Improvements in Electric Mains.
Year: 1892

page_text: Date of Application, 6th May, 1892
Complete Specification Left, 6th Feb., 1893-Accepted, 11th Mar., 1893
PROVISIONAL SPECIFICATION.
Improvements in Electric Mains.
I, THOMAS TOMLINSON, of Lynton, Durham Road, Raynes Park, in the
County of Surrey, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
:-
It has often been proposed to insulate electric conductors by placing them in a
trough and whilst they are kept apart by spacing pieces to fill in the trough
with asphalte or some asphalte like compound with sufficiently good insulating
properties.
This system gives very good results so long as there is no material heating of the
conductors but it gives no facilities for extension.
According to this invention I adopt this system of insulation but instead of
employing solid conductors as has hitherto been done I employ tubular conductors
with their ends open to the air in manholes, across which the conductors are joined
by insulated cables. By these means the heat is readily dissipated. The arrange-
ment also has the advantage of making provision for extension of demand by the
drawing of bare or insulated conductors into the copper pipes.
"
Dated this 5th day of May 1892.
THOMAS TOMLINSON.
COMPLETE SPECIFICATION.
Improvements in Electric Mains.
I, THOMAS TOMLINSON, of Lynton, Durham Road, Raynes Park, in the
County of Surrey, Electrical Engineer, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
It has often been proposed to insulate electric conductors by placing them in a
trough and whilst they are kept apart by spacing pieces to fill in the trough
with asphalte or some asphalte like compound with sufficiently good insulating
properties.
This system gives very good results so long as there is no material heating of the
conductors but it gives no facilities for extension.
According to this invention I adopt this system of insulation but instead of
employing solid conductors as has hitherto been done I employ tubular conductors
with their ends open to the air in manholes, across which the conductors are joined
by insulated cables. By these means the heat is readily dissipated. The arrange-
ment also has the advantage of making provision for extension of demand by the
drawing of bare or insulated conductors into the pipes.
The invention may be carried out as is shown in longitudinal and cross section
by Figures and 2.
A trough a preferably of concrete, but it may be of brickwork, cast or wrought
iron or other suitable material is first laid in the ground and into this are laid the
conductors in the form of tubes bb suitably supported on pottery rings cc threaded
upon the tubes and serving as insulators. Into the trough around the tubes is
poured a suitable asphaltic compound of sufficiently good insulating properties.
Over this compound when filled to the top of the trough a piece of calico or other
suitable material d is placed to prevent the intrusion of stones, dirt, etc., from the
sides of the trench. While in this condition the insulation may be practically

page_text: tested by high tension (1000) volts from tube to tube and from tube to earth. The
presence of any dirt, stones or moisture will be shown by the bubbling of the
compound at the point, when the current can be stopped and the imperfection
removed.
་
Over the calico is then placed a line of slates tiles or the like and more concrete e
to form a covering.
If a higher insulation is required than is given by the compound it may be
gained by lightly insulating the tubes preferably with an insulating varnish.
The asphaltic composition which I prefer to employ is made of coal tar 5 parts,
pitch 5 parts. The tar is boiled until all moisture is expelled and then the pitch
is added and melted in the tar. On cooling a sample of the material it should
harden but still remain somewhat plastic, if it be at all brittle more tar is to be
added.
At convenient distances apart the tubes terminate with open ends in manholes
which may conveniently be built in brick.
Figures 3 and 4 are vertical sections and show one of these manholes,
The tubes bb at their entrance into the manholes pass through holes in special
bricks of glazed pottery made with recesses ff into which rubber rings are forced
-they fit round the tubes and make tight joints.
On the ends of the tubes are copper connectors upon which the electrical
connections of the coupling cables g g are made. When required copper wires or
rods are drawn through the tubular main to increase its metallic section and
consequently its ability to carry current. The wires or rods may be made fast to
the flanges at the ends of the tubes.
If water in the manholes is likely to prove troublesome short pieces of rubber
tubing h are fitted on the outside of the tubes and led up close to the surface. If
the ends of the connectors are insulated no short circuit from water can occur.
When laying mains intended to carry high tension currents I use woven wire or
metallic gauze as a cover for the asphaltic composition either alone or in conjunction
with cotton cloth and I connect this metallic covering to earth at short intervals,
this I do as a precaution and to protect workmen opening the ground in the
neighbourhood of the main.
The principal advantages which I derive from the use of tubular conductors
opening into manholes and embedded in asphaltic cement are that the small amount
of heat generated in consequence of the resistance of the conductor finds ready
escape and risk of injury to the insulation is avoided. Also that the dimension of
the conductor can be virtually increased at will by drawing in copper wires or rods
through the interior of the tubes.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. Electric mains substantially as described consisting of copper tubes embedded
in asphaltic cement and open at the extremities.
2. Electric mains substantially as described consisting of a trough, tubular
conductors open at the end laid therein, insulators supporting the conductors and a
filling of asphaltic composition.
3. Electric mains substantially as described consisting of copper tubes embedded
in asphaltic composition, and with copper wires or rods drawn through them and
aiding the tubular conductor in conveying the current.
4. Electric mains substantially as described consisting of copper tubes open at
the ends and embedded in asphaltic composition, and laid in a series of lengths
coupled together in manholes by short connecting pieces of cable.
Dated this 6th day of February 1893.
THOMAS TOMLINSON.