JPS63253814A - Method of keeping communication cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to communication carrier cables, internal and external lead-sheathed cables,
Relay cables, coaxial cables, etc. (below).

It is called a communication cable. ) related to maintenance methods aimed at maintaining performance.

(Prior art) Communication cables are usually installed over long distances.
If a problem occurs in even one part of the network, communication will become impossible and there is a danger that a wide range of areas will become isolated for a long period of time. Due to poor insulation due to rainwater intrusion or condensation of moisture inside the cable due to damage to the cable sheath, or due to a single rusting (in order to prevent an increase in contact resistance and other problems,
Major communication cables have long been permanently sealed with nitrogen gas.

Some 1 communication cable jackets inevitably deteriorate over time due to electrolytic corrosion, chemical radiation, bending fatigue, vibration, ground subsidence, or human damage during construction, and as they get older, gas pressure inspection is required. , the amount of work required for cable maintenance such as gas refilling increases rapidly.

The nitrogen gas used is produced in a factory using cryogenic separation equipment, etc., filled into high-pressure gas cylinders, and transported to the location where the communication cable terminal is installed.

Communication cables are installed in the air or underground and span long distances, and in reality, it is extremely difficult to detect and repair minute pinholes of 0.5 mm diameter or less.In most cases, maintaining internal pressure relies on gas replenishment, which is heavy. As the frequency of replacing high-pressure gas cylinders increases, communication cable maintenance becomes a major problem. As a countermeasure to this problem, dry air supply devices of the refrigerating type or using a desiccant have been installed at communication cable terminals, etc., and the permanent gas filling system has been partially replaced with a streamer gas system.

゛In the early days, desiccant-based equipment consisted of an air compressor and a desiccant filling tank, and the desiccant in the tank was replaced regularly, but multiple filling tanks were installed to regenerate the desiccant by heating on site. A method was tried. However, this dry air supply device is complicated and takes a long time to regenerate, and there are maintenance problems due to troubles, so the desiccant regeneration method has gradually shifted to reduced pressure regeneration.

Nitrogen gas is extremely effective in preventing rusting of metals or oxidative deterioration of organic insulators that cause contact resistance in communication circuits, and remaining moisture has a negative effect on insulation resistance.

The residual moisture content of air dried by the refrigeration method is usually in the vicinity of -14°C to -21°C as an atmospheric dew point, and methods using a desiccant are not necessarily at a satisfactory level.

Therefore, many overhead cables in cold regions and other important communication cables still use the nitrogen gas filling method because of dew condensation caused by ambient temperature as well as oxygen concentration.

Under these circumstances, there has been an increasing demand for the development of a method that is more reliable and reduces the amount of work involved in maintaining the 9 communication cables.

(Problems to be solved by the invention) In recent years, pressure fluctuation adsorption methods (hereinafter referred to as PS) using air as a raw material have been developed.
It is called method A. )'s nitrogen gas separation equipment has become widely known. This type of nitrogen gas separation equipment generally requires an air compressor, a dehumidifier such as a refrigerating type to prevent performance deterioration of the molecular sieve charcoal used as an adsorbent, and two operations: oxygen adsorption and desorption and desorption regeneration. Two adsorption tanks for alternate repetition, a vacuum pump to reduce the pressure during desorption and regeneration, a storage tank to equalize the performance of the nitrogen gas obtained, piping to connect these, and a control system. It is possible to continuously produce nitrogen gas with high purity and low atmospheric pressure dew point over a long period of time.

Originally, nitrogen gas obtained by a PSA type nitrogen gas separation device was mainly used in the industrial field, and is in competition with liquid nitrogen produced by existing cryogenic separation devices. As explained above, the PSA type nitrogen gas separation device consists of many devices.

As the scale becomes smaller, the proportion of fixed costs in nitrogen gas costs increases significantly.

Therefore, the nitrogen gas generation capacity of the PSA type nitrogen gas separation equipment that has been put into practical use is usually 1ONrrr/Hr to 50'
It is within the range of ONrI'r/Hr.

On the other hand, what is the amount of gas required to be supplied to one communication cable?

After once replacing the air existing in the cable, it will be 100g depending on the scale of the target equipment and usage conditions.
/cIflG - This corresponds to the amount of leakage from pinholes etc. required to maintain a pressurized state to a specific value near 1,000g/c1ilG.

Therefore, the gas supply device for supplying the cable is 0.5N 1 /m1n (0.03Nnf/1lr)
It must have a capacity of ~100Nl/m1n (6Nnf/Hr) and be inexpensive.

(Means for Solving the Problems) The present inventors have developed an ultra-compact PS that can stably obtain nitrogen gas of low cost, high purity, and low atmospheric pressure dew point, as illustrated in the two drawings.
We succeeded in developing a Type A nitrogen gas separation device, and as a result of intensive research into an excellent maintenance method for communication cables using this device, we arrived at the invention described below.

That is, this communication cable maintenance method is characterized by separating nitrogen from the air using a PSA type gas separation device and continuously supplying the obtained nitrogen gas into the communication cable.

The present invention will be explained in more detail below.

The capacity of the PSA type nitrogen gas separation equipment corresponds to the equipment scale of one communication cable, and is 0.5Nffi/min"1oO
Although it is in the ultra-small region of Nf - /min, it must have all the functions necessary to ensure the quality of the nitrogen gas obtained.

However, in order to supply inexpensive nitrogen gas, a drastic reduction in equipment costs is inevitable. The present inventors have succeeded in solving these conflicting problems.

As adsorbents used in PSA nitrogen gas separation equipment, molecular sieve charcoal, which has a high initial adsorption rate for oxygen gas in the air, and synthetic zeolite adsorbents, which have a high equilibrium adsorption amount of nitrogen gas, have been put into practical use. When considering ultra-small size, the former method is more preferable because of its simple process. In addition, if the raw air supply side of the adsorption tank is filled with a moisture absorbent such as activated alumina that can be regenerated under reduced pressure in a volume of 1/20 to 1/3 of the molecular sieve charcoal, and a two-layer structure with the 1-molecular sieve charcoal is created, a dehumidifier is not required. Furthermore, the adsorption tank itself is reduced to one, and the same compressor alternately performs the original compression function and the depressurization function equivalent to a vacuum pump during desorption. It is very effective for orientation.

These adsorbents can be used semi-permanently and continuously by automatically repeating adsorption and regeneration/desorption operations.
All communication cable maintenance work associated with cylinder or desiccant replacement, which was conventionally performed, can be eliminated.

Regarding the nitrogen gas quality of the PSA type nitrogen gas separator that supplies communication cables, the amount of moisture required to maintain the normal function of the communication cables is an atmospheric pressure of -40'C or less, preferably -60'C or less. Dew point, and nitrogen gas purity (
Total volume % of nitrogen and argon (hereinafter omitted) uses uncoated metal parts.

95% or more to prevent oxidation of organic insulating materials.

Preferably, equipment specifications are selected to ensure 98% or more.

The nitrogen gas pressure obtained from a PSA type nitrogen gas separation device is controlled by the adsorption pressure, and is usually 2 to 6 kg/kg in the storage tank.
cnlG range and supplying to 9 communication cables 2
100g/cfflG to 1000g/cffl at 0°C
The pressure is reduced using a control valve to a specific value that matches the characteristics of the cable in the vicinity of G.

If this pressure is too high, it will cause damage to the communication cable, and if it is less than the χ limit pressure, there will be insufficient supply for the amount of leakage, and moisture will enter the cable, making it impossible to perform its original function.

When the same PSA nitrogen gas separator is used to supply multiple communication cables, the pressure is adjusted to a specific level and then the gas is distributed to each cable. For maintenance purposes, it is desirable to install a flow meter at the inlet of each cable. Also, if the required pressure of each cable is not the same, it is necessary to use a plurality of pressure gauges or to adjust the pressure to a specific pressure just in front of each cable.

Communication cables are often constructed over long distances, and the effective section for supplying gas is approximately 10 km, with relay points set up every 20 km and nitrogen gas injected from both ends. Furthermore, if a plurality of pressure sensors are installed within this gas section, the location of abnormalities such as pinholes can be limited from the pressure gradient situation, which can be useful for early repair.

The storage tank of the PSA type nitrogen gas separation equipment is equipped with pressure and lower limit sensors, and an automatic control system is installed that stops the operation of the PSA type nitrogen gas separation equipment when the upper limit is exceeded, and resumes operation when the lower limit is reached. Add. If there is a risk that the nitrogen gas purity will fall below the standard when restarting operation, measures such as automatically releasing nitrogen gas to the outside of the system until it reaches a normal value are required.

These processes use high-purity, low-dew point nitrogen gas obtained by a PSA nitrogen gas separation device, and are merely examples of communication cable maintenance, and are not equally restricted in the present invention.

The present invention makes it possible to continuously and stably supply extremely high-quality gas to maintain the performance of communication cables. This invention not only prevents problems with the cable itself, but also makes it possible to maintain the performance of communication cables. Frequent replacement of cylinders, etc., which used to be a work, no longer needs to be carried out, and maintenance of communication cables is no longer necessary.

This provides an extremely superior method.

(Example) Hereinafter, two embodiments of the present invention will be described based on the drawings.

The raw air taken in from the three-way valve 8 is pressurized by the compressor 1, and after removing dust contained in the outside air and condensed water produced by compression in the filter 2, it enters the adsorption tank 3. Inside the adsorption tank 3, there is an activated alumina moisture absorbent 4 on the inlet side. It has a two-layer structure filled with molecular sieve charcoal 5 on the outlet side,
Most of the moisture in the air is removed in advance using a moisture absorbent, oxygen gas and most of the remaining moisture are adsorbed by molecular sieve charcoal, and nitrogen gas, which is highly pure and has an extremely low atmospheric dew point, is stored in the storage tank 6.

In the separation of oxygen and nitrogen using carbon molecular sieve, the initial adsorption rate difference is utilized, so the adsorption operation must be completed in a short time of 30 seconds to 180 seconds, and then the regeneration operation must be started.

Although the optimum value differs depending on the characteristics of the molecular sieve charcoal, the purity of the nitrogen gas obtained changes depending on the adsorption time.

In the regeneration operation for desorbing the gas adsorbed on the adsorbent and molecular sieve coal, the valve 11 and the three-way valve 9 are closed, the valve 10 is opened, and the desorbed gas is released into the atmosphere through the silencer, and the adsorption tank 3
Temporarily reduce the pressure inside to near atmospheric pressure. Next, the valve 10 is closed, and the remaining desorbed gas is released through the three-way valve 8 through the three-way valve 9 by utilizing the compressor 1 as a vacuum pump, thereby bringing the inside of the adsorption tank 3 below atmospheric pressure.

The regeneration time may be approximately the same as the adsorption time. When the regeneration operation is completed, the adsorption operation is performed again, and the two operations are continuously repeated.

The storage tank 6 also has the purpose of uniformizing the quality of the nitrogen gas obtained intermittently, and a minimum internal volume is required to achieve this effect.

Further, pressure sensors 7 and residual oxygen concentration meters 12 inside the storage tank and at the exit of the storage tank are not shown in the figure, but they are all connected to the control system, and are used to operate and stop the device 20, open and close valves, etc.
All other operations are automatically controlled.

By using the above-mentioned apparatus 20 and selecting appropriate conditions, it was possible to sufficiently demonstrate the quality of the nitrogen gas obtained with a purity of 99% or more and an atmospheric pressure dew point of -60°C or less.

Nitrogen gas pressure in storage tank 6 & 7.2 kg/cAG~6
kg/cJG cannot be directly supplied to communication cables. Therefore, the nitrogen gas is reduced in pressure by the control valve 16 to the set supply pressure of the cable, filtered, and then distributed by the header after dust removal in the filter 13.

The valve 17 is opened (thereby supplying the respective communication cables 15). During this process, a safety valve 18 or the like is installed to protect the flowmeter 14 or the communication cable 15, if necessary.

If the communication cable 15 is new and the leakage amount is small, P
The supply capacity of the SA type nitrogen gas separation device 20 is excessive, so if the pressure sensor 7 detects that the pressure in the storage tank 6 has reached the upper limit, the system will continue to operate until the pressure drops to the lower limit. 2
0 operation will be automatically stopped.

Also, if an abnormality occurs in the coating of the communication cable 15 and the amount of gas leaks rapidly, the flow rate sensor 14 installed near the gas inlet of the cable. Early detection is possible by detecting changes with a pressure sensor 19 installed in the middle of the gas section of the IHA cable and activating an alarm.

[Brief explanation of drawings]

The drawing is a flow sheet showing an example of the present invention. In the figure,
1 is an air compressor, 2.13 is a filter, 3 is an adsorption tank,
4 in the tank is a moisture absorbent, 5 is a molecular sieve charcoal, 6 is a nitrogen gas storage tank,
7.19 is a pressure sensor. 12 is an oxygen concentration meter, 14 is a flow rate sensor, 15 is a communication cable, 8.9 is an automatic three-way valve, 10.11 is an automatic two-way valve, 16 is a control valve, 17 is a manual valve, 18 is a safety valve, 20 is a PSA This is a nitrogen gas separation device.

Claims (3)

[Claims] (1) A communication cable maintenance method characterized by separating nitrogen from the air using a pressure fluctuation adsorption type gas separation device and continuously supplying the obtained nitrogen gas into the communication cable. (2) The communication cable maintenance method according to claim 1, wherein part or all of the adsorbent constituting the pressure fluctuation adsorption type gas separation device is molecular sieve charcoal. (3) The purity of nitrogen gas supplied into the communication cable is 95
% (volume) or more, and the amount of moisture remaining in the nitrogen gas is -40°C or less at atmospheric pressure dew point, Claims 1 and 2
Communication cable maintenance method described in section.