Note: Descriptions are shown in the official language in which they were submitted.
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~owe~ ~i~ Si~s~alli~s System
The present invention rel_tes to signalling over power linea and is mainly
concerned with signalling over overhead power lines of low or inte~ - ' Ate vol-tage
M~ in~ di~tri h~ti ~ n - Isener~l
In most major countrie~ electricity i9 supplied on a wide scale by electricity
&encr~Ling and distribution companies (electricity utilities) The distribution
network normally consists of a large number of low voltage networks (often
termed the mains) to which domestic and amall b ~inç~s consumers are connected
with the low voltage networkR being ~upplied through a higher volta~se distribu-tion network or system (often termed the grid) The low voltage (consumer)
networks may for example operate at 110 V or 230 V (or 440 V 3-phase)
The distribution network will normally operate at more than one voltage
with long-distance distribution at voltages of say 132 kV or 275 kV which are
stepped down (possibly through 2 or more stages) to a voltage of say 11 kV or
33 kV We will term the former voltages (ie the voltoges u~ed for long-distance
distribution) high voltages and the latter voltages (ie the voltages relatively close
to the final mains voltage 2) intermediate voltages
Mains ~gnAllin~ - general
The use of the mains for signalling has often been proposed System~ are
available for intercommllni~ation b~ cn rooms in domestic premises (typically for
"baby alarms") for coupling to the telephone system and for transmission of databetween computer units Many proposals have also been made for the use of
mains Rignalling for remote meter reading (primarily for electricity meters
though gas and other meters can be coupled to the mains for this purpose pref-
erably through electricity meters)
There is in fact an international standard now for such signalling using
frequencies in the general region of 3 to 150 kHz The standard is CENELEC
EN50065 1 which specifies that frequencies in the band 3 kHz - 148 5 kHz are
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available for ~ignalling on low voltage electrical inatallations. Thia bandwidth i3
divided into several smaller bands with various uae~ and permiaaions as-ociated
with them; for example. the 9 kHz - 95 kHz band is reacr ve~ for electricity aup-
pliera ond their licenceea.
The signalling which iq performed by the electricity suppliera iq likely to
be largely concerned with metering and more generally with load ~nd ayatem con-
trol. This will therefore largely operate over the low voltage portions of the
main~. However as noted above the distribution network will normally include
intcr-_ ate and high voltage levels all coupled through power tranaformers. It
will often be deairable for metering information collected over the low voltage
portions of the network to be paa-ed on over the intel I - ate and/or high vol-
tage portions and for control information to be paa~ed similarly in the oppoaitedirection. This control information may include information to be paased to the
conaumers connected to the low voltage level and alao signal~ for controlling the
electricity distribution sy3tem itself.
Coupling to i"te~ ~e volt~ge 2_tu.r}~a
Techniques are therefore re~uired for coupling signals to inte~ te
voltage networks. These signala may be gencr~Led or uaed at the coupling
pointa ie the qubatationq where the inte- - ~te voltage networks are coupled
with either the high or the low voltage networks or may be paaaed between the
intermediate voltage network and a low voltage network coupled to it.
It may be noted that aignalling frequency signola generally do not paas
through power ~diatribution) tran~formers effectively. Some means of coupling
PLC ~ignalq round such transformera i~ therefore nccca~ary if signalling b~t~._cn
low and inte~ te voltage portion~ of a network iq to be achieved. Thi~ will
normally involve signal reception and retran~mia~ion. The signals are thus
coupled ~eparately with the two qideq of a tranaformer and paased around the
tran~former L_L~_cn its two sides with the signala being proc~ed to remove
noise. It may also be de- irable to uqe different frequency bandq on the two
sides of the tran~former. (This has the advantage that any ~ignal feedthrough
which does occur at power tranqformera will be irrelevant.)
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c Moins ~ in~5 - r clc~ncc of mains volto~e le-vel
J Signal trAn-lmi~aion and reception techniques are relatively ~traightforward
for low voltage (mains) networks. The signal trAn~mi~ion and reception equip-
ment can be connected directly to the network wiring.
An inter~ te voltage network however pre~ent4 more difficulty for both
electrical and I _-h~nical reasons. Inter-..eJiate voltoge network~ require physi-
cally robu~t in~ulation which i~ largely incompatible with direct connections tothe intermediate voltage. Also fairly delicate and ~ensitive electronic equipment
is largely incompstible with direct connection to inte~ - ' Ate voltages <we areusing the term "intermediate" voltage of course in connection with diatribution
networkc; 11 kV for example i~ exceedingly high relative to most electronic
equipment).
0~_. h~d ond ~ cr~5. c,u..d ~._tu_ h~
Di~tribution networks may be overhead underground or both. The high
volt~ge portion~ are normally overhead ~ince they generally cros~ long di~tanceaof fairly open country and the cost of burying them underground would be pro-
hibitive. In many countrie~ the low voltage portion~ are normally underground
~ince they are in densely populated area~ where overhead wire~ would be unduly
intrusive and potentially dangerous. The inte- ~,.ciiate voltage portion~ may beoverhead or underground; a~ with the low voltage portions they are generally
uncl_~rground in urban and suburban area~. We are here concerned primarily
with overhead inter _~i~te-voltage network~.
For main~ ~ignalling over intermediate-voltage overhead networks it i~
obviou~ly .~cce~ry to couple a ~ignal to the network at one point and to be ableto pick up the ~ignal from the network at another point. Variou~ ways of
coupling signal~ onto overhead networks have been propo~ed including inductive
coupling. For thi~ a transducer compriaing a magnetic core i~ placed around
one of the conductors forming a transformer. The core ha~ a signal winding
wound round it ~s a primary winding and the conductor itself effectively forms asingle-turn secondary winding (for transmi~ion; for reception the conductor
form~ a ~ingle-turn primary and the signal windin~; form- u multi-turn ~econ-
dary). We ~Ire here concerned with such inductive coupling.
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3--phase " _ L
Distribution systems are generally 3-phase at int~ te (and high)
voltages and often at low voltages as well The di-tribution system therefore
consists generally of 3 live supply lines and usually a neutral (earth) line as
well The supply lines are conventionally termed R Y and B (red yellow and
blue) forming a star connection with the neutral line
Large consumers are often supplied with a 3-phase supply How-ver ~mall
consumers (~uch as domestic customers) are normally only provided with a sinE51e-
I?h~-e supply The supply companies endeavour to arrange the connections of
the (cingle-phase) consumers so that the loads or the three phases are broadly
matched or b~l~nre~ In particular an overhead inter _' ~te voltage 3-phaae
network can have various single-phase branche~ or spurs because the co~t of
in~t~llinE~ such a spur is significantly smaller than that of installing a 3-phase
spur (Single-phnse spurs are also possible in principle with underground net-
works but for various reason~ are rare in practice )
A true aingle-phase spur would uae a single one of the 3 phases ~R Y and
B) together with earth or neutral but for various reasons this is gener~lly
undesirable So-called single-phase spurs therefore normally use 2 of the 3
phases at the inte~ cliate voltage with the transformer at the low voltage end
reducing the voltage between those 2 phaaes to the normal mains voltage (eg
110 V or 230 V)
With a 3-phase system and inductive coupling the signals are carried on
whichever phase the injecting transducer is coupled to ~nd the det~ting trans-
ducer detects signals on whichever pha~e it is coupled to This has dictated
that a single phase be used for signalling with all transducers coupled to that
phase ~It is convenient to describe the phase to which the transducers are
coupled as the primary phase and the other two phases as the secondary phases )
Thia has required that the primary phase be identified at all points in the
system where transducers are atlnche l It has alQO meant that signalling could tonly be carried out over single-phase spurs if they included the primary phase '~
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The p ~3~nt invention
According to the pre-ent invention, there i~ provided a ~ignalling ~yJtem
for ~ignalling over a 3-pho-e di~tribution network, char~cterized in that the
~ignal~ ore coupled inductively to ond from the network, ond are coupled to
different pho-es at different point- in the network The ~ignal frequency is
preferably in the region of 10 kHz to 100 kHz
The pre~ent invention re~t~ on the di-covery or r~liz~tion that the pri-
mary pha~e i~ coupled to the ~econdory pha~es (at the si~5nal frequency) suffi-
ciently well for the ~ignal injected onto the primary pho~e to be ~atisfoctorilydetect~hle on the ~econdary pha~e~ a3 well a~ the primary phase Of course, the
'primary phose" is now defined by reference to a particular ~ignal injecting
transducer; if another injecting tran~ducer is con~idered, its primory phose maybe different
Signals will normally be coupled to the sy-tem near a transformer, and thi-
coupling to the secondary pha~e~ ari~e~ Iorgely capacitively at the tran~former
Ao~ume that the transformer is a 3-phaYe delta tran~former ~if it i~ octuolly o
otor tran~former, we con con~ider it- delta equivolent circuit) The wir ~iinga of
the tranc~former present high impe~l~nce ot the 3ignol frequency, but there are
effectively shunt capacitance- ocro~ the win~ g~ from the primary pho-e to
each of the two secondary phooes, and the~e capacitonces couple the si~snal on the
primary pha~e to the two ~econdary pha~ea (If the actual configuration i~ a
delta, there is no real neutral point If the actual configuration is a ~tar,
there i5 a real neutral point, which may or may not have a neutral line connected
to it; in either case, the neutral point is ideally at the some voltoge as the earth
but i~ not normally connected to eorth Iground) )
There i~ also effectively a capacitance between each of the three delta
points of the winrlings and eorth The two secondary-to-eorth caparit~nce~ will
act, in conjunction with the capacitances acroas the two primary-to-~econdary
windings, ac~ ~ignal dropper~; also, the primary-to-eorth capa~it~nce will tend to
shunt the ~ignal on the primory phase to eorth But although the~e effect~
reduce the secondory signal ~trength, they do not reduce it to an unocceptoble
degree
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There is alao a capacitance across the winding b~ cn the two ~ccondary
phaaea. Under balanced load conditions the two aecondary phaaes receive equal
aignala ao this capacitance is irrelevant; if the conditiona are unh~l~nr ed thia
capa~;tan~e will help to equalize the aignala on the two aecondary phaaea.
At a 3-phaae termination and receiving point the aignal coupling may be
coupled to any of the three pha?es. If it is coupled to the primary phaae it
will of courae pick up the primary phaae aignal. If it is coupled to either of
the two aecondary phaaea it will pick up a aecondary phoae ~i~snal which will beamaller than the primary phaae aignal but atill of acceptable atren~;th. Similarly,
at a ainE51e-phase ~pur and receivinEj point (ie one fed with Z of the intel, _ ~te
voltage phaaes) the signal coupling will pick up either a primary or a aecondaryphaae signal depending on which 2 phaaea are uaed for the apur and which of
thoae 2 phaaea the aignal coupling i5 coupled to. Aa with 3-phaae terminationa
the net signal current into the termination is zero, ~o there may alao be an earth
current.
For signalo injected at a single-phase spur one of the 2 inter _diate
voltage phaaea at the spur will neceaaarily be the primary phaae for aignala
injected by the tranaducer there. There is likely to be an imh~lPn~e b_ ~.__n the
aecondary phaae for the apur and the r -ini~S aecondary ph~ae but at a 3-
phaae termination cignal~ on the primary phaae will divide between the two
aecondary phaaea so that they can be received there on either aecondary phaae
(os well as on the primary phase of courae) even though the two aecondary
phnae signals m~ly be of different strengtha. Similcr me~h~niam~ will alao
normally ensure that signals injected on one aingle-phase ~pur will be received at
other aingle-phaae apurs.
Specific e a~ of the in~ention
A 3-pha~e inter, _liate voltage diatribution network including a si~;nalling
ayatem and e~...boJying the invention will now be deacribed by way of example
with reference to the drawing-i in which:
Fig. 1 is a general circuit diagram of the ayatem; and
Fi~;. 2 is a more detailed circuit diagram of the supply tr~msformer station.
~S~TUTF C~E~ ~RULG ~6~
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Referring to Fig 1 the system is fed from a tran-former ~tation 10 which
iQ fed from a high voltage grid by me~n9 of a 3-pha-e tran-former driving a
3-phase inter, - ate voltage power di-tribution sy-tem having 3 pha-e- R Y and
The 3 phases are fed to a 3-pha-e 9uh~l ~tion 11 at which the power i~
transformed down to low voltngc by a 3-pha-e transformer There ore al-o two
single-phese spurs from the ~ystem a spur consisting of the R and Y phases
feeding a substation 12 and a spur consisting of the Y and B pha~s feeding a
substation 13 Obviou-ly the ~y-t-m may have further 3-pha-e ~Yt~n~ions and
ain~sle-phase spurs
For simplicity only the inte~ - ~te voltag~ WiT~ ng~ of the transformers
are shown with the high voltage wjn~in~5~ (for tran~form~r lO) and the Iow vol-
toge windings (for tran-formers 11 to 1 3~ omitted The primary of the high-
voltage transformer 10 will normally b- a delta win~ling; the ~econdary of the
Iow-voltage transformer 11 will normally be a ~tar winding giving 3 seporate low-
voltage phases; and the secondarie- of low-voltage tran~former~ 12 and 13 will
normally each be a single winding giving a sin~sle low-voltage pha~e
The station 10 has a transducer 1 OT coupled to the R phase; this trans-
ducer comprises a magnetic core with the R phase power line pa~sing through it
(so formin1~ a single-turn WiT~ing) and with (multi-turn) drive and ~en~e windings
coupled to it (indicated symbolically by a U ) The 3-pha-e substution 11 ha~ a
transducer 1 ZT coupled to its B pha-e power line; the ~ingie-pha-e ~ubatation 12
ha- a tran~ducer 1 2T coupled to its Y pha~e power line; and the single-phase
substation 13 has a transducer 1 3T coupled to it~ Y phase power line
The driving transducer 1 OT is coupled to the R pha-e so that pha-e i~ the
primary phase and the Y and B phases are the ~econdary pha--s In th- pre--nt
system the receiving transducers 11 T to 1 3T may ~ach be coupled to any pha-e
and in particular may be coupled to the ~condary pha~s as shown Hith-rto it
has been regarded as mandatory for the receiving transduc-rs to be coupl-d to
the primary phase so that the transducers at sub~tations 11 and 12 would have
to be located a~ in~ie~ted at 1 lT and 12T; it wa~ not thought possible to couple
a transducer to s~lh~te~ion 13 as that substation is not fed by the primary phase
It will of course be understood that while tr~rc ducer 1OT acts a~ the dri-
ving tran~dIleer and transduc-rs 1 lT to 13T act as receiving transduc-r- for
signals being fed from the station 10 any of the transducers can act as a dri-
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-- 8
ving transducer for signals from its own substation with the other tr~naduc rs
actin~; as receiving transducers The R phase is by definition the primary
phase for si~5nals from tran-ducer 10T but other phases may be the primary
phase for ignals injected by other transducers
~ ig 2 show- the effective circuit of the ~y-tem at transformer 10 in more
detail The transformer has three intel, _ iate volta~;e windings Wl to W3 in
delta configuration (If the transformer is actually ~ ~tar configuration it can
be converted to the equivalent configuration shown by a standard transformation )
Fach winding is at the signal f requency shunted by a shunt capacitance shown
as C 1 to C3 Each delta point is also coupled to earth by an earth cap~it~r~e~
shown as C4 to C6
Considering the system in voltage terms, the tr~rl~duc~r 10T induces a vol-
talSe on the R power line This voltage is coupled to earth through 3 parallel
paths capacitances C1 and C6 in series caparit~nre~ C3 and C4 in series and
capacitance C5 The two series paths C 1-C6 and C3-C4 result in voltages being
induced on the Y and B phase power lines Hence all three power lines have
voltages induced on them; a primary voltage on the primary (R) phase and two
equal and somewhat smaller voltages of opposite pha-e on the Y and B power
lines
In current term 2 a primary current IR is induc~d in the R ph~se power
line two equal and somewhat smaller secondary return currents Iy and IB, of
opposite phase are induced on the Y and B power lines and an earth or l!;round
return current I G, also of opposite phase to the primary current is induced in
the earth at the transformer 10 Obviously IR = IY + 1~ + IG. The primary
current travels out along the primary phase power iine to the various substa-
tions and passes to the secondary phases and earth at those substations At the
signal frequencies the power lines act as transmission lines b~ cn the sub-
station~ and switchin~; points where the power di-tribution sy~tem forks <into 2-
phase or 3-phase branche~)
It is evident that each of the two secondary phase return currents is effec-
tively divided between the various substations but that each of the s lha~ions
will in general receive si~Snificant portions of the two total ~econdary phase
return currents In particular sub-tation 11 will receive a significant portion
of the B phase return current and substations 12 and 13 will each receive sig-
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nificant portions of the Y phase return current. The receivin~; transducer~
llT 12T and 13T will therefore all receive siE;nificant 5ignals from the tran~-
ducer 1 OT.
At signal frequencies the windinga of the tran5form-ra at the ~ub~tation~
are each effectively ~hunted by capa~ nC~ . and ~re al50 effectively coupled to
earth by earth capacitance~. _ The currents in the power lines to which the
transducers are coupled find their return routea throu~Sh these capacitancea.
(The oper~tion can of course also be explained in volta~se terms.)
The present invention c~n advantaE5eoualy employ the power line ~iEsnallin~;
device described in our copendinE; application entitled Power Line Si~;nallin~s
Device filed simultaneously herewith.
C~JBST~TU~ E~T ~Rl~L~
