Electrical engineering & Electromechanics (Oct 2019)
A CHOICE OF CRITICAL SECTIONS OF ELECTRIC WIRES AND CABLES IN POWER CIRCUITS OF ELECTRICAL EQUIPMENT OF POWER INDUSTRY
Abstract
Purpose. Implementation of close calculation determination of critical sections of SCi and critical amplitudes of density of alternating current δCi of frequency 50 Hz in wires and cables of power circuits of electrical equipment of power industry, characterized flowing in it at malfunctions of operation current ik(t) of short circuit (SC) with set amplitude-temporal parameters (ATP). Methodology. Scientific and technical bases of power engineering, electrophysics bases of technique of high-voltage and large pulsed currents, theoretical bases of the electrical engineering. Results. The results of the developed electrical engineering approach are resulted in a calculation choice on the condition of electric explosion (EE) of current-carrying parts of cable and conductor products (CCP) of critical sections of SCi for the copper (aluminum) cores of the uninsulated wires, and also for the insulated wires and cables with a polyvinilkhloride (PVC), rubber (R) and polyethylene (PET) insulation with copper (aluminum) cores (shells) on which in the power circuits of electrical equipment of the general industrial equipment in malfunction the current of SC ik(t) flows with set ATP. On the basis of determination of sizes of the real critical sections SCi for the indicated wires and cables the calculation numeral estimation of critical amplitudes of density δCi of SC current ik(t) is executed with set ATP in current-carrying parts of investigated CCP of power circuits of the examined electrical equipment. It is determined that in the power circuits of electric equipment of the general industrial installations (for permanent time of slump of Ta=50 ms of аperiodic to the constituent of current of SC) critical amplitudes of density δCi of SC current ik(t) at time of his disconnecting tk=100 ms in copper (aluminum) cores for the uninsulated wires and insulated wires (cables) with copper (aluminum) cores (shells), PVH, R and PET it is numeral made an insulation according to approximately 1,57 (1,18) kA/mm2. At time of disconnecting tk=160 ms of SC current ik(t) in the power circuits of the examined electrical equipment (Ta=50 ms) critical amplitudes of density δCi of SC current ik(t) for the copper (aluminum) cores (shells) of indicated CCP become accordingly numeral equal approximately 1,33 (0,99) kA/mm2. Originality. First by a calculation way taking into account information for ATP of SC current ik(t) and quantitative values of time of his disconnecting tk in the power circuits of electrical equipment of the general industrial installations the numerical values of critical sections SCi and critical amplitudes of density δCi of AC SC current ik(t) are certain for the uninsulated wires, and also insulated wires and cables with copper (aluminum) cores (shells), PVH, R and PET insulation. Practical value. Obtained results for the critical sections SCi and amplitudes of density δCi of AC SC current ik(t) of frequency 50 Hz (at the period of oscillations of Tp=20 ms for of periodic constituent of emergency current of SC) can be utilized in power industry in practice at a choice thermally by a bar to the action of large SC currents ik(t) of CCP with copper (aluminum) bars (shells), intended for reliable operation in the power circuits of electrical equipment of industrial power industry.
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