Thermal Distortion of Signal Propagation Modes Due to Dynamic Loading in Medium-Voltage Cables

Abstract

Temperature variation from dynamic cable loading affects the propagation characteristics of transient signals. The distortion of modal signal components as a function of temperature in a three-phase medium-voltage cable is investigated. The temperature influence arises mainly through the complex insulation permittivity, which has a non-linear relationship with temperature. Near the maximum operating temperature of the cross-linked polyethylene insulation, the propagation velocity increases by 0.56% per degree centigrade but is an order of magnitude less sensitive at ambient temperature. The paper presents modeling results based on cable impedance and admittance matrices obtained from electromagnetic field simulation, taking into account the time-varying temperature distribution in the cable cross-section. The results are verified by applying Rayleigh–Schrödinger perturbation analysis. In the time domain, signal patterns shift when the modal propagation velocities change upon cable loading. Moreover, separation of degenerate modes is observed when the cable phase conductors carry an unbalanced current. The perspectives for exploiting the temperature dependency of signal propagation for pinpointing cable defects and for dynamic rating of underground power cables are discussed.

Wave-Velocity Based Real-Time Thermal Monitoring of Medium-Voltage Underground Power Cables

“…2a shows that for PILC the velocity decreases close to linear with temperature, whereas for XLPE a non-linear increase is observed. The relative permittivity has also been measured for a 1.22 mm thick XLPE material sample up to a temperature of 110 °C, controlled within ±0.1 °C [16]. The effect on the velocity is shown with the dashed curve.…”

A Proposed New Approach for the Assessment of Selected Operating Conditions of the High Voltage Cable Line

“…At the same time, this paper analyzes all possible thermal parameters that occur in different climatic zones for the most extensive ways of laying the cable line. In addition, such an assessment is made before the commencement of construction and use of the cable line.However, the literature also proposes methods that concern the improvement of the existing methods of cable condition assessment [27,28]. Such studies take into account the dependence that also results from the relative permeability of the cable, which decreases with increasing temperature.…”