A Choice of Critical Sections of Electric Wires and Cables in Power Circuits of Electrical Equipment of Power Industry

Abstract

Implementation of close calculation determination of critical sections of S Ci and critical amplitudes of density of alternating current δ Ci 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 i k (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 S Ci 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 i k (t) flows with set ATP. On the basis of determination of sizes of the real critical sections S Ci for the indicated wires and cables the calculation numeral estimation of critical amplitudes of density δ Ci of SC current i k (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 T a =50 ms of аperiodic to the constituent of current of SC) critical amplitudes of density δ Ci of SC current i k (t) at time of his disconnecting t k =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/mm 2. At time of disconnecting t k =160 ms of SC current i k (t) in the power circuits of the examined electrical equipment (T a =50 ms) critical amplitudes of density δ Ci of SC current i k (t) for the copper (aluminum) cores (shells) of indicated CCP become accordingly numeral equal approximately 1,33 (0,99) kA/mm 2. Originality. First by a calculation way taking into account information for ATP of SC current i k (t) and quantitative values of time of his disconnecting t k in the power circuits of electrical equipment of the general industrial installations the numerical values of critical sections S Ci and critical amplitudes of density δ Ci of AC SC current i k (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 S Ci and amplitudes of density δ Ci of AC SC current i k (t) of frequency 50 Hz (at the period of oscillations of T p =20 ms for of periodic constituent of emer...

A Choice of Acceptable Sections of Electric Wires and Cables in on-Board Circuits of Aircraft Electrical Equipment

“…It can be seen that the indicated values of the skin layer thickness Δ i turn out to be comparable with the radii (thicknesses) of the current-carrying cores (shells) of wires and cables, usually used in electrical circuits of the aircrafts under consideration (in particular, in aircraft networks [7]). As in [1,2], we use the condition of the adiabatic nature of the action of the current i k (t) of a single-phase SC in the on-board network of the aircraft, no more than t kC =40f -1 =100 ms in the conductive materials of the cores (shells) of the thermal process in CCP under consideration, in which the influence of heat transfer from the surfaces of their current-carrying parts having current temperature θ iS ≥θ 0 , and the thermal conductivity of the layers of their electrically conductive materials and insulation on the Joule heating of the current-carrying parts of the cores (shells) of the studied wires (cables) can be neglected. It is required by calculation in an approximate form, taking into account the nonlinear nature of the change, due to the Joule heating of the investigated CCP of the specific conductivity γ i of the material of its cores (shells) and the conditions of the thermal resistibility of the CCP to the action of the current i k (t) of a single-phase SC in the onboard network of the aircraft to determine in the range of change of AC frequency f = (50-400) Hz in the power circuits of its electrical equipment the maximum permissible cross-sections S il of current-carrying parts for uninsulated copper (aluminum) wires, as well as for insulated wires and cables with copper (aluminum) cores (shells), PVC, R and PET insulation, through which in emergency operation mode of the aircraft single-wire onboard network (with a common «minus» on its massive metal casing, which serves as a reverse current lead [10]) or two-wire on-board aircraft network [11] current of a single-phase SC i k (t) flows with known duration t kC and with specified amplitude-temporal parameters (ATPs).…”

“…Introduction. In [1,2], as applied to the tasks of industrial electric power industry, the issues of a refined choice of the maximum allowable S il and critical S iC cross-sections of uninsulated electric wires, as well as insulated wires and cables with polyvinyl chloride (PVC), rubber (R) and polyethylene (PET) insulation and copper (aluminum) cores (sheaths) according to conditions of their, respectively, thermal stability and electric explosion (EE) are considered. As is known, the calculation modes for choosing the maximum allowable cross-sections S il of cable-conductor products (CCP) used in power circuits of electrical equipment with alternating current of frequency f=50 Hz are the modes of single or three-phase short circuit (SC) [3,4].…”

“…As is known, the calculation modes for choosing the maximum allowable cross-sections S il of cable-conductor products (CCP) used in power circuits of electrical equipment with alternating current of frequency f=50 Hz are the modes of single or three-phase short circuit (SC) [3,4]. The technical data given in [1][2][3][4] for the selection of CCP relate to power circuits of electrical equipment used in land-based stationary objects during their industrial power supply with AC with frequency of f=50 Hz. And what about the choice of the maximum allowable cross-sections S il of CCP for objects of aviation and rocket and space technology, in the on-board electrical networks of which it is possible to use alternating current with frequency f, significantly different from the traditional power frequency of 50 Hz?…”

“…As an example of the calculation estimation according to condition (7) of the thermal resistibility of the CCP of the aircraft on-board network (f=400 Hz; J ill ≠0; θ 0i =θ ll =65 С), we consider the case when for its aviation shielded wire of the БПВЛЭ brand with PVC insulation and the split copper core [7,15] in the emergency mode of a single-phase SC, the following initial data are satisfied: I mk =5 kA; t kC =5 ms; T a =3 ms. According to Table 4, for the indicated initial parameters, the maximum permissible cross-section S il of the wire considered is numerically approximately 2.71 mm 2 . In this case, the value of the action integral J ak of the current i k (t) of a single-phase SC in the on-board network of an aircraft according to (6) will be numerically about 9.86•10 4 A 2 •s (see Table 3).…”