High-energy low-voltage surge arrester

Claim 1

A surge arrester for protecting against high energy and very fast surges imposed upon a line comprising two conductors, each connected between a source and a load, the surges being capable of rising to thousands of amperes in less than 100 nanoseconds, said surge arrester comprising: (a) a first conductive electrode for connection in series with one of said conductors between said source and said load, (b) a second conductive electrode for connection in series with the other of said conductors between said source and said load, (c) metal oxide varistor disk structure having a thickness of several tenths of an inch or less and external surfaces at opposite ends of its thickness, (d) thin metallic coatings respectively coating said external surfaces, (e) means for mounting said metal oxide varistor disk structure between said two electrodes with one of said electrodes contacting one of said metallic coatings and the other electrode contacting the other of said metallic coatings, and further characterized by: (f) said first electrode having a central region and, at generally diametrically-opposed sides of said central region, a source terminal and a load terminal for connection to said one conductor in such a manner that a load current in said one conductor normally flowing between said source and said load flows through said first electrode via a path that extends in series through said source terminal, said central region, and said load terminal, (g) said second electrode having a central region and, at generally diametrically-opposed sides of said central region, a source terminal and a load terminal for connection to said other conductor in such a manner that said load current in returning through said other conductor normally flows between said load and said source through said second electrode via a path that extends in series through said load terminal, said central region, and said source terminal, (h) the source terminals of said two electrodes being generally aligned with each other about the periphery of said disk structure, (i) the distance between the source terminal and the load terminal of each electrode being at least three times the thickness of said disk structure, (j) the inductance of said two electrodes between the source and load terminals of each electrode coacting with the resistance of said disk structure when the disk structure is rendered conductive by a current surge entering through the source terminal of one electrode to form a low-pass L/R filter that substantially reduces the voltage appearing at the load terminal of said one electrode in comparison to that appearing at the source terminal during passage of said surge, (k) at least one of said electrodes being sufficiently narrow transversely of the normal current path therethrough that the electrode provides no conductive bypass between the source terminal and the load terminal thereof that is located outside the periphery of said varistor disk structure in the region of said electrode, and (l) the effective length of any lead between each line conductor and the electrode connected thereto being essentially zero.