Electrical engineering & Electromechanics (Jun 2019)
REFINED SELECTION OF ALLOWABLE CROSS-SECTIONS OF ELECTRICAL CONDUCTORS AND CABLES IN THE POWER CIRCUITS OF INDUSTRIAL ELECTRICAL EQUIPMENT TAKING INTO ACCOUNT EMERGENCY OPERATING MODES
Abstract
Purpose. Implementation and clarification of the existing engineering approach for determination in industrial power engineering for allowable sections of cable-conductor products (CCP) Sil of electric wires and cables in the circuits of electrical equipment of the general industrial installations characterized flowing in malfunction of current ik(t) of short circuit (SC) with different amplitude-temporal parameters (ATPs). Methodology. Scientific and technical bases of electrical power engineering, electrophysics bases of technique of high voltage and high pulse currents, theoretical bases of the electrical engineering. Results. The results of the developed engineering approach are resulted in the calculation determination on the condition of thermal resistibility of CCP permissible sections of Sil of the uninsulated wires, insulated wires and cables with copper (aluminum) cores (shells), polyvinyl chloride (PVC), rubber (R) and polyethylene (PET) insulation, on which in malfunction of their operation the current ik(t) of SC can flow with the set by normative documents of ATP. It is shown that divergence between the values of basic calculation coefficient of Cik by existing and offered to the engineering calculations selection of permissible sections of Sil of cores (shells) of the tested wires and cables for normal of their operating time at the nominal current load of CCP makes no more (3-8) %, and in the mode of de-energizing of CCP arrives at to (9-26) %.. Analytical correlation is got for the specified calculation determination of integral of action of Jak of current ik(t) of SC (Joule integral) in the power circuits of the tested electrical equipment. It is set that in the circuits of of the general industrial installations (for permanent time of slump of Ta=20 ms of aperiodic constituent of current of SC) maximum possible amplitudes of density of δilm≈Imk/Sil of SC current at time of his disconnecting tkC=100 ms for the uninsulated wires with copper (aluminum) cores make according to approximately 0.64 (0.36) кА/mm2, for cables with copper (aluminum) cores (shells), PVC and R insulation – 0.47 (0.30) кА/mm2, and for cables with copper (aluminum) cores ( shells) and PET insulation – 0.39 (0.25) кА/mm2. At time of disconnecting tkC=160 ms of SC current in the circuits of electrical equipment (Ta=20 ms) permissible amplitudes of current density of δilm of SC for the unsuolated wires with copper and aluminum cores are accordingly about 0.52 (0.29) кА/mm2, for cables with copper (aluminum) cores (shells), PVC and R insulation of 0.39 (0.25) кА/mm2, and for cables with copper (aluminum) cores (shells) and PET insulation – 0.32 (0.21) кА/mm2. Originality. First by a calculation the specified numeral values of sections of Sil and amplitudes of density δilm of SC current are determined for the uninsulated wires, insulated wires and cables with copper (aluminum)cores shells), PVC, R and PET insulation. New analytical correlation is offered for the calculation estimation of thermal resistibility of tested CCP to the action of current of SC. Practical value. The obtained results will be useful in the increase of thermal resistibility of CCP with copper (aluminum) cores (shells), PVC, R and PET insulation, widely applied in the power circuits of electrical equipment of the general purpose industrial installations.
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