Patent GB-866402-A (GB)
Title: Improvements in or relating to the insulation of electrical apparatus
Inventor: FORD JAMES G
IPC: H01F27/32
Filed: 1958-12-17
Abstract: Electrical apparatus such as a transformer capacitor, cable or switchgear has a winding or other wire conductor operating at over 100 DEG C. insulated by cellulosic material and immersed in oil containing up to 10% by weight of urea, or non-acidic compounds derived from urea, for stabilizing the cellulosic insulation, the wire being enamelled by a heat-hardened resin which consists of either:-(A) from 50 to 80 parts by weight of glycidyl polyether of a dihydric phenol having a 1, 2-epoxy equivalency greater than 1 and from 50 to 15 parts by weight of at least one thermosetting resin selected from the group consisting of melamine-aldehyde and urea-aldehyde resins or, (B) (1) 100 parts by weight of a polyamide resin composition derived by admixing and heating (i) from 1 to 2 mols of an unsaturated acidic compound selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, and the monomethyl substitution derivatives for the non-carboxyl hydrogen thereof and (ii) one mol of a diamine compound from the group consisting of primary hydrocarbon diamines having from 2 to 6 carbon atoms or polyamide reaction products having terminal amino groups and having an average molecular weight not in excess of 1500 and from (2) one part to 50 parts by weight of a solvent-soluble heat-hardenable organosiloxane resin having from 1,3 to 1,95 hydrocarbon groups per silicon atom or, (C) from 50% to 67% by weight of polyvinyl formal and 50% to 33% by weight of phenol aldehyde resin.  Other stabilizing compounds usable instead of urea include thiourea, tert-butyl urea, tertamyl urea, 1, 1-diethyl urea, 1, 3-dimethyl urea, 1, 3-dibutyl urea, methylol urea, guanidine carbonate, dicyandiamide, biuret, 1, 3-diethyl thiourea, 1, 3-diisopropyl thiourea and hexamethylenetetramine.  When paper is used for insulating purposes the stabilizing compound may be placed in the paper during its manufacture or when it is wrapped round the conductor or coils instead of or in addition being put in the oil.  The enamelling material.  The Specification gives details of the materials and method used for preparation of a glycidyl polyether. It also gives details of the preparation of polyamide reaction products, solvents such as cresol or dichlorbenzene, which do not enter into the reaction, being used, the polyamides, when admixed and reacted with the organosiloxanes being dissolved in solvents such as butanol, xylene or dichlorbenzene to form the enamel. Solvents which may be used in preparing the enamel composition from epoxy resin and a urea or melamine-aldehyde include benzene, toluene, xylene, methyl-ethyl ketone, methyl propyl ketone, methyl isobutyl ketone with diacetone alcohol, cellosolve acetate, methyl cellosolve acetate or cresol. The enamelling material may be applied to bare wire or the wire may be covered with cotton, asbestos, glass fibre or cellulosic material before, after or during the enamelling.  The enamel is applied to the wire by a flowing or dipping process and baked.  A number of examples of the preparation and application of the enamel coatings with details of the characteristics of the finished product are given.