  In the existing literatures for the risk evaluation of electricity-gas
integrated energy system (EGIES), the impacts of gas leakage in pipelines are
ignored. This paper presents a method to incorporate the failure modes of gas
pipeline leakage in EGIES risk evaluation. A Markov state transition model of
gas pipeline with multi-state and multi-mode transition process, and a bi-level
Monte Carlo sampling method for this model are developed. A stochastic topology
change based network model of EGIES considering the pipeline leakage failure
modes is presented. The risk indices for EGIES based on the load shedding,
including those specifically for gas leakage risks, are also proposed. An EGIES
with a modified RBTS and a 7-node gas system was used to demonstrate an
application of the proposed method and models. The results indicate that
pipeline leakage failures have significant impacts on the risk of EGIES.
Ignoring pipeline leakage failures in the risk evaluation of EGIES will result
in an overly underestimation of system risk and most likely a misleading
conclusion in system planning.
