JPH0576247B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improved cross-bond grounding method for cables with metal sheaths.

(Technical Background of the Invention) In a cable with a metal sheath, an induced voltage is generated in the sheath. Therefore, in the case of a long cable, a pair of ordinary connection parts is grounded, and a plurality of metal sheaths are connected between the ordinary connection parts. The sheath voltage is limited by the cross-bond grounding method, which is divided by the insulated connections of the

In this cross-bond grounding method, conventionally, the cross-bond section between normal connections is divided into three spans by two insulated connections, and when each span length is equal, the sheath potential at each span is Since the vector sum becomes almost zero, sheath circuit loss can be reduced.

(Problems with the Background Art) However, in reality, the span lengths between the cross section bonds become non-uniform depending on the situation of the cable installation route, and sometimes they have to be made non-uniform.

In addition, in the cables that have already been laid, 3
In order to form a cross-bond section of a span, the metal sheaths of two adjacent spans may be connected at an ungrounded common connection; in this case, the two adjacent spans are electrically connected to one span. Therefore, the span length was often uneven. Since the sheath current increases when the span length is uneven in this way, the sheath current has conventionally been controlled by limiting the allowable cable current or by installing a sheath current suppressor.

(Object of the Invention) An object of the present invention is to provide a cross-bond grounding system for cables that does not require limiting the allowable cable current even if each span has a non-uniform length.

(Summary of the Invention) The present invention is characterized in that the cross-bond section is divided into four or more spans, and spans at predetermined positions with different span lengths are combined to divide the cross-bond section into three electrically equivalent spans. shall be.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a cable 1 having a metal sheath installed by the cross-bond grounding method according to the present invention. , a cross bond section m is formed. The cable sheath of this cross-bond section m is divided into four spans by three insulating connections 3. Then, from the one normal connection part 2 side, the first to fourth
If the span is Am, the first span length is Am, and the second span length is Am.
The span length of the third span is Bm, the third span length is Cm, the fourth
The span lengths of each have length Dm,
The second span length Bm and the third span length Cm are set to be substantially the same length, and the first span length Am and the fourth span length Dm are smaller than the second and third span lengths, And the sum of these (Am + Dm) is the second
The length is set to be approximately the same as the span length Bm (third span length Cm). Therefore, the relationship between each span length Am, Bm, Cm, and Dm can be expressed by the following equation.

A+D≒B≒C...(1) Therefore, by the above formula (1), the cross bond section m
As shown in FIG.
It is divided into three electrically equivalent spans.

As a result, the vector sum of the sheath potentials becomes almost zero in the cross-bond section m divided into four spans in FIG. 1, so there is no need to limit the allowable current of the cable 1.

From the above, if it is not possible to divide the span into 3 equivalent spans and provide a cross-bond section, then divide the cross-bond section into 4 spans using the three insulated connections 3 so as to satisfy the relationship in equation (1) above. What is necessary is to form a bond section.

Another embodiment of the invention is shown in FIG. That is, in this embodiment, the cross bond section m
is divided into 5 spans by four insulated connections 3, with a first span length Am and a fourth span length Am.
The sum of Dm (Am+Dm), the sum of the second span length Bm and the fifth span length Em (Bm+Em), and the third
The span lengths are set so that the span lengths Cm and Cm of .

A+D≒B+E≒C...(2) Therefore, as shown in FIG.
It is divided into three electrically equivalent spans.

FIG. 5 shows yet another embodiment of the invention. That is, in this embodiment, the cross bond section m is divided into six spans by five insulated connection parts 3, and the sum of the first span length Am and the fourth span length Dm (Am+Dm) and the second span length Span length Bm
Each span length is set so that the sum of the fifth span length Em (Bm + Em) and the sum of the third span length Cm and the sixth span length Fm (Cm + Fm) are approximately the same, and the following formula The relationship shown in (3) is established.

A+D≒B+E≒C+F...(3) Therefore, as shown in FIG.
It is divided into three electrically equivalent spans.

(Effects of the Invention) According to the present invention, by dividing a cross bond section into four or more spans and combining spans at predetermined positions with different span lengths, the cross bond section can be divided into three spans of electrically equivalent length. can be formed into a configuration. Therefore, even if it is impossible to divide the cross-bond section into three spans of equal length depending on the cable installation conditions, it is possible to install the cable sheath so that the vector sum of the sheath potentials is approximately zero. Therefore, there is no need to limit the permissible current of the cable or provide a sheath current suppressor.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the cross-bond grounding method of the present invention, Fig. 2 is a diagram equivalently showing the grounding example of Fig. 1, and Fig. 3 is a diagram showing another example of the grounding of the present invention. , FIG. 4 is a diagram equivalently showing the grounding example in FIG. 3,
FIG. 5 is a diagram showing still another example of grounding according to the present invention, and FIG.
This figure is a diagram equivalently showing the grounding example of FIG. 5. 1... Cable, 2, 2'... Normal connection part, 3,
3'...Insulated connection part.

Claims (1)

[Claims] 1 The metal sheath of a long cable is grounded at a pair of normal connections to form a cross-bond section, and the metal sheath of the cross-bond section is divided into four or more spans at a plurality of insulated connections. A cross-bond grounding system for a cable, characterized in that the sum of at least two spans selected from the spans and half of the sum of the remaining spans are each set to be substantially the same.