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The integration of renewable energy sources into existing electric power systems is connected with an increased interdependence between natural gas and electricity transmission networks. To analyse this interdependence and its impact on security of supply, we developed a novel quasi-dynamic simulation model and implemented it into the simulation tool SAInt (Scenario Analysis Interface for Energy Systems), the first published software application that allows the combined simulation of gas and electric power systems in a single time frame and simulation environment. The model is composed of a transient hydraulic simulation model for the gas system and an augmented AC-Optimal Power Flow model for the electric power system, which includes a model for dispatchable power system loads and considers time transitional constraints, such as the ramp rate and the start-up time of generation units. Both models take into account the control and constraints of the most relevant facilities present in both systems. The bidirectional interconnection between both systems is considered and established by coupling equations describing the fuel gas offtake for power generation in gas fired power plants, and the electric power supply to LNG terminals and electric driven compressors in gas compressor stations. The resulting system of equations for the combined model are solved in a single simulation time frame. In order to quantify the impact of different contingencies on the operation of the combined system, a number of security of supply parameters are proposed, which can be utilised to compare the impact of different contingencies on security of supply and the effectiveness of countermeasures to mitigate this impact. The capabilities of the combined model and the functionality of the simulation tool SAInt are demonstrated in a case study of a sample gas and power transmission system. Results indicate how the combined simulation of gas and electric power systems can give insight into important and critical information, such as the timing and propagation of contingencies cascading from one system to the other or the grace period to react to these contingencies. Such information can contribute to improving the coordination between gas and power transmission system operators in the event of a disruption, thus, increasing the resilience and the level of security of supply in the combined energy system. The information provided by the combined model cannot be obtained by the traditional co-simulation approach, where both systems are solved in different time frames. Furthermore, the studies stress the importance of using transient gas simulation models for security of supply analysis instead of steady state models, where the time evolution of gas pressure and linepack are not reflected appropriately.

This paper deals with multi-objective optimization of a single-model stochastic assembly line balancing problem with parallel stations. The objectives are as follows: (1) minimization of the smoothness index and (2) minimization of the design cost. To obtain Pareto-optimal solutions for the problem, we propose a new solution algorithm, based on simulated annealing (SA), called m_SAA, m_SAA implements a multinomial probability mass function approach, tabu list, repair algorithms and a diversification strategy. The effectiveness of m_SAA is investigated comparing its results with those obtained by another SA (using a weight-sum approach) on a suite of 24 test problems. Computational results show that m_SAA with a multinomial probability mass function approach is more effective than SA with weight-sum approach in terms of the quality of Pareto-optimal solutions. Moreover, we investigate the effects of properties (i.e., the tabu list, repair algorithms and diversification strategy) on the performance of m_SAA. (C) 2010 Elsevier Ltd. All rights reserved.

Gas and power networks are tightly coupled and interact with each other due to physically interconnected facilities. In an integrated gas and power network, a contingency observed in one system may cause iterative cascading failures, resulting in network wide disruptions. Therefore, understanding the impacts of the interactions in both systems is crucial for governments, system operators, regulators and operational planners, particularly, to ensure security of supply for the overall energy system. Although simulation has been widely used in the assessment of gas systems as well as power systems, there is a significant gap in simulation models that are able to address the coupling of both systems. In this paper, a simulation framework that models and simulates the gas and power network in an integrated manner is proposed. The framework consists of a transient model for the gas system and a steady state model for the power system based on AC-Optimal Power Flow. The gas and power system model are coupled through an interface which uses the coupling equations to establish the data exchange and coordination between the individual models. The bidirectional interlink between both systems considered in this studies are the fuel gas offtake of gas fired power plants for power generation and the power supply to liquefied natural gas (LNG) terminals and electric drivers installed in gas compressor stations and underground gas storage facilities. The simulation framework is implemented into an innovative simulation tool named SAInt (Scenario Analysis Interface for Energy Systems) and the capabilities of the tool are demonstrated by performing a contingency analysis for a real world example. Results indicate how a disruption triggered in one system propagates to the other system and affects the operation of critical facilities. In addition, the studies show the importance of using transient gas models for security of supply studies instead of successions of steady state models, where the time evolution of the line pack is not captured correctly.

This paper aims at analysing the impacts of interdependencies between electricity and natural gas systems in terms of security of energy supply. When analysing both systems several interdependencies can be observed, however, the most significant interdependencies are as follows: (1) gas dependency of gas fired power plants in electricity system and (2) electric dependency of electric-driven compressors in gas system. Since both systems depend on each other, it is of major interest from an energy security perspective to investigate how failures triggered in either of the systems propagate from one system to the other. We proposed an integrated simulation model that aims at reflecting the dynamics of the systems in case of disruptions and takes the cascading effects of these disruptions into account. While developing the integrated model, first electricity and gas systems are modelled separately and then linked by an (MATLAB-based) interface. The effectiveness of the proposed model is investigated using characteristic disruption scenarios. Computational results demonstrate that the integrated simulation model is very user-friendly and quite effective and efficient in analysing the interactions between electricity and gas systems., JRC.F.3-Energy security