Multi-port frequency-dependent network equivalent for electromagnetic transient studies

Network equivalents can be used to represent parts of a power system to reduce the complexity and the computation time during the simulation of electromagnetic transients. The goal is to simplify the representation while preserving the accuracy of transients in the remainder. In this work a method is developed for construction of single and multi-port frequency dependent network equivalent (FNDE). In this equivalent model the input admittance matrix is approximated by a rational function in the frequency domain. This method is developed for both single and multi phase systems. Several examples showing the accuracy and efficiency of the developed FDNE is presented.

I. INTRODUCTION

ELECTROMAGNETIC transients take place in electrical power systems during daily operations. They arise from faults, resonance, or any change in either the topology or the operating condition of the system. These transients can activate the control/protection systems, lead to power interruptions, or can even result in component failures [1]. Time-domain simulation is the only practical approach available for the study and evaluation of electromagnetic transients of electric power transmission/distribution systems. Time-domain simulation is carried out via two methods: (i) off-line digital simulation programs like the ElectroMagnetic Transients program (EMTP) [2], [3], and or (ii) real-time simulators. As a consequence of recent significant developments in computer technology, both in hardware and software, EMTP-like programs are well established as reliable and cost effective tools for the study of electromagnetic transients. In such studies, there is usually a study zone, a restricted portion of the system, and an external system, which comprises the rest of the system. If a complete representation is adopted for the external system, the computation effort required for the calculations may be excessive. This is particularly true for the case of large systems especially when frequency dependent models are used for transmission lines [4]. Even if only a part of the external system is to be used in the calculation, it is difficult to establish which part should be neglected.