What are the methods for detecting and preventing unintentional islanding?

Islanding occurs when distributed generation continues operating isolated from the utility, creating safety and power quality risks. Detection methods include: passive (monitors voltage, frequency, harmonic changes when utility disconnects), active (injects disturbances and monitors response - frequency shift, impedance measurement), and communication-based (direct transfer trip, power line carrier). IEEE 1547 requires DG to detect islanding and disconnect within 2 seconds. Anti-islanding protection becomes more challenging with high DG penetration.