RU2558266C1 - Method of finding of distance to places of earth faults on two power lines in networks with low earth fault currents - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method consists in measurement of active and reactive components of zero sequence current and phase voltage of damaged lines in emergency mode and subsequent calculation of inductive resistance to each place of earth fault proportional to the distance to places of damages.

EFFECT: improvement of accuracy of finding of distance to places of double earth faults on power lines.

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Description

The invention relates to the electric power industry and can be used to determine the places of damage during earth faults on two different power lines of a distribution network with low earth fault currents.

The article "Determining the distance to places of double earth faults in electric networks of 35 kV" (Glovatsky V.G., Khalidov A.G. - Energetik, 1985, No. 9, p. 31) describes the results of tests of the fixing resistance organs performing measurements resistance of the damage circuit with double earth faults on different lines of the 35 kV network. It is noted that a double fault on the ground of different lines by the measuring body is perceived as a single-phase damage, and the fixing resistance organs themselves can be used to determine the distance of not only interphase, but also double faults to the ground.

The disadvantage of this method is that in this method, a double circuit to ground of different lines by the measuring body is perceived as a single-phase damage, and the measuring resistance element is connected to the current and voltage measuring transformers installed on the supply input of the substation switchgear, which complicates the determination of damaged outgoing lines.

There is a method of determining the distance to places of earth faults (E.P. Vanzovich, A.-S.S. Saukhatas, V.G. Golovatsky, copyright certificate No. 1569752, 06/07/90), adopted as a prototype, in which the isolation and measurement of the active and reactive component of the voltage and current of the direct sequences of the intact phase in the pre-emergency and emergency modes, followed by the determination of the active and reactive component of the pre-emergency load resistance of the direct sequence and taking into account the obtained values when calculating the resistance short circuits to each circuit.

The disadvantage of this method is that the measuring resistance element is installed on the supply input of the switchgear and is switched on to phase currents and phase voltages. In addition, in this method, a damaged outgoing line is not detected.

The objective of the invention is to increase the accuracy of determining the distance to the places of damage during earth faults of one phase on two different power lines by installing a measuring resistance element connected to triple the zero sequence current and phase voltage of the lines extending from the substation switchgear. In addition, the task is to identify damaged outgoing lines.

This technical result is achieved by the fact that in the method for determining the distance to places of earth faults on two power lines in networks with low earth fault currents, a zero-sequence current and phase voltage are measured using a resistance measuring organ, according to the invention, the resistance measuring organ is turned on for currents zero sequence and phase voltage of damaged lines extending from one substation bus, determine the occurrence of single-phase earth faults th one phase on two lines from the appearance of a zero sequence current filter outputs zero sequence currents 3I ₀₁ on the first line and 3I ₀₂ on the second line, the absolute value of the inductive reactance X is _Q-1 and X _p2 circuits damaged different phases F1 and F2 by the following expressions:

and calculate the distance to the place of damage l _1k on the first line and the distance to the place of damage l _2k on the second line according to the formulas:

where Re (3I _{01 (2)} ), Im (3I _{01 (2)} ), Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ) are the real and imaginary components of the zero sequence current and phase voltage of the damaged lines, X _0lud , X _1lud - specific inductive resistances of direct and zero sequence power lines.

The main difference of the proposed method is the control of the resistance of the damage loop on each line, which increases the selective effect of protection when this type of damage occurs. The measuring resistance element is connected to the zero-sequence current filter of the outgoing line and to the phase voltage from the voltage transformer on the buses of the switchgear.

- ЭДС питающей системы;

(9, 10, 11) - эквивалентные сопротивления прямой последовательности системы фаз A (9), B (10) и C (11); измерительный трансформатор напряжения TV (12); измерительные трансформаторы тока отходящих линий: фазы A ТA1 (13), ТA2 (14), фазы В ТA3 (15), ТA4 (16), фазы C ТA5 (17), ТA6 (18); измерительный орган сопротивления ОС отходящих линий (19, 20);

(21)

(22) - сопротивления прямой и нулевой последовательности до места повреждения первой отходящей линии;

(23),

(24) - сопротивления прямой и нулевой последовательности до места повреждения второй отходящей линии;

- сопротивление соответствующих фаз A (25), B (26), C (27, 28) отходящих линий; R_п1 (29), R_п2 (30) - переходные сопротивления в месте замыканий; R_З (31) - сопротивление земли.The proposed technical solution is illustrated by two drawings, which show a single-line network diagram (Fig. 1), consisting of a system (1), outgoing power lines (2, 3) with phase short circuits at different distances from the substation l _1k (4), l _2k (5), and the network equivalent circuit in the double-circuit mode of the phases A and B on different parts of the network (Fig. 2), where

- EMF supply system;

(9, 10, 11) - equivalent resistance of the direct sequence of the system of phases A (9), B (10) and C (11); voltage measuring transformer TV (12); measuring current transformers of the outgoing lines: phases A ТА1 (13), ТА2 (14), phases В ТА3 (15), ТА4 (16), phases C ТА5 (17), ТА6 (18); measuring organ of OS resistance of outgoing lines (19, 20);

(21)

(22) - resistance of the direct and zero sequence to the point of damage of the first outgoing line;

(23)

(24) - resistance of the direct and zero sequence to the point of damage of the second outgoing line;

- resistance of the corresponding phases A (25), B (26), C (27, 28) outgoing lines; R _p1 (29), R _p2 (30) - transition resistance in the circuit; R _З (31) - resistance of the earth.

The occurrence of zero sequence currents 3I ₀₁ and 3I ₀₂ at the output of a zero sequence current filter determines the occurrence of single-phase earth faults on two lines, on different phases.

определяется какEarth Fault Current $${\dot{I}}_{d\mathrm{at}}$$

defined as

Where

The general formula for calculating the earth fault current is as follows:

Where

The stresses of the damaged phases at the installation site of the measuring resistance element (on the substation tires) are determined by the expressions

With known values of current and voltage in emergency mode, the resistance measuring body (OS) to determine the distance to the places of damage should be set up in this way:

и току нулевой последовательности

поврежденной линии, зависит также и от активного переходного сопротивления в местах повреждений и активного сопротивления земли. Поэтому влияние дополнительных активных сопротивлений можно исключить путем выделения индуктивной составляющей сопротивления Х_ф1 и Х_ф2:As you can see, the resistance at the terminals of the relay connected to the phase voltage

and zero sequence current

damaged line, also depends on the active transition resistance in places of damage and the active resistance of the earth. Therefore, the influence of additional active resistances can be eliminated by isolating the inductive component of the resistance X _f1 and X _f2 :

where Re (3I _{01 (2)} ), Im (3I _{01 (2)} ), Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ) are the real and imaginary components of the zero sequence and phase voltage of the damaged lines.

Using the calculated inductive resistances of the damaged phases X _{f1 (2)} , the distances to two places of damage l _1k and l _{2k are} determined by the following formulas:

where X _0lud , X _1lud - specific inductive resistances of direct and zero sequence of damaged power lines.

The use of zero sequence currents 3I ₀ reduces the influence of the load current on the accuracy of determining the distance to two fault points l _1k and l _2k , since in networks with small earth fault currents (for example: medium voltage networks with isolated neutral), the zero sequence current 3I ₀ does not occur (small) in normal mode, with any non-symmetry in the network load.

The practical implementation of the proposed measuring body of resistance is possible on the basis of modern microprocessor-based distance protection systems. The measuring resistance element included in the zero-sequence current and phase voltage corresponds to the requirement of proportionality of the resistance at the terminals of the measuring resistance element to the distance to the place of damage in the double earth fault mode in the distribution network with low earth fault currents.

Thus, the proposed method allows with high accuracy to determine the distance to the places of damage during earth faults on two different power lines by installing a measuring resistance element connected to the zero sequence current and phase voltage of the damaged lines.

Claims (1)

A method for determining the distance to places of earth faults on two power lines in networks with low earth fault currents, which consists in measuring the zero sequence current and phase voltage using a resistance measuring organ, characterized in that the resistance measuring organ includes zero sequence and phase currents voltage of damaged lines extending from one substation bus, determine the occurrence of single-phase earth faults of one phase on two lines on the appearance of the output x zero-sequence current filters of zero-sequence currents 3I ₀₁ on the first line and 3I ₀₂ on the second line, calculate the absolute values of the inductive resistance X _f1 and X _f2 of the damaged circuits of different phases f1 and f2 according to the following expressions:

and calculate the distance to the place of damage l _1k on the first line and the distance to the place of damage l _2k on the second line according to the formulas:

where Re (3I _{01 (2)} ), Im (3I _{01 (2)} ), Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ) are the real and imaginary components of the zero sequence current and phase voltage of the damaged lines, X _0lud , X _1lud - specific inductive resistances of direct and zero sequence power lines.

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