Pellet Type of Oxide Film Lightning Arrester

Practise has confirmed the theory that a valve type of lightning arrester is the best; that is, one which has a very large resistance or impedance at rated voltage, but which has a resistance of only a comparatively few ohms at say double rated voltage. The aluminum arrester was the first of this type and its success is well known. Somewhat later the oxide film (OF) arrester was developed to overcome the disadvantage of charging, and this type too has had remarkable success. A modification of this ``OF´´ type is now announced. Briefly, pills or pellets of lead peroxide, the chemical powder used in the present ``OF´´ type, are made and coated with an insulating film of powder. They are about the size of the familiar sugar coated pills. These are simply poured in an insulating tube, terminals put on each end in contact with the pellets, a series gap added, and the arrester unit is complete. In action, each pellet is a miniature ``OF´´ cell, so the arrester tube contains a number of them in series and parallel. The over-voltage surge discharges through the pellets, which have a low resistance after the powder film is punctured, and sealing occurs at the contact of the various pellets. No dynamic or normal frequency current passes. The characteristics are similar to those of the present ``OF´´ arrester, giving it the fundamental characteristics a successful arrester must have. The pellet construction permits of a simple, flexible and comparatively cheap design.