  In an integrated electricity-gas system (IEGS), the tight coupling of power
and natural gas systems is embodied by frequent changes in gas withdrawal from
gas-fired units to provide regulation services for the power system to handle
uncertainty, which may in turn endanger the secure operation of the natural gas
system and ultimately affect the safety of the whole IEGS. Hence, it is
necessary to accurately and efficiently evaluate the dynamic security region
(DSR) of the natural gas system in the IEGS by considering the real-time
dynamic characteristics of natural gas systems, which are not satisfactorily
handled in state-of-the-art works. To bridge this gap, this paper first
conceptionally verifies the necessity of the DSR and establishes its
mathematical model. Then, a dimensionality reduction method is proposed for the
efficient solution and visualization of the high-dimensional DSR evaluation
model. A fast evaluation (FE) algorithm is developed to address the
difficulties of the nonconvex dynamic constraints in the reduced DSR model.
Finally, the necessity and notable advantages of the proposed DSR model and FE
are verified based on small and relatively large test systems in comparison
with common security region models and algorithms. To the best of our
knowledge, this is the first paper that comprehensively presents models and
efficient algorithms regarding the DSR of natural gas systems in an IEGS.
