Transient Analysis of Power Systems

Chapter 9Creation of Libraries

Juan A. Martinez Velasco and Jacinto Martin‐Arnedo

9.1 Introduction

The Alternative Transients Program (ATP) is a circuit‐oriented tool based on a time‐domain solution method: users supply parameters of components and their interconnection, the program itself builds the system equations. A simulation is carried out with a fixed time‐step, selected by the user, using the trapezoidal rule of integration [1]. The trapezoidal rule converts the differential equations of the network components into algebraic equations involving voltages, currents, and past values. These algebraic equations are assembled using a nodal approach. The resulting conductance matrix is symmetrical and remains unchanged as the integration is performed with a fixed time‐step size. As this scheme can only be used to solve linear networks, some approaches to cope with nonlinear and time‐varying elements have been implemented; see Chapter 3.

A steady‐state phasor solution can be carried out to establish initial conditions for the transient solution, to analyse harmonic propagation (Harmonic Frequency Scan (HFS) [2]) or to obtain system impedance as a function of frequency (Frequency Scan (FS)). The steady‐state solution of linear networks at a single frequency is a simple task, and can be obtained using nodal admittance equations. However, this task can be very complex in the presence of nonlinearities, which can produce steady‐state harmonics. No solution method is available in ATP ...