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Vol. 27 (2024 year), No. 4, DOI: 10.21443/1560-9278-2024-27-4

Petrov A. R., Gracheva E. I., Miftakhova N. K.
Improvement of the methodology for assessing power losses in in-plant power grids

To improve the reliability of calculations of electric power losses in low-voltage electric networks, it is necessary to take into account the influence of the main parameters of electrical equipment. In the course of the study, a structural diagram and an algorithm for determining the equivalent resistance of the section of the shop network have been proposed; the main factors determining the equivalent resistance of the circuit (resistance of low-voltage switching devices, heating temperature of conductors, ambient temperature, equipment load factor) have been identified; graphical dependencies of the change in the equivalent resistance of the radial and trunk sections of the circuit on the mean square equipment load factor and the heating temperature of conductors have been shown. The total error in estimating the equivalent resistance when calculating without taking into account the main studied parameters of equipment for radial, trunk and mixed circuits is 40 % or more. The error in the results of calculations without taking into account the resistance of contact connections of switching devices can reach 80 %. The obtained dependencies of the equivalent resistance on the main parameters of the equipment are recommended for use to improve the reliability of estimating electric power losses in intra-plant electric networks.

(in Russian, стр.10, fig. 4, tables. 4, ref 17, AdobePDF, AdobePDF 0 Kb)

Vol. 28 (2025 year), No. 4, DOI: 10.21443/1560-9278-2025-28-4/1

Petrova R. M., Gracheva E. I., Miftakhova N. K.
Assessment of reliability parameters of power supply systems' schemes of industrial facilities of electrical complexes when changing the load power and area of the facility while performing technical and economic calculations

The relevance of the study lies in the assessment of the reliability parameters and economic efficiency of intra-shop power supply systems of enterprises with 10/0.4 kV transformer substations. The study analyzes the reliability indicators for intra-shop power supply circuits with different types of redundancy: without redundancy; with redundancy at low voltage (LV); with redundancy at medium voltage (MV), without redundancy at LV; and with double redundancy. The reliability parameters of the system are studied, namely the failure rate parameter and the mean time between failures of the circuit when the number of distribution transformers (Ndtr) changes from 1 to 5, with different rated capacities of 10/0.4 kV shop transformers (from 25 to 2,500 kVA), as well as when the load power and the area of the enterprise change. The obtained results show that the mean time between failures T for the circuit without redundancy is 2.03 and 2.04 times less compared to the circuit with redundancy on the MV and LV, respectively, and 2.09 times less for the circuit with double redundancy. The conducted studies show that it is rational to use the minimum number of distribution transformers Ntr, equal to 1 (in the absence of redundancy) or 2, since at Ndtr = 3–5 the mean time between failures T is minimal and equal to 0.97 years. The research has established that the maximum mean time between failures, equal to 6.01 years, is obtained for the circuit with double redundancy, and the minimum, equal to 0.97 years, is obtained in the absence of redundant elements in the circuit with 5 transformers. The discounted payback period of equipment for 4 scheme options has been calculated and it has been found that the shortest payback period (for a scheme without redundancy) is 7.75 years taking into account inflation equal to 8.6 % per year.

(in Russian, стр.19, fig. 9, tables. 4, ref 18, AdobePDF, AdobePDF 0 Kb)