  Weather and environmental factors are verified to have played significant
roles in historical major cascading outages and blackouts. Therefore, in the
simulation and risk assessment of cascading outages in power systems, it is
necessary to consider the weather and environmental effects. This paper
proposes a method for the risk assessment of weather-related cascading outages.
Based on the analysis of historical outage records and temperature-dependent
physical outage mechanisms of transmission lines, an outage rate model
considering weather condition and conductor temperature is proposed, and the
analytical form of outage probability of lines are derived. With the
weather-dependent outage model, a two-stage risk assessment method based on
Markovian tree (MT) search is proposed, which consists of offline full
assessment, and online efficient update of risk assessment results and
continued MT search using updated NWP data. The test cases on NPCC 140-bus test
system model in winter and summer scenarios verify the advantages of the
proposed risk assessment method in both accuracy and efficiency.
