With reference to the classic three phase transmission line equations, the equivalent formulation in terms of Park components is obtained. A radiative model of a finite dimension transmission line. valid when high frequency harmonics are present, is then developed by taking advantage of some significant simplifications introduced by the same Park transform.A numerical example is then given by considering a medium voltage line fed by pulse width modulation (PWM).
lntroductionThe TEM mode model is characteristic of the infinite length conservative line. Since it does not consider the radiative effect however, it leads to approximate results. This is due to the fact that according to this model Poynting's vector only takes in account the longitudinal component (i.e. parallel to the direction of the power line itself). which is specific of power transmission and which disregards any Lateral radiation.In the more realistic case of a finite length line the rigorous solution of Maxwelt's equations shows, on the contrary, the presence of a theoretically infinite number of complementary waves, due to the discontinuities of the terminal connections and which superimpose themselves over the principal TEM mode wave associated with the infinite length hypothesis. From the spatial point of view these field components, due to the complementary waves become more and more dominant as the distance from the line increases, whereas the component related to the principal wave becomes negligible. Strictly speaking. radiation is only caused by the component of Poynting's vector associated to the complementary waves that show significant radial components. In this phenomenon the current associated with the complementary waves, in accordance with the works of Carson and SchelkunoK is only a small fraction of the principal wave current due to TEM mode propagation. The rigorous determination of radiation from a line would require the complete solution for the complementary waves and then finding the resultant field at any point. The aforementioned analysis performed by Schelkunoff and Carson is mainly related to the case of monophase transmission. Due to the formal complexity of this approach, the extension to the case of three phase power sytems appears to be rather articulate from the analyticaf viewpoint. Because of this. the present paper, which. has the aim of evaluating the radiative contribution associated to any non sinusoidal and unbalanced case, employs the Park transform, by means of which the instantaneous d. q and 0 sequence components necessary to more readily calculate Poynting's vector can be obtained.
Park's Model o f the Three Phase Transmission LineIn the case of a three phase transmission line. application of Maxwell's equations together with the classical TEM hypothesis leads to the Characteristic three phase transmission line equations:
t)]} arrays represent the voltage and current values for each phase and the matrixes {[R],[G],[L],[C])respectively denote the self and mutual resistance. conductance. inductance and ca...