Analytic continuation as the origin of complex distances in impedance approximations. (February 2019)

• Record Type: Journal Article
• Authors: Li, Songyan; Tylavsky, Daniel
• Is Part Of: International journal of electrical power & energy systems. Volume 105(2019)
• Page Start: 699
• Page End: 708
• Publication Date: 2019-02
• Subjects: Analytic continuation -- Padé approximants -- Transmission line impedance -- Underground cable impedance -- Green's functions; Electrical engineering -- Periodicals; Electric power systems -- Periodicals; Électrotechnique -- Périodiques; Réseaux électriques (Énergie) -- Périodiques; Electric power systems; Electrical engineering; Periodicals; 621.3
• DOI: 10.1016/j.ijepes.2018.09.022
• Languages: English
• ISSNs: 0142-0615

Abstract

Highlights: Historically, obtaining closed-form approximations required trial and error. We show such approximations can be derived without iterative trial and error. After impedance approximations we successfully test our method on Green's functions. The method can be used on any series or integral that has no closed form solution. Abstract: Engineering approximations of physical systems sometimes produce models in which real-valued model-based physical-distances are added to complex-valued distances and/or (for electrical systems), real-valued current/charge image intensities are replaced with complex-valued quantities. These models are arrived at often using ad hoc approximations that allow infinite integrals or series to be approximated in closed form. Arriving at accurate ad hoc approximations in a compatible analytic form is often the difficult step in the derivation of these approximations. In this paper, we show that this difficult ad hoc step can be replaced for many classes of functions with the use of analytic continuation via Padé approximants, along with some reasonable engineering judgement. We apply our approach to several existing approximations in the electrical engineering field (overhead transmission line impedance, underground cable impedance and Green's functions used in ground potential rise calculations) and show that these approximations can be derived elegantly, without the need for grand leaps of insight, and provide a basis for both distance parameters and current/charge intensities that are complex-valued.