Electrical transmission or interconnection systems – Anti-electrolysis
Patent
1994-08-23
1996-07-30
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Anti-electrolysis
204196, C23F 1306, H01B 728
Patent
active
055414591
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a device for compensation of an alternating voltage which occurs between a medium and a metallic pipeline disposed in the medium, the pipeline being surrounded by a layer (mantle) of electrically insulating material.
BACKGROUND ART
In case of parallelism between a.c. transmission lines and metal pipes for, for example, natural gas, the normal operating current of the transmission line induces a voltage in the metal pipe. For example, from a 400 kV line with an operating current of 1000 A at a distance of 50 m from the pipeline, an induced voltage of about 20 V/km can be obtained.
A metal pipe of the above kind may, for example, constitute part of a long gas conduit, which is disposed in the ground and possibly partially also in water. A conduit of this kind is usually divided into sections with the aid of electrically insulating joints. The length of one section may vary from several kilometers up to several tens of kilometers. If a transmission line runs parallel to such a line for a distance of some length, induced voltages of a considerable magnitude may therefore occur.
When the alternating voltage between the pipe and the surrounding ground (water) exceeds a few tens of volts, this may entail an increased risk of corrosion damage to the pipeline because of electrolytic corrosion. Metal pipes of the kind in question are provided with a protective coating of an electrically insulating material. However, damage unavoidably arises in this coating, whereby the metal pipe is brought into electrical contact with the surrounding medium. At these points the above-mentioned risk of corrosion occurs.
Different types of measures for protection against corrosion are previously known. However, these do not provide any protection against the risk of corrosion which is caused by alternating voltages induced in a pipeline.
SUMMARY OF THE INVENTION
The invention aims to provide a device which, in a simple and advantageous manner, provides good protection against the risks of corrosion which, in pipelines of the kind mentioned in the introduction, are caused by alternating voltages induced in the pipelines.
What characterizes a device according to the invention will become clear from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail with reference to the accompanying FIGS. 1-5, wherein
FIGS. 1a-1c show an example of a device according to the invention, wherein FIG. 1a shows a general diagram of the device, FIG. 1b shows the transformer included in the device and the location of the transformer around the pipeline, and FIG. 1c illustrates the reduction of the voltage between the pipeline and the surrounding medium which can be obtained with the aid of the device shown in FIG. 1a and FIG. 1b.
FIG. 2a shows how, in equipment according to the invention, several transformers can be arranged along a section of the pipeline, and FIG. 2b shows the reduction of the voltage between the pipeline and ground which can be obtained in this way,
FIG. 3 shows an alternative embodiment in which the transformer included in the device is supplied from a power amplifier,
FIG. 4 shows how a controllable transformer coupling can be used as an alternative for supply of the transformer of the equipment, and
FIGS. 5a and 5b show an alternative method for sensing the voltage induced in the pipeline and for controlling the supply voltage to the transformer included in the equipment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1a shows an elementary diagram of a piece of equipment according to the invention. The figure shows a section 1 of a metallic natural gas conduit 1 disposed in the ground, the conduit being provided with an electrically insulating coating and being electrically insulated from adjoining pipe sections with the aid of electrically insulating joints 11 and 12. To provide a measure of the alternating voltage which can be induced in the section 1 by electric transmission lines, which extend in the vicinity of and wholly or
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patent: 1962696 (1934-06-01), Rhodes
patent: 2053214 (1936-09-01), Brown
patent: 2483397 (1949-10-01), Bonner
patent: 2862177 (1958-11-01), Titterington
patent: 2893939 (1959-07-01), Reid
patent: 4219807 (1980-08-01), Speck et al.
patent: 5126654 (1992-06-01), Murphy et al.
Jonsson Uno
Karlsson Dan
Elms Richard T.
Shoop Jr. William M.
STRI AB
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