Comparison of dielectrical properties of LV cables with different fire barriers ensuring circuit integrity under fire conditions at high ambient temperatures

Systematic and a long-term care has been paid to questions regarding safe operation of electrical equipment, being reflected into new requirements for all their components. Many electrical devices in industrial and building units are apart from so-called expected projected stresses arising from their attribution, exposed to stresses, subjected to their application environments or incident and are seldom considered at the planning stage of the complex. Qualified estimate of their effect on the preservation of operational life and functionality requires a comprehensive analysis of equipment and fixing of conditions of continued use on desired level of reliability and safety. Materials, mainly insulation materials are the most important components of power system. However, currently, we witness contradictory trend of the operational life of cables, being functional under fire conditions. The first is the requirement for increasing temperatures to simulate fire conditions during the test from the initial temperature of 650 °C (IEC60331 in 1970) to today's early 1040°C (EN50577 still being in the process of proposal) [1]. The second is the evaluation of their dependable operation at normal and limit temperatures that can occur during energy transfer [2].In this paper we want to compare the efficiency of various materials and constructions of cables' fireproof barriers, ensuring their functionality in the fire, not only in terms of their behaviour in the fire, but also in term of the transmission of energy at high temperatures. In this paper we compare the dielectric parameters after exposure of selected cable types to temperatures above the allowed operating temperatures and fixation of their dielectric changes.