This paper discusses the theoretical justification of the BCU method for th
e evaluation of power system stability, Recent literature has suggested tha
t the method can be mathematically justified in terms of a one-parameter de
formation between two systems, This paper shows that the assumptions of thi
s method do not hold generically for power system models. In particular, th
e one-parameter transversality conditions inherent in the deformation argum
ent do not apply for a large region in parameter space, thus, the validity
of the BCU method cannot be theoretically justified by this procedure.