Communications: electrical – Systems – Selsyn type
Reexamination Certificate
1999-04-06
2001-01-09
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C340S315000
Reexamination Certificate
active
06172597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a method of signal injection, transmission, interconnection (termination), and detection, and to a power transmission network, i.e. a mains electricity distribution and/or transmission network, and a filter therefor. In particular it relates to the use of electricity transmission networks and/or lines for telecommunications transmission (e.g. voice and/or data).
2. 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” 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) power lines for the transmission of additional control, speech and data signals. However, with such transmissions, the frequency spectrum must be allocated for and restricted to particular applications in order to avoid interference with other telecommunications services. In addition, the strength of signals which can be transmitted is 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 must therefore be of low power and confined within a specific frequency band allocated by international agreement for such purposes, so this mechanism is unsuitable for large scale voice and/or data transmission where signals extend well into the radio spectrum (e.g. 150 kHz and above).
It has been known to use spread spectrum techniques to transmit data at carrier frequencies of between 6 kHz and 148 kHz on underground and overhead power networks. 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 telecommunication signals cannot be sent.
Although papers such as 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 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 signals.
A further situation where power networks are also used for the transmission of speech and data signals is on the electricity wiring inside buildings. In such configurations the internal 240V mains wiring is used for the transmission of data, with appropriate filtering being provided to add and separate the data signals from the power signals. Additionally a filter, such as the Emlux filter described in European Patent Application 141673, may be provided to prevent data signals leaving the building and entering the power supply network external to the building. The Emlux filter described consists of a tuned ferrite ring which acts effectively as a band stop filter. In order to be effective the band stop filter must be of narrow band width and therefore is not suitable for use with high speed data communications, since a large number of such band stop filters would be required.
SUMMARY OF THE INVENTION
The present invention aims to provide a transmission network which alleviates some or all of the above problems.
Accordingly, in a first aspect, the present invention provides a power transmission and/or distribution network including input means for the input of a telecommunication signal having a carrier frequency greater than approximately 1 MHz onto the network, (e.g. an underground electricity transmission and/or distribution network), and output means for removal of similar telecommunication signal from the network.
Contrary to the teachings of the prior art, use of carrier frequencies of this magnitude is not impractical due to attenuation effects. This is because, at these higher frequencies, the cables of the power transmission and/or distribution network exhibit pseudo-coaxial characteristics and therefore attenuation is reduced.
In this way both speech and data signals can be transmitted at carrier frequencies of greater than approximately 1 MHz allowing for a larger available spectrum and greater transmission capacity. The carrier frequency may in fact be less than 1 MHz ie. 800 kHz or even as low as 600 kHz, but as it is reduced so is the bandwidth.
The term “carrier frequency” refers to the unmodulated frequency of the carrier signal, and not to the frequency of the telecommunication signal once modulated.
On, for example, a 415V network the carrier frequency may preferably be between 1-10 MHz, and on, eg., a 11 kV network may be between 5-60 MHz. However the frequency may be up to 100's of MHz depending on the network and the application. For example, over short distances (10-20 m) a frequency range of 1-800 MHz may be used.
Preferably the power network is a major underground power network including e.g. 132 kV, 33 kV, 11 kV, 415 V and 240 V sections. The voice and data signals may be transmitted over any or all of the sections of the power network by suitable detection, amplification and/or regeneration and reintroduction as and when necessary.
In preferred embodiments, full duplex facilities are provided i.e. signals may be transmitted and/or received in all directions simultaneously.
A network according to the first aspect of the present invention may be used for many speech and/or data transmission purposes, such as remote reading of electricity meters, remote banking and shopping, energy management systems, telephony (voice), switched telephony, security systems and/or interactive data services and television.
In a second aspect, the present invention provides a “network conditioning unit” for use with a network according to the first aspect of the present invention. The network conditioning unit includes a low pass filter portion or portions for filtering out the low frequency high amplitude mains power signal, a coupling element for input and removal of telecommunication signals from the network and, preferably, a terminating element of similar impedance to the characteristic impedance of the network at that point.
The use of such a unit ensures that the high frequency telecommunications signals do not contaminate the internal low voltage wiring present inside a premises, and/or that noise sources from the internal low voltage premises wiring do not contaminate or corrupt the high frequency telecommunications signals being transmitted over the external electricity transmission and/or distribution network.
Preferably, the variable electrical loading effects (i.e. the load impedances) of all items which are coupled onto the network, from
Howrey Simon Arnold & White , LLP
Lefkowitz Edward
Norweb PLC
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