Abstract: An electrical capacitor of a non-impregnated, self-curing type includes a roll or wound body provided with metallic layers. Interspaces between the windings of the roll are filled with a gaseous or vaporous additive substance of a polyatomic hydrocarbon compound which is free of halogens and whose ionization potential is less than the ionization potential of at least a part of decomposition products of dielectric substance of the capacitor. The additive substances makes it possible that in an electric arc of a disruptive breakdown in the dielectric material of the capacitor the charge is taken over by positive ions of the decomposition product and subsequent clusters of breakdowns are substantially prevented. In addition, the additive substances absorb during a breakdown UV photons so that the emission of secondary electrons on the metallic lining is avoided.