Phase Selection Method

Abstract

A method is provided for determining a type of fault in a power line. The method includes obtaining voltage and current measurements at measurement points on the power line. The method further includes determining transient energy over a first time period for several phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements. The method further includes determining a transient energy ratio for the phase-to-ground loop and the phase-to-phase loop. The method further includes comparing the transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop and determining a type of fault based on the comparison.

Description

[Technical field]

[0001] Technical Field The present disclosure relates generally to fault detection in power systems. In particular, it relates to a method for determining a fault on a power line. [Background technology]

[0002] background Transmission lines are a critical part of the electric distribution system as they provide a path for transferring power between generation and loads. Transmission lines are ideally tightly interconnected for reliable operation. Factors such as deregulated market environments, economics, right-of-way clearances, and environmental requirements force utilities to operate transmission lines close to their operational limits. If a fault is not detected and quickly isolated, it can cascade into a system-wide failure, causing widespread outages of tightly interconnected systems operating near their limits. Transmission protection systems are designed to identify the point of the fault and isolate only the section where the fault occurs. A key challenge for transmission line protection is in reliably detecting and isolating faults that compromise the security of the system.

[0003] Phase selection is the determination of which phase is involved in the fault. Phase selection function is one of the important protection functions for selective tripping in case of transmission line faults. In many implementations, single phase tripping can be highly advantageous in case of phase-to-ground faults, which is more than 60% of transmission line faults. By using phase selection logic, it is possible to trip only the faulted phase so that healthy phases are connected in the remaining system. In this way, the stability of the overall power system can be maintained.

[0004] In wind farm connected power grid, the distance protection located at the wind farm side meets new challenges in both phase selection and line fault identification due to the nonlinear behavior of the system. As a weak system source with nonlinear behavior during fault conditions, it is desirable to provide a new solution for reliable phase selection.

[0005] Previous solutions provide phase selection based on phase current changes or phase voltage changes. It has been found that in wind farm connected power grids, methods based on phase current changes cannot provide perfect selectivity. On the other hand, it has also been found that phase selection methods based on phase voltage changes may work in wind farm connected grids, but may not perform well in the case of strong system conditions.

[0006] It has therefore become desirable to develop a more generalized phase selection solution using single-ended measurements, which can meet both weak end and strong source system conditions. Summary of the Invention [Problem to be solved by the invention]

[0007] overview It is therefore an object of the present invention to overcome at least some of the above-mentioned drawbacks and provide improved fault determination and phase selection for power lines. [Means for solving the problem]

[0008] This and other objects are achieved by a method, an apparatus and a computer readable medium comprising instructions as defined in the accompanying independent claims. Further embodiments are defined by the dependent claims.

[0009] According to a first aspect of the disclosure, a method for determining a type of fault in a power line is provided. The method includes obtaining voltage and current measurements at measurement points on the power line. The method further includes determining transient energy over a first time period for several phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements. The method further includes determining a transient energy ratio for the phase-to-ground loop and the phase-to-phase loop. The method further includes comparing the transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop. The method further includes determining a type of fault based on the comparison.

[0010] It is common for power lines to be three-phase. For such three-phase power lines, there are three phase-to-phase loops and three phase-to-ground loops.

[0011] According to some embodiments, determining the transient energy ratio may include dividing the phase-grounded loop transient energy by the lowest of the phase-grounded loop transient energies. Determining the transient energy ratio may further include dividing the phase-to-phase loop transient energy by the lowest of the phase-to-phase loop transient energies.

[0012] The method may include dividing each inter-phase loop transient energy by the lowest of the inter-phase loop transient energies.

[0013] The method may include dividing each phase ground loop transient energy by the lowest of the phase ground loop transient energies.

[0014] Thereby, the transient energy of a loop of a certain type (meaning phase-to-phase and / or phase-to-ground type) may be normalized to other loops of the same type. Normalizing the transient energy of a loop of a certain type may facilitate comparison of the relative size of the transient energy of that loop type. Specifically, when the transient energy ratio is based on the normalization of the transient energy, at least one transient energy of each loop type, i.e., the lowest energy, will be equal to 1.

[0015] According to some embodiments, determining the transient energy ratios may include replacing each phase-to-phase loop transient energy ratio by a first replacement value if the absolute value of the lowest one of the phase-to-phase loop transient energies is below a first predetermined minimum value, and replacing each phase-to-phase loop transient energy ratio by a second replacement value if the absolute value of the lowest one of the phase-to-phase loop transient energies is below a second predetermined minimum value.

[0016] If the minimum transient energy for a loop type (i.e., minimum phase-to-phase loop transient energy or minimum phase-to-ground loop transient energy) is too close to zero, the algorithm may become unstable. Therefore, if a divisor is too close to zero (i.e., absolute value below a predefined minimum / threshold), the associated ratio may be replaced by a larger number, such as 1000.

[0017] According to some embodiments, the method may further include obtaining further voltage and current measurements at the measurement points during the second time period. The method may further include determining further transient energy over the second time period for some of the phase-to-ground loops and some of the phase-to-phase loops. The method may further include determining further transient energy ratios for the phase-to-ground loops and the phase-to-phase loops. The method may further include comparing the further transient energy ratios to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop. Determining the type of fault may be based on the comparison of the transient energy ratios and the comparison of the further transient energy ratios.

[0018] In this case, the determination of failure is based on measurements made over at least two time periods. Thus, the determination of failure may be confirmed at least once before a final determination is made. Such an embodiment may provide a more reliable method for determining failure.

[0019] According to some embodiments, the type of fault to be determined may include a phase-to-ground fault and a phase-to-phase fault.

[0020] Different types of faults can occur on power lines. For example, a single-phase to earth fault can occur when one conductor falls to the ground or makes contact with the neutral conductor of the power line. In such a fault, there is a dielectric breakdown between one of the phases and earth. Similarly, in a two-phase to earth fault, two phases are connected to ground. In a phase-to-phase fault, two phases are connected together, and in a three-phase fault, all three phases are connected together.

[0021] The method may be (or may include) a phase selection method. The method may determine which phases of the power line are involved in the fault.

[0022] According to some embodiments, the method may further include obtaining at least one fault candidate loop among the number of phase-grounded loops and phase-to-phase loops. Determining a type of fault may be further based on the at least one obtained fault candidate loop.

[0023] The at least one fault candidate loop may be a list of loops that have previously been determined as possibly having a fault. Such a determination may be based, for example, on measurements made on the power line. The method for determining the type of fault in the power line may be triggered by the presence of the at least one fault candidate loop.

[0024] There are different methods for determining fault candidate loops. For example, the determination of fault candidate loops may be performed as part of a starting function. Some methods for determining fault candidate loops may include determining a fault indication quantity for each of several phase-to-ground loops and phase-to-phase loops of the power line based on the acquired voltage and current measurements. Obtaining at least one fault candidate loop may further include comparing each fault indication quantity with a dedicated interval, and if any one of the fault indication quantities is outside its dedicated interval, identifying each phase-to-ground loop and / or phase-to-phase loop whose associated fault indication quantity exceeds its dedicated interval as a fault candidate loop.

[0025] The fault indication quantity may be a value obtained or calculated from the obtained voltage and current measurements. The fault indication quantity may be, for example, one of a current, an incremental current, a voltage, or an incremental voltage. The fault indication quantity may be compared to a dedicated interval to see if the fault indication quantity is within normal operating conditions. A fault indication quantity being outside of its dedicated interval may be an indication that a fault may have occurred in the loop associated with the fault indication quantity.

[0026] According to some embodiments, a three-phase fault may be determined when a zero-mode voltage obtained from the obtained voltage and current measurements is below a first zero-mode voltage threshold, a zero-mode current obtained from the obtained voltage and current measurements is below a first zero-mode current threshold, all determined phase-to-ground loop transient energy ratios are below a first threshold level, and the at least one fault candidate loop includes all three phase-to-phase loops and all three phase-to-phase loops.

[0027] In a three-phase fault, a connection is made between the three phases. In theory, such a fault may not result in zero-mode current or voltage. Thus, in practice, in the case of a three-phase fault, the zero-mode current may fall below the first zero-mode current threshold. Furthermore, in practice, in the case of a three-phase fault, the zero-mode voltage may fall below the first zero-mode voltage threshold.

[0028] Furthermore, theoretically, and in the case of a three-phase fault, the absolute value of the transient energy of each of the phase-grounded loops may be substantially equal, and therefore the difference between the transient energy ratios of the phase-grounded loops may be small or even less than the first threshold level.

[0029] Furthermore, in a three-phase fault on a three-phase power line, all loops (phase-to-ground and phase-to-phase) may contain the faulted phase. Therefore, the fault candidate loop determination may flag / identify all loops as fault candidate loops.

[0030] According to some embodiments, for a given phase, a single phase-to-ground fault may be determined if the phase-to-ground loop transient energy ratio for the given phase is higher than the other phase-to-ground loop transient energy ratios, the phase-to-phase loop transient energy ratio including the given phase is higher than the phase-to-phase loop transient energy ratio not including the given phase, and the phase-to-ground loop for the given phase is a fault candidate loop.

[0031] In a single phase to ground fault, a connection is made between one phase and ground. In such a fault, the transient energy of the phase-to-ground loop containing the faulted phase may be greater than the transient energy of the other phase-to-ground loops. The transient energy ratio of the phase-to-ground loop containing the faulted phase may be higher than a threshold value, and the transient energy ratio of the other phase-to-ground loops may be lower than the same threshold value (e.g., the first single phase to ground threshold value).

[0032] Additionally, the transient energy of the inter-phase loop that includes the faulted phase may be higher than the transient energy of the inter-phase loop that does not include the faulted phase. The transient energy ratio of the inter-phase loop that includes the faulted phase may be higher than a threshold value, and the transient energy ratio of the other inter-phase loop may be lower than the same threshold value (e.g., a second single-phase ground threshold value).

[0033] Further, the determination of fault candidate loops may include flagging / identifying all loops that contain a faulty phase as fault candidate loops.

[0034] According to some embodiments, for two given phases, a two-phase-to-ground fault is determined if the incremental zero-mode voltage obtained from the obtained voltage and current measurements is above a first incremental zero-mode voltage threshold level, the phase-to-ground loop transient energy ratio for the two given phases is higher than the other phase-to-ground loop transient energy ratios, all phase-to-phase loop transient energy ratios are lower than a second threshold level, and the phase-to-ground loop including the given phase and the phase-to-phase loop including the given phase are fault candidate loops.

[0035] In a two-phase to ground fault, a connection is made between the two phases and the ground. In the case of a ground fault, the zero-mode values ​​(current or voltage) may become large. Thus, if the incremental zero-mode voltage exceeds the first incremental zero-mode voltage threshold, a two-phase to ground fault may be determined.

[0036] Additionally, the absolute value of the phase-to-ground loop transient energy of the included phase may be higher than the absolute value of the other phase-to-ground loop transient energy. Thus, for a two-phase-to-ground fault, the phase-to-ground loop transient energy ratio for two given phases may be higher than a threshold value, and the other phase-to-ground loop transient energy ratio may be lower than the same threshold value (e.g., a two-phase-to-ground threshold).

[0037] Furthermore, for a two-phase to ground fault, the difference between the phase-to-phase loop transient energies may be fairly small such that all phase-to-phase loop transient energy ratios are below the second threshold.

[0038] Further, the determination of fault candidate loops may include flagging / identifying all loops that contain a faulty phase as fault candidate loops.

[0039] According to some embodiments, for two given phases, a two-phase fault is determined if the phase-to-ground loop transient energy ratio involving the given phase is higher than the other phase-to-ground loop transient energy ratios, all phase-to-phase loop transient energy ratios are lower than a third threshold, and the phase-to-ground loop involving the given phase and the phase-to-phase loop involving the given phase are fault candidate loops.

[0040] In a two-phase fault, a connection is made between two phases of a power line. In the case of a two-phase fault, the transient energy of the phase-to-ground loop that contains the faulted phase can be higher than the transient energy of the other phase-to-ground loops. The transient energy ratio of the phase-to-ground loop that contains the faulted phase may be higher than a threshold value, and the transient energy ratio of the other phase-to-ground loops may be lower than the same threshold value (e.g., a two-phase fault threshold).

[0041] Furthermore, in the case of a two-phase fault, the difference between the phase-to-phase loop transient energies may be fairly small such that all inter-phase loop transient energy ratios are below the third threshold.

[0042] Furthermore, the previous determination of faulty candidate loops may flag / identify all loops that contain a faulty phase as faulty candidate loops.

[0043] According to a second aspect of the present disclosure, a (second) method is provided for determining a type of fault in a power line. The (second) method includes obtaining current measurements at a first measurement point on the power line and at a second measurement point on the power line. ) method is and determining incremental differential currents over a first time period for a number of phase-to-ground and / or phase-to-phase loops of the power line based on the obtained current measurements. The (second) method further includes determining incremental differential current ratios for the phase-to-ground and / or phase-to-phase loops. The (second) method further includes comparing the incremental differential currents to a threshold value corresponding to the phase-to-ground or phase-to-phase loops and determining (4060) a type of fault based on the comparison.

[0044] According to a third aspect of the present disclosure, an apparatus is provided for determining a type of fault in a power line. The apparatus is configured to obtain voltage and current measurements from measurement points on the power line. The apparatus is further configured to determine transient energy over a first time period for a number of phase-to-ground loops and phase-to-phase loops based on the obtained voltage and current measurements. The apparatus is further configured to determine a transient energy ratio for the phase-to-ground loop and the phase-to-phase loop. The apparatus is further configured to compare the transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop, and determine a type of fault based on the comparison.

[0045] The device may be configured to cooperate with other devices / units / elements in a fault detection / isolation system, for example the device may be (or comprise) a phase selection unit for determining the type of fault in the power line.

[0046] According to some embodiments, the apparatus may further comprise or communicate / cooperate with an initiating element or a fault candidate loop determining element. The initiating element may be configured to determine at least one fault candidate loop of the number of phase-to-ground loops and phase-to-phase loops based on voltage and current measurements from measurement points on the power line. The apparatus may further be configured to determine a type of fault based on the at least one fault candidate loop.

[0047] Further embodiments of the apparatus may be configured to carry out the methods according to embodiments of the first and / or second aspect of the present disclosure.

[0048] According to a fourth aspect of the disclosure, a computer-readable medium is provided that includes instructions. The instructions, when executed by a processor, cause the processor to obtain voltage and current measurements at a measurement point on a power line. The instructions, when executed by the processor, further cause the processor to obtain at least one fault candidate loop of several phase-grounded and phase-to-phase loops of the power line. The instructions, when executed by the processor, further cause the processor to determine a transient energy over a first time period for several phase-grounded and phase-to-phase loops based on the obtained voltage and current measurements. The instructions, when executed by the processor, further cause the processor to determine a transient energy ratio for the phase-grounded loop and the phase-to-phase loop. The instructions, when executed by the processor, further cause the processor to compare the transient energy ratio to a threshold value corresponding to the phase-grounded or phase-to-phase loop, and determine a type of fault based on the comparison, and optionally based on the at least one fault candidate loop.

[0049] A processor for executing instructions may, for example, be part of an apparatus according to the third aspect of the present disclosure.

[0050] Other embodiments of the third aspect may include instructions that, when executed by a processor, cause the processor to perform the methods described above with reference to embodiments of the first aspect of the present disclosure.

[0051] It should be noted that other embodiments may be envisioned that use all possible combinations of the features recited in the above embodiments, and therefore the present disclosure also relates to all possible combinations of the features referred to herein.

[0052] BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments are described in more detail below with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0053] [Figure 1]FIG. 1 is a schematic diagram of a power line connected to a protective relay via a current transformer and a voltage transformer. [Diagram 2] FIG. 1 is a schematic diagram of a power line connected to a protective relay via a current transformer and a voltage transformer. [Diagram 3] 1 is a schematic diagram of a system for determining a type of fault in a power line, according to some embodiments. [Figure 4] 4 is a flowchart illustrating a method for determining a type of fault in a power line, according to some embodiments. [Diagram 5] 4 is a flow chart illustrating a portion of a method for determining a type of fault in a power line, according to some embodiments. [Figure 6] 4 is a flowchart illustrating a method for determining a type of fault in a power line, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] As shown in the figures, the sizes of elements and regions may be exaggerated for illustrative purposes and are thus provided to illustrate the general structure of the embodiments. Like reference numerals refer to like elements throughout the description.

[0055] Detailed Description Exemplary embodiments are described more fully below with reference to the accompanying drawings, in which presently preferred embodiments are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to those skilled in the art.

[0056] In the figures, features are identified by reference numbers consisting of the number of the figure to which it relates followed by the number of the feature, which are equivalent across all exemplary embodiments, e.g., common feature "10" is designated "110" in FIG. 1 and the corresponding feature is designated "210" in FIG. 2.

[0057] To facilitate understanding of the methods and apparatus provided by the present disclosure, the methods and apparatus are presented in the context of a power line fault determination / handling system.

[0058] FIG 1 is a diagram of a power line fault detection system 100. FIG 1 shows two power sources: a first local power source S at a local point L; L and a second remote power source S at remote point R. R 1 shows a power line 102 connected between the local point L and the remote point R. The power source may be, for example, a voltage source or a current source. The power line 102 may be, for example, a three-phase power line. The phases may be, for example, denoted A, B, and C. There is also an apparatus at local point L for determining a power line fault. The apparatus is implemented in this example as a protective relay 104 connected to the power line 102 via a current transformer 106 and a voltage transformer 108 at a measurement point at one end of the power line, this measurement point being the local point L mentioned above. The protective relay 104 measures the current i(t) and voltage v(t) of the power line 102 at discrete points in time or time instances, often denoted by sampling times. In the figure, a first fault F1 is also present on the power line between the local point L and the remote point R. The fault F1 is represented by a resistor R connected to ground. F and voltage source U F When a fault occurs on the power line, the current and / or voltage on the power line is affected, which can be detected with measurements made by the protective relay 104. In FIG. 1, a first fault F1 is located between the relay 104 and a remote point R. Thus, the first fault F1 causes a negative transient energy E1 measured at a measurement point L. If the protective relay 104 detects the negative transient energy E1, a forward fault F1 can be determined.

[0059] FIG. 2 is a diagram of the same fault detection system 200. All features in FIG. 2 are the same except that in FIG. 2 a second fault F2 occurs at the local power supply S L1 except that a second fault F2 is shown on the power line 202 between the power line F1 and the local point L. A second fault F2 causes positive transient energy E2 to be detected by the protective relay 204. If the protective relay 204 detects negative transient energy E2, a backward fault F2 can be determined.

[0060] 3 is a block diagram illustrating a system 320 for determining a type of fault in a power line, according to some embodiments. The system 320 may be implemented in a processor / controller, for example. Methods of the present disclosure may be performed in the system 320. In particular, at least a portion of the method may be performed in a phase calculation / selection module 326. According to some embodiments, an apparatus for determining a type of fault in a power line may include at least the phase calculation / selection module 326.

[0061] The system 320 includes a measurement acquisition module 322. The measurement acquisition module 322 is configured to acquire voltage and current measurements from measurement points on the power line, such as the local point L of the power line 102, 202 described above with reference to Figures 1 and 2. The voltage and current measurements include phase-to-ground loop currents and voltages, and phase-to-phase loop currents and voltages. For a three-phase power line, the phase-to-ground loops may be represented as AG, BG, and CG, and the phase-to-phase loops may be represented as AB, BC, and CA. The phase-to-ground loop currents and voltages are represented as i A (t), i B (t), i C (t), u A (t), u B (t), and u C (t). The phase-to-phase loop current and voltage are expressed as i AB (t), i BC (t), i CA (t), u AB (t), u BC (t), and u CA It may also be expressed as (t).

[0062] The measurement acquisition module 322 is further configured to provide / output the acquired measurements to the initiation module 324 , the phase selection module 326 , and the range calculation module 328 .

[0063] The methods of the present disclosure may be implemented primarily in the phase selection module 326. Certain embodiments of the methods may be implemented in part in the start-up module 324.

[0064] The fault determination method may include or be a phase selection method. The phase selection method may be preceded by a triggering function, and a particular outcome of an action in the triggering function may trigger execution of the phase selection method. For example, if the triggering function operates to indicate that there is a fault or failure on the power line, a phase selection scheme may be initiated to determine the fault type.

[0065] The initiation module 324 is configured to acquire / receive current and voltage measurements from measurement points on the power lines 102, 202 from the measurement acquisition module 322. The initiation module 324 is further configured to determine which phases, if any, may be involved in the fault. The initiation module 324 is further configured to provide / output the resulting at least one fault candidate loop to the phase selection module 326 and the coverage calculation module 328.

[0066] The phase calculation module 326 may obtain voltage and current measurements from measurement points on the power lines 102, 202 via the measurement acquisition module 322 and obtain at least one fault candidate loop from the starting module 324. The phase calculation module 326 determines a transient energy and a transient energy ratio for each of the phase-to-ground loop and the phase-to-phase loop based on the obtained voltage and current measurements. The phase calculation module 326 is further configured to determine a type of fault based on the transient energy ratio. Optionally, the determination may be further based on the obtained fault candidate loop.

[0067] The phase calculation module 326 is further configured to provide / output the determined type of fault to the trip decision module 330 .

[0068] System 3 2 3.0 optionally further comprises a coverage calculation module 328. The coverage calculation module 328 is configured to receive / acquire voltage and current measurements from measurement points on the power lines 102, 202 via the measurement acquisition module 322, and to acquire at least one fault candidate loop from the start-up module 324. Based on the acquired measurements and the fault candidate loop, the coverage calculation module 328 determines whether the fault is within the scope of the present fault handling system 3. 2 0. Along the power lines 102, 202, multiple fault handling systems 3 2 In such a case, each fault processing system 3 2 0 may be responsible for a fault occurring along a particular portion of the power line. The range calculation module 328 may, for example, determine the point of the fault or the distance between the measurement point L and the fault based on the range calculation.

[0069] The range calculation module 328 may output / provide its results to the trip decision module 330 .

[0070] The trip decision module 330 is configured to receive the determined type of fault from the phase calculation module 326. The trip decision module 330 may further receive / obtain input regarding the location / point of the fault from the coverage calculation module 328. The trip decision module 330 may determine to trip one of the multiple phases of the power line based on the fault determination based on the information received from the calculation module 326 and / or the coverage calculation module 328. The trip decision module 330 may perform a general trip decision T gen , or one or more individual phases T A , T B , and T C A trip decision for may be output.

[0071] A fault determination / handling system 3 includes one or more of a measurement acquisition module 322, a start-up module 324, a phase selection module 326, a reach calculation module 328, and a tripping module 330. 2 The functionality of the module may be implemented in at least one integrated circuit, such as an Application-Specific Integrated Circuit (ASIC) or Field-Programmable Gate Arrays (FPGAs). Alternatively, the module may be realized as one or more processors operating on computer program instructions in one or more computer memories that implement the module functions.

[0072] 4 is a flow chart illustrating an embodiment of a method for determining a type of fault according to a first aspect of the present disclosure. The method may be implemented, for example, in the system 3 described above with reference to FIG. 2 The present invention may be implemented in a device or system such as a digital camera or a computer.

[0073] The method 4000 includes, at step 4010, obtaining voltage and current measurements at measurement points on a power line, such as the power lines 102, 202 described above with reference to the previous figures.

[0074] The voltage and current measurements are A (t), i B (t), i C The phase-to-ground loop current represented by (t) and the voltage u A (t), u B (t), u C (t), and the phase-to-phase loop current i AB (t), i BC (t), i CA (t) and voltage u AB (t), u BC (t), and u CA Includes (t).

[0075] In step 4020, the method 4000 may optionally include receiving / obtaining at least one fault candidate loop among the phase-grounded loops AG, BG, CG, and the phase-to-phase loops AB, BC, CA.

[0076] In step 4030, the method 4000 further includes determining (4030) transient energy over a first time period for a number of phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements.

[0077] The transient energy may be calculated as follows:

[0078]

number

[0079] where Δu is the incremental voltage in a loop and Δi is the incremental current in the same loop. The incremental loop current Δi(t) is the difference between the loop current at a current point in time (or time instance), t, and a previous point in time (or time instance), tT, which may be a corresponding point in a previous fundamental frequency (50Hz / 60Hz) period (T) of the loop current.

[0080]

number

[0081] The incremental loop voltage Δu(t) is the difference between the loop voltage at a current point in time (or time instance), t, and a previous point in time (or time instance), tT, which may be the corresponding point in the previous fundamental frequency (50Hz / 60Hz) period (T) of the measured loop voltage.

[0082]

number

[0083] For a three-phase power line having phases A, B, and C, the transient energy may be calculated for three phase-to-ground loops (AG, BG, and CG), and three phase-to-phase loops (AB, BC, and CA), resulting in a total of six transient energy indices ΔE A , ΔE B , ΔE C , ΔE AB , ΔE BC , ΔE CA may be calculated.

[0084] In step 4040, the method 4000 includes determining a transient energy ratio for the phase-to-ground loop and the phase-to-phase loop of the power line.

[0085] In this step, the phase-to-ground loop transient energy ratio R A , R B , R C and the phase-to-phase loop transient energy ratio R AB , R BC , R CA may be determined.

[0086] The transient energy ratio may optionally be determined as the phase-grounded loop transient energy or the phase-to-phase loop transient energy divided by the lowest of the phase-grounded loop transient energy or the phase-to-phase loop transient energy, respectively.

[0087] Therefore, the transient energy ratio may be normalized, which may make the calculation more stable and easier to set. At the same time, it is also useful to improve the sensitivity and operating speed. For a three-phase power line, the phase-to-ground loop transient energy ratio may be determined as follows:

[0088]

number

[0089] The phase-to-phase loop transient energy ratio may be determined as follows:

[0090]

number

[0091] However, all the transient energies ΔE X is determined using Equation (1). Note that when determining the transient energy ratios using Equations 2 and 3, at least one phase-to-ground loop transient energy ratio and at least one phase-to-phase loop transient energy ratio is always equal to 1.

[0092] In some practical applications, the transient energy in the ratio calculation may be very small. When the transient energy is very small, the divisor min(ΔE A ,ΔE B ,ΔE C ) or min(ΔE AB ,ΔE BC ,ΔE CA ) may also be small. To stabilize the ratio calculation (division algorithm), in such cases, the divisor may first be compared to a threshold representing a minimum acceptable divisor value. If the divisor is smaller than the threshold (e.g., is zero or near zero), the ratio to be determined using that divisor may be replaced with a preset (large) value, such as 1000, to avoid problems with division by zero.

[0093] In step 4050, the method 4000 calculates the determined transient energy ratio R A , R B , R C , R AB , R BC , R CA to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop. Each transient energy ratio may be compared to its own dedicated threshold value. Alternatively, there may be a first set of threshold values ​​for the phase-to-ground loop transient energy ratio and a second set of threshold values ​​for the phase-to-phase loop transient energy ratio.

[0094] In step 4060, the method includes determining a type of fault based on the comparison, and optionally based on the (list of) at least one fault candidate loop. The determination of different types of faults is further described below with reference to FIG.

[0095] If a fault type can be determined based on the comparison, the method may proceed to notifying the fault in step 4070. If a fault cannot be determined, the method may return to obtaining (new) measurements in step 4010. The new measurements may be taken, for example, during a second, different period of time.

[0096] 5 is a flow chart illustrating an embodiment of at least a portion of a method for determining a type of fault according to a first aspect of the present disclosure. In particular, method 5060 illustrates an embodiment of step 4060 of method 4000 of determining a type of fault based on a comparison.

[0097] In step 5062, the method 5060 includes identifying a type of fault based on the comparison and (optionally) based on the at least one fault candidate loop.

[0098] For example, a three-phase fault may be identified if the following criteria are met: 1. The zero mode voltage V0 obtained from the voltage and current measurements is below a first zero mode voltage threshold:

[0099]

number

[0100] 2. The zero-mode current I0 obtained from the voltage and current measurements is the first zero-mode current Below threshold:

[0101]

number

[0102] 3. Three-phase ground loop transient energy ratio R A , R B , R C are all sufficiently small or below a first threshold S1:

[0103]

number

[0104] 4. All loops AG, BG, CG, AB, BC, and CA are fault candidate loops. For a given phase (using A as an example), a single-phase to earth fault may be identified if the following criteria are met: 1. Phase-to-ground loop transient energy ratio R involving a given phase A is the other phase ground loop ratio R B , R C Greater than:

[0105]

number

[0106] or

[0107]

number

[0108] However, S AG1 is the first single phase ground threshold. 2. Phase-to-phase loop transient energy ratio R involving a given phase AB , R CA is the other interphase loop transient energy ratio R BC Greater than:

[0109]

number

[0110] or

[0111]

number

[0112] However, S AG2 is the second single phase ground threshold. 3. The loop (AG, AB, CA) containing a given phase is a fault candidate loop.

[0113] For two given phases (using BC as an example), a two-phase to ground fault may be identified if the following criteria are met: 1. The incremental zero-mode voltage ΔV0 obtained from the voltage and current measurements is sufficiently large, i.e., above a first incremental zero-mode voltage threshold:

[0114]

number

[0115] where the incremental zero-mode voltage is the difference between the zero-mode voltage at a current point in time or time instance t and a previous point in time or time instance (tT), where the previous point in time is the corresponding point in the fundamental frequency period (T) prior to the zero-mode voltage:

[0116]

number

[0117] 2. Phase-to-ground loop transient energy ratio R involving a given phase B , R C is the other phase ground loop ratio R A Greater than:

[0118]

number

[0119] or

[0120]

number

[0121] However, S BCG1 is the first two-phase ground threshold. 3. Three interphase loop transient energy ratios R AB , R BC , R CA are all sufficiently small or below the second threshold S2:

[0122]

number

[0123] 4. Phase-to-ground loops (BG, CG) involving a given phase and phase-to-phase loops (BC) involving a given phase are fault candidate loops.

[0124] For two given phases (using BC as an example), a two-phase fault may be identified if the following criteria are met: 1. Phase-to-ground loop transient energy ratio R involving a given phase B , R C is the other phase ground loop ratio R A Greater than:

[0125]

number

[0126] or

[0127]

number

[0128] However, S BC1 is the first two-phase fault threshold. 2. Three interphase loop transient energy ratios R AB , RBC , R CA are all sufficiently small or below the third threshold S3:

[0129]

number

[0130] 3. Phase-to-ground loops (BG, CG) involving a given phase and phase-to-phase loops (BC) involving a given phase are fault candidate loops.

[0131] If no fault is determined in step 5062 , the method may return to obtaining (new) measurements in step 5010 .

[0132] After a fault is determined in step 5062, the method 5060 may optionally increment a counter associated with the type of fault in step 5064.

[0133] In step 5066, the method may optionally verify whether a counter associated with the type of fault has reached a value above a predetermined number, i.e. whether the type of fault has been identified a predetermined number of times. If the type of fault has not been identified a predetermined number of times, the method may return to taking (new) measurements in step 5010. If the type of fault has been identified a predetermined number of times, the type of fault may be determined and the method may proceed to signaling the fault in step 5070.

[0134] Steps 4070, 5070 may include presenting information regarding the determined fault to a tripping module, which may go ahead and trip one or more of the power line phases based (at least in part) on the information.

[0135] FIG. 6 is a flow chart illustrating one embodiment of a method for determining a type of fault according to a first aspect of the present disclosure.

[0136] In FIG. 6, the method 6000 begins by obtaining 6010 measurements as described above with reference to FIG.

[0137] However, in method 6000, there may be a start-up function prior to phase selection in steps 6022-6026 to determine if a fault candidate loop exists.

[0138] In step 6022, the method may include determining a fault indication for each of a number of phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements.

[0139] For example, the fault indication may be an incremental current Δi(t). The incremental current Δi(t) for each loop may be the difference between the loop current at a current point in time or time instance t and a previous point in time or time instance (tT), where the previous point in time is a corresponding point in a previous fundamental frequency period (T) of the loop current.

[0140]

number

[0141] In step 6024, the method may include comparing each fault indication quantity to a dedicated interval, and if any one of the fault indication quantities is outside its dedicated interval, identifying each phase-to-ground loop and / or phase-to-phase loop whose associated fault indication quantity exceeds its dedicated interval as a fault candidate loop.

[0142] If the fault indication quantity is an incremental current Δi(t), the comparison with the threshold may be as follows:

[0143]

number

[0144] where Δi(t) is the incremental loop current. I Nis the rated current of the current transformer 106. RMS is the RMS value for a given loop current. K1 and K2 are the settings for the fixed and floating thresholds.

[0145] A starting element / method based on incremental current may work well for example on power lines in wind farm applications even though wind farm controls may introduce non-linear phenomena into the fault current.

[0146] At step 6026, the method may include determining whether there is a fault candidate loop. If there is not a fault candidate loop, the method may return to obtaining measurements at step 6010. If there is a fault candidate loop, the method may proceed to determining 6030 a transient energy, determining 6040 a transient energy ratio (not shown), and comparing 6050 the transient energy ratio to a corresponding threshold (not shown), as described above with reference to steps 4030, 4040, and 4050 of method 4000 in FIG.

[0147] In some embodiments of the method described in this disclosure, only potential faults that include a fault candidate loop are further investigated. For example, if the (list of) at least one fault candidate loop does not include a loop that includes phase A, the method may include deciding not to investigate an AG (phase A to ground) fault.

[0148] Additionally, the method may include determining whether any zero mode quantities obtained from the measured currents and voltages exceed a corresponding zero mode threshold. The presence of a zero mode quantity exceeding the threshold may be an indication that there is a ground fault. Thus, if there is a zero mode quantity above the threshold (a "high" zero mode quantity), a ground fault may be investigated. On the other hand, if there is no zero mode quantity above the threshold (a "low" zero mode quantity), a phase-to-phase fault may be further investigated.

[0149] 4, in other embodiments, phase selection may be based on differential current. Method 4000 may be equivalent, except for the following: In step 4010, the method may include obtaining current (and voltage) measurements from two measurement points (eg, L and R in FIGS. 1 and 2).

[0150] In step 4030, instead of determining the transient energy, the method further comprises determining a differential current I for each of the phase-to-ground loops and / or each of the phase-to-phase loops. diffA , I diffB , I diffC and / or I diffAB , I diffBC , I diffCA The differential current is the difference between current measurements for a phase at two different measurement locations in a given protected transmission line, such as local point L and remote point R of the power lines 102, 202 in Figures 1 and 2. For example, the differential current for a phase-to-ground loop A G at time t may be calculated as follows:

[0151]

number

[0152] Here, I L,A (t) is the local power supply S L is the phase A current measured at the local measurement point L, and I R,A (t) is the remote power supply S R is the A phase current measured at the remote measurement point R. In most cases, the local power supply S L and remote power supply S R provides the same current but in the opposite direction.

[0153] The method further comprises: determining an incremental differential current ΔI for each of the phase-to-ground loop and / or the phase-to-phase loop based on the determined differential current. diffA , ΔI diffB , ΔI diffC and / or ΔI diffAB , ΔI diffBC , ΔI diffCA The method may further include determining:

[0154] The incremental differential currents in the phase-to-ground loop (e.g., AG) and the phase-to-phase loop (e.g., AB) may be calculated using the following equations for a time instance t, where time point (tT) is the time point in the previous fundamental frequency period (T):

[0155]

number

[0156] In step 4040, the method may include determining an incremental differential current ratio instead of determining a transient energy ratio.

[0157]

number

[0158] In step 4050, the method may include comparing the incremental differential current ratio to a corresponding threshold instead of comparing the transient energy ratio to a corresponding threshold.

[0159] In step 4060, the method may include determining a type of fault based on a comparison of the incremental differential current ratio to a corresponding threshold value.

[0160] A three-phase fault may be determined based on the incremental differential current ratios if: 1. The incremental zero mode voltage falls below the second incremental zero threshold:

[0161]

number

[0162] 2. The incremental differential current ratios of all phase-to-ground loops are below the fourth threshold:

[0163]

number

[0164] 3. All loops AG, BG, CG, AB, BC, and CA are fault candidate loops. For a given phase (using A as an example), a single-phase to ground fault may be determined based on the incremental differential current ratios when: 1. Phase-to-ground loop incremental differential current ratio R involving a given phase Ai is the other phase ground loop ratio R Bi , R Ci Greater than:

[0165]

number

[0166] 2. Interphase loop incremental differential current ratio R involving a given phase ABi , R CAi is the other interphase loop incremental differential current ratio R BCi Greater than:

[0167]

number

[0168] 3. The loop (AG, AB, CA) containing a given phase is a fault candidate loop. For two given phases (using BC as an example), a two-phase to ground fault may be determined based on the incremental differential current ratios if: 1. The incremental zero-mode voltage ΔV0 obtained from the voltage and current measurements is sufficiently large, i.e., above the third incremental zero-mode voltage threshold:

[0169]

number

[0170] 2. Phase-to-ground loop incremental differential current ratio R involving a given phase Bi , R Ci is the other phase ground loop ratio R Ai Greater than:

[0171]

number

[0172] 3. Three interphase loop incremental and differential current ratios R ABi , R BCi , R CAi are all sufficiently small or below the fifth threshold S5:

[0173]

number

[0174] 4. Phase-to-ground loops (BG, CG) involving a given phase and phase-to-phase loops (BC) involving a given phase are fault candidate loops.

[0175] For two given phases (using BC as an example), a two-phase fault may be determined based on the incremental differential current ratio if: 1. Phase-to-ground loop incremental differential current ratio R involving a given phase B , R C is the other phase ground loop ratio R A Greater than:

[0176]

number

[0177] 2. Three interphase loop incremental and differential current ratios R AB , R BC , R CA are all sufficiently small or below the sixth threshold S6:

[0178]

number

[0179] 3. Phase-to-ground loops (BG, CG) involving a given phase and phase-to-phase loops (BC) involving a given phase are fault candidate loops.

[0180] It should be noted that although the method in the above description is based on calculation of currents, voltages and energy in the time domain, the method may also be implemented in the phasor domain.

[0181] Those skilled in the art will understand that the present invention is in no way limited to the above-described preferred embodiments, but on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0182] Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements, or in various combinations with or without the other features and elements.

[0183] Furthermore, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

1. A method (4000) for determining a type of fault in a power line, comprising: obtaining (4010) voltage and current measurements at measurement points on the power line; determining (4030) transient energy for several phase-to-ground and phase-to-phase loops of the power line over a first time period based on the obtained voltage and current measurements; determining (4040) a transient energy ratio for the phase-to-phase loop and the phase-to-phase loop; comparing (4050) the transient energy ratio with a threshold value corresponding to the phase-to-phase loop or the phase-to-phase loop; determining a type of fault based on said comparison (4060); A method comprising:

2. Determining the transient energy ratio comprises: Dividing a phase-grounded loop transient energy by the lowest of the determined phase-grounded loop transient energies; dividing the interphase loop transient energy by the lowest of the determined interphase loop transient energies; The method of claim 1 , comprising:

3. if the absolute value of the lowest one of the phase ground loop transient energies is below a first predetermined minimum value, each phase ground loop transient energy ratio is replaced by a first replacement value; 3. The method of claim 2, wherein if the absolute value of the lowest of the phase-to-phase loop transient energies is below a second predetermined minimum value, then each phase-to-ground loop transient energy ratio is replaced by a second replacement value.

4. obtaining further voltage and current measurements at the measurement points during a second period of time; determining additional transient energy for the several phase-to-ground and phase-to-phase loops of the power line over a second time period based on the additional voltage and current measurements obtained; determining a further transient energy ratio for the phase-to-ground loop and the phase-to-phase loop; comparing the further transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop; Further comprising: determining the type of fault is based on the comparison of the transient energy ratios and the comparison of the further transient energy ratios.

13. A method according to any preceding claim.

5. 2. A method according to any preceding claim, wherein the types of faults to be determined include phase-to-ground faults and phase-to-phase faults.

6. obtaining at least one fault candidate loop among the number of phase-grounded loops and inter-phase loops; 2. The method of claim 1, wherein determining the type of fault is further based on the at least one obtained fault candidate loop.

7. A three-phase fault is a zero mode voltage obtained from the voltage and current measurements is below a first zero mode voltage threshold; a zero mode current obtained from the voltage and current measurements is below a first zero mode current threshold; all of the determined phase ground loop transient energy ratios are below a first threshold level; The at least one fault candidate loop includes all three phase-to-phase loops and all three phase-to-phase loops. The method of claim 6, wherein the determination is made if

8. For a given phase, a single phase to earth fault is the phase ground loop transient energy ratio for the given phase is higher than the other phase ground loop transient energy ratios; the interphase loop transient energy ratio including the given phase is higher than the interphase loop transient energy ratio not including the given phase; The phase-grounded loop for the given phase is a fault candidate loop. The method according to claim 6 or 7, wherein the determination is made in the case.

9. For two given phases, a two-phase to earth fault is an incremental zero-mode voltage obtained from the voltage and current measurements exceeds a first incremental zero-mode voltage threshold; the phase ground loop transient energy ratio for the two given phases is higher than the phase ground loop transient energy ratio for the other of the two given phases; all of said phase-to-phase loop transient energy ratios are below a second threshold; The phase-to-phase loop including the given phase and the inter-phase loop including the given phase are fault candidate loops. The method according to any one of claims 6 to 8, wherein the determination is made in the case.

10. For two given phases, a two-phase fault is the phase-grounded loop transient energy ratio including the given phase is higher than the other phase-grounded loop transient energy ratios; all of said phase-to-phase loop transient energy ratios are below a third threshold; The phase-to-phase loop including the given phase and the inter-phase loop including the given phase are fault candidate loops. The method according to any one of claims 6 to 9, wherein the determination is made in the case.

11. 1. A method for determining a type of fault in a power line, comprising: obtaining (4010) current measurements at a first measurement point on the power line and at a second measurement point on the power line; determining (4030) incremental differential currents over a first time period for several phase-to-ground and / or phase-to-phase loops of the power line based on differential currents calculated from the obtained current measurements; determining (4040) incremental differential current ratios for the phase-to-ground loop and / or the phase-to-phase loop; comparing (4050) the incremental differential current to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop; determining a type of fault based on said comparison (4060); A method comprising:

12. 1. An apparatus (326) for determining a type of fault in a power line, comprising: obtaining voltage and current measurements from measurement points on the power line; determining transient energy for a number of phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements over a first time period; determining a transient energy ratio for the phase-to-ground loop and the phase-to-phase loop; comparing the transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop; Determine the type of fault based on said comparison The apparatus is configured so as to

13. A computer-readable medium containing instructions that, when executed by a processor, cause the processor to: obtaining voltage and current measurements at measurement points on the power line; determining transient energy for a number of phase-to-ground and phase-to-phase loops of the power line based on the obtained voltage and current measurements over a first time period; determining a transient energy ratio for the phase-to-phase loop and the phase-to-phase loop; comparing the transient energy ratio to a threshold value corresponding to the phase-to-ground loop or the phase-to-phase loop; determining a type of fault based on said comparison; Computer-readable medium.

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