METHOD FOR LOCATING A FAULT POINT ON A HIGH-VOLTAGE THREE-PHASE AC CABLE, AND SYSTEM FOR LOCATING A FAULT POINT
20230324449 · 2023-10-12
Inventors
Cpc classification
G01R19/2513
PHYSICS
G01R31/52
PHYSICS
International classification
Abstract
Method for locating a fault point (F) on a high-voltage three-phase AC cable with single point connection system. The method includes the following steps: (a) determining the conductor (R, S, T) in fault based on previously measured conductor currents (I.sub.R1, I.sub.1S, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2). In the event the cable includes more than one section (P.sub.1, P.sub.2), determining section (P.sub.1, P.sub.2) in fault based on previously measured shield currents (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2). The fault point (F) being located by means of a model of section (P.sub.1, P.sub.2) in fault of the earth continuity conductor (ECC), the only unknown being the distance (x) to the fault point (F) from an end of said section (P.sub.1, P.sub.2) in fault.
Claims
1. A method for locating a fault point (F) on a high-voltage three-phase AC cable (1) comprising a first end (10), a second end (11), and at least one section (P.sub.1, P.sub.2) extending between the first and second ends (10, 11), the cable (1) comprising first, second and third conductors (R, S, T) and respective first, second and third shields (S.sub.R, S.sub.S, S.sub.T), the first, second and third shields (S.sub.R, S.sub.S, S.sub.T) being connected to a surge arrester device (3, 4) connected to ground (G) at one end of the at least one section (P.sub.1, P.sub.2), the first, second and third shields (S.sub.R, 5S, S.sub.T) being connected to a grounding element (2) at the other end of said at least one section (P.sub.1, P.sub.2), the cable (1) comprising an earth continuity conductor (ECC) establishing a common ground (G) connecting the ground connections (20, 30, 40) of the grounding element(s) and the surge arrester device(s) (3, 4), the method comprising: measuring the conductor current (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2) circulating through each of the first, second and third conductors (R, S, T) both at the first end (10) and at the second end (11) of the cable (1); measuring the shield current (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2) circulating through each of the first, second and third shields (S.sub.R, S.sub.S, S.sub.T) in each section (P.sub.1, P.sub.2) at a point close to the grounding element; measuring the earth continuity conductor current (I.sub.ECC1, I.sub.ECC2) circulating through each section (P.sub.1, P.sub.2) at a point close to the grounding element; determining a conductor (R, S, T) in fault based on the previously measured conductor currents (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2); in the event that the cable (1) comprises more than one section (P.sub.1, P.sub.2), determining section (P.sub.1, P.sub.2) in fault based on the previously measured shield currents (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2); and locating the fault point (F) by means of a model of section (P.sub.1, P.sub.2) in fault of the earth continuity conductor (ECC), the only unknown being the distance (x) to the fault point (F) from an end of said section (P.sub.1, P.sub.2) in fault.
2. The method according to claim 1, wherein for determining the conductor (R, S, T) in fault, the conductor current (I.sub.R1; I.sub.S1; I.sub.T1) measured at the first end (10) of the cable (1) for each of the first, second and third conductors (R, S, T) is compared with the conductor current (I.sub.R2; I.sub.S2; I.sub.T2) measured at the second end (11) of the cable (1), determining that the conductor (R, S, T) in fault being the conductor in which the conductor current (I.sub.R, I.sub.R2; I.sub.S1, I.sub.S2; I.sub.T1, I.sub.T2) at the ends (10, 11) is different.
3. The method according to claim 1, wherein the cable (1) comprises at least two sections (P.sub.1, P.sub.2), section (P.sub.1, P.sub.2) in fault being determined taking into account that in said section in fault (P.sub.1, P.sub.2), one of the shield currents (I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2) will have an overcurrent value.
4. The method according to claim 1, wherein the model of the earth continuity conductor (ECC) of section (P.sub.1, P.sub.2) in fault takes into account the self-resistance (R.sub.ECC) and the self-inductance (L.sub.ECC) of the earth continuity conductor (ECC), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4), the mutual inductance (M.sub.R, M.sub.S, M.sub.T) between said earth continuity conductor (ECC) and each of the first, second and third conductors (R, S, T), and the mutual inductance (M.sub.SR, M.sub.SS, M.sub.ST) between said earth continuity conductor (ECC) and the shield in fault (S.sub.R, S.sub.S, S.sub.T) from the fault point (F) to the point where the shields are connected to ground (G).
5. The method according to claim 4, wherein the location of the fault point is calculated using the following formula:
0=I.sub.ECCF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCNFRR.sub.g−I.sub.ECCNFRR.sub.g+jwxl.sub.CNF1M.sub.CNF1+jwxl.sub.CNF2M.sub.CNF2+jwxl.sub.CF1M.sub.CF+jw(1−X)I.sub.CNF1M.sub.CNF1+jw(1−X)I.sub.CNF2M.sub.CNF2−jw(1−X)I.sub.CF2M.sub.CF+jw(1−X)I.sub.SFM.sub.SF wherein, I.sub.ECCF=The current circulating through the section of the earth continuity conductor (ECC) which is in fault, I.sub.ECCNFL=The current circulating through the section of the earth continuity conductor (ECC) to the left of the section in fault; in the event that there is no section to the left of the section in fault its value will be zero, I.sub.ECCNFR=The current circulating through the section of the earth continuity conductor (ECC) to the right of the section in fault; in the event that there is no section to the right of the section in fault its value will be zero, R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device, R.sub.ECC=The self-resistance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), L.sub.ECC=The self-inductance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), I.sub.CNF1=Current circulating through a first conductor which is not in fault, both at the first end (10) of the cable (1) and at the second end (11) of the cable (1), I.sub.CNF2=Current circulating through a second conductor which is not in fault, both at the first end (10) of the cable (1) and at the second end (11) of the cable (1), I.sub.CF1=Current circulating through the conductor in fault at the first end (10) of the cable (1), I.sub.CF2=Current circulating through the conductor in fault at the second end (11) of the cable (1),
I.sub.CF1≠I.sub.CF2 I.sub.SF=Current circulating through the shield in fault in the section in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.SF=Mutual inductance between the shield which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), and x=The distance to the fault point from the end of the section in fault at which the surge arrester device is arranged to the fault point (F).
6. The method according to claim 4, wherein when the cable (1) comprises more than one section (P.sub.1, P.sub.2), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4) is determined by means of a model of the earth continuity conductor (ECC) of one of the sections (P.sub.1, P.sub.2) which is not in fault, said model comprising the self-resistance (R.sub.ECC) and the self-inductance (L.sub.ECC) of the earth continuity conductor (ECC), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4), the mutual inductance (M.sub.R, M.sub.S, M.sub.T) between said earth continuity conductor (ECC) and each of the conductors (R, S, T), the only unknown being said ground resistance (R.sub.g).
7. The method according to claim 5, wherein when the cable (1) comprises more than one section (P.sub.1, P.sub.2), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4) is determined by means of a model of the earth continuity conductor (ECC) of one of the sections (P.sub.1, P.sub.2) which is not in fault, said model comprising the self-resistance (R.sub.ECC) and the self-inductance (L.sub.ECC) of the earth continuity conductor (ECC), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4), the mutual inductance (M.sub.R, M.sub.S, M.sub.T) between said earth continuity conductor (ECC) and each of the conductors (R, S, T), the only unknown being said ground resistance (R.sub.g).
8. The method according to claim 6, wherein the ground resistance (R.sub.g) is calculated using the following formula:
0=I.sub.ECCNF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCLR.sub.g−I.sub.ECCRR.sub.g+jwI.sub.CNF1M.sub.CNF1+jwI.sub.CNF2M.sub.CNF2+jwI.sub.CFM.sub.CF wherein, I.sub.ECCNF=The current circulating through the section which is not in fault the model of which is used to calculate ground resistance (R.sub.g), I.sub.ECCL=The current circulating through the section to the left of the section which is not in fault; in the event that there is no section to the left of the section which is not in fault, its value will be zero, I.sub.ECCR=The current circulating through the section to the right of the section which is not in fault; in the event that there is no section to the right of the section which is not in fault, its value will be zero, R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device at one of the ends of the section in fault, R.sub.ECC=The self-resistance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), L.sub.ECC=The self-inductance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), I.sub.CNF1=Current circulating through a first conductor which is not in fault at the first end (10) of the cable (1), I.sub.CNF2=Current circulating through a second conductor which is not in fault at the first end (10) of the cable (1), I.sub.CF=Current circulating through the conductor in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), and M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable 1.
9. The method according to claim 7, wherein the ground resistance (R.sub.g) is calculated using the following formula:
0=I.sub.ECCNF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCLR.sub.g−I.sub.ECCRR.sub.g+jwI.sub.CNF1M.sub.CNF1+jwI.sub.CNF2M.sub.CNF2+jwI.sub.CFM.sub.CF wherein, I.sub.ECCNF=The current circulating through the section which is not in fault the model of which is used to calculate ground resistance (R.sub.g), I.sub.ECCL=The current circulating through the section to the left of the section which is not in fault; in the event that there is no section to the left of the section which is not in fault, its value will be zero, I.sub.ECCR=The current circulating through the section to the right of the section which is not in fault; in the event that there is no section to the right of the section which is not in fault, its value will be zero, R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device at one of the ends of the section in fault, R.sub.ECC=The self-resistance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), L.sub.ECC=The self-inductance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), I.sub.CNF1=Current circulating through a first conductor which is not in fault at the first end (10) of the cable (1), I.sub.CNF2=Current circulating through a second conductor which is not in fault at the first end (10) of the cable (1), I.sub.CF=Current circulating through the conductor in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), and M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable 1.
10. The method according to claim 4, wherein when the cable (1) comprises a single section (P.sub.1) the ground resistance (R.sub.g) of the ground connections (20, 30) of the grounding element and the surge arrester device (3) is estimated.
11. The method according to claim 5, wherein when the cable (1) comprises a single section (P.sub.1) the ground resistance (R.sub.g) of the ground connections (20, 30) of the grounding element and the surge arrester device (3) is estimated.
12. A system for locating a fault point (F) on a high-voltage three-phase AC cable (1) comprising a first end (10) and a second end (11) and at least one section (P.sub.1, P.sub.2) extending between said ends (10, 11), the cable (1) comprising first, second and third conductor (R, S, T) and respective first, second and third shield (S.sub.R, S.sub.S, S.sub.T), the first, second and third shields (S.sub.R, S.sub.S, S.sub.T) being connected to a surge arrester device (3, 4) connected to ground (G) at one end of said at least one section (P.sub.1, P.sub.2) and the first, second and third shields (S.sub.R, S.sub.S, S.sub.T) being connected to a grounding element at the other end of said at least one section (P.sub.1, P.sub.2), the cable (1) comprising an earth continuity conductor (ECC) establishing a common ground (G) connecting the ground connections (20, 30, 40) of the grounding element(s) (2) and the surge arrester device(s) (3, 4), the system comprising: first current measuring equipment (5) configured for measuring the conductor current (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2) circulating through each of the first, second and third conductors (R, S, T) both at the first end (10) and at the second end (11) of the cable (1); second current measuring equipment (6) configured for measuring the shield current (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2) of each of the first, second and third shields (S.sub.R, S.sub.S, S.sub.T) in each section (P.sub.1, P.sub.2) at a point close to the grounding element; third current measuring equipment (7) configured for measuring the earth continuity conductor current (I.sub.ECC1, I.sub.ECC2) of the earth continuity conductor (ECC) in each section (P.sub.1, P.sub.2) at a point close to the grounding element (2); and a computer configured for executing the method according to any of claims 1 to 11 based on the current measurements performed by said first, second and third current measuring equipment (5, 6, 7).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
[0027]
[0028]
[0029]
DETAILED DESCRIPTION
[0030] A first aspect of the invention relates to a method for locating a fault point F on a high-voltage three-phase AC cable 1.
[0031] The method of the invention is configured for locating a fault point F on a cable 1 extending between a first end 10 and a second end 11, said cable 1 comprising at least one section P.sub.1, P.sub.2 extending between said ends 10, 11. The cable 1 comprises one conductor R, S, T per phase and a shield S.sub.R, S.sub.S, S.sub.T associated with each conductor R, S, T.
[0032] As discussed above, fault point F is considered the point where one of the conductor R, S, T, of the cable 1 has electrical contact with the corresponding shield S.sub.R, S.sub.S, S.sub.T, such that a short circuit occurs between said conductor R, S, T and the corresponding shield at said fault point F. Furthermore, in the context of the invention, section in fault will be considered section P.sub.1, P.sub.2 of cable 1 at which the fault point F is arranged.
[0033] The method of the invention is configured for being applied on cables 1 with single point connection systems, i.e., on cables 1 in which the shields S.sub.R, S.sub.S, S.sub.T are connected to a surge arrester device 3, 4 connected to ground G at one end of each section P.sub.1, P.sub.2, shields S.sub.R, S.sub.S, S.sub.T being connected to a grounding element at the other end of each section P.sub.1, P.sub.2.
[0034] Cables 1 of this type with single point connection systems comprise an earth continuity conductor ECC establishing a common ground G of the system connecting the ground connection(s) 20 of the grounding element(s) and the ground connection(s) 30, 40 of the surge arrester device(s) 3, 4 of the cable 1.
[0035] The method of the invention comprises the following steps: [0036] measuring the conductor current I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2 circulating through each conductor R, S, T both at the first end 10 and at the second end 11 of the cable 1, [0037] measuring the shield current I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2 circulating through each shield S.sub.R, S.sub.S, S.sub.T in each section P.sub.1, P.sub.2 at a point close to the grounding element 2, [0038] measuring the earth continuity conductor current I.sub.ECC1, I.sub.ECC2 circulating through each section P.sub.1, P.sub.2 at a point close to the grounding element 2, [0039] determining the conductor R, S, T in fault based on the previously measured conductor currents I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2, [0040] in the event that the cable 1 comprises more than one section P.sub.1, P.sub.2, determining section P.sub.1, P.sub.2 in fault based on the previously measured shield currents I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2, and [0041] locating the fault point F by means of a model of section P.sub.1, P.sub.2 in fault of the earth continuity conductor ECC, the only unknown being the distance x to the fault point F from an end of said section P.sub.1, P.sub.2 in fault.
[0042] Preferably, for determining the conductor R, S, T in fault, the conductor current I.sub.R1; Isi; I.sub.T1 measured at the first end 10 of the cable 1 for each conductor R, S, T is compared with the conductor current I.sub.R2; I.sub.S2; I.sub.S2 measured at the second end 11 of the cable 1, determining that the conductor R, S, T in fault will be the conductor in which the conductor current I.sub.R1, I.sub.R2; I.sub.S1, I.sub.S2; I.sub.T1, I.sub.T2 at said ends 10, 11 is different.
[0043] Preferably, for determining section P.sub.1, P.sub.2 in fault, the shield currents I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2, of each section P.sub.1, P.sub.2 are analysed, determining that section P.sub.1, P.sub.2 in fault will be the conductor in which one of the shield currents I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2 has an overcurrent value. The shield current I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2 circulating through the shields S.sub.R, S.sub.S, S.sub.T when there is no fault is a low-value eddy current, for example a current of up to 10 A. However, when a fault occurs, an overcurrent that is much higher than the eddy current, for example a current higher than 10,000 A, circulates through the corresponding shield S.sub.R, S.sub.S, S.sub.T. Therefore, when a fault occurs, simply looking at the shield currents I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2 of each section P.sub.1, P.sub.2 is sufficient to determine which of the sections P.sub.1, P.sub.2 is in fault. It should be pointed out that since each section P.sub.1, P.sub.2 is connected at one of its ends to ground G, the overcurrent circulating through the shield S.sub.R, S.sub.S, S.sub.T in fault circulates towards ground G such that the rest of the sections P.sub.1, P.sub.2 are not affected by said fault.
[0044] Preferably, the model of the earth continuity conductor ECC of section P.sub.1, P.sub.2 in fault takes into account the self-resistance R.sub.ECC and the self-inductance L.sub.ECC of the earth continuity conductor ECC, the ground resistance R.sub.g of the ground connections 20, 30, 40 of the grounding element and the corresponding surge arrester device 3, 4, the mutual inductance M.sub.R, M.sub.S, M.sub.T between said earth continuity conductor ECC and each of the conductors R, S, T, and the mutual inductance M.sub.SR, M.sub.SS, M.sub.ST between said earth continuity conductor ECC and the shield in fault S.sub.R, S.sub.S, S.sub.T from the fault point F to the point where the shields are connected to ground G.
[0045] Determining the parameters of the model can be accomplished through the use of an electromagnetic transients simulator (EMT simulator) which estimates parameters based on the features of the cable 1 (i.e., layers, thickness, material, etc.), the arrangement of said cable 1 (i.e., depth, separation, etc.) and the features of the land where it is disposed. For example, the EMT simulator PSCAD™ manufactured by PSCAD can be used. See pscad.com.
[0046] When defining the model of the earth continuity conductor ECC, values relevant for the purpose of current have been taken into account, and capacitive inputs have been disregarded since they are of little value in fault situations.
[0047] Furthermore, mutual inductance between the shields S.sub.R, S.sub.S, S.sub.T which are not in fault and earth continuity conductor ECC have been ignored for defining the model since they input scarcely any coupling on the cable ECC and are therefore negligible values, and the same occurs with the shield in fault to fault point F.
[0048] Preferably, the location of the fault point is calculated using the following formula:
0=I.sub.ECCF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCNFRR.sub.g−I.sub.ECCNFRR.sub.g+jwxl.sub.CNF1M.sub.CNF1+jwxl.sub.CNF2M.sub.CNF2+jwxl.sub.CF1M.sub.CF+jw(1−X)I.sub.CNF1M.sub.CNF1+jw(1−X)I.sub.CNF2M.sub.CNF2−jw(1−X)I.sub.CF2M.sub.CF+jw(1−X)I.sub.SFM.sub.SF
wherein, [0049] I.sub.ECCF=The current circulating through the section that is in fault, [0050] I.sub.ECCNFL=The current circulating through the section which is not in fault to the left of the section in fault; in the event that there is no section to the left of the section in fault its value will be zero, [0051] I.sub.ECCNFR=The current circulating through the section which is not in fault to the right of the section in fault; in the event that there is no section to the right of the section in fault its value will be zero, [0052] R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device at one of the ends of the section in fault, [0053] R.sub.ECC=The self-resistance of the earth continuity conductor ECC of the section in fault, calculated taking into account the characteristics of the cable 1, [0054] L.sub.ECC=The self-inductance of the earth continuity conductor ECC of the section in fault, calculated taking into account the characteristics of the cable 1, [0055] I.sub.CNF1=Current circulating through a first conductor which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0056] I.sub.CNF2=Current circulating through a second conductor which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0057] I.sub.CF1=Current circulating through the conductor in fault at the first end 10 of the cable 1, [0058] I.sub.CF2=Current circulating through the conductor in fault at the second end 11 of the cable 1,
I.sub.CF1≠I.sub.CF2 [0059] I.sub.SF=Current circulating through the shield in fault in the section in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, [0060] M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0061] M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor EC, is calculated taking into account the characteristics of the cable 1, [0062] M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0063] M.sub.SF=Mutual inductance between the shield which is in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, and x=The distance to the fault point from the end of section P.sub.1 in fault at which the surge arrester device is arranged to the fault point F.
[0064] Preferably when the cable 1 comprises more than one section P.sub.1, P.sub.2, ground resistance R.sub.g is determined by means of a model of the earth continuity conductor ECC of a section P.sub.1, P.sub.2 which is not in fault, said model comprising the self-resistance R.sub.ECC and the self-inductance L.sub.ECC of the earth continuity conductor ECC, the ground resistance R.sub.g of the ground connections 20, 30, 40 of the grounding element and the corresponding surge arrester device 3, 4, the mutual inductance M.sub.R, M.sub.S, M.sub.T between said earth continuity conductor ECC and each of the conductors R, S, T, the only unknown being said ground resistance R.sub.g.
[0065] Preferably, ground resistance R.sub.g is calculated by means of the following formula:
0=I.sub.ECCNF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCLR.sub.g−I.sub.ECCRR.sub.g+jwI.sub.CNF1M.sub.CNF1+jwI.sub.CNF2M.sub.CNF2+jwI.sub.CFM.sub.CF
wherein, [0066] I.sub.ECCNF=The current circulating through the section which is not in fault the model of which is used to calculate ground resistance R.sub.g, [0067] I.sub.ECCL=The current circulating through the section to the left of the section the model of which is used to calculate ground resistance R.sub.g; in the event that there is no section to the left its value will be zero, [0068] I.sub.ECCR=The current circulating through the section to the right of the section the model of which is used to calculate ground resistance R.sub.g; in the event that there is no section to the right its value will be zero, [0069] R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device at one of the ends of the section in fault, [0070] R.sub.ECC=The self-resistance of the earth continuity conductor ECC of the section the model of which is used to calculate ground resistance R.sub.g, calculated taking into account the characteristics of the cable 1, [0071] L.sub.ECC=The self-inductance of the earth continuity conductor ECC of the section the model of which is used to calculate ground resistance R.sub.g, calculated taking into account the characteristics of the cable 1, [0072] I.sub.CNF1=Current circulating through a first conductor which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0073] I.sub.CNF2=Current circulating through a second conductor which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0074] I.sub.CF=Current circulating through the conductor in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, [0075] M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0076] M.sub.CNF=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, and [0077] M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1.
[0078] Conversely, when the cable 1 comprises a single section P.sub.1, preferably the ground resistance R.sub.g of the ground connections 20, 30 of the grounding element and the surge arrester device 3 is estimated, for example, taking into account parameters such as: ground humidity, ground temperature, etc.
[0079] A second aspect of the invention relates to a system for locating a fault point F on a high-voltage three-phase AC cable 1.
[0080] The system of the invention is configured for locating a fault point F on a cable 1 extending between a first end 10 and a second end 11, comprising said cable 1 at least one section P.sub.1, P.sub.2 extending between said ends 10, 11. The cable 1 comprises one conductor R, S, T per phase and a shield S.sub.R, S.sub.S, S.sub.T associated with each conductor R, S, T.
[0081] The system of the invention is configured for being applied on cables 1 with single point connection systems, i.e., on cables 1 in which the shields S.sub.R, S.sub.S, S.sub.T are connected to a surge arrester device 3, 4 connected to ground G at one end of each section P.sub.1, P.sub.2, being the shields S.sub.R, S.sub.S, S.sub.T connected to a grounding element at the other end of each section P.sub.1, P.sub.2. Cables 1 of this type with single point connection systems comprise an earth continuity conductor ECC establishing a common ground G of the system connecting the ground connection(s) 20 of the grounding element(s) and the ground connection(s) 30, 40 of the surge arrester device(s) 3, 4 of the cable 1.
[0082] The system of the invention comprises a first current measuring equipment 5 configured for measuring the conductor current I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2 circulating through each conductor R, S, T both at the first end 10 and at the second end 11 of the cable 1.
[0083] The system of the invention also comprises a second current measuring equipment 6 configured for measuring the shield current I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2 of each shield S.sub.R, S.sub.S, S.sub.T in each section P.sub.1, P.sub.2 at a point close to the grounding element 2.
[0084] Furthermore, the system of the invention also comprises a third current measuring equipment 7 configured for measuring the earth continuity conductor current I.sub.ECC1, I.sub.ECC2 of the earth continuity conductor ECC in each section P.sub.1, P.sub.2 at a point close to the grounding element 2.
[0085] The system of the invention comprises a computer configured for executing the method described in the first aspect of the invention based on the current measurements performed by said current measuring equipment 50, 51, 52, 53, 54, 55, 60, 61, 62, 63, 64, 65, 70, 71.
[0086] In at least one embodiment, the computer used to implement the method of the invention may include one or more processors, one or more memory elements, storage, a bus, one or more network processing units interconnected with one or more network input/output (I/O) interfaces, one or more I/O interfaces, and a computer program.
[0087] The computer program comprises a plurality of instructions which, when executed by the processor, cause the processor to execute the steps of the method of the invention. In at least one embodiment, the processor or processors are at least a hardware processor configured to execute various tasks, operations and/or functions for the computer according to the software and/or the instructions configured for the computer, for example, in the computer program.
[0088] In at least one embodiment, the memory element and/or storage are configured to store data, information, software, and/or instructions associated with the computer, and/or the logic configured for the memory element and/or storage. In an embodiment of the computer, the computer program is stored in any combination of memory element(s) and/or storage.
[0089] In at least one embodiment, the bus can be configured as an interface that enables one or more elements of the computer to communicate with each other so as to exchange information and/or data. The bus can be implemented with any architecture designed for exchanging control, data, and/or information between processors, memory elements/storage, peripheral devices, and/or any other hardware and/or software component that may be configured for the computer.
[0090] In several embodiments, the network processor unit(s) may enable communication between the computer and other systems, entities, etc., through the network I/O interface(s) (wired and/or wireless). In several embodiments, the network processor unit(s) can be configured as a combination of hardware and/or software, as one or more Ethernet drivers and/or controllers or interface cards, fibre channel (e.g., optical) driver(s) and/or controller(s), wireless receivers/transmitters/transceivers, baseband processor(s)/modem(s) and/or other similar network interface driver(s) and/or controller(s) that are known now or may be developed hereinafter so as to enable communications between the computer and other systems, entities, etc., to facilitate the operations for the various embodiments of the method described herein. In several embodiments, the network VO interface(s) can be configured as one or more Ethernet ports, fibre channel ports, any other I/O port(s) and/or antennas/antenna array that are known now or may be developed in the future. Therefore, the network processor unit(s) and/or the network VO interface(s) may include suitable interfaces for receiving, transmitting, and/or otherwise communicating data and/or information in a network environment.
[0091] I/O interfaces allow the input and output of data and/or information with other entities which may be connected to the computer. For example, the VO interfaces may provide a connection to external devices such as a keyboard, numerical keypad, a touch screen, and/or any other suitable input and/or output device that is known now or may be developed in the future. In some instances, the external devices can also include (non-transitory) computer-readable storage media such as database systems, USB memories, portable optical or magnetic discs and memory cards. In still some instances, the external devices can be a mechanism for displaying data to a user, such as a computer monitor, a display screen, or the like.
[0092]
[0093] The cable 1 according to the first configuration comprises one conductor R, S, T per phase and a shield S.sub.R, S.sub.S, S.sub.T associated with each conductor R, S, T and it extends between a first end 10 and a second end 11.
[0094] Furthermore, the cable 1 according to the first configuration has a single point connection system, the connection to ground G of the shields S.sub.R, S.sub.S, S.sub.T being performed at an intermediate point 12 by means of a grounding element, with the cable 1 being divided into two sections P.sub.1, P.sub.2. Furthermore, the shields S.sub.R, S.sub.S, S.sub.T are connected to a surge arrester device 3, 4 connected to ground G both at the first end 10 and at the second end 11 of the cable 1.
[0095] The cable 1 according to the first configuration also comprises an earth continuity conductor ECC connecting the ground connection 20 of the grounding element and the ground connections 30, 40 of the devices surge arrester 3, 4 establishing a common ground G of the system.
[0096] In the first embodiment, the system comprises a first current measuring equipment 5 configured for measuring the conductor current I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2 circulating through each conductor R, S, T both at the first end 10 and at the second end 11 of the cable 1. As shown in
[0097] In the first embodiment, the system comprises a second current measuring equipment 6 configured for measuring the shield current I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2 of each shield S.sub.R, S.sub.S, S.sub.T in each section P.sub.1, P.sub.2 at a point close to the grounding element. As shown in
[0098] Furthermore, in the first embodiment the system comprises a third current measuring equipment 7 configured for measuring the earth continuity conductor current I.sub.ECC1, I.sub.ECC2 of the earth continuity conductor ECC in each section P.sub.1, P.sub.2 at a point close to the grounding element. As shown in
[0099] The system of the invention comprises a computer, not shown in the figures, configured for executing the method of the invention based on the current measurements performed by said current measuring equipment 50, 51, 52, 53, 54, 55, 60, 61, 62, 63, 64, 65, 70, 71.
[0100] A fault between the conductor T and its shield S.sub.T in the first section P.sub.1 has been depicted in
[0101] Measuring the conductor current I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2 circulating through each conductor R, S, T both at the first end 10 and at the second end 11 of the cable 1 by means of the first current measuring equipment 5.
[0102] Also, measuring the shield current I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2 circulating through each shield S.sub.R, S.sub.S, S.sub.T in each section P.sub.1, P.sub.2 at a point close to the grounding element by means of the second current measuring equipment 6. Also, measuring the earth continuity conductor current I.sub.ECC circulating through each section P.sub.1, P.sub.2 at a point close to the grounding element by means of the third current measuring equipment.
[0103] Comparing the conductor current I.sub.R1; I.sub.S1; I.sub.T1 measured at the first end 10 of the cable 1 for each conductor R, S, T with the conductor current I.sub.R2; I.sub.S2; T.sub.2 measured at the second end 11 of the cable 1. In this case, the conductor current I.sub.R1 of the conductor T at the first end 10 of the cable 1 will be different from the conductor current I.sub.R2 at the first end 11, such that it will be determined that conductor T is the conductor which is in fault.
[0104] Also, analysing the shield currents I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2 of each section P.sub.1, P.sub.2. In this case, the shield current I.sub.ST1 will be observed as having an overcurrent value, determining that section P.sub.1 is the section which is in fault.
[0105] Once conductor T in fault and section P.sub.1 in fault have been determined, defining the model of the earth conductor ECC shown in
[0106] The net representing section P.sub.2 which is not in fault comprises the self-resistance R.sub.ECC and the self-inductance L.sub.ECC of the earth continuity conductor ECC, the ground resistance R.sub.gm, R.sub.g2 of the ground connections 20, 40 of the grounding element and the surge arrester device 4, and the mutual inductance M.sub.R, M.sub.S, M.sub.T between said earth continuity conductor ECC and each of the conductors R, S, T. Therefore, all the parameters of the net of section P.sub.2 which is not in fault can be calculated by knowing the characteristics of the cable 1, the conductor currents I.sub.R2, I.sub.S2, 1T.sub.2 circulating through the conductor R, S, T at the second end 11 of the cable 1, and the earth continuity conductor currents ECC I.sub.ECC1, I.sub.ECC2 circulating through both sections P.sub.1, P.sub.2, the only unknown being the ground resistances R.sub.gm, R.sub.g2. All the ground resistances R.sub.g, R.sub.g2, R.sub.gm, R.sub.g2 of the model of the earth conductor ECC are considered equal.
[0107] Therefore, in this case ground resistance R is calculated using the following formula:
0=I.sub.ECC2(R.sub.g2+R.sub.gm+R.sub.ECC+jwL.sub.ECC)−I.sub.ECC1R.sub.gm−jwI.sub.R2M.sub.R−jwI.sub.S2M.sub.S−jwI.sub.T2M.sub.T
wherein, [0108] I.sub.ECC1=The current circulating through section P.sub.1 which is in fault, [0109] I.sub.ECC2=The current circulating through section P.sub.2 which is not in fault, [0110] R.sub.gm=The ground resistance of the grounding device 2, [0111] R.sub.g2=The ground resistance of the surge arrester device 4 arranged at the second end 11 of the cable 1, [0112] R.sub.ECC=The self-resistance of the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0113] L.sub.ECC=The self-inductance of the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0114] I.sub.R2=Current circulating through the conductor R which is not in fault at the second end 11 of the cable 1, [0115] I.sub.S2=Current circulating through the conductor S which is not in fault at the second end 11 of the cable 1, [0116] I.sub.T2=Current circulating through the conductor T which is in fault at the second end 11 of the cable 1, [0117] M.sub.R=Mutual inductance between the conductor R and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0118] M.sub.S=Mutual inductance between the conductor S and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, and [0119] M.sub.T=Mutual inductance between the conductor T and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1.
[0120] The net representing section P.sub.1 in fault comprises the self-resistance R.sub.ECC and the self-inductance L.sub.ECC of the earth continuity conductor ECC, the ground resistance R.sub.g of the ground connection 20 of the grounding element and of the ground connection 30 of the surge arrester device 3, the mutual inductance M.sub.R, M.sub.S, M.sub.T between said earth continuity conductor ECC and each of the conductors R, S, T, and the mutual inductance M.sub.ST between said earth continuity conductor ECC and the shield S.sub.T in fault from the fault point F to the point where the shields are connected to ground G. Taking into account that the ground resistance R.sub.g is obtained from the net of section P.sub.2 which is not in fault, all the parameters of the net of section P.sub.1 in fault can be calculated by knowing the characteristics of the cable 1, the conductor currents I.sub.R1, I.sub.S1, I.sub.T1 circulating through the conductor R, S, T at the first end 1 of the cable 1, the shield current I.sub.ST1 circulating through the shield S.sub.T in fault in section P.sub.1 in fault and the currents of earth continuity conductor ECC I.sub.ECC1, I.sub.ECC2 circulating through both sections P.sub.1, P.sub.2, the only unknown being the distance x to the fault point F.
[0121] Therefore, the location of the fault point is calculated using the following formula:
0=I.sub.ECC1(R.sub.g1+R.sub.gm+R.sub.ECC+jwL.sub.ECC)−I.sub.ECC2R.sub.gm+jwxI.sub.RM.sub.R+jwxI.sub.SM.sub.S+jwxI.sub.T1M.sub.T++jw(1−x)I.sub.RM.sub.R+jw(1−x)I.sub.SM.sub.S−jw(1−x)I.sub.T2M.sub.T+jw(1−x)I.sub.STM.sub.ST
wherein, [0122] I.sub.ECC1=The current circulating through section P.sub.1 which is in fault, [0123] I.sub.ECC2=The current circulating through section P.sub.2 which is not in fault, [0124] R.sub.g1=The ground resistance of the surge arrester device 3 arranged at the first end 10 of the cable 1, [0125] R.sub.gm=The ground resistance of the grounding device 2, [0126] R.sub.ECC=The self-resistance of the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0127] L.sub.ECC=The self-inductance of the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0128] I.sub.R=I.sub.R1=I.sub.R2=Current circulating through the conductor R which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0129] I.sub.S=I.sub.S1=I.sub.S2=Current circulating through the conductor S which is not in fault, both at the first end 10 of the cable 1 and at the second end 11 of the cable 1, [0130] I.sub.T1=Current circulating through the conductor T which is in fault at the first end 10 of the cable 1, [0131] I.sub.T2=Current circulating through the conductor T which is in fault at the second end 11 of the cable 1,
I.sub.T1≠I.sub.T2 [0132] I.sub.ST=Current circulating through the shield S.sub.T in fault in section P.sub.1 in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, [0133] M.sub.R=Mutual inductance between the conductor R and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0134] M.sub.S=Mutual inductance between the conductor S and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0135] M.sub.T=Mutual inductance between the conductor T and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, [0136] M.sub.ST=Mutual inductance between the shield S.sub.T in fault and the earth continuity conductor ECC, calculated taking into account the characteristics of the cable 1, and x=The distance to the fault point from the end of section P.sub.1 in fault at which the surge arrester device is arranged to the fault point F.
[0137]
[0138] The cable 1 according to the first configuration comprises one conductor R, S, T per phase and a shield S.sub.R, S.sub.S, S.sub.T associated with each conductor R, S, T and extends between a first end 10 and a second end 11.
[0139] Furthermore, the cable 1 according to the first configuration has a single point connection system, the connection to ground G of the shields S.sub.R, S.sub.S, S.sub.T being performed at the first end 10 of the cable 1, with shields S.sub.R, S.sub.S, S.sub.T being connected to a surge arrester device 4 connected to ground G at the second end 11 of the cable 1. The cable 1 thereby comprises a single section P.sub.1.
[0140] The cable 1 according to the first configuration also comprises an earth continuity conductor ECC connecting the ground connection 20 of the grounding element and the connection 40 of the surge arrester device 4 establishing a common ground G of the system.
[0141] In the second embodiment, the system comprises a first current measuring equipment 5 configured for measuring the conductor current I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2 circulating through each conductor R, S, T both at the first end 10 and at the second end 11 of the cable 1. The first current measuring equipment 5 comprises six current sensors 50, 51, 52, 53, 54, 55, with one current sensor 50, 51, 52, 53, 54, 55 being arranged at each end of each conductor R, S, T.
[0142] In the second embodiment, the system comprises a second current measuring equipment 6 configured for measuring the shield current I.sub.SR1, I.sub.SS1, I.sub.ST1 of each shield S.sub.R, 5S, S.sub.T at a point close to the grounding element 2. The second current measuring equipment 5 comprises three current sensors 60, 61, 62, with one current sensor 60, 61, 62 being arranged in each shield S.sub.R, S.sub.S, S.sub.T at a point close to the grounding element 2.
[0143] Furthermore, in the second embodiment the system comprises a third current measuring equipment 7 configured for measuring the earth continuity conductor current I.sub.ECC1 of the earth continuity conductor ECC at a point close to the grounding element 2. The third current measuring equipment 7 comprises a single current sensor 70 arranged at a point close to the grounding element 2.
[0144] The system of the invention comprises a computer, not shown in the figures, configured for executing the method of the invention based on the current measurements performed by said current measuring equipment 50, 51, 52, 53, 54, 55, 60, 61, 62, 70.
[0145] The method of the invention would be applied in a manner similar to that explained for the first embodiment, with the main difference being the obligation to estimate the value of the ground resistance R.sub.g since the cable 1 of the second embodiment comprises a single section P.sub.1, and therefore, the model of the earth conductor ECC will comprise a single net.
[0146] The clauses that follow disclose additional embodiments or combinations of embodiments:
[0147] Clause 1. A method for locating a fault point (F) on a high-voltage three-phase AC cable (1) comprising a first end (10), a second end (11), and at least one section (P.sub.1, P.sub.2) extending between said ends (10, 11), the cable (1) comprising a conductor (R, S, T) and a respective shield (S.sub.R, S.sub.S, S.sub.T) per phase, shields (S.sub.R, S.sub.S, S.sub.T) being connected to a surge arrester device (3, 4) connected to ground (G) at one end of said at least one section (P.sub.1, P.sub.2), and shields (S.sub.R, S.sub.S, S.sub.T) being connected to a grounding element (2) at the other end of said at least one section (P.sub.1, P.sub.2), the cable (1) comprising an earth continuity conductor (ECC) establishing a common ground (G) connecting the ground connections (20, 30, 40) of the grounding element(s) and the surge arrester device(s) (3, 4), the method comprising the following steps: [0148] measuring the conductor current (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2) circulating through each conductor (R, S, T) both at the first end (10) and at the second end (11) of the cable (1), [0149] measuring the shield current (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2) circulating through each shield (S.sub.R, S.sub.S, S.sub.T) in each section (P.sub.1, P.sub.2) at a point close to the grounding element, [0150] measuring the earth continuity conductor current (I.sub.ECC1, I.sub.ECC2) circulating through each section (P.sub.1, P.sub.2) at a point close to the grounding element, [0151] determining the conductor (R, S, T) in fault based on the previously measured conductor currents (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2), [0152] in the event that the cable (1) comprises more than one section (P.sub.1, P.sub.2), determining section (P.sub.1, P.sub.2) in fault based on the previously measured shield currents (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2), and [0153] locating the fault point (F) by means of a model of section (P.sub.1, P.sub.2) in fault of the earth continuity conductor (ECC), the only unknown being the distance (x) to the fault point (F) from an end of said section (P.sub.1, P.sub.2) in fault.
[0154] Clause 2. The method according to clause 1, wherein for determining the conductor (R, S, T) in fault, the conductor current (I.sub.R1; I.sub.S1; I.sub.T1) measured at the first end (10) of the cable (1) for each conductor (R, S, T) is compared with the conductor current (I.sub.R2; I.sub.S2; I.sub.T2) measured at the second end (11) of the cable (1), determining that the conductor (R, S, T) in fault will be the conductor in which the conductor current (I.sub.R1, I.sub.R2; I.sub.S1, I.sub.S2; I.sub.T1, I.sub.T2) at said ends (10, 11) is different.
[0155] Clause 3. The method according to clause 1 or 2, wherein the cable (1) comprises at least two sections (P.sub.1, P.sub.2), section (P.sub.1, P.sub.2) in fault being determined taking into account that in said section in fault (P.sub.1, P.sub.2), one of the shield currents (I.sub.SR1, I.sub.SS1, I.sub.ST1; I.sub.SR2, I.sub.SS2, I.sub.ST2) will have an overcurrent value.
[0156] Clause 4. The method according to any of clauses 1 to 3, wherein the model of the earth continuity conductor (ECC) of section (P.sub.1, P.sub.2) in fault takes into account the self-resistance (R.sub.ECC) and the self-inductance (L.sub.ECC) of the earth continuity conductor (ECC), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4), the mutual inductance (M.sub.R, M.sub.S, M.sub.T) between said earth continuity conductor (ECC) and each of the conductors (R, S, T), and the mutual inductance (M.sub.SR, M.sub.SS, M.sub.ST) between said earth continuity conductor (ECC) and the shield in fault (S.sub.R, S.sub.S, S.sub.T) from the fault point (F) to the point where the shields are connected to ground (G).
[0157] Clause 5. The method according to claim 4, wherein the location of the fault point is calculated using the following formula:
0=I.sub.ECCF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCNFRR.sub.g−I.sub.ECCNFRR.sub.g+jwxl.sub.CNF1M.sub.CNF1+jwxl.sub.CNF2M.sub.CNF2+jwxl.sub.CF1M.sub.CF+jw(1−X)I.sub.CNF1M.sub.CNF1+jw(1−X)I.sub.CNF2M.sub.CNF2−jw(1−X)I.sub.CF2M.sub.CF+jw(1−X)I.sub.SFM.sub.SF
wherein, [0158] I.sub.ECCF=The current circulating through the section of the earth continuity conductor (ECC) which is in fault, [0159] I.sub.ECCNFL=The current circulating through the section of the earth continuity conductor (ECC) to the left of the section in fault; in the event that there is no section to the left of the section in fault its value will be zero, [0160] I.sub.ECCNFR=The current circulating through the section of the earth continuity conductor (ECC) to the right of the section in fault; in the event that there is no section to the right of the section in fault its value will be zero, [0161] R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device, [0162] R.sub.ECC=The self-resistance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), [0163] L.sub.ECC=The self-inductance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), [0164] I.sub.CNF1=Current circulating through a first conductor which is not in fault, both at the first end (10) of the cable (1) and at the second end (11) of the cable (1), [0165] I.sub.CNF2=Current circulating through a second conductor which is not in fault, both at the first end (10) of the cable (1) and at the second end (11) of the cable (1), [0166] I.sub.CF1=Current circulating through the conductor in fault at the first end (10) of the cable (1), [0167] I.sub.CF2=Current circulating through the conductor in fault at the second end (11) of the cable (1),
I.sub.CF1≠I.sub.CF2 [0168] I.sub.SF=Current circulating through the shield in fault in the section in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, [0169] M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), [0170] M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), [0171] M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), [0172] M.sub.SF=Mutual inductance between the shield which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), and x=The distance to the fault point from the end of the section in fault at which the surge arrester device is arranged to the fault point (F).
[0173] Clause 6. The method according to clause 4 or 5, wherein when the cable (1) comprises more than one section (P.sub.1, P.sub.2), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4) is determined by means of a model of the earth continuity conductor (ECC) of one of the sections (P.sub.1, P.sub.2) which is not in fault, said model comprising the self-resistance (R.sub.ECC) and the self-inductance (L.sub.ECC) of the earth continuity conductor (ECC), the ground resistance (R.sub.g) of the ground connections (20, 30, 40) of the grounding elements and/or the surge arrester device(s) (3, 4), the mutual inductance (M.sub.R, M.sub.S, M.sub.T) between said earth continuity conductor (ECC) and each of the conductors (R, S, T), the only unknown being said ground resistance (R).
[0174] Clause 7. The method according to claim 6, wherein the ground resistance (R.sub.g) is calculated using the following formula:
0=I.sub.ECCNF(R.sub.g+R.sub.g+R.sub.ECC+jwL.sub.ECC)−I.sub.ECCLR.sub.g−I.sub.ECCRR.sub.g+jwI.sub.CNF1M.sub.CNF1+jwI.sub.CNF2M.sub.CNF2+jwI.sub.CFM.sub.CF
wherein, [0175] I.sub.ECCNF=The current circulating through the section which is not in fault the model of which is used to calculate ground resistance (R.sub.g), [0176] I.sub.ECCL=The current circulating through the section to the left of the section which is not in fault; in the event that there is no section to the left of the section which is not in fault, its value will be zero, [0177] I.sub.ECCR=The current circulating through the section to the right of the section which is not in fault; in the event that there is no section to the right of the section which is not in fault, its value will be zero, [0178] R.sub.g=The ground resistance of the grounding of the shields or of the grounding of the surge arrester device at one of the ends of the section in fault, [0179] R.sub.ECC=The self-resistance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), [0180] L.sub.ECC=The self-inductance of the earth continuity conductor (ECC) of the section in fault, calculated taking into account the characteristics of the cable (1), [0181] I.sub.CNF1=Current circulating through a first conductor which is not in fault at the first end (10) of the cable (1), [0182] I.sub.CNF2=Current circulating through a second conductor which is not in fault at the first end (10) of the cable (1), [0183] I.sub.CF=Current circulating through the conductor in fault; if the current flows from the first end to the second end, it will be considered positive; in contrast, if it flows from the second end to the first end, it will be considered negative, [0184] M.sub.CNF1=Mutual inductance between the first conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), M.sub.CNF2=Mutual inductance between the second conductor which is not in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable (1), and M.sub.CF=Mutual inductance between the conductor which is in fault and the earth continuity conductor (ECC), calculated taking into account the characteristics of the cable 1.
[0185] Clause 8. The method according to clause 4 or 5, wherein when the cable (1) comprises a single section (P.sub.1) the ground resistance (R.sub.g) of the ground connections (20, 30) of the grounding element and the surge arrester device (3) is estimated.
[0186] Clause 9. A system for locating a fault point (F) on a high-voltage three-phase AC cable (1) comprising a first end (10) and a second end (11) and at least one section (P.sub.1, P.sub.2) extending between said ends (10, 11), the cable (1) comprising a conductor (R, S, T) and a respective shield (S.sub.R, S.sub.S, S.sub.T) per phase, shields (S.sub.R, S.sub.S, S.sub.T) being connected to a surge arrester device (3, 4) connected to ground (G) at one end of said at least one section (P.sub.1, P.sub.2) and shields (S.sub.R, S.sub.S, S.sub.T) being connected to a grounding element at the other end of said at least one section (P.sub.1, P.sub.2), the cable (1) comprising an earth continuity conductor (ECC) establishing a common ground (G) connecting the ground connections (20, 30, 40) of the grounding element(s) (2) and the surge arrester device(s) (3, 4), the system comprising: [0187] a first current measuring equipment (5) configured for measuring the conductor current (I.sub.R1, I.sub.S1, I.sub.T1, I.sub.R2, I.sub.S2, I.sub.T2) circulating through each conductor (R, S, T) both at the first end (10) and at the second end (11) of the cable (1), [0188] a second current measuring equipment (6) configured for measuring the shield current (I.sub.SR1, I.sub.SS1, I.sub.ST1, I.sub.SR2, I.sub.SS2, I.sub.ST2,) of each shield (S.sub.R, S.sub.S, S.sub.T) in each section (P.sub.1, P.sub.2) at a point close to the grounding element, [0189] a third current measuring equipment (7) configured for measuring the earth continuity conductor current (I.sub.ECC1, I.sub.ECC2) of the earth continuity conductor (ECC) in each section (P.sub.1, P.sub.2) at a point close to the grounding element (2), and [0190] a computer configured for executing the method according to any of clauses 1 to 8 based on the current measurements performed by said current measuring equipment (5, 6, 7).