Communications: electrical – Systems – Selsyn type
Patent
1996-09-26
1999-01-05
Tong, Nina
Communications: electrical
Systems
Selsyn type
34031006, 34031007, 34031008, H04M 1104
Patent
active
058567763
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned generally with communication over electricity supply networks (sometimes termed PLC, Power Line Communication), and more particularly over underground networks operating at voltages above the final supply voltage to consumers.
BACKGROUND OF THE INVENTION
Mains distribution--general
In most major countries, electricity is supplied on a wide scale by electricity generating 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 small business consumers are connected, with the low voltage networks being supplied through a higher voltage distribution network or system (often termed the grid). The low voltage (consumer) networks may for example operate at 230 V (or 440 V 3-phase).
The distribution network will normally operate at more than one voltage. There is long-distance distribution at voltages of say 132 kV or 275 kV, which we will term high voltages. These high voltages are stepped down (possibly through 2 or more stages) through transformer and switching stations (which we will term primary or high voltage stations) to voltages of say 11 kV or 33 kV, which we will term intermediate voltages. These are in turn stepped down through further transformer and switching stations (which we will term substations) to the final consumer mains voltage.
Mains signalling--general
The use of the mains for signalling has often been proposed. Systems are available for intercommunication between rooms in domestic premises (typically for "baby alarms"), for coupling to the telephone system, and for transmission of data between computer units. Many proposals have also been made for the use of mains signalling for remote meter reading (primarily for electricity meters, though gas and other meters can be coupled to the mains for this purpose, preferably 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 available for signalling on low voltage electrical installations. This bandwidth is divided into several smaller bands with various uses and permissions associated with them; for example, the 9 kHz-95 kHz band is reserved for electricity suppliers and their licencees.
The signalling will normally involve users, and will therefore operate over the low voltage portions of the network. However, as noted above, the distribution network will normally include intermediate and high voltage levels, coupled through power transformers. The transformers between the intermediate and the final low (consumer) voltage levels are normally located at unattended sites which have no ready means of communication over other communication networks such as telephone systems. It is therefore often desirable to couple PLC (power line carrier) signals between the low and intermediate voltage portions of the network and over intermediate voltage portions of the network.
Signalling frequency signals do not pass through power (distribution) transformers effectively. Some means of coupling PLC signals round such transformers is therefore necessary if signalling between low and intermediate voltage portions of the network is to be achieved. This will normally Involve signal reception and retransmission, with the signals being processed to remove noise. It may also be desirable to use different frequency bands on the two sides of the transformer. (This has the advantage that any signal feedthrough at power transformers will be irrelevant.)
Mains signalling--relevance of mains voltage level
Signal transmission and reception techniques are relatively straightforward for low voltage mains. The signal transmission and reception equipment can be connected directly to the mains wiring.
An intermediate voltage network, however, presents more difficulty, for both electrical and mechanical reasons. Int
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patent: 4686382 (1987-08-01), Shuey
patent: 4745391 (1988-05-01), Gajjar
C.Nunn et al, Remote Meter Reading And Control Using High-Performance PLC Communications Over The Low Voltage And Medium Voltage Distribution Networks, Proceedings of Seventh International Conference on Metering Apparatus and Tariffs for Electricity Supply, Nov. 1992, pp. 304-308.
Armstrong Donald Stuart
Halse Nigal John
Moore Paul Martin
Wells Joseph Anthony
Remote Metering Systems Ltd.
Tong Nina
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