Insulation coordination is essential for designing and testing HV cable systems properly. In transient conditions, i.e., in the presence of transient voltage surges, insulation coordination is based on the individuation of a certain maximum acceptable risk of failure under the switching and lightning overvoltages that the insulation may encounter in service, and translates into a maximum number of expected failures per year per length of line that the cable line has to match. Given the design of the cable in steady-state conditions, the number of expected failures per year and per length of cable line can be reduced by a proper design of the shield wires of overhead lines, of the grounding systems of line towers and so on [1], and by selecting and installing properly voltage-surge arresters when needed. However, insulation coordination in transient conditions implies that the design of the cable for its service in steady-state conditions, i.e., in the presence of constant levels of applied rated stresses, has already been accomplished properly, and this in turn implies that proper insulation coordination in steady-state conditions has been performed as well. Differently from transient conditions, insulation coordination in steady-state conditions can be defined as the selection of the stress levels that cable insulation is capable to withstand throughout a certain design life (time to failure) t0L with an acceptable design failure probability P0L. This article recalls some popular modelistic tools for HV cables, namely, the life models, Weibull distribution, and the enlargement law, and describes how they can be integrated into a multipurpose probabilistic model for cable-insulation coordination in steady-state conditions. First, the probabilistic framework of insulation-life modeling is outlined and the traditional phenomenologic approach to insulation-life modeling is recalled, by presenting some fundamental life models available in the literature and that can be used for time-to-failure estimation of HV cable insulation. Then the so-called enlargement law is introduced, which enables evaluation of how much the electric stress has to be reduced in order to keep the same failure probability as the volume of insulation increases (e.g., from specimens or cable loops tested in the lab to full-size cables installed in the field).Finally, all these tools are merged into a multipurpose model for cable-insulation coordination in steady-state conditions.
M. Marzinotto, G. Mazzanti (2015). The practical effect of the enlargement law on the electrothermal life model for power-cable lines. IEEE ELECTRICAL INSULATION MAGAZINE, 31(2), 14-22 [10.1109/MEI.2015.7048133].
The practical effect of the enlargement law on the electrothermal life model for power-cable lines
MAZZANTI, GIOVANNI
2015
Abstract
Insulation coordination is essential for designing and testing HV cable systems properly. In transient conditions, i.e., in the presence of transient voltage surges, insulation coordination is based on the individuation of a certain maximum acceptable risk of failure under the switching and lightning overvoltages that the insulation may encounter in service, and translates into a maximum number of expected failures per year per length of line that the cable line has to match. Given the design of the cable in steady-state conditions, the number of expected failures per year and per length of cable line can be reduced by a proper design of the shield wires of overhead lines, of the grounding systems of line towers and so on [1], and by selecting and installing properly voltage-surge arresters when needed. However, insulation coordination in transient conditions implies that the design of the cable for its service in steady-state conditions, i.e., in the presence of constant levels of applied rated stresses, has already been accomplished properly, and this in turn implies that proper insulation coordination in steady-state conditions has been performed as well. Differently from transient conditions, insulation coordination in steady-state conditions can be defined as the selection of the stress levels that cable insulation is capable to withstand throughout a certain design life (time to failure) t0L with an acceptable design failure probability P0L. This article recalls some popular modelistic tools for HV cables, namely, the life models, Weibull distribution, and the enlargement law, and describes how they can be integrated into a multipurpose probabilistic model for cable-insulation coordination in steady-state conditions. First, the probabilistic framework of insulation-life modeling is outlined and the traditional phenomenologic approach to insulation-life modeling is recalled, by presenting some fundamental life models available in the literature and that can be used for time-to-failure estimation of HV cable insulation. Then the so-called enlargement law is introduced, which enables evaluation of how much the electric stress has to be reduced in order to keep the same failure probability as the volume of insulation increases (e.g., from specimens or cable loops tested in the lab to full-size cables installed in the field).Finally, all these tools are merged into a multipurpose model for cable-insulation coordination in steady-state conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
