Electric transmission lines and distribution stations, especially those of the outdoor variety and substation classification, are especially exposed to and vulnerable to voltage surges, transients, and atmosphere discharges, including those caused directly and indirectly by lightning.
Various methods, means, and devices are known to protect electric distribution systems and transmission lines and equipment supplied by them.
There is considerable prior art concerning protection of fixed structures. Indeed, Ben Franklin two hundred years ago pioneered the use of lightning rods, describing a cone of protection. Since then the cone of protection has been refined, and recently scientists have come to an understanding why it does not work exactly as predicted. A new art was introduced as the Dissipation Array.RTM. System by Lightning Eliminators & Consultants, Inc. which prevents a direct strike.
Low voltage surge suppression devices are also common. They are used routinely to protect electronic devices from large voltage surges, as for example caused by lightning strikes. A few work by burning out. Their low cost allows them to be economically replaced.
Neither of the above two approaches alone is realistically feasible for use with high voltage transmission lines and electrical distribution systems. While it is practical to shield transformers with the lightning rods and dissipation arrays, it is not economically practical to likewise protect the high voltage lines coming into and leaving such transformers. However, by their vary nature high voltage lines continuously receive numerous lightning induced high voltage surges, and thus destructive protection is also not economically practical.
U.S. Pat. No. 4,743,997 (1988) to Roy Carpenter Jr. discloses a high-voltage type surge elimination system. It shows a system where two surge arrestors are used to ground high voltage lightning surges. The two surge arrestors are separated by a surge interceptor, which by the use of an induction delays a fast rising surge long enough for the first arrestor to operate. The performance of this system is an improvement over the use of surge arrestors without the intervening surge interceptor.
FIG. 9 shows the '997 surge elimination system 118. High voltage power enters 150 the system 118. There is a high energy surge arrestor 120 connected between the input 152 and ground 154. The high energy arrestor 120 is comprised of a spark gap 122 and a solid state device 124. The high voltage power then flows through a surge interceptor (SI) 130 connected between the high energy arrestor 120 and a lower energy arrestor 140. The SI has a core 132 and an inductor 134. The low energy surge arrestor 140 is comprised of a solid state device. It is connected between the SI 156 and ground 158. High power leaving 160 the system 118 is limited as to its maximum voltage.
The current invention improves upon the '997 invention in several ways. First, three 90.degree. right hand turns are introduced into the high voltage circuit. These exploit the fact that lightning strike induced surges have high inertia, and thus resist right angle turns. This was not disclosed in the '997 patent.
Secondly, the surge interceptor is improved. The '997 patent shows a surge interceptor that has toroidal rings around one metal cylinder, located in another cylinder. The surge interceptor in the instant invention comprises a low capacitance wirewrapped hollow fiberglass tube encased in ceramic insulation.
Finally, a high energy resistor is added in parallel to the inductor in the surge interceptor. This has the effect of dampening the ringing or oscillation found on the output side of the '997 surge interceptor. The addition of a high energy resistor was also not present in the '997 patent.
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