A Comparison of Residual Current Devices with Insulation Resistance Monitoring Devices when Considering Safety in DC Systems

P.J.L. Van Tichelen, D. Weyen, and G.K.J. Meynen (Belgium)


safety, instrumentation, DC system.


This paper focuses on the safety requirements for the DC bus systems. High DC bus voltages are attractive for keeping the current and copper weight low. However, if the DC bus voltage exceeds 75 VDC additional safety measures are required. Regulations require double protection measures. The first protection is mostly provided by proper electrical insulation. A second active protection system is also installed; this detects insulation failures and switches off the power supply. Often the residual current detector (RCD) is used which detects leakage current in earthed systems but is difficult to build for DC systems. Another active technique is to install a floating or unearthed system with an insulation resistance monitoring device (IMD). In this paper the advantages and disadvantages of both systems are compared. A new simple IMD technique is presented together with a simulation and an evaluation of a photovoltaic test installation.

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