Latch structure for insulator spacer

A support insulator disk for a flexible high voltage transmission line supports a flexible central conductor along the central axis of a conductive outer housing which is transversely corrugated for flexibility. A plurality of such axially spaced disks are provided along the axis of the transmission line. Each disk consists of identical halves which are snapped together over the central conductor by identical snap latch pairs on the opposite sides of the halves. Each latch pair consists of an extending flexible member centrally located on the outer rim of the disk, and which overlies the other half and snaps into a depression in the other half. A direct line-of-sight is prevented from the central conductor to the outer conductive enclosure at the joint between the two halves of the insulator.

RELATED APPLICATIONS 
This application is related to copending applications S.N. 734,965, filed 
Oct. 22, 1976, in the name of Philip C. Netzel and Thomas F. Brandt, 
entitled INSULATION SER FOR FLEXIBLE GAS-INSULATED TRANSMISSION LINE; 
S.N. 808,709 filed June 21, 1977, in the name of Thomas F. Brandt, 
entitled OFFSET CONSTANT THICKNESS WEB FOR INSULATOR, and application S.N. 
808,707 filed June 21, 1977, in the name of Philip C. Netzel and Jonathan 
Z. Ponder, entitled IMPROVED INSULATOR FOR FLEXIBLE GAS-INSULATED 
TRANSMISSION LINE,. 
BACKGROUND OF THE INVENTION 
This invention relates to flexible gas-insulated transmission lines, and 
more specifically relates to a novel support insulator for supporting a 
central flexible conductor within an outer corrugated grounded housing. 
Flexible high voltage gas-insulated transmission lines are well known, 
wherein a central conductor is supported within a grounded housing which 
is filled with an insulation gas, such as sulfur hexafluoride, under 
pressure. Flexible transmission lines of this type are disclosed in 
above-noted copending application S.N. 734,965. Transmission lines of this 
type and support insulators therefor are also disclosed in U.S. Pat. No. 
3,789,129, in the name of Ditscheid, and in U.S. Pat. No. 3,996,414, in 
the name of Artbauer et al. 
The prior art latch structure consists of a split latch having, side by 
side, an extending positive latch member, and a recessed latch depression. 
When the latch members are engaged, there is an interruption in the solid 
rim of the insulator, which provides a line-of-sight from the central 
conductor to the outer housing. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
The improved latch structure of the present invention consists of an 
extending latch member which is centrally located on the insulator rim, 
and extends from one insulator half over to the identical opposite 
insulator half and into a cooperating recess on the other insulator. The 
recess then contains the extending latch member both circumferentially and 
axially, and prevents a line-of-sight from the central conductor to the 
outer housing at the joint between the two halves of the insulator. This 
increases the creepage path between the central conductor and its 
enclosure. The insulator halves are formed of any desired relatively 
inexpensive thermoplastic insulation material, which has a thin support 
wall which connects the circular inner and outer rims of the insulator 
half.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring first to FIGS. 1 and 2, there is shown a section of typical 
flexible gas-insulated transmission line for conducting electric power at 
low frequency, for example, 60 Hz., and at high voltage, for example, 
230,000 volts. The transmission line consists of a central flexible 
conductor 20, an outer flexible grounded housing 21, and spaced support 
insulators 22 and 23 which support conductor 20 within housing 21. 
The central conductor 20 can be constructed in any desired manner, and is 
shown as consisting of concentric corrugated copper tubes 24 and 25 which 
support segmented groups of conductive strands between them, including 
typical groups 26 and 27. The effective cross-sectional area of central 
conductor 20 is 3600 square millimeters, and conductor 24 has an outer 
diameter of about 100 millimeters. 
Outer conductor 21 consists of a corrugated aluminum tube having an outer 
diameter of about 300 millimeters. Conductor 21 is formed by wrapping 
sheet material around insulators 22 and 23 formed on conductor 20, and is 
then welded on a longitudinal weld seam. The tube is then corrugated with 
corrugations which are parallel to one another and perpendicular to the 
axis of tube 21, or with corrugations which are threaded around the axis 
of tube 21. The corrugations may have a depth of about one inch, and a 
crest-to-crest spacing of about two inches. 
The support insulators 22 and 23 are only schematically shown in FIGS. 1 
and 2 and each consists of inner and outer rims 30, 31 and 32, 33, 
respectively, joined by thin transverse webs 34 and 35, respectively. The 
construction of the insulators 22 and 23 is the subject of the present 
invention and will be described in detail in connection with FIGS. 3 to 
13. 
The interior of housing 21 is filled with clean sulfur hexafluoride at a 
pressure of about 45 p.s.i.g. at room temperature, and the assembly is 
provided with terminals at either end and is sealed. 
The assembly of FIGS. 1 and 2 can have any desired length and may be reeled 
on a 3.7 meter diameter reel for shipment to an installation site. 
FIGS. 3 is a perspective view of an insulator 40 which is constructed in 
accordance with the present invention wherein the insulator 40 is made of 
two halves 41 and 41a, which are identical to one another. Halves 41 and 
41a can be snapped over the central conductor of a transmission line, such 
as the conductor 24 in FIGS. 1 and 2, to serve the function of one of the 
insulators 22 or 23 in FIG. 2. 
FIGS. 4 to 12 show the details of the construction of one of the halves 41 
of the insulator of FIG. 3. Thus, the insulator half 41 consists of an 
inner hub 42 which has an interior surface shape adapted to follow the 
corrugation of the central conductor of the gas-insulated transmission 
system so that the inner hub section will nest within the troughs of the 
outer corrugated section of the central conductor. The insulator half 41 
is also provided with an outer rim 43 which fits within the interior of 
the outer conductive housing 21 of the gas-insulated transmission line as 
shown in FIGS. 1 and 2. The outer rim 43 is fixed to the inner hub 42 by a 
support web 44, which is of offset configuration, as will be later 
described, in order to increase the mechanical strength of the insulator. 
The outer rim 43 of insulator 41 is provided with two spring-like sections 
50 and 51 which are formed by transverse cuts through rim 43, and by 
slotting the web 44 with slots 52 and 53, respectively, which communicate 
with the cuts in rim 43. Sections 50 and 51 of the rim 43 project beyond 
the outer circumference of the rim 43 when unstressed. They have a 
cross-section thicker at the center than at the outer ends, as shown in 
FIG. 12, from member 51 to increase their spring constant. Thus, as shown 
in FIG. 12, the center region 54 of rim 51 is thicker than the edge 
regions 55 and 56. Sections 51 and 52 serve as springs which are securely 
gripped by the interior diameter of the outer conductive housing 21 of 
FIGS. 1 and 2 to help retain the insulator in its proper location. 
In order to center the hub 42 of half 41 with respect to the cooperating 
hub of the half 41a in FIG. 3, one side of the face of the hub half is 
provided with a projecting key section 60, which is seen in FIGS. 4, 5, 6 
and 11, while the opposite side of the face of hub 42 has a keying 
depression 61 as seen in FIGS. 4 and 10. When the two hubs of the two 
cooperating halves 41 and 41a are to be assembled, the keying projection 
60 of one enters the keying depression 61 of the other in order to lock 
the hub sections against relative axial motion with respect to one another 
after the two insulator halves are latched in place over the central 
conductor. 
The outer latch structure on the outer rim 43 consists of a flexible 
central latching projection 70 (that is centrally located on the rim 43) 
which has a centrally disposed raised latch section 71 as best seen in 
FIGS. 4, 5, 6, 7 and 8. Projection 70 is made flexible by virtue of a thin 
slot 72 in the web 44 as shown in FIGS. 5 and 6. The opposite side of the 
insulator half 41 has a latch-receiving portion 80 which consists of a 
reinforced rim region having a central latch-receiving depression 81 
therein as best shown in FIGS. 4 to 7. The latch-receiving depression 81 
is contoured to cooperate in shape with the latch structure 71 on the 
opposite end of the half 41. In addition, the portion 80 is provided with 
a camming surface 82 leading to the latch depression 81. Thus, when two 
halves 41 and 41a of the insulator are to be snapped together, each 
latch-raised section 71 will be cammed up each ramp section 82 and then 
will snap into depression 81 in order to lock the opposite halves of the 
two insulator halves together. 
When the halves are completely latched, the keying members 60 will also be 
disposed in their keying projections 61. It will be noted that the latch 
member 71 fits securely within the side-to-side confines of 
latch-receiving depression 81 and thus the outer rim 43 will be fixed in 
axial position at the region where the two insulator halves are latched 
together. 
It will also be noted that, since the latched member 70 completely overlies 
the latch member 80 over the full width of rim 43 when two insulator 
halves are brought together, there will be no line-of-sight from the 
central hub 42 of the insulator, where the central conductor is contained, 
to the outer conductive housing which surrounds the outer rim 43. Thus, 
the insulator of the present invention provides improved creepage distance 
between the central conductor and the outer grounded housing in the 
gas-insulated transmission system. 
The web 44 which joins the hub 42 to the outer rim 43 is provided with 
several offsets in order to increase the web strength while still using a 
relatively thin section for the web. Thus, when molding insulators, it has 
been found the use of heavy web sections tends to create voids in the web 
which is deleterious to the dielectric performance of the insulator. 
Moreover, relatively thick web sections have a deleterious affect on the 
dielectric behavior of the insulator. 
The arrangement shown in FIGS. 3 to 12 permits the use of a constant 
thickness, thin web section without requiring enlarged ribs for 
strengthening the web section. Thus, the web has several offsets in its 
axial direction on either side of a plane through the axial center of the 
insulator. These offset sections are shown in FIGS. 5 to 9. As seen in 
FIGS. 6 and 7, the web portions 80a, 81a and 82a lie to the right of the 
axial center of the insulator half 41 while the web regions 83 and 84 lie 
to the left of the axial center of the insulator half 41. The staggered 
web regions 80a, 81a, 82a, 83 and 84 are joined by suitable wall sections 
which extend at an angle to the plane of the insulator 41-41a. By way of 
example, the drawings show three sections 80a, 81a and 82a in a common 
plane which is spaced from the common plane containing sections 83 and 84 
by about one inch. Note further that the sections 80a, 81a, 82a, 83 and 84 
may be generally pie-shaped as shown. Any desired number of sections could 
have been chosen. It has been found that, when this configuration is used, 
a constant web thickness, for example, four millimeters, may be used for 
the web 44. 
FIG. 9 shows two sections 90 and 91 which join web portions 83 and 84 to 
the web sections 81a and 82a, respectively. It can be seen that connecting 
portions 90 and 91 have components in both the axial direction and radial 
direction of the plane of the insulator half, and specifically the 
interconnecting sections 90 and 91 are at about 45.degree. to the plane of 
the insulator half. When using this configuration of a relatively thin but 
constant thickness web with offset regions, it has been found that the 
stiffness modulus of the insulator is 2 to 3 times the stiffness modulus 
of the same insulator using a web contained in a single plane. 
Clearly, other configurations could be used for the offset web other than 
the specific offset pattern illustrated, and different numbers of offsets 
can be used having a different cross-section from that shown. 
The insulator material to be used in connection with the insulator body of 
the present invention may be of any desired type and one insulation 
material which has been found useful is acrylic plexiglass DR61k. This is 
a clear material and permits visual inspection of the insulator for flaws 
created during the molding process. 
Although a preferred embodiment of this invention 10 has been described, 
many variations and modifications will now be apparent to those skilled in 
the art, and it is therefore preferred that the instant invention be 
limited not by the specific disclosure herein but only by the appended 
claims.