The equal-area criterion is a graphical energy-balance method for assessing transient (large-disturbance) rotor angle stability of a single synchronous machine connected to an infinite bus, in which system stability following a disturbance (line switching, fault, or fault-plus-clearing) is determined by comparing the accelerating area swept by the rotor angle against the maximum available decelerating area on the power-angle (P-δ) curve. The critical clearing angle is the boundary rotor angle at which these two areas are exactly equal, marking the limit beyond which the machine loses synchronism; it is derived analytically from the pre-fault, during-fault, and post-fault power-angle characteristics using the machine's transient reactance and network transfer reactances. This belongs to power system stability analysis (transient/rotor-angle stability), a subfield of power system analysis concerned with a synchronous machine's ability to remain in synchronism after large disturbances, distinguished from small-signal stability analysis of the linearized swing equation.
The equal-area criterion is a graphical energy-balance method for assessing transient (large-disturbance) rotor angle stability of a single synchronous machine connected to an infinite bus, in which …