Short-Term and Long-Term Electrical Strength of MV Fire-Resistant Cables

The insulation of fire–resistant medium voltage cables contains a layer made of mica tape and a layer of extruded dielectric, which may be cross-linked polyethylene or ethylene propylene rubber. The former is subject to electrical aging under the effect of partial discharges, and the latter to thermal aging. The article presents data on the short-term electrical strength of cables containing mica tapes of different thicknesses, the life curves of mica materials and cable layouts, as well as the results of tests carried out on the full-scale samples of cables developed by the authors for resistance to electrical, thermal and combined electrothermal aging. The thermal stability of a medium-voltage fire-resistant cable at the end of a one-year combined aging cycle has been analyzed. It is shown that the "residual" thermal stability margin is very significant.