GB1339038A - Arc-expansion chamber system for an overvoltage arrester - Google Patents

Abstract

1339038 Protective apparatus BROWN BOVERI & CO Ltd 12 May 1971 [12 May 1970] 14505/71 Heading H2H A voltage surge arrester of the type in which an arc is elongated by electromagnetic means is provided with at least two are expansion chambers which may be placed one above the other or side by side, means be provided to cause an arc to be initiated in one chamber wherein it is lengthened and thereafter passes to the next chamber wherein it is further lengthened. An arrestor comprises two arc expansion chambers 1, 2 made of three porous discs of insulating refractory material. Each chamber is formed between the opposed, complementary surfaces of two of the discs, and the common intermediate disc has its upper and lower surfaces formed with a "wave" configuration. The peripheral wall 14 of each chamber has castellations 3 formed therein. When a voltage surge occurs on a line 15 the primary spark gap 12 breaks down and an arc is established between arc horns 4. The initial arc current is carried by a resistor 10 but as the arc establishes itself the arc current commutates from the resistor 10 to the coil 9 thus setting up a magnetic field which causes the arc between the horns 4 to become elongated and spread out across the arc expansion chamber 1. As the arc expands ions are expelled from the chamber 1 to the chamber 2 thereby ionizing a secondary spark gap 13 in the chamber 2. When the arc in the chamber 1 reaches the inside wall of the chamber a part of the arc spans a pair of electrodes 7 which are electrically connected to arc horns 5 in the chamber 2. The spark gap 13 is shorter than the spark gap 12 so that, at this point the spark gap 13 breaks down and further expansion of the arc takes place in chamber 2. Further chambers may be provided so that continued expansion of the are may be effected if desired. Numerous embodiments are described in which the arc horns are situated radially in the chamber, one being placed at the centre so that in each chamber the arc is elongated to double the length. Furthermore the arc elongation path may be formed in a spiral in which ease the duct 8 and arcing horns 5 may be dispensed with.