RU2558265C1 - Determination of distance to points of double earth connection at electric power transmission lines in networks with low earth currents - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: proposed method consists in measurement of active and reactive components of phase current and voltage under emergency. Then, inductive reactance is calculated to every earth point proportional to distance to pints of faults.

EFFECT: higher accuracy of determination.

1 dwg

Description

The invention relates to the electric power industry and can be used to determine the places of damage during double earth faults on one power line of a 6-35 kV 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 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 fault on the ground of different lines by the measuring body is perceived as a single-phase damage, and it is not possible to determine the distance to each place of the fault on the ground.

The well-known "Method for determining the distance to the places of earth faults" (EP Vanzovich, A.-S. Saukhatas, VG Golovatsky, copyright certificate No. 1569752, 07.06.90), adopted for the prototype, which produce 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 circuit 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, this method does not determine which point of earth fault is closer to the measuring body, which is further, and without this it is impossible to unambiguously determine the distance to each circuit point.

The objective of the invention is to increase the accuracy of determining the distance to the places of double earth faults on one power line by installing a measuring resistance element connected to the phase current and phase voltage of the damaged line. In addition, the task is to automatically determine the near and far point of a short circuit to ground.

This technical result is achieved by the fact that in the method for determining the distance to places of double earth faults on power lines in networks with low earth fault currents, the phase current and phase voltage are measured using a resistance measuring organ, according to the invention, the resistance measuring organ is connected to phase the currents and phase voltages of the damaged line determine the occurrence of a double earth fault on the same line by the growth of phase currents I _f1 and I _{f2 of the} damaged phases f1 and f2, subtracting Absolute values of the inductive resistance X _f1 and X _{f2 of the} circuits of the damaged phases f1, f2 are expressed according to the following expression:

the damage f1 closest to the measuring body is determined through the minimum absolute value of the inductance of the damaged phase circuit X _f1 <X _f2 and the distances to the nearest damage location l _1k and the furthest damage location l _2k are calculated by the following expressions:

l _1к = X _ф1 / X _{1 луд} ,

l _2k = l _1k +3 (X _f2 -X _f1 ) / (X _{0 flood} + 2X _{1 flood} ),

where Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ), Re (I _{ф1 (2)} ), Im (I _{ф1 (2)} ) are the real and imaginary components of the phase current and voltage of the damaged phases, X ₀ , X _1lud - specific inductive resistance 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 phase current of the line current transformer and the phase voltage from the voltage transformer on the busbars of the switchgear.

, $${\dot{E}}_B\left(2\right)$$

, $${\dot{E}}_C\left(3\right)$$

- ЭДС питающей системы; $${\dot{Z}}_{1c}\left(\mathrm{4,}\mathrm{5,}6\right)$$

- эквивалентные сопротивления прямой последовательности системы фаз А (4), В (5) и С (6); $${\dot{Z}}_{1л}$$

- сопротивления (7, 8, 9) прямой последовательности до первого места повреждения; $${\dot{Z}}_{0л}^{\text{'}}\left(10\right)$$

, $${\dot{Z}}_{1л}^{\text{'}}\left(11\right)$$

- сопротивления нулевой и прямой последовательности участка линии между повреждениями; R_п1 (12), R_п2 (13) - переходные сопротивления в месте замыканий; R_З (14) - сопротивление земли; l_1к (15), l_2к (16) - расстояния до мест ближнего и дальнего замыканий на землю.The proposed technical solution is illustrated by the drawing, which shows the equivalent circuit of the network in the dual-circuit mode of the phases A and B in different parts of the network (figure 1), where $${\dot{E}}_A\left(\mathrm{one}\right)$$

, $${\dot{E}}_B\left(2\right)$$

, $${\dot{E}}_C\left(3\right)$$

- EMF supply system; $${\dot{Z}}_{\mathrm{one}c}\left(\mathrm{four,}\mathrm{5,}6\right)$$

- equivalent resistance of the direct sequence of the phase system A (4), B (5) and C (6); $${\dot{Z}}_{\mathrm{one}l}$$

- resistance (7, 8, 9) of the direct sequence to the first place of damage; $${\dot{Z}}_{0l}^{\text{'}\text{'}}\left(10\right)$$

, $${\dot{Z}}_{\mathrm{one}l}^{\text{'}\text{'}}\left(\mathrm{eleven}\right)$$

- resistance to zero and direct sequence of the line section between the damages; R _p1 (12), R _p2 (13) - transition resistance in the circuit; R _C (14) - earth resistance; l _1k (15), l _2k (16) - distances to places of near and far earth faults.

The occurrence of a double earth fault is determined by the growth of phase currents I _f1 and I _{f2 of} damaged phases f1 and f2.

определяется какEarth Fault Current $${\dot{I}}_{D\mathrm{AT}}$$

defined as

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

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 to determine the distance to the places of damage should be set up in this way:

и фазному току $${\dot{I}}_{ф}$$

поврежденной линии, зависит также и от активного переходного сопротивления в месте повреждения.As you can see, the resistance at the terminals of the relay connected to the phase voltage $${\dot{U}}_f$$

and phase current $${\dot{I}}_f$$

damaged line, also depends on the active transition resistance at the site of damage.

Therefore, the influence of transition resistance can be eliminated by isolating the inductive component of the resistance

where Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ), Re (I _{ф1 (2)} ), Im (U _{ф1 (2)} ) are the real and imaginary components of the phase current and voltage of the damaged phases.

The determination of the distance to the nearest place of damage l _{1k is} made through the minimum absolute value of the inductive resistance of the damaged phases X _f :

1. Calculate X _ф1 and X _ф2 .

2. The earth fault point, which has a lower absolute value of the inductive resistance of the damaged phases (relative to another phase), is taken as the nearest point of the earth fault.

3. Accordingly, the second fault point, which has a larger absolute value of the inductive resistance of the damaged phases, is taken as the distant point of the short circuit to ground.

We take the calculated resistance X _f1 for the minimum, X _f2 - for the maximum: X _f1 <X _f2 .

Then, taking into account the above, the distance to the nearest place of damage l _{1k is} determined

l _1к = X _ф1 / X _{1 луд} ,

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

The distance between the circuit points Δl = (l _2к -l _1к ) is determined from the difference of the resistances X ₁ and X ₂ :

Δl = 3 (X _f2 -X _f1 ) / (X _{0 ice} + 2X _{1 ice} ).

The distance l _2k = l _1k + Δl is the distance to the far point of the circuit:

l _2k = l _1k +3 (X _f2 -X _f1 ) / (X _{0 flood} + 2X _{1 flood} ).

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, connected to the phase current and phase voltage, meets the requirement of proportionality of the resistance at the relay terminals to the distance to the place of damage in the double earth fault mode in a distribution network with low earth fault currents.

Thus, the proposed method allows to determine with high accuracy the distance to the places of double earth faults on one power line by installing a measuring resistance element connected to the phase current and phase voltage of the damaged line.

Claims (1)

A method for determining the distance to places of double earth faults on power lines in networks with low earth fault currents, according to which the phase current and phase voltage are measured using a resistance measuring organ, characterized in that the resistance measuring organ is switched on for phase currents and phase voltages faulted line, they define the appearance of double ground fault on the same line on the growth phase currents I _F1 and I _p2 faulty phases F1 and F2 are calculated absolute values of inductance the resistivity and X _F1 X _F2 F1 circuits damaged phases Q2 by the following expression:

the damage f1 closest to the measuring body is determined through the minimum absolute value of the inductance of the damaged phase circuit X _f1 <X _f2 and the distances to the nearest damage location l _1k and the furthest damage location l _2k are calculated by the following expressions:
l _1к = X _ф1 / X _{1 луд} ,
l _2k = l _1k +3 (X _f2 -X _f1 ) / (X _{0 flood} + 2X _{1 flood} ),
where Re (U _{ф1 (2)} ), Im (U _{ф1 (2)} ), Re (I _{ф1 (2)} ), Im (I _{ф1 (2)} ) are the real and imaginary components of the phase current and voltage of the damaged phases, X ₀ , X _1lud - specific inductive resistance of direct and zero sequence power lines.