NAP - Network Analysis and Planning

Load Flow

The optimal load flow has to solve the problem of minimizing cost in which the variables are restricted by:

  • Equality constraints: the power flow equations.
  • Inequality constraints: operating limits on controllable variables.

Calculation is divided into 3 steps: ILF, CPF and OPF.

ILF - Initial Load Flow

This first step consists of solving a standard power flow problem ignoring the inequality constraints, using the Newton-Raphson mathematical technique.

CPF - Constrained Power Flow

As the ILF solution may be unfeasible, this second stage consists of moving the ILF solution into the feasible subspace, satisfying all voltage, generation, transit and tap transformer constraints. If no feasible solution is found, the unsatisfied constraints are highlighted.

OPF - Optimum Power Flow

This third step consists of finding the power flow solution, which minimises the generators operating cost while not violating the inequality constraints.

Due to this powerful approach, the OPF also calculates the marginal costs of real and reactive demand at each node. This information is a powerful help when designing new systems or upgrading existing ones.

SCC - Short Circuit

The objective of the Short Circuit simulation is to estimate the status of the generation and transmission system a few voltage cycles after the occurrence of a fault. Transient or sub-transient responses can be analysed. The program simulates symmetrical faults (3 phases to ground) and non-symmetrical faults (1 phase to ground, 2 phases to ground, or phase to phase). The OPF solution is used as the pre-fault status of the system.

OUTSIM – Contingency Analysis

OUTSIM is a N-1 incident simulator, i.e. it simulates lines, transformers and generators outages one by one. Starting from the OPF solution, a full AC power flow simulation is performed in order to predict the impact of outages on branch loading, voltages limits and generation capacity.

STABIL - Transient Stability

STABIL simulates the dynamic behaviour of an electric power system during the first few seconds following a major disturbance of that system (e.g. a short-circuit, the loss of a generator or a major branch opening). The main result is a set of curves describing the evolution of the generator rotor angles during the simulation period (generator swing curves). Additional phenomena can also be studied such as the action of the voltage and speed regulators.

Sensitivity analysis

This module analyses the evolution of any result as a function of any data varying within the user-defined limits.


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