Doctor of Science Yu. V. Khrushchev, Candidate of Science N. L. Batseva , postgraduate student L. V. Abramochkina

National Research Tomsk Polytechnic University, Russia

The method of identifying of overhead power line attenuation parameters in prefault conditions

Abstract

This report provides the idea of identifying of overhead power line parameters on base of current and voltage instantaneous values registered by Emergency Signal Recorders in prefault conditions.

Keywords: Overhead power lines, power network, identification of fault location, line attenuation parameters, Emergency Signal Recorders, current and voltage instantaneous values.

I. Introduction.

Overhead power lines are very often damaged elements of power network. Overhead power line faults lead to power supply interruption and electrical energy quality degradation. Therefore one of the most important functions of operational staff is fast fault location identification. As for today a lot of different methods and techniques of fault location identification [1 − 3] have been developed but all of them steel allow to define point of fault incorrectly.

One of the reasons for error appearance concludes using of line attenuation parameters specifically: r₀, x₀ – active and reactive resistances, [Ohm/km]; g₀, b₀ – active and reactive conductivities, [1/Ohm∙km]. In result of using attenuation parameters in calculations consequences of lines operation are not taken into account for example environment influence, thermal affects, ground conductivity. Hence increasing of accuracy of fault location identification can be achieved by means of real line parameters during determination of fault point on overhead power lines.

II. Theoretical analysis.

For the moment the Emergency Signal Recorders are widely used in power networks. These units allow to measure and record current and voltage instantaneous values, which include adequate information about physical phenomenon in network.

Therefore in this report the idea of identifying line parameters on base of current (i₁(t_j), i₂(t_j)) and voltage (u₁(t_j), u₂(t_j)) instantaneous values registered by Emergency Signal Recorders in prefault conditions is considered.

Figure 1 illustrates symmetrical four-pole equivalent circuit of overhead line to describe the idea.

Figure 1 − Symmetrical four-pole equivalent circuit of overhead line

Passive four-pole is specified with generalized coefficients A, B, C, D which can be defined via line parameters [2]:

; ; ,

(1)

where − natural impedance of line; − propagation constant of electromagnetic mode in line; l – line length.

Relations between natural parameters, generalized coefficients A, B, C and line parameters can be got from equation (1) as:

; ;	(2)
; .	(3)

III. Design procedure.

Fundamental equations of four-pole wrote down respectively to the beginning and the end of a line [4]:

,

(4)

where I₁, I₂ - vector current value, U₁, U₂ - vector voltages value at the beginning and the end of a line correspondingly.

Formulas for the determination of generalized coefficients A, B, C can be got from the system of equations (4) under:

; ;

(5)

Current and voltage vectors used in expressions (5) can be defined on the base of current (i₁(t_j), i₂(t_j)) and voltage (u₁(t_j), u₂(t_j)) instantaneous values registered by Emergency Signal Recorders in prefault conditions at the beginning and the end of a line with using the generalized vectors [5]:

; ; ,

(6)

where h₁(t_j), H₁, - instantaneous and absolute values of voltage or current correspondingly; - massif scale numbering, - signal cycle, – discretization interval.

Summing up the proposed method of identifying line parameters includes following steps:

1) The respective vector values of currents and voltages are identified by means of equations (6) on the base of current (i₁(t_j), i₂(t_j)) and voltage (u₁(t_j), u₂(t_j)) instantaneous values registered by Emergency Signal Recorders in prefault conditions;

2) Generalized coefficients of two-port A, B, C are determined by formulas (5);

3) Natural parameters of a line are calculated by equations (2);

4) Line parameters are evaluated by means of relations (3).

IV. Calculation example.

Described method of line parameters definition was approbated by the example of 500 kV single-circuit multiple-conductor overhead line, 600 km length. This line transmits power to the load S = 600+j250 MVA. Reference dates of line parameters are presented in the Table 1.

Table 1 - Reference dates of line parameters

L, km	r0, Ohm/km	x0, Ohm/km	b0, 10^-^9 1/Ohm∙km	g0, 10^-^6 1/Ohm∙km
600	0,022	0,301	7,333	3,694

Firstly there were calculated currents and voltages in the beginning and the end of line by discretization interval =0,1 ms. Then there were identified line parameters according to the method described above. Calculation results are presented in the Table 2.

Table 2 − Calculation results

A	0,807+j0,014
B, Ohm	11,295+j168,747
C, 1/ Ohm	-6,394·10^-^6+j2,072·10^-^3
D	0,807+j0,014
Zv, Ohm	285,544-j9,987
	3,9·10^-^5+j1,055·10^-^3
r0, Ohm /km	0,022
x0, Ohm /km	0,301
b0, 10^-^9 1/Ohm∙km	7,333
g0, 10^-^6 1/Ohm∙km	3,694

It can be seen that defined line parameters correspond to their reference dates (Tables 1 and 2) and described method of defining line parameters is very correct.

V. Conclusion

1. Presented method is applicable to stretched lines, as it takes into account dispersion of line parameters by means of using fundamental equations for a long-distance line;

2. The method allows to identify real line parameters which can be used in fault location identification algorithms decreased their errors;

3. The method demonstrates high accuracy at defining of line parameters.

References

1. Mustafa Kizilcay, Piergiovanni La Seta, Daniele Menniti, Michael Igel. A New Fault Location Approach For Overhead HV Lines With Line Equations // Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference. June 23^th–26^th. Bologna. Italy.

2. The research center «Bresler» [An electronic resource]: Cheboksary, 2008-2011. URL: http://www.ic-bresler.ru/.

3. Kulibin incorporated center of development of the Russian innovations [the electronic resource]: working out modular high-precision reflectometer for cable and overhead 2009. URL: http:// ru.domain1fc6c2.kulibin.org/.

4. Ryzhov Yu. Long-distance ultra high voltage power transmission. – Moscow: MPEI publishing house, 2007. – 488 p.

5. Method of calculation of phase shift between two harmonical signals: pat. 2242014 Russia. ¹ 2003138149; decl. 31.03.03; publ. 10.12.04; bull. ¹ 30.- 17 p.