Method for identifying a ground fault in a polyphase electrical power supply system having a compensated or isolated star point, wherein the following steps are carried out: - detecting zero phase sequence system current and zero phase sequence system voltage measurement values indicating a zero phase sequence system current and a zero phase sequence system voltage present at a measurement location (16a-c), by means of an electrical protective device (14a-c), wherein the measurement location (16a-c) is arranged in the region of a section of the power supply system which is monitored by the protective device; - storing the detected zero phase sequence system current and zero phase sequence system voltage measurement values in a measurement value memory of the protective device (14a-c); - comparing the zero phase sequence system voltage measurement values with a zero phase sequence system voltage threshold value and generating a trigger signal if a zero phase sequence system voltage measurement value exceeds the zero phase sequence system voltage threshold value; - selecting a profile of zero phase sequence system current measurement values from the measurement value memory in the case where the trigger signal is present; - calculating a profile of zero phase sequence system charge values from the profile of the selected zero phase sequence system current measurement values; and - using the profile of the zero phase sequence system charge values for identifying a ground fault in the monitored section; characterized in that for identifying a ground fault - using the profile of zero phase sequence system charge values and associated zero phase sequence system voltage measurement values, a zero phase sequence system capacitance value is determined for the monitored section; - using the profile of zero phase sequence system charge values and the zero phase sequence system capacitance value, on the one hand, and the associated zero phase sequence system voltage measurement values, on the other hand, a deviation characteristic value is formed; and - a fault signal indicating a ground fault on the monitored section is generated if the deviation characteristic value exceeds a predetermined first deviation threshold value. - detecting zero phase sequence system current and zero phase sequence system voltage measurement values indicating a zero phase sequence system current and a zero phase sequence system voltage present at a measurement location (16a-c), by means of an electrical protective device (14a-c), wherein the measurement location (16a-c) is arranged in the region of a section of the power supply system which is monitored by the protective device; - storing the detected zero phase sequence system current and zero phase sequence system voltage measurement values in a measurement value memory of the protective device (14a-c); - comparing the zero phase sequence system voltage measurement values with a zero phase sequence system voltage threshold value and generating a trigger signal if a zero phase sequence system voltage measurement value exceeds the zero phase sequence system voltage threshold value; - selecting a profile of zero phase sequence system current measurement values from the measurement value memory in the case where the trigger signal is present; - calculating a profile of zero phase sequence system charge values from the profile of the selected zero phase sequence system current measurement values; and - using the profile of the zero phase sequence system charge values for identifying a ground fault in the monitored section; - using the profile of zero phase sequence system charge values and associated zero phase sequence system voltage measurement values, a zero phase sequence system capacitance value is determined for the monitored section; - using the profile of zero phase sequence system charge values and the zero phase sequence system capacitance value, on the one hand, and the associated zero phase sequence system voltage measurement values, on the other hand, a deviation characteristic value is formed; and - a fault signal indicating a ground fault on the monitored section is generated if the deviation characteristic value exceeds a predetermined first deviation threshold value.