Communications: electrical – Systems – Selsyn type
Reexamination Certificate
1999-09-13
2001-07-03
Crosland, Donnie L. (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C340S315000, C333S02400C
Reexamination Certificate
active
06255935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of communication via electrical power supply networks. It is based on an apparatus for injecting signals into electrical power lines.
2. Discussion of Background
The use of existing power distribution networks for data communication is of major economic importance. Electricity supply utilities would like, for example, to interrogate devices in the electrical power distribution network without reinstallation of lines and control them remotely, or optimize the utilization of the network by remote interrogation and control of end users.
German Patent Specification DE 196 48 382 C1 discloses a method and an apparatus for transmitting signals via electrical power supply lines, in which communication signals are transmitted via the phase conductor shields of electrical power cables. The signals are modulated onto the shields via inductive couplers. This method is obviously applicable only to electrical power cables having shields, and is unsuitable for unshielded cross country lines. Furthermore, the circuit for a signal transmission device is described, in which the communication signals are infected and/or output via a coupling capacitor to and/or from at least one phase conductor of the electrical power line.
The coupling capacitor (KK) is connected to a phase conductor at the medium-voltage or high-voltage level by means of a connecting cable (AK) through which no current passes. The AK and KK are normally connected outside a housing which surrounds the KK and is grounded. The bushing (which is compatible with medium voltage or high voltage) through this housing comprises means for field reduction, in order to avoid field peaks. A suitable way to achieve this is, for example, by means of a field-controlling layer composed of a material having a high dielectric constant, which layer is arranged as a flexible tube or strip around the electrical power conductor (cable termination). A capacitive field controller disclosed in WO 80/00762 is suitable for bushings through grounded metal walls. This is based on a number of conductive metal foils arranged concentrically around the central conductor.
The connection of the connecting cable to the bushing requires a high level of insulation complexity and occupies a large amount of space. Furthermore, it is not feasible in modern compact switchgear assemblies owing to the excessively short isolation spacings with conventional cable terminations. As a substitute, connections by means of insulated high-voltage coaxial connectors are feasible, but these are expensive and complex to install.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel, cost-effective, space-saving and efficient apparatus for capacitive signal injection into an overhead line or an electrical power cable of a medium-voltage or high-voltage network. According to the invention.
The essence of the invention is for one end of the insulated connecting cable to be directly integrated in a housing which encloses the coupling capacitor. This avoids the connection mentioned above which is expensive and is complex in terms of insulation. Such integration of an insulated medium-voltage or high-voltage cable in a grounded housing requires field control or field grading in the region of the bushing, that is to say at the point where the cable shield is interrupted. In the present invention, the electrical field is reduced by means of a specific specification for the shape of the housing. Suitable rounding of the formed region (according to the invention) of the housing wall on the cable side results in a field distribution which is not critical.
Known and proven standard components (coupling capacitors (KK) and connecting cables (AK)) can be used to implement the invention. The unit according to the invention and formed from KK and AK is compact and is protected against direct contact, and it is possible to achieve further volume and weight savings by using dry capacitors. The configuration (which is intended to provide field grading) of the housing surrounding the KK can be produced by simple and cost-effective mechanical machining.
REFERENCES:
patent: 3771069 (1973-11-01), Levacher et al.
patent: 4142178 (1979-02-01), Whyte et al.
patent: 5192231 (1993-03-01), Dolin, Jr.
patent: 5406249 (1995-04-01), Pettus
patent: 5559377 (1996-09-01), Abraham
patent: 195 10 659 C1 (1995-03-01), None
patent: 196 48 382 C1 (1996-11-01), None
patent: 2 685 562 (1993-06-01), None
patent: 56-007532 (1981-01-01), None
patent: 08264330 (1996-11-01), None
patent: 80/00762 (1980-04-01), None
Doser Bernhard
Lehmann Josef
Postma Ate
Rhyner Jakob
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Crosland Donnie L.
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