Data-Transmission Characteristics of Power Cables with Star-Quad Cross-Section

In this paper, the transmission of high-frequency signals for power line communications (PLC) along four-conductor power cables with star-quad cross-section is analyzed. In the derivation, the power cable is treated as a uniform and lossless multiconductor transmission line (MTL), and modal analysis is applied. The cable propagation modes are derived by literal solution of the MTL wave equations and related to the specific structure of the per-unit-length matrix parameters of the cable. The influence of coupling/decoupling schemes on the involved mode propagation paths is analyzed. For different values and configuration of the power cable loads, the signal attenuation (SA) of the PLC channel is evaluated in closed form. It is shown that intra-phase (differential) coupling should be used in order to excite a single propagation mode via balanced connections to a specific pair of phase conductors; under such conditions a two-conductor transmission line (TL) analogy holds. Different three-phase terminal loads and the possible presence of a branch point are considered in order to assess their effect in terms of degradation of the channel SA.