The combined simulation of gas and electricity is one of the unique model features of **SAInt**. In a
combined simulation, the equations describing the gas and power system are linked through a number
of coupling equations reflecting the physical interlink between the two energy vectors. The resulting
system of equations are solved simultaneously for each time step. The coupling between both vectors
includes:

- the gas offtake from gas networks to generate electricity in gas fired power plants connected to electricity networks,
- the power offtake from electric networks to operate the electric engines in gas compressor stations, and
- the power offtake from electric networks to operate LNG regasification terminals.
- the power offtake and the gas injection of power to gas facilities.

One of the most powerful features of the combined simulation model is its ability to define conditional
control changes, which may include state information of both energy vectors. For instance, the startup
and shutdown of a gas fired power plant in the electric network, which depend on the available gas
pressure and linepack in the gas network, can be modelled realistically by conditional expressions.

The following combined gas and electricity network simulation models are available:

**(1.)** Combined Steady Gas and Steady AC-Power Flow Simulation

**(2.)** Combined Steady Gas and Steady AC-Optimal Power Flow Simulation

**(3.)** Combined Dynamic Gas and Quasi-Dynamic AC-Power Flow Simulation

**(4.)** Combined Dynamic Gas and Quasi-Dynamic AC-Optimal Power Flow Simulation