Note: Descriptions are shown in the official language in which they were submitted.
o
The present invention relates to a method
and apparatus for the cooling of electric cables hav-
ing distinct insulating oil channels and relates
particularly methods and apparatus for causing the oil
mass in the cable channels to oscillate.
It is known that cables for conveying electric
energy, being as they are subject to heating caused by
the current passage, require an adequate cooling for
keeping the temperature within values consistent with
both the life and service of said cables. For this
reason, various inst~llations are used for moving the
insulating oil longitudinally in a cable for the purpose
of removing heat due to current passage and of avoiding
the formation of localized overheated areas, coincident
with the joints, if any, used for joining various cable
units together. A known type of installation provides a
pump inserted into the insulating oil circuit, so that
oil under pressure is sent into one of the channels while
oil is sucked from the remaining channels arranged in
parallel with each other.
Unfortunately, in this known case, two unaccept-
able inconveniences arise, as follows: -
.~ .
(1) The first inconvenience originates ~-
from the fact that mechanical impurities
caused by pump parts cause deterioration
of the insulating oil dielectric character-
istics.
8~
(2) The second inconvenience, which, for
example, can be noted in a tern of in-
dividual cables, originates from the fact
that longitudinal motion of the insulating
oil would be obtained along the channel
of one phase, in the forward direction and
along the remaining two channels in the
backward direction. Consequently, a non-
uniformity in cooling conditions for the
various phases would be obtained.
A further known type of installation provides
the separation of the circuit in which the insulating oil
flows from circuit in which the pump oil circulates. Sub-
stantially, said installation includes, at a first extrem-
ity of a cable channel, a centrifugal pump, a first tank
containing a liquid and a second tank containing a number
of lenticular cells filled with insulating oil and hav-
ing deformable walls. Said cells are connected to each
other by a collector pipe which in turn communicates the
interior of the cells with cable oil, and said second
tank, exteriorly of the cells, is filled with the same
liquid as the first tank. At the cable second extremity,
there is a third fluid-tight closed tank, in the interior
of which there are a number of deformable closed cells
filled with gas. Said third tank also communicates with
the oil of the cable.
During operation, said pump takes liquid from
the first tank and it introduces said liquid into the
second tank, thereby causing a variation of the volume
8~ 0
of the cells and causing, therefore, an oil flow from
the cells to the cable and, therefrom, into the third
tank. Thereafter, the pumping direction of the pump
is reversed, the pressure within the second tank decreases
and oil flows from the third tank through the cable to-
wards the second tank cells.
The latter described installation would allow
for the elimination of the cited inconveniences, because
the insulating oil would remain separate from the pump
parts and each phase would be cooled down in the same
manner as the other ones. However, it is evident that
the use of a centrifugal pump for each cell-containing
tank would involve a high cost when a number of cables
and corresponding channels in which the insulating oil
has to be oscillated are dealt with. Further, it should
be particularly noted, that centrifugal pumps find a
practical applieation only with pressure of 3 or 4
atmospheres, whereas present aooling installations may -
require service pressures of over 10 atmospheres.
One might think that the wanted pressure could
be attained by way of increasing the number ôf pumps.
However, in such a case only an inconvenience of a tech-
nical nature would be overcome, while, onthe other hand,
the inconvenience of an economic nature, the cost of
numerous pumps, would be enhanced and worsened.
Unfortunately, for the reasons given herein-
before, said present known types of installations have
various inconveniences which, up to date, have not been
solved.
In addition, further difficulties have been observed in cases
where one wishes to associate an installation suitable for enforced cooling
by means of pumps, to another installation provided with traditional
tanks containing insulating oil and capable of counterbalancing oil volume
variations due to cable temperature changes. Such tanks are arranged at
the ends of the channels in a manner such that they send out or absorb
insulating oil according to oil volume variations within cable channels,
e.g. because of lowering ambient temperature as between day and night.
In general, the difficulties as hereinbefore described present a
number of problems to be solved. In fact, a solution thereof should be ;~
reached which permits obtaining a single installation which does not foul
the insulating oil, which is effective in enforced cooling and also
effective for counterbalancing oil volume in channels due to cable tempera-
ture variations, and which at the same time is also simple and has a low
cost both for materials used and for the necessary equipment installation.
Unfortunately, up to date, all of the known solutions do not allow for the
simultaneous solution of all said problems.
One object of the present invention, is, therefore, to provide an
installation for oil mass oscillation in distinct channels of electric
cables which is capable of solving the cited problems and overcoming the
cited inconveniences.
According to the present invention, there is provided a pumping
installation for cooling electric energy cables, said cables having a
plurality of channels for the flow of insulating oil, said channels having
first adjacent ends and opposite, second adjacent ends, said installation
comprising: a pair of pumps, each having a plurality of cylinders equal in
number to the number of said channels, each cylinder having a suction side
and a delivery side and a bellows-like separator which is fluid actuable
and which separates said suction side and said delivery side from said fluid
and each pump having a common actuating means for its cylinders, one pump
being adjacent said first adjacent ends and the other pump being adjacent
said second adjacent ends; a first plurality of insulating oil tanks equal
` ~f, -4-
.
.
lQ81~10
in number to the number of said channels disposed adjacent to said one
pump; a second plurality of insulating oil tanks equal in number to the
number of said channels disposed adjacent said other pump; a plurality of
valves equal in number to the number of cylinders; means connecting each
of the delivery sides of the cylinders of said one pump respectively to
one of the first adjacent ends of said channels; means connecting the suction
sides of the cylinders of said one pump respectively to one of said first
pl~rality of tanks; means connecting the delivery sides of the cylinders
of said other pump respectively to the said second adjacent ends of said
channels; means cGnnecting the suction sïdes of the cylinders of said other
pump respectively to one of said second plurality of tanks; and means
connecting said valves respectively between the delivery side and the suction
side of each cylinder whereby when a valve is open, direct flow of insulating
oil from the associated channel to its corresponding tank is permitted and
when a valve is closed, oil is pumped by a pump to its associated channel
from its corresponding tank.
Said installation of the invention is of particular advantage
with electric cables for which oil volume variations within cable channels
have to be counter-balanced and for cooling down the cables by means of
enforced oil mass oscillations in the channels, for example, for limiting
within acceptable values the cable temperatures each time electric energy
at a higher power than the nominal one has to be conveyed. This advantage
arises from the characteristics of said installation, which
~818~0 ~ ~
are substantially the following:
a) the use of pumps with volumetric cylinders
and bellows-cylinders capable of sucking and
compressing cable insulating oil in circuits : ~.
wholly free from mechanical impurities;
b) a first system for enforced cooling of
cables including, in practice, only two
multi-cylinder pumps with each cylinder
associated, through a driving mechanism,
with a motor and a tank for each channel
end. In this first sy~tem each pump is -
at the respective cable ends, each pump
cylinder has a portion for oil delivery
associated with a channel and a portion ;.
for oil suction associate with a tank;
c) a second system for counterbalancing oil
volume variations in channels, including the
same tanks as used in said first system, and
simple piping for hydraulically connecting
said tanks to said channels by means of elec-
trovalves. ..
As will better appear from the description given
hereafter, said characteristics allow for the cooling of
electric cables, without altering the characteristics
of insulating oil, in an effective manner for every elec-
tric load condition, with a simple construction and a low
installation cost. In addition, an installation according
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: .. :
1810
to the present invention is, in particular, suitable
for the cooling down of three unipolar cables of a
three-phase system with three distinct insulating oil
channels. -
A further object of the present invention is
a method for operating an electric cable cooling installa-
tion, as herein described, which method is characterized
in.-that it includes the following steps:
a) the alternate actuation of said pumps,
the closing of electrovalves at ends of
channels next to the actuated pump and the
opening of electrovalves at ends of the
channels opposite to the actuated pump;
b) the withdrawing of oil from tanks by
the actuated pump;
c) the sending of oil under pressure from
actuated pump cylinders toward the adjacent
channel ends and from the latter towards
the tanks at the channel en~s opposite to
the actuated pump;
d) the stopping of the actuated pump
and opening of the ~previously closed electro-
valves;
e) the actuation of the pump and closing of
electrovalves at the channel ends opposite
to p~eviously actuated pump, and repeating
with opposite oil flow steps a), b), c) and;d).
: .
:
lQ818~ ~
.
The objects and advantages of the invention
will be better understood from the following description
of the presently preferred embodiments thereof, which
description should be considered in conjunction with
the accompanying drawings, in which:
Fig. 1 is a schematic diagram of a cable
cooling installation of the invention;
Fig. 2 is a cross-sectional, end view of
three separate electrical cables illustrated
diagramatically in Fig. 1 which may be part
of a three phase system;
Fig. 3 is a cross-sectional view of one
cylinder of the groups forming part of
the pumps illustrated in Fig. l; and
Fig. 4 is a perspective view of the driving
mechanism forming part of a pump.
The installation 1 shown in Fig. 1 is suitable for the
cooling of a three-phase system formed by three individual -
cables 2, 3, 4, each of them with an insulating layer
5, 6, 7 (Fig. 2) around conductors 8, 9, 10 which in turn
include a central channel for insulating oil 11, 12, 13,
respectively. These channels 11-13 are schematically
shown in Fig. 1 and extend from terminals A, B, C, and
to terminals A', B', C'. The installation 1 includes
two pumps 14, 15, each of them having three equal cylin-
ders 16, 17, 18 and 19, 20, 21 respectively, which are
capable of sucking and delivering insulating oil under
pressure through suction and delivery valves illustrated
in detail in Fig. 3 and described in connection therewith.
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~ , .
.. . . ~ . . .
'' ' ' , : ~ ,
- -
1~181~
The pumps 14 and 15 are driven by two motors 22, 23, .
two actuation mechanisms 24 and 24' between said motors
and said pumps (as illustrated in Fig. 4 and described
in connection therewith). The installation also includes
three tanks 28, 29, 30 in proximity to terminals A', B',
C' .
Cylinders 16, 17, 18 of pump 14 have delivery
valves connected at terminals A, B, C with first delivery
pipes 31, 32, 33 and suction valves connected to second
suction pipes 34, 35, 36. Tanks 25, 26, 27 are connected
at terminals k, B, C, with third pipes 37, 38, 39. Said
second pipes 34, 35, 36 have a limited length between
suction valves of cylinders 16-18 and connections 40, 41,
42 between the ends of the third pipes 37-39.
Oil flow between the tanks 25-27 and the oil
channels 11~13 is permitted, or shut off, by appropriate
conventional electrovalves 43, 44, 45 connected to the
third pipes 37, 38, 39 between the connections 40, 41,
42 and the terminals A, B, C.
Connections of the pump 15 with the tanks 28, 29,
30 and of said pump 15 and said tanks 28, 29, 30 with
the terminals A', B', C' are the same as those already
described for pump 14. Accordingly, in Fig. 1, conn-
ections in proximity to the terminals A', B', C', which
are the same as those in proximity to the terminals A,
B, C are indicated with the same numbers, but primed.
The general diagram of the installation has
_g_
o
been set forth hereinbefore, and a description of the
individual parts thereof, i.e. pump cylinders, actuating
mechanism and the tanks will be given hereinafter.
For simplification-reasons the description which follows
hereinafter will be limited to the cylinder 16, the
mechanism 24 and the tank 25, it being understood that
the remaining actuating mechanism and tanks are the same
in~construction and operation.
Cylinder 16 (Fig. 3) is essentially the same
as the cylinder illustrated in Fig. 1 of our copending
Canadian application Serial No. 260, 663, filed Septem-
ber 7, 1976 and entitled "Bellows Pump and Pumping Plant
for Oil-filled Electric Cables" and includes an internal
chamber 46 with bases 46' and 46", and a central horizontal
axis, a delivery valve 47 and a suction valve 48, and a
cylindrical bellows 49, the axis of which is aligned
with the axis of the chamber 46. One extremity of the
bellows 49 is arranged in fluid-tight relation to the
base 46' of the chamber 46, and the opposite extremity
of the bellows 46 is secured, in the interior of chamber
46, to a plate 49'. The~cylinder 16 also includes a
fluid-dynamic cylinder 50, completely internal to and
co-axial with the bellows 49, a piston 51 sliding in the
interior of the second cylinder 50, and a cylindrical stem
52 secured to the center of the bellows plate 49' which
stem 52 slides in a central guide 53 at an extremity
50' of said second fluid-dynamic cylinder 50.
Said piston 51, in its resting condition, is
--10--
1:. ' . '
~ 8~
pushed from the left to the right hand side of Fig. 3
by means of a spring 59 arranged between a bearing
shoulder 59' of said piston 51 and the extremity 50'
of said cylinder 50. Between the base 46" of the chamber
46 and a circular flange 49" carried by the plate 49',
there is arranged an oppositely acting spring 54 which
acts on one extremity of bellows 49.
~he internal space of the chamber 46 is occupied
by two distinct and wholly separate fluids which are in-
dependent of each other, and specifically there are:
(1) an actuation fluid which fills the
space between the second fluid-dynamic
cylinder 50 and the bellows 49, and which
through the ports 50" at the extremity
50' of this second cylinder, occupies the
remaining space in the interior of the
bellows 49 interior;
(2) insulating oil at installation rated
pressure which occupies the space between
the internal walls of the chamber 46 and
the external walls of the bellows 49.
Valves 47 and 48 can be of any known type and,
merely by way of example, a particular embodiment thereof
is hereinafter described in connection with Fig. 3.
Delivery valve 47 includes an internally truncate con-
ical seat 47' w~ith a central port 47" which aligns ~ith
a corresponding port 47'n in the wall of the chamber 46
--11--
81~
and an upper opening F communicating with the first
delivery pipe 31 associated with the terminal A of oil
channel 11 (Fig. 1). Said valve 47 has an operating
element M, the truncate conical end portion of which is
pushed against the truncate conical seat 47' by means of
a spring N, engaging a stop surface N' of said valve,
and has an upper portion with guide spokes R contacting
the internal walls of the valve 47. Said spring N is
selected in a manner such that it permits the element M
to move away from the truncate conical seat 47' only when
the insulating oil pressure within chamber 46 reaches
a pre-set value selected for the enforced cooling of cables.
Suction valve 48 has, internally, a truncate
conical seat 48' with a central port 48" communicating
with the second suction pipe 34, and an upper opening F'
communicating with a port 48llt in the wall of the chamber
46. The valve 48 has an operation element M', the truncate
conical end portion of which is~lpressed by its own weight
against the truncate conical seat 48', and has an upper
portion with guide spokes R' contacting the internal wall
of the valve.
The pump cylinders and the associated suction
and delivery valves having been described, the actuating
mechanism 24 which is capable of causing shifting of
the pistons in interior of t~e cylinders 16, 17, 18 (Fig.l)
will now be described.
The actuating mechanism 24 (Fig. 4) has an
: : ' ' ' ', ' '
B~
eccentric or cam 55 carried by a shaft 56 drivable by
motor 22 (Fig. 1), and a multi~faced prismatic member
57, of which three faces 57' are provided with roller
bearings 58 arranged with their axes parallel to the
axis of the shaft 56, and three further faces 57" alter-
nating with the faces 57' and not engaging bearings.
Said prismatic member 57 extends around the eccentric 55
and is held in place due to the thrust that the three pis-
tons 51, 51', 51" of the cylinders 16, 17, 18 (Fig. 1),
through the springs 59, 60, 61, bring to bear on the
faces 57'.
During the rotation of the eccentric 55, the
piston 51 always remains in contact with the same face
57' provided with bearings, receiving, first, a thrust
which, in Fig. 4, is directed away from the axis of
shaft 56 towards the exterior, and, in Fig. 3 from the
right to the left hand side in the interior of the chamber
46 of the cylinder 16, and thereafter, when said eccentric
55 permits said face 57' to move towards the axis of the
shaft 56 (Fig. 4) and back into its original position
due to the action of ~previously loaded spring 59. In
a similar manner, during the rotation of the 55, the
pistons 51' and 51" similarly move, remaining always
in contact, through the corresponding bearings, with the
same faces. The presence of roller bearings is of advan-
tage in that sliding friction between the pistons and
the faces 57' is avoided.
In embodiment shown in Fig. 4, the prismatic
':, - ' ' , . ' ' . .
P~lg18~0
member 57 has only three active faces 57' to effect
shifting of the pistons. However, the number of pistons
and related active faces can also be increased when an
higher oil delivery within the cables is wished. For
example, the use of two cylinders for each oil channel
extremity could be provided, and in this case also, the
faces 57" could be made so-that they are plane, as are
the faces 57', and through roller bearings would be in
contact with as many pistons.
Having described the pumps and their actuation
mechanism, the tanks containing insulating oil will now
be described. Tank 25 is of a known type, e.g., is of
the type described in Italian patent No. 893,A~2 of
the present applicant, and therefore, the internal details
of the tank 25 are not illustrated in the present patent
application. In general, said tank 25 has a substantially
cylindrical shape, and has in its interior an elastic
cylindrical chamber composed of a rigid bottom coinciding
with tank base, a peripheral surface formed by an elastic, ;~
bellows-like diaphragm, and a mobile rigid closure applied
to upper edge of diaphragm. Said elastic chamber con-
tains degasified insulating oil at the rated installation
pressure, and it communicates with the third pipe 37
(Fig. 1), associated with the terminal A of the oil
channel 11, and through the connection 40 with the second
suction pipe 34. Around the bellows-like diaphragm,
there is a space which is subject to a gas which is under
the same pressure as insulating oil within elastic
chamber.
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. ~
':'" . ' ' ' ' ~ , : ~ : -
.
~818~0
When, for example, the insulating oil pressure
in third pipe 37 lowers below a pre-set value, gas
pressure at elastic chamber exterior prevails, and
therefore, a deformation of the diaphragm and oil flow
from said chamber towards the inlet of said pipe occurs.
The operation of the installation of the in-
vention will now be described.
When an enforced cooling of cables is desired,
first one and then the other of the pumps 14, 15 is actuated
so that enforced oscillations of the oil mass within the
individual channels 11-13 in alternately opposite direc-
tions are caused. For example, for a better understand-
ing of what is meant, the operation may be started with
the pump 14 in operation, the pump 15 stopped, electro-
valves 43lï 441, 45' simultaneously deactivated, i,e., open,
so that oil flow between the channels 11, 12, 13 and the
tanks 28, 29,30 is allowed, whereas electrovalves 43, 44,
45 are activated, i.e., closed, for preventing a portion
of the insulating oil sent under pressure by cylinders 16,
17, 18 from flowing back into the tanks 25, 26, 27 through
the third pipes 37, 38, 39. Under such conditions, motor
22 rotates, and therefore, the eccentric 55, driven by
the shaft 56, cyclically applies thrust to the faces 57
of the prismatic member 57, and cyclically permits them
to return to their original position (Fig. 4).
Accordingly, when the pistons 51, 51', 51" are
subject to thrust as transmitted by said eccentric 55,
-15-
.. .. .
1~8`~
a shift of said pistons occurs, which, in Fig. 4,
is directed away from the axis of the shaft 56. In
particular, for a more ready understanding, reference
is made to Fig. 3 and the operation of the cylinder 16
is taken into consideration, wherefrom it can be noted
that there is a shift of piston 51 from the right to the
left hand side, in the interior of the second fluid-
dynamic cylinder 50, causing movement of the driving fluid
through the ports 50" and against the plates 49'. Such
driving ftluid movement causes dilation of bellows 49
whose stem 52 slides in the central guide 53 overcoming
the force of the opposing spring 54. Then, when said
eccentric 55 permits the face 57' of said prismatic member
to move towards the axis of the shaft 56 (Fig. 4) a return
of the piston 51 to its original position due to the action
of spring 59 occurs, and the bellows 49 (Fig. 3) is com-
pressed by the action of said spring 54, as well as by
pressure of insulating oil which corresponds to the rated
one for the installa~on and which in any case exists
even when the pumps are stopped.
During the compression phase of the bellows 49
in the cylinder 16 (Fig. 3) in the interior of chamber 46,
a lowering of pressure occurs which is sufficient for
lifting the element M' from the truncate conical seat 48'
of valve 48. Consequently, insulatfmg oil from the
tank 25 flows into the interior of chamber 46 through
the second pipe 34 and the port 48'~ of the valve 48.
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, . . ~ - :, ., . . - :. .
:. .
1810
During the bellows dilation phase which is directed
from the base 46' toward the base 46" of the chamber 46,
insulating oil previously sucked is pushed against
operating element of the valve 47 causing said element
to move away from the truncate conical seat 47' against
the resistance of the spring N, and moves operating element
M' against the truncate conical seat 48', thus causing
the valve 48 to shut. Under such conditions, insulating
oil, through the central port 47"'`of valve and the open-
ing F, flows into the first pipe 31 (Fig. 1), into channel11 and then, through the third pipe 37', into the tank 28.
Cylinders 17 and 18 similarly operate and pro-
duce similar oil flows. Subsequently, after a selected
pre-set time, the pump 14 is stopped, the valves 43, 44.
45 are deactivated (opened) so that the insulating oil
from channels 11, 12, 13 is allowed to flow towards the
tanks 25, 26, 27, and the valves 43', 44', ~5' are activated,
i.e., closed, for preventing insulating oil as sent into
the channels from flowing back to the tanks 28 30 through
the third pipes. Under such conditions, there are the
suction and compression phases of the pump 15, with delivery
of oil under pressure into channels 11, 12, 13 towards tanks
25, 26, 27. Said phases are the same as those which have
been hereinbefore explained with reference to the pump 14,
and, for simplicity reasons, will not be repeated.
It will be noted that the operation cycles
whichhave been described hereinbefore advantageously provide
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i~8~8~0
a uniform cooling down of all of channels. In fact,
the same elements having been arranged at the extremity
of each channel, and cyclical actuation of the elements
at either of the ends of the cables, produces oscillations
of oil mass in all channels. Consequently, all of the
electrical phases are cooled down in an equal manner.
The operation cycle which has been described
is repeated by alternate actuation of the pumps 14 and
15 and control of the electrovalves until the temperature
of the cables is brought to an acceptable pre-set value.
When then the operating conditions correspond to normal
service temperatures for the cables, both said pumps 14
and 15 are stopped and the electrovalves 43, 44, 45 and 43',
44', 45' are simultaneously deactivated so that all tanks
25-30 are directly connected with the respective channels
11-13. Therefore, the installation, always with the
same tanks used in its enforced cooling system and with
the help of simple electrovalves is capable of counter-
balancing, in a known manner, the oil volume variations
within the cable channels due to normal temperature varia-
tions of cables, by means of the insulating oil contained
in the elastic chambers of the tanks. Because of this
feature said installation is simple.
Further, the use of only two pumps and of only
two motors together with the consequent possibility of
housing such active units in places of limited dimensions,
makes the installation advantageous and of low cost.
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,
~0~3~810
A further advantage of the installation of
the present invention is offered by the special arrange- -
ment of the hydraulic circuits as hereinbefore described,
which provide that the oil mass oscillations of the
individual channels are independent of each other. Such
arrangement is important, for the possible oil pollution,
if any, in a channel, does not spread to oil of the other
channels, and in addition, in the case of a breakdown,
inactivity time of the installation is limited to the time
required for oil purification steps in only one channel.
Another advantage of the installation originates
from the fact that operating personnel are not necessary
because all of the operation phases can be easily made
automatic with a pre-fixed program capable of defining
for each extremity of channels the operation of a single
motor or of three normal electrovalves. For example, the
motors 23 and 24 and the electrovalves 43-45 and 43'-45'
may be electrically connected in an obvious manner to a
conventional timed switching means 70 (Fig. 1) so as to
energize and de-energize the motors 23 and 24 and the
electrovalves 43-45 and 43'-45' in the sequences described
hereinbefore when forced cooling is required and to de-
energize all of them when forced cooling is not required.
The switching means 70 may be controlled by any device
which is responsive to conditions which indicate that en-
forced cooling is required, e.g., cable current or
temperature, or by a power distribution supervisor located
at a remote point and having a communication line extend-
--19--
~8~8~0
ing to the means 70 from such remote point.
Further, due to the reduced numbers of activeparts in the installation, the cost for control equip-
ment for said parts is lower, and a smaller breakdown
percentage is attained.
Another advantageous feature of the present
invention is the fact that whatever the number of side-
by-side channel terns, it is always possible to only use
two-multi-cylinder pumps, only two motors and only two
actuating mechanisms. In addition, in this manner,
installation active parts are easily and simply arranged
even when extremities of channels involved are in proximity
to small spaces.
Although preferred embodiments of the present
invention have been illustrated and described, it will be
apparent to those skilled in the art that various modifica-
tions may be made without departing from the principles
of the invention.
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