What is black start capability and how is a power system restored after a blackout?

Black start is the process of restoring a power system from complete blackout without external power supply. Black start units (typically hydro or gas turbines with self-contained starting) energize sections of the system progressively. Restoration involves: starting black start units, energizing transmission backbone, synchronizing additional generators, gradually picking up load in controlled blocks. Challenges include: voltage control with light load (Ferranti effect), frequency stability with small generation, protection coordination for degraded conditions, and coordination among utilities.