Method and monitoring device for determining a partial insulation resistance and a partial system leakage capacitance in a branched ungrounded power supply system

Abstract

A method and monitoring device for selectively determining partial insulation resistance and partial system leakage capacitance of an outgoing line in a branched ungrounded power supply system monitored using an insulation monitoring device actively superposing a measuring alternating voltage on the ungrounded power supply system. Using an equivalent circuit diagram of the branched ungrounded power supply system as a basis, the partial insulation resistance having the current/voltage ratios applicable in linear systems are derived from the known measuring voltage and the inner resistance of the insulation monitoring device and from the total insulation resistance and the stationary partial current measured in the corresponding outgoing line and in the settled state. To calculate the partial system leakage capacitance, the temporal derivative of the measured non-stationary conductor-to-ground voltage is evaluated in conjunction with the non-stationary partial current and the previously determined partial insulation resistance.