The aim of the study is to develop a method for parametric matching of insulation monitoring devices, unearthed DC distribution systems and discrete inputs of relay protection. The use of unearthed DC distribution systems for power supply to relay protection devices and other responsible consumers makes it possible to ensure high reliability and safety during their operation. It is necessary to ensure uninterrupted power supply to these consumers even in the event of a ground fault in one of the DC distribution network poles. Insulation monitoring of the network poles and the prompt execution of repair work when the insulation resistance falls below the critical level set by the response value, are a guarantee of high reliability of power supply. The article discusses the reasons leading to dangerous levels of pole voltage unbalance and false triggering of relay protection discrete inputs during ground faults of the signal lines connected to them. A method based on multivariate DC analysis is proposed to determine the matched insulation monitoring response value with the DC network parameters and discrete inputs parameters, when the conditions for the occurrence of such accidents are excluded. The influence of insulation monitoring devices in a DC system on pole voltages unbalance and relay protection operation is also considered. A modification of the insulation monitoring active method is proposed, which does not create additional pole voltage unbalance and risks of relay protection misoperation. The operating range of the static characteristics of the pole voltages and leakage current measuring transducers is narrowed in the grid unbalanced modes by using a modified active insulation monitoring met hod. Estimates of the increase in the insulation resistance measurement error arising in these modes are obtained
