Detecting electrical islands using wide-area measurements

Islanding events are detected using measurement information taken from several places in a network, e.g., from a system of intelligent electronic devices (IEDs). In an example method of island detection, phase angle differences between local phase angles and remote phase angles in remote subnetworks are evaluated (850), and whether power is stable at the local and remote subnetworks is determined (860), using the local power data and the remote power data. An island condition at the local subnetwork is detected (870), responsive to determining (i) that power is stable at the local subnetwork and the remote subnetworks, (ii) that remote phase angles at each of the remote subnetworks are stable, and (iii) that there is a change in phase angle differences between each remote subnetwork and the local subnetwork, each of said changes exceeding a predetermined threshold. An alarm indicator is triggered (880) in response to the detection of the island condition.