  The line potential energy in the cutset is used as the criterion for
monitoring the generator instability, but the criterion has the following two
limitations due to narrowly defined conditions. The assumption of an ideal
constant power load is difficult to satisfy, and the condition of the critical
cutset is too narrow. The limitations are addressed by analyzing the
relationship between the power of the load elements and the power of the cutset
based on the two-machine equivalent. Modifications of the theoretical
derivation steps of this criterion are presented to extend the applications of
the criterion and provide theoretical support for its online use. Two simple
strategies are proposed to ensure early detection of the generator instability.
