Method for detecting a fault in an electrical energy supply network (10, 40), wherein - state values are determined for a plurality of measuring points (M1, M2, M3) in the energy supply network (10, 40), which state values indicate an electrical state of the energy supply network (10, 40) that is present at the respective measuring point (M1, M2, M3); - the state values are transmitted to a centralised control center device which comprises an evaluation device; and - the state values are used by the evaluation device for the purpose of detecting a fault that is present in the energy supply network (10, 40); - the evaluation device is used to perform a state estimation which makes use of a model description of the electrical energy supply network (10, 40) that is suitable for describing possible electrical states of the energy supply network (10, 40) on the basis of state variables; characterised in that - a check is carried out during the state estimation to determine whether the model description allows an electrical state of the energy supply network (10, 40) to be described which, in respect of the state variables used for the respective measuring points (M1, M2, M3), at least approximately agrees with the respective state values, in that a minimisation of a cost function of states of the energy supply network (10, 40) which are described by means of the model description is performed by means of the evaluation device in order to determine, from all of the possible state variables, that set of state variables by means of which the state values actually present in the energy supply network can be mapped by the model description; - an absence of a describable state is inferred if the result of the cost function lies above a selectable threshold value; and - in the absence of such a state the evaluation device generates a fault detection signal which indicates the presence of a fault in the energy supply network (10, 40). - state values are determined for a plurality of measuring points (M1, M2, M3) in the energy supply network (10, 40), which state values indicate an electrical state of the energy supply network (10, 40) that is present at the respective measuring point (M1, M2, M3); - the state values are transmitted to a centralised control center device which comprises an evaluation device; and - the state values are used by the evaluation device for the purpose of detecting a fault that is present in the energy supply network (10, 40); - the evaluation device is used to perform a state estimation which makes use of a model description of the electrical energy supply network (10, 40) that is suitable for describing possible electrical states of the energy supply network (10, 40) on the basis of state variables; characterised in that - a check is carried out during the state estimation to determine whether the model description allows an electrical state of the energy supply network (10, 40) to be described which, in respect of the state variables used for the respective measuring points (M1, M2, M3), at least approximately agrees with the respective state values, in that a minimisation of a cost function of states of the energy supply network (10, 40) which are described by means of the model description is performed by means of the evaluation device in order to determine, from all of the possible state variables, that set of state variables by means of which the state values actually present in the energy supply network can be mapped by the model description; - an absence of a describable state is inferred if the result of the cost function lies above a selectable threshold value; and - in the absence of such a state the evaluation device generates a fault detection signal which indicates the presence of a fault in the energy supply network (10, 40).