An anhydride-free insulation system for current-carrying construction parts of an electric engine which comprises: a mica paper or mica tape for wrapping parts of said electric engine that are potentially current-carrying during operation of the engine, which mica paper or mica tape is impregnable via vacuum pressure impregnation with a thermally curable epoxy resin formulation and comprises a thermally activatable curing initiator for the epoxy resin formulation containing one or more quarternary ammonium salts of an aromatic-heterocyclic compound, which contains 1 or 2 nitrogen atoms, and a complex anion selected from the group consisting of BF 4 -, PF 6 -, SbF 6 -, SbF 5 -, AsF 6 - and Al[OC(CF 3) 3] 4 - in an amount sufficient to cure the epoxy resin taken up by the mica paper or mica tape and the construction part of the engine during the vacuum pressure impregnation step; a thermally curable bath formulation for the vacuum pressure impregnation comprising one or more epoxy resins, which formulation is substantially or, preferably, entirely free of a thermally activatable curing initiator for the epoxy resin formulation, in particular of quarternary ammonium salts of aromatic-heterocyclic compounds containing 1 or 2 nitrogen atoms, and of a complex anion selected from the group consisting of BF 4 -, PF 6 -, SbF 6 -, SbF 5 -, AsF 6 - and Al[OC(CF 3) 3] 4 -, and one or more co-initiator for the thermally activatable curing initiator selected from a diarylethane derivative of formula: wherein Ar is phenyl, naphthyl, or C 1 -C 4 alkyl- or chloro-substituted phenyl, R1 is hydroxy, C 1 -C 4 alkoxy, -O-CO-R3 or -OSiR4R5R6, wherein R3 is C 1 -C 8 alkyl or phenyl, and R4, R5 and R6 are each independently of one another C 1 -C 4 alkyl or phenyl, and R2 is C 1 -C 4 alkyl or cyclohexyl or has the same meaning as Ar, wherein one or more of said co-initiators may be contained in the mica paper or mica tape of the system and/or one or more of said co-initiators may be contained in the thermally curable epoxy resin bath formulation of the system and is present in said mica paper or mica tape and/or in said thermally curable epoxy resin bath formulation in an overall amount sufficient to cure the epoxy resin taken up by the mica paper or mica tape and the construction part of the engine during the vacuum pressure impregnation step after said step. a mica paper or mica tape for wrapping parts of said electric engine that are potentially current-carrying during operation of the engine, which mica paper or mica tape is impregnable via vacuum pressure impregnation with a thermally curable epoxy resin formulation and comprises a thermally activatable curing initiator for the epoxy resin formulation containing one or more quarternary ammonium salts of an aromatic-heterocyclic compound, which contains 1 or 2 nitrogen atoms, and a complex anion selected from the group consisting of BF 4 -, PF 6 -, SbF 6 -, SbF 5 -, AsF 6 - and Al[OC(CF 3) 3] 4 - in an amount sufficient to cure the epoxy resin taken up by the mica paper or mica tape and the construction part of the engine during the vacuum pressure impregnation step; a thermally curable bath formulation for the vacuum pressure impregnation comprising one or more epoxy resins, which formulation is substantially or, preferably, entirely free of a thermally activatable curing initiator for the epoxy resin formulation, in particular of quarternary ammonium salts of aromatic-heterocyclic compounds containing 1 or 2 nitrogen atoms, and of a complex anion selected from the group consisting of BF 4 -, PF 6 -, SbF 6 -, SbF 5 -, AsF 6 - and Al[OC(CF 3) 3] 4 -, and one or more co-initiator for the thermally activatable curing initiator selected from a diarylethane derivative of formula: wherein Ar is phenyl, naphthyl, or C 1 -C 4 alkyl- or chloro-substituted phenyl, R1 is hydroxy, C 1 -C 4 alkoxy, -O-CO-R3 or -OSiR4R5R6, wherein R3 is C 1 -C 8 alkyl or phenyl, and R4, R5 and R6 are each independently of one another C 1 -C 4 alkyl or phenyl, and R2 is C 1 -C 4 alkyl or cyclohexyl or has the same meaning as Ar, wherein one or more of said co-initiators may be contained in the mica paper or mica tape of the system and/or one or more of said co-initiators may be contained in the thermally curable epoxy resin bath formulation of the system and is present in said mica paper or mica tape and/or in said thermally curable epoxy resin bath formulation in an overall amount sufficient to cure the epoxy resin taken up by the mica paper or mica tape and the construction part of the engine during the vacuum pressure impregnation step after said step.