The transmission characteristics of underground medium-voltage/broadband over power line (MV/BPL) channels are examined analytically. By appropriately modifying multiconductor transmission-line theory, the bottom-up approach, already used to treat overhead MV/BPL transmission, is extended to analyze BPL transmission in three-phase underground MV lines with common shield and armor. ThIS analysis shows that these cables may support five modes, giving rise to five separate transmission channels which reduce to three if the shield and armor are grounded. The numerical results concerning attenuation in underground MV/BPL channels have been validated against relevant sets of measurements and compared to the relevant results of overhead MV/BPL channels. It has been verified that the attenuation in underground MV/BPL channels exhibits a lowpass behavior and is significantly higher than that of overhead ones.

Broadband Transmission via Underground Medium-Voltage Power Lines—Part I: Transmission Characteristics

The aim of this paper is to illustrate the development of a theoretical and experimental study on the characterization of medium voltage (MV) cables in the frequency range 25-200 kHz. Two transmission line configurations, line-ground and line-line, were considered in order to evaluate the main parameters, such as the characteristic impedance and the attenuation constant alpha. A simplified model of the line-ground configuration is proposed which allows one to evaluate the characteristic impedance and the attenuation constant by means of geometrical dimensions. The model was verified by experimental measurements on commonly used MV cables, RG7H1R, with an aluminium core of different sections, 95 mm2 and 185 mm2. Moreover, the experimental tests were carried out for the line-line configuration.

Power Line Communication in Medium Voltage Systems: Characterization of MV Cables

Boggs and Stone (1982) defined the fundamental limits to the electrical detection of corona and partial discharge (PD), i.e., wideband detection of a PD-induced pulse in the presence of thermal noise. This paper treated the effect of frequency-dependent attenuation in shielded power cable in that context. However, most of the plots in that paper were the result of numerical computations. In the same year, Stone and Boggs set out a theory for high-frequency attenuation of shielded power cable. They showed good agreement between attenuation predicted from measured material properties and measured, high-frequency attenuation of shielded power cable. Since 1982, measurements of high-frequency cable attenuation have been reported by a number of authors for a variety of cables. In addition, software tools have become available that facilitate an analytic solution for the parameters of interest. This article summarizes the theory for PD propagation in shielded power cable for both symmetric (Gaussian) and asymmetric PD-pulse waveforms, based on the assumption that the attenuation constant (dB/m or Nepers/m) of the cable is proportional to frequency. This appears to be the most complete possible analytic exposition of PD attenuation in shielded-power cable, which has obvious applications to field PD measurements of such cable.

Partial Discharge Pulse Propagation in Shielded Power Cable and Implications for Detection Sensitivity

Propagation losses occur in medium voltage power cables as pulses propagate through them. Since cables have many components, these can make different contributions to the propagation losses. The relative contributions of the conductors, insulation and semi-conducting screens to the propagation characteristics of the cable are analyzed. The propagation characteristics of the cables are studied by a developed "approximate" model providing analytical expressions that can quantify the contributions to the losses by the different parts of the conductor and dielectric system. The model is compared with an "exact" model and is tested on four cables

Dependence of XLPE insulated power cable wave propagation characteristics on design parameters

A novel approach for the calculation of transient fault current contributions from capacitive network components in HVDC cable networks during pole-to-ground faults is presented in this paper. Analytic approximations considering the skin effect and the resulting distortion of the waveshape of the fault surge are proposed. Only fault current contributions from capacitive components, such as dc capacitors and adjacent cable feeders, are taken into account in this paper, since they are dominant during the first few milliseconds and yield the highest rates of rise of fault current. The results of the proposed expressions are compared with a benchmark model implemented in PSCAD and exhibit an accurate representation of the time development of the fault current. The derived approximations may serve as a starting point for a short-circuit calculation standard for HVDC networks and the specification of HVDC circuit-breaker requirements.

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Analytic Approximation of Fault Current Contributions From Capacitive Components in HVDC Cable Networks

This paper provides an overview of the mechanisms of high frequency (HF) loss in shielded power cables and discusses the challenges in the measurements of cable material properties at HF.

J.Y. Zhou

Papers

High frequency properties of shielded power cable - part 1: overview of mechanisms