  This paper analyzes the mechanisms of the superimposed machine and also its
inherit problems in TSA. Based on the global monitoring of the original system
trajectory, the transient energy is mistakenly defined as the superimposition
of the transient energy of all machines in the system. This "energy
superimposition" directly causes the superimposed machine to become a pseudo
machine without any equation of motion, and in this way the superimposed
machine completely violates all the machine paradigms. The violations bring the
two inherit defects in TSA: (i) the stability of the superimposed machine is
unable to be characterized precisely, and (ii) the variance of the original
system trajectory is unstable to be depicted clearly. The two defects are also
reflected in the definitions of the superimposed-machine based transient
stability concepts. In particular, the swing and the critical stability of the
system are unable to be defined strictly, and the potential energy surface
cannot be modeled precisely. Simulation results show that the problems of the
pseudo superimposed-machine in TSA.
