Pv energy generation plant with central inverter

A method for monitoring fault currents of a PV energy generation plant comprising a PV generator and a central inverter unit or circuit, wherein the PV generator comprises a plurality of PV main strings which are connected together in parallel and are connected, on an input side of the PV generator, to the central inverter unit or circuit via DC lines in each case, and are connected to an alternating voltage grid on an output side of the PV generator via a DC link circuit of the central inverter unit, and wherein the PV generator further comprises a DC/AC converter, an AC isolating switch, a transformer, and a grid connection circuit, wherein each pair of DC lines assigned to a respective PV main string of the plurality of PV main strings is assigned a monitoring circuit that comprises a differential current measurement circuit, an isolating switch, and a monitoring controller, wherein the monitoring controller is configured to open the isolating switch within a reaction time, after a differential current threshold value has been exceeded, in order to isolate the respective PV main string, and further comprising a ground fault monitoring circuit arranged between a pole of the DC link circuit and a grounding connection, wherein the ground fault monitoring circuit comprises a ground current measurement circuit, an isolating circuit, and a controller, wherein the controller of the ground fault monitoring circuit is configured to trip the isolating circuit after a defined delay time, after a ground fault has been detected by virtue of a ground current threshold value being exceeded, when the ground fault persists after elapse of the delay time, wherein the delay time is selected to be greater than the reaction time, the method comprising:

• after the ground fault monitoring circuit detects a ground fault, tripping of the isolating switch is delayed by a defined delay time,
• after detecting a differential current fault, using the monitoring controller of the monitoring circuit, opening the isolating switch within a reaction time, and
• using the ground fault monitoring circuit tripping the isolating element when the ground fault persists after the defined delay time, wherein the delay time is selected to be greater than a reaction time of the monitoring circuit.