China's protection technique in preventing power system blackout to world

There have been 23 large blackouts which have occurred worldwide since 1965 each with a power loss ≥8,000MW. Blackouts usually occur through two stages: Stage one is related to voltage collapse/transient instability and the reason why most of the instability has occurred is because of the ‘cascading trips’ by impedance relays due to load transfer initiated by a single disturbance and a heavy load superimposed to long distance/high impedance circuits. Stage two is that the transient instability may spread out to “blackout” due to ‘cascading trips’ by impedance relays of transmission and out-of-step relays of generators operating during system instability.