METHOD AND PROTECTIVE DEVICE FOR DETECTING A SINGLE-PHASE GROUND SHORTAGE

Description

[0001] The invention relates to a method for detecting a single-phase earth fault of an electrical phase conductor in a line section of a three-phase electrical power transmission line, wherein in the method, at a measuring point located at one end of the line section, phase current and phase-earth voltage are measured to form a phase current phasor and a phase voltage phasor, taking into account the phase current phasor, the phase voltage phasor and a compensation current phasor, an error impedance is calculated, and the presence or absence of an earth fault of the phase conductor is determined on the basis of the error impedance.

[0002] Such a method is disclosed, for example, in the publication "Precise Impedance Based Fault Location Algorithm with Fault Resistance Separation" (Marie Washer and Jean-Claude Maun, École polytechnique de Bruxelles, Université Libre de Bruxelles, Brussels, Belgium; Cezary Dzienis, Matthias Kereit, Yilmaz Yelgin and Joerg Blumschein, EM EA PRO D, Siemens AG Berlin, Germany).

[0003] German patent DE 603 ​​17 344 T2 discloses a method for locating a short circuit by compensating so-called shunt capacitances. This compensation process requires iterative calculations. In the first iteration, a compensation current phasor is defined, the calculation of which is based on deriving the shunt current from the positive sequence current.

[0004] Further state of the art is disclosed in EP 2 738 561 A2 and WO O3 / 044547 A1.

[0005] The invention is based on the objective of further improving a method of the type described above.

[0006] This problem is solved according to the invention by a method with the features according to claim 1. Advantageous embodiments of the method according to the invention are specified in the dependent claims.

[0007] According to the invention, the compensation current phasor is calculated as a function of a correction value, the calculation of which includes a multiplication of a capacitance value indicating the capacitance of the line section and a reference voltage phasor.

[0008] A significant advantage of the method according to the invention is that the compensation current phasor, already known from the aforementioned publication, additionally takes into account a correction value that depends on the line capacitance of the line section and a voltage phasor relating to the line section. By additionally incorporating capacitance effects, earth faults can be detected particularly reliably, even at very small fault currents.

[0009] It is advantageous if a detected earth fault is also located, i.e., if the distance of a detected earth fault from the measurement location is also determined.

[0010] It is considered particularly advantageous if the calculation of the compensation current phasor includes a multiplication of the capacitance value indicating the capacitance of the line section, the reference voltage phasor and the rotational frequency of the electrical power transmission line.

[0011] In a particularly preferred embodiment of the method, fault detection is performed with reference to the zero-system current. It is advantageous, for example, if a zero-system current phasor indicating the zero-system current at the measuring point is calculated based on the method of symmetrical components, and the compensation current phasor is calculated taking the zero-system current phasor into account.

[0012] The compensation current phasor is preferably calculated in relation to the zero system by subtracting a multiple of the correction value, preferably three times, from a multiple, preferably three times, of the zero system current phasor.

[0013] It is also advantageous if, based on the method of symmetrical components, a zero-system voltage phasor indicating the zero-system voltage at the measuring point is calculated, a zero-system capacitance value indicating the zero-system capacitance of the line section is used as the mentioned capacitance value for calculating the correction value, and the zero-system voltage phasor is used as the mentioned reference voltage phasor for calculating the correction value.

[0014] The correction value is preferably calculated in relation to the zero system according to: KW = jω ⋅ C 0 , L ⋅ U _ A , 0 where C 0,L is the zero-system capacitance value of the line section, KW is the correction value and U A,0 denotes the zero-system voltage phasor.

[0015] The compensation current phasor is preferably calculated in a zero-system reference manner according to: I _ A , Cmp = 3 ⋅ I _ A , O − jω ⋅ C 0 , L ⋅ U _ A , 0 where I A,Cmp the compensation current phasor, IA,0 the zero-system current phasor at the measuring point, C 0,L the zero-system capacitance value of the line section, KW the correction value and U A,0 denotes the zero-system voltage phasor.

[0016] It is also advantageous to calculate a compensation factor according to δ _ A , B = Z _ A , 0 + m ⋅ Z _ L , 0 1 − m ⋅ Z _ L , 0 + Z _ B , 0 + 1 where δ A,B the compensation factor, Z A,0 is the zero-sequence impedance of the line section at the measuring point, Z B,0 denotes the zero-system impedance of the line section at the other end of the line section and m denotes the relative error distance from the measuring point assumed for the calculation.

[0017] The aforementioned error impedance is preferably calculated according to Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp ∗ ⋅ δ _ A , B ∗ Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp ∗ ∗ δ _ A , B ∗ R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ∗ Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ ⋅ I _ A , Ph ∗ where Z F the fault impedance, RF the real part of the fault impedance, XF the imaginary part of the fault impedance, φ the conduction angle, I A,Cmp the compensation current, δA,B the compensation factor, U A,Ph-E the phase voltage phasor, I A,Ph the phase current phasor, I A,E an earth current indicator and k 0 denotes an earth compensation factor.

[0018] The Earth compensation factor k 0 can also be called the Earth impedance matching factor and is calculated, for example, by dividing the complex Earth impedance. Z E through the complex line impedance Z.

[0019] If the fault impedance Zf is available, it can advantageously be checked whether it lies in one or more predefined fault regions in the complex plane. If this is the case, a conclusion is drawn that a ground fault in the phase conductor exists, and preferably a corresponding fault signal is generated.

[0020] Alternatively or additionally, according to a second method variant considered particularly advantageous, fault detection can be carried out in relation to the opposing system by using the compensation current phasor. I A,Cmp and the correction value KW are calculated relative to the opposite system.

[0021] Regarding the second method variant, it is considered advantageous if, on the basis of the method of symmetrical components, a counter-system voltage phasor indicating the counter-system voltage at the measuring point is calculated, a counter-system capacitance value indicating the counter-system capacitance of the line section is used as the aforementioned capacitance value for calculating the correction value, and the counter-system voltage phasor is used as the aforementioned reference voltage phasor for calculating the correction value.

[0022] The correction value is preferably calculated in relation to the opposing system according to: KW = jω ⋅ C 2 , L ⋅ U _ A , 2 where C 2,L is the counter-system capacitance value of the line section, KW is the correction value and U A,2 denotes the counter-system voltage phasor.

[0023] With respect to the counter system, the compensation current phasor is preferably calculated according to: I _ A , Cmp = 3 ⋅ I _ A , 2 − jω ⋅ C 2 , L ⋅ U _ A , 2 where I A,Cmp the compensation current phasor, I A,2 denotes the counter-system current at the measuring point, C 2,L the counter-system capacitance value of the line section and KW the correction value.

[0024] The compensation factor is preferably calculated in relation to the opposing system according to δ _ A , B = Z _ A , 2 + m ⋅ Z _ L , 2 1 − m ⋅ Z _ L , 2 + Z _ B , 2 + 1 where δ A,B the compensation factor, Z A,2 the opposite system impedance of the line section at the measuring point, Z B,2 denotes the opposite system impedance of the line section at the other end of the line section and m denotes the assumed relative error distance from the measuring point.

[0025] The calculation of the error impedance in relation to the opposite system can be carried out using the formulas already mentioned for the calculation of the error impedance in relation to the zero system, i.e. according to Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp * ⋅ δ _ A , B * Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp * ⋅ δ _ A , B * R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E * Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ ⋅ I _ A , Ph * where the corresponding values ​​related to the opposing system are inserted into the formulas.

[0026] The described method is preferably used in three-phase electrical power transmission lines where the neutral point is grounded via an impedance, for example, a Petersen coil. During measurement, earth fault detection, and, if necessary, location tracing, a further measuring impedance can be connected in parallel to the existing impedance to increase the current flow and improve fault detection. The invention further relates to a protective device for detecting a single-phase earth fault in an electrical phase conductor in a section of a three-phase electrical power transmission line, as defined in independent claim 12.

[0027] Such a protective device is designed, among other things, to measure the phase current and phase-to-earth voltage at the end of a section of the conductor for the phase conductor, generating a phase current phasor and a phase voltage phasor. Taking into account the phase current phasor, the phase voltage phasor, and a compensation current phasor, a fault impedance is calculated, and the fault impedance is used to determine whether or not a ground fault in the phase conductor is present. Such a protective device is also described in the aforementioned publication "Precise Impedance Based Fault Location Algorithm with Fault Resistance Separation".

[0028] According to the invention, the protective device is designed in such a way that it calculates the compensation current phasor as a function of a correction value, the calculation of which includes a multiplication of a capacitance value indicating the capacitance of the line section and a reference voltage phasor.

[0029] Regarding the advantages of the protective device according to the invention and its advantageous embodiments, reference is made to the above statements in connection with the method according to the invention and its advantageous embodiments.

[0030] The protective device preferably comprises a computing unit and a memory. The memory preferably contains a software program or software program product which, when executed by the computing unit, performs the calculation steps described above in connection with the method according to the invention and its advantageous embodiments.

[0031] It is advantageous if the protective device is also designed to locate a detected earth fault, in particular to determine the distance of the detected earth fault from the point of measurement.

[0032] The invention is explained in more detail below with reference to exemplary embodiments; these show, by way of example, Figure 1 shows a section of a three-phase power transmission line, which serves as an example to illustrate embodiments of methods according to the invention; Figure 2 shows an embodiment of an equivalent circuit diagram that can be used for fault detection; Figure 3 shows an embodiment of a protective device according to the invention; and Figure 4 shows a further embodiment of a protective device according to the invention.

[0033] For the sake of clarity, the same reference symbols are always used in the figures for identical or comparable components.

[0034] The Figure 1Figure 1 shows two switching devices 10 and 20 that limit a conductor section 30 of a three-phase power transmission line, i.e., a power transmission line with three phase conductors 31, 32, and 33. A neutral point of the three-phase power transmission line (not shown) is grounded via a neutral point impedance (also not shown for clarity), for example, in the form of a Petersen coil, or remains insulated.

[0035] At one in the Figure 1 At the left end of section A of line section 30, a protective device 40 is connected to the phase conductors 31, 32 and 33 of line section 30 via current and voltage transformers 61, 62 and 63.

[0036] The current and voltage transformers 61, 62, and 63 transmit measurement signals and / or measured values ​​M, which enable the protective device 40 to measure the currents flowing in the phase conductors 31, 32, and 33, or the voltages applied to them. Since, in the embodiment according to Figure 1Since the current and voltage transformers 61, 62 and 63 are connected to the left end of section A of the line section 30, this left end of section A forms the measuring point of the protective device 40.

[0037] The operation of the protective device 40 will be described below by way of example in connection with the detection of a single-phase earth fault in one of the phase conductors, for example, the one in the Figure 1 The lowest phase conductor 31 will be explained. For the other two phase conductors 32 and 33, earth fault detection can be carried out in parallel or with a time delay in a corresponding or identical manner.

[0038] Using the measurement signals or measured values ​​M acquired by means of the current and voltage transformers 61, 62 and 63, the protective device 40 first calculates a phase current phasor and a phase-earth voltage phasor for each of the phase conductors 31, 32 and 33, as is generally known in the field of protection technology and as is described, for example, in the aforementioned publication.

[0039] In the Figure 1 is for the one in the Figure 1 lowest phase conductor 31 of the phase current phasor with the reference sign I A,Ph and the phase-earth voltage pointer with the reference symbol U A,Ph-E are labeled. For the other two phase conductors 32 and 33, the phase current phasors are labeled with the reference symbols. I A,Ph2 or I A,Ph3 and the phase-earth voltage vectors with the reference symbols U A,Ph2-E or U A,Ph3-E labeled.

[0040] For further calculations, the protection device 40 takes into account a system component-related equivalent circuit diagram 100, which is exemplified in the Figure 2 The system component-related equivalent circuit diagram 100 comprises a positive system 110, a negative system 120, and a zero system 130, as shown in principle, for example, in the aforementioned publication (see in particular). Figure 2 this publication) are known and described therein. In addition, and in contrast to the previously known equivalent circuit diagram, the system component-related equivalent circuit diagram 100 comprises according to Figure 2 Capacity effects through additional consideration of a zero-system capacity value C 0,L and a counter-system capacity value C 2,L, which are explained in more detail below.

[0041] Based on the method of symmetrical components, the protective device 40 can, according to a first method variant considered particularly advantageous, generate a zero-system-related compensation current phasor for the equivalent circuit diagram 100. I Calculate A,Cmp according to: I _ A , Cmp = 3 ⋅ I _ A , O − KW where I A,0 denotes a zero-system current phasor at the measuring point or the left end of section A and KW denotes a (here zero-system-related correction value).

[0042] Calculating the zero-system current phasor I A,0 and the zero-system voltage phasor U A,0 for the measuring point or the left end of section A is carried out in a known manner.

[0043] The correction value KW is preferably determined in the first method variant according to KW = jω ⋅ C 0 , L ⋅ U _ A , 0 where C 0,L denotes the zero-system capacitance value of the line section 30 and ω denotes the angular frequency of the three-phase power transmission system.

[0044] The zero-system capacitance value C 0,L can be calculated using phase conductor-related capacitance values ​​that have been measured or calculated on the basis of geometric conductor specifications, and on the basis of the method of symmetrical components; this is also generally known.

[0045] The protection device 40 then calculates an impedance Zf, which is referred to here as the fault impedance, since it is used to verify whether a fault actually exists or not. The fault impedance Zf is preferably calculated as follows: Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp * ⋅ δ _ A , B * Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp * ⋅ δ _ A , B * R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E * Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ ⋅ I _ A , Ph * where RF is the real part of the fault impedance, X 2 the imaginary part of the fault impedance, φ the conduction angle of the line section 30 or the phasor angle of the line impedance of the line section 30, δ A,B a compensation factor, I A,E an earth current indicator and k0 denotes an Earth compensation factor. The symbol "*" marks the complex conjugation of the respective complex phasor.

[0046] The Earth compensation factor k 0 can also be called the Earth impedance matching factor and is calculated, for example, by dividing the complex Earth impedance. Z E through the complex line impedance Z.

[0047] The compensation factor δ A,B is preferably calculated as follows: δ _ A , B = Z _ A , 0 + m ⋅ Z _ L , 0 1 − m ⋅ Z _ L , 0 + Z _ B , 0 + 1 where Z A,0 the zero-system impedance in the zero system 130 at the left end of section A, Z B,0 the zero-system impedance in the zero system at the other, in the Figure 1 right section end B of line section 31, m the assumed relative fault distance from the left section end A and ZL,0 denotes the line impedance in the zero-sequence system 130. The impedances mentioned can be calculated in a known manner using the method of symmetrical components, in particular including phase-line-related resistance values, capacitance and inductance values ​​and the section length and / or on the basis of geometric line specifications, as is generally known.

[0048] If the fault impedance Zf is present, it can be checked whether it lies in one or more predefined fault regions in the complex plane. If this is the case, the protective device 40 concludes that there is a ground fault in the phase conductor 31 and generates a corresponding fault signal FE31.

[0049] Alternatively or additionally, the protective device 40 can, according to a second method variant considered particularly advantageous, the compensation current indicator ICalculate A, Cmp and the correction value KW in relation to the opposite system according to: I _ A , Cmp = 3 ⋅ I _ A , 2 − KW where I A,2 denotes a counter-current phasor at the measuring point or the left end of section A. The calculation of the counter-current phasor I A,2 is carried out in the known manner.

[0050] The correction value is preferably determined in relation to the opposing system according to KW = jω ⋅ C 2 , L ⋅ U _ A , 2 where C 2,L is the counter-system capacity value of line section 30, KW is the counter-system-related correction value and U 3.2 denotes the counter-system voltage phasor at the measuring point or the left end of section A.

[0051] The compensation factor δ A,B is then also calculated in relation to the opposite system according to δ _ A , B = Z _ A , 2 + m ⋅ Z _ L , 2 1 − m ⋅ Z _ L , 2 + Z _ B , 2 + 1 where Z A,2 the opposite system impedance of the line impedance of line section 30 at the measuring point or the section end A, ZB,2 denotes the opposite system impedance of the line impedance of the line section 30 at the other, right end B of the line section 30 and m denotes the assumed relative error distance from the measuring point or the left end A of the section.

[0052] The fault impedance is preferably calculated in the same way as in the zero-current relationship when referenced to the opposite system, i.e., according to Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp ∗ ⋅ δ _ A , B ∗ Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp ∗ ⋅ δ _ A , B ∗ R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ∗ Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ I _ A , Ph ∗

[0053] If the opposing system-related fault impedance Zf is present, it can be checked again whether it lies in one or more predefined fault regions in the complex plane. If this is the case, the protective device 40 concludes that there is a ground fault in the phase conductor 31 and generates the corresponding fault signal FE31.

[0054] The Figure 3Figure 1 shows an embodiment of a protective device 40 according to the invention. The protective device 40 comprises a computing unit 41 and a memory 42. A software program product SW is stored in the memory 42, which, when executed by the computing unit 41, performs the functions described above in connection with the Figure 1 and 2 executes the described calculation steps.

[0055] For this purpose, the software program product SW includes according to Figure 3 preferably a phasor formation module ZBM for forming the phase current phasors I A,Ph , I A,Ph2 and I A,Ph3 and the phase-earth voltage pointer U A,Ph-E U A,Ph2-E and U A,Ph3-E based on sample values ​​that are generated on the basis of the measurement signals or measured values ​​M of the current and voltage transformers 61, 62 and 63 or are already contained in them.

[0056] Furthermore, the software program product SW includes according to Figure 3preferably an equivalent circuit diagram module ESM for determining and considering the system component-related equivalent circuit diagram 100 according to Figure 2 .

[0057] Furthermore, the software program product SW includes according to Figure 3 preferably a correction value module KWM0 for determining the zero-system-related correction value KW according to KW = jω ⋅ C 0 , L ⋅ U _ A , 0

[0058] Furthermore, the software program product SW includes according to Figure 3 preferably a zero-system-related compensation current module ICMO for calculating the zero-system-related compensation current phasor I A,Cmp according to I _ A , Cmp = 3 ⋅ I _ A , O − jω ⋅ C 0 , L ⋅ U _ A , 0

[0059] Furthermore, the software program product SW includes according to Figure 3 preferably a zero-system-related compensation factor module KFMO for calculating a compensation factor according to δ _ A , B = Z _ A , 2 + m ⋅ Z _ L , 2 1 − m ⋅ Z _ L , 2 + Z _ B , 2 + 1

[0060] Furthermore, the software program product SW includes according to Figure 3preferably an error pointer calculation module FBM for calculating a zero-system-related error impedance Zf according to Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp ∗ ⋅ δ _ A , B ∗ Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp ∗ ⋅ δ _ A , B ∗ R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ∗ Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ I _ A , Ph ∗

[0061] Furthermore, the software program product SW includes according to Figure 3 preferably a fault area testing module FGPM0 for checking whether the zero-system-related fault impedance Zf in the complex plane lies in one or more predefined fault areas or not, and for generating a corresponding fault signal FE31.

[0062] Furthermore, the software program product SW includes according to Figure 3 preferably a correction value module KWM2 for determining the counter-system-related correction value KW according to KW = jω ⋅ C 0 , L ⋅ U _ A , 0

[0063] Furthermore, the software program product SW includes according to Figure 3 preferably a counter-system-related compensation current module ICM2 for calculating the counter-system-related compensation current phasor I A,Cmp according to I _ A , Cmp = 3 ⋅ I _ A , 2 − jω ⋅ C 2 , L ⋅ U _ A , 2

[0064] Furthermore, the software program product SW includes according to Figure 3 preferably a counter-system-related compensation factor module KFM2 for calculating a counter-system-related compensation factor according to δ _ A , B = Z _ A , 2 + m ⋅ Z _ L , 2 1 − m ⋅ Z _ L , 2 + Z _ B , 2 + 1

[0065] The software program product SW according to Figure 3 A separate error phasor calculation module FBM2 may be used to calculate a counter-system error impedance; alternatively, the calculation of the counter-system error impedance may be performed by the error phasor calculation module FBM, which also performs the calculation of the zero-system error impedance.

[0066] Furthermore, the software program product SW includes according to Figure 3 preferably a fault area testing module FGPM2 for checking whether the counter-system-related fault impedance in the complex plane lies in one or more predefined fault areas or not, and for generating a corresponding fault signal FE31.

[0067] The Figure 4 shows a further embodiment of a protective device 40 according to the invention. In the protective device 40 according to Figure 4 The earth fault test is only performed in relation to the zero system, so only the relevant software modules are present, as already mentioned above in connection with the Figure 3 have been explained.

[0068] Finally, it should be mentioned that the features of all the embodiments described above can be combined with each other in any way to form further embodiments of the invention, as long as these fall within the scope of protection of the attached claims.

Claims

1. Method for detecting a single-phase earth fault of an electrical phase conductor (31) in a line section (30) of a three-phase electrical power transmission line, wherein, in the method, - phase current and phase-earth voltage are measured at a measuring point for the phase conductor (31) at a section end (A) of the line section (30) so as to form a current phase vector (IA,Ph) and a voltage phase vector (UA,Ph), - a fault impedance is calculated taking into account the current phase vector and the voltage phase vector and a compensation current vector, and - the fault impedance is used to infer the presence or absence of an earth fault of the phase conductor (31), characterized in that - the compensation current vector is calculated as a function of a correction value, the calculation of which includes a multiplication of a capacitance value indicating the capacitance of the line section (30) and a reference voltage vector, wherein - a negative phase-sequence system current vector (IA,0) indicating the negative phase-sequence system current (130) at the measuring point is calculated based on the symmetrical component method, and the compensation current vector is calculated taking into account the negative phase-sequence system current vector (IA,0), and wherein - the compensation current vector is calculated by subtracting the correction value from a multiple of the negative phase-sequence system current vector (IA,0), or wherein - a positive phase-sequence system voltage vector (UA,2) indicating the positive phase-sequence system voltage at the measuring point is calculated based on the symmetrical component method, - a positive phase-sequence system capacitance value (C2,L) indicating the positive phase-sequence system capacitance of the line section (30) is used to calculate the correction value as said capacitance value, and - the positive phase-sequence system voltage vector is used to calculate the correction value as said reference voltage vector.

2. Method according to Claim 1, characterized in that the calculation of the compensation current vector includes a multiplication of the capacitance value indicating the capacitance of the line section (30), the reference voltage vector and the rotational frequency of the electrical power transmission line.

3. Method according to either one of the preceding claims, characterized in that - a negative phase-sequence system voltage vector indicating the negative phase-sequence system voltage at the measuring point is calculated based on the symmetrical component method, - a negative phase-sequence system capacitance value (C0,L) indicating the negative phase-sequence system capacitance of the line section (30) is used to calculate the correction value as said capacitance value, and - the negative phase-sequence system voltage vector is used to calculate the correction value as said reference voltage vector.

4. Method according to Claim 3, characterized in that the correction value is calculated according to: KW = jω ⋅ C 0 , L ⋅ U _ A , 0 where C0,L denotes the negative phase-sequence system capacitance value of the line section (30), KW denotes the correction value and UA,0 denotes the negative phase-sequence system voltage vector.

5. Method according to any one of the preceding claims, characterized in that the compensation current vector is calculated according to: I _ A , Cmp = 3 ⋅ I _ A , O − jω ⋅ C 0 , L ⋅ U _ A , 0 where IA,Cmp denotes the compensation current vector, IA,0 denotes the negative phase-sequence system current vector at the measuring point, C0,L denotes the negative phase-sequence system capacitance value of the line section (30), KW denotes the correction value and UA,0 denotes the negative phase-sequence system voltage vector.

6. Method according to Claim 5, characterized in that a compensation factor is calculated according to δ _ A , B = Z _ A , 0 + m ⋅ Z _ L , 0 1 − m ⋅ Z _ L , 0 + Z _ B , 0 + 1 where δA,B denotes the compensation factor, ZA,0 denotes the negative phase-sequence system impedance of the line section (30) at the measuring point, ZB,0 denotes the negative phase-sequence system impedance of the line section (30) at the other line end of the line section (30) and m denotes the relative distance of the fault from the measuring point.

7. Method according to Claim 1, characterized in that the correction value is calculated according to: KW = jω ⋅ C 2 , L ⋅ U _ A , 2 where C2,L denotes the positive phase-sequence system capacitance value of the line section (30), KW denotes the correction value and UA,2 denotes the positive phase-sequence system voltage vector.

8. Method according to Claim 7, characterized in that the compensation current vector is calculated according to: I _ A , Cmp = 3 ⋅ I _ A , 2 − jω ⋅ C 2 , L ⋅ U _ A , 2 where IA,Cmp denotes the compensation current, IA,2 denotes the positive phase-sequence system current at the measuring point, C2,L denotes the positive phase-sequence system capacitance value of the line section (30) and KW denotes the correction value.

9. Method according to Claim 8, characterized in that a compensation factor is calculated according to δ _ A , B = Z _ A , 2 + m ⋅ Z _ L , 2 1 − m ⋅ Z _ L , 2 + Z _ B , 2 + 1 where δA,B denotes the compensation factor, ZA,2 denotes the positive phase-sequence system impedance of the line section (30) at the measuring point, ZB,2 denotes the positive phase-sequence system impedance of the line section (30) at the other line end of the line section (30) and m denotes the relative distance of the fault from the measuring point.

10. Method according to any one of the preceding claims, characterized in that the fault impedance is calculated according to Z _ F = R F + j X F with X F = sin φ ⋅ Im U _ A , Ph − E ⋅ I A , Cmp ∗ ⋅ δ _ A , B ∗ Im e jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E ⋅ I _ A , Cmp ∗ ⋅ δ _ A , B ∗ R F = Im U _ A , Ph − E ⋅ e − jφ ⋅ I _ A , Ph − k _ 0 ⋅ I _ A , E * Im I _ A , Cmp ⋅ δ _ A , B ⋅ e − jφ ⋅ I _ A , Ph * where ZF denotes the fault impedance, RF denotes the real part of the fault impedance, XF denotes the imaginary part of the fault impedance, φ, IA,Cmp denotes the compensation current, δA,B denotes a compensation factor, UA,Ph-E denotes the voltage phase vector, IA,Ph denotes the current phase vector, IA,E denotes an earth current vector and k0 denotes an earth compensation factor.

11. Method according to any one of the preceding claims, characterized in that the method is used in a three-phase electrical power transmission line in which the neutral point is earthed via an impedance.

12. Protective device (40) for detecting a single-phase earth fault in an electrical phase conductor (31) in a line section (30) of a three-phase electrical power transmission line, wherein the protective device (40) is designed - to detect phase current and phase-earth voltage for the phase conductor (31) for a section end (A) of the line section (30) so as to form a current phase vector and a voltage phase vector, - to calculate a fault impedance taking into account the current phase vector and the voltage phase vector and a compensation current vector, and - to use the fault impedance to infer the presence or absence of an earth fault in the phase conductor (31), characterized in that the protective device (40) is designed in such a way that it calculates the compensation current vector as a function of a correction value, the calculation of which includes a multiplication of a capacitance value indicating the capacitance of the line section (30) and a reference voltage vector, wherein the protective device - calculates a negative phase-sequence system current vector indicating the negative phase-sequence system current (130) at a measuring point based on the symmetrical component method, and calculates the compensation current vector taking into account the negative phase-sequence system current vector, and wherein - calculates the compensation current vector by subtracting the correction value from a multiple of the negative phase-sequence system current vector, or wherein the protective device - calculates a positive phase-sequence system voltage vector indicating the positive phase-sequence system voltage at the measuring point based on the symmetrical component method, - uses a positive phase-sequence system capacitance value indicating the positive phase-sequence system capacitance of the line section (30) to calculate the correction value as said capacitance value, and - uses the positive phase-sequence system voltage vector to calculate the correction value as said reference voltage vector.