Arrangement for stabilizing an electrical power supply grid, wherein - the arrangement comprises a first device which has a rotating mass and, during normal operation of the power supply grid, rotates together with said rotating mass in sync with a setpoint grid frequency of the power supply grid, automatically feeds a current into the power supply grid in the event of a short circuit in the power supply grid, and automatically adjusts its rotational speed in the event that the grid frequency (f) of the power supply grid deviates from the setpoint grid frequency, and - the arrangement has a first control unit (11, 11i) which is connected to the first device and which is adapted to control the first device and thereby cause the first device to feed a reactive power into the power supply grid in the event that a grid disturbance of a predefined first type is identified, characterized in that - the arrangement comprises a second control unit (21, 21i) and a second device which has a converter and an energy store and is controlled by the second control unit (21, 21i), - wherein the second control unit (21, 21i) is adapted to control the converter in such a way that the latter feeds reactive power, in particular the maximum possible reactive power, into the power supply grid from the converter in the event that a grid disturbance of the first type is identified, - wherein the second control unit (21, 21i) is additionally adapted to feed reactive power into the power supply grid from the energy store via the converter if the reactive power fed into the power supply grid by the first device corresponds to the nominal reactive power (Qn) thereof. - the arrangement comprises a first device which has a rotating mass and, during normal operation of the power supply grid, rotates together with said rotating mass in sync with a setpoint grid frequency of the power supply grid, automatically feeds a current into the power supply grid in the event of a short circuit in the power supply grid, and automatically adjusts its rotational speed in the event that the grid frequency (f) of the power supply grid deviates from the setpoint grid frequency, and - the arrangement has a first control unit (11, 11i) which is connected to the first device and which is adapted to control the first device and thereby cause the first device to feed a reactive power into the power supply grid in the event that a grid disturbance of a predefined first type is identified, characterized in that - the arrangement comprises a second control unit (21, 21i) and a second device which has a converter and an energy store and is controlled by the second control unit (21, 21i), - wherein the second control unit (21, 21i) is adapted to control the converter in such a way that the latter feeds reactive power, in particular the maximum possible reactive power, into the power supply grid from the converter in the event that a grid disturbance of the first type is identified, - wherein the second control unit (21, 21i) is additionally adapted to feed reactive power into the power supply grid from the energy store via the converter if the reactive power fed into the power supply grid by the first device corresponds to the nominal reactive power (Qn) thereof.