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ANALYSIS ECONOMIC LOAD INTERVALS FOR SELECTION OF CORE SECTIONS
POWER LINE Taslimov A.D.1, Rakhimov F.M.2
1Taslimov Abdurakhim Dekhkanovich - Doctor of Technical Sciences, Professor, Department of Power Supply, TASHKENT STATE TECHNICAL UNIVERSITY NAMED I. KARMOV, TASHKENT;
2Rakhimov Farrukh Movlidinovich - Doctor of Philosophy, Associate Professor, Department of Power Engineering, NAVOI STATE MINING AND TECHNOLOGICAL UNIVERSITY, NAVOI, REPUBLIC OF UZBEKISTAN
Abstract: this article discusses the development of the electric power industry, conducting large-scale activities to use a modern approach to choosing the main parameters of energy systems, including special attention is paid to the development of methods for optimal construction, updating and improving the reliability of rural electrical networks, determining the optimal parameters of electrical networks and increasing their reliability. In addition, it is important to carry out theoretical and scientific work and obtain appropriate recommendations for their implementation in the design, construction, modernization and operation of rural electrical networks. Keywords: economic interval, operation, billing period, shift factor, long-term allowable current, allowable voltage loss.
ИСПОЛЬЗОВАНИЕ ЭКОНОМИЧЕСКИХ ИНТЕРВАЛОВ НАГРУЗКИ ДЛЯ
ВЫБОРА СЕЧЕНИЙ КАБЕЛЬНЫХ ЛИНИЙ
12 Таслимов А.Д. , Рахимов Ф.М.
1Таслимов Абдурахим Дехканович - доктор технических наук, профессор, кафедра электроснабжения, Ташкентский государственный технический университет им. И. Каримова, г. Ташкент;
2Рахимов ФаррухМовлидинович - доктор философии по техническим наукам, доцент,
кафедра электроэнергетики, Навоийский государственный горно-технологический университет, г. Навои, Республика Узбекистан
Аннотация: в данной статье рассматривается вопрос развития сельских электрических сетей с использованием современного подхода к выбору основных параметров электрических сетей, особое внимание уделяется разработкам методов оптимального построения, обновления и повышения надежности сельских электрических сетей, а также определения оптимальных параметров электросетей. Приводятся научные результаты теоретического и научного исследования и соответствующие рекомендации по их внедрению при проектировании, сооружении, модернизации и эксплуатации сельских электрических сетей.
Ключевые слова: экономический интервал, эксплуатация, расчётный период, коэффициент сдвига, длительный допустимый ток, допустимая потеря напряжения.
The problem of choosing the optimal cross-sections of the conductors of power lines has always been and is being given great attention now. The method of economic intervals has received recognition and the greatest application for solving this problem. The development of the theoretical aspects of this method was reflected in the works of such scientists as academician Budzko I.A., Venikov V.A., Levin M.S., Kholmsky V.G., Blok V.N. and a number of other researchers [1, 2, 3, 4, 5, 6, 7, 8,]. Further research developed and improved this method, both in terms of its theoretical justifications and in terms of practical application. In [9], the necessary and sufficient conditions for the existence of economic load intervals for wires and cables are shown. If initially the economic load intervals were determined for static loads, then later, when determining them, they began to take into account the dynamics of load growth [10], and such a possible reconstruction of power lines.
However, it should be noted that, in general, the economic load intervals were calculated and widely used to select the wires of overhead power lines. To select the cross sections of cable conductors of cable power lines, the economic current density is widely used to date, which does not meet the condition of minimum reduced costs. In this regard, it became necessary to determine the economic load intervals for the selection of cross-sections of cable cores and related tasks in this work.
The boundaries of economic load intervals are determined from the condition [10]:
Zi = Zi+i (1)
where Zi- reduced costs for a cable line with a cross section of cable cores Fi; Zi+1 - the same, with the cross section of the cable cores Fi+1;
With regard to the definition of economic load intervals, the reduced costs for cable transmission lines can be determined as follows.
When constructing cable power lines with a voltage of 10 kV, capital investments are made within one year. Since the reconstruction of a cable line in order to increase its capacity is difficult and impractical during its service life, no new investments are made in it. Taking into account these features of cable lines, the given capital investments are as follows
£n £ [= i Kt ( 1 + c) T _ 1 = ^ (2)
where - normative coefficient of efficiency of capital investments; capital investment in year , -coefficient of normalization of costs at different times; t - cost reduction year.
At the same time, we assume that the costs are given to the first year of operation, those. t=1.
Since depreciation charges remain constant due to the invariance of capital investments, we can write
£L i (U,1 - U,( t_ i ) ) ( 1 + £nc) 1 " * = i/a 1 = Pd^ (3)
where , - costs to cover electricity losses in the line in the year and , respectively; -
depreciation rate.
Operating costs in accordance with do not depend on the cross section of the cable cores and do not change over time. Therefore, when determining the economic load intervals, they can be ignored.
Taking into account the above, as well as expressions (2) and (3), the expression for determining the reduced costs for a power line can be written as
Z = (£n + Pd)№ + £ L2 (St2 - St2_ i) (1 + £nc) 1 _ *] (4)
unyt
U, - costs to cover electricity losses in the line in the year; Un - rated voltage, kV; y - conductivity of conductive material, km/Om-mm2; F - conductor cross section, mm2; St - load, kVA;
An analysis of the technical and economic indicators of cable transmission lines in rural areas showed that, in accordance with the conditions for the existence of economic intervals [6], all standard sections of cable cores have economic load intervals.
If the load during the entire period under consideration is constant and does not change over time, i.e.
St = St_1 = s
then and in expression (1) in accordance with (4) will take the form
z = (i?n + Pd) (5)
unYtl
Z+i = (in + Pd) (6)
unYtl+1
Equating expressions (5) and (6) in accordance with condition (1) and solving the resulting equation for the load, we obtain an expression for determining the boundaries of economic intervals for adjacent sections for the case that does not take into account the dynamics of load growth
s _ l(En+pdXKi+1-Ki)ugrFi+1F
b V ^ ( )
It can be seen from expression (7) that the sectors that determine the boundaries of economic load intervals can be divided into two groups: fixed and variable. The first ones include specific conductivity and standard sections and Fj+^The group of constant factors can also conditionally include the standard efficiency coefficient in, the depreciation rate and the voltage .
The value of the standard coefficient of efficiency of capital investments is determined in accordance with [10] and is equal to 0,12. The analysis showed that in can fluctuate slightly within the range from 0,08 to 0,15. However, at present there are no trends indicating the possibility of reducing the value of . At the same time, for new technology it is recommended to take in=0,15. Therefore, it is advisable to consider the change in in within 0,12^0,15. Qualitative analysis shows that an increase in in leads to a shift in the boundaries of economic intervals towards an increase. The value of the rate of depreciation is determined according to [10] and for cable power lines with cables with aluminum sheath, laid in the ground, is 4.3%. It is related to the service life of the cable and the possibility of changing it is limited. With an increase in the service life to 30 years, the value of p d will decrease to 3.36%. It is possible to increase pd due to an increase in the cost of overhaul. However, this increase is insignificant. The voltage for the considered class of lines to determine the losses of electricity is taken equal to the nominal voltage and its changes are not taken into account. The conductivity of a conductive material is also constant for a given material. Strictly fixed are also standard cross-sections of cable cores. Of the second group of factors, capital investments in the construction of cable transmission lines can vary within a fairly wide range. Their value depends on the brand of the cable, the cross section of the cores, the laying method, the soil group, and so on [11-14].
From the point of view of a qualitative assessment of the impact of changes in the value of capital investments on the boundaries of economic intervals, on the basis of expression (7), it can be shown that it significantly affects the value of . Therefore, a careful quantitative assessment of this effect is necessary.
From (2.4), it is obvious that the boundaries of economic load intervals are significantly affected by taking into account the dynamics of load changes over time. For a quantitative study of this effect, it is advisable to consider the load growth according to various laws: exponential, linear and modified exponential load growth.
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