On the accuracy of the Phase-domain model for EMT analysis of transmission lines and cables

Abstract

The Phase-domain (or Universal) line and cable model (ULM) is one of the most advanced in its class. This model is synthesized from frequency-domain transmission line relations in three stages involving rational fitting, state-space analysis and numeric integration. Each one of these stages implies an approximation and this paper presents an evaluation their impact on the accuracy of the final model. First, a version of ULM is produced in the MatLab platform. Then, the numericerror increase at each stage is evaluated in the implemented version through the Numerical Laplace Transform technique (NLT). Next, the accuracy of the implemented model is tested under three different numeric integration rules: Trapezoidal, Backward Euler and Gear Second Order. Finally, the implemented model is compared with the one available in an industrial-grade EMTP.

Improving the performance of a lumped transmission line model used in electromagnetic transient analysis

“…In the frequency domain, travelling-wave-based TL models, such as the universal line model (ULM), can include all frequency effects of TL parameters [3]. For multi-phase TLs, the ULM is synthesised from a set of relations that are described by two matrix functions: the characteristic admittance matrix Y c and the propagation matrix H [4]. However, the ULM employs fitting techniques to fit both matrices by rational functions, whose accuracy depends on the previous identification and extraction of the travelling times for a correct fitting process [5,6].…”

“…This technique is performed numerically, and this process may cause errors in the estimation of travelling times [6]. Another frequency line model consists of a two-port TL representation in which currents and voltages are calculated by hyperbolic equations and then converted to a time domain using the numerical Laplace transform (NLT) [4,6,7]. However, the main limitation of this approach is the complexity in the representation of non-linear elements, multiple switching, faults, and time-variant devices.…”