Transmission flow solver (network)
[Runtime modules]

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Detailed Description

The network module implements a balanced three-phase positive sequence power flow solver using the Gauss-Seidel method as described by Kundur [Kundur 1993, pp.259-260].

The Gauss-Seidel (GS) method is a linear iterative method (as opposed to the Newton-Raphson or NR method, which uses a quadratic iterative method). The only differences between the two methods are the rate of convergence and the robustness of convergence when the starting state is bad. Because GridLAB-D is quasi-steady time-series simulation, most state changes are small and result in only 1 or 2 iterations in either method. However, the GS method can be more easily implemented using parallel processing systems (such as multicore systems). In addition, the GS method is more likely to solve for new conditions that are far from the current solution. However, the GS method can have difficulty computing flows under high-transfer conditions.

The GS method uses an iterative approach proposed by Seidel in 1874. The GS method iterates using the first-order approximation of the Taylor expansion, and the NR method uses a second-order approximation. In the GS method the fundamental equation for the k^th node can written as

The GS method is often criticized as inferior. This is categorically not true. It is true that it has strengths and weaknesses when compared to the NR method. Depending on circumstances, these differences may cause one to prefer one method over the other. But both (indeed all) valid methods produce the same answers. Indeed, many commercial power flow solvers implement both methods concurrently, recognizing the necessity to exploit the appropriate method under any given circumstance. Hence, the implementation of the GS method does not make GridLAB-D's solution method inferior in any way. It is simply a recognition that the circumstances of the power flow solution needed in GridLAB-D leads one to choose the GS as the default power flow solver. Other power flow solvers can and should be implemented to address different circumstances. We encourage users and developers to consider doing so.

Modules
	Capacitor bank
	Network check
	The check() function implements a network validation check on the current model.
	Model export
	Fuse
	Generating unit
	Model import
	The only import format currently supported is the IEEE .cdf format (find it) .
	Network link (branch)
	The link object implements the general solution elements for branches using the Gauss-Seidel method.
	Meter
	Network node (bus)
	The node object implements the general node solution elements of the Gauss-Seidel solver.
	Voltage regulator
	Relay
	The primary relay time is determined by .
	Transformer