Method for calculating the fault point distance to a single-pole earth fault within an electric power network

State of the art

0001The invention is based on a method for calculating a distance of a fault location of a single-pole ground fault from a measuring location in an electrical energy supply network, in particular in a compensated operated power supply network. The invention also relates to a corresponding electrical energy supply network with a computing device for carrying out the method.

0002In known methods for determining the fault location of a single-pole earth fault, transient compensation processes are usually evaluated after the occurrence of the earth fault. However, these compensation processes are dependent on the fault resistance of the earth fault, which leads to inaccuracies of these methods. Likewise, these methods can not be repeated several times with one and the same ground fault.

0003The object of the invention is to provide a method for calculating a distance of a fault location of a single-pole ground fault from a measurement location in an electrical energy supply network, which has a higher accuracy.

Solution and advantages of the invention

0004This object is achieved by a method according to claim 1.

0005The inventive method is not based on transient compensation processes, but on stationary variables. This allows the repetition of measurements in the context of the method, so that then the difference method for the evaluation of the measured quantities can be applied. The application of the difference method brings with it the significant advantage of increased accuracy of the method according to the invention. Furthermore, due to the use of the difference method, the method according to the invention can also be used with a large error resistance of the ground fault. In addition, the use of the differential method results in a relatively high degree of independence from the load current present on the line, so that an improved accuracy also results in this respect.

0006It is particularly advantageous to calculate the fault current from the difference between the zero current and the symmetrical zero current. The required voltages and currents and the zero admittance can be derived from the resulting variables of the difference method.

0007A further advantage is that the difference method can be realized by a simple change in the impedance of a ground fault coil and the two different measurement passes resulting therefrom.

0008Further applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, alone or in any combination form the subject of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

Embodiments of the invention

0009<dl id="dl0001" compact="compact"><dt>FIG. 1</dt><dd>shows a schematic equivalent circuit diagram of a single-pole fault in an electrical, compensated operated power grid, and</dd><dt>FIG. 2</dt><dd>shows a schematic representation of an embodiment of a method according to the invention for calculating the distance of the unipolar fault from a measuring location.</dd></dl>

0010An energy supply network, for example an electrical high-voltage network, has, inter alia, a multiplicity of transmission lines. In such transmission lines, there is the possibility that so-called earth faults occur. These can arise, for example, through a tree coming into contact with the transmission line, via which one of the phases of the high-voltage network then has a short circuit to ground.

0011Figure 1 shows the equivalent circuit of the compensated operated high-voltage network after the occurrence of such a ground fault.

0012In the figure 1 is - from top to bottom - the Mitsystem, the negative sequence and the zero system of the high voltage network shown. For all three systems, it is assumed that, for example, there is a substation on the left and a load on the right. In between, for example, the transmission line runs.

0013In all three systems, transformer impedances Z are on the left_T1, Z_T2, Z_T0 available. In the co-system and the negative sequence are Netzvorimpedanzen Z_VN1, Z_VN2 specified. Furthermore, in the zero system, the impedance Z_NE an earth leakage coil specified, which is changeable.

0014To the right of these impedances is a measuring location where voltages and currents can actually be measured. This measuring location is located, for example, within the substation, preferably immediately before leaving the transmission lines. The measuring location is indicated in FIG. 1 by a dashed line and the reference number M.

0015At the measuring location, the conductor-earth voltages U_R, U_S, U_T, the conductor currents I_R, I_S, I_T, as well as the zero voltage U₀ and the zero current I₀ be measured. At the zero voltage U₀ it is the voltage that is present from one star point of the three phases R, S, T of the high voltage network to earth.

0016The transmission line M subsequent transmission line is through the line impedances Z_11A, Z_11B, Z_22A, Z_22B, Z_00A, Z_00B characterized.

0017Between the two line impedances Z_11A, Z_11B of the co-system is a fault resistance R_F switched to earth. This fault resistance R_F For example, represents the tree that causes the ground fault. The location of the fault resistance R_F represents the fault location and is marked in Figure 1 with a dashed line and the reference numeral F.

0018The line impedances as well as variables derived therefrom to the left of the fault location F contain the marking A, while corresponding quantities to the right of the fault location have the marking B.

0019In the three systems, the load connected to the high-voltage network is shown on the right, by the load impedances Z_last1, Z_last2.

0020In the zero system, the zero admittance is Y_{00 line} through the conductance G_00A, G_00B and by the capacities C_00A, C_00B specified. This zero admittance Y_{00 line} in this case represents the mean value of the admittances of all phases R, S, T to ground. The markings A, B relate in turn to the presence of the conductances or capacities left and right of the fault location F.

0021The distance between the measuring location M and the fault location F is indicated by the reference number 1 in FIG.

0022FIG. 2 shows a method with which the distance 1 of the fault location F from the measuring location M can be calculated. This method can be carried out in continuation of the operation of the high-voltage network.

0023The method is performed by means of a computing device, such as a personal computer. The computing device is preferably present at the measuring location.

0024In a step 21, the conductor-earth voltages U_R, U_S, U_T, the conductor currents I_R, I_S, I_T, as well as the zero voltage U₀ and the zero current I₀ measured. These measurements take place after the decay of transient compensation processes. It should be noted that the zero voltage U₀ and the zero current I₀ theoretically also from the conductor-earth voltages U_R, U_S, U_T and the conductor currents I_R, I_S, I_T could be calculated. This is indicated in the step explained below.

0025In a step 22, the associated symmetrical components are calculated from the measured quantities. These are the currents I₀, I₁, I₂ and the voltages U₀, U₁, U₂ of the zero system, the co-system and the counter-system. The calculation represents a transformation and is dependent on the phase-earth voltages U_R, U_S, U_T and the conductor currents I_R, I_S, I_T carried out. The equations provided for the transformation are indicated in step 22 of FIG. The existing value a is a known, fixed, complex variable.

0026As already mentioned, the zero voltage U₀ and the zero current I₀ of the zero system can also be measured directly.

0027In the equivalent circuit of Figure 1, a branch V is particularly emphasized. There apply for the flowing into the branch V zero current I₀ following equations:<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext>I</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> = I</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><msub><mrow><mtext> + I</mtext></mrow><mrow><mtext>0S</mtext></mrow></msub></mrow></math><img file="EP1304580A2_D0001.tif" /></maths> With<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext>I</mtext></mrow><mrow><mtext>0S</mtext></mrow></msub><msub><mrow><mtext> = I</mtext></mrow><mrow><mtext>0SA</mtext></mrow></msub><msub><mrow><mtext> + I</mtext></mrow><mrow><mtext>0SB</mtext></mrow></msub><mtext>.</mtext></mrow></math><img file="EP1304580A2_D0002.tif" /></maths>

0028With I_F In these equations, a fault current is indicated, while with I_0S a symmetrical zero current is introduced, resulting from the left and right sides of the fault location F caused zero currents I._0SA, I_0SB composed.

0029The aforementioned symmetrical zero current arises from the fact that an asymmetry, for example due to a ground fault, is present on one of the phases of the high-voltage network. This unbalance results in a zero voltage exceeding the zero-admittance Y_{00 line} drops. According to FIG. 1, the zero admittance Y is set_{00 line} thereby admittances left and right of the fault location F together. The falling zero voltage then has the associated zero currents I_0SA, I_0SB result.

0030In a subsequent step 23, the symmetrical zero current I_0S and the fault current I_F calculated. This is done on the basis of the above equations and explanations as well as in dependence on the equations given in the step 23.

0031The zero admittance Y required for this purpose_{00 line} For example, it is possible to calculate in advance by means of a method in which two different measurements of the zero current I occur during fault-free operation of the high-voltage network₀ and the zero voltage U₀ are performed, from which then the zero admittance Y_{00 line} can be calculated by division.

0032The above-described steps 21, 22, 23 are performed at a first value of the impedance Z_NE carried out the Erdschlussspule. The obtained current and voltage values ​​are stored. Then the impedance Z_NE the earth leakage coil set to a second value and thus to different conditions. This can be done by a direct detuning of the ground fault coil or by the addition and / or switching off additional dummy switching elements in the star point.

0033Thereafter, the steps 21, 22, 23 with the second value of the impedance Z_NE go through the ground fault coil again. The obtained current and voltage values ​​are stored again.

0034In a subsequent step 24, difference values ​​are calculated from the stored values ​​of the two measurement runs. The values ​​of the two measurement passes are distinguished from each other by the parentheses (1), (2) in the equations given in step 24 of FIG.

0035In step 24, those equations of the applied differential method are specified, which are required to calculate the difference sizes of the two measuring sequences for the symmetrical zero current I_0S, the fault current I_F, the current I₁ in the co-system, the current I₂ in the opposite system, the voltage U₀ in Nullsysstem, the voltage U₁ in the positive system and the voltage U₀ to calculate in the negative sequence.

0036In a subsequent step 25, the distance l between the measuring location M and the fault location F and the fault resistance R are calculated from the differential variables calculated above_F calculated. The equations provided for this purpose are given in step 25. This calculation is based on the mesh equation of the fault circuit of the equivalent circuit of FIG. This is as follows:<maths id="math0003" num=""><math display="block"><mrow><mtext>Δ</mtext><munder accentunder="true"><mrow><mtext>U</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext>+ Δ</mtext><munder accentunder="true"><mrow><mtext>U</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><mtext>+ Δ</mtext><munder accentunder="true"><mrow><mtext>U</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext>= (Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext>+ Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>2</mtext></mrow></msub><mtext>)·</mtext><munder accentunder="true"><mrow><mtext>Z</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>'</mtext></mrow><mrow><mtext>11</mtext></mrow></msub><mtext>· 1 + (Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext>+ </mtext><mfenced open="(" close=")"><mrow><mtext>Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext>+</mtext><mfrac><mrow><mtext>1</mtext></mrow><mrow><mtext>2</mtext></mrow></mfrac><mtext>Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>0S</mtext></mrow></msub></mrow></mfenced><mtext> ·</mtext><munder accentunder="true"><mrow><mtext>Z</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>'</mtext></mrow><mrow><mtext>00</mtext></mrow></msub><mtext>* 1 + 3 · Δ</mtext><munder accentunder="true"><mrow><mtext>I</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><msub><mrow><mtext>· R</mtext></mrow><mrow><mtext>F</mtext></mrow></msub></mrow></math><img file="EP1304580A2_D0003.tif" /></maths>

0037In the above mesh equation, the assumption is made that the two zero currents I_0SA, I_0SB the same size, namely 1 / 2xI each_0S are. This assumption is necessary because the division of the two zero currents I_0SA, I_0SB depends on the fault location F, whose determination is ultimately the aim of the method described. The above assumption has the consequence that the calculation of the distance l has a slight error.

0038In the two equations given in step 25 of FIG. 2, the terms Re and Im have the meaning of real parts and imaginary parts. The impedances Z 'likewise indicated there₀₀ and Z'₁₁ The values ​​of these referenced impedances can be determined with the aid of measurements, for example during the commissioning of the high-voltage network or on the basis of the geometry of the high-voltage network or with the aid of simulations. The referenced impedances Z '₀₀ and Z'₁₁ can be assumed to be known.