METHOD AND PROTECTIVE DEVICE FOR LOCING A FAULT

Description

[0001] The invention relates to a method for locating a fault in a line section of a three-phase electrical power transmission line, wherein in the method at least one iteration step is carried out, which comprises a location calculation method in which a fault location is determined taking into account an auxiliary value, and a modification method in which a modified auxiliary value is formed, with which the location calculation method can be repeated in order to form a new fault location, wherein the iteration step is repeated within the scope of an iteration until a predetermined termination criterion is met.

[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] The invention is based on the object of further improving a method of the type described above with a view to improving the convergence behavior of the iteration.

[0004] This object is achieved according to the invention by a method having the features according to claim 1. Advantageous embodiments of the method according to the invention are specified in subclaims.

[0005] According to the invention, the auxiliary information is a compensation information which describes an estimated location at which the error could be located, and at least two different modification methods are available and in each iteration step it is checked which of the modification methods is to be used in the respective iteration step, wherein the choice of the modification method depends on a sensitivity information which quantitatively describes the influence of the compensation information on the error location information.

[0006] A significant advantage of the method according to the invention is that the iteration already known from the above-mentioned publication can be achieved in most cases by providing at least two different modification methods, because an unbridled iteration in the wrong iteration direction with an increasing deviation between the compensation information used in the iteration step and the optimal compensation information and thus an increasing deviation between the correct error location information to be determined and the error location information determined in the iteration step can always be avoided, at least in most cases.

[0007] It is advantageous if the sensitivity value is calculated by deriving the fault location value from the compensation value according to E = dMm / dMc where E is the sensitivity value, Mm is the fault location value and Mc is the compensation value.

[0008] The compensation specification preferably describes an estimated location where the error could be located. Accordingly, the compensation specification could also be referred to as an estimated location specification.

[0009] The fault location information and the compensation information are preferably relative information and preferably define the distance of the fault from the measuring point in relation to the length of the line section.

[0010] The sensitivity is preferably determined by numerical differentiation.

[0011] It is considered particularly advantageous if, in each of the two modification methods, the modified compensation information is determined as a function of the last determined fault location information.

[0012] In a particularly preferred embodiment of the method, it is provided that one of the at least two modification methods is a modification method of the first type, in which the last error location information determined in the previous location calculation method is defined as a modified compensation information for the next iteration step.

[0013] In the latter variant, it is advantageous if the modification method of the first type is selected in the respective iteration step if the sensitivity value is smaller than 1.

[0014] It is also advantageous if one of the at least two modification methods is a second type modification method in which it is calculated back how the compensation value should have been dimensioned in the last location calculation method in order to obtain the estimated location defined by the previous compensation value as the error location value, and the thus determined back-calculated compensation value is defined as the new compensation value for the next iteration step.

[0015] In the latter variant, it is advantageous if the modification method of the second type is selected in the respective iteration step if the sensitivity value is greater than 1.

[0016] The iteration is preferably repeated until the deviation between the fault location information and the compensation information falls below a predetermined threshold.

[0017] Alternatively or additionally, it can be provided that the iteration is aborted when a specified maximum number of iteration steps has been carried out.

[0018] The invention further relates to a protective device for locating a fault in a line section of a three-phase electrical power transmission line, wherein the protective device is designed to carry out at least one iteration step, which comprises a location calculation method in which a fault location is determined taking into account an auxiliary value, and a modification method in which a modified auxiliary value is formed with which the location calculation method can be repeated in order to form a new fault location, wherein the protective device repeats the iteration step within the scope of an iteration until a predetermined termination criterion is met.

[0019] Such a protective device also results from the publication "Precise Impedance Based Fault Location Algorithm with Fault Resistance Separation" mentioned above.

[0020] According to the invention, the protective device is designed such that the auxiliary information is a compensation information that describes an estimated location where the fault could be located, and at least two different modification methods are available to the protective device and the protective device checks in each iteration step which of the modification methods should be used in the respective iteration step, wherein the choice of the modification method depends on a sensitivity information that quantitatively describes the influence of the compensation information on the fault location information.

[0021] With regard to 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.

[0022] The protective device preferably comprises a pre-stage and an iteration stage downstream of the pre-stage.

[0023] The pre-stage is preferably equipped with a start module, a location calculation module and a difference former.

[0024] The iteration stage preferably comprises an abort module, a sensitivity calculation module, a test module, a modification device comprising a first modification module and a second modification module, a count-up module, a location calculation module and a difference former.

[0025] It is advantageous if the protective device comprises a computing device and a memory. A software program or software program product is preferably stored in the memory, which, when executed by the computing device, carries out the calculation steps described above in connection with the method according to the invention and its advantageous embodiments, and / or emulates one, several, or all of the above-mentioned modules in software.

[0026] The invention is explained in more detail below using exemplary embodiments; by way of example, Figure 1 shows a line section of a three-phase power transmission line which is equipped with an embodiment of a protective device according to the invention and on the basis of which exemplary embodiments of methods according to the invention are explained, Figure 2 shows components of a preferred embodiment of the protective device according to Figure 1, Figure 3 shows, using three curves, the influence of the sensitivity specification on the convergence behavior of the iteration, and Figure 4 shows a preferred software implementation of the Figure 2 shown protective device.

[0027] For the sake of clarity, the same reference symbols are always used in the figures for identical or comparable components.

[0028] The Figure 1 shows two switching devices 10 and 20 that delimit a line section 30 of a three-phase power transmission line, i.e., having three phase conductors 31, 32, and 33. A star point (not shown) of the three-phase electrical power transmission line can be grounded or remain insulated via a star point impedance (also not shown for reasons of clarity), for example in the form of a Petersen coil.

[0029] At one in the Figure 1At 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.

[0030] 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 thereto. Since in the embodiment according to Figure 1 the current and voltage transformers 61, 62 and 63 are connected to the left section end A of the line section 30, this left section end A forms the measuring point of the protective device 40.

[0031] The operation of the protective device 40 will be explained below by way of example in connection with the location of a two-phase short circuit between two of the phase conductors, for example between the Figure 1lowest phase conductor 31 and the middle phase conductor 32. For the other two phase conductor pairs 31 / 33 and 32 / 33, the location can be carried out in parallel or at a different time in a corresponding or identical manner.

[0032] 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 vector for each of the phase conductors 31, 32 and 33, as is generally known in the field of protection technology and as described, for example, in the publication cited at the beginning.

[0033] In the Figure 1 For the lowest phase conductor 31, the phase current indicator is marked with the reference symbol I A,L1 and the phase-to-earth voltage vector with the reference symbol U A,L1. For the other two phase conductors 32 and 33, the phase current indicators are marked with the reference symbols I A,L2 respectively IA,L3 and the phase-to-earth voltage vectors with the reference symbols U A,L2 respectively U A,L3 marked.

[0034] The Figure 2 shows components of an embodiment of the protective device 40 according to Figure 1 . The embodiment according to Figure 2 includes a preliminary stage 100 and a subsequent iteration stage 200.

[0035] The pre-stage 100 is equipped with a start module 110, a location calculation module 120 and a difference former 130.

[0036] The iteration stage 200 comprises an abort module 210, a sensitivity calculation module 220, a test module 230, a modification device 240 comprising a first modification module 241 and a second modification module 242, an increment module 250, a location calculation module 260, and a difference former 270.

[0037] The protective device 40 according to Figure 2preferably works as follows: After receiving a start signal S, the start module 110 initially sets a counting variable n to a start value n=0.

[0038] The location calculation module 120 then calculates a first fault location information Mm(n=0) using a fixed first compensation information Mc(n=0), which describes an estimated location, specified as a starting value for the protective device 40, where the fault could be located. Accordingly, the compensation information could also be referred to as an estimated location information.

[0039] The fault location information Mm and the compensation information Mc are preferably relative values ​​that indicate the distance of the fault from the measuring point – relative to the length of the line section. The first compensation information Mc(n=0) can, for example, be 0.5.

[0040] The calculation of the first fault location Mm(n=0) can be done, for example, as follows: Mm n = 0 = X n = 0 Im Z _ L with X n = 0 = sinφ ⋅ Im U _ A , Lx − U _ A , Ly ⋅ I _ A , Cmp ∗ ⋅ δ _ ∗ A , B ⋅ Mc n = 0 Im e jφ ⋅ I _ A , Lx − I _ A , Ly ⋅ I _ ∗ A , Cmp ⋅ δ _ ∗ A , B ⋅ Mc = 0 where Z L is the line impedance, ϕ is the line angle, I A,Cmp a compensation current, δ A,B a compensation factor, U A,Lx is the phase voltage phasor of the x-th phase measured by the protection device, I A,Lx is the phase current phasor measured by the protection device in the x-th phase, U A,Ly is the phase voltage phasor of the y-th phase measured by the protection device and I A,Ly denotes the phase current phasor in the y-th phase measured by the protection device.

[0041] The indices x and y can each be 1, 2 or 3 and denote the first, second or third phase, whereby for the calculation of the fault location in the embodiment it should apply that x is not equal to y, i.e. two different phases are used.

[0042] The values ​​for the compensation current I A,Cmp and the compensation factor δA,B are preferably calculated as described in the reference cited above (see, for example, formula 16 in Table 1 of the reference); in this regard, reference is made to the explanations therein.

[0043] The difference former 130 then calculates the difference D(n=0) between the calculated fault location information Mm(n=0) and the compensation information Mc(n=0) according to D n = 0 = Mm n = 0 − Mc n = 0

[0044] The difference D(n=0) is passed to the termination module 210 of iteration stage 200. Iteration stage 200 checks whether the magnitude of the difference D(n=0) falls below a predetermined difference threshold Dmax, so: D n = 0 < Dmax

[0045] If the difference D(n=0) is smaller than a difference threshold Dmax (see path Y), the calculated fault location information Mm(n=0) is output as the final location information Mfinal of the location procedure.

[0046] If, however, the difference D(n=0) is not smaller than the difference threshold Dmax, an additional check is performed to determine how often the error location Mm has already been calculated, i.e., the value of the counting variable n. If the counting variable n is greater than a specified maximum value Nmax, the following applies: n > Nmax , the calculated fault location information Mm(n=0) is output as the final location information Mfinal of the location procedure (see path Y); otherwise, iteration stage 200 is run through (see path N).

[0047] In the iteration stage 200, the sensitivity calculation module 220 will first calculate a sensitivity value E, preferably by deriving the fault location value Mm from the compensation value Mc according to E = dMm / dMc where E is the sensitivity value, Mm is the fault location value and Mc is the compensation value.

[0048] The sensitivity value E is preferably determined by numerical differentiation. For example, the fault location value can be calculated using two additional compensation values ​​Mc' and Mc", one of which is slightly larger than the current compensation value Mc(n) and the other slightly smaller, thus: Mc ' n = 1 + q ⋅ Mc n and Mc " n = 1 − q ⋅ Mc n where q is a constant greater than zero but much less than 1, for example 0.01.

[0049] The sensitivity calculation module 220 then receives two fault location specifications Mm(Mc'(n)) and Mm(Mc"(n)) and can calculate or estimate the sensitivity specification E according to: E = Mm Mc ' n − Mm Mc " n / 2 q

[0050] The sensitivity value E is sent to the test module 230, which checks whether the sensitivity value E falls below a predetermined sensitivity threshold Emax. The sensitivity threshold Emax is preferably 1 or at least approximately 1 (e.g., 1 ± 10%).

[0051] If the sensitivity value E falls below the specified sensitivity threshold Emax (see path Y), then E < Emax , the first modification module 241 carries out a modification method of the first type by modifying the previous compensation information to form a modified compensation information, depending on the last determined fault location information Mm(n).

[0052] Preferably, the first modification module 241 defines the last error location information Mm(n) determined in the previous location calculation method directly or unchanged as a modified compensation information for the next iteration step; the following then applies: Mc n + 1 = Mm n

[0053] However, if the sensitivity value E does not fall below the specified sensitivity threshold Emax (see path N), the second modification module 242 performs another modification method, i.e., a second-type modification method, whereby it calculates back how the compensation value Mc(n) should have been calculated in the last location calculation method in order to obtain the estimated location defined by the previous compensation value Mc(n) as the fault location value Mm(n). The second modification module 242 calculates the new or modified compensation value Mc(n+1), preferably by numerically solving the following formula: Mc n + 1 = X − 1 mc n ⋅ Im Z _ L with X n = sin φ ⋅ Im U _ A , Lx − U _ A , Ly ⋅ I _ ∗ A , Cmp ⋅ δ _ ∗ A , B ⋅ Mc n Im e jφ ⋅ I _ A , Lx − I _ A , Ly ⋅ I _ ∗ A , Cmp ⋅ δ _ ∗ A , B ⋅ Mc n

[0054] After the first modification module 241 or the second modification module 242 has calculated the new or modified compensation value Mc(n+1), the counting module 250 can increment the counting variable by one.

[0055] The location calculation module 260 then calculates - analogously to the location calculation module 120 - the error location information Mm(n) for the new superscript counting variable n according to: Mm n = X n Im Z _ L with X n = sin φ ⋅ Im U _ A , Lx − U _ A , Ly ⋅ I _ ∗ A , Cmp ⋅ δ _ ∗ A , B ⋅ Mc n Im e jφ ⋅ I _ A , Lx − I _ A , Ly ⋅ I _ ∗ A , Cmp ⋅ δ _ ∗ A , B ⋅ Mc n

[0056] The downstream difference former 270 then calculates - analogously to the difference former 130 - the difference D(n) between the calculated fault location information Mm(n) and the compensation information Mc(n) according to D n = Mm n − Mc n

[0057] The difference D(n) is returned to the termination module 210 of iteration stage 200, so that iteration stage 200 has now been completely run through.

[0058] The iteration procedure is repeated with the next iteration step, and iteration stage 200 is run through again if the termination module 210 so requests (see path N), i.e., if the absolute value of the difference D(n) does not yet fall below the predefined difference threshold Dmax or the counting variable n does not yet exceed the predefined maximum value Nmax; otherwise (see path Y), the current error location information Mm(n) of the last run of iteration stage 200 is output as the final error location information Mfinal.

[0059] The Figure 3shows the influence of the sensitivity value E on the convergence behavior of the iteration using three curves 300, 310 and 320; curve 300 shows a typical curve of the error location value Mm as a function of the compensation value Mc for a very small sensitivity value E (|E| << 1), curve 310 shows a typical curve for a small sensitivity value E (|E| < 1) and curve 320 shows a typical curve for a large sensitivity value E (|E| > 1).

[0060] For a small sensitivity value E with |E| < 1, the iteration converges based on the modification method of the first kind, and the smaller the magnitude of the sensitivity value E, the faster iteration converges.

[0061] If the sensitivity value is large in magnitude (|E| > 1), the iteration no longer converges based on the modification method of the first kind, but it converges based on the modification method of the second kind, and the larger the magnitude of the sensitivity value E, the faster the iteration converges.

[0062] In summary, by selecting a suitable modification method depending on the sensitivity specification E, convergence of the iteration can always be ensured.

[0063] The Figure 2The components shown, i.e. the start module 110, the location calculation module 120, the difference former 130, the abort module 210, the sensitivity calculation module 220, the test module 230, the first modification module 241, the second modification module 242, the increment module 250, the location calculation module 260 and the difference former 270, can be separate components, which can be formed, for example, by separate electronic components; alternatively, the aforementioned components can also be formed by software modules, as will be explained in more detail below in connection with Figure 4.

[0064] The Figure 4 shows a preferred software implementation of the Figure 2 The protective device 40 comprises a computing device 41 and a memory 42. In the memory 42, a software program product SW is stored, which, when executed by the computing device 41, carries out the functions described above in connection with the Figures 1 and 2 described calculation steps.

[0065] For this purpose, the software program product SW includes Figure 4 preferably a vector formation module ZBM for forming the phase current vectors I A,L1 , I A,L2 and I A,L3 and the phase-to-earth voltage vector U A,L1 , U A,L2 and U A,L3 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.

[0066] In addition, the software program product includes for each of the Figure 2shown components, i.e. the start module 110, the location calculation module 120, the difference former 130, the abort module 210, the sensitivity calculation module 220, the test module 230, the first modification module 241, the second modification module 242, the increment module 250, the location calculation module 260 and the difference former 270, each have a corresponding software module M110, M120, M130, M210, M220, M230, M241, M242, M250, M260 and M270, which when executed by the computing device 41 each implement the function of the respectively assigned component.

[0067] The invention is defined by the appended claims.

Claims

1. Method for locating a fault in a line section (30) of a three-phase electrical power transmission line, wherein, in the method, at least one iteration step is carried out, which comprises - a location calculation method in which a fault location indication (Mm) is determined taking into account an auxiliary indication, and - a modification method in which a modified auxiliary indication is formed, which enables the location calculation method to be repeated in order to form a new fault location indication (Mm), - wherein the iteration step is repeated as part of an iteration until a predetermined termination criterion is met, characterized in that - the auxiliary indication is a compensation indication (Mc) describing an estimated location where the fault could be located, and - at least two different modification methods are available and, in each iteration step, a check determines which of the modification methods is to be used in the respective iteration step, - wherein the selection of the modification method depends on a sensitivity indication (E) which quantitatively describes the influence of the compensation indication (Mc) on the fault location indication (Mm).

2. Method according to Claim 1, characterized in that the sensitivity indication (E) is calculated by deriving the fault location indication (Mm) according to the compensation indication (Mc) according to E = dMm / dMc wherein E denotes the sensitivity indication, Mm denotes the fault location indication and Mc denotes the compensation indication.

3. Method according to either one of the preceding claims, characterized in that the sensitivity indication (E) is determined by numerical differentiation.

4. Method according to any one of the preceding claims, characterized in that the modified compensation indication (Mc) is determined in each of the two modification methods depending on the last determined fault location indication (Mm).

5. Method according to any one of the preceding claims, characterized in that one of the at least two modification methods is a modification method of the first type, in which the last fault location indication (Mm) determined in the previous location calculation method is defined as the modified compensation indication (Mc) for the next iteration step.

6. Method according to Claim 5, characterized in that the modification method of the first type is selected in the respective iteration step if the sensitivity indication (E) is less than 1.

7. Method according to any one of the preceding claims, characterized in that one of the at least two modification methods is a modification method of the second type, in which - how the compensation indication (Mc) should have been dimensioned in the last location calculation method is recalculated in order to obtain the fault location indication (Mm) that was defined by the previous compensation indication (Mc), and - the compensation indication (Mc) recalculated in this way is defined as the new compensation indication (Mc) for the next iteration step.

8. Method according to Claim 7, characterized in that the modification method of the second type is selected in the respective iteration step if the sensitivity indication (E) is greater than 1.

9. Method according to any one of the preceding claims, characterized in that the iteration is repeated until the deviation between the sensitivity indication (E) and the compensation indication (Mc) falls below a specified threshold.

10. Method according to any one of the preceding claims, characterized in that the iteration is terminated if a specified maximum number of iteration steps has been performed.

11. Method according to any one of the preceding claims, characterized in that the fault location indication (Mm) and the compensation indication (Mc) are relative indications and define the distance between the fault and the measuring point in relation to the length of the line section (30).

12. Protective device (40) for locating a fault in a line section (30) of a three-phase electrical power transmission line, wherein the protective device (40) is designed to carry out at least one iteration step comprising - a location calculation method in which a fault location indication (Mm) is determined taking into account an auxiliary indication, and - a modification method in which a modified auxiliary indication is formed, which enables the location calculation method to be repeated in order to form a new fault location indication (Mm), - wherein the protective device (40) repeats the iteration step as part of an iteration until a predetermined termination criterion is met, characterized in that - the auxiliary indication is a compensation indication (Mc) describing an estimated location where the fault could be located, and - at least two different modification methods are available to the protective device (40) and the protective device (40) checks in each iteration step which of the modification methods is to be used in the respective iteration step, - wherein the selection of the modification method depends on a sensitivity indication (E) which quantitatively describes the influence of the compensation indication (Mc) on the fault location indication (Mm).