###### Abstract
For electricity networks, intermittent renewable energy sources have no fuel costs and only have a fixed operating cost for operation. To achieve robust power system operations, natural gas units may provide flexible dispatch and rapid ramping capability. Turning to variable renewables, it is expected that the intermittency in generation due to, for example, wind will have an impact on other generation units, which will be required to increase and decrease their generation, as the wind generation falls and rises, to meet the shortfall between generation and demand. Naturally, gas turbines will have a greater role to play in generating electricity due to their ability to ramp up/down quickly. Natural gas fired units (NGFUs) gradually replace coal fired units due to the operation flexibility, great efficiency and little capital costs in many countries [9]. In China, NGFUs occupy 4% of total generating capacity, while in the USA, it reached 39% [10]. Therefore, integrating natural gas systems with power systems is challenging. A great amount of overall electricity production is produced by gas-fired power plants for several countries. It is projected to rise to 7600 TWh by 2035. With increasing gas demand, gas networks need to expand capacity to provide fuel to additional gas-fired power plants. Reference [11] presents an integrated gas and electricity network expansion planning model. Gas fired generation plants were seen as connections between the two networks. The model concurrently minimizes electricity and gas operational and network development costs. Various research works were performed on optimal operation strategy and interdependency of the integrated electricity-natural gas system. Reference [7] examined the influence of natural gas infrastructure on the electricity system by focusing on particular constraints of the natural gas network. Reference [12] presented an in-depth integrated model for examining the influence of interdependency between natural gas and electricity networks on power system security, considering constraints of natural gas network in the security-constrained unit commitment (SCUC) problem for power systems. References [13,14]formulated the co-planning process as a mixed-integer nonlinear programming problem to consider recent challenges, including congestions, demand response effect, etc. The growing reliance of the power system on NG systems has demanded an integrated planning approach for the two systems [12]. Reference [15] proposed a decentralized operation strategy and applied it to coordinate energy flow in a multi-area integrated electricity-natural gas system (IEGS). The complete decentralized operation of interconnected large-scale IEGS is achieved with the iterative alternating direction method of multipliers (ADMM) algorithm. IEGS was represented by several subsystems that were tied by electricity and natural gas networks. An optimal operation strategy based on decentralization was developed for multi-area IEGS. Reference [10] showed that integrated natural gas and electricity networks operation can be attained in a distributed method with ADMM. Results showed that the ADMM-based approach gives enhanced convergence performances than the classical Lagrange Relaxation (LR), as well as augmented LR-based methods. Reference [16] propose a mixed integer programming model to characterize the electricity portfolio of large consumers. References [17,18] propose electricity and natural gas networks by considering energy hubs. As reported in Reference [19], the changes of natural gas unit's generation dispatch will provide natural gas demand profile changes. The changes may harm the natural gas network's security. Electricity and natural gas infrastructure's coordinated operation can enhance reliability and security for the infrastructure and avoid demand curtailment risks. Reference [20] presented a novel robust operation model for IEGS but without the solution algorithm. With ADMM, reference [21] presented a study on robust optimization for IEGS with distributed structures.