GB1255685A - Vacuum type circuit interrupter - Google Patents

Abstract

1,255,685. Vacuum switch contacts. HITACHI Ltd. 25 Aug., 1969 [26 Aug., 1968], No. 42228/69. Heading H1N. [Also in Division C7] The arc supporting regions of vacuum switch contacts 12, 14 are formed of an alloy of a composition such that a thin brittle film 74 is formed on the surfaces to reduce the effects of contact welding; the alloy consists of more than 40% by weight of copper, up to 60% of iron, cobalt, nickel or chromium (or a mixture thereof) and between 0À035 and 7% of lead; the proportion of iron-group metal is to be much greater than its solubility limit in copper so that the alloy has a composite structure of a copper rich phase 70 of high electrical and thermal conductivity and an iron-group rich phase 68 giving the contacts high dielectric strength and the proportion of the lead is also greater than its solubility limit in copper so that it precipitates at 76 on the grain boundaries of the alloy and is readily exuded from the contact under arcing conditions to form the brittle film 74 on the surfaces. The film is sufficiently thin that it does not cover portions of iron-group metals 72 projecting from the contact surface and therefore does not reduce the electrical strength of the contacts. The Specification discusses in detail a large number of more specific alloys within the above set limits. The switch described has two cylindrical body portions 16, 16<SP>1</SP> of borosilicate glass joined by seals 17, 17<SP>1</SP> of iron-nickel-cobalt alloy of equal expansion to the glass; shields 18, 18<SP>1</SP> inside the envelope and 19, 20 attached to the electrodes 10, 13; getters 38, 38<SP>1</SP> and a sheet steel bellows 22.