Method of monitoring capacitor bushings (2a, 2b, 2c) for an alternating current mains, wherein - the alternating current mains has a first, second and third phase (A, B, C) and comprises: • a first mains line, with which the first phase and a first capacitor bushing are associated and at which a first mains voltage is present, • a second mains line, with which the second phase and a second capacitor bushing are associated and at which a second mains voltage is present, • a third mains line with which the third phase and a third capacitor bushing are associated and at which a third mains voltage is present; - each of these capacitor bushings (2a, 2b, 2c) comprises: • a conductor connected with the associated mains line (5a, 5b, 5c), • an electrically conductive foil enclosing this conductor; - for each of these phases (A, B, C) • at a predetermined initial instant for a characteristic variable, which is characteristic for the respective capacitor bushing (2a, 2b, 2c), a corresponding characteristic value is determined characterized in that; • at a predetermined later instant (tn) after the initial instant for the characteristic variable a corresponding normalised characteristic value is determined in dependence on the respective characteristic value and/or on at least one of the remaining characteristic values of the remaining phases; • at the initial instant, a corresponding initial reference voltage value is determined for a reference voltage; • the determination of the normalised characteristic variable is additionally dependent on the respective initial reference voltage value and/or of at least one of the remaining initial reference voltage values of the remaining phases. • it is checked whether the normalised characteristic value has impermissibly changed and; - the characteristic variable is the upper capacitance of a respective upper-voltage capacitor and/or the loss factor of the respective capacitor bushing, wherein the respective upper-voltage capacitor is formed by the respective foil and conductor. - the alternating current mains has a first, second and third phase (A, B, C) and comprises: • a first mains line, with which the first phase and a first capacitor bushing are associated and at which a first mains voltage is present, • a second mains line, with which the second phase and a second capacitor bushing are associated and at which a second mains voltage is present, • a third mains line with which the third phase and a third capacitor bushing are associated and at which a third mains voltage is present; • a first mains line, with which the first phase and a first capacitor bushing are associated and at which a first mains voltage is present, • a second mains line, with which the second phase and a second capacitor bushing are associated and at which a second mains voltage is present, • a third mains line with which the third phase and a third capacitor bushing are associated and at which a third mains voltage is present; - each of these capacitor bushings (2a, 2b, 2c) comprises: • a conductor connected with the associated mains line (5a, 5b, 5c), • an electrically conductive foil enclosing this conductor; • a conductor connected with the associated mains line (5a, 5b, 5c), • an electrically conductive foil enclosing this conductor; - for each of these phases (A, B, C) • at a predetermined initial instant for a characteristic variable, which is characteristic for the respective capacitor bushing (2a, 2b, 2c), a corresponding characteristic value is determined characterized in that; • at a predetermined later instant (tn) after the initial instant for the characteristic variable a corresponding normalised characteristic value is determined in dependence on the respective characteristic value and/or on at least one of the remaining characteristic values of the remaining phases; • at the initial instant, a corresponding initial reference voltage value is determined for a reference voltage; • the determination of the normalised characteristic variable is additionally dependent on the respective initial reference voltage value and/or of at least one of the remaining initial reference voltage values of the remaining phases. • it is checked whether the normalised characteristic value has impermissibly changed and; • at a predetermined initial instant for a characteristic variable, which is characteristic for the respective capacitor bushing (2a, 2b, 2c), a corresponding characteristic value is determined characterized in that; • at a predetermined later instant (tn) after the initial instant for the characteristic variable a corresponding normalised characteristic value is determined in dependence on the respective characteristic value and/or on at least one of the remaining characteristic values of the remaining phases; • at the initial instant, a corresponding initial reference voltage value is determined for a reference voltage; • the determination of the normalised characteristic variable is additionally dependent on the respective initial reference voltage value and/or of at least one of the remaining initial reference voltage values of the remaining phases. • it is checked whether the normalised characteristic value has impermissibly changed and; - the characteristic variable is the upper capacitance of a respective upper-voltage capacitor and/or the loss factor of the respective capacitor bushing, wherein the respective upper-voltage capacitor is formed by the respective foil and conductor.