Gas pipe cable

A three phase gas pipe cable is disclosed which has at least one gas pipe cable section in which three phase conductors are arranged in a triangular configuration within an enclosing pipe. Each phase conductor is supported by at least one supporting insulator such that the longitudinal axis of each phase conductor is substantially parallel to the longitudinal axis of the enclosing pipe. The supporting insulator is connected by a slide bearing member to the enclosing pipe. The slide bearing member accommodates an insulator foot end of the supporting insulator in such a manner that the supporting insulator is capable of motion in the direction of the longitudinal axis of the enclosing pipe. When the phase conductors linearly expand as a result of differential heating of the phase conductors, each phase conductor is free to expand in the longitudinal direction thereby moving the supporting insulator associated with each individual phase conductor a corresponding amount in the axial direction with no detrimental mechanical effects to any part of the gas pipe cable. A single compensator for each phase conductor in each gas pipe cable section is sufficient to absorb the thermal expansion of each phase conductor.

BACKGROUND OF THE INVENTION 
The present invention relates to gas pipe cables, and more particularly to 
a three phase gas pipe cable having three phase conductors arranged in an 
enclosing pipe and supported therein by supporting insulators. 
In a conventional gas pipe cable, such as that disclosed in U.S. Pat. No. 
3,919,456, three phase conductors are arranged within a common enclosing 
pipe. The phase conductors are arranged in a triangular configuration, and 
are each held on ring supports by supporting insulators. At each 
supporting location of each phase conductor two supports are provided. The 
longitundinal axes of the two supports intersect at an angle. Each axis is 
positioned with respect to the axes of the supports of the other phase 
conductors such that when the gas pipe cable is viewed in cross-section, 
the axis of each supporting insulator passes substantially through the 
centers of two phase conductors. In this simple and effective gas pipe 
arrangement, electrodynamic current forces occurring between the phase 
conductors, particularly in the case of a short circuit, may be controlled 
with little effort. However, such conventional gas pipe cables are subject 
to detrimental mechanical effects caused by differential heating of the 
phase conductors. 
In conventional gas pipe cables the phase conductors are supported by 
supporting devices arranged periodically in the enclosing pipe. When the 
phase conductors are exposed to differential heating, the phase conductors 
undergo differential linear expansion. The differential linear expansion 
applies nonuniform shear stresses or torques to the supporting devices. 
Therefore, the supporting devices must be solidly anchored to the 
enclosing pipe using special methods which are cumbersome, labor intensive 
and costly. If such special methods are not employed, however, the 
differential linear expansion of the phase conductors may cause the 
supporting devices to overturn. 
It is therefore an object of the present invention to provide a gas pipe 
cable in which the differential heating of the phase conductors, even in 
the case of short circuits, will not have detrimental mechanical effects 
on any part of the cable. 
SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, a gas pipe 
cable includes phase conductors which are supported in an enclosing pipe 
in such a manner that each phase conductor is individually dilatable. As 
such, when the phase conductors are exposed to differential heating, each 
phase conductor is free to individually expand in the axial or 
longitudinal direction. Consequently, the supporting insulators cannot be 
stressed to overturning. In a gas pipe cable according to the present 
invention, a single thermal expansion compensator is sufficient for each 
phase conductor in each section of the gas pipe cable. 
According to a preferred embodiment of the present invention, a gas pipe 
cable includes shielding electrodes which permit relatively uniform fields 
to exist between the phase conductors and the enclosing pipe even though 
the phase conductors may each be in relatively different positions with 
respect to their supporting insulators and associated apparatus as a 
result of differential thermal expansion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a gas pipe cable includes a phase conductor 4a 
supported at each of two supporting locations 4 by a supporting insulator 
1. Each supporting insulator 1 is fixedly connected to the phase conductor 
4a at the support points 4 of the phase conductor by an inlet fitting 1b 
included at the end of the supporting insulator facing the phase conductor 
4a. The inlet fitting includes a threaded lug 1c which threadedly engages 
a threaded piece 4d included on the phase conductor 4a. The threaded piece 
4d includes two threaded holes which receive the threaded lugs 1c 
associated with each of the supporting insulators 1 supporting the phase 
conductor 4a. A washer 9 is included between each supporting insulator 1 
and the phase conductor 4a. 
When the threaded lugs 1c are threadedly connected to the threaded piece 4d 
so that the supporting insulators 1 are connected to the phase conductor 
4a, the longitudinal axes of the supporting insulators 1 intersect 
substantially at the center of the phase conductor 4a. An angle of 
intersection is included between the axes of the supporting insulators. 
The angle of intersection between the longitudinal axes of the supporting 
insulators associated with phase conductor 4a, and the angles of 
intersection between the supporting insulators associated with phase 
conductors 4b and 4c (FIG. 3b) are equal in magnitude. 
Each supporting insulator 1 includes a foot 1a which accommodates an inlet 
fitting 1d. Each supporting insulator 1 includes a shielding electrode 7 
at the foot 1a. 
The inlet fitting 1d connects the supporting insulator 1 to a slide bearing 
2. A sliding bolt 2c of the slide bearing 2 is connected by a coupling nut 
11 to the foot 1a of the insulator. A fastening device 11a, such as a lock 
washer, is included. And, an intermediate piece 10 is included between the 
sliding bolt 2c and the inlet fitting 1d. 
The sliding bolt 2c is accommodated in a groove 2b included in a slide 
bearing block 2a in a bearing-like manner. The groove 2b is substantially 
parallel to the longitudinal axis of the phase conductor 4a, and is 
substantially parallel to the longitudinal axis of an enclosing pipe 3. So 
accommodated, the sliding bolt 2c is capable of slide motion in the 
direction of the longitudinal axis of the enclosing pipe 3, and of the 
phase conductors 4a, 4b and 4c. 
The slide bearing block 2a is fastened to the enclosing pipe 3. The slide 
bearing block includes a bearing block foot 2h which accommodates a lock 
nut 12. The lock nut 12 is fastened to an arcuate sheet metal part 8 
welded to the enclosing pipe 3. Alternately, the slide bearing block 2a 
may be directly welded to the arcuate sheet metal part 8 and to the 
enclosing pipe 3. The arcuate sheet metal part 8 spatially separates the 
two slide bearing blocks 2a associated with a particular phase conductor 
from each other. 
When differential heating of the phase conductors occurs in a gas pipe 
cable according to the present invention, such as that which may occur 
between phase conductors located at the top and at the bottom of an 
underground or buried three phase gas pipe cable, the corresponding 
differential linear expansion of the phase conductors will not stress the 
gas pipe cable according to the present invention to failure. The slide 
bearings 2 allow each phase conductor 4a, 4b and 4c to freely expand in 
the axial direction by permitting each supporting insulator 1 rigidly 
connected to a phase conductor to freely slide in the axial direction in 
response to the linear expansion of that phase conductor. In a gas pipe 
cable according to the present invention, neither the individual 
insulators 1, nor the slide bearing block 2a, nor any other part 
associated with the mounting of the phase conductors 4a, 4b or 4c will be 
stressed to failure as a result of differential heating of the phase 
conductors. 
Due to the differential linear expansion of the phase conductors, the slide 
bearing blocks associated with each phase conductor may be located at 
relatively different locations in the enclosing pipe 3 with respect to the 
slide bearing blocks associated with each of the other phase conductors. 
In order to render the fields between the phase conductors 4a, 4b, 4c and 
the enclosing pipe 3 as uniform as possible, the shielding electrode 7 is 
included at the foot 1a of each supporting insulator 1. 
Referring to FIG. 2a, in one embodiment of the present invention the 
sliding bolt 2c includes a cylindrical part 2e and two ends 2d in the 
shape of truncated conical sections. The slide bearing block 2a includes 
an end face 2f at each end of the slide bearing block. The truncated 
conical section ends 2d facilitate mounting of the sliding bolt 2c. 
Referring to FIG. 2b, in another embodiment of the present invention the 
sliding bolt 2c includes two annular grooves 2g. Each annular groove 2g 
accommodates a locking washer 6. When so accommodated, the locking washers 
6 are separated from each other by a distance equal to the distance 
separating the end faces 2f of the slide bearing block 2a. The locking 
washers 6 cooperate with the end faces 2f to prevent relative movement 
between the sliding bolt 2c and the slide bearing block 2a in the axial 
direction. 
Referring to FIG. 3a, a gas pipe cable according to the present invention 
includes a gas pipe cable section 5 having ends 5a. A thermal expansion 
compensator 13 associated with phase conductor 4a is included between ends 
of phase conductor sections 4a.sub.1 and 4a.sub.2. Similarly, a thermal 
expansion compensator 13 is included between ends of phase conductor 
sections 4b.sub.1 and 4b.sub.2 of phase conductor 4b, and between ends of 
phase conductor sections 4c.sub.1 and 4c.sub.2 of phase conductor 4c (not 
illustrated). 
Slide bearings 2j located at each end 5a of the gas pipe cable section 5 
are locked by locking washers 6 as illustrated in FIG. 2b. Consequently, 
linear thermal expansion of the phase conductors located between the two 
ends 5a may take place only in the direction of the compensators 13, which 
absorb such expansions. The slide bearings 2 located between locked slide 
bearings 2j are not locked. 
Referring to FIG. 3b, a cross-sectional view of the gas pipe cable section 
5 of FIG. 3a is illustrated. The phase conductors 4a, 4b, 4c are each 
supported by two supporting insulators 1. The supporting insulators 1 are 
arranged in the enclosing pipe 3 such that the longitudinal axis of each 
supporting insulator substantially corresponds to that of another 
supporting insulator. So arranged, the longitudinal axis of each 
supporting insulator substantially passes through the longitudinal axis of 
two phase conductors. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing specification. The 
invention which is intended to be protected herein, however, is not to be 
construed as limited to the particular forms disclosed, since these are to 
be regarded as illustrative rather than restrictive. Moreover, variations 
and changes may be made by those skilled in the art without departing from 
the spirit of the present invention.