Note: Descriptions are shown in the official language in which they were submitted.
CA 02370661 2001-10-17
WO 00/63500 PCT/EP00/03358
"AN APPARATUS FOR LAYING UNDERGROUND ELECTRIC CABLES"
The present invention relates to an apparatus for laying
underground electric cables.
In more detail, said apparatus is intended for laying
electric cables in a trench, in particular when medium- or
high-voltage cables and preferably high- voltage cables are
concerned, of a value as high as, or greater than 150 kV,
where arrangement of a mass of inert material of suitable
thickness around the cable is particularly wished, which mass,
in addition to performing a function of mechanical protection
of the cable, also enables dissipation of the heat generated
by the cable when passed through by current.
Laying of electric cables for accomplishment of medium- or
high-voltage earth lines usually takes place within trenches
digged in the ground.
On laying, the cable is incorporated into a mass of inert
material, e.g. sand or poor concrete, usually carrying out a
mechanical protection of the cable itself (see US Patent
4,050,261, for example, and the article by F. Donazzi, E.
Occhini, A. Seppi, "Soil thermal and hydrological
characteristics in designing underground cables", Proc. IEE,
Vol. 126, No. 6, June '79) .
In more detail, for cable laying it is required that
preliminarily a base layer of inert material should be laid
down at the bottom of a trench, previously made by an
excavation operation. The cable unwound from a reel is then
deposited onto the base layer.
Subsequently, a covering layer of inert material is deposited
so as to form, with the previously deposited base layer, a
mass of inert material completely incorporating the cable.
The Applicant has perceived that laying of cables carried out
CA 02370661 2005-03-31
_ 2 -
by manual operations, in addition to involving an important
loss of time and manpower, does not offer sufficient
assurances as regards achievement of the prescribed
technical features in the inert material placed around the
cable. The Applicant has also become aware of the fact that
the thermal features of this material can vary to a great
extent depending on the compacting degree given to the
material during installation and that this compacting
degree, if the material is laid down manually, is not very
uniform and cannot be easily checked.
Document EP 0 585 188 Al discloses an apparatus for laying
underground electric cables comprising: a vehicle
longitudinally movable along a trench arranged to receive at
least one electric cable; a first deposition unit to form a
base layer of inert material at the bottom of said trench,
said first deposition unit comprising at least a first
conveying duct connected at the upper part thereof with feed
means for said inert material and at the lower part thereof
with a downwardly-turned discharge opening; at least one
guide structure, having an inlet end portion turned towards
the vehicle front, to engage at least one stretch of said
cable extended over the trench, and an outlet end portion
disposed at a lower position and turned to the back of the
first deposition unit for laying the cable on said base
layer; a second deposition unit operating at the rear of the
guide structure to form a covering layer of inert material
upon the base layer and the cable.
In accordance with one aspect of the present invention there
is provided an apparatus for laying at least an underground
electric cable, comprising: a vehicle longitudinally movable
over a trench arranged to receive at least one electric
cable; a first deposition unit to form a base layer of inert
material at the bottom of said trench, said first deposition
CA 02370661 2005-03-31
- 2a -
unit comprising at least a first conveying duct connected at
the upper part thereof with feed means for said inert
material and at the lower part thereof with a downwardly-
turned first discharge opening; at least one guide
structure, having an inlet end portion turned towards the
vehicle front, to engage at least one stretch of said cable,
and an outlet end portion disposed at a lower position and
turned to the back of the first deposition unit for laying
the cable on said base layer, said guide structure having at
least one central portion laterally disposed relative to
said first conveying duct; and a second deposition unit
operating at the rear of the guide structure to form a
covering layer of inert material upon the base layer and the
cable.
In accordance with embodiments of the present invention,
laying of underground electric cables is made by an
apparatus characterized in that the guide structure has at
least one portion laterally disposed relative to said first
conveying duct.
Preferably, said apparatus further comprises at least a first
compacting unit operatively interposed between the first
18-05-2001 EP 000003358
3 _
deposition unit and the outlet end portion of said guide
structure for compacting the base layer deposited at the
trench bottom.
In more detail, this compacting unit comprises a vibrating
plate acting against the base layer by a lower surface thereof
preferably having a substantially V-shaped cross-section
outline. Preferably, said V-shaped outline has a=rounded
vertex in the form of an arc of * a circle of a radius
substantially corresponding to half diameter of the cable.
Advantageously, said first conveying duct and said first
discharge opening have a width reduced by an amount of at
least 10% relative to the width of said trench.
Preferably, the first discharge opening is delimited at the
rear part thereof'by an outlet edge di:sposed at a higher level
than the lower surface of said vibrating plate. The vibrating
plate,.in turn, has a lead-in portion rising from said lower
surface in the direction of the outlet edge of the discharge
opening, and terminating at a higher level than said outlet
edge:
At least one presser roller elastically acting against the
cable to push it towards the base layer laid at the trench
bottom may be advantageously associated with the outlet end
portion of the guide structure.
The second deposition unit may advantageously comprise a
second conveying duct connected at the upper part thereof with
feed means 'for said .inert material, and at the lower part
thereof with a second.downwardly-turned discharge opening.
Preferably, said second conveying duct and said second
discharge opening have a width reduced by an amount of at
least 10% relative to the trench width.
CA 02370661 2001-10-17 AMENDED SHEET
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
4
Furthermore, with the second deposition unit may be associated
adjustment means operating at an outlet edge located at the
rear of the second discharge opening to adjust thickness of
said covering layer.
In accordance with a further aspect of the present invention,
the vehicle comprises a first van and a second van removably
engaged in mutual alignment and carrying the first deposition
unit and second deposition unit, respectively.
Moreover, said vehicle may comprise adjustable suspension
means operatively associated with respective wheels of the
vehicle for modifying the height of said first and second
deposition units and of said guide structure relative to the
trench bottom.
Preferably, said first and second vans are mutually in
engagement by at least one fluid-operated connecting actuator.
Further features and advantages will become more apparent from
the detailed description of a preferred, non exclusive,
embodiment of an apparatus for laying underground electric
cables, in accordance with the present invention. This
description will be set forth hereinafter with reference to
the accompanying drawings, given by way of non-limiting
example, in which:
- Fig. 1 is a diagrammatic side view, partly in section, of
an apparatus in accordance with the present invention, during
laying of an electric cable in a trench;
- Fig. 2 is a partially fragmentary top view of the apparatus
of Fig. 1;
- Fig. 3 is a sectional view taken along line III-III of Fig.
1.
With reference to the drawings, an apparatus for laying
underground electric cables in accordance with the present
invention has been generally identified by reference numeral
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
1. Apparatus 1 essentially comprises a vehicle 2 lending
itself to be longitudinally moved over a trench 3 previously
digged in the ground.
5 Advantageously, vehicle 2 is essentially comprised of a first
van 4 and a second van 5 removably linked in mutual alignment,
first van 4 being disposed at the front relative to the feed
direction of the vehicle itself.
Preferably, the mutual engagement between first and second
vans 4, 5 is obtained by at least one fluid-operated
connecting actuator 6, having one end 6a hinged along a
horizontal axis at the rear of first van 4 and a second end 6b
carrying a hooking element to be operatively engaged in a
respective housing arranged at the front of second van S. Upon
the action of fluid-operated actuator 6, the hooking element
lends itself to be moved away from or close to first van 4 in
order to facilitate engagement with second van 5 and enable
subsequent displacement of the two vans close to each other,
even in the presence of possible misalignments between them.
Preferably, vehicle 2 is arranged to be towed by a tractor,
not shown, through a drawbar 7 linked at the front with first
van 4. Associated with first van 4 is a pair of front wheels
8 mounted on a first axle 8a, whereas second van 5 is provided
with two pairs of wheels, front wheels 9 and rear wheels 10
respectively, which are mounted on a second and a third axles
9a, 10a, respectively.
A pair of auxiliary rollers 11, associated with first van 4 at
the rear thereof and adapted to be positioned in a vertical
direction by means of telescopic supports 11a equipped with an
adjustment handwheel llb are suitable for conveniently
supporting the rear portion of the first van when the latter
is disengaged from second van S.
Associated with first van 4 is a first deposition unit 12
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
6
adapted to form a base layer 13 of inert material for heat
dissipation at the bottom of trench 3. The employed inert
material may consist for example of poor concrete which, just
as an indication, will contain sand mixed with cement in a
percentage included between 5 and 10% by weight and water in
a percentage included between 8 and 10% by weight.
For this purpose, first deposition unit 12 essentially
comprises at least a first conveying duct 14 vertically
extending towards the bottom of trench 3 and connected, at the
upper part thereof, with feed means for the inert material,
e.g. consisting of a first loading hoop 15. The lower portion
of first conveying duct 14 terminates with a first downwardly-
facing discharge opening 16, close to the bottom of trench 3.
Advantageously, first conveying duct 14 is delimited by
perimetric walls substantially defining a bearing framework or
chassis 4a for first van 4, to which first axle 8a is applied,
as well as the other components associated with the first van.
First conveying duct 14 and first discharge opening 16 are
also advantageously provided to have a width reduced by an
amount of at least 10%, and preferably included between 15 and
25%, relative to the nominal width of the trench.
First discharge opening 16 is delimited at the back by an
outlet edge 16a preferably disposed at a raised position
relative to the remaining perimetric extension of the outlet
opening itself, at a given distance from the bottom of trench
3, just as an indication included between 250 mm and 400 mm.
Consequently, following to the forward movement of vehicle 2
along trench 3, the inert material flowing into first
discharge opening 16 through first conveying duct 14 is laid
down on the trench bottom to form a base layer 13 of a
starting thickness corresponding to the distance of outlet
edge 16a from the trench bottom.
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
7
Preferably, apparatus 1 further comprises at least one
compacting unit 17, operating immediately downstream of first
deposition unit 12, with reference to the feed direction of
vehicle 2 along trench 3, in order to compact base layer 13
previously deposited on the trench bottom.
In more detail, compacting unit 17 comprises at least one
vibrating plate 18, oscillatably linked to first van 4, e.g.
by elastic supports, and driven by a motor 19 provided with an
eccentric device to impart a vibratory motion to the plate
itself.
Vibrating plate 18 acts against base layer 13 by a lower
surface 18a thereof preferably having a shaped cross-section
outline, adapted to interact with a predetermined portion of
the cable surface. Preferably, said outline is substantially
V-shaped, as clearly shown in Fig. 3, according to a summit
angle "a" advantageously included between 100 and 160 , and
preferably of 130 . In addition, the vertex of the V-shaped
outline of lower surface 18a of vibrating plate 18 is
preferably provided to be radiused according to an arc of a
circle of a radius substantially corresponding to half the
diameter of electric cable 21 to be laid in trench 3.
Advantageously, outlet edge 16a of the first discharge opening
is disposed at a raised level relative to lower surface 18a of
vibrating plate 18. Vibrating plate 18, in turn, has a lead-in
portion 18b rising from lower surface 18a in the direction of
outlet edge 16a, and terminating at a higher level than said
edge.
Due to the action of e vibrating plate 18, the inert material
forming base layer 13, initially laid down with a width
corresponding to that of first conveying duct 14 and of first
discharge opening 16, is compacted and moved towards the side
walls of the trench.
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
8
Consequently, when the passage of vibrating plate 18 has been
completed, base layer 13 takes up the whole width of trench 3,
and even compensates for possible unevennesses inevitably
produced during excavation, and has an upper surface 13a with
a substantially V-shaped cross-section outline. The minimum
detectable thickness on base layer 13 after passage of
vibrating plate 18 is included, just as an indication, between
80 and 120 mm.
Furthermore, apparatus 12 comprises at least one guide
structure 20, having an inlet end portion 20a turned to the
front of vehicle 2, an outlet end portion 20b disposed below
and turned to the back of first deposition unit 12, and an
intermediate portion 20c extending between the inlet and
outlet end portions 20a and 20b.
Inlet end portion 20a comprises at least one front trestle 23
removably fastened to first van 4, e.g with the aid of
extractable pegs or equivalent removable connecting means.
More particularly, front trestle 23, having an upper portion
susceptible of being opened, is externally in engagement with
first conveying duct 14, close to the upper end of said duct,
and has a substantially funnel-shaped lead-in portion 23a
supported in cantilevered fashion at the front of first van 4
to longitudinally engage an electric cable 21 at the inside
thereof, in particular a high-voltage electric cable of the
fluid-oil-cooled type.
Cable 21 comes for example from a reel placed before vehicle
2. Alternatively, cable 21 can be previously laid down on the
ground along one side of trench 3. In both cases cable 21,
when engaged through the guide structure, has at least one
section thereof substantially longitudinally outstretched over
trench 3, before vehicle 2.
Inlet end portion 20a further comprises a plurality of front
rollers or equivalent sliding members 22, at least partly
WO 00/63500 CA 02370661 2001-10-17
PCT/EP00/03358
9
rotatably supported by front trestle 23 and such distributed
that they cause cable 21 to be obliquely deviated downwardly,
along a curvilinear path of travel of a sufficiently wide
radius of curvature, at all events not lower than the
admissible minimum radius for the cable itself. By way of
example, for a 400 kV electric cable 21, of an outer diameter
of 100 mm, with a linear weight of 27 kg/m, the admissible
minimum radius of curvature is 1.75 metres.
Downstream of inlet end portion 20a, cable 21 travels over
central portion 20c of a substantially rectilinear extension,
that for the above cable has a length substantially equal to
2 metres, being obliquely oriented downwardly away from the
inlet end portion itself. Preferably this central portion 20c
is defined, at a laterally outer position relative to first
conveying duct 14, by an inclined sliding surface 24 formed in
the side walls delimiting the conveying duct itself.
Rear end portion 20b, in turn, comprises a plurality of
externally-disposed rear sliding rollers or equivalent sliding
members 25, located downstream of first conveying duct 14, to
horizontally deviate cable 21 on the longitudinal centre line
of trench 3 and close to the trench bottom, following a
curvilinear path of travel of a radius of curvature not lower
than the admitted minimum radius of curvature for the cable
itself.
At least part of rear sliding rollers 25, and more
specifically at least those rollers arranged to act above
cable 21, are rotatably supported by a rear trestle 26
removably engaged, e.g. by extractable pegs or equivalent
removable connection means, between two rear side walls 27
parallelly spaced apart and rearwardly projecting relative to
first conveying duct 14.
Remaining sliding rollers 25, that are not supported by rear
trestle 26, are rotatably in engagement directly with side
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
walls 27 and/or between auxiliary side walls 28 provided at
the front of second van 5 in the extension of rear side walls
27.
5 At the end of rear end portion 20a, is also advantageously
provided at least one presser roller 29 elastically acting
against cable 21 to push it towards base layer 13 laid down at
the bottom of trench 3. In more detail, as diagrammatically
shown in Fig. 1, presser roller 29 is rotatably supported
10 between two runners (not shown in the figure) vertically
sliding along guides integral with auxiliary side walls 28 and
elastically loaded by at least one spring 29a pushing the
presser roller downwardly.
Second van 5 carries a second deposition unit 30 operating at
the rear of guide structure 20 to form at least one covering
layer 31 of inert material of appropriate thickness, just as
an indication included between 500 and 800 mm, on top of base
layer 13 and cable 21.
In the same manner as described with reference to first
deposition unit 12, second deposition unit 30 essentially
comprises a second conveying duct 32 substantially extending
in a vertical direction towards the bottom of trench 3 and
delimited by perimetric walls substantially defining bearing
structure 5a of second van 5, with which second and third
axles 9a, 10a are engaged, as well as all other members
associated with the second van.
Second conveying duct 32 terminates at the upper part thereof
with a second loading hopper 33 or equivalent feed means for
the inert material intended to form covering layer 31.
On the opposite side from loading hopper 33, second conveying
duct 32 terminates with a second downwardly-turned discharge
opening 34. Advantageously, second conveying duct 32 and
second discharge opening 34 have a maximum width which is
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
11
reduced by an amount of at least 10%, and preferably included
between 15 and 25%, relative to the nominal width of trench 3.
Second discharge opening 34 is delimited at the back by an
outlet edge 34a defining the maximum deposition thickness of
covering layer 31.
Preferably, adjustment means 35 operates at said outlet edge
34a in order to adjust covering layer 31 thickness between a
minimum value and said maximum value defined by the outlet
edge itself.
Said adjustment means 35 preferably comprises at least one
partition 36 hinged along outlet edge 34a of second discharge
opening 34 and adjustable as regards orientation by means of
a driving handwheel 37a acting on an adjusting screw 37.
Partition 36 has an end edge 36a to be positioned relative to
outlet edge 34a, depending on the orientation taken by the
partition itself and acting like a doctor blade on covering
layer 31 to level it to the desired height, simultaneously
causing a side displacement of said layer so as to fill
trench 3 according to the whole width of same.
Moreover, in accordance with a further preferred feature o'L
the invention, apparatus 1 comprises adjustable suspensicn
means 38 operatively associated with front wheels 8, 9 of
first and second vans 4, 5 as well as with rear wheels 10 of
second van 5, to modify the height of first and second
deposition units 12, 30, as well as of guide structure 20 and
of compacting unit 17, relative to trench 3 bottom.
Preferably, this suspension means 38 essentially comprises a
first fluid-operated levelling actuator 39 operating between
bearing structure 4a of first van 4 and first axle 8a of front
wheels 8, a second fluid-operated levelling actuator 40
operating between bearing structure 5a of second van 5 and
axle 9a of front wheels 9 of the second van itself, as well as
WO 00/63500 CA 02370661 2001-10-17 PCT/EP00/03358
12
a third fluid-operated levelling actuator 41 operating between
bearing structure 5a of second van 5 and axle l0a of rear
wheels 10. First, second and third levelling actuators 39, 40
and 41, as well as actuator 6 for connection between first and
second vans 4, 5 are hydraulically driven by a distribution
and control box 43 fed with fluid under pressure supplied from
a feed unit that can be installed on a tractor for towing
vehicle 2, for example.
Cable laying by the above described apparatus takes place as
follows.
As vehicle 2 is towed along trench 3, the inert material
coming from first loading hopper 15 along first conveying duct
14 is deposited to the bottom of trench 3 and compacted by
vibrating plate 18, so as to form base layer 13 with
substantially V-shaped upper surface 13a. The height of base
layer 13 can be easily adjusted by first levelling actuator
39. Simultaneously, electric cable 21 runs over guide
structure 20 and is then guided towards trench 3 bottom to be
deposited therein, close to the longitudinal centre line of
same, at the bottom of the V-shaped outline exhibited by upper
surface 13a of base layer 13. It is to be noted that,
advantageously, while cable 21 is being passed through whole
guide structure 20, it is conveniently guided according to a
predetermined path of travel enabling the cable itself to
reach base layer 13 without being submitted to too many
stresses and/or deformations that could damage it. The action
of spring 29a on presser roller 29 ensures that, on laying of
cable 21 against base layer 13, said cable is not subjected to
too many stresses also due to possible displacements in height
undergone by first and/or second vans 4, 5, e. g. as a result
of unevennesses encountered on the ground or for other
reasons.
Passage of second deposition unit 30 over base layer 13 and
cable 21 causes formation of covering layer 31 of a thickness
WO 00/63500 CA 02370661 2001-10-17 PCT/EPOO/03358
13
adjusted by adjustable partition 36.
Furthermore, a second compacting unit operating on the
covering layer 31 may be associated with apparatus 1
immediately downstream of second deposition unit 30, in the
same manner as described with reference to compacting unit 17.
In fact, said apparatus enables laying of underground electric
cables, in particular for high-voltage lines, to be carried
out in an automated manner and with an important saving of
time and manpower costs.
Moreover, the automated laying carried out by said apparatus
ensures constancy in the thickness and compacting degree of
the mass of inert material placed around the cable.
Thus a perfect correspondence between the heat dissipation
degree and the planned data is ensured, excess deposition of
inert material being also avoided.
The high degree of compactness carried out by compacting unit
17 causes an advantageous side displacement of inert material
that will occupy the whole trench width, in spite of the
reduced width of conveying duct 14 and discharge opening 16.
Due to the reduced sizes in width of the discharge ducts,
movement of the whole vehicle along the trench is facilitated,
without interferences occurring with the trench side walls,
even in the presence of bends along the longitudinal extension
of the trench itself.
An easy running of the vehicle along the curved lengths of the
trench extension is also facilitated by the arrangement of
first and second deposition units 12, 30 on two distinct vans
4, 5, consecutively linked with each other in an articulated
manner. In addition, due to the arrangement of two vans 4, 5
that can be released from each other, cable 21 can be easily
WO 00/63500 CA 02370661 2001-10-17 PCT/EPOO/03358
14
disengaged from whole guide structure 20 in case of emergency,
e.g. for carrying out possible repairings or if, due to any
other event, removal of apparatus 1 from the partly laid cable
should be required.
In fact, in this case, second van 5 can be unhooked and moved
away from first van 4, to enable free access to cable 21 along
guide structure 20. Front trestle 23 can be opened by lifting
its upper portion, and rear trestle 26 can be removed to free
the cable from guide structure 20, after optionally moving van
4 forward, to enable engagement of the cable stretch coming
out of the trench with an appropriate support structure
resting on the ground.
Furthermore, said apparatus ensures cable laying in a complete
absence of too many stresses and/or deformations of the cable
itself. This aspect is of particular importance above all when
high-voltage electric cables of the fluid-oil type are
concerned, which cables are to be handled with particular
care.
It is also to be noted that formation of base layer 13b with
an upper surface 13a having a V-shaped outline ensures an
advantageous holding of cable 21 at a centred position in
trench 3 and enables accomplishment of a complete and even
covering of the cable with the inert material forming the base
and covering layers. Achievement of the above result,
furthermore facilitated by the fact that the vertex of the V-
shaped outline is radiused, would be hardly reached if the
base layer should be deposited in such a manner as to exhibit
a flat upper surface, because the inert material would find it
difficult to fill the undercut space that would be created
between the lower and upper cable portions.
