  Power transfer limits or transfer capability (TC) directly relate to the
system operation and control as well as electricity markets. As a consequence,
their assessment has to comply with static constraints, such as line thermal
limits, and dynamic constraints, such as transient stability limits, voltage
stability limits and small-signal stability limits. Since the load dynamics
have substantial impacts on power system transient stability, load models are
one critical factor that affects the power transfer limits. Currently, multiple
load models have been proposed and adopted in the industry and academia,
including the ZIP model, ZIP plus induction motor composite model (ZIP + IM)
and WECC composite load model (WECC CLM). Each of them has its unique
advantages, but their impacts on the power transfer limits are not yet
adequately addressed. One existing challenge is fitting the high-order
nonlinear models such as WECC CLM. In this study, we innovatively adopt double
deep Q-learning Network (DDQN) agent as a general load modeling tool in the
dynamic assessment procedure and fit the same transient field measurements into
different load models. A comprehensive evaluation is then conducted to quantify
the load models' impacts on the power transfer limits. The simulation
environment is the IEEE-39 bus system constructed in Transient Security
Assessment Tool (TSAT).
