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Патент USA US2403468

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July 9, 1946.
I
L. K. SWART
2,403,468
PROTECTION OF COMMUNICATION CIRCUIT ELEMENTS
Filed Sept. '22, 1944
97/1
lNVENTO/Q
B
L. K. SWAP T
Patented July 9, 1946
2,403,468
UNITED STATES‘ PATENT OFFICE
2,403,468
PROTECTION OF COMMUNICATION
CIRCUIT ELEMENTS
Leland K. Swart, Mountain Lakes, N. 1., assignor
to Bell Telephone Laboratories, Incorporated,
New York, N. Y., a corporation of New York
Application September 22, 1944, Serial No. 555,241
6 Claims.
1
(Cl. 1'78—45)
2
This invention relates to protection of com
munication circuit elements, and more particu
larly to means for and methods of protecting cir
tion against over-voltages for loading coils placed
within the narrow con?nes of the connector units.
cuit elements included in line circuits, subject to
damage by currents of the nature of those pro
over-voltage protection of this nature which will
have a breakdown voltage that may be depended
duced by lightning.
For certain communication installations there
may be and have been used‘certain portable
cables laid in the open or lightly buried and sec
It is a further object of the invention to provide
on to remain constant under prolonged service,
and which will be effective to permit unimpaired
transmission, or to permit fairly satisfactory
transmission during storms, at least until neces
tionalized into convenient lengths which are in~ 10 sary repairs or replacement can be made.
terconnected by coupling or connector units. Dii~
It is a still further object of the inventionvto
ferent types of apparatus are inserted in these
provide protection of this nature which will not
cables at different intervals, depending upon their
interfere with normal operation and which may
nature and the transmission requirements.
be inserted Within the narrow con?nes of the con“
Since the circuits of such installations may 15 necting units without limiting the electrical and
reach over considerable distances and cover large
physical requirements already established in view
areas, they are subject to damage by lightning,
of the rough handling incident to this type of
especially where the cables are located on or in
service.
the ground. The nature and extent of the dam~
The invention will now be described more in den
age in each case, of course, depends upon. the 20 tail as applied to a speci?c embodiment typical of
proximity of the cable to the point where light
the broader principles and features of the inven
ning strikes. In the case of a direct hit, the dis
tion; and in this description reference will be
charge current may follow the cable for a con“
made to the attached drawing, in which:
siderable distance, and damage to the cable, as
Fig. l is a diagrammatic representation of a
well as to the inserted apparatus, is practically 25 pair of connector units showing end portions of
unavoidable. However, in the more common case.
the associated cables and. arranged for quadded
when lightning strikes at some distance, induced
cables, and indicating the protection provided in
currents will flow in the cable, the magnitude of
accordance with the invention;
which depends greatly upon the conductive con“
Fig. 2 is a perspective view of a connect-or unit
dition of the surrounding earth or other media. '
for a quadded cable. with. parts broken away to
Under these conditions the high conductivity of
show details of its interior, and including the pro
the cable conductors is not likely to establish volt
tecting
means provided in accordance with the
ages high enough to break through the cable in~
invention in the preferred form;
sulation. However, most apparatus included in
Fig. 3 is a detailed perspective view of a con»
such cable circuits have appreciable impedance to U! tacting
member of the connector shown in Fig.‘ 2,
across which excess voltages will readily be set up,
with the protecting means attached thereto; and
with the consequent breakdown. of the associated
Fig. 4 is a view similar to Fig. 3. showing an al
insulation and with the possible interruption of
ternative form of the protecting means.
service through the cable.
Referring now particularly to Fig. 1, the cir~
It is, therefore, a principal object of the in“ 40
cuits and outlines for a pair of connector units
vention to provide simple and effective protection
20-20 are shown diagrammatically with end por
of such apparatus against damage caused by dis
tions
of their associated quadded cables ill—l0.
charge of over-voltages due to lightning dis
Each cable II! has a pair of individually insulated
charges or, for that matter, due to any other
conductors II and I2, and another similar pair
cause.
45 of conductors l3 and M. The double winding
Such cables often contain a quad of conductors.
loading coil 40, wound upon a toroidal core of
The circuits are frequently lump loaded by the
suitable magnetic material, has its windings in
inclusion of loading coils, suitably mounted in
cluding in the conductors I! and 13 of each pair.
side the connector units, so that the loading may
be automatically increased as a cable is extended 50 The cable circuits through the windings are ter~
minated in female contacting members GI and
by the addition of sections. It has been found
63, respectively; and conductors l2 and I4 termi
that these loading coils are particularly suscept
nate in male contact members 62 and 64, respec“
ible to damage due to lightning.
tively.
It is, therefore, a more speci?c object of the
As will be described more in detail, each con
invention to provide simple and effective protec
55 nector has an outer meta1 shell, having pins and
2,403,468
3
4
lugs matching corresponding parts on its mate
shell 2i having a pair of lugs 22-22 with slots
23 and a pair of pins 24 (only one is shown),
these parts being adapted. to cooperate with sim
ilar parts on the mating unit to form a locking
for a locking bayonet joint. The interior of the
shell is ?lled with a molded compound of insulat
ing material, entirely ?lling the space from the
cable insulation, around the loading coil, to the
end surface in which the contacting members
6l—64 are mounted.
Upon joining of the pair of connector units,
four separate ‘circuits may be traced, from right
to left, as follows:
Conductor ll, lower winding of coil Ml, female
contact 6|. male contact 62, conductor l2,
.
bayonet coupling.
The loading coil all is embedded in the solid
body of insulation 33 which fills the interior of
‘the shell .22. Portions of this shell are shown
broken away in the drawing to reveal the ele~
merits in the interior and the insulating material
is omitted in the immediate vicinity of the loaded
coil for the sake of clearness. It should, how
ever, be understood that the insulation 38 com»
Conductor I2, male contact 52, female contact
pletely ?lls all spaces within and around the coil
6|, upper winding of coil 40, conductor l l,
15 4E and about the connections from the coil and
Conductor l3, upper winding of coil 40, female
the cable.
contact 63, male contact 64, conductor I4, and
The single toroidal coil 40 in the unit has its
Conductor l 4, male contact 64, female contact 63,
two windings wound about a core of suitable
lower winding of coil 40, conductor l3.
magnetic material, such as permalloy, and con~
It will be observed that four continuous cir 20 nected into the cable ‘circuit as shown schemat~
cuits are established in this manner, each in
ically in Fig. l. The metallic terminals 5! to
cluding a winding of the two loading coils. These
M for the two windings are mounted. on suitable
four circuits thus will provide paths for lightning
washers of insulating material which may be
induced currents and in each the sudden rise of
held in position on the coil by means of taping.
current will induce a high voltage across the
Thus, one winding is connected between the ter
terminals of the included winding which usually
minals 5i and 52 and the other between the ter
breaks down the winding insulation and in most
iiiiuals
and. 54. Conductors H and i3 are
cases open~circuits the winding, thereby com-A
connected to the terminals 5! and 53 respec~
pletely interrupting the transmission.
tively. Conductors l2 and M are brought through
In accordance with the invention a by-path is 30 the center of the coil to the :male contacting
provided for each winding which includes a
members 52 and 64. The female contacting mom“
breakdown gap 10 having a breakdown voltage
lower than that of the winding. These gaps and
their connections are embedded in the solid body
of insulation ?lling the shell of the connector ‘
unit. The general arrangement of each gap is
such that the metal parts on opposite sides of
the gap are ?xedly spaced apart to be separated
by a thin layer of air or other dielectric which
establishes the required breakdown voltage.
It has been found that by this provision of a
protecting gap, discharges which break through
the layer of air will in many cases leave the gap
intact, but in cases of heavier discharges a con
bers ill and B3 are connected back to the termi~
nals 52 and 54.
The female members 6i and 63 are completely
embedded in the solid insulation 33 and are
shaped as elongated rods 55, one of which is
shown in detail in Fig. 3. The rod has a hole 66
with solid bottom for reception of the male con
tacting member from the mating unit. At the
opposite end. of the rod a hole 6'! is provided for
soldering of the connection 63 or 529, as the case
may be, to the terminal 52 or
The male con
tacting members $2 and 64 are only partly em
bedded in the insulation and extend beyond the
ducting bridge is established across the gap which 45 surface 3i of the insulating body for cooperation
with the corresponding female members in the
opposite unit. With this arrangement the mount
discharge will open the bridge across the gap and
ing of the contacting members Bl to 84 is suffi
restore the circuit to normal efficiency of trans~
ciently elastic to allow for the short twisting
mission. The protection may be made so effective 50 movement necessary for the locking of the bay~
that only in the ‘cases of very heavy discharges,
onet coupling.
such as caused by very close or direct hits by
‘The protecting means provided in accordance
lightning, the coil will be damaged, but in such
with the invention in one of its preferred forms,
cases the cable proper will usually also be dam
comprises a double-bent conductor ll for each
aged.
Winding of the coil. As shown more in detail in
A practical and preferred embodiment of the
Fig. 3, the conductor ll has a single wrapping
invention is shown in Fig. 2 as applied to a con
of cotton '12 and the end near the bight T3 is
hector unit now in extensive use for military
placed against the outer surface of the female
purposes.
contacting member 6i and held in position against
The connector unit 20 shown in Fig. 2. corre 60 it by means of a taping 14. At the opposite end
sponds to one of the pair of mates shown in Fig.
the double conductor ‘H is bared and soldered
1. This unit has been standardized and the pro
to the terminal 51 or 53.
tecting means incorporated therein is arranged
Time, a breakdown gap is established between
in such a manner that the design of the con
the metal rod 65 connected to terminal 5'2 and
nector unit would remain unaffected. Only the 85 the bight portion of the double conductor "H con
parts of a connector unit essential to the inven
nected to terminal 5| of the same winding. The
tion are illustrated in the drawing and even the
spacing between the two sides oiv the gap is so»
illustrated parts are shown in somewhat simpli~
curely maintained by the cotton wrapping l2 and
?ed manner for the sake of simplicity.
su?icient air is entrapped between the cotton
The cable I!) includes the four line conductors 70 fibers to form continuous paths across the gap
II, l2, l3 and I4 forming the two pairs of a quad.
for over-voltage discharges. The outer taping 14
The cable is usually provided with an armoring
serves the further purpose of preventing the com‘
protected by an outer abrasive layer, which are
pound 30 from replacing the air in the gap at the
anchored to the shell of the connector unit.
time the insulation is poured in liquid form into
The connector unit comprises an outer metallic 75 the connector shell.
short~circuits its associated winding; however,
it has been found that quite often a succeeding
2,403,468
With this arrangement the breakdown voltage
of the gap may be accurately predetermined by
the thickness of the cotton wrapping ‘l2 and the
amount of discharge current that the gap will
carry without injury may be predetermined by
the lateral extent of the opposed surfaces be
tween the insulated wire ‘II and the rod 65. It
has been found that with greater separation there
is less tendency for metallic particles to be car
6
ductor separated from one of said terminals by
a light layer of ?brous insulation to establish a
gap capable of breaking down under excessive
voltages to pass current through said conductor
in protection of said element, said element and
protecting means being embedded in a mass of in
sulating material.
2. A communication circuit subject to light
ning surges and including a reactive element hav
ried across the gap and establish a permanent 10
ing an input and an output terminal, and an over
conducting bridge. By using air as the dielectric
voltage discharge path connected in parallel to
the widest gap is possible for practical purposes.
said element at said terminals and comprising a
As shown in Fig. 2 the gap ‘Hi is located on the
pair
of closely associated conducting elements,
side of the female terminal furthest away from
electrically separated by a thin layer of ?brous
the shell 20 in order not to reduce the effective 15
insulation to establish an air gap having a safe
insulation between the cable circuit and the
break-down voltage for protection of said ele
grounded shell 2 I.
ment.
An alternative manner of forming the protect
3. A sectionalized two-wire communication
ing gap is shown in Fig. 4 where the double con~
ductor 8i, insulated with the cotton wrapping 20 circuit including a pair of connector units be
tween two adjacent sections of said circuit, each
82, has its bight portion 83 wound with a few
of said units comprising a connector body of in
turns about the rod 65, the turns being held in
sulating material, a loading coil serially included
position against the rod by the binding tape 84.
in said circuit and having a pair of terminals, a
An advantage of this arrangement over that in
female
contacting member embedded in said body
Fig. 3 is the greater gap surface which may be
and connected to one of said terminals, and over
secured thereby.
voltage discharge means within the con?nes of
As is well known, a single cotton Wrapping
said
body and connected to form a path in paral
easily unwinds from the conductor when the con
lel to 'said coil and comprising a piece of ?ber
ductor is cut, and it is somewhat difficult to pre
vent that the layer be disturbed thereby for some 30 insulated conductor placed with its insulation in
close engagement with a portion of said contact
distance from the out. By the use of a double
ing member and electrically connected to the
bent conductor ‘i i, it is insured that only an un
other of said terminals.
disturbed portion of the conductor is used for
‘2. A long communication circuit subject to
the gap.
lightning surges and including a pair of oon~
A protecting gap between two metal parts sep
nector units for interconnecting adjacent sec
arated by spacing material admitting air to the
tions of said circuit, each of said units compris
gap may, of course, be formed in other manners
ing a connector body of insulating material, a
than those shown in the drawing, without a den
loading coil having a pair of terminals, a female
parture from the spirit of the invention. Thus,
instead of the double conductor ‘H a single con~ 40 contacting member connected to one of said ter
minal's, a male contacting member, and over-volt
ductor may be used, provided precautions are
age discharge means connected to form a dis
taken against the free end accidentally making
charge path around said coil and comprising a
electrical contact with the rod 65 and against the
piece of ?ber-insulated conductor having a
wrapping being disturbed by raveling. Other
double-bent portion placed with its continuous
separating materials besides cotton may be used,
insulation in close engagement with a surface of
such as paper, which may be placed in the gap
said female contacting member and having a
in any convenient manner without unduly re
bared end portion electrically connected to the
ducing the air passages. It has, however, been
other of said terminals, said coil, female contact
found that ordinarily the gap must be very short
to provide the necessary protection for the coils 50 ing member, and discharge means being embed
ded in said body of insulating material.
and that such short gaps may conveniently be
5. A loading coil having connecting means for
established by a single wrapping of cotton, silk
connection into a communication circuit subject
or the like. The outer covering 14 may alter
to over-voltage surges, a protecting circuit con
natively be in the form of a sleeve of insulating
nected in shunt to said coil comprising two con
material.
55 ducting elements closely associated and separat
It should be understood, of course, that the
ed by a single layer of thin ?brous strands and
means for and method of providing protection in
a molded body of insulating material completely
accordance with the invention may be varied as
embedding said coil and protecting circuit.
to details and that the invention is applicable
6. An electric reactive element having con
to connectors for cables with a single pair and 60
necting means for connection into a communi»
including only a single winding, and also that
cation circuit subject to over-voltage surges, an
the protection may be applied across other types
air gap, two conducting element's delimiting said
of electrical elements than coil windings, where
air gap, ?brous insulation in said air gap for
excessive voltages are likely to damage the equip
ment. The principles and essential elements of 65 spacing said conducting elements and connections
from said conducting elements to opposite sides
the invention are, however, those de?ned in the
of said reactive element, respectively, for pro
appended claims. ‘
tection thereof against over-voltage, insulating
What is claimed is:
holding means for holding Said conducting ele
1. A communication circuit including a circuit
element subject to interruption of the circuit 70 ments in ?xed mutual relation and a molded body
of insulating material completely embedding said
therethrough by currents of the nature of those
elements and enclosing said air gap.
resulting from lightning and having terminals,
LELAND K. SWART.
and protecting means connected in shunt to said
element at said terminals and comprising a con
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