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This paper investigates the influence of metallic sheaths on alternating current (AC) losses and ampacity of power cables. The AC losses are expressed as AC/direct current (DC) resistance in power cables, which is the main factor in loss computations. With regard to the importance of harmonic contents of the currents, a comprehensive study is performed on AC/DC resistance of medium-voltage cables in the presence of harmonics. Different harmonic frequencies include triple and nontriple orders are considered. A derating factor is proposed on the basis of cable constructions. Two types of sheathed and unsheathed medium-voltage power cables are considered. Also for metallic sheathed cables, 2 types of sheath grounding are investigated. It is shown that single-point bonding and both-ends bonding of sheaths have different effects on cable ampacity in harmonic frequencies. Moreover, different conductor cross sections and distances between cables are considered, and their effects on AC/DC resistance and ampacity derating are assessed. It is shown that these factors have important effects on AC/DC resistance and thus power cable losses. Furthermore, all cases are investigated in both flat and trefoil formations that are the most popular formations in power cables. To achieve precise results, we performed this study on the basis of finite element simulation, which is an exact way to cable losses computations in each configuration. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive model for electro-thermal analysis of metal oxide surge arresters based on finite element method. The input of the proposed model has been derived from power loss curve using adaptive network based fuzzy inference system (ANFIS). Moreover, degradation factor has been introduced as a new index to represent operating history of metal oxide surge arrester. Therefore, applied voltage, temperature, and degradation factor have been considered as inputs in the ANFIS model to obtain accurate power loss which is of paramount importance in electro-thermal analysis. High voltage experimental setup and an oven have been prepared to acquire data for the proposed model. Degrading effect has been undertaken by measurement of the voltage-current characteristic of used and degraded varistors. The effect of assembling process, in addition, has been considered using different virgin (not degraded) varistors in experimental measurements. In addition, according to the IEC standard, the aging effect has been obtained experimentally by putting the varistor under 115 °C and continuous operating voltage for 1000 h. To validate the results of the electro-thermal model, thermal infrared camera has been used under different applied voltages. Obtained results show that the electro-thermal behavior of surge arrester is predictable with high precision through the proposed artificial model. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]