MONITORING QUALITY OF ELECTRIC POWER AT DISTRIBUTION NETWORKS

Ilkhombek Khosiljonovich Kholiddinov

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

MONITORING QUALITY OF ELECTRIC POWER AT DISTRIBUTION

NETWORKS

Ilkhombek Khosiljonovich Kholiddinov

Fergana Polytechnic Institute, Power engineering Department

i.xoliddinov@ferpi.uz

ABSTRACT

The paper reports quality analysis and evaluation at 0.4 kV low-voltage distribution grids in Uzbekistan. Power quality frequently does not correspond to the rated value which is largely due to unbalanced phase loading in grids and which also results in increased power loss. The study of the asymmetrical operating modes of the rural distribution networks of 0.4 kV was conducted in three steps: measurement, calculations and analysis of relevant data; providing practical guidelines and finally, implementing instruments to normalize grid operation. Measuring was conducted using certified instrumentation analyzer «Malika» designed by authors. The study and analysis of additional power losses as the function of indicators of asymmetrical features of voltage and current in operating 0.4kV grids revealed that, quality of electric power at grids under investigation merely does not meet the requirements of the Interstate Standard.

Keywords: electric power quality indicators, power grids, power losses, voltage unbalance, Malika-01 analyzer.

INTRODUCTION

The power sector of the Republic of Uzbekistan as one of the key economic sectors has been developing quite intensively since the country gained its independence and meets the country's electric power needs. Moreover, the country has become an exporter of electric power by large.

Electric power efficiency is generally defined by such a condition of its consumption that ensures the availability of required quality of electrical energy while minimum production losses will have been inherent to the process [1].

As any other product, electric power requires mandatory certification and is characterized by certain features such as uninterrupted and simultaneous processes of its production and consumption. Electric power transfer is carried out by consuming certain portion of the product itself which means the loss of power might be unavoidable.

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

Among a variety of the existing evaluation criteria of electric power quality there are indices characterizing asymmetrical property of three-phase system of voltage. Two indices of quality such as the voltage unbalance coefficient on reverse-sequence and the voltage unbalance coefficient on zero- sequence (the rated values of coefficients are regulated by GOST 32144-2013 standards) serve as the criteria of assessment of voltage unbalance [2]. Besides, symmetrical components of reverse- and zero-sequence currents, running through elements of an electrical grid, create substantial additional active losses in the electrical grid itself.

METHODOLOGY

Phase currents- and voltage- unbalances stemming from prevalence of singlephase household appliances turns out to be the main factor having impact on electric power quality and loss in the course of its transfer [transmission] from a production site to consumers. Among the most widely used techniques of calculation of losses of power and energy in electrical grids one could mention the technique of calculation at unbalanced loading which is based on the method of symmetrical components. The 0,4 kV line with single-phase consumers of various power consumption rate (Fig. 1), who are evenly distributed across phases, can be considered otherwise as the line with several distributed symmetrical three-phase receivers formed by three groups of singlephase ones of various power consumption rate, the zero-point of which being connected to neutral wire [3].

Fig. 1. The line with single-phase consumers of various power consumption rate

evenly distributed across phases

Any asymmetrical three-phase receiver can be replaced by an equivalent symmetrical one and two single-phase consumers connected to phase voltage. Equality of voltage and currents at receiver clips and equality of complexes of pulsing power output serve as a condition of equivalence of this replacement.

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

For asymmetrical three-phase system at receiver clips there are following equations

[3]:

IA — UAYma, IR - UrYi

IA — UAYNA, IB — uBYNB, IC — Ù.CYNC

Ir — ùrY*

(1)

where: Ua, Ub, Uc are phase voltages; YnA, YnB, Ync - conductivity of phase wires. On the basis of the technique of symmetrical components the system of voltage can be presented by three equations [4, 5, 6]:

Ua = Um sin (wt + ^0); UB = Um sin (wt + 120°); (2)

UC = Um sin (wt + ^0-240°).^ where: yo - initial phase of voltage UA.

Proceeding from the method of symmetrical components, any asymmetrical three-phase system can be divided into three symmetrical components: direct-, reverse-and zero-sequence that can be represented by three vector systems:

Ua(i) — 1 (Ùa + a • Ùb + a2 • Ùc);

Ù

A(0)

— 1(ÙA + ÙB + ÙC)

(3)

where: a — ej120° — ej-240° a2 — ej240° — ej-120°

Similar expressions can be written for asymmetrical system of currents as well:

IA(1) — 1 (IA + a • IB

+ a2

IA(2)

I

A(0)

+ a2 • IB + a

— 1(IA + IB + IC).

• IC); Ic);

(4)

Evaluation of asymmetrical values of currents or voltage in three-phase grids is made by means of currents- or voltage-unbalance. Meanwhile, voltage- and currents-unbalance coefficients (the coefficient of unbalance k2, in general) are presented by following equations:

k2u=U^100 % , k2i=-^100 %. (5)

Ui Ii

where I2, U2 are operating values of current and voltage of reverse sequence and Ii, Ui are operating values of current and voltage of direct sequence of basic frequency of three-phase system of currents or voltage.

Loss of power is characterized by the following factor:

Kp —

APn — 1 + K2i + K2iR0 ;

AP

(6)

}

1

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

where: PN, P1 - losses of power at asymmetric load and caused by currents of direct sequence; K2i=I2/I1, K0i=I0/I1 - coefficients of reverse and zero sequences of currents, respectively; Ro, Ri - active resistances of zero and direct sequences for grid section, respectively; Ii, I2, Io - currents of direct, reverse and zero sequences at the same section of grid.

Relative values of phase losses of voltage at certain section of grid are defined as follows:

SA=^=1 + K2i + KorKz; "

AU1 AUe AU1

ÔB=T^ = a2+a^K2i + Koi^Kz;

AUr o

-c = = a + a2 • K2i + Koi • Kz}

(7)

where: AUa> AUb, AUc - complexes of phase losses of voltage at grid section; AUX -complex of phase loss of voltage of direct sequence at grid section; K2i, K0i - complex coefficients of reverse and zero sequences of currents; Ii, I2, Io - complexes of currents

Y—^

of direct, reverse and zero sequences; a = eK 3 ' - complex multiplier of turn of vector for 120°.

ANALYSIS AND RESULTS

Researchers in the "Power Plants, Grids and Systems" Department of the Tashkent State Technical University developed the multi-purpose analyzer "Malika" [7]. The instrumentation is designed for conducting measurements of indicators of quality of electric power (IQEP) in electrical grids of220 - 380V. The analyzer proved irreplaceable for carrying out monitoring and evaluation of electrical power quality by using statistical methods, including at limited product indicators according to the relevant requirements of the GOST standards.

The general view of the analyzer is presented on the Fig. 2. The results of measurements provide us with parameters necessary for analysis of electric power quality:

- Grid frequency f (in Hz), with discretization of 10 seconds;

- Operating values of voltage U (in V) and current I (in A) across each of 3-phase grid with discretization of 10 minutes;

- Active P (in kW) and reactive Q (in kVar) power outputs of a first harmonic across each of 3-phase grid with discretization of 10 minutes;

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

- Power coefficient cos 9 = arctg (Q / P) (angles between vectors of currents and voltage) of a first harmonic across each of 3-phase grid with discretization of 10 minutes;

- Amplitudes of direct sequence of U1 (V) and currents I1 (A) on each of 3-phase grid with discretization of 10 minutes;

- Coefficient of unbalance of voltage of reverse K2U (%) sequence with discretization of 10 minutes;

- Coefficient of unbalance of voltage of zero K0U (%) sequence with discretization of 10 minutes;

- Coefficient of unbalance of current of reverse K2I (%) sequence with discretization of 10 minutes;

- Coefficient of unbalance of current of zero K0I (%) sequence with discretization of 10 minutes.

The analyzer is delivered as a stand-alone unit in plastic casing designed for mechanical and electrical protection both for the analyzer and the personnel who might be operating it. The analyzer is equipped with 3 current-measuring pincers for hookup to current channels in case of its using as a mobile analyzer (Fig. 2) [6]. The built-in non-volatile memory provides for storage of data and stores the results of measurements obtained for last 10 days. The face section of the analyzer is equipped with four plugs of voltage and six fixed current inputs. The opposite face section of the analyzer is equipped with the output channel, i.e. the SD/MMC card reader.

Fig.2. General View of the «Malika» analyzer

The methods of quality indices measurement of electric power in electrical grids in systems of power supply of alternating three-phase and single-phase currents with a

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

frequency of 50 Hz are established by interstate GOST 32144-2013 standards "Electrical energy. Electromagnetic compatibility of technical means. The methods of measurements of quality indicators of electrical energy" [2].

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Results of measurements at the third feeder of this transformer sub-station are presented hereunder. The feeder supplies electricity to more than 50 households [8].

Fig. 3. The voltage curve, the basic Fig. 4. The currents curve, the basic frequency considered frequency considered

Fig. 5. The curve of the angle between voltage and current (cos 9)

Fig. 6. The diagram of change of harmonic of current, the basic frequency considered

Fig.7. The curve of change of the coefficient of non-sinusoidal property of current, the basic frequency considered

Fig. 8. The curve of change of the coefficient of unbalance of current of reverse sequence %

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

-KM«*;,,

Kiwi.. 21-1«-:,.

ILTH

Ш

&Л 11=10 ЗГ.« 11:» ¡7.« IfcSD 37.« I»;» 17.« îlilO НЛ 35.« И ЗО И.« » W îfr « 07-,W ÎS-W

1-a KûfcutTent %

Fig. 9. The curve of change of the coefficient of unbalance of current of zero

sequence %

DISCUSSION

The results of measurements of power quality given on the Fig. 3-9, reveal that quality:

• against the established deviation voltage - doesn't meet the requirements of GOST standards;

• against frequency deviation - meets the requirements of GOST standards;

• against the coefficient of distortion of sinusoidal feature of voltage - doesn't meet the GOST standards;

• against the coefficient of n- harmonic component of voltage - does not meet the GOST standards;

• against the coefficient of unbalance of voltages on reverse sequence - does not meet the GOST standards;

• against the coefficient of unbalance of voltages on zero sequence - does not meet the GOST standards.

Unbalance of voltage at about 2% leads to 4% decrease in service life of transformers, whereas the unbalance coefficient on current at about 10% and more, leads to the decrease of service life of isolation of transformers by 16%. Besides, voltage unbalance may lead to lower reliability of operation of household appliances

[9].

CONCLUSION

The analysis (Fig. 8 and 9) has shown that this feeder is characterized by the coefficient of unbalance of current on reverse sequence of K2i = 30,3%, whereas the

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

coefficient of unbalance of current on zero sequence turns out to be K0i = 33,5%. Obviously, there is a systematic unbalance on this feeder. Therefore, there is a possibility to lower coefficients of reverse and zero sequences of current down to 15% by merely aligning loads across phases during the evening peak hours. This, in turn, will lead to the decrease in additional losses by more than 30% [8].

Therefore, unbalance of currents and voltages at 0.4 kV grids can be eliminated by ensuring certain arrangements namely by: replacing transformers with the scheme of connection of Y/YN and Y/ZN, redistributing loads of single-phase consumers, etc.

In order to eliminate the existing unbalance of currents and voltages at 0.4 kV grids, it is also necessary to ensure availability of balancing devices.

As the precondition of effective management of power quality, one might anticipate means to use the above analyzer designed to carry out measurement periodically (in summer and winter) and on continuous basis.

REFERENCES

1. Allayev of K.R. Electrical power sector of Uzbekistan and the world. - Tashkent: Moliya.-2010. - 256 pages.

2. GOST 32144-2013 Normy kachestva elektricheskoi energii v sistemakh elektrosnabzheniya obshchego naznacheniya/ Mezhdos.sovet po standartizasii, metrolog. I sertifik. - M.: Standartinform, 2014. -16 s.

3. Bessonov L. A. Theory of electrical engineering - M.: Gardariki, 2007. - 685 pages.

4. K.F. Wagner, R. D. Evans, the Method of symmetrical components applied to the analysis of asymmetric electrical chains with K.L. Fortescue's introduction. Translated from English by L.E. M. E. Syrkinykh, edited by D. A. Gorodsky. Publishing House "Power and energy literature", Leningrad 1936 Moscow. - 48s.

5. Kosoukhov, F. D., Naumov I.V. Calculation of voltage and capacity drop in rural distribution grids at current unbalance. -Irkutsk, 2003. -260 pgs.

6. Kholiddinov I., Tuychiev Z., Eraliev Kh. and Kholiddinova M. Influence Of Asymmetrical Modes On The Value Of Additional Power Losses In Low-Voltage Electrical Networks. Vol:54 Issue:10:2021 DOI 10.17605/OSF.IO/S

7. Allayev K.R., Kholiddinov I.Kh., Shaismatov S. A., Patent of the Republic of Uzbekistan for useful model, No. FAP 01166 Analyzer for registration of additional losses of electric power at asymmetry of loadings in low-voltage electric grids//Agency on intellectual property of the Republic of Uzbekistan.

Central Asian Research Journal For Interdisciplinary Studies (CARJIS)

DOI: 10.24412/2181-2454-2022-3-309-317

8. The report on business contract No. 9/15 with JSC "Tashkentskoye TPES", "Development of methods, software and hardware products aimed at ensuring quality of electric power in 0,4 kV distribution grids ", 2015. - 65 pages.

9. Electric power quality management/ I. I. Kartashev, V. N. Tulsky, R. G. Shamonov, etc.; edited by Yu. V. Sharov. - M.: MEI Publishing House, 2006. - 320 pages with illustrations.

MONITORING QUALITY OF ELECTRIC POWER AT DISTRIBUTION NETWORKS Текст научной статьи по специальности «Электротехника, электронная техника, информационные технологии»

Аннотация научной статьи по электротехнике, электронной технике, информационным технологиям, автор научной работы — Ilkhombek Khosiljonovich Kholiddinov

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Текст научной работы на тему «MONITORING QUALITY OF ELECTRIC POWER AT DISTRIBUTION NETWORKS»