Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Patent
1997-06-05
1999-03-16
Brown, Glenn W.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
324525, G01R 3108
Patent
active
058835172
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for locating faults on subsea telecommunications links that may be constituted, for example, by optical fiber cables or by coaxial cables, with fault location being done by determining the resistance of a conductor of the cable presenting a fault, in association with defective insulation relative to the sea.
The basic element of a subsea telecommunications link is a subsea cable. There are two main categories of subsea telecommunications link: coaxial cable links, and optical fiber cable links. Coaxial cable links generally use analog transmission, whereas optical fiber links generally use digital transmission.
When it is desired that an analog subsea link (i.e. a link implementing analog transmission) should cover a great distance, it normally comprises a plurality of cable sections interconnected by repeaters which are active devices whose main function is to amplify the signal so as to compensate for attenuation of the analog signal due to propagation of the signal along the cable sections.
When it is desired that a digital subsea link (i.e. implementing digital transmission) should cover a great distance, it normally comprises a plurality of cable sections interconnected by regenerators or repeaters. The role of regenerators is to reconstitute as faithfully as possible the digital information transmitted by a signal after it has been attenuated, deformed, and disturbed by travelling along a transmission cable.
For example, digital subsea links of great length, having optical fiber cables operating at 560 Mbit/s, may be implemented with regenerators, while faster links (specifically 5 Gbit/s) may be designed to have repeaters including optical amplifiers.
Subsea links may be complex in structure, having a main trunk, plus one or more branches connected to the trunk by branching units. Under such circumstances, the link includes more than two landing points.
Coaxial subsea telecommunications cables, which are normally used solely for analog subsea links, typically comprise, from the inside towards the outside: a composite conductor constituted by a steel wire core and a copper tube; an insulating sheath of polyethylene; an outer conductor formed by a strip of copper or aluminum; and an insulating sheath of polyethylene. Additional layers may be added to provide the cable with mechanical protection.
Subsea optical fiber cables which are normally used solely for digital subsea links, typically comprise, from the inside towards the outside: an optical unit containing optical fibers; a composite conductor surrounding the optical unit and comprising armoring of steel wires that provide the cable with mechanical strength in traction, and a copper tube surrounding the armoring; and an insulating sheath of polyethylene. Additional layers may be added to provide the cable with mechanical protection.
For a link using regenerators or repeaters, electrical power is generally fed to such active apparatuses by injecting current into a conductor of the cable, with the various active apparatuses being fed in series by a process that is well known to the person skilled in the art, who refer to "remote power feeding". For example, both for a coaxial subsea telecommunications cable and for a subsea optical fiber cable as described above, remote power feeding for the link is generally provided via the composite conductor.
For a subsea optical fiber cable of this kind, the go remote power current travels along the composite conductor while the return current travels through seawater and optionally through the ground, with the remote power feeding equipment (PFE) delivering the remote electrical power being appropriately grounded by a grounding contact in the earth or by a grounding contact in the sea. These equipment are generally installed on land, close to the landing points of the link.
For a subsea coaxial cable, the outer conductor is normally grounded at the ends of the link, and the remote power feeding takes place in a manner similar to that used for an optical fiber cable, with
REFERENCES:
patent: 4929900 (1990-05-01), Hastings et al.
patent: 5210498 (1993-05-01), Paananen
Broyde Frederic
Clavelier Evelyne
Brown Glenn W.
Excem
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