JPH0218006B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an improvement in a heat pipe for cooling an underground cable line, which is installed along an underground cable line and suppresses a rise in temperature due to heat generated by the cable. [Prior Art] A heat pipe cooling method is available as a cooling method for underground cables (mainly power cables). In this method, a heat pipe is drawn into a conduit near the conduit where the cable is drawn, the heat generated by the cable is absorbed by the heat pipe, and the heat is carried to the heat dissipation part of the heat pipe. It is a mechanism that radiates heat from the inside to the outside. This heat pipe cooling method differs from other water cooling methods and air cooling methods in that it is difficult to determine whether or not it is working properly. For example, in the water circulation cooling system used for indirect cooling in the trough, if the pump is rotating, you can confirm that it is operating normally, and with the air cooling system, if the fan is rotating, you can confirm that it is operating normally. I can confirm that there is. However, in the case of the heat pipe cooling method, the refrigerant simply repeats the cycle of boiling, vapor transfer, condensation, and reflux inside the closed pipe without the help of any power, so it is difficult to tell whether or not it is working properly. , causing anxiety to users and equipment maintainers. For example, if a pipe is damaged and there is no refrigerant inside, but it is not detected, the heat pipe will not be able to remove heat when the load on the cable increases, causing an abnormal temperature rise, and the insulation There is a risk of destruction. Therefore, it is essential to promptly detect loss of refrigerant in a heat pipe due to pinholes, external damage, etc. in order to ensure system reliability. Generally, heat pipes for cooling underground cable lines use fluorocarbon-based refrigerants. A fluorocarbon detector is known as a device that detects a fluorocarbon gas leak. However, considering that it is not known where a leak point will occur in a long heat pipe, or that even if there is a leak, it will be blown away by the wind,
It is not appropriate to use a freon detector. In addition, there are two ways to check the operation of the heat pipe: A viewing window is installed in the heat dissipation section, and maintenance personnel can condense the refrigerant at appropriate intervals.
Observe how the refrigerant drips, and if no refrigerant is dripping, determine that the heat pipe is not working.
Utilizing the isothermality in the longitudinal direction of the heat pipe, when the temperature distribution in the longitudinal direction of the heat pipe is no longer uniform, for example, the temperature of the heat dissipation part is several degrees Celsius or more higher than the temperature of the heat absorption part (the part along the cable). Set it to sound an alarm when it gets hot. However, the problem with this method is that when a viewing window is provided, the number of sealing points with flanges and gaskets increases, which reduces reliability in terms of refrigerant leaks, and that when there is no or only a small load on the cable, the amount of refrigerant condensation occurs even if the heat pipe is normal. There are problems in that there is no or very small amount of light, which may lead to false detection, and it is inconvenient because it is impossible to confirm operation unless you look directly at it. Another method is that when the load on the cable is small and the outside temperature is high, for example, the temperature at the heat absorbing part underground is 20°C, and the temperature at the heat dissipating part exposed to the outside air is 32°C, which can cause malfunctions. There is a problem. [Object of the Invention] In view of the problems of the prior art as described above, the object of the present invention is to provide a method for reliably detecting whether or not it is operating normally, regardless of the size of the load or the high or low external temperature. The purpose of the present invention is to provide a heat pipe for cooling underground cable lines. [Structure of the Invention] The heat pipe for cooling underground cable lines of the present invention which achieves the above object is filled with a refrigerant whose vapor pressure at the soil base temperature is always higher than atmospheric pressure, so that the pressure inside the pipe becomes equal to atmospheric pressure. It is characterized by being equipped with a pressure detector that is activated when the [Embodiment] The drawings show a heat pipe according to an embodiment of the present invention and how it is used. 1 is soil, 2A and 2B are pipes buried underground, and 3 is a power cable drawn into the pipe 2A. Reference numeral 4 denotes a heat pipe according to an embodiment of the present invention, the heat absorbing part 5 of which is drawn into the pipe line 1B, and the heat radiating part 6 being installed in the atmosphere. The heat generated by the cable 3 heats the soil 1 via the pipe line 2A, and further heats the heat absorption part 5 of the heat pipe 4 via the pipe line 2B. In the heat pipe 4, the enclosed refrigerant is vaporized by this heat. The vaporized refrigerant moves to the heat radiation section 6, where it is cooled and condensed. The condensed refrigerant flows back to the heat absorption section 5 through the wick on the inner surface of the tube. The heat absorbed by the heat absorption part 5 in this way is carried to the heat radiation part 6.
This means that heat is radiated to the outside. A pressure gauge 7 with an alarm contact is attached to the heat radiation part 6 of the heat pipe 4. This pressure gauge 7 detects the pressure inside the heat pipe 4, and closes (or opens) a contact when the pressure inside the pipe becomes equal to atmospheric pressure, that is, when the difference from atmospheric pressure becomes less than a predetermined value, for example. Turn on the alarm lamp 8. Instead of the alarm lamp 8, a buzzer or a controller that operates in response to a contact closing signal may be provided. The heat pipe 4 is filled with a refrigerant whose vapor pressure at the soil base temperature is always higher than atmospheric pressure. The base temperature of the soil is normally 17 to 25°C, and when the cable 3 is unloaded, the ambient temperature of the heat absorbing part 5 of the heat pipe is around this level. The vapor pressure of the refrigerant decreases as the temperature decreases. If the vapor pressure becomes atmospheric pressure or lower near the soil bottom temperature, the above-mentioned pressure gauge with alarm contact 7 indicates whether the pressure inside the pipe has reached atmospheric pressure due to a refrigerant leak, or whether it has increased due to a drop in temperature. I can't tell if it's atmospheric pressure or not. For this reason, the refrigerant sealed in the heat pipe 4 is one whose vapor pressure at the soil base temperature is always higher than atmospheric pressure (the vapor pressure becomes even higher at a temperature higher than the soil base temperature). Usually, heat pipes for underground cable line cooling are
Designed to operate at 30-50℃, the refrigerant includes:
Assuming that it is compatible with the heat pipe material and that the vapor pressure is within a safe pressure range within the operating temperature range,
Freon 11 is used. However, Freon 11
has a boiling point of 23.8℃, so its vapor pressure is equal to or lower than atmospheric pressure near the soil base temperature. Therefore, the use of Freon 11 is not appropriate. The following table shows the vapor pressures of refrigerants that can be used in Freon 11 and the heat pipe of the present invention. The unit is Kg/cm ² G (gauge pressure).

〔Effect of the invention〕

As explained above, according to the present invention, the inside of the pipe becomes atmospheric pressure only when a refrigerant leak occurs, and this is detected by a pressure detector, so regardless of the size of the cable load or the high or low outside temperature. First, it is possible to reliably detect whether or not the heat pipe is operating normally, which greatly contributes to improving the reliability of the underground cable line system.

[Brief explanation of drawings]

The drawing is a sectional view showing an underground cable line cooling heat pipe according to an embodiment of the present invention and its usage state. 1...Soil, 2A, 2B...Pipeline, 3...Cable, 4...Heat pipe, 5...Heat absorption part, 6...
...Heat radiation part, 7...Pressure gauge with alarm contact, 8...Alarm lamp.

Claims (1)

[Claims] 1. A refrigerant whose vapor pressure at the base temperature of the soil is always higher than atmospheric pressure is sealed, and a pressure detector is attached that operates when the pressure inside the pipe becomes equal to atmospheric pressure. Heat pipe for cooling underground cable lines. 2. The heat pipe according to claim 1, wherein the pressure detector is attached to a heat radiation part of the heat pipe.