Power cable, power cable system, method of grounding power cable system and method of constructing power cable system

1. A power cable comprising:

a conductor;

an insulator;

an inner shield layer;

an inner corrosion-proof layer;

an outer shield layer; and

an outer corrosion-proof layer, provided from center toward outside,

wherein only the inner shield layer among the inner shield layer and the outer shield layer is directly grounded at one end of the power cable in an axial direction, and

wherein only the outer shield layer among the inner shield layer and the outer shield layer is directly grounded at the other end of the power cable in the axial direction.

2. The power cable according to claim 1 , wherein the power cable is configured such that, for both cases when a power source that supplies electric power to the conductor is connected to the one end of the power cable in the axial direction, and to the other end of the power cable in the axial direction, when a ground fault occurs in the power cable, a fault current flows to an earth ground at a power source side through either of the inner shield layer and the outer shield layer.

3. A power cable system comprising:

a power cable including a conductor, an insulator, an inner shield layer, an inner corrosion-proof layer, an outer shield layer, and an outer corrosion-proof layer, provided from center toward outside,

wherein only the inner shield layer among the inner shield layer and the outer shield layer is directly grounded at one end of the power cable in an axial direction, and

wherein only the outer shield layer among the inner shield layer and the outer shield layer is directly grounded at the other end of the power cable in the axial direction.

4. The power cable system according to claim 3 , further comprising a pipe line buried in the ground and through which the power cable is inserted.

5. The power cable system according to claim 4 , further comprising:

a plurality of the power cables; and

a plurality of the pipe lines that are provided to be apart from each other in a horizontal direction,

wherein the plurality of the power cables are inserted in the plurality of pipe lines, respectively.

6. The power cable system according to claim 5 , wherein the power cable is configured such that, for both cases when a power source that supplies electric power to the conductor is connected to the one end of the power cable in the axial direction, and to the other end of the power cable in the axial direction, when a ground fault occurs in the power cable, a fault current flows to an earth ground at a power source side through either of the inner shield layer and the outer shield layer.

7. A method of grounding a power cable system, comprising:

preparing a power cable including a conductor, an insulator, an inner shield layer, an inner corrosion-proof layer, an outer shield layer, and an outer corrosion-proof layer, provided from center toward outside;

directly grounding only the inner shield layer among the inner shield layer and the outer shield layer at one end of the power cable in an axial direction; and

directly grounding only the outer shield layer among the inner shield layer and the outer shield layer at the other end of the power cable in the axial direction.

8. A method of constructing a power cable system, comprising:

excavating a pipe line inserting hole in the ground;

inserting a pipe line in the pipe line inserting hole;

inserting a power cable including a conductor, an insulator, an inner shield layer, an inner corrosion-proof layer, an outer shield layer, and an outer corrosion-proof layer, provided from center toward outside, in the pipe line;

directly grounding only the inner shield layer among the inner shield layer and the outer shield layer at one end of the power cable in an axial direction; and

directly grounding only the outer shield layer among the inner shield layer and the outer shield layer at the other end of the power cable in the axial direction.