Integration of natural gas and electricity transmission systems has strengthened interdependence between the two systems. Due to the close interconnection through coupling elements between the power system (PS) and natural gas system (NGS) when a disturbance happens in one system

a series of complicated sequences of dependent events may follow in another system. Therefore

an integrated planning model jointing security-constrained considering cascading effects is proposed in this paper. Meanwhile

natural gas and electricity transmission systems considering stochastic failures and various operating characteristics of components can be viewed as a multistate systems. Moreover

power-to-gas (P2G)

as a promising technology proposed to store surplus renewable energy

is considered in the integrated planning. First

multi-state models for different components are developed to describe realistic operating conditions in natural gas and electricity transmission systems. Furthermore

a mixed-integer linear programming (MILP) approach considers N-1 contingency and cascading effects between natural gas and the electrical power systems. Therefore

a security-constrained integrated planning model of natural gas and electricity transmission systems is represented. The proposed methods are validated using an integrated gas and power test system.