JPS6346645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a cooling power cable line,
In particular, the present invention relates to a cooling power cable line in which the amount of heat absorbed by a refrigerant can be averaged along the length of the cable.

Generally, power cables are designed so that the temperature rise due to heat generated by the cable is below the maximum permissible temperature of the insulator, which limits the power transmission capacity of the cable.

Therefore, in order to increase the power transmission capacity, it is sufficient to cool the power cable by some method. Common cooling methods include internal direct cooling, external direct cooling, and external indirect cooling, and each method will be briefly explained below.

As shown in Figure 1, the internal direct cooling method cools the power cable by flowing a refrigerant 4 into a refrigerant passage 3 provided inside a conductor 2 covered with an insulator 1. As 4, water or oil is generally used.

In the external direct cooling method, as shown in FIG. 2, a power cable 5 whose conductor 2' is covered with an insulator 1' is placed inside a watertight tube 6, and the space created between the power cable 5 and the watertight tube 6 is (not shown) to cool the power cable by flowing a refrigerant 4' into the
Water is generally used as a refrigerant.

In the external indirect cooling system, for example, as shown in FIG. It cools the air and indirectly cools the power cable 5', and water is generally used as the refrigerant.

The above three cooling methods cool the power cable by flowing a refrigerant in the length direction of the cable, and the flow of the refrigerant is generally as shown in FIG. 4.

That is, the cooling stations 9 are installed at appropriate intervals along the cable line, and the refrigerant cooled by the cooling stations 9 flows through the cooling passage 10, thereby cooling the power cable. The cooling passage 10 is the refrigerant passage 3 in the case of an internal direct water cooling system, the space created between the watertight pipe 6 and the power cable 5 in the case of an external direct water cooling system, and the cooling passage in the case of an internal trough indirect cooling system. This is tube 8.

The refrigerant that has reached a high temperature after fulfilling its cooling role is recovered to the cooling station 9 through the return pipe 11.

However, these cooling methods have the disadvantage that temperature distribution occurs in the length direction, as will be described later. That is, as shown in FIG. 5, an example of the temperature distribution in the case of indirect cooling in the trough, the line 12 indicating the conductor temperature indicates that the maximum permissible temperature of the cross-linked polyethylene cable, for example, is 85°C at the refrigerant outlet point 13. However, at the refrigerant inlet point 14, the introduction temperature is 40°C. Thus, the cable conductor temperature is highest at the refrigerant exit point and is lower than the maximum permissible temperature of 85°C elsewhere. In other words, this means that the cable is being cooled more than necessary near the refrigerant inlet. Additionally, as can be seen from line 15, which shows the amount of heat absorbed by the refrigerant, the refrigerant absorbs more heat than necessary near the refrigerant inlet, and the amount of heat absorbed near the refrigerant outlet decreases, resulting in overall low cooling efficiency. This means that you are doing the following.

The present invention was made in view of the above-mentioned circumstances, and by using cooling pipes with high thermal resistance near the refrigerant inlet and cooling pipes with low thermal resistance as they approach the refrigerant outlet, the amount of heat absorbed by the refrigerant is made almost uniform. The purpose is to provide an efficient cooling power cable line.

The present invention will be explained below based on the drawings of one embodiment.

In FIG. 6, in which the same parts as in FIG. 4 are given the same numbers, cooling passages 10 with different heat reduction resistances are used in three sections A, B, and C.

That is, the thermal resistance of the cooling passage in section A is made the largest, the thermal resistance of the cooling passage in section C is made the smallest,
The thermal resistance of the cooling passage in section B is set to an intermediate value between sections A and C. As a method of changing the thermal resistance of a cooling passage, for example, a heat insulating tape (not shown) having a constant thermal resistance is wrapped around the outer periphery of the cooling passage or attached vertically, and the number of layers of the heat insulating tape is varied along the length. It is possible to think of ways to change the

Ideally, the cooling passage 10 should have a radial thermal resistance value that varies continuously along the length of the cooling passage.

Figure 7 shows the temperature distribution in the length direction of the conductor and refrigerant in the case of Figure 6, and the line 12' indicating the cable conductor temperature has a step-like distribution in each section A, B, and C. However, when compared with the line 12 indicating the conductor temperature in FIG. 5, the temperature distribution is almost uniform in the length direction. The line 15' indicating the amount of heat absorbed by the refrigerant is also approximately uniform in the length direction.
Since excess heat is not absorbed near the refrigerant inlet, the temperature of the refrigerant does not rise much, and the temperature near the refrigerant outlet is also lower in FIG. 7 than in FIG. 5.

Note that in the figure, 16 and 16' indicate lines indicating the refrigerant temperature.

As described above, in the present invention, since the power cable is cooled by making the thermal resistance in the radial direction of the cooling passage gradually smaller along the length of the cooling passage, the amount of heat absorbed per unit length of the refrigerant is It is possible to provide a cooling power cable line in which the temperature of the cable conductor can be averaged in the length direction. In other words, in the present invention, since the amount of heat absorbed by the refrigerant can be suppressed to the necessary minimum, the load on the refrigerator can be reduced to 1/2 to 1/3 compared to the conventional system, resulting in good cooling efficiency. It can provide a cooling power cable line.

Note that this method is particularly easy to implement in the trough indirect cooling system, and its effects are great.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a cooled power cable line in an internal direct cooling system, Figure 2 is a cross-sectional view of a cooled power cable line in an external direct cooling system, and Figure 3 is a cross-sectional view of a cooled power cable line in an external indirect cooling system. A cross-sectional view of the line, Figure 4 is an explanatory diagram showing the flow state of refrigerant in a conventional cooling power cable line, and Figure 5 is an explanatory diagram showing the state of temperature distribution of the refrigerant and cable conductor in the conventional indirect trough cooling system. FIG. 6 is an explanatory diagram showing the distribution state of the refrigerant in the cooling power cable line in the present invention, and FIG. 7 is an explanatory diagram showing the state of temperature distribution of the refrigerant and the cable conductor in the cooling power cable line in the present invention. . 9... Cooling station, 10... Cooling passage,
11... Return pipe, A, B, C... Cooling passage section, 12, 12'... Line indicating conductor temperature, 15,
15'...A line showing the amount of heat absorbed by the refrigerant.

Claims (1)

[Claims] 1. A cooling power cable line in which a power cable is cooled by flowing a refrigerant through a cooling passage,
A cooling power cable line characterized in that the radial thermal resistance of the cooling passage gradually decreases from the inlet side to the outlet side of the refrigerant. 2. The cooling power cable line according to claim 1, wherein a heat insulating tape is wound around the outer periphery of the cooling passage or attached longitudinally so that the number of winding layers changes sequentially along the length of the cooling passage.