Method and monitoring device for selectively determining a partial system leakage capacitance in an ungrounded power supply system

A monitoring device (10) for selectively determining a partial system leakage capacitance (Ce) in an ungrounded power supply system (2) which comprises a main system (4) and a plurality of partial systems (6), comprising an extended insulation monitoring system (20) which is configured for determining an overall insulation resistance (Reges) and an overall system leakage capacitance (Ceges) of the power supply system (2);

• an extended insulation fault location system (30);
• a test-current generator (32) for continuously generating and feeding a test current (Ip) into the main system (4), having test-current sensors (36) for capturing a partial test current (Ie) in at least one partial system (6) being monitored and having an insulation-fault evaluation device (34) to which the test-current sensors (36) are connected;
• said extended insulation fault location system (30) being configured for determining an ohmic and a capacitive partial test-current portion (Ire, Ice) as real and imaginary parts for each captured complex-valued partial test current (Ie) and said monitoring device (10) further comprising an impedance evaluation system (40) which comprises an impedance evaluation unit (42) for determining a partial insulation resistance (Re) and a partial system leakage capacitance (Ce) for each partial system (6) to be monitored from the overall insulation resistance (Reges), from the overall system leakage capacitance (Ceges), from the test current (Ip) and from the ohmic and capacitive partial test-current portions (Ire, Ice) as well as comprising an impedance assessment unit (44) for assessing the identified partial insulation resistance (Re) in regard of the partial insulation resistance falling below a partial insulation-resistance threshold and for assessing the identified partial system leakage capacitance (Ce) in regard of the identified partial system leakage capacitance exceeding a partial system-leakage-capacitance threshold.