Life loss of insulated power cables: an integrative criterium to improve the ANSI/IEEE and the CENELEC/IEC method for overload protection

A comparison between the ANSI/IEEE and the CENELEC/IEC approach to overload protection of electric cables has allowed a determination of which of the two methods is more restrictive depending on power cable size and overload duration. This paper introduces a methodology to calculate the life-loss of a power cable due to an overload current of given magnitude and duration. The proposed methodology is then applied to repeat the above-mentioned comparison between ANSI/IEEE and CENELEC/IEC in more objective terms, that is to say by determining the actual ageing of power cables caused by the overloads they could experience in service as a consequence of: the prescribed operating currents in conventional time of protective devices, within the CENELEC/IEC rules; and the admissible emergency loading temperatures and currents in the case of the ANSI/IEEE standards. Therefore it has been outlined an innovative and versatile criterium to protect cables against overloads: innovative because, unlike the traditional ANSI/IEEE and CENELEC/IEC methods, it is based on the prescription of the cable life-loss considered expendable to face an overload (it has been assumed that the progressive life-loss could be checked by a smart protective device provided with a simple electronic controller able to perform the proposed calculating methodology); versatile because the admissible life-loss can be varied according to plant configuration.