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УДК: 621.316.11 ГРНТИ: 44.29
ANALYSIS OF POWER LOSSES IN PHASES IN DISTRIBUTION NETWORKS
AT LOAD IMBALANCE
Allaev Kakhraman Rakhimovich Musinova Gulasalkhon Foziljon kizi
Tashkent State Technical University named after Islam Karimov
АНАЛИЗ ПОТЕРЬ МОЩНОСТИ В ФАЗАХ РАСПРЕДЕЛИТЕЛЬНЫХ СЕТЕЙ ПРИ
НЕБАЛАНСЕ НАГРУЗКИ
Аллаев Кахраман Рахимович Мусинова Гуласалхон Фозилжон кизи
Ташкентский государственный технический университет имени Ислама Каримова
DOI: 10.31618/ESU.2413-9335.2020.1.75.821
ABSTRACT
In this paper is being presented the problem of power quality in low voltage networks. Also is being considered the estimation of additional power losses caused by the asymmetry of the load in phases in distribution networks. The load imbalance in phases leads to a significant irrational increase in power losses in the power system. Therefore, special attention should be paid to the correct phasing of loads, in order to prevent significant imbalance, in order to prevent, among other things, significant excess losses in the systems.
АННОТАЦИЯ
В данной статье представлена проблема качества электроэнергии в сетях низкого напряжения. Также рассматривается оценка дополнительных потерь мощности, вызванных несимметрией нагрузки по фазам в распределительных сетях. Небаланс нагрузки по фазам приводит к значительному нерациональному увеличению потерь мощности в энергосистеме. Поэтому особое внимание следует уделять правильной фазировке нагрузок, чтобы предотвратить значительный небаланс, чтобы предотвратить, среди прочего, значительные избыточные потери в системах.
Key words. Electrical networks, power quality, asymmetry, negative sequence, zero sequence, power losses.
Ключевые слова. Электрические сети, качество электроэнергии, несимметрия, обратная последовательность, нулевая последовательность, потери мощности.
Introduction
The criterion for assessing additional power losses at an asymmetrical load can be the power loss coefficient, which is equal to the ratio of power losses in the asymmetrical mode of operation of the 0.4 kV network to losses due to the flow of positive sequence current (conditionally symmetrical mode of operation of the network)[1,6].
When calculating additional power losses due to the asymmetry of currents, the electrical network is considered as a set of separate elements, each of which is characterized by separate values of currents, and, therefore, the negative and zero sequences components of current. Such network elements include sections of 0.4 kV lines between two branches, transformers of consumer substations, from which several lines depart. In cases where only one line departs from the TC, its head section and the transformer with the connection circuit of the Y, YN windings can belong to the same calculated network element, since the currents of the transformer windings and the head section of the line will be the same. Based on the method of symmetrical components, power losses with an asymmetrical system of currents APa add up to losses caused by currents of the forward, reverse, and zero sequences [2,3]:
APa = 3I? • Rx + 3I22 • R2 + 3I02 • Ro (1)
where, I1, I2, I0 are the symmetrical components of the currents, respectively, of the forward, reverse and
zero sequences, Ri, R2, Ro are the active resistances of the forward, reverse and zero sequences of the network section.
Methods and materials
On the day of calculating the additional power losses in the network element due to the asymmetry of the currents, we define the power loss coefficient as the ratio of power losses in the asymmetrical mode of the network APa to power losses in the symmetrical mode Ps=3Ii2-Ri (in this case, reverse and zero currents sequences are equal to zero, and power losses will be caused only by positive sequence currents [4]:
AP^ „ . I^ R, . In'Ri
PS IlRl IlRl
as well as the
Kp = ^ = 1 + Ip2 + IP (2)
P Ре I?R1 I?R1 V '
Given that I2 = K21 and I0 = K20, I1 I1
equality of the resistance of the negative and forward sequences R1=R2 for transformers and power lines, we obtain
Kp = 1 + K2i + K2! • Kn (3)
where, Kp = - multiplicity of active resistance
Rl
of the zero sequence.
In a particular case, for a three-phase line with a zero wire:
D
R0 = R„ + 3Rn and Kn = 1 + 3 • — , (4)
Rp
where, Rp, Rn are the resistances of the phase and zero wires of the power line, respectively.
Substituting (4) into (3) we obtain the following expression for the power loss coefficient:
Kp = 1 + K|1 + Kg1-Kn-(l+ 3-^) (5)
From the obtained expression (5) it follows that the power loss coefficient for a network element depends on the coefficients of the negative and zero sequences of currents and the ratio of the active resistances of the zero and positive sequences of this element.
Thus, calculation of power losses in the 0.4 kV network at unbalanced load can be performed in the following sequence:
1.The electrical network is divided into separate sections (elements), within which the currents remain unchanged.
2.The parameters for each network element are calculated (including the active resistance of the positive and zero sequences).
3.For these sections of the network, the coefficients of the negative and zero sequences of currents are calculated.
4.Using the formula (5), the power loss coefficients are calculated in the asymmetrical mode.
For three-phase four-wire lines, the coefficient Kp is calculated by the formula (5).
In three-phase three-wire lines (without a neutral wire), the zero current from the sequence is zero, therefore K0=0. In this case, additional power losses will be caused only by the currents of the negative sequence, and expression (3) can be written as follows:
Kp = 1 + K|i (6)
5.The power loss APs is calculated for each network element in the symmetrical mode. The methods for calculating power and energy losses at symmetrical modes are described quite fully in many literature.
6. Based on the calculated values of Kp and APs, power losses are determined in the asymmetrical mode for individual elements of the network q:
APAq — KPq
P
Sq
Power loss in an n-element network
AP — £q=
1 APAq — Hq=
1 KPq '
AR
Sq
(7)
(8)
Zero-sequence currents have a more significant effect on power losses in 0.4 kV networks. So, when the coefficient of the zero sequence of currents decreases from 0.5 to 0 (at K21 = 0.), additional power losses in the 0.4 kV overhead line at Rn=Rp decrease by 2 times, and at Rat = 2Rp - by 2.75 times [3,4,5].
Results and discussing
For experimental research, the transformer point (TP) .№ 399 of the Zangiata district, Tashkent territorial enterprise of electric networks was selected.
Electrical energy is transferred from TP to residential houses, shops, pharmacies and workshops. During the day of receiving test results, PQI measurements were performed on each outgoing five lines.
In accordance with, the weighted average values of the measured values were sampled.
'"Time. iio
Fig. 1. Phase voltage wa\>eforms
0000000
CO CO CO СП CO CO CO
ю ^ n m -Г- см о о
сососососпсососососососососососососососо
1Л -г- СО СО 1Л -Г- СМ О О
^СОС01Л^СОСО!Л СМ О -Г- JCM О Q -lime, hour: nun
n m и m си 1Л
см о о
см о о
со со см о о
Fig. 2. Phase active power waveforms
Fig. 3. Phase reactive power waveforms
Fig. 4. Waveforms of current zero and negative sequences components
In figures 1-4 show seven-day waveforms of changes in the parameters of PQI obtained at the beginning of the low side with a voltage of 0.4 kV, TP № 399. From the presented waveforms, it is seen that the asymmetry parameters of the current do not meet the requirements. For a thorough study, we examined each line separately.
Based on the data of measurements and calculations, we have constructed time diagrams of the changes in these quantities over the studied time periods.
As an example, we consider the results of measurements and calculations for one power transmission line, characterized by the highest level of asymmetry of currents and voltages. The most typical
example is the measurement data taken at the third outgoing power line from TP № 399.
Electricity consumers (EC) receiving power according to power transmission lines are represented by utility bills. The main EC in houses are: electric heaters, electric furnaces, refrigerators, air conditioners, washing machines, irons, lighting installations, television sets, hand-held power tools, etc.
Let us consider how the level of asymmetry of currents and voltages changes, as well as additional losses of electricity on the third outgoing line. The waveforms of phase current and voltage depending on the load of line 3 is shown in Fig. 5 and 6. The average currents at phase "A" were determined - 20.6 A, "B" -8.4, "C" - 11.1 A line 3 during the study period. In this line, phase A received an overload of 30%.
2W.07I j__________4...........s.„_________;___________< .________;__________4-—-—-4...........
27.OB 12]DO 27.08 14:30 27.06 17:30 27.03 20:00 27.03 21:00 26.03 01:30 23.08 0J:30 23.0ft 07:00 28.08 (^:07 day. time
I I phas e A | phase B | phase C
Fig. 5. Change diagram of phase voltages in line 3
J3.243
27.0Ï 11:10 27.08 U:00 27.03 14:10 27.03 1Î:(K> 27,03 21:30 2Я.0А 00:00 28.06 02:30 28.0» 05:00 2Ï.08 07:30 23.08 (№:07 day. time
| phase A I phase B ~ phase C
Fig. 6. Change diagram of phase currents in line 3
if.№ 11:10 ÎÎ-W 14:00 27.0B 16:3027.M 1fc00 Î7.QS 21:30 28-06 0Q;00 ÏB-09 Oî:30 23.W 05:00 2Î-04 07:30 2A-0B 0№
day .time □ miti. % I ave. % I mas. %
Fig. 7. Change diagram of asymmetry voltage coefficient of negative sequence K2U in line 3.
27.08 11:30 27,08 14:00 27,08 lé: 10 27.03 IS:» 27,08 21:30 28,08 OOr» 28,08 02:30 28.08 05:00 28,08 07:10 28.03 09:07 day. ttm=
□ K2
Fig. 8. Change diagram of asymmetry current coefficient of negative sequence K2I in line 3
day. titus
D min,«
ave. %
Fig. 9. Change diagram of asymmetry voltage coefficient of zero sequence K0U in line 3
22231.....
27,08 11:10 27.,08 14;» 27.06 li;J0 27,08 tî:» ¿7.08 2U30 2Î.08 00:00 28,08 02:10 23.08 05:00 28,06 07:30 28,08 09:07
day. tims □ Km. %
Fig. 10. Change diagram of asymmetry current coefficient of zero sequence K0I in line 3
Uneven load distribution is the source of the Power losses in real asymmetrical mode are 1.45
asymmetry coefficient of the currents in the negative times higher than losses due to the flow of only positive
and zero sequences (fig. 8 and 10), the average values current sequence.
of which are K2I - 0.303 Ki - 0.33. As a result of this, Conclusion
the value of the coefficient of additional losses In modern conditions, low-voltage distribution
increases, on average, equal to Kp = 1.45. networks with a voltage of 0.4 kV operate with
significant asymmetry of currents and voltages, due to
the non-linearity and uneven distribution of singlephase loads across the phases of the network and the random nature of their operation. It was revealed that this leads to a significant deterioration in quality indicators and the accompanying additional losses of electricity.
References
1.Allaev K.R., Kholiddinov I.Kh. Analysis of indicators of power quality in distribution networks of 6-10 / 0.4 kV. // Problems of energy and automation. IEA, 2015. -№6. - P. 61-65. (in Russian)
2.Kholidinov I.Kh. Development of a measuring device for determining additional energy losses with asymmetric loads. // The 21st Century - The Age of Intelligent Generation: A Conference of Young Scientists and Students. - Tashkent 2015 .-P. 314-319. (in Russian)
УДК 159. 923 614.885
3.Kholiddinov I.Kh., Ponomarenko O.I. Providing the instrument base of the power quality control system in modern power supply systems.//Universum: Engineering: elect. Scient. Jour. 2016. No8 (29). (in Russian)
4.Kholiddinov I. Kh., Akhmedov N. J., Musinova G.K. Information-measuring system for electric power quality analysis 0.38 kV distribution networks. VI International scientific conference. Theoretical and Applied Sciences in the USA, New York 26 October, 2015. p.31-38. (in English)
5.Allaev K.R., Mirzabaev A.M., Shaismatov S.E., Kholiddinov I.Kh., Makhmudov T.F., Musinova G.F., Kholiddinova M.M. Providing of power quality./T .: Publishing house "Fan va texnologiya", 2019.160 s. (in Russian)
6.www.entp.ru/catalog/pke/13 Official Site PKE-Source UF2M.
ЗНАЧЕНИЕ ПСИХОЛОГИЧЕСКОЙ ПОДГОТОВКИ ПРИ ОКАЗАНИИ ПЕРВОЙ ПОМОЩИ ПОСТРАДАВШИМ В ПРОЦЕССЕ ОБУЧЕНИЯ ВОДИТЕЛЕЙ В АВТОШКОЛАХ
Гафуров Немат Нозирович
кандидат медицинских наук, профессор Института гражданской защиты при Академии МЧС Республики Узбекистан,
г. Ташкент
DOI: 10.31618/ESU.2413-9335.2020.1.75.823
АННОТАЦИЯ
В данной статье рассмотрено значение психологической подготовки водителей при оказании первой помощи пострадавшим в процессе обучения в автошколах. Актуальность данного вопроса обусловлена недостаточным вниманием со стороны исследователей именно к психологической подготовке водителей, хотя теоретическая подготовка водителей по оказанию первой помощи пострадавшим имеет одно из первостепенных значений в процессе обучения в автошколах.
ANNOTATION
This article discusses the importance of psychological training of drivers in providing first aid to victims in the process of training drivers in driving schools. The relevance of this issue is due to insufficient attention from researchers. psychological training of drivers, although the theoretical training of drivers to provide first aid to victims is one of the primary values in the process of training in driving schools.
Ключевые слова: психологическая подготовка, оказание первой помощи, обучение водителей, дорожно-транспортные происшествия.
Keywords: psychological training, first aid, driver training, road accidents.
Введение. За последние десятилетия травмы, полученные в результате дорожно - транспортных происшествий (ДТП), превратились в одну из серьезнейших проблем современной медицины. По данным различных исследователей, травмы при ДТП в среднем составляют 34,5 % от общего количества регистрируемых травм, а процент смертельных случаев в подобной ситуации возрастает до 60%. По данным, предоставленным Всемирной Организацией Здравоохранения, каждый год в ДТП во всем мире погибает около 1,2 млн. человек, и еще около 50 млн. получают травмы различной степени тяжести.
Зачастую травмы при ДТП не являются фатальными. Множество пострадавших погибают из-за осложнений, предотвратить которые возможно было бы на раннем этапе оказания медицинской помощи. При оказании первой помощи пострадавшим в ДТП решающим
фактором является время ее начала. Очевидно, что главную роль в догоспитальном этапе играет служба скорой помощи, и в силу различных причин, прибытие ее на место ДТП в среднем занимает 15-20 минут, а в загородной зоне данный показатель значительно выше. Именно за столь короткий промежуток времени решается судьба значительного числа пострадавших при ДТП. К сожалению, первая помощь от лица участников дорожного движения не всегда оказывается эффективной или же не оказывается вовсе. Причиной тому является недостаточная подготовленность в процессе обучения, как теоретическая, так и психологическая [4].
Роль психологии в процессе обучения водителей. Умение применить своевременно и эффективно знания по оказанию первой медицинской помощи является актуальным не только для кандидата в водители, но и для
