Communications: electrical – Systems – Selsyn type
Patent
1997-02-21
1999-09-07
Hofsass, Jeffery A.
Communications: electrical
Systems
Selsyn type
34031005, 34031006, 34031007, 455 33, 375258, H04M 1104
Patent
active
059493275
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of signal injection, transmission, interconnection (termination) and detection, and to a power transmission network, ie. a mains electricity distribution and/or transmission network, and a filter therefor. In particular it relates to the use of overhead mains electricity networks and/or lines for telecommunications transmission (e.g. voice, data, image and/or video).
BACKGROUND ART
In the UK, it is conventional to describe a power network for 33 kV and above as a "transmission network", and one for less than 33 kV as a "distribution network". In this specification the term "electricity distribution and/or power transmission network" (EDN) is normally used, but general references to power networks and to transmission of signals are to be construed as applying to all such networks.
Traditionally telecommunications signals have been transmitted on independent networks e.g. telephone lines. More recently, in order to simplify and increase efficiency of telecommunications services to domestic or industrial premises, there have been investigations into using existing electricity transmission and distribution networks to carry telecommunications services.
It has been known to utilise above ground (overhead)(OH) power lines for the transmission of additional control, speech and data signals. However, with such transmissions, in the past the frequency spectrum has been allocated for and restricted to particular applications in order to avoid interference with other telecommunications services. In addition, the strength of signals which could be transmitted was generally thought to be limited since the amount of radiation produced by the transmission is related to the strength of the signal and this radiation must be kept to a minimum.
Such transmission signals have therefore been of low power and confined within a specific frequency band allocated by international agreement for such purposes, so this mechanism has been thought to be unsuitable for large scale voice and/or data transmission where signals extend well into the radio spectrum (e.g. 150 kHz and above).
Furthermore, if signals are to be transmitted on overhead power networks then other problems need to be overcome, such as the problems of noise on the networks, varying customer loads attached to the network, and impedance matching between communications equipment attached to the network and the network itself.
It has been known to use spread spectrum techniques to transmit data at carrier frequencies of between 6 kHz and 148 kHz on underground (UG) and overhead (OH) EDN's. Again, in this allocated frequency band such transmissions suffer from low data rates and low traffic capacities due to power line noise characteristics. Due to the limited spectrum available and high noise levels encountered wideband telecommunications signals have not been sent.
Although papers such as that by J. R. Formby and R. N. Adams, ("The mains network as a high frequency signalling medium", The Electricity Council, January 1970) suggested a communications potential for the low and medium voltage networks, no further work was undertaken. Even today, with the prospect of remote meter reading and selective load control, solutions tend to employ techniques such as telephony and radio communications, thus avoiding the mains network where possible.
Ideas have been put forward but few have proceeded past the theoretical stage, due to the hostile environment presented by the mains network. The problems to be overcome include electrical noise, (both constant background noise and transient spikes) and high attenuation of high frequency signals due to skin and proximity effects.
Messrs Formby and Adams suggested using frequencies in the range of 80 to 100 kHz. 100 kHz was recommended as a maximum because theory suggested that higher frequencies would suffer from excessive attenuation. Other papers recommend a maximum of 150 kHz due to the fact that radiated signals higher than 150 kHz would interfere with broadcast radio
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JP62
Hofsass Jeffery A.
La Anh
Norweb PLC
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