JP3802659B2 - Power cable - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power cable having a reduced peripheral magnetic field.
[0002]
[Prior art]
In recent years, a magnetic field generated around a power cable has been regarded as a problem, and reduction thereof has been demanded. A characteristic of this magnetic field is that it is difficult to shield because it has a very low frequency of 50 Hz or 60 Hz.
[0003]
Conventionally, as a power cable used to power the power of three-phase alternating current, as shown in FIG. 6, each conductor a three-phase, and those disposed b, and c in an equilateral triangle, as shown in FIG. 7 each conductor a three-phase, and those disposed b, and c coaxially, as shown in FIG. 8, the three-phase conductors a, b, using two conductors respectively as c, each conductor radius r Are arranged alternately on the same circumference for each phase and at equal intervals, and as shown in FIG. 9 , three conductors are used as the three-phase conductors a, b and c, respectively, and three at the center. of each one conductor of the conductor arranged in an equilateral triangle, and and those disposed remaining conductors of the two alternately Moreover equidistantly on the same circumference of the radius r, as shown in FIG. 10 4 conductors are used for each of the three-phase conductors a, b, and c, and each one of the four conductors is arranged in an equilateral triangle at the center. And those placed remaining conductors of the three equidistantly Moreover alternately on the same circumference of the radius r are known.
[0004]
The magnetic field around the power cable shown in FIG. 6 is calculated as follows. That is, as shown in FIG. 11 , the strength of the magnetic field at point P separated from the three-phase conductors a, b, c by the distances ra, rb, rc is as follows. However, the conductor is assumed to be linear and infinitely long, and is considered in two dimensions. Since the current and magnetic field considered here are alternating current, they are treated as a function of time. It is assumed that currents Ia (t), Ib (t), and Ic (t) flow through the conductors a, b, and c.
Ha (t) = Ia (t) / 2πra
Hb (t) = Ib (t) / 2πrb
Hc (t) = Ic (t) / 2πrc
[0005]
As an example of the combined value H (t), a magnetic field vector at the instant t1 when Ha (t) is maximized is illustrated. Hb (t1) and Hc (t1) are directed almost in the opposite direction to Ha (t1), and the magnitude is ½ of the maximum amplitude. This is because the phases of Ia (t), Ib (t), and Ic (t) are shifted by 120 °.
[0006]
Figure 12 is obtained by calculating the magnetic field around the power cable shown in Figure 7 above. Conditions are the same as those shown in FIG 11. In this power cable, since ra = rb = rc and the phases of Ia (t), Ib (t), and Ic (t) are shifted by 120 °, the combined value H (t) is always zero. . Thus, if ra = rb = rc, the external magnetic field can be made zero.
[0007]
[Problems to be solved by the invention]
As described above, the power cable shown in FIG. 6 has a problem that the magnetic field around it becomes large, and the power cable shown in FIG. 7 can make the peripheral magnetic field zero, but an equilateral triangular array having the same capacity. There is a problem that the size is larger than that of the power cable and insulation is difficult at a high voltage. Further, although the power cables shown in FIGS. 8 to 10 can reduce the magnetic field around the power cables in the equilateral triangle arrangement, there is a problem that the power cables are still insufficient.
[0008]
[Means for Solving the Problems]
The present invention provides a power cable that solves the above-described problems. The configuration of the power cable is a three-phase AC power cable in which one of the three phases is arranged at the center using two or more conductors. The other two-phase conductors are arranged on one or a plurality of the same circumference centering on the one phase, and the other two-phase conductors each use two or more conductors, It is characterized by being arranged alternately and at equal intervals.
[0009]
If two or more conductors of one phase of the three phases are arranged at the center as described above, and other two-phase conductors are alternately arranged on the same circumference at equal intervals, the distance between the observation points is increased. since it can be regarded as almost equal both 3-phase distance between the plurality of conductors constituting the respective phases and the observation point, a structure close to a power cable of the coaxial arrangement shown in FIG. For this reason, the peripheral magnetic field can be reduced.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of a power cable according to the present invention. This power cable uses two one-phase conductors a and two other two-phase conductors b and c, and arranges the two one-phase conductors a at the center, r (m) Two conductors of each of the other phases b and c are alternately arranged at equal intervals on the same circumference.
[0011]
FIG. 2 is a schematic configuration diagram showing another embodiment of the power cable according to the present invention. This power cable uses three one-phase conductors a and three other two-phase b and c conductors, and arranges three one-phase conductors a at the center, r (m) Three conductors of each of the other phases b and c are alternately arranged at equal intervals on the same circumference.
[0012]
FIG. 3 is a schematic configuration diagram showing another embodiment of the power cable according to the present invention. This power cable uses four one-phase conductors a and four other two-phase b and c conductors, and is arranged around the four one-phase conductors a, r (m) Four conductors of each of the other phases b and c are alternately arranged at equal intervals on the same circumference apart.
[0013]
FIG. 4 is a schematic configuration diagram showing another embodiment of the power cable according to the present invention. This power cable uses six one-phase conductors a and six other two-phase b and c conductors, and arranges six one-phase conductors a at the center, r (m) Two conductors of each of the other phases b and c are alternately arranged at equal intervals on the same circumference apart from each other.
[0014]
【Example】
Example 1
A power cable having the structure shown in FIG. 1 was produced. That is, two conductors a of one phase are arranged at the center, and two conductors of other phases b and c are alternately arranged at equal intervals on the same circumference separated by 0.3 (m). Is. The current value was set to 100 A / phase, and the current was equally distributed to the two conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0015]
Example 2
A power cable having the structure shown in FIG. 2 was produced. That is, the three conductors a of one phase are arranged at the center, and the three conductors of the other phases b and c are alternately arranged at equal intervals on the same circumference separated by 0.3 (m). Is. The current value was 100 A / phase, and the current was equally distributed to the three conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0016]
Example 3
A power cable having the structure shown in FIG. 3 was produced. That is, four conductors a of one phase are arranged at the center, and four conductors of other phases b and c are alternately arranged at equal intervals on the same circumference separated by 0.3 (m). Is. The current value was 100 A / phase, and the current was equally distributed to the three conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0017]
Comparative Example 1
A power cable having the structure shown in FIG. 6 was produced. That is, the three-phase conductors a, b, and c are arranged in an equilateral triangle. The current value was 100 A / phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0018]
Comparative Example 2
A power cable having the structure shown in FIG. 8 was produced. That is, two conductors are used as the three-phase conductors a, b, and c, respectively, and the conductors are alternately arranged at equal intervals for each phase on the same circumference. The current value was set to 100 A / phase, and the current was equally distributed to the two conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0019]
Comparative Example 3
A power cable having the structure shown in FIG. 9 was produced. That is, three conductors are used as the three-phase conductors a, b, and c, each of the three conductors is arranged in an equilateral triangle at the center, and each remaining conductor on the same circumference. Two conductors are alternately arranged at equal intervals. The current value was set to 100 A / phase, and the current was equally distributed to the two conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0020]
Comparative Example 4
A power cable having the structure shown in FIG. 10 was produced. That is, four conductors are used as the three-phase conductors a, b, and c, one of the four conductors is arranged in an equilateral triangle at the center, and each remaining conductor on the same circumference. Three conductors are alternately arranged at equal intervals. The current value was set to 100 A / phase, and the current was equally distributed to the two conductors constituting one phase. The measurement point was set to 1 to 10 m in the perpendicular direction starting from the line center.
[0021]
The measurement results are shown in FIG. As is apparent from FIG. 5, the power cable according to the present invention has a reduced magnetic field around it, and the attenuation becomes more significant as the distance increases. It can also be seen that the distance attenuation increases as the number of conductors per phase is increased. The reason why the distance attenuation increases when the number of conductors per phase is increased in this way is that the distance between the plurality of conductors constituting each phase and the observation point is almost equal for all three phases. This is because the configuration is close to. Therefore, it is preferable to increase the number of conductors per phase. However, since the cable structure becomes complicated as the number of conductors increases, the number of conductors is preferably 2 to 6, particularly 2 to 4. Since the background noise was 0.8 mG at the time of measuring the magnetic flux density, the magnetic field was reduced to substantially background noise in about 3 m in particular in Examples 2 and 3.
[0022]
【The invention's effect】
As described above, the power cable according to the present invention is a three-phase AC power cable in which one of the three phases is arranged at the center using two or more conductors, Alternatively, other two-phase conductors are arranged on the same circumference, and the other two-phase conductors each use two or more conductors, and are alternately arranged at equal intervals for each phase. It is characterized by. Therefore, the surrounding magnetic field can be effectively reduced.
[Brief description of the drawings]
FIG. 1 is a main part explanatory view showing an embodiment of a power cable according to the present invention.
FIG. 2 is an explanatory diagram showing a main part of another embodiment of the present invention.
FIG. 3 is a main part explanatory view showing still another embodiment of the present invention.
FIG. 4 is a main part explanatory view showing still another embodiment of the present invention.
FIG. 5 is a graph showing measurement results.
FIG. 6 is a main part explanatory view showing an embodiment of a conventional power cable.
FIG. 7 is a main part explanatory view showing another embodiment of a conventional power cable.
FIG. 8 is a main part explanatory view showing another embodiment of a conventional power cable.
FIG. 9 is a main part explanatory view showing another embodiment of a conventional power cable.
FIG. 10 is a main part explanatory view showing another embodiment of a conventional power cable.
FIG. 11 is an explanatory diagram of a magnetic field of a conventional power cable.
FIG. 12 is an explanatory diagram of a magnetic field of a conventional power cable.
[Explanation of symbols]
a, b, c conductor

Claims (1)

In a three-phase AC power cable, one of the three phases is arranged in the center using two or more conductors, and the other two A power cable comprising phase conductors, the other two-phase conductors using two or more conductors, and alternately arranged at equal intervals for each phase.

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