EP0335948A1

EP0335948A1 - Decoupling network and communication system

Info

Publication number: EP0335948A1
Application number: EP88909190A
Authority: EP
Inventors: Ronald James Coomer
Original assignee: South East Queensland Electricity Board
Current assignee: South East Queensland Electricity Board
Priority date: 1987-10-15
Filing date: 1988-10-17
Publication date: 1989-10-11
Also published as: WO1989003623A1; EP0335948A4; JPH02501700A; AU2551988A; AU606478B2; KR890702349A

Abstract

A decoupling network for blocking high frequency communication signals on power lines. The network includes a filter having a first series element (10) for connection to a power line, a second series element (11) for connection to the same or another power line, and a shunt element (12) connected between the series elements and across two power lines. The shunt element acts as a short circuit to high frequency signals, thereby blocking passages of communication signals through the network. In one embodiment, a signal processing circuit (13) is inductively coupled to the series elements for processing communication signals from the supply authority and from consumers. The network prevents the communica tion signals from passing directly from the supply authority to the consumers, or vice versa.

Description

DECOUPLING NETWORK AND COMMUNICATION SYSTEM

The invention relates to a decoupling network fo a communication system and to a communication syste including such a network.

Various techniques have been proposed for providin communication between a supply authority and a consume receiving electrical energy generated by the authority. Th need for such communication has arisen because of requirement to provide supply at a variety of tariff depending upon supply demands, to enable remote control o the continuance or otherwise of the supply to the consumer a a selected circuit or circuits and to provide for remot metering of consumption by the consumer.

Currently, one way or two way communication betwee the supply authority and the consumer is possible by using a existing telephone network controlled and established by telephone authority and not the supply authority, employing power line carrier or a radio link between the suppl authority and the consumer.

The methods for communicating referred to above i most cases provided for one way communication from the suppl authority to the consumer and there was no ready way o determining whether or not the transmitted command or contro signal was indeed received and acted upon by the consumer. The use of a telephone network to provide for communicatio was not cost effective since each time a signal was sent th cost of a telephone call was incurred. Even where the cos for the call was that for a local call, the cost was stil prohibitive because of the large number of consumer concerned. The use of a radio link was not an effectiv alternative since only a finite number of frequency bands were available and thus it was not practical to use such link to communicate with a large number of consumers.

The power line carrier technique involved the injection of control signals onto supply lines in the distribution network and was subject to interference because it was not possible to guarantee the communication dynamics of such a system since the dynamics constantly changed and noise was injected onto the supply lines both by the supply authority, external influences and by load switchings by the consumer.

Generally speaking, where the supply network has some 600,000 individual consumers, there wo^'uld be some 15,000 to 20,000 low voltage transformers and approximately 30 to 80 consumers associated with each low voltage transformer. For this reason, confusion between the various signals some times results.

It is an object of the present invention to provide a decoupling network and a communication system including such a network which at least minimises the disadvantages referred to above.

According to one aspect of the invention there is provided a decoupling network for a communication system, a decoupling network including an input and an output, a filter between the input and the output, said filter blocking high frequency signals from passing from the input to the output and from the output to the input whilst enabling low frequency signals to pass in either direction, said filter presenting a defined impedance for the high frequency signals irrespective of impedance connected to the input or the outpu .

According to another aspect the decoupling network provided by the invention is as described above but wherein the filter includes a first and a second series element coupled between the input and the output, at least one of said series elements including a transformer and the othe said series elements comprising a coil, a shunt elemen coupled between a junction between the series elements and reference or between the series elements and said networ including a further filter associated with said one series elemen . According to another aspect of the invention ther is provided a communication system including the decouplin network described above associated with a consumer, sai input being adapted for coupling to supply lines of a suppl authority and the output to load lines fo a consumer, sai lines each including an active line and a common referenc line, said system including a computer for receiving contro inputs and providing control outputs and having a modulato for connection to said one series element to enable transmit signal to be impressed onto the supply lines at low impedance, a demodulator for connection to said on series element to enable communication signals on said suppl lines to be received at a high impedance and A/D converters, and said shunt element together with said one series elemen being effective to short high frequency signals appearing o the supply lines to a reference and said shunt impedanc together with the other series short high frequency signals appearing on the load lines to the reference.

It is preferred that at the customer both series elements be coupled to the same line rather than to differen lines with said series element having a junction between the with the short element between the junction and the other line or reference line.

The decoupling network of the invention may have both series elements consisting of transformers with a primary winding of one of the transformers being coupled between the active line of the supply line and the junction and the other transformer has a primary winding coupled between the junction and a load circuit. The primary windings may be associated with the same or a different magnetic circuit. Where the primary windings are associated with different magnetic circuits it is preferred that both of these windings have a corresponding number of turns and have good decoupling between them at the frequency of operation. A ferrous shield may be required. The transformers include secondary windings. Clearly, each secondary winding is associated with the magnetic circuit of the respective primary winding. It is prefe^'rred that the secondary windings have a number of turns different from the primary windings. In one embodiment, each transformer functions as a step-down transformer. Where each transformer has primary windings of say 10 turns it is preferred that the secondary windings liave 50 turns each although a different number of turns for each of the windings may be employed. Where the series elements consist of transformers having a common magnetic circuit it is preferred that the primary windings of each transformer included in each series element be wound in a different sense. This ensures that the common magnetic circuit is not driven into saturation. Where a common magnetic circuit is used it is preferred that the primary windings of the transformers included in the series elements have a slightly different number of windings. Fo example, one primary winding may have 13 turns whilst th other may have 14 turns. In this way, a resultant number o turns, where the windings are wound in a different sense, o one is left remaining. The purpose of this will become clea in the following description.

Where the primary windings of the two serie elements appear on a common magnetic circuit, it is preferre that the respective secondary windings also appear on tha common circuit and in close proximity to the associate primary windings. Whilst the secondary windings may have an number of turns, it is preferred that they each have 60 turn although a different number of turns may be employed. It i also preferred that the magnetic core be of a low grad material to ensure poor high frequency coupling.

It is preferred that the network include a curren transformer. Where the transformers included in the serie elements are on a common magnetic circuit, the windings o the current transformer may also be included on that circui or alternatively may be provided as a separate device. Where the turns of the current transformer are included on common magnetic circuit, because the resultant number o turns remaining where the primary windings are of a differen sense and are slightly different in number, the number o turns for the current transformer may be reduce commensurately. Thus, the number of turns for the curren transformer may for example be 800 where the resultant turn of the two primary windings is 1. In this way, the turn ratio provided by the current transformer is 800:1. It ca be seen that this is the case in the embodiment mentione above where the series elements are provided on separat magnetic circuits and where the primary windings eac consists of 800 turns. With the second embodiment, where th series elements are provided on a common magnetic circuit, i is possible to obtain current transformation with a curren transformer having a substantially reduced number of turns.

Where the transformers of the series elements ar associated with different magnetic circuits it is preferre that at least one of those magnetic circuits includes current transformer winding although, where a curren transformer is required, that transformer may be included as a separate device having a magnetic circuit separate from th magnetic circuit of the series element(s). The curren transformer winding may consist of any desired number o turns. It has been found, where the primary winding consists of 10 turns that the current transformer winding have 8,000 turns although a different number than that may be employed. It is preferred that the magnetic circuit of each series element include a current transformer winding. Each series element preferably also includes a filter. The filter is arranged to be able to present a lo impedance for facilitating transmission of communication signals onto the supply lines and a high impedance when listening for communication signals impressed on the supply lines by the supply authority. Preferably, the filter is a band pass filter. The band pass filter is connected across the secondary winding of the series element and may consist of passive components connected to provide a high pass filter and a low pass filter of suitable cut-off frequencies to provide a band pass filter. The band pass filter may for example be an active filter. The filter may be tunable.

One of the- series elements, namely the one coupled to the supply line and the junction may be employed for receiving and transmitting signals from and to the supply lines respectively whilst the other series element in its simplest form comprises a coil which blocks high frequenc signals and the shunt element shorts high frequency signals on the load line to the reference. Alternatively, the secon series element may be identical to the first element. The shunt element functions to present a shor circuit between the junction and the reference to hig frequency signals whereby, high frequency signals in exces of the frequency of the supply impressed upon the suppl lines is shunted to the reference potential by the shun element whilst the energy at supply frequencies may pas through the series elements unhindered and be made availabl to the consumer. With such a configuration, any hig frequency noise generated across the load lines by th consumer will be blocked by the second series element of th decoupling network and shunted to the reference by the shun element. Thus, the shunt element effectively decouples th consumer from the supply lines insofar as high frequenc components are concerned. The shunt element may consist o a low pass filter which shunts frequency components in exces of the supply frequency to the reference. The low pas filter may consist of a capacitor coupled between th junction and the reference. The capacitor may be protecte by an overvoltage limiter. In one embodiment, a metal oxid varistor may be connected in parallel with the capacitor t protect it and consumer loads against overvoltage. It is preferred that the system of the inventio includes a power supply for deriving an unregulated and/or regulated power supply from the supply lines. The powe supply may include an integrated power supply and a voltag regulator. It is preferred that the power supply provide regulated output voltage and an unregulated input voltage a well as a reference potential.

The system may include a voltage divider from whic a signal may be obtained which may be tested to establis whether the frequency of the supply line voltage is nominall at the desired frequency. The voltage divider may comprise resistive dividing network. The divided voltage obtained i this way may be compared for its frequency with a referenc frequency. The reference frequency may be established by a oscillator. Preferably, the comparison is made by a softwar timer or a phased locked loop is employed to produce a stabl wave form at the supply frequency. The voltage signa obtained from the divider network may be shaped prior to thi comparison. The voltage signal obtained from the divide network may also be used to derive an output signal fo controlling an audio frequency relay network such as Zellweger relay network. The divided voltage may first b monitored to determine whether a Zellweger signal has bee applied to the supply lines. This monitoring may includ filtering. Preferably, band pass filtering is used. A active band pass filter or digital filter may be used fo this purpose. The output from the filter may be shaped in a comparator to provide a useful signal for controlling a Zellweger relay network. Digital means may be used to decode the audio frequency signals to produce the appropriate rela response. ^~

The divided voltage may be combined with the output derived from the current transformer of the network to enable an indication of power consumed by the consumer to be achieved. A constant phase compensation may be required to adjust for errors due to the current transformer phase shift. The phase shifting can be achieved by software if a digital multiplier is used. The divided voltage and current output from the current transformer may first be digitised and then multiplied. An analogue to digital converter may be used for this purpose. Alternatively, the divided voltage obtained from the divider network and the current derived from the current transformer may be multiplied in an analogue fashion to obtain an indication of power consumed.

The system of the invention, as mentioned above, includes a modulator and a demodulator. The modulator and demodulator may be selectively coupled to the first series element to respectively transmit signals onto the supply lines and receive signals applied to the supply lines by the supply authority. The demodulator may be adapted to receive signals from the supply lines at a plurality of frequencies. The frequency at which signals may be received may be selectively varied. In one embodiment, the demodulator may receive signals, for example within the range of 50kHz to 80kHz o between, for example, 110kHz. The demodulator may functio at any desired baud rate. For example, the baud rate may b 300, 600, 1200 or 2400 or any other convenient rate. Whils any convenient demodulator may be employed it is preferre that the demodulator be Differential phase shift keyin demodulator. Preferably, a demodulator of the type XR2211 i employed.

The modulator or transmitter if the demodulator i a DPS demodulator, is a DPSK modulator. Amplitude shif keying may be used instead of DPSK. Whilst the demodulator and modulator have bee described as being ASK or DPSK modulators and demodulators, it should be appreciated that any other type of modulatio and complementary demodulation may be employed.

Where the power supplied to the consumer is spli into several power supply circuits, the system may include series element like the second series element of th decoupling network associated with each separate circuit Thus, each separate circuit may have a transformer with th primary winding thereof coupled to the junction in th decoupling network and the other end of the primary windin being available, for supplying power to the consumer on separate circuit. The secondary winding of the transforme may then be coupled to a filter like that described i relation to the other series elements of the decouplin network. That filter may be coupled to a demodulator whereb that demodulator may "listen" to communication signal impressed at a high impedance on that separate load circui by the modulator of the system. The filter may also b selectively coupled to the modulator of the system to enabl signals to be transmitted at a low impedance to the suppl lines. Where such a further series element is present, it i preferred that a further current transformer for that loa circuit be also present. In this way, where there are plurality of load circuits and each one of them has a serie element with an associated current transformer it is possibl to sum all of the current transformer outputs and compar them to the output of the current transformer associated wit the first series element. If the comparison shows that th current provided by the current transformer of the firs series element does not equal the sum of all of the outputs of the other current transformers then there is an error i the system and this information may be conveyed to the suppl authority.

The system includes a computer as mentioned above. The computer may have memory in the form of random access memory (RAM) programmable read only memory (EPROM) as well as an analogue to digital and digital to analogue converter. The computer controls the operation of the demodulator and modulator as well as various other aspects of the system. For example, the current signal obtained from the current transformer and the voltage signal obtained from the voltage divider may be digitised and multiplied to obtain an indication of power consumption and the power consumed may be stored and subsequently transmitted onto the supply lines when prompted to do so by a control signal sent onto those lines by the supply authority. The computer may be employed to provide the modulator/demodulator functions by software control. Preferably, the computer includes an A/D converter so that analogue signals may be received, converted and be processed. Similarly any Digital signals outputted by the computer may be transmitted as analogue signals. In a preferred form signals transmitted to the consumer are encoded by the computer. Amplitude shift keying (ASK) may be used. The signals transmitted for the supply authority may also be encoded. Differential phase shift keying may be used. The computer may control the A/D conversion by software. Preferably the computer is an INTEL 80C196 device or equivalent or substitute.

The invention will now be described with reference to the drawings in which: Figure 1 is a block diagram of a decoupling networ according to an embodiment of the invention;

Figure 2 is a detailed circuit diagram of th network of. Figure 1;

Figure 3 shows a magnetic circuit of a networ according to one embodiment of the invention;

Figure 4 shows an alternative magnetic circuit t that shown in Figure 3;

Figure 5a shows one way in which the transformer of Figure 4 may be implemented; Figure 5b shows another transformer implementation;

Figure 6a shows details of how the decouplin network may be used at a distribution transformer;

Figure 6b shows an implementation of that shown i part of Figure 6a; Figure 7 shows a block diagram of a communicatio system according to an embodiment of the invention; and, _ Figure 8 shows an alternative decoupling networ for high current loads.

As shown in Figure 1 the decoupling networ includes a first series element 10 and a second serie element- 11. Whilst both of these elements are shown couple between the supply and active line, one of ^*the elements ma be located in the neutral line (see figure 6a). The outpu from the second series element 11 may be the active for on supply circuit for a consumer. A shunt element 12 extend between the active supply by line or the junction betwee elements 10, 11 to a common or neutral line of the supply. processing circuit is coupled to receive from and provid signals to the series elements and from the shunt element. Series element 10 has associated therewith a curren transformer which provides an indication of the curren supplied to the active supply line A and this current is indicated by the line identified by I . As shown in this diagram, the consumer is provided with various powe circuits identified as CCT1 to CCTN where N is an intege greater than 1. Each circuit has a series element whic receives signals from circuit 13 and has associated therewith a current transformer to provide a current signal I_n representative of the current supplied to that circuit. The individual currents I, to In are supplied to circuit 13 which sums these individual currents and compares them to current I_in. This provides a check to determine whether each circuit is supplying current to a respective load. Clearly, when the individual currents I, to In do not add up ^{~^} to IAn then there is an error in the system. The shunt element provides a signal V indicative of the voltage magnitude supplied to the consumer and this together with I_irι enables circuit 13 to determine the power supplied to the consumer. The circuit 13, includes processing circuitry including an A/D converter and provides a signal 0, to mix in mixer 14 with a signal from the supply authority to produce a difference signal more readily detectable by circuit 13. Similarly signal 0₂ is supplied for mixer 15 to enable the circuit 13 to produce and receive difference signal from element 11 which is more readily detectable by circuit 13. The circuit 13 output signals D_o to element 10 and output signals D, to element 11. The consumer is able to communicate with circuit 13 throug element 11 whilst element 12 acts as a high frequency shor circuit to these signals^* and prevents them from bein directly transmitted to the supply side of the network. Similarly, any signals supplied to element 11 from circuit 13 are only available to the consumer and are shorted t reference potential by the shunt element. These signals ar typically at 96kHz or the like.

The element 10 enables circuit 13 to receiv signals from the supply authority and these also do not pas element 12. The circuit 13 may transmit signals to th supply authority via element 10 and once again these signal do not find their way to the consumer side of the network. Typically, these signals may be between 50 and 100 kHz.

Figure 2 is a detailed circuit diagram of th network shown in figure 1. Transformer Tl corresponds t series element 11 of Figure 1 whilst transformer T corresponds to series element 10. Both of these element have a band pass filter (BPF) located in a feedback path o an active element. The BPF comprises elements Cl, C2 and Rl. Coupling capacitor C3 and resistor R2 are associated with th active device which in this case is amplifier Al which ha diode Dl coupled in its feedback path. This circui functions to listen for signals on transformer T , whils presenting a high impedance and when signals are transmitte to the transformer T_χ it presents a low impedance. When i the listening mode +5V is applied to both inputs of Al an thus the secondary of T__ sees effectively an open circuit Signals appearing at the inverting terminal of Al appear a the output of Al and are amplified, level controlled by D and divided by Cl, C2 and made available to the secondary o . Transformer T₂ has capacitors C4, C5, C6, R2 an active amplifier A2 associated with it and functions a described for T except that signals are transmitted to o received from the supply authority. Shunt element 12 of figure 1 is implemented b series connected capacitors C7, C8. Capacitors C7, C function to short high frequency components to the neutra line N and thus signals at the consumer end cannot b supplied between lines A and N. Similarly signals betwee lines A and N cannot be detected at the consumer end of th network. A two way flow of signals is only possible throug circuit 13 and in a controlled manner. ^*The components i parallel with C8 provide a power supply for other parts o the circuit and include diode D2 (a 24V zener diode), protection diode D3, filter capacitor C9, regulator R an filter components R3, CIO. Coil LI and capacitor Cll ar resonant components and provide regulated +5V between them. Positive 24V is available across CIO. Transformer T3 is current transformer and provides signals to circuit 13. metal oxide varistor MVl functions to suppress surges an transients.

At the consumer end of the network circuits CCTO, CCT1, CCT2 and CCT3 are available. Current transformers may be provided in circuits CCT1 to CCT3 if desired. Switches SW1, SW2, SW3 may be bi-stable switches controlled by signals supplied by circuit 13 through connector Jl.

Capacitor C12 and resistor R4 enable signals to be detected from Tl. R4 is coupled to a 2.5V reference and the junction between C12 and R4 has a signal from Tl available for mixing in mixer Ml. Switch SW4 switches between a position coupling the signal from T2 to mixer M2 in the listening mode and in its other position couples a communication signal to T2.

Current transformer T3 has resistors and metal oxide varistors R5, R6, MV2, MV3 coupled in the fashion shown to enable circuit 13 to control T3 to operate either in a high current or low current mode. As shown in figure 2 circuit 13 in this case is an INTEL microcontroller although other equivalent or substitute devices may be used. INTEL 80C196 device is preferred. Circuit 13 is software controlled to cater for various inputs and provide various outputs. RAM and ROM memory chips 20, 21 are coupled to circuit 13. An address latch 22 is interposed between circuit 13 and the memory chips. Optical service ports RXD and TXD are provided for receiving and transmitting signals for diagnostics, maintenance and interrogation functions. A crystal CR is coupled to terminals 1 & 2 whilst components coupled to pin P10 provide tamper and reset functions. Connector Jl enables the connection of non-volatile memory 23 to be coupled to circuit 13. This memory may be used to store information such as consumer power consumption and other information in the case of power failure. Various input and output ports of circuit 13 are coupled to connector Jl.

Diode D4 provides a 2.5V reference whilst diode D5 provides a 5V reference. The inverting input of A2 receives a signal when in the transmit mode and a transmit enable signal from circuit 13 is applied to transistor Ql. Output from pin Z/D controls the position of switch SW4. Signals received by T2 once mixed in mixer M2 provide a difference signal which serves as an input to circuit 13. A signal representative of the line voltage is derived from divider R7 and is applied to pin V connector Jl and then to circuit 13. Pins DH, DL are able to receive either high or low current signals from transformer T3. Signals detected at Tl are mixed in mixer Ml to provide a difference signal at pin A of circuit 13. Counter 24 provides a mixing frequency for mixer Ml. Pin S505 provides an output onto Tl.

Figure 3 of the drawings shows one embodiment of a decoupling network according to the invention. In this figure, voltage limiting varistor 25 is shown in parallel with the shunt element 12. The first series element 10 includes a transformer having a primary winding 30 and a secondary winding 31. A main current transformer having a winding 32 is arranged on the same magnetic circuit as windings 30 and 31. It is the current transformer winding 32 which provides the current I referred to in relation to figure 1. A band pass filter 33 is coupled across secondary winding 31 and is shown connected to a circuit 13.

Whilst the second series element may merely consist of a coil 40, in this figure, the second series element includes not only coil 40 which forms the primary winding of a transformer but also has winding 41 which forms a secondary winding of a transformer made up by windings 40 and 41. A current transformer winding 42 is arranged on the same magnetic circuit as windings 40 and 41 and provides the current I_χ referred to in relation to figure 1. A band pass filter 43 is connected across secondary winding 41. The band pass filter is shown connected to circuit 13. As illustrated in figure 3, the consumer may be provided with a plurality of load circuits and in which case, each of those load circuits is provided with a transformer having a primary winding in series with the load circuit, a secondary winding terminating in a filter and a current transformer on the same magnetic circuit for providing a current signal indicative of the current drawn on that load circuit. The filter may be coupled to circuit 13. That circuit may function to control switch 44 associated with that load line.

A particular preferred circuit for a decoupling network is shown in figure 4. The network has primary windings 30 and 40 wound on the same magnetic circuit but in an opposite sense. Windings 30 and 40 differ slightly in the number of turns employed and in the embodiment illustrated, the resultant turn remaining is one. Secondary windings 31 and 41 are shown wound on the same magnetic circuit and closely adjacent to their respective primary windings 30 and 40. A single current transformer winding 45 is shown wound on the common magnetic circuit. By having primary windings 30 and 40 wound in an opposite sense and differing slightly in the number of turns, it is possible -for current transformer winding 45 to have a substantially smaller number of windings than the current transformer windings 32 and 42 in figure 3 whilst still providing the same current transformation. Band pass filters 33 .and 43 are shown coupled across secondary windings 31 and 41 respectively. The circuit 13 is shown.

Figure 5a shows a magnetic circuit of one series element comprising two E cores 50, 51 of ferrite material arranged with a gap G. The transformer Tl (or T2) has one winding wound around the centre leg of the E cores and its other winding is wound about the first winding.

Figure 5b shows an alternative magnetic circuit to that of figure 5b. In this embodiment a C core 52 is used with windings wound on the C ferrite core.

In figure 6a a distribution transformer T4 is shown. That transformer has a high voltage primary and low voltage secondaries. Consumers derive their supply from the secondaries. Associated with the supply lines of one of the secondary are series elements 53, 54. Clearly a similar arrangement is used for the other secondaries. A shunt element 55 is coupled between the φ and N lines from the secondary of transformer T4. A circuit 13 like that of figure 2 is present for receiving from and transmitting to series elements 53, 54. In this embodiment the series elements are shown in different lines. One is in the φ (one phase) line from transformer whilst the other is in the neutral line. Clearly, both series elements can be in the φ line if desired. Shunt element 55 functions to prevent signals transmitted onto line φ via element 54 from proceeding to the consumer. These signals, typically at sa 5 to 15 kHz are reflected through transformer T4 and may be detected by the supply authority on the high voltage lines. Any signals emanating from the high voltage side of the transformer may be received by element 54 but do not pass downstream of element 55. Similarly any signals emanating downstream at the consumer are detected by element 54 and are not passed to transformer T4 because of element 55. The circuit 13 may transmit signals to the consumer via element 53 and these signals are blocked from T4 by element 55. Typically the signals emanating from or transmitted to the consumer are between say 50 to 100 kHz. Element 55 acts as a short circuit.

Figures 6b shows the manner in which element 53 may receive and transmit signals onto or from line N. Element 54 is configured in a like fashion. Element 53 includes a transformer having a secondary winding 56 which may simply be a single turn around line N. The primary windings 57, 58 are configured as shown. Winding 57 has filter components C20, R30 and is adapted to receive signals impressed onto line N and reflected by winding 56. Reception occurs at a relatively high impedance. Winding 58 is tapped and has MOSFETS Fl and F2 arranged in push pull to enable an oscillating signal to be impressed onto the winding for reflection to winding 56 for transmission onto line N. Inverters INI to IN5 are present to provide this push pull operation and to provide sufficient drive for Fl and F2. Resistor R31 and capacitor C21 are chosen for filtering to provide a sinusoidal carrier. Transmission occurs at a low. impedance. The inset drawing shows a typical way of winding the primary 56 about the φ line.

In figure 7, a complete communication system is shown in diagrammatic form. A 11KV transformer T4 is shown. As previously mentioned, up to as many as 80 or as few as say 30 consumers may be associated with transformer Tl. Information from the supply authority may be transmitted as a power line carrier to the transformer or alternatively by radio or via a telephone network to a distribution data concentrator (DDC) 60a. Alternatively the arrangement of figures 7a and 7b may be used. This unit applies data or control signals onto consumer supply lines 61a. Each consumer has a decoupling network and associated circuitry as shown in block diagram form in figure 1 and as shown in detail in figures 2 and 3. As previously described, the consumers each have a decoupling network and associated circuitry which for convenience will be termed a consumer switchboard unit (CSU) 62. The CSU 62 is intended to replace traditional kilowatt hour meters and load control relays and provides integrated load control and metering functions and has two low voltage mains communication interfaces for remote programming and interrogation either by the supply authority or the consumer. As also described, various CSU's can be used inside each consumer installation for sub-metering applications and for collecting other information from the installation. The CSU at the mains switchboard of the consumer acts as the "gateway" for information exchange between the consumer and the supply authority. The use of low voltage mains communication minimises installation wiring costs and allows the system to be easily expanded for future needs. A feature of the system is the separation of communication signals, which allows the supply authority to communicate with the main CSU in each installation but prevents each consumer's internal signals from entering the low voltage mains and possibly causing interference to other consumers. Associated with the CSU 62 is a GPO console 63 and a keyboard and display 64. The console 63 enables the consumer to directly control the supply of power to various ones of the load circuits or alternatively, control may be achieved by the consumer with unit 64.

The decoupling network illustrated in figure 2 and 3 is suitable for domestic or commercial loads up to 100 amps. For loads greater than 100 amp in commercial or industrial applications, the decoupling network may be configured as shown for example in figure 8. In this figure, supply terminals A and N have series elements or transformers 70 and 71 and connected to them to provide a low load output. Series elements 70 and 71 may be thought of as being identical to the series elements described in relation to earlier embodiments. Capacitor 72 provides a shunt element for preventing high frequency noise signals from passing in either direction. Capacitor 73 is optional and may be omitted if desired. Current transformer 74 or an equivalent for it may be provided to enable the load current to be monitored. A high load output of greater than 100 amps is shown available at the top right hand end of the circuit and high frequency signals are eliminated from the high load output by series element 70 and capacitor 72.

The series elements in the decoupling network of the invention may include a current transformer and a coupling device or secondary winding to enable bidirectional high frequency communication signals to be transferred between low voltage mains and a low power modem and may have a high current switching device rated up to the maximum load of the installation. Associated with the shunt or transverse element there may be a 50Hz voltage transducer, a circuit to power the system of the invention from the power line and a device for limiting voltage surges past the shunt element. The processing element of circuit 13 in figure 1 may provide a facility for processing the signals from the voltage and current transducers to produce digital quantities representing various real time quantities in the associated mains circuit, one or more high frequency modems for digital communication purposes, one or more control outputs for operating high current switching devices for switching consumer circuits, one or more digital inputs for status, alarm, or metering applications and a Zellweger receiver. The decoupling network and system of the invention provides the supply authority with an effective means of communicating with each consumer installation in a distribution network in an hierarchical manner as well as significantly reducing high frequency mains borne interference between consumer installations. In addition, real time load and metering information can be provided and remotely collected by the supply authority. With the system of the invention it is possible to control loads in individual consumer installations to reduce the maximum demand and improve local system load factors . The system enables energy management within each installation including monitoring and control of other functions such as fire and security alarms.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A decoupling network including an input and an output, a filter between the input and the output, said filter blocking high frequency signals from passing from the input to the output and from the output to the input whilst enabling low frequency signals to pass in either direction, said filter presenting a defined impedance for the high frequency signals irrespective of impedance connected to the input or the output.

2. The decoupling network of claim 1 wherein said filter includes a first and a second series element coupled between the input and the output, at least one of said series elements including a transformer and the other said series element comprising a coil, a shunt element coupled between a junction between the series elements and a reference or between the series elements and said network including a further filter associated with said one series element.

3. The network of claim 2 wherein said transformer and said coil have a common magnetic circuit.

4. The network of claim 2 or 3 wherein said coil is a winding of a transformer and said transformers have primary windings in series coupled with the junction between them, said primary windings having the same or different number of turns.

5. The network of claim 4 wherein the transformers have secondary windings with a number of turns greater than the primary windings.

6. The network of claim 4 or 5 wherein, when said transformers have a common magnetic circuit the primary windings are wound in opposite sense.

7. The network of claim 5 or 6 wherein the secondary windings have the same number of turns.

8. The network of any one of claims 4 to 7 including a current transformer in the same magnetic circuit as one or both said series transformers.

9. The network of claim 8 wherein the current transformer has a substantially greater number of turns than either said series transformer.

10. The network of claim 9 wherein said current transformer has about 800 turns and the primary windings of the series transformers have about 13 and 14 turns respectivel .

11. The network of any one of claims 2 to 10 wherein each said series element has a respective said filter associated with it.

12. The network of claim 11 wherein each said filter presents a low impedance for facilitating transmission of communication signals and a high impedance for receiving communication signals.

13. The network of claim 11 or 12 wherein said filters are band pass filters and said filters include mixers.

14. The network of any one of claims 2 to 13 wherein said shunt element functions to present a short circuit for high frequency signals between the junction and the reference.

15. The network of claim 14 wherein the shunt impedance is a low pass filter and includes a voltage divider network for providing a scaled voltage indicative of the potential across the shunt element.

16. The network of any one of claims 2 to 15 including a voltage divider for providing a voltage signal indicative of the maximum voltage level at the input and from which the frequency at the input may be monitored.

17. The network of claim 16 when appended to claim 8 wherein power supplied at the input may be determined from the divider voltage and current supplied by the current transformer.

18. A decoupling network substantially as herein described with reference to the drawings.

19. A communication system including the decoupling network of any one of claims 1 to 17, associated with a consumer, said input being adapted for coupling to supply lines of a supply authority and the output to load lines for a consumer, said lines each including an active line and a common reference line, said system including a computer for receiving control inputs and providing control outputs and having a modulator for connection to said one series element to enable a transmit signal to be impressed onto the supply lines at a low impedance, a demodulator for connection to said one series element to enable communication signals on said supply lines to be received at a high impedance and an A/D converter, and said shunt element together with said one series element being effective to short high frequency signals appearing on the supply lines to a reference and said shunt impedance together with the other series short high frequency signals appearing on the load lines to the reference.

20. The system of claim 18 wherein said computer provides the modulator, demodulator and A/D converter under software control and controls sub etering and supply circuits of the consumer and enables the consumer to interrogate the authority_, and control the supply circuits if desired and permitted by the authority.

21. The system of claim 20 wherein the computer is an INTEL 80C196 micro controller.

22. The system of claim 19 including a distribution transformer with a high voltage primary winding and a plurality of low voltage secondary windings and further including a decoupling network according to any one of claims 1 to 18 associated with each said secondary winding and said secondary windings providing the supply line for the consumer and including a computer for receiving control inputs and providing control outputs and having a modulator for connection to said one series element of said further network to enable a transmit signal to be impressed onto the supply line at a low impedance, a demodulator for connection to said one series element to enable communication signals on said supply lines to be received at a high impedance and an A/D converter, and said shunt element together with said one series element of said further network being effective to short high frequency signals appearing on the supply line to a reference potential and said shunt element together with the other series element of said further network short high frequency signals transmitted by the consumer onto the supply line to the reference, said computer of said further network controls the communication between the distribution transformer and the authority.

23. The system of claim 22 wherein the series elements of the network associated with the secondary windings each have a primary winding and two secondary windings one of which said two secondary windings is tapped.

24. The system of claim 23 wherein the untapped secondary winding of each said series element is adapted to receive signals and the tapped windings are adapted to transmit signals.

25. The system of claim 19 when appended to claim 16 including memory means for storing said signal indicative of the maximum voltage level and of the frequency of the input.

26. The system of claim 19 when appended to claim 17 including memory means for storing the product of the maximum voltage signal and the current of the current transformer to provide an indication of power consumption.

27. The system of claim 19 wherein said computer outputs signals for controlling power circuits supplied to the consumer.

28. The system of claim 19 when appended to claim 16 including deriving an output signal from the divider voltage signal for controlling an audio frequency relay network.

29. A system substantially as herein described with reference to the drawings.