GB1470503A - Electrical apparatus - Google Patents

Abstract

1470503 Electrical stress-controlling compositions RAYCHEM Ltd 19 March 1974 [20 March 1973] 49724/76 Divided out of 1470501 Heading C3P Electrical apparatus comprises electrical stress relieving compositions comprising a polymeric material having dispersed therein a particulate compound selected from (a) compounds having a perovskite type crystal structure; (b) compounds having a spinel crystal structure other than γ-Fe 2 O 3 and spinel itself; (c) compounds having an inverse spinel crystal structure; (d) compounds having a mixed spinel crystal structure; (e) dichalcogenides of transition metal and tin; (f) AgI, Rochelle salt or other alkali metal tartrates, Prussian blue, compounds of formula XH 2 YO 4 where X is K, Rb or Cs and Y is P or As, ammonium fluoroberyllate, thiourea, ammonium sulphate and triglycine sulphate; and (g) Si 3 N 4 ; the composition containing at least 10% of the particulate compound based on the weight of the polymeric material and having a γ-value of at least 1À5 at least at some direct current stress between 0À01 kV/mm. and 10 kV/mm. The compositions may also contain particulate electrically conductive fillers and/or silicon carbide. They may be used in high voltage cable terminations and heating elements. Examples describe compositions comprising EP and EPDM rubbers, polyethylene, ionomer resins, ethylene/ethyl acrylate copolymers, vinylidene fluoride/hexafluoropropylene copolymers, chlorinated polyethylene and chlorosulphonated polyethylene; non-stoichiometric Fe 3 O 4 , Co 3 O 4 , strontium titanate, barium stannate, barium titanate, molybdenum disulphide, molybdenum ditelluride, molybdenum diselenide, silicon nitride, copper chromite, cobalt ferrite, Mn 3 O 4 , copper manganite, magnesium ferrite and zinc ferrite; and optionally finely divided carbon black, aluminium, copper, iron, manganese, chromium, lead, nickel, nickel/aluminium, zinc and silver.