S / N ratio of the level detected by is deteriorated, this causes a number of pulsed lights to be emitted from the laser light source 8 and the detection signal of the photodetector 9 obtained each time is averaged by the averaging process 10. By doing so, random noise can be removed and the S / N ratio can be greatly improved.

The pulse train signal 12 obtained in this way is processed by the signal processor 11
Is converted into the humidity of each connection part and displayed.

Next, the configuration of the optical humidity sensor 3 suitable for being applied to the above system will be described.

FIG. 3 shows a cross section of the optical humidity sensor 3 and the power cable connecting portion. The actual connecting portion 2 of the power cable is housed in the connection box 20, and the case 30 of the humidity sensor 3 is hermetically connected to the compound filling hole 21 provided in the connection box 20. A pipe 22 for transmitting humidity from the cable portion is guided to the compound filling hole 21, and is connected to a communication hole 31 provided in the center of the lower wall of the sensor case 30.

From the side walls on both sides of the sensor case 30, the optical fibers 5a, 5a
b is airtightly inserted, and its ends are opposed to each other with a predetermined space 13 inside the case to form an end face abutting portion of the optical fiber. In this embodiment, the ferrule 17 is hermetically inserted and held in the side wall of the sensor case 30 as a means for forming the end face abutting portion by disposing the optical fiber tips facing each other, and the optical fiber core wire 14 is aligned with this. The optical fibers are connected in this state, and the sleeve 15 is filled with the adhesive 15 and fixed. The ferrule 17 has a lens 18 at the tip.

In the space 13 of the optical fiber end face abutting portion in the sensor case 30, that is, between the ferrules 17, a transmission plate 32 having different in-plane transmittances is arranged with its center supported by a rotating shaft 33. The rotary shaft 33 of the transmission plate 32 is connected to a moisture sensitive material 34, and when the moisture sensitive material 34 is displaced according to humidity, the transmission plate 32 is rotationally displaced correspondingly. .

Now, when a humidity change occurs in the cable at each power cable connecting portion 2, the humidity change is propagated through the pipe 22 into the sensor case 30, and the humidity sensitive material is transmitted according to the humidity.
34 expands and contracts. As a result, the transmission plate 32 is rotationally displaced, and the area of the transmission plate 32 interposed between the optical fiber tips 13, 13 changes, that is, the transmittance changes. For this reason optical fiber
The light intensity obtained at 5a and 5b becomes a signal corresponding to humidity.

In this way, the humidity sensor 3 of FIG. 3 and the system of FIG. 1 can detect the humidity of the power cable.

The system of FIG. 1 uses the transmission fiber to transmit the signal from the optical fiber type humidity sensor 3 provided in the power cable connection box.
This is a method to obtain the pulse from one side of 6a and 6b and to obtain it from the time change of the pulsed light returning from the other side. Since it is possible to measure the humidity at multiple points at a time, compactness and safety are greatly improved.

In the embodiment shown in FIG. 3, the optical humidity sensor is constituted by using the transmissive plate which is rotationally displaced, but an optical humidity sensor having another constitution may be used. For example, (1) a method of interposing a moisture sensitive film such as a cellulose film between the abutting portions of the optical fiber, or (2) a method of using an optical fiber having a SiO ₂ porous layer formed on the optical fiber core is adopted. It is possible to further downsize the sensor storage portion by using these.

[Effects of the Invention] As described above, according to the present invention, the following excellent effects can be obtained.

(1) It is possible to detect the distribution of connection portions in a long power cable at a time, and perform high-sensitivity and quick humidity detection.

(2) Among a large number of optical humidity sensors provided in the longitudinal direction, even if an abnormality occurs in a certain humidity sensor on the way, the detection signals of other humidity sensors are not affected at all. Therefore, stable detection can be performed.

(3) Since the humidity sensor section does not require a power source or the like, is small in size, and is easy to handle, the power cable does not require a special structure.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a measurement system showing an embodiment of a method for detecting humidity of a power cable line according to the present invention, FIG. 2 is a diagram showing measurement results of optical pulses detected by a light receiver, and FIG. It is sectional drawing which shows the structural example of a humidity sensor. In the figure, 1 is a power cable, 2 is a power cable connecting portion, 3
Is an optical humidity sensor, 4 is an optical branching / coupling device, 5a and 5b are optical fibers for sensors, 6a is an optical fiber for transmission (first optical fiber for optical pulse path), and 6b is an optical fiber for transmission (optical pulse). Second optical fiber for receiving path), 7 is a pulse drive circuit, 8 is a laser light source, 9 is a light receiver, 10 is an averaging processor, 11 is a signal processor, 12 is a pulse train signal, 13 is optical fiber end face butting Space, 14 is an optical fiber core wire, 15 is an adhesive, 16 is a sleeve, 17 is a ferrule, 18 is a lens, 20 is a connection box,
Reference numeral 21 is a compound filling hole, 22 is a pipe, 30 is a sensor case, 31 is a communication hole, 32 is a transparent plate, and 34 is a moisture sensitive material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiichi Hashiba, Keiichi Hashiba 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Hitachi Cable Company, Ltd. (56) Reference JP 63-311148 (JP, A)

Claims (1)

[Claims] 1. An optical humidity sensor is provided at each connection portion of a power cable, and two optical fibers for transmission are arranged along the longitudinal direction of the power cable to provide an optical branching coupler and an optical fiber for sensor. Connect to each of the above optical humidity sensors via
In the above optical branching / coupling device, the branching ratio of the optical fiber for sensor and the optical fiber for transmission is selected so that the optical fiber for transmission is remarkably large, and an optical pulse is sent from one end to the first optical fiber for transmission. Optical branching couplers are used to branch the light at each location corresponding to each connection, and the light is input to each optical humidity sensor via the input sensor optical fiber, and the optical loss changes due to the humidity emitted from these optical humidity sensors. The received optical pulse is coupled to the second optical fiber by the optical branching / coupling device via the optical fiber for sensor for output,
A number of optical pulses are emitted from one end of the first transmission optical fiber, the signal of the optical pulse returned to one end of the second transmission optical fiber is averaged each time, and sent from one end of the first optical fiber. A humidity detecting method for a power cable line, characterized in that the humidity of each connection part is obtained in consideration of a temporal change of an optical pulse returned to one end of the second optical fiber.