## 2 State of the Art  
The area of analyzing interdependencies between gas and power systems is relatively new. It is encouraging that the number of publications on integrated gas and electricity systems found in the literature is increasing, although still limited. Comprehensive reviews of past publications can be found in [5; 6; 7; 8]. The different types of analysis undertaken in integrated gas and power systems literature can be categorized as; economic and market perspective analysis, operation planning and control (e.g., optimization, demand response), design and expansion planning, and security analysis. Studies on the medium and long-term economic evaluations aiming at exploring the interactions between the mechanisms of pricing of each carrier are reported in [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17], where the influence of technical constraints is often ignored or taken into account in a simplified way. Additionally in [18], the authors proposed a dynamic model representation of coupled natural gas and electricity network markets to test the potential interaction with respect to investments while considering network constraints of both markets. In [19], two methodologies for coupling interdependent gas and power market models are proposed in a medium-term scope, where the two systems are formulated separately as optimization problems and the obtained primal dual information is utilized. From the operational viewpoint, unit commitment models relating to short term security constrained operation of combined gas and power systems are developed in [20; 21; 22]. In [21], the authors considered the natural gas network constraints in the optimal solution of security constrained unit commitment (SCUC). Additionally dual fuel units are modelled for analyzing different fuel availability scenarios. In [22], the model proposed in [21] is extended using a quadratic function of pressure for describing the gas flow in pipelines and also including the gas consumption of the compressors. In [23], an economic dispatch model (ED) is developed for integrated gas and power systems. The security constraints for both systems are integrated in the ED which aims to minimize power system operating costs. The optimal power flow (OPF) of the coupled gas and power systems are investigated in [24; 25; 26; 27; 28; 29]. A method for OPF and scheduling of combined electricity and natural gas systems with a transient model for natural gas flow is investigated in [27] and the solutions for steady-state and transient models of the gas system are compared. A multi-time period OPF model was developed for the combined GB electricity and gas networks in [28; 29]. The impact of uncertainties on integrated gas and power system operation caused by variable wind energy is discussed in [30; 31; 32; 33]. In [30] the impacts of abrupt changes of power output from GFPPS, to compensate variable power output from wind farms, on the Great Britain (GB) gas network is analyzed. In [32], the authors developed partial differential equation (PDE) model of gas pipelines to analyze the effects of intermittent wind generation on the fluctuations of pressure in GFPPs and pipelines. The coordination between the gas and power systems based on an integrated stochastic model for firming the variability of wind energy is presented in [33]. Gas transmission system constraints and the variability of wind energy is considered in the optimal short-term operation of stochastic power systems with a scenario based approach. Studies considering the implementation of demand side response in order to mitigate the pressure of peak demand can be found in [34; 35; 36; 37]. An operating strategy for short-term scheduling of integrated gas and power system is proposed in [36] while considering demand response and wind uncertainty,In [37], the impact of demand side response on integrated gas and power supply systems in GB is analyzed for the time horizon from 2010 to 2050.