A method, arrangement and computer program product for enhancing the reliability of wide area control in a power transmission system where the wide area control is performed in the power transmission system based on measurements of system data. The arrangement includes an estimating unit configured to generate estimated measurement values based on at least one control signal being sent into the system and a model of the system, where the estimated measurement values correspond to a set of actual measurement values that are provided by a number of measurement providing devices in the system. The arrangement also includes a control unit configured to replace, if one or more deviation condition associated with at least one actual measurement value is fulfilled, at least the actual measurement values of the set being associated with the one or more deviation condition with corresponding estimated measurement values.