In the paper, transient stabw analysis of an N-machine power system is carried
out using the decomposition-aggregation via vector Lyapunov fimction method. It is
considered in the anatysis, transfer conductances, non-uniform mechanical damping,
and generators flux decay effect. Each of the system generators 1s represented by a
more sophisticated model, that is, the one-axis model in which the generator internal
voltage component Elq is assumed to be changed with time. Note that, using the sta‌bility direct methods the voltage Elq is usually assumed, for simplicity, constant. The
III&~&c~ model of the whole system is derived and is decomposed into [(N-1) 1
3 ] eleventh-order interconnected subsystems, each of them includes tbree machines in
addition to the reference machine. The system aggregation is carried out using a const‌ructed vector Lyapunov fimction whose elements are scalar Lygunov functions, each
in the form of" quadratic form + sum of thc integrals of six noniincar fimctions". It is
obtained a square aggregation matriv of the order [(N-1) 131, and stabii of this mat‌rix implies asymptotic stabiity of the system equilibrium.
In a numerical example, the developed stabihty approach is used to cany out
transient stability studies of a 10-machine,ll-bus power system The stablhty compu‌tations are canied out assuming occurrence of a 3 - phase short circuit fault near a
bus, and also for connection of a pulsating load to one of the system buses. In addition
it is assumed two composite faults defined as, disconnection of two tie-lines (due to
false openRion of circuit breakers near fault location), or addition of a pulsating load,
just after clearing a 3-phase short circuit fault (the faulted line is switched off) at two
different locations. It is found that the developed stability approach is suitable and can
be easily used for practical, and on-line stability studies of large- scale power systems
(number of machincs may be more than 10)