JPS5918809B2 - Chika Denryoku Cable House - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to underground power cable cooling systems, and more particularly to systems using closed cycle evaporative condensation methods to dissipate heat generation in underground power cables.

When using underground power cables, the power transmission capacity is limited by the maximum working temperature of the power cables.

The temperature of a power cable is directly related to its heat output and its ability to dissipate this heat to its surroundings. Regardless of how power cables are installed, heat dissipation from power cables has traditionally been carried out by the surrounding soil. However, due to the low thermal conductivity of soil and its variation depending on local climatic conditions and soil moisture, underground power cables need to be provided with a high degree of safety in terms of current rating. Higher current ratings can be obtained by using special backfill materials with improved thermal conductivity and moisture retention properties. However, even with the use of such materials, the heat dissipation capacity of the soil has almost reached its practical limit, and there is still a need for the development of underground power cables capable of supplying higher rated currents. It is already known to cool underground power cables by circulating water or oil through pipes buried adjacent to the length of the power cable, or through large diameter pipes within which the power cable is housed.

This water or oil is then circulated through air-cooled or water-cooled heat exchangers evenly spaced along the power transmission line. Consideration has been given to using cooling units in conjunction with heat exchangers to cool circulating fluids. The major disadvantages of such methods are the significant fluid flow rates required to extract the useful heat and the large power plants and other equipment required to cool this fluid. be. moreover,
When using long cables, as the circulating fluid flows through the tubes, its temperature gradually increases, thereby reducing its effectiveness as a coolant. These drawbacks can be overcome by using a closed cycle evaporation condensation method with effective heat dissipation. When using this method, the heat generated by the power cable evaporates the volatile liquid in the vicinity of the power cable. The steam is condensed in the heat exchanger and the resulting condensate is returned to the vicinity of the power cable by gravity. No external power source is required to perform this evaporative condensation method. The present invention does not need to be kept horizontally, and the cooling effect does not deteriorate significantly even if the blocked pipe is locally curved or twisted. Therefore, the present invention has a structure that can be used even on uneven terrain. The purpose is to provide a simple underground power cable cooling device.

In accordance with the present invention, an apparatus for cooling underground power cables with a volatile fluid is provided having an elongated enclosed chamber and an elongated porous layer defining a space for receiving the power cable. The porous layer is disposed longitudinally within the closed chamber and has an upper portion and a lower portion. The upper and lower portions each extend the entire length of the porous layer. The lower portion is located within the chamber so as to be in contact with the liquid phase of the volatile fluid within the chamber. The upper portion is located within the closed chamber so as to be separated from the liquid phase of the volatile fluid. A closed heat exchanger is connected to the closed chamber at a connection point, the connection point and the closed heat exchanger being located above the liquid phase of the volatile fluid within the closed chamber. In this way, capillary action uniformly disperses the volatile liquid in liquid phase on the surface of the porous layer. The liquid is evaporated in the closed chamber due to the heat generated in the power cable, and the evaporated liquid is transported from the closed chamber to the closed heat exchanger by the differential pressure. The evaporated liquid is condensed in the heat exchanger and returned to the closed chamber by gravity. The porous layer is provided on the outer surface of a tube extending in the longitudinal direction of the closed chamber, and this tube is a space for storing the cable and is shielded from the closed chamber. 1st
As clearly shown in Figures 1 and 2, the high-voltage power transmission circuit of the high-pressure tubular system includes a high-pressure oil-filled (HPOF) cable 10 disposed within an elongated steel pipe 12; The gap is filled with oil 14 at a pressure of 200 psig.

To simplify the invention, the cable connections and ends have been omitted, but a similar cooling system can be applied to these parts. In the electrical circuit shown in FIGS. 1 and 2, the oil 14 surrounding the cable 10 is oscillated between sub-stations to prevent hot spots (HOtspOt) from forming in the cable 10. Furthermore, vibrating the oil in this way makes it possible to make the operation of the system of the invention safe, as described below. The evaporator section of each cooling device, shown in FIGS. 1 and 2 as a circular cross-section tube 18 fitted over a steel tube 12, has a closed chamber 16. A circular end plate 20 is secured to each end of the circular tube 18 by welding or other suitable means, and the steel tube 12 passes through an aperture in the end plate 20. Each end plate 20 is secured in place on the steel tube 12 by welding or other suitable means, thereby forming a hermetic closure between the steel tube 12 and the circular tube 18.
Before securing the end plate 20 to the steel tube 12 and the circular tube 18, the portion of the steel tube 12 to be placed within the closed chamber 16 is coated with a porous layer 22 on its outer surface.

The porous layer 22 has a space 13 or inner diameter for receiving the power cable and its accessories. In this embodiment, the space 13 includes the steel pipe 12, the cable 10 and the oil 14.
occupied by The porous layer 22 contains a volatile liquid 24
The upper and lower parts 23a and 23b act to uniformly disperse the volatile liquid 24 at the bottom of the closed chamber 16 onto the heat transfer surface of the steel pipe 12. , thereby making it unnecessary to fill the closed chamber 16 with liquid. The porous layer 22 used has a large capillary effect on the particular volatile liquid used and is chemically compatible with the volatile liquid and the conduit for this liquid. As an example, the porous layer 22 is formed of untreated fiberglass that is chemically inert, but whose capillary capacity varies depending on tissue density, layer thickness, etc. Other fabrics and metal meshes can also be used. The condensing section of the cooling system has a closed heat exchanger 26 which is connected to one end of the closed chamber 16 at a connection point by suitable connection means such as a flexible joint 28 (FIG. 1). .

The soft fitting 28 has a flange end 30, the lower flange end 30 being removably secured to a flange adapter 32 secured to the top of the closure chamber 16. Soft joint 28
The upper flange end 30 of engages another flange adapter 33 attached to the lower end of the closed heat exchanger 26. The heat exchanger 26 is disposed vertically above the closed chamber 16 so that the condensed volatile liquid within the heat exchanger 26 is returned to the closed chamber 16 by gravity. The closed chamber 16 is sloped downwardly from the closed heat exchanger 26 to facilitate flow of the volatile liquid 24 toward the end of the closed chamber 16 remote from the heat exchanger 26. You can also do it. Furthermore, the closed heat exchanger 26 is generally located above the ground to promote heat dissipation.
As shown in FIGS. 3-7, the closed heat exchanger 26 could be disposed within the utility pole 40, but this is not necessary.

The dimensions and shape of the heat exchanger 26 vary depending on its location. Pole condensers are used with the main underground cables that supply electricity to Obe City and connect sub-stations that typically run adjacent to highways and major roads. As best seen in Figures 5-7, condensation of the liquid occurs on the inner surface 34 of the pole, the outer surface of which has fins 36 to increase the heat transfer area to the atmosphere. Telephone pole 4 in Figure 7
0 has an external passageway 38 for accommodating the electric bulb wire. Depending on the location of the pole condenser relative to the length of the circuit, connections to the closed chamber 16 may be made using rigid or flexible tubing of the required length, provided this does not impede the flow of steam and condensate. can be done. The volatile liquid 24 used must meet the following requirements.

(a) be chemically compatible with the walls of the closed chamber 16 and the heat exchanger 26, and with the porous layer 22;

(b) Have a vapor pressure of less than 180 psig at a maximum working temperature of about 60°C.

(c) having high latent heat of volatilization, high vapor density and high surface tension;

Ammonia, propane, fluorocarbon refrigerants and water meet the above requirements.

These liquids, which allow the system to work at pressures above atmospheric pressure, allow the system to continue working even after a small leak occurs until all the volatile liquid 24 has leaked out as vapor. It also offers the advantage of Even if a leak occurs in the steel pipe 12, the working pressure is 2
If the pressure is below 00 psig, contamination of the oil 14 can be avoided.
A pressure sensitive device can be used with each evaporative condenser.

This pressure sensitive device is connected to the nearest sub-station to detect the performance and failure of each unit.
The flow of oil 14 within the steel tube 12 helps dissipate heat from the power cable while the evaporative condenser is being repaired. The operation of the evaporative condenser device is based on the evaporation of the volatile liquid 24 in its vicinity due to the heat generation of the steel pipe 12 surrounding the power cable.

At the bottom of the closed chamber 16 and at the lower part 23 of the porous layer 22
The volatile liquid 24 in contact with the steel tube 12 due to capillary action
is pulled up to the upper part 23a of the porous layer 22 wrapped around the . The generated steam flows along the closed chamber in the direction of arrow 38 in FIG.
8 and adapter 33 to the closed heat exchanger 26. The flow of steam in the direction of arrow 38 is induced by a slight pressure difference between heat exchanger 26 and closed chamber 16 . This differential pressure is due to the low temperature within heat exchanger 26. The steam is condensed by imparting its heat content to a coolant such as circulating ambient air or cooling air. Next, the condensate is returned to the closed chamber 16 by power, completing the operation of the -cycle. In this way, a complete cycle of operation can be performed without the use of pumps or other power equipment. The evaporator and condenser sections are configured as a closed system containing a volatile liquid in balance with its vapor.

Since the liquid evaporates and condenses at the same temperature, the evaporating section and the condensing section are kept at almost the same temperature. Furthermore, the heat transfer process takes place in an almost constant volume, leading to an interdependence between temperature and pressure. As a result, the system can be operated at any temperature above the freezing point of the liquid. In general, more efficient cooling can be obtained by increasing the operating temperature. However, this phenomenon reverses as the critical temperature approaches. The cooling system achieves high heat transfer coefficients for long circuits while requiring only small temperature differentials. Furthermore, the response for heat transfer is short since only a relatively small amount of liquid is used.
The surrounding soil acts to dissipate some heat, and its large heat storage capacity acts to even out daily fluctuations in cable temperature caused by uneven loading. As described above, the present invention coats the entire outer surface of a power cable member with a porous layer and contains a very small amount of volatile liquid in a closed chamber, sufficient to contact only the bottom of the power cable member in liquid phase. , since most of the other part of the power cable member is brought into contact with the vapor phase of the volatile liquid, firstly, the power cable is completely immersed in the volatile liquid or the heat of the closed room is removed through the supply pipe. The heat exchanger has separate inlets and outlets because there is no need to return condensed volatile liquids to the opposite end of the exchanger, and there is no need to artificially encircle volatile liquids along the power cable members. Furthermore, the heat exchanger in the device of the invention need only be connected to the closed tube by a single tube having a length that allows the passage of both steam and condensate; As a result, the present invention has the advantage of a simple configuration. Second, in the present invention, since the gas phase part within the closed chamber is considerably larger than the liquid phase, there is no need to bury the closed chamber completely horizontally, and local curvature or twisting does not occur in the closed tube. Even if the steam is not circulated at a certain point in the upper part of the closed chamber, it will not form a high temperature spot and significantly reduce the cooling effect. Due to the porous material layer along the entire length, the cooling effect remains effective regardless of the levelness of the closed chamber, and even if the upper or lower portion of the closed chamber is twisted. However, it has the advantage of being useful for use in uneven terrain. Embodiments of the present invention will be described below.

1. The heat exchanger is connected to one end of the closed chamber and extends upwardly, and the closed chamber is tilted downwardly from the heat exchanger so that the condensed volatile liquid is directed in the longitudinal direction of the closed chamber. Apparatus according to the claims that are distributed.

2. 7. The apparatus of claim 1, wherein the heat exchanger is located above the ground and housed within a utility pole.

3. 7. The device of claim 1, wherein said porous layer is formed of untreated fiberglass.

4. The apparatus of claim 1, wherein the volatile liquid is selected from the group consisting of ammonia, propane, and fluorocarbon refrigerants.

5. 7. The device of claim 1, wherein a flexible joint is used at the connection point between the closed chamber and the heat exchanger.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a closed cycle evaporative condenser according to the present invention. FIG. 2 is a sectional view of the evaporation section of the device. FIG. 3 is a side view of a utility pole housing the condensing section of the device. FIG. 4 is a side view of a utility pole according to another embodiment. Figure 5 is V-V of Figure 4.
Linear view. FIG. 6 is a side view of a utility pole according to another embodiment. FIG. 7 is a view taken along the - line in FIG. 6. 10 is an underground power cable, 12 is a steel pipe, 14 is oil, 16 is a closed chamber, 18 is a circular pipe, 22 is a porous layer, 23a and 23b are the upper and lower parts of the porous layer, respectively, 24 is a volatile liquid, 26 is a heat exchanger, 28 is a soft joint, and 40 is a utility pole.

Claims (1)

[Claims] 1 A closed chamber that accommodates a power cable member, a volatile liquid that fills a part of the closed chamber to form a gas phase part and a liquid phase inside the closed chamber, and a closed chamber that is located above the closed chamber and is closed. The device is airtightly connected to the chamber and communicates with the gas phase of the closed chamber to condense the volatile liquid evaporated due to the heat generated by the power cable member and return it to the closed chamber by gravity, thereby closing the closed chamber. In the cooling system of underground power cables with a heat exchanger forming a cycle heat dissipation liquid circulation,
The liquid phase portion of the volatile liquid contained in the closed chamber contacts only the bottom portion of the power cable member at the bottom of the closed chamber, and the portion of the power cable member other than the bottom portion contacts the gas phase portion of the volatile liquid. , and the outer surface of the power cable member is coated along its entire length with a porous layer having excellent wicking ability due to capillary action, so that liquid phase accumulated or condensed at the bottom of the closed chamber is volatilized. 1. A cooling device for an underground power cable, characterized in that the cooling device is configured to uniformly disperse a liquid over the entire heat transfer surface of a power cable member.