A method for determining a division of a total insulation resistance (Riso) in an ungrounded power supply system (2, 12) comprising active conductors (L+, L−, L×) between which a conductor-conductor voltage (Udc, Uac, Uacxy) occurs, the method comprising the method steps of:
- determining the total insulation resistance (Riso) of the ungrounded power supply system (2, 12), characterized by
- measuring displacement voltages (UL+_E, UL−_E, UL×_E) between each of the active conductors (L+, L−, L×) and ground (E),
- determining a resistance division factor (rR), which describes the division of the total insulation resistance (Riso) into partial insulation resistances (Riso+, Riso− Riso×) related to the active conductors (L+, L−, L×), as a function of at least one of the parameters amplitude, frequency, phase of the displacement voltages (UL+_E, UL−_E, UL×_E) measured.