The invention discloses a method for detecting a
grid fault online under the condition of a limited number of PMUs based on the least square method. According to the method, the area disperse
policy decision structure is adopted, and the
wide area protection information of a home substation and an adjacent substation is collected through RDS; when it is found that protective action is carried out on a circuit, the online detection process of the circuit and an adjacent circuit is started; the current and
voltage measurement values of the related PMUs are collected, the current and
voltage estimated values of each node are worked out, the current
residual value of each circuit is obtained, two suspected circuits are obtained through
ranking and searching; for the two suspected circuits, according to the topological
link relation between the two suspected circuits, criteria of a fault of a single circuit and combination faults of two adjacent circuits and the like are established; according to three groups of PMU measurement values, the positions of three groups of fault points of each suspected circuit are worked out, fault criteria are established, and then a faulty element is judged and detected. By the adoption of the method, the three fault conditions including the fault of a single circuit, combination faults of adjacent circuits and dual faults of non-adjacent circuits can be distinguished, and the situation that an oversized communication load is added to the SDH of a
wide area communication network is avoided.