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• Optimal power and gas flow problem considering power-to-gas. • Quasi-stationary modeling considering DC power flow and gas dynamics. • Scalable approach using successive linear programming. • Use case analyzing dispatch of renewable energy systems. The integrated modeling of power and gas systems gains importance as a result of increasing interdependencies due to bidirectional coupling in renewable energy systems through power-to-gas and gas-fired power plants. The optimal power and gas flow problem (OPGF) aiming to minimize system dispatch costs is mostly applied to small test systems. However, to investigate system-wide effects of sector coupling, large-scale transmission grids must be considered. Due to nonlinearities especially in the pressure loss equation, a nonlinear optimization problem results. This paper aims to demonstrate that successive linear programming, in contrast to other discussed approaches, is suitable for solving large-scale and multi-period OPGF-problems. The presented approach shows high solution quality despite short computing time even for large-scale systems such as the German power and gas transmission grid. [ABSTRACT FROM AUTHOR]

• Coupled steady-state and dynamic reactive power planning. • Assessment and planning of voltage control in intra-hour transitions. • Technology-dependent optimisation of active compensation devices to ensure short-term voltage stability. • Mixed-integer linear optimisation considering various voltage control requirements. Planning of reactive power compensation devices as part of the grid planning process is becoming increasingly important due to decreasing reactive power reserves from conventional power plants. Planning such devices requires the consideration of the reactive power demand both during steady-state operation and disturbances as well as gradual power-flow shifts. To control the voltage in these scenarios, a portfolio comprising location, rated power and technology of reactive power compensation devices must be identified. In this paper, a planning approach with a coupled determination of steady-state and dynamic reactive power demand is applied to a generic transmission system. Different characteristic grid use cases are analysed for the identification of the steady-state reactive power demand. The determination of the dynamic demand involves the analysis of critical power-flow shifts within an hourly generation time series. Shifts leading to insufficient voltage stability reserves and high voltage gradients are considered in the planning approach. Furthermore, critical line-outage and short-circuit scenarios are analysed in connection with an increasing demand for dynamic reactive power compensation. Results emphasise that the coupled determination of steady-state and dynamic reactive power demand identifies suitable portfolios of different compensation devices using synergies for voltage control during steady-state operation, disturbances and power-flow shifts. [ABSTRACT FROM AUTHOR]