Thermal analysis of low-voltage power cables considering the presence of current harmonics
Abstract
In practical design and selection of low-voltage power cables, the heating effects caused by current harmonics are often not sufficiently considered. In addition, with the increasing penetration of nonlinear loads and renewable energy sources in low-voltage distribution networks, harmonic current components tend to increase the AC resistance and Joule losses, thereby leading to a rise in cable operating temperature depending on the harmonic magnitude and order. When harmonics are present, the increased conductor losses may cause the actual cable core temperature to significantly exceed that observed under purely fundamental current conditions. In this study, a thermal model originally developed for underground cables is improved and its heat exchange parameters are recalibrated to accurately represent the thermal dissipation characteristics of overhead PVC-insulated low-voltage cables, which are widely used in Vietnamese distribution networks. By employing harmonic current spectra together with the electro-thermal parameters of the cable as input data, the proposed model enables the evaluation of cable heating behavior under various operating scenarios, while simultaneously considering variations in both harmonic magnitude and harmonic order. The study focuses on: (i) improving the thermal balance model for low-voltage cables; (ii) evaluating the impact of current harmonics on cable core temperature; (iii) analyzing insulation lifetime degradation under harmonic conditions; and (iv) assessing the influence of ambient temperature. Based on the numerical results, appropriate operating current derating levels are recommended to maintain cable temperature within permissible limits, thereby ensuring safe operating conditions and reducing the risk of insulation degradation in low-voltage power networks.