  Integration of renewable energy resources with the electric grid is necessary
for a sustainable energy future. However, increased penetration of inverter
based resources (IBRs) reduce grid inertia, which might then compromise power
system reliability. Therefore, power utilities are often interested in
identifying the maximum IBR penetration limit for their system. The proposed
research presents a methodology to identify the IBR penetration threshold
beyond which voltage, frequency, and tie-line limits will be exceeded. The
sensitivity of the IBR penetration threshold to momentary cessation due to low
voltages, transmission versus distribution connected solar generation, and
stalling of induction motors are also analyzed. Dynamic simulation studies
conducted on a 24,000-bus model of the Western Interconnection (WI) demonstrate
the practicality of the proposed approach.
