Power grid remote grounding fault section positioning system and method

Abstract

A system for remotely locating ground faults in a multi-phase electrical network powered by a power source, the system further comprising at least one remote detector (361, 362, 363, 364, 36N, 36N + 1, 36N + 2) arranged in the electrical network but not communicatively connected with a control unit, where each at least one remote detector has a unique current pattern identification. The control unit, when in a remote ground fault detection mode, is configured to adjust an output voltage of the AC voltage source according to a determined ground fault impedance RF and a corresponding incremental angle step X to generate a zero sequence current pattern based on the impedance and the incremental angle step X, wherein each of the at least one remote detector (361, 362, 363, 364, 36N, 36N + 1, 36N + 2) is configured to identify a zero sequence current pattern and to determine which remote detector has a unique current pattern identification corresponding to the identified current pattern. Preferably, the determined remote detector is then configured to open a fault section associated with the determined remote detector by applying a circuit breaker (421, 422, 423, 424, 42N, 42N + 1) associated with the remote detector.

Description

Background Art

[0001] The present disclosure relates to polyphase power grid ground fault current detection, compensation, and location. The present invention is based on the technology described in WO2017 / 200469, which relates to using communicatively connected detectors to locate a faulty feeder containing a ground fault.

[0002] More specifically, the present invention relates to a system and method that can perform ground fault location up to the faulty feeder section without a remotely connected detector connected communicatively and without measuring admittance Y0, only by measuring current I0. The present invention also relates to a computer program and a process-readable medium.

[0003] Existing technical solutions today are to locate ground faults up to the faulty feeder section without a passively connected detector connected communicatively. However, the problem with these known solutions lies in the limitations of detection sensitivity, which can detect low-ohm ground faults, but cannot reliably detect high-ohm ground faults because the measured current is too small. High-ohm faults may be ground faults with an impedance up to 25 kOhm or higher.

[0004] Once the detector disconnects the faulty section, the main system needs to retune the zero-point reactor to match the size of the "new network". This solution is part of the system and is described in this method.

[0005] WO2014 / 021773 discloses a solution in which a controllable ground transducer is arranged to compensate for the residual operating current in a ground fault of an AC voltage supply network having a power transformer. The primary winding of the ground transformer is coupled to the power grid, the secondary coil of the ground transformer is coupled between the zero point of the power grid and the ground, the ground transformer includes two or more winding couplers and a control unit, and the control unit controls the secondary voltage of the ground transformer via the winding couplers with respect to the amplitude and phase angle of the voltage signal of the power transformer.

[0006] WO02 / 15355 relates to a method and apparatus for selectively locating high-ohm single-pole ground faults in a neutral point compensated power supply network.

[0007] The above-mentioned known technologies have some technical problems.

[0008] By applying the solution described in WO2017 / 200469, a faulty feeder containing a ground fault can be located with as high a sensitivity as possible using communicatively connected detectors.

[0009] Feeder lines are usually divided into several sections and can be connected or disconnected using circuit breakers. It is advisable to use detectors at the location of the circuit breakers to determine in which section the ground fault lies.

[0010] Prior art using passive fault path indicators connected in a non - communication way attempts to identify this, but has poor sensitivity and cannot work reliably in the case of high - ohmic ground faults.

[0011] Although the technique disclosed in WO2017 / 200469 has been proven to have excellent performance, there is still room for improvement. The limitation of the technique of WO2017 / 200469 does not lie in limited detection sensitivity, but in the need to measure both the U0 voltage and the I0 current to calculate the zero - sequence admittance Y0, so the U0 voltage that is not available at a remote location needs to be measured. In remote areas, communication and U0 voltage measurement are usually not possible, so another solution is needed. Summary of the Invention

[0012] The main object of the present invention is to solve the problem of high - impedance ground fault location up to the faulty feeder section in a multi - phase power grid without U0 voltage measurement and without access to communication. This must be achieved by keeping the ground fault current below a certain value (e.g., 0.5 A) in order to reduce the risk of a ground fault causing a fire.

[0013] The above object is achieved by the systems and methods defined in the independent claims. Preferred embodiments are stated in the dependent claims.

[0014] Therefore, a challenge is to be able to achieve this without communication between the control unit 370 and the remote detector(s). The systems and methods of the present invention solve this problem. The systems and methods of the present invention can achieve this by only reading the I0 current from existing current sensors near the circuit breakers installed in the network, where U0 voltage measurement is usually not possible. Additionally, the systems and methods of the present invention also solve the problem of re - tuning the zero - point reactor once the various parts of the network are tripped by the detector(s).

[0015] This is beneficial for several reasons. An important reason is safety, because the detector can detect any type of ground fault and use the existing circuit breaker to disconnect the faulty section. This reduces the risk of fire, equipment damage, and improves personal safety. Another reason is that only the smallest section of the network is disconnected, so the number of customers affected by the power outage is minimized. And another reason is that since the ground fault has been located up to the faulty feeder section, the power outage time required is the shortest.

[0016] To be able to achieve the above object, the central control unit must perform several steps, which are for example byFigure 8 and Figure 9 The flowcharts in Figure 9 are described in the detailed implementation. The remote detector requires the action of the control unit to detect a specific current pattern.

[0017] According to the present invention, the control unit first needs to use the method described in WO2017 / 200469 to detect the ground fault impedance using its central detector in the substation. The ground fault impedance determines the incremental angle step to be used for the so-called fault path indicator (FPI) positioning. For low-impedance faults, only a smaller incremental step is required to detect the fault, while for high-impedance faults, a much larger incremental step is required to achieve a large enough (but below the predetermined current threshold, preferably approximately 0.5A) ground fault current. Once the ground fault impedance is determined, the control unit determines the corresponding angle increment to be used for remote detector ground fault location.

[0018] In the remote detector ground fault detection mode, the control unit is configured to first determine the magnitude of the phase angle step based on the ground fault impedance. Then, based on the timing and the number of executions, the magnitude of the phase angle step is intermittently controlled according to a predetermined pattern. As shown in Figure 6 and Figure 7 , the remote detector in the ground fault current path can detect this pattern. In a symmetric polyphase system, when only the phase angle of the central controller at the neutral point of the transformer is changed, the ΔI0 current will be measured, but it can only be measured by the remote detector in the ground fault current path. If the magnitude changes, all remote detectors will detect the ΔI0 current - this is not ideal. This is an important aspect of the present invention. Since the magnitude can change for other purposes in addition, the predetermined remote detector ground fault location current pattern must be determined in a way that does not interfere with other actions in the network. Figure 6 and Figure 7 This system is advantageous because the fault location can be found without the risk of exceeding the maximum power current at the fault location. It is not a problem for the control unit to adjust the voltage of the AC voltage source so that its output current in the fault detection mode is below a certain predetermined current threshold (e.g., approximately 0.5A). This current is the limit for post-locating ground faults in some areas of Australia and the United States (which are particularly sensitive to forest or grassland fires).

[0019] According to this aspect of the present invention, the control unit is configured to switch to the fault compensation mode after the fault detection mode. Thus, power transmission via the malfunctioning device part can continue until the exact location of the fault has been established and the resources required to repair the fault have been developed.

[0020]

[0021] ​According to another aspect of the present invention, this object is achieved by a software program that can be loaded into the memory of at least one processor, wherein the computer program includes software that is used to execute the method proposed above when the computer program runs in at least one processor.

[0022] According to another aspect of the present invention, this object is achieved by a computer-readable medium in which a program is stored, and the program is configured to cause at least one processor to execute the method proposed above when the program is loaded in at least one processor.

[0023] Other advantages, advantageous features and applications of the present invention will become apparent from the following description and the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will now be explained in more detail by way of example embodiments illustrated with reference to the drawings.

[0025] Figure 1 Illustrates a first prior art solution for resonant grounding.

[0026] Figure 2 Illustrates a second prior art residual current compensation solution.

[0027] Figure 3 Shows a single-line diagram of the ground fault location system disclosed in WO2017 / 200469.

[0028] Figure 4 and Figure 5 Shows a single-line diagram of the ground fault location system of the present invention.

[0029] Figure 6 and Figure 7 Illustrates the structure of a typical multi-phase resonant grounding system with local and remote detectors in which the present invention is applied.

[0030] Figure 8 and Figure 9 Illustrates the method of an embodiment of the present invention by means of a flowchart. DETAILED DESCRIPTION

[0031] First, refer to Figure 1 , which shows the first mentioned known solution for so-called resonant grounding in a multi-phase power grid. Figure 1 Shows the transformation of the power grid into its symmetrical components. Here, the power grid includes a power source 110 that supplies a driving voltage E to the power grid, source impedances Z + , Z - and Z0, and the payload Z L in the power grid.

[0032] If a ground fault occurs in the form of a single-phase ground fault, the fault current can be reduced by means of the zero-sequence reactor 120, which is connected between the zero point N and the ground E. The zero-sequence reactor 120 is a variable inductance L, which forms a parallel resonance circuit with the leakage current capacitance 3C0 of the power grid. On the one hand, the transmission of the payload Z L must be limited to the positive-sequence and negative-sequence systems, that is, between faults; on the other hand, the zero-sequence reactor 120 must be able to match the changing leakage current occurring in the power grid during operation.

[0033] In the vast majority of existing power grids, the basic prerequisites for limiting power transmission to the positive-sequence and negative-sequence are given. Resonant grounding is the dominant system in today's existing high-voltage distribution networks.

[0034] Single-phase ground The direct impact of the current limitation at the fault is that the optical arc superimpositions are self-sealing, and these optical arc superimpositions are the most common errors in overhead line networks. Therefore, the zero-sequence reactor 120 is also called an arc suppression coil, or a Petersen coil named after the inventor Waldemar Petersen.

[0035] At the ground fault, the zero-sequence reactor 120 compensates for the capacitive leakage current. The resistive leakage current does not need to be compensated, and the resistive leakage current usually accounts for 5% to 10% of the total ground fault current.

[0036] As more and more overhead line networks are replaced by underground cables, the capacitive leakage current of the power grid generally increases. This also increases the resistive leakage current in the power grid. Therefore, the uncompensated resistive residual current will also increase, which in turn risks the part of the power grid that still includes the overhead line network losing its self-extinguishing function. For safety reasons, this is of course unacceptable.

[0037] Figure 2 Illustrated is a second prior art solution for residual current compensation, which is a further development of the Figure 1 structure. For the sake of clarity, the now tuned parallel resonance circuit 3C0 / / L is omitted here.

[0038] Similar to Figure 1 that, Figure 2 shows the drive voltage E output by the power source 210, the source impedance Z + 、Z - and Z0 as well as the payload Z LIn addition, it further includes a residual current compensation device 220, which in turn includes a voltage source (-)E synchronized with the power grid. The residual current compensation device 220 injects a compensation current between the zero point of the power grid and the ground, and the compensation current is equal to the residual current, but the phase angle with respect to the residual current is phase-distorted by 180°. The voltage source (-)E of the residual current compensation device 220 is connected in parallel with the sum of the resistive currents R0 / 3 of the power grid. Then, as mentioned above, the known solutions cannot locate the fault position during the residual current compensation while meeting the regulatory requirements for the maximum current intensity. The present invention aims to solve this problem.

[0039] Figure 3 FIG. shows the prior art system of WO2017 / 200469, specifically, a single-line diagram for locating ground faults in a multi-phase power grid.

[0040] Generally speaking, the methods disclosed therein assume that once an error has been detected and the ground fault current has been compensated according to the above reference Figure 2 stated, while measuring appropriate parameters in the power grid, it is assumed that the voltage / current at the fault location will gradually increase. In this fault detection mode, the same AC voltage source is used, which is used for residual current compensation in the fault current compensation mode.

[0041] More specifically, in the fault detection mode, a fault location signal is provided by means of a superimposed voltage source (-)E for residual current compensation. The relationship between the current and voltage at the fault location is jointly determined by the initially unknown fault impedance and the source impedance of the fault circuit. To ensure that the current generated by the location signal does not exceed a given limit, the voltage of the location signal is gradually increased until the fault location is determined by means of a specially modified detector, or until the maximum voltage level has been reached, whichever comes first.

[0042] Figure 3 FIG. shows a multi-phase power grid fed by a power source 310. The prior art system includes a power grid-synchronized AC voltage source 380, which is connected between the zero point N of the power grid and the ground E.

[0043] The system further includes a control unit 370, which is capable of controlling the AC voltage source 380 in the fault current compensation mode to compensate any ground fault current ΔI in the resonant grounded power grid to a value below the threshold level. Further, a three-phase measuring transformer 340 is connected to the controller 370, and the three-phase measuring transformer 340 is configured to measure the zero-sequence voltage 3U0 to determine whether there is a ground fault in the power grid.

[0044] The system further includes at least one detector, exemplified here as 351, 352, 35N, 361, 362 and 36N, which is arranged in the power grid and communicatively connected to the control unit 370. At least one of the detectors 351, 352, 35N, 361, 362 and 36N is further configured to detect and record measured values Y representing zero-sequence current and zero-sequence admittance OL1P , Y OL1D , Y OL2P , Y OL2D , Y OLNP and Y OLND so that these parameters can be reported to the control unit 370.

[0045] During the current residual current compensation, the fault detection mode can be activated automatically or in response to a command to the control unit 370 generated by an operator of the power grid.

[0046] In the fault detection mode, the control unit 370 is configured to gradually adjust the output voltage U of the AC voltage source 380 according to the amplitude and / or phase angle P so as to change the zero-sequence current and / or zero-sequence admittance between the AC voltage source 380 and the possible fault location.

[0047] At least one of the detectors 351, 352, 35N, 361, 362 and 36N detects and records measured values Y representing zero-sequence current and / or zero-sequence admittance OL1P , Y OL1D , Y OL2P , Y OL2D , Y OLNP and Y OLND , and transmits these measured values Y OL1P , Y OL1D , Y OL2P , Y OL2D , Y OLNP and Y OLND to the control unit 370.

[0048] In the fault detection mode, the control unit 370 is configured to locate the ground fault GF based on at least one of the measured values Y of zero-sequence current and / or zero-sequence admittance detected and recorded by at least one of the detectors 351, 352, 35N, 361, 362 and 36N OL1P , Y OL1D , Y OL2P , Y OL2D , Y OLNP and Y OLND . At the same time, by measuring the current in the grounding 390 of the zero-point reactor 330, the control unit 370 checks that the change in the ground fault current ΔI does not exceed the maximum allowable level.

[0049] If a ground fault GF has been located, the control unit 370 is configured to switch to a fault compensation mode after the fault detection mode has ended. Alternatively, a branch wire associated with the ground fault GF (such as Figure 3 the L in N ) can be disconnected from the power source 310. In Figure 3 , current selectors 321, 322, and 32N are shown, which are arranged on respective lines L1, L2, and L N and can be separately controlled in relation to the control unit 370 on the basis of a control signal CtrI SW .

[0050] If no ground fault is detected, the control unit 370 is configured to disconnect the AC voltage source 380.

[0051] According to a variant of a known system, the control unit 370 is configured, in a fault detection mode, to control the AC voltage source 380 to output an AC voltage to the power grid, the AC voltage being (i) overlapping with the voltage of the power grid, (ii) changing gradually, and (iii) having a frequency different from the frequency of the power grid. Thus, at least one of the detectors 351, 352, 35N, 361, 362, and 36N helps to detect the signal.

[0052] Particularly preferably, the control unit 370 is configured to control the AC voltage source 380 to output an AC voltage having an overlapping signal pattern to the power grid, and at least one of the detectors 351, 352, 35N, 361, 362, and 36N is configured to detect such an overlapping signal pattern.

[0053] Generally, the control unit 370 is configured to operate the processes described above in a fully automated manner (e.g., by executing a computer program in a processor). Thus, the control unit 370 preferably includes a memory device 375 that stores a computer program that includes software for performing the processes when the program runs in a processor.

[0054] The present invention is closely related to and based on the systems and methods disclosed in WO2017 / 200469, and the thermology applied herein is the same as or similar to that in WO2017 / 200469.

[0055] Figure 4 and Figure 5 show a single-line diagram of the ground fault location system of the present invention. Figure 4 illustrates the structure of a substation of the system, Figure 5The remote part of the structure is illustrated, where the circled numbers 1 to 3 indicate the connection points between the corresponding structures. Now, for Figure 4 and Figure 5 a detailed description will be given. However, Figure 4 and Figure 5 some items of the structure shown in have been combined with Figure 3 and described above, so they will not be elaborated here.

[0056] Accordingly, the present invention relates to a system for locating a ground fault in a polyphase electrical network powered by a power source 310. The system includes an alternating current voltage source 380 synchronized with the electrical network, the alternating current voltage source 380 being connected between the neutral point (N) of the electrical network and the ground (E); and a control unit 370 configured to control the alternating current voltage source 380 in a fault current compensation mode to compensate any ground fault current in the electrical network to a value below a threshold level. The system includes at least one local detector 351, 352, 35N arranged in the electrical network and communicatively connected to the control unit 370, the at least one local detector 351, 352, 35N being configured to detect and record measured values representing zero-sequence current and zero-sequence admittance. The control unit 370, when in a fault detection mode, is configured to gradually adjust the output voltage of the alternating current voltage source 310 according to the amplitude and / or phase angle so that the change in the zero-sequence current and zero-sequence admittance between the alternating current voltage source 310 and the location point can be measured by at least one local detector 351, 352, 35N. The at least one local detector 351, 352, 35N is configured to apply the detected and recorded measured values representing zero-sequence current and / or zero-sequence admittance to the control unit 370. The control unit 370, when in a fault detection mode, is configured to locate the ground fault based on at least one of the measured values representing the change in zero-sequence current and / or zero-sequence admittance, wherein the control unit 370 is configured to switch to a fault compensation mode after the fault detection mode.

[0057] The at least one local detector 351, 352, 35N is also configured to detect and record the measured values to be applied by the control unit 370 to determine the ground fault impedance R Fand the measured value corresponding to the incremental angle step X. The system further includes at least one remote detector 361, 362, 363, 364, 36N, 36N + 1, 36N + 2, which is arranged in the power grid but not communicatively connected to the control unit 370. Each of the at least one remote detector has a unique current mode identifier. The remote detector has an identifier related to the number of remote detectors installed on a specific feeder. The first current mode detection triggers the remote detector with the identifier ID1, the second current mode detection triggers the remote detector with the identifier ID2, and the Nth current mode detection triggers the remote detector with the identifier IDN.

[0058] When in the remote ground fault detection mode, the control unit 370 is configured to adjust the output voltage of the AC voltage source 380 according to the determined ground fault impedance R F and the corresponding incremental angle step X to generate a zero-sequence current mode based on the impedance and the incremental angle step X. Further, each of the at least one remote detector 361, 362, 363, 364, 36N, 36N + 1, 36N + 2 is configured to identify the zero-sequence current mode and determine which remote detector has a unique current mode identifier corresponding to the identified current mode. Preferably, the determined remote detector is then configured to disconnect the fault section associated with the determined remote detector by controlling the operation of the circuit breakers 421, 422, 423, 424, 42N, 42N + 1 associated with the determined remote detector.

[0059] According to one embodiment, after disconnecting the fault section, the control unit 370 is configured to control the zero-point reactor 330 to be retuned to match the adjusted network size and continue the fault current compensation mode to compensate any ground fault current in the power grid to a value below the threshold level.

[0060] Therefore, the determined ground fault impedance R F and the corresponding incremental angle step X are the ground fault impedance and the corresponding incremental angle step required by the AC voltage source 380 to generate a large enough incremental current ΔI0 for the detector to detect and still meet the requirement of not exceeding 0.5A, so that no fire is triggered during the remote ground fault location process.

[0061] Figure 6 and Figure 7 illustrates the detailed structure of a typical multi-phase resonant grounded power grid in which the present invention is applied. Figure 6 illustrates the structure of the substation of the system, Figure 7 illustrates the remote part of the structure, where the circled numbers 1 to 4 indicate the connection points between the corresponding structures.

[0062] In the power grid, as shown by C and R, there is natural coupling in each phase, and their magnitudes increase with distance (the size of the power grid).

[0063] The network is required to be symmetric, which means that the sum of all the coupling elements to ground on feeder 1 is substantially equal. Thus, (C11 + C14 + C17) = (C12 + C15 + C18) = (C13 + C16 + C19), and (R11 + R14 + R17) = (R12 + R15 + R18) = (R13 + R16 + R19).

[0064] The coupling elements to ground on feeder 2 are substantially equal. Thus, (C21 + C24 + C27) = (C22 + C25 + C28) = (C23 + C26 + C29), and (R21 + R24 + R27) = (R22 + R25 + R28) = (R23 + R26 + R29).

[0065] And, the coupling elements to ground on feeder N are substantially equal.

[0066] Thus, (C31 + C34 + C37 + C312) = (C32 + C35 + C38 + C311) = (C33 + C36 + C39 + C310), and (R31 + R34 + R37 + R312) = (R32 + R35 + R38 + R311) = (R33 + R36 + R39 + R310).

[0067] If a ground fault occurs in the form of a single-phase ground at the location of R F the ground fault current path is shown by the line diagram specified by ΔI0, which runs through the entire network.

[0068] The direct impact of the current limitation at the single-phase ground is as follows: Since the voltage of feeder L3 will be controlled to be as close to 0 as possible, the ground fault current through resistor R F is limited to be close to 0 by the control unit.

[0069] When the network is in the ground fault mode, all the detectors in the network will measure the I0 current, the magnitude of which is determined by the size of the network, which is determined by the sum of all the capacitors (C11 to C312) and resistors (R11 to R312) connected to the feeder to which the detector is connected. Further away in the network, the I0 current will decrease because the size of the network "behind" the detector becomes smaller. Measuring the I0 current above a specific threshold is not a criterion for locating the ground fault.

[0070] Once the control unit 370 detects an error and the ground fault current has been compensated, while measuring appropriate parameters in the power grid, the voltage / current at the assumed fault location is gradually increased, which is achieved by the system disclosed above and in accordance with the disclosure of WO2017 / 200469. In this fault detection mode, the same AC voltage source is used, which is used for residual current compensation in the fault current compensation mode.

[0071] Once the gradual increase is performed during the fault detection mode, the ground fault impedance is known, and the required incremental phase X degrees to be applied in the subsequent remote detector ground fault mode is also known.

[0072] In the remote detector ground fault mode of the present invention, the current mode is generated by the control unit 370, so as to control the variable power source 380 to achieve X degrees (increment) (duration XXX ms), 0 degrees (increment) (duration XXX ms), X degrees (increment) (duration XXX ms), 0 degrees (increment) (duration XXX ms). By generating this mode (which is also known to all remote detectors), the ground fault current path can be determined. In a variant, the duration XXX is 500 ms, but can be naturally set to other values, preferably in the range of 100 ms to 1000 ms.

[0073] Each remote detector 361, 362, 363, 364, 36N, 36N+1, 36N+2 has a unique current mode identifier. Additionally, each remote detector is also provided with a circuit breaker 421, 422, 423, 424, 42N, 42N+1, which is used to disconnect the faulty section associated with the remote detector.

[0074] In the illustrated scenario, when the main controller 380 changes the angle in the remote ground fault location mode, only the detectors in the current path will detect the ΔI0 current. The reason is that all feeders are symmetric with respect to equivalent ground coupling elements, and in the illustrated scenario, the faulty feeder is no longer equal with respect to the ground coupling level. (C31+C34+C37+C312)=(C32+C35+C38+C311)=(C33+C36+C39+C310), but (R31+R34+R37+R312)=(R32+R35+R38+R311)≠(R33+R36+R39=R310+RF).

[0075] If a feeder contains multiple remote detectors and a ground fault occurs at the farthest point on the feeder, all detectors will measure the ground fault path and indicate the fault. To prevent all remote detectors from tripping, the current mode can be repeated so that remote detectors with ID1 (36N + 2) are triggered by the first current mode detection, detectors with ID2 (36N + 1) are triggered by the second current mode detection, and detectors with ID 3 (36N) are triggered by the third current mode detection.

[0076] During current residual current compensation, the fault detection mode can be activated automatically or in response to a command to the control unit 370 that has been generated by an operator of the power grid.

[0077] In the fault detection mode, the control unit 370 is configured to gradually adjust the output voltage U of the AC voltage source 380 according to the amplitude and / or phase angle P , thereby changing the zero-sequence current and / or zero-sequence admittance between the AC voltage source 380 and the possible fault location.

[0078] In the remote ground fault detection mode, the control unit 370 is configured to use the phase angle determined in the fault detection mode and reuse this output for remote ground fault detection. At least one of the remote detectors 361, 362, 363, 364, 36N, 36N + 1, and 36N + 2 detects the current mode of the I0 current, and once detected, can send a signal to the corresponding circuit breaker (ACR) (421, 422, 423, 424, 42N, 42N + 1, 42N + 2) to trigger the fault section of the network.

[0079] If a section is disconnected during a ground fault, the central controller 370 must be able to detect this by measuring the sum of I0 of all its central detectors. If the sum of I0 changes during a ground fault, the zero-point reactor 330 must be tuned to match the new size of the entire network. ΔI0 can be directly converted into ΔI for the control of the zero-point reactor 330.

[0080] If no ground fault is detected, the control unit 370 is preferably configured to disconnect the AC voltage source 380.

[0081] Generally preferably, the control unit 370 is configured to operate the processes described above in a fully automatic manner (e.g., by executing a computer program in a processor). Therefore, the control unit 370 preferably includes a memory device 375 that stores a computer program that includes software for performing the process when the program runs in the processor.

[0082] In summary, and referring to Figure 8 andFigure 9 For the flowchart of Figure 9 , we now describe an embodiment of the method of the present invention.

[0083] In step 410, it is checked whether the fault current compensation mode is to be applied. If this is not the case, the process loops and stops at step 410. If a ground fault has been detected in step 410, then step 420 follows, in which the ground fault current is compensated so that the ground fault current is below a threshold. In step 420, the currents of all local detectors are added together to obtain a current sum I 01 , and it is stored for later use. Then, step 430 follows.

[0084] In step 430, it is checked whether the fault detection mode is to be activated. If this is not the case, the process loops back to step 420 to continue compensating the ground fault current. If it is determined in step 430 to activate the fault detection mode, steps 440 and 450 are activated, preferably in parallel with each other.

[0085] In step 440, the AC voltage source is controlled to gradually adjust the output voltage of the AC voltage source according to the amplitude and phase angle so that the zero-sequence current and zero-sequence admittance between the AC voltage source and the fault location are changed.

[0086] In step 450, the zero-sequence current and / or zero-sequence admittance between the AC voltage source and the fault location are measured by means of a specially adapted detector communicatively connected to the control unit. R F and the incremental angle step X are determined and will be used for remote ground fault location.

[0087] After step 440, step 480 follows, in which it is checked whether the output voltage U P of the AC voltage source is below or equal to the maximum allowable value U Pmax . If so, the process proceeds to step 460, otherwise, step 490 follows.

[0088] At step 490, the AC voltage source is disconnected. Then, the process returns to step 410.

[0089] After step 450, step 460 follows, in which it is investigated whether a ground fault has been detected by the measurement in step 450. If so, then steps 510 and 520 follow and these two steps are executed in parallel, otherwise the process loops back to steps 440 and 450 to continue with the fault location.

[0090] The above part of the method corresponds essentially to the method disclosed in WO2017 / 200469. An important difference is in step 450, in which RF and an incremental angular step X.

[0091] In step 510 (see Figure 6 ), control the AC voltage source at a fixed angular step as previously determined in step 450. The incremental angular step X is used to generate a predetermined current pattern for detection by the remote detector.

[0092] In step 520, configure the remote detector to look for the current pattern generated by the AC voltage source.

[0093] In step 530, determine whether the faulty section should be tripped. Based on the number of times the current pattern is detected, the remote detector determines whether to trip the circuit breaker (ACR).

[0094] In step 540, if the number of remote detectors installed on the faulty feeder exceeds 1, the control unit 370 may repeat step 520. Otherwise, the control unit proceeds to step 550.

[0095] At step 550, measure the sum of the currents I 02 of all local detectors. Next is step 560.

[0096] At step 560, compare I 01 and I 02 . If the I 02 current is less than I 01 , this means that a section in the network has been disconnected.

[0097] At step 570, tune the zero - sequence reactor 330 to match the new network size. If a larger section is tripped, this means that the ground - fault compensation may be overloaded and step 440 cannot be repeated. After this step, repeat step 440 until the ground fault is cleared.

[0098] The steps described above and reference Figure 8 and Figure 9Any random sequence described can be controlled by a programmed processor. Additionally, although the embodiments described above of the present invention refer to computers and computer-implemented processes with reference to the accompanying drawings, the present invention extends specifically to being on or in a carrier, thereby being adapted to implement the present invention in a practical manner. The program can take the form of source code, object code, an intermediate code representing between the source code and the object code (such as in a partially compiled form), or any other form suitable for use in implementing the present invention. The carrier can be any entity or device capable of carrying the program. For example, the carrier can include a storage medium (such as flash memory, ROM (read-only memory) (e.g., CD (compact disc) or semiconductor ROM), EPROM (electrically programmable ROM), EEPROM (erasable EPROM)), or a magnetic recording medium (such as a floppy disk or a hard disk). Additionally, the carrier wave can be an overloaded carrier wave, such as an electrical signal or an optical signal, which can be transmitted through a cable or an optical fiber or via radio or by other means. When the program consists of a signal that can be directly guided by a cable or other device or component, the carrier wave can be such a cable, device, or component. Alternatively, the carrier can be an integrated circuit embedded with the program, where the integrated circuit is adapted to execute the relevant process or to be used for carrying out the relevant process.

[0099] The present invention is not limited to the embodiments described with reference to the accompanying drawings and can vary freely within the scope of the appended claims.

[0100] The term "comprising", when used herein, is understood to mean the presence of the specified features, integers, steps, or components. However, the term does not exclude the presence or addition of one or more additional features, integers, steps, or components, or groups thereof.

Claims

1. A system for remotely locating a ground fault in a polyphase power grid powered by a power source (310), the system comprising: An AC voltage source (380), synchronized with the power grid and connected between the neutral point (N) and the ground (E) of the power grid; A control unit (370), configured to control the AC voltage source (380) in a fault current compensation mode to compensate any ground fault current in the power grid to a value below a threshold level, and At least one local detector (351, 352, 35N), arranged in the power grid and communicatively connected to the control unit (370), the at least one local detector (351, 352, 35N) being configured to detect and record measurement values representing zero-sequence current and zero-sequence admittance; Characterized in that the at least one local detector (351, 352, 35N) is further configured to detect measurements of records to be applied by the control unit (370) to determine the ground fault impedance R F and the corresponding incremental angular step X; The system further comprises at least one remote detector (361, 362, 363, 364, 36N, 36N+1, 36N+2), the at least one remote detector being arranged in the power grid but not communicatively connected to the control unit (370), wherein each at least one remote detector has a unique current mode identifier; When in the remote ground fault detection mode, the control unit (370) is configured to adjust the output voltage of the AC voltage source (380) according to the determined ground fault impedance R F and the corresponding incremental angle step X to generate a zero-sequence current pattern based on the impedance and the incremental angle step X; Each at least one remote detector (361, 362, 363, 364, 36N, 36N+1, 36N+2) is configured to identify a zero-sequence current mode and determine which remote detector has a unique current mode identifier corresponding to the identified current mode.

2. The system according to claim 1, wherein the determined remote detector is configured to disconnect a fault section associated with the determined remote detector by applying a circuit breaker (421, 422, 423, 424, 42N, 42N+1) associated with the remote detector.

3. The system according to claim 2, wherein after disconnecting the fault section, the control unit (370) is configured to control the neutral reactor (330) to be retuned to match the adjusted network size and continue the fault current compensation mode to compensate any ground fault current in the power grid to a value below a threshold level.

4. An application method for a system for remotely locating a ground fault in a polyphase power grid powered by a power source (310), the system comprising: An AC voltage source (380), synchronized with the power grid and connected between the neutral point (N) and the ground (E) of the power grid; A control unit (370), configured to control the AC voltage source (380) in a fault current compensation mode to compensate any ground fault current in the power grid to a value below a threshold level; At least one local detector (351, 352, 35N), arranged in the power grid and communicatively connected to the control unit (370), the at least one local detector (351, 352, 35N) being configured to detect and record measurement values representing zero-sequence current and zero-sequence admittance, Characterized in that the system further comprises at least one remote detector (361, 362, 363, 364, 36N, 36N+1, 36N+2), the at least one remote detector being arranged in the power grid but not communicatively connected to the control unit (370), wherein each of the at least one remote detector has a unique current mode identifier; wherein the method comprises: - Detecting, by means of the at least one local detector (351, 352, 35N), measurements of records to be applied by the control unit (370) to determine the ground fault impedance R F and the corresponding incremental angular step X; - When in the remote ground fault detection mode, the output voltage of the AC voltage source (380) is adjusted by the control unit (370) according to the determined ground fault impedance R F and the corresponding incremental angle step X; - generating a zero-sequence current mode based on the impedance and the incremental angle step X; - identifying the zero-sequence current mode by each of the at least one remote detector (361, 362, 363, 364, 36N, 36N+1, 36N+2), and - determining which remote detector has a unique current mode identifier corresponding to the identified current mode.

5. The method according to claim 4, wherein the method further comprises: Disconnecting a fault section associated with the determined remote detector by the determined remote detector by applying a circuit breaker (421, 422, 423, 424, 42N, 42N+1) associated with the remote detector.

6. The method according to claim 5, wherein after disconnecting the fault section, the method further comprises: - controlling, by the control unit, the zero-point reactor (330) to be retuned to match the adjusted network size, and - continuing the fault current compensation mode to compensate any ground fault current in the power grid to a value below a threshold level.

7. A computer program capable of being loaded into the memory (375) of at least one processor, comprising software for performing the method according to any one of claims 4 to 6 when the program runs in the at least one processor.

8. A processor-readable medium (375) storing a program, wherein when the program is loaded into at least one processor, the program is arranged to cause the at least one processor to perform the method according to any one of claims 4 to 6.

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