Transformerless Inverters and RCD: What's the Problem?

Abstract

Considering the structure of PV systems, a stray capacitance can appear between the PV arrays and the ground. When transformerless inverters are used, this capacitance can cause leakage currents to the ground. According to the French standards, a Residual-Current Device (RCD) has to be installed at the AC side of the PV installation, for the protection of individuals. Yet, when the value of the leakage currents reaches a threshold (30 mA in homes in France), the RCD may switch off and unintended disconnections of the PV installation occur with accompanying production losses. Based on simulations and experimental tests, this project aims at giving information to PV system designers and inverter manufacturers about the best suitable type of RCD to use for several PV system configurations. This issue is relevant for countries with TT grounded networks like France where many operations of PV systems with unexplained disconnections of RCD have been reported.