Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1984-11-01
1987-05-12
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361117, 339 14R, 339109, 343845, 174 6, 174 78, H01T 402
Patent
active
046654607
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of the transmission of electrical energy by overhead lines and more particularly improved means to protect such lines and installations which are electrically connected to them against lightning.
It is known that lightning may take place in the form of an electric discharge under very high voltage between the ground and, for instance, cloud masses, using preferably the electroconductive path offered by objects which are elevated above the ground such as trees, buildings and, of course, overhead electrical systems. It is known how to protect overhead electrical energy transmission systems by devices known as arresters, formed by a pair of electrodes each consisting of a galvanized steel rod bent to about 45.degree.; the electrodes are arranged in the vicinity and generally directly above a group of insulators, a tower or a pole in the same plane, the bends thereof facing each other and being separated by a certain distance, one of the electrodes being connected to the electric line and the other being connected to the ground; one of the electrodes is supported via a crossbar directly by the line cable; the other electrode is also supported by a crossbar integral with a cable or rod for fastening the insulators to the poles; this fastening cable may also serve, since it is connected to the ground, as ground conductor for the second electrode; generally, the electrodes, their support crossbar and the fastening cable are of steel. The use of such a manner of protection in actual practice has shown that systems under voltage such as transformers, for instance, were protected in the case of discharges not exceeding 15 kilo-amperes; in the case of discharges of higher intensity, the grounding of the line by arresters of the present design is inadequate; a number of transformers and other apparatus forming part of the systems are thus damaged by lightning each year.
Furthermore, for a very long time devices have been known for the grounding of lightning protection means, these devices generally consisting of an electric conductor buried in the earth or, even better, extending into a shaft so as, by means of the underground water, to find in the earth an electroconductive mass having the lowest resistance possible. Now the ground connections proposed up to the present time, while they are entirely suitable for dissipating a continuous electric voltage, seem poorly suited to dissipating energy of an electric wave of very great amplitude and short period such as that with which the phenomenon of lightning generally takes place.
The basic idea of the present invention rests, on the one hand, on recent knowledge as to the nature and behavior of the current forming the discharge of the lightning in conductors and, on the other hand, on consideration of the fact, which has been known for a longer time, that electric charges distribute themselves on the surface of conductors. Studies carried out during the last decades have shown that an atmospheric discharge entailed a phase of increasing intensity (the discharge front) of about 8 microseconds and a phase of decreasing intensity (the discharge tail) of about 20 microseconds; it is this intensity wave which is propagated along the "discharge channel" and into the conductors encountered; thus, while the techniques of the prior art did not take this oscillatory, dynamic aspect of the discharge into account, the present invention is directed precisely at placing greater store in it, trying to reduce to a maximum the impedance of the ground evacuation circuits, in particular, by striving to preserve the surface or film conduction effect of these circuits.
Thus the improvements proposed by the invention relate to three kinds of means: First of all, the arresters and their manner of connection, secondly, the ground connections and their connection; and thirdly, connecting or junction means.
First of all, in accordance with the present invention, an arrester of the type comprising a pair of electrodes which are supported by a support wh
REFERENCES:
patent: 1755324 (1930-04-01), Jacobs
patent: 1769101 (1930-07-01), Becker
patent: 3370122 (1968-02-01), Ichikowa
patent: 3377609 (1968-04-01), Shannon
"Optimum Design of Substation Grounding in a Two Layer Earth Structure" Part III by Dawalibi et al., IEEE Transactions on Power Apparatus and Systems vol. PAS-94, Mar./Apr. 1975.
Ebert Michael
Jennings Derek S.
Pellinen A. D.
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