Note: Descriptions are shown in the official language in which they were submitted.
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Descri~tion o~ the Prior Art:
Automated po~Jer distribution systems which perform
various functions, such as remote meter reading and selective
load reducing, require the use o~ a distribution power line
communication system. The distribution portion of the
communication system conveys information between a substation
and the electrical load at the customer location. m is
information must be transferred along the subtransmission or
primary distributlon line, the seconda~r distribution lines,
and the service lines l~hich extend to the customer locations.
Many different types of distribution power line
communication systems have been described in the literature
and have been used to some extent for actual communication
purposes. One type of communication system transfers signals
along the primary portion of the distribution system by
using one of the high-voltage conductors and the common
neutral return or ground conductor~ Other types o~ communi-
cation systems use two of the high-voltage conductors. ~lith
either method, difficulty is encountered due to power *actor
correcting capacitors connected to the primary distribution
line which severely attenuate the communication si~nals.
Other types of communication systems have been used, but the
probelms of considerable signal attenuation and multipath
propagation have not been satisfactorily solved.
The use of existing conductors located along the
power distribution system is advantageous from the standpoint
of providing an economical communication system. Conse~uently,
it is advantageous to use a minimum amount of additional
equipment or facilities to provide the carrier communication
3~ system. In addition, expensive components, such as couplers
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between the primary and secondary dist~ibution lines, must
be used sparingly to provide an economical communication
system. Therefore, it is desirable, and it is an object o~
this invention~ to provide an economical distribution power
line communication system which provides hi~h ~uality in~orma-
tion transmission with a minimum o~ additional cost to the
power distribution system.
SUMMARY OF THE INVENTION
mere is disclosed herein a new and use~ul arrange-
ment for economically providing a suitable communication
system along the distribution portion of a power transmission
facllity. The communication system makes maximum use of
existing facilities to reduce the cost o~ additional components
required to provide the communication system. -
The distribution portion of the communication
system extends between a substation communication terminal
and communication terminals at customer locations. The
commun~cation terminal at the substation is coupled to one
of the high-voltage conductors o~ the subtransmission or
primary distribution line. At the location where a distri-
bution trans~ormer is conn~cted to the primary distribution
line, the conductor carrying the communication signal is
coupled to a metallic wire which is normally used to support
another type o~ transmission line, such as a telephone line.
m is metallic wire is used as one conductor o~ the portion
of the communication system which conveys in~ormation across
the primary portlon of the power distribution system.
; me support or messenger conductor is coupled to
the secondary portion of the distribution system at positions
where the messenger wire is located conveniently to the
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secondary power distribution lines. The communication
signal is transferred between the locations where the messen-
ger wire is coupled to the secondary distribution lines and
the customer loads by propagation along the secondary distri-
bution lines and the service lines extending to the customer
locations,
By using the messenger wire arrangement disclosed
herein, only one connection to the primary portion of the
distribution line is necessary to serve several separate
secondary portions of the distribution line. Thus, a signifi-
cant reduction in the number of relatively expensive coupling
devices used to couple the primary distribution line to the
secondary distribution lines can be achieved, In additionJ
since a ma~or portion of the communication path does not
extend along the entire primary distribution line, the
e~fect of power ~actor correcting capacitors positioned
along the primary portion of the distribution line is reduced,
BRIEF DESCRIPTION OF THE DRAWING
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Further advantages and use of this invention will
become more apparent when considered in view of the following
detailed de~cription an~ drawing, in which:
Figure 1 is a schematic diagram of a communication
--; system constructed according to this invention;
Figure 2 is a block diagram Or a communication
system constructed according to this invention;
Figure ~ is a view illustrating the physical
arrangement of a communication system constructed according
to this invention;
Figure 4 is a schematic diagram illustrating an
30 arrangement for isolating a messenger wire from ground ac-
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cording to one embodiment of this invention; and
Figure 5 is a schematic diagram illustrating an
arrangement rOr isolating a messenger wire from ground
according to another embodiment of this invention~
DESCE~ or ~Hr PREFERRED EMBODIMENTS
- ` Throughout the ~ollowing description, similar
- reference characters refer to similar elements or members in
all of the figures of the drawing.
Re~erring now to the drawing, and to Figure 1 in
particular, there ls shown the distribution portion of an
electrical power system which is arranged ~or the transfer
of communication signals across the distribution system.
me subtransmission or primary distribution line 10 receives
electrical energy ~rom the substation 12 which would normally
` be connected to a high-voltage transmission line. me dis- -
tribution line 10 illustrated in this specific embodiment
includes the phase conductors 14J 16 and 18, Although
represented as a three-conductor three-phase line, a single
phase line may be used within the contemplation of this
invention.
The distribution transformers 20 and 22 are connected
to the phase conductor 18 of the primary distribution line
10 and to ground. ThUSJ electrical energy may be trans~erred
from the primary windings 2l~ and 26 to the secondary windings
28 and 30 of the distribution transformers 20 and 22. me
secondary distribution lines 32 and 34 transfer electrical
energy ~rom the distribution transformers to the customer
loads 36 and 38. As illustrated in Figure 1, the secondary
distribution lines 32 and 34 incluae the service lines which
normally extend from a customer load to the pole on which
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the distribution lines are connected. Although only two
distribution transformers are illustrated in Figure 1, it is
within the contemplation of this invention that more than
two distribution transformers may be used with the communi-
cation system o~ this invention.
The desired communication link exists betT,Jeen the
communication terminal 40 which is located at the substation
12 and the communication terminals 42 and 44 which are
located at the customer load locations. Normally, these
communication systems are of the two-way type in which
signals are generated and received by each communication
terminal, In describing the path of the communication
signal between the communlcation terminals in this specific
embodiment, the direction ~f communication propagation will
be assumed to be from the substation communication terminal
40 to the customer load communication terminals,
me communication terminal 40 generates a communi-
cation signal between ground potential and the phase conductor
18 by use of a signal coupler 46 which includes the coupling
transformer 48 and the capacitor 50. The communication
signal is propagated along the conductor 18 until it reaches
the terminal 52 of the distribution transformer 20. Assuming
that any power factor correcting capacitor banks are connected
to the primary distribution line 10 beyond the distribution
transformer 20, negligible attenuat~on of the communication
signal arriving at the terminal 52 is caused by the capacitor
ban~s. me communication slgnal applied to the distribution
transformer 20 is coupled, through the coupling capacitor 54
and the coupling transformer 56, to the conductor 58. A
repeater or signal amplifier may also be used to transfer
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communication signals between the terminal 52 and the con-
ductor 58.
Conductor 58 is an electrical conductor which is
independent of the primary or secondary distribution lines
and has a high resis~ance compared to the conductors of the
primary and secondary distribution lines. mus, the conductor
58 is not used for the transmission of electrical energy
between the various locations ln the primary distribution ~ -
system. Such a conductor may consist of the support or
messenger wire which is normally used to support other
transmission lines~ such as telephone lines and community
antenna television cables, between conventional power line
supporting structures. Figure 3, ~hich will be referred to
hereinafter in more detail, illustrates the use of a messenger
wire to support another transmission line between poles,
me conductor 58 i5 used to provide part o~ the
communication signal path between the various distribution
transformers connected to the primary distrlbution line 10
The conductor 58 is coupled ~o the secondary distribution
lines 32 and 34 by the coupling capacitors 60 and 62J respec-
tively. At the cuætomer loads, the conductors 64 and 66 are
appropriately connected to the communication terminals 42
and 44J respectively. Thus, a communication path exists
bet~een the messenger wire or conductor 58 and the communica-
~ tion termlnals associated with the various customer loads
-~ whlch are supplied by the power distribution system.
~ Figure 2 is a block diagram o~ the arrangement
`~ shown in Figure 1 with more distr~bu~ion transformers ~llu-
ætrated to indicate the interconnections between the system
elements~ me system substat1on 70 delivers energy to the
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primary distribution lines 72 and 74 and, through the distri-
bution transformers "T", to the customer loads 76 and 78,
Communication signals applied to the primary distribution
lines 72 and 74 at the substation 70 are propagated outwardly
from the substation 70 to the signal couplers 80, 82 and 84.
mese couplers may be constructed from suitable isolating
components, such as the transformer 56 and capacitor 54
shown in Figure lo
The location of a signal coupler is determined
primarily by the continuity of the messenger wire between
the various secondary distribution lines associated with the
power distribution system, In general, only one signal
coupler is needed for each portion of the distributlon
system wherein the secondary distribution line is accesslble
to the same messenger wire or conductor. merefore, di~ferin~
numbers of distribution trans~ormers and secondary distri-
bution lines may be associated with a particular signal
coupler. For illustrative purposes, Figure 2 indicates the
use of the signal coupler 80 with the distribution trans-
formers 86 and the messenger wire 88. Similarly, the signalcoupler 82 is associated with the distribution transformers
90 and the messenger wire 92, and the signal coupler 84 is
associated with the distribution transformers 94 ~ld the
messenger wire or conductor 96. merefore, it can be seen
that communication signals are required to be propagated
along the distrlbution lines 72 and 74 only as ~ar as the
furthest signal coupler.
Communication signals propagated along the distribu-
tion line 72 are transferred to the conductor or messenger
0 wire 88 by the signal coupler 80, By suitable coupling
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apparatlls, indicated ~enerally by the coupling capacitors
98, the communication signals on the messenger ~ire 88 are
transferred to seconda~y distribu~ion lines~ such as the
line 100, which are associated with the distribution trans-
~ormers 86, The communication signal is transferred from
the secondary distribution lines through service lines, such
as ~he line 102, to the various customer loads 76. Thus,
only one signal coupler is required between the high-vol~age
primary distribution line 72 and the lower voltage components
of the communication system where such components are assoc-
ciated with a common messenger wire. Coupling of the communi-
cation signals to the other service lines illustrated in
Figure 2 is accomplished by similar apparatus, with the
ma~or distinction illustrated in Figure 2 being the number
of distribution transformers associated with a particular
messenger wire. It is emphasized ~hat the signal path
described is the path conducted by the portion of the communi-
cation signal transmission system which is isolated from
ground potential that is, is "above ground". me return or
second conductor of the communication system is provided by
the grounded conductors of the electrical power system, In
addition, it may be practical in some installations to
connect together two or more, messenger wires by appropriate
conductors to extend the useful range of a messenger wire
and reduce the number of required couplers.
Figure 3 is a view illustrating a conventional
electrical power system pole arrangement wherein a messenger
wire is utilized~ me pole 106 supports the cross-arm 10~ -
and the insulators 110. The primary distribution line
consists of the conductors 112, 114 and 116. The secondary
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distribution line consists o~ the conductors 118, 120 and
122. The messenger wire 124 exten~s between the pole 106
and the ad~acent poles to help support the cable 126.
Couplin~ o~ the communication signal to the secon-
dary distribution line conductors 118) 120 and 122 is not
indicated in Figure ~. ~ormally~ this would be acco~plished
at the location in the power distribution system where the
secondary distribution line is connected, through a distri-
bution transformer, to the primary distribution line. Also,
the service lines which would be connected to the secondary
distribution lines shown in Figure 3 are not illustrated in
the interest of clarity.
In some installations, the messenger wire 124 is
not directly connected to ground potential throughout the
distribution system. Therefore, the messenger wire 124 can
be used conveniently as a conductor for the "above ground"
portion o~ the communication signal path. However, when an
electrical ground is desired between the messenger wlre 124
and a conductor at ground potential, such as the ground wire
1~0, a suitable isolator 132 may be provided. The isolator
132 isolates the messenger wire 124 ~rom ground potential at
the carrier communication frequencies.
Figure 4 represents schematically the connection
of an isolator between the messenger wire 124 and ground
potential, The lsolator illustrated in Figure 4 consists o~ -
an inductor 136 which has a relatively high impedance at the
carrier communication frequency and a relativ~ly low impedance
at the power line ~requency. Figure 5 illustrates the use
; of an inductor 1~8 and a capacitor 140 connected in parallel
; ~0 to provide isolat~on between the messenger wire 124 and
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glound potential. This arrangement ha~ the advanta~e that
the isolator presents a relatively low impedance between the
messenger ~ire 12LI and ground potential at polJer line frequen-
cies, and also presents a relatively low impedance at extremely
high frequencies, such as frequencies present due to lightning
surges.
me carrier communication signal arrangement
described herein makes novel use of existing components
often found in conventional power distribution ~ystems. By
10 suitable isolation o~ the messenger wire when needed, and by ~ -
using the messenger wire as a part of the "above ground"
path for the communication signal, an efficient substation
to customer load communication path may be provided. In
addition, the effect Or attenuation of communication signals
around distribution transformers is practically eliminated.
Also, the requirement that a limited number o~ couplers are
needed for connection to the high-voltage primary distri-
bution line is attractive from an economic standpoint.
Slnce numerous~changes may be made in the above
described apparatus, and since different embod~ments of the
invention may be made without departing from the spirit
thereor, it is intended that all of the matter contained in
the foregoing description, or shown in the accompanying
drawing, shall be interpreted as illustrative rather than
limiting.
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