Method for determining power system faults

Abstract

A method for determining faults in an electric power system includes estimating a voltage at a second location of a transmission line in the electric power system based on measured electrical quantities at a first location of the transmission line, the measured electrical quantities being related to three phases of the electric power system and including a voltage at the first location of the transmission line (601), determining at least one phase angle between the voltage at the first location and the estimated voltage at the second location (602), and detecting a fault based on the at least one phase angle during power oscillations (603). In the method according to the present disclosure, three-phase faults during power oscillations are identified in a shorter time and therefore tripping is performed faster, resulting in improved stability and safety of the electric power system.

Description

[Technical Field] 【0001】 Embodiments of this disclosure relate to power transmission in general, and more specifically to methods for determining faults in power systems. [Background technology] 【0002】 In power systems, system failures such as power system malfunctions, power line switching, generator disconnections, and load losses can cause power fluctuations. When a power system experiences stable power fluctuations, it can maintain stability and return to a new equilibrium state. However, some serious system failures can lead to a loss of synchronization between generator groups, for example. Both stable and unstable power fluctuations can cause undesirable relay behavior, further exacerbating system failures and potentially leading to large-scale blackouts or power outages. 【0003】 Generally, distance relays are equipped with a power fluctuation blocking (PSB) function to avoid such undesirable relay operation during power fluctuations. In particular, the PSB function can distinguish between faults and power fluctuations and block the operation of distance relay elements or other relay elements during power fluctuations. 【0004】 PSB (Power Station Breakdown) functionality must also consider faults that occur during power fluctuations. In this case, the PSB must unblock and relays must operate to eliminate such faults, such as three-phase faults. Unfortunately, identifying faults during power fluctuations is difficult, and conventional solutions require long periods of time to identify faults in order to avoid mis-tripping. Slow fault protection during power fluctuations negatively impacts the stability and safety of the power system. [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 Embodiments of this disclosure provide an improved solution for determining power system faults. [Means for solving the problem] 【0006】 In a first embodiment, a method for determining a fault in a power system is provided. The method includes estimating a voltage at a second location of a transmission line based on a measured amount of electricity at a first location of the transmission line in a power system, wherein the measured amount of electricity is associated with the three phases of the power system and includes the voltage at the first location of the transmission line; determining at least one phase angle between the voltage at the first location and the estimated voltage at the second location; and detecting a fault based on the at least one phase angle during a power fluctuation. 【0007】 In some embodiments, determining at least one phase angle between a voltage at a first position and an estimated voltage at a second position includes determining a first phase angle between the phase voltage of a first phase at the first position and an estimated phase voltage of the first phase at the second position, and determining a second phase angle between the phase-to-phase voltage of a second to a third phase at the first position and an estimated phase-to-phase voltage of a second to a third phase at the second position. 【0008】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of the three phases, determining the phase angle between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position. 【0009】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of three two-phase combinations, determining the phase angle between the inter-phase voltage of each two-phase combination at the first position and the estimated inter-phase voltage of the same two-phase combination at the second position. 【0010】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of the three phases, determining a first phase angle between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position; for each of the three two-phase combinations, determining a second phase angle between the phase voltage of each two-phase combination at the first position and the estimated phase voltage of the same two-phase combination at the second position; and determining at least one phase angle based on the first phase angle of the three phases and the second phase angle of the three two-phase combinations. 【0011】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes determining the phase angle between the positive-sequence component of the phase voltage of one of the three phases at the first position and the positive-sequence component of the estimated phase voltage of the same phase at the second position. 【0012】 In some embodiments, detecting a fault based on at least one phase angle during a power fluctuation includes determining a time threshold for each of the at least one phase angle based on a measured duration during which the respective phase angle was previously within a predetermined range, and determining a fault if the duration during which any of the at least one phase angle was within the predetermined range exceeds the respective time threshold. 【0013】 In some embodiments, detecting a fault based on at least one phase angle during a power fluctuation includes detecting a fault based on the rate of change of at least one phase angle with respect to time during a power fluctuation. 【0014】 In some embodiments, detecting a fault based on the rate of change of at least one phase angle with respect to time during a power fluctuation includes: determining the rate of change of each of the at least one phase angles with respect to time, such that each phase angle falls within a predetermined range; determining a time threshold for each of the at least one phase angles based on the determined rate of change and the predetermined range; and determining a fault if the duration of any of the at least one phase angles within the predetermined range exceeds the respective time threshold. 【0015】 In some embodiments, determining the rate of change of each phase angle with respect to time includes determining the instantaneous rate of change of each phase angle with respect to time, such that each phase angle falls within a predetermined range. 【0016】 In some embodiments, determining the rate of change of each phase angle with respect to time includes determining the average rate of change of each phase angle with respect to time in the recent cycle of the power fluctuation, depending on whether each phase angle falls within a predetermined range. The recent cycle of the power fluctuation includes the period from when it previously entered the predetermined range to when it is currently entered within the predetermined range. 【0017】 In some embodiments, detecting a fault based on the rate of change of at least one phase angle with respect to time during a power fluctuation includes determining the instantaneous rate of change of each of the at least one phase angles with respect to time, such that each phase angle falls within a predetermined range, and determining a fault when the instantaneous rate of change of any of the at least one phase angles exceeds a predetermined threshold. 【0018】 In some embodiments, estimating the voltage at a second location on a transmission line involves calculating the voltage at the second location on the transmission line in the time domain based on a measured amount of electricity. 【0019】 In a second embodiment, an electronic device is provided, comprising: at least one processor unit; and at least one memory coupled to the at least one processor unit and storing instructions that can be executed by the at least one processor unit. When an instruction is executed by the at least one processor unit, the device causes the device to perform the method according to the first embodiment. 【0020】 In some embodiments, the electronic device includes a distance relay used in a power system. 【0021】 In a third aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores computer-readable program instructions, which, when executed by a processor unit, cause the processor unit to execute the method according to the first aspect. [Brief explanation of the drawing] 【0022】 The drawings provided herein are for further illustrative purposes and constitute part of the Disclosure. Exemplary embodiments and descriptions thereof are used to illustrate the Disclosure, not to unduly limit it. [Figure 1A] A schematic diagram of the measured oscillation impedance and PSB characteristics from the relay when no fault occurs is shown. [Figure 1B] This diagram shows a schematic representation of the measured oscillation impedance from a relay and the PSB characteristics when a fault occurs during power oscillation. [Figure 2] A schematic diagram of a simple two-power supply system connected by impedance transmission lines according to an embodiment of the present disclosure is shown. [Figure 3] A schematic diagram of the voltage vector during power fluctuation according to an embodiment of this disclosure is shown. [Figure 4] The waveform diagram of a power system during power fluctuations according to an embodiment of this disclosure is shown. [Figure 5]A schematic diagram of the dual power supply system in the event of a failure is shown. [Figure 6] A flowchart of a method for determining a failure in a power transmission system according to an embodiment of this disclosure is shown. [Figure 7] In some embodiments, flowcharts are shown to detect faults based on the rate of change of at least one phase angle with respect to time. [Figure 8A] The waveform diagram of the phase angle during power fluctuations is shown. [Figure 8B] An enlarged waveform diagram of the phase angle is shown. [Figure 9A] This shows the logic diagram for fault detection and tripping. [Figure 9B] This shows the logic diagram for fault detection and tripping. [Figure 10] An alternative implementation for determining the rate of change of the phase angle with respect to time is shown. [Figure 11] A schematic diagram of a two-power supply system, showing the system frequencies, is provided. [Figure 12] A schematic block diagram of an exemplary apparatus suitable for carrying out the embodiments of this disclosure is shown. 【0023】 Throughout the drawings, identical or similar reference numerals are used to indicate identical or similar elements. [Modes for carrying out the invention] 【0024】 Next, the principles of this disclosure will be described with reference to some exemplary embodiments shown in the drawings. While the drawings show exemplary embodiments of this disclosure, it should be understood that these embodiments are provided solely to facilitate a better understanding and implementation of the disclosure by those skilled in the art, and are not intended to limit the scope of the disclosure in any way. 【0025】 The terms “equipped with” or “include” and their variations are interpreted as open terms meaning “include, but not limited to.” The term “or” is interpreted as “and / or” unless the context clearly indicates otherwise. The term “based on…” is interpreted as “at least partially based on….” “Operable” means that a function, action, movement, or state can be achieved by an action induced by a user or an external mechanism. The terms “one embodiment” and “embodiment” are interpreted as “at least one embodiment.” The term “another embodiment” is interpreted as “at least one other embodiment.” Terms such as “first,” “second,” etc., may refer to different or the same subject. The following may include other explicit and implicit definitions. Definitions of terms are consistent throughout the description unless the context clearly indicates otherwise. 【0026】 Unless otherwise specified or limited, the terms “attachment,” “connection,” “support,” and “joining,” and their variations, are used broadly to encompass direct and indirect attachments, connections, supports, and joinings. Furthermore, “connected” and “joined” are not limited to physical or mechanical connections or joinings. In the following description, the same reference numbers and labels are used in the figures to describe identical, similar, or corresponding parts. The following content may include other explicit and implicit definitions. 【0027】 Figure 1A shows a schematic diagram of the measured oscillation impedance and PSB characteristics from the relay when no fault occurs. Figure 1B shows a schematic diagram of the measured oscillation impedance and PSB characteristics from the relay when a fault occurs during power oscillation. 【0028】 As shown in Figure 1A, the PSB characteristics may include an inner characteristic and an outer characteristic, indicated by the inner and outer circles, respectively. If the oscillation impedance remains between the inner and outer characteristics for a longer period than a predetermined time, power oscillation is detected and the distance relay is blocked. In other regions outside the operating characteristics of the distance relay, the distance relay is not blocked. 【0029】 As shown in Figure 1B, when the oscillation impedance moves along the curve to point M, a fault occurs, and the fault impedance is maintained at point N. 【0030】 During power fluctuations, the impedance enters the operating characteristics of the distance relay, and it is understood that the impedance also enters the operating characteristics in the case of a fault (e.g., a three-phase fault). The relay cannot know whether it is a power fluctuation or a fault. To identify and eliminate this fault, conventional solutions are based on the assumption that when a fault occurs, the impedance remains in the operating region of the distance relay, and in the case of power fluctuations, the impedance enters the operating region of the distance relay and leaves the operating region after a waiting period. In other words, the relay can determine the fault by waiting for a sufficient amount of time. Conventional solutions clearly require a long waiting period to avoid mistripping. Furthermore, determining the waiting time requires parameters of the power system and power lines, which makes the settings of conventional solutions complex. 【0031】 To address the above and other potential problems at least partially, embodiments of the present disclosure provide an improved solution for determining faults in a power transmission system. This solution allows for fault determination based on the angular difference between the voltages at two locations on a power line. As a result, the waiting time for fault determination is significantly reduced, tripping is performed more quickly, and the safety of the power system is improved. 【0032】 Figure 2 shows a schematic diagram of a simple two-power system connected by impedance transmission lines according to an embodiment of the present disclosure. The system shown in Figure 2 is a three-phase power system, E m and E n The points at both ends refer to the power sources. Point P indicates the first position of the transmission line, for example, power source E m This refers to the buses of the power system on the side. Point Q indicates a second position on the transmission line, such as a pre-installed point on the transmission line. Z has resistance R and inductance L. set This shows the impedance of the transmission line between point P and point Q.m Between point Q and power source E n Please note that there is also an impedance between these two points, which is not shown in the diagram. 【0033】 The electrical quantities at point P can be measured or obtained by a relay or other measuring device located at point P, such as a relay located on or near the bus between the power source and the transmission line. These electrical quantities include the three-phase voltage, current, and other parameters at point P. The voltage at point P is sometimes called the local voltage, and the voltage at point Q is sometimes called the compensation voltage, and is calculated based on the electrical quantities obtained at point P. The compensation voltage at a given point Q can be calculated by the following formula. 【0034】 【number】 【0035】 Figure 3 shows a schematic diagram of the voltage vector during power fluctuation according to an embodiment of the present disclosure. Figure 4 shows a waveform diagram of the power system during power fluctuation according to an embodiment of the present disclosure. Angle α is the power source E m and E n The phase angle difference is shown, and angle δ represents the phase angle difference between the local voltage at point P and the compensation voltage at a predetermined point Q. Specifically, angle δ may be expressed by the following equation. 【0036】 【number】 【0037】 When a power system begins to fluctuate, angle δ increases as angle α increases. During power fluctuations, if angle α changes periodically from 0° to 360°, angle δ also changes periodically from 0° to 360°. In other words, since angle δ reflects angle α, angle δ can be used as an indicator of the state of power fluctuations. 【0038】 FIG. 5 shows a schematic diagram of the two-power-source system of FIG. 2 when a fault (e.g., a three-phase fault) occurs. As shown in FIG. 5, the fault occurs at point F on the transmission line. The fault point F is located between point P and point Q, and Z F represents the impedance between point P and the fault point F. For example, in the case of a three-phase fault, when a phase-to-phase short circuit occurs between the three phases, it can be assumed that the impedances Z F and Z set have substantially the same impedance angle, and Z F <Z set is. Therefore, when a three-phase fault occurs, the angle δ may be calculated by the following formula. 【0039】 【Equation】 【0040】 From the above, it can be seen that when an internal three-phase fault occurs, the angle δ is maintained at 180 degrees. Hereinafter, this will be referred to as the fault angle δ. However, if there is only power fluctuation, the angle δ changes periodically from 0 degrees to 360 degrees. The 180 degrees of the fault angle δ is merely exemplary, and due to the arrangement of the impedance of the power line or other errors, generally the impedances Z F and Z set may have different impedance angles, and thus it should be noted that the angle δ in the fault may be other angles higher or lower than 180 degrees. 【0041】 Furthermore, such changes in the angle δ may also exist in other types of faults other than three-phase faults. For example, when a single-phase fault or a two-phase fault occurs at some positions on the transmission line, for example, at a position on the transmission line close to point P, the angle δ also changes to and is maintained at the fault angle δ. Based on this discovery, the faults in the power system can be effectively distinguished from power fluctuations. 【0042】 Based on the characteristics described above discovered by the inventors, an improved method is proposed to quickly identify faults during power fluctuations when a fault occurs and to trip more quickly. Figure 6 shows a flowchart of a method 600 for determining faults in a power transmission system according to an embodiment of the present disclosure. This method can be performed by a processor unit or controller of an electronic device such as a relay, as described above. For example, in some embodiments, the processor unit for performing the method may be an integral part of an existing processor or control unit located in the relay. In some alternative embodiments, the processor for performing the method may be a separate processor independent of the relay's existing processor. 【0043】 In some other alternative embodiments, the processor may be the processor of a device such as a computer located outside the relay. In practice, any suitable processor capable of performing the following methods may be used. 【0044】 As shown in Figure 6, in block 601, the voltage at a second location on a transmission line is estimated based on the measured electrical quantities at a first location on the transmission line within the power system. The measured electrical quantities are related to the three phases of the power system and include the voltage at the first location on the transmission line. For example, the first location may be point P in Figure 2 (e.g., a bus), and the second location may be point Q in Figure 2 (e.g., a predetermined point on the transmission line). As an example, the distance between the first and second locations may be 80-90% of the total length of the transmission line in the power system. However, the first and second locations may be any suitable locations within the power system. A relay such as an mho relay, or other measuring device, located at the first location (e.g., point P), can measure the electrical quantities at the first location. These electrical quantities include the voltage at the first location, e.g., the phase voltages and inter-phase voltages of the three phases. Furthermore, the electrical quantities also include other electrical quantities related to the three phases for use in estimating the voltage at the second location. The voltage at the second position can be estimated using equation (1) and the measured electric quantity at the first position. For example, the phase voltage and current at point P (e.g., phase A) and the impedance Z between point P and point Q. set Based on this, the phase voltage at point Q (for example, phase A) is calculated using equation (1). Similarly, the phase voltages of phase B and phase C at point Q can be calculated, and from this, the phase-to-phase voltages between phase A and phase B, phase B and phase C, or phase C and phase A can also be obtained. 【0045】 In block 602, at least one phase angle is determined between the voltage at the first position and the estimated voltage at the second position. For example, since the A-phase voltages at points P and Q are obtained from block 601, the phase angle δ between the A-phase voltages at the first and second positions (e.g., points P and Q) is determined. a This can be simply calculated and determined. Similarly, the phase angle δ between other phase voltages and phase-to-phase voltages. b , δ c , δ ab , δ bc , δ ca You can obtain this. 【0046】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes determining a first phase angle between the phase voltage of the first phase at the first position and the estimated phase voltage of the first phase at the second position, and determining a second phase angle between the phase voltages of the second to third phases at the first position and the estimated phase voltages of the second to third phases at the second position. For example, the phase angle δ between the voltages of phase A at the first and second positions. a The phase angle δ between the phase voltages from phase B to phase C at the first and second positions. bc This is sufficient to represent the state of all three phases of the power system during power fluctuations, therefore the phase angle δ a and phase angle δ bc You may calculate only that. Alternatively, you can calculate the phase angle δ. b , δ ca Only, or phase angle δ c , δ ab We may obtain only this. In this way, all phase angles δ a , δ b , δ c , δ ab , δ bc , δ ca Instead of determining the phase angle, calculating only two phase angles reduces the work involved in calculating and subsequently evaluating the phase angle, thereby speeding up fault detection. 【0047】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of the three phases, determining the phase angle between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position. For example, phase angle δ a , δ b , δ cThis may be calculated as at least one phase angle. In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of the three two-phase combinations, determining the phase angle between the inter-phase voltage of each two-phase combination at the first position and the estimated inter-phase voltage of the same two-phase combination at the second position. For example, as at least one phase angle, the phase angle δ ab , δ bc , δ ca You may also calculate this. In these two implementations, all phase angles δ a , δ b , δ c , δ ab , δ bc , δ ca Instead of determining the phase angles, calculating only three phase angles reduces the work involved in calculating and subsequently evaluating them. 【0048】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position includes, for each of the three phases, determining a first phase angle between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position; for each of the three two-phase combinations, determining a second phase angle between the phase voltage of each two-phase combination at the first position and the estimated phase voltage of the same two-phase combination at the second position; and determining an average angle as at least one phase angle based on the first phase angle of the three phases and the second phase angles of the three two-phase combinations. Specifically, the average of all phase angles can be used for fault assessment during power fluctuations and can be calculated by the following equation. δ average =( δ a +δ b +δ c +δ ab +δ bc +δ ca ) / 6 (4) This allows for subsequent evaluation or fault detection based on a single phase angle, simplifying subsequent work. 【0049】 In some embodiments, determining at least one phase angle between the voltage at a first position and the estimated voltage at a second position involves determining the phase angle between the positive-sequence component of the phase voltage of one of the three phases at the first position and the positive-sequence component of the estimated phase voltage of the same phase at the second position. Specifically, based on all the phase voltages of the three phases at the first position (e.g., point P), the positive-sequence component of any phase at the first position can be obtained, and similarly, the positive-sequence component of the phase at the second position can be obtained, according to approaches known in the art. This makes it possible to determine the phase angle between the positive-sequence components of the phase voltages (e.g., phase A, phase B, or phase C) at the first and second positions, which can be used to evaluate faults during power fluctuations. As a result, subsequent evaluations can be performed for a single phase angle, thus simplifying fault determination. 【0050】 In block 603, a fault is detected based on at least one phase angle during power fluctuations. For example, as described above for equation (3), if a fault occurs, the phase angle changes to 180 degrees and is then maintained at 180 degrees. Thus, the phase angle δ a , δ b , δ c , δ ab , δ bc , δ ca Based on the change in the phase angle δ, faults can be detected quickly. In some embodiments, the phase angle δ a , δ bc The fault can be detected by the phase angle δ. b , δ ca , phase angle δ c , δ ab , phase angle δ a , δ b , δ c , or phase angle δ ab , δ bc , δ ca It is also possible to detect faults by this method. In some embodiments, the fault is detected by all phase angles δ a , δ b , δ c , δ ab , δ bc , δ caIt can be detected by the average of the following. In some embodiments, a fault can be detected by the phase angle between the positive-sequence voltage components of the phase (e.g., phase A, phase B, or phase C) at the first and second positions. 【0051】 Compared to conventional solutions, fault detection described in Method 600 can be performed much faster without having to wait for a long time corresponding to the time it takes for the oscillation impedance to enter and exit the operating region of the relay, thus improving the stability and safety of the power system. Furthermore, in Method 600, the power system and power line parameters necessary to predetermine the time it takes for the oscillation impedance to enter and exit the operating region are conveniently omitted, thus simplifying fault detection. 【0052】 Figure 7 shows a flowchart for detecting faults based on the rate of change of at least one phase angle with respect to time in some embodiments. In some embodiments, detecting faults based on at least one phase angle during power fluctuations includes detecting faults based on the rate of change of at least one phase angle with respect to time during power fluctuations. As shown in Figure 7, in block 701, for each of the at least one phase angle, the rate of change of each phase angle with respect to time is determined in such a way that each phase angle falls within a predefined range. In block 702, a time threshold is determined for each of the at least one phase angle based on the determined rate of change and the predefined range. In block 703, a fault is determined if the duration of any of the at least one phase angles within the predefined range exceeds the respective time threshold. 【0053】 For illustrative purposes, Figure 8A shows the phase angle δ during power fluctuation. a , δ b , δ c , δ ab , δ bc , δ ca The waveform diagram is shown, and Figure 8B shows the phase angle δ a The enlarged waveform diagrams are shown. As shown in Figures 8A and 8B, each phase angle δ during power fluctuations. a , δb , δ c , δ ab , δ bc , δ ca varies from 0 degrees to 360 degrees in each cycle. As shown in the figure, if a fault occurs 4.5 seconds after a certain period, all phase angles will quickly change to 180 degrees and be maintained. 【0054】 To identify the fault, an angular range [δ1, δ2] including 80 degrees may be predefined. For example, the angular range [δ1, δ2] is [170, 190], that is, the range from 170 degrees to 190 degrees as shown in Figure 8B. Alternatively, the angular range [δ1, δ2] may be other appropriate ranges. When a fault occurs, obviously, the phase angles δ a , δ b , δ c , δ ab , δ bc , δ ca will surely fall within the predefined range. Furthermore, it is understood that the phase angles will also fall within this predefined range during power fluctuations. When each phase angle falls within the predefined range, the rate of change of each phase angle with respect to time is determined. As shown in Figure 8B, in some embodiments, the rate of change may be the instantaneous rate of change dδ / dt of each phase angle with respect to time when each phase angle enters the predefined range. And the reference threshold T0 may be calculated by the following formula. 【0055】 【Equation】 【0056】 To improve the reliability of fault detection and avoid mis-tripping, the time threshold T may be greater than the reference threshold T0, and thus can be calculated by the following formula. T = k rel × T0(6) For example, k rel may be 1.2 - 2.0, ensuring that T > T0. 【0057】 Figures 9A and 9B show the logic diagrams for fault detection and tripping. As shown in Figure 9A, a three-phase fault may be detected if, during the time threshold T, each phase angle δ remains within the range of [δ1, δ2] (e.g., [170, 190]). For example, the logic shown in Figure 9A is that all phase angles δ a , δ b , δ c , δ ab , δ bc , δ ca This may be performed on the phase angle δ, and a three-phase fault is determined when the duration of any one of these phase angles that falls within the range [δ1, δ2] reaches or exceeds a time threshold T. As shown in Figure 9B, in some embodiments, the phase angle δ a , δ bc A three-phase fault may be determined if either of the following remains within the range [δ1, δ2] (e.g., [170, 190]) for the duration of the time threshold T. Alternatively, the phase angle δ b , δ ca Either of the above, or phase angle δ c , δ ab A three-phase fault may be determined if either of the following remains within the range [δ1, δ2] (e.g., [170, 190]) for the duration of the time threshold T. Alternatively, the phase angle δ a , δ b , δ c Either of the above, or phase angle δ ab , δ bc , δ ca A three-phase fault may be determined if either of the following remains within the range [δ1, δ2] (e.g., [170, 190]) during the time threshold T. Similarly, the phase angle associated with the positive-sequence voltage component, or all phase angles δ a , δ b , δ c , δ ab , δ bc , δ ca A three-phase fault may be determined by the average of the values. 【0058】 As can be seen from the above, the reference threshold T0 represents the predicted time required for the phase angle to pass through a predetermined range (e.g., [170, 190]) during power fluctuations. In general, since the predetermined range (e.g., [170, 190]) is a relatively small interval, the instantaneous rate of change dδ / dt can be considered constant within this interval. In this situation, the calculated T0 has relatively high accuracy and is very close to the real-time interval required for the phase angle to pass through the predetermined range during power fluctuations. Furthermore, the time threshold T is given a coefficient k to allow for a margin. rel Therefore, it is slightly larger than T0. Thus, the time during which the phase angle remains within a predetermined degree range reaching the time threshold T is sufficient to determine that the phase angle is maintained at 180 degrees, i.e., a failure has occurred. Note that this time threshold T is not a constant value but is calculated in real time. In particular, during a failure, the instantaneous rate of change dδ / dt of each phase angle becomes large, so the time threshold T calculated in real time by equations (5) and (6) is very small. For example, when a failure occurs, the phase angle suddenly changes from another value such as 30 degrees to 180 degrees in a very short time (e.g., 20 ms). The reference threshold T0 is obtained by the following equation (5): dδ / dt = (180-30) / 0.02 = 7500 degrees / s, and T0 = (190-170) / 7500 = 27 ms. rel Assuming = 1.48, the time threshold may be calculated as 40 ms by equation (6). That is, according to the solution of the present invention, the duration for tripping a fault may be very short, for example, tens of milliseconds. In contrast, the predetermined time in conventional solutions must be set longer than the maximum time the impedance remains in the operating region of the relay during power fluctuations, so conventional solutions typically require 2 seconds or more for fault detection and tripping. 【0059】 Furthermore, the solution of the present invention offers further advantages in avoiding mistrip. In particular, in the case of reverse closure failures and forward external failures, the phase angle δ = 0. Therefore, the phase angle δ does not fall within the relatively small predefined range [δ1, δ2] (e.g., [170, 190]). Thus, with this solution, mistrip due to external failures does not occur. 【0060】 Furthermore, in embodiments where the rate of change of the phase angle is considered as an instantaneous rate of change dδ / dt, the reference threshold T0 and the time threshold T are independent of the power fluctuation period or cycle, thus providing an advantage in terms of operating speed independent of the power fluctuation period or cycle. In other words, no matter how long the power fluctuation period is (e.g., typically 300ms to 3s), the duration required for tripping is related only to the instantaneous rate of change dδ / dt at the time the fault occurs. 【0061】 Figure 10 shows an alternative implementation for determining the rate of change of the phase angle with respect to time. In some embodiments, each phase angle δ a , δ b , δ c , δ ab , δ bc , δ caHowever, the average rate of change of each phase angle with respect to time in the recent cycle of power fluctuations is determined depending on whether it falls within a predetermined range (e.g., [170, 190]). The recent cycle of power fluctuations includes the period from the time when it previously entered the predetermined range to the time when it is currently in the predetermined range. For example, as shown in Figure 10, if the phase angle δ reaches 190 degrees at time t1, the phase angle δ falls within the predetermined range [170, 190], and time t1 may be recorded. Then, if the phase angle δ reaches 190 degrees again at time t2, time t2 may be recorded. Based on the recorded times t1 and t2, the duration of the recent cycle of power fluctuations is determined. The average rate of change of the phase angle δ with respect to time in the recent cycle can be calculated as 360 / (t2-t1). The average rate of change of the phase angle δ in the recent cycle also allows for the estimation of the time during which the phase angle δ remains within the predetermined range. In particular, a reference threshold T0 and a time threshold T can be obtained in calculations similar to those in equations (5) and (6). Here, equation (5) may be replaced with T0 = (δ2 - δ1) * (t2 - t1) / 360. In this implementation, the time required for fault detection varies according to the real-time period of power fluctuation. For example, if δ2 is 190 degrees, δ1 is 170 degrees, k rel If we assume that is 1.2, then when the oscillation period is 1 s (i.e., t2-t1=1 s), the time required for tripping is T=1.2*55ms=66 ms; when the oscillation period is 300 ms (i.e., t2-t1=300 ms), the time required is T=1.2*17ms=20 ms; and when the oscillation period is 3 s (i.e., t2-t1=3 s), the time required is T=1.2*167ms=200 ms. Compared to conventional solutions, this implementation can be seen to trip faulty power lines at a faster speed, thereby improving the stability of the power system. 【0062】 Instead of equation (5), the reference threshold T0, and by extension the time threshold T, may be determined by other means to determine a fault. In some embodiments, detecting a fault based on at least one phase angle during a power fluctuation includes determining a time threshold for each of at least one phase angle based on the measured duration during which each phase angle was previously within a predetermined range, and determining a fault if the duration during which any of the at least one phase angle was within the predetermined range exceeds the respective time threshold. For example, during a power fluctuation, the time when the phase angle δ first entered and exited a predetermined range [δ1, δ2] (e.g., [170, 190]) can be measured, and the duration during which the phase angle δ was within the predetermined range can be measured or determined. The measured or determined duration can be used directly as the reference threshold T0, which can then be used to determine the time threshold T from equation (6). When the predetermined range [δ1, δ2] is entered a second time, the determined time threshold T is used to determine a fault in a manner similar to that of the embodiment in Figure 9A. In other words, a fault is determined to have occurred if the duration of the phase angle δ within a predetermined range [δ1, δ2] exceeds a time threshold T; otherwise, no fault is determined to have occurred. If there is no fault, the duration can be determined by measuring the time when the phase angle δ enters and exits the predetermined range [δ1, δ2] (e.g., [170, 190]) for the second time. The determined duration is used to update the reference threshold T0, which helps in determining a fault when the phase angle δ enters the predetermined range [δ1, δ2] for the third time. Fault detection can be performed similarly in subsequent cycles of power fluctuations. In the detection described above, during the first cycle of power fluctuations, the reference threshold T0 may be defined in other ways; for example, the initial value of T0 may be predetermined based on past data, or it may be calculated based on the instantaneous rate of change of the phase angle δ. Alternatively, during the first cycle of power fluctuations, a fault may be determined by other means that do not require the use of T0. In this implementation, the calculation of the rate of change of the phase angle is avoided, reducing the processor load and speeding up fault detection. 【0063】 Figure 11 shows a schematic diagram of a two-power system with the frequencies of the power grids indicated. Generally, during power fluctuations, the frequency of the generator or power source is no longer the fundamental frequency. For example, as shown in Figure 11, E m The frequency is 49Hz, E n The frequency is 52Hz, current I m The frequency is 50.5 Hz. Since the frequencies of current and voltage are not the same, calculating the voltage at a second location on the transmission line (e.g., point Q) in the frequency domain using equation (1) may not be accurate. In some embodiments, estimating the voltage at a second location on the transmission line (e.g., point Q) involves calculating the voltage at the second location on the transmission line in the time domain based on the measured electric quantity at a first location (e.g., point P). When calculating the voltage at the second location in the time domain, equation (1) may be replaced with the following equation. 【0064】 【number】 【0065】 When performing calculations in the time domain, the voltage and current at the first position can be obtained by sampling. These sampled voltages and currents can be used to calculate the voltage at the second position using equation (7). After obtaining the voltages at the first and second positions, the real and imaginary parts of each voltage at the first position and each voltage at the second position can be calculated by Fourier transform. This allows for the calculation of at least one phase angle between the voltages at the first and second positions, and consequently, the rate of change of at least one phase angle with respect to time. 【0066】 In previous discussions, we have described an approach to setting T0 and T based on the rate of change of the phase angle δ in order to identify a fault. However, as can be seen, identifying a fault based on the rate of change of the phase angle δ is possible with other suitable approaches. In some embodiments, detecting a fault based on the rate of change of at least one phase angle with respect to time during a power fluctuation includes: determining the instantaneous rate of change of each of the at least one phase angles with respect to time, such that each phase angle falls within a predefined range including 180 degrees; and determining a fault when the instantaneous rate of change of any of the at least one phase angle exceeds a predefined threshold. 【0067】 Specifically, when a fault occurs, the phase angle δ changes abruptly to 180 degrees, so in the case of a fault, the rate of change of the phase angle δ increases significantly. Therefore, a threshold for the rate of change may be predefined to monitor the change in the phase angle δ, and this threshold needs to be much larger than the rate of change of the phase angle during normal power fluctuations. When the phase angle falls within a predefined range [δ1, δ2] (e.g., [170, 190]), the instantaneous rate of change of the phase angle is compared with the threshold, and a fault can be determined if the instantaneous rate of change exceeds the threshold. In this way, fault identification is performed by comparing the rate of change with the threshold in real time without a waiting time T, so fault detection requires only measurement and calculation time, further reducing the time required for fault tripping during power fluctuations. However, if a fault occurs within the predefined range [δ1, δ2], this approach may not work as it may not detect the abnormal increase in the rate of change of the phase angle δ. In such situations, faults occurring within the predefined range [δ1, δ2] may be detected by other methods. Examples include the aforementioned approach of setting T0 and T based on the rate of change of the phase angle δ, or conventional solutions that require a waiting time until the impedance leaves the operating region of the distance relay. 【0068】 Furthermore, the proposed solution, which identifies faults based on the rate of change of the phase angle δ, may miss faults in some cases. For example, if a fault occurs at a first position and a second position (e.g., points P and Q in Figure 2), the voltage at either the first or second position is zero, making it impossible to obtain the phase angle δ in equation (2), and consequently, the proposed solution cannot function under these conditions. Therefore, if a fault occurs at point P or Q in Figure 2, the fault may be detected by other methods, such as conventional solutions with slower protection speeds. In other words, the method proposed by the present invention may be implemented in parallel with conventional solutions to achieve reliable and efficient fault protection during power fluctuations. 【0069】 Other aspects of this disclosure provide electronic devices capable of carrying out embodiments of the disclosure as described above. Figure 12 shows a schematic block diagram of an exemplary device 1200 suitable for carrying out embodiments of the disclosure. For example, a fault detection device may be implemented by device 1200. As shown, device 1200 comprises a central processor unit (CPU) 1201. The central processor unit (CPU) 1201 may perform various appropriate operations and processes based on computer program instructions stored in read-only memory (ROM) 1202 or computer program instructions loaded from storage 1208 into random access memory (RAM) 1203. RAM 1203 further stores various programs and data necessary for the operation of device 1200. The CPU 1201, ROM 1202, and RAM 1203 are connected to each other via a bus 1204. An input / output (I / O) interface 1205 is also connected to the bus 1204. 【0070】 The I / O interface 1205 is connected to elements of the device 1200, such as input units 1206 (keyboard, mouse, etc.), output units 1207 (various displays, speakers, etc.), storage units 1208 (magnetic disks, optical disks, etc.), and communication units 1209 (network cards, modems, wireless communication transceivers, etc.). The communication unit 1209 allows the device 1200 to exchange information / data with other devices via computer networks such as the Internet and / or various types of telecommunications networks. 【0071】 The various processes and operations described above, such as method 600, may be performed by the processor unit 1201. For example, in some embodiments, method 600 may be implemented as a computer software program embodied in a machine-readable medium, such as a storage unit 1208. In some embodiments, part or all of the computer program may be loaded and / or mounted into the device 1200 via ROM 1202 and / or communication unit 1209. Once the computer program is loaded into RAM 1203 and executed by CPU 1201, one or more operations of method 600 described above may be performed. 【0072】 In some embodiments, the electronic device may be a distance relay such as the MHO relay described above. By incorporating the method according to the embodiments of this disclosure into a distance relay, the reliability of the power transmission line can be significantly improved. 【0073】 According to another aspect of this disclosure, a computer-readable storage medium (or media) having computer-readable program instructions for performing an aspect of this disclosure is provided. 【0074】 A computer-readable storage medium can be a tangible device capable of holding and storing instructions used by an instruction execution device. A computer-readable storage medium may, but is not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination thereof. A more specific list of computer-readable storage mediums includes, but is not limited to, portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disk read-only memory (CD-ROM), digital multipurpose disks (DVDs), memory sticks, floppy disks, mechanical encoding devices such as punch cards or grooved raised structures on which instructions are recorded, and any suitable combination thereof. The computer-readable storage medium as used herein is not construed as an instantaneous signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmitting media (e.g., light pulses passing through fiber optic cables), or electrical signals transmitted through wires. 【0075】 The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to each computing / processing device, or to an external computer or external storage device via a network such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical transmission fibers, wireless transmitters, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface of each computing / processing device receives computer-readable program instructions from the network and transfers the computer-readable program instructions for storage on a computer-readable storage medium within each computing / processing device. 【0076】 The computer-readable program instructions for performing the operations of the Disclosure may be assembler instructions, instruction set architecture (ISA) instructions, machine language instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk and C++, and conventional procedural programming languages ​​such as the "C" programming language. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the remote computer scenario, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or wide area network (WAN), or the connection may be to an external computer (for example, via the Internet using an Internet service provider). In some embodiments, the state information of the computer-readable program instructions can be used to customize electronic circuits, such as programmable logic circuits, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs). An electronic circuit may execute computer-readable program instructions in order to perform an aspect of the present disclosure. 【0077】 Herein, embodiments of the present disclosure have been described with reference to flowcharts and / or block diagrams of methods, apparatus (systems) and computer program products relating to embodiments of the present disclosure. As can be understood, each block in a flowchart and / or block diagram, and combinations of blocks in a flowchart and / or block diagram, can be implemented by computer-readable program instructions. 【0078】 Computer-readable program instructions, executed by the processor of a computer or other programmable data processing device, may be provided to the processor of a general-purpose computer, a dedicated computer, or other programmable data processing device to create a machine, such that the instructions generate means for performing functions / operations defined in one or more blocks of a flowchart and / or block diagram. These computer-readable program instructions may be stored in a computer-readable storage medium that enables computers, programmable data processing devices, and / or other devices to function in a particular way. Thus, a computer-readable storage medium containing instructions comprises a product containing instructions that perform modes of functions / operations defined in one or more blocks of a flowchart and / or block diagram. 【0079】 Computer-readable program instructions executed on a computer, other programmable data processing device, or other device may be loaded into a computer, other programmable data processing device, or other device to perform a function / operation defined in one or more blocks of a flowchart and / or block diagram, thereby causing a series of operational steps on the computer, other programmable data processing device, or other device to create a process performed by the computer. 【0080】 The detailed embodiments described above in this disclosure are for illustrative or illustrative purposes only and do not limit the disclosure. Therefore, any modifications, equivalent alternatives, and improvements that do not deviate from the spirit and scope of this disclosure are included within the scope of this disclosure. On the other hand, the claims attached to this disclosure are intended to cover all variations and modifications that fall within the scope and boundaries of the claims, or their equivalents. The invention described in the original claims of this application is listed below. [C1] A method for determining a fault in a power system, Estimating the voltage at a second location of a transmission line based on the amount of electricity measured at a first location of the transmission line within the power system, wherein the measured amount of electricity is related to the three phases of the power system and includes the voltage at the first location of the transmission line. Detecting the fault based on the at least one phase angle during power fluctuations, including, method. [C2] Determining the at least one phase angle between the voltage at the first position and the estimated voltage at the second position is: Determining a first phase angle between the phase voltage of the first phase at the first position and the estimated phase voltage of the first phase at the second position, Determining a second phase angle between the phase-to-phase voltage from the second phase to the third phase at the first position and the estimated phase-to-phase voltage from the second phase to the third phase at the second position, including, The method described in C1. [C3] Determining the at least one phase angle between the voltage at the first position and the estimated voltage at the second position is: The process includes determining the phase angle between the phase voltage of each of the three phases at the first position and the estimated phase voltage of the same phase at the second position. The method described in C1. [C4] Determining the at least one phase angle between the voltage at the first position and the estimated voltage at the second position is: For each of the three two-phase combinations, the method includes determining the phase angle between the phase voltage of each two-phase combination at the first position and the estimated phase voltage of the same two-phase combination at the second position. The method described in C1. [C5] Determining the at least one phase angle between the voltage at the first position and the estimated voltage at the second position is: For each of the three phases, a first phase angle is determined between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position. For each of the three two-phase combinations, a second phase angle is determined between the phase-to-phase voltage of each two-phase combination at the first position and the estimated phase-to-phase voltage of the same two-phase combination at the second position. The average angle based on the first phase angle of the three phases and the second phase angle of the combination of the three two phases is determined as the at least one phase angle. including, The method described in C1. [C6] Determining the at least one phase angle between the voltage at the first position and the estimated voltage at the second position is: This includes determining the phase angle between the positive-sequence component of the phase voltage of one of the three phases at the first position and the positive-sequence component of the estimated phase voltage of the same phase at the second position. The method described in C1. [C7] Detecting the fault based on the at least one phase angle during the power fluctuations means determining a time threshold for each of the at least one phase angle based on the measured duration during which each phase angle previously fell within a predetermined range, and determining the fault if the duration of any of the at least one phase angle within the predetermined range exceeds the respective time threshold. including, The method described in C1. [C8] Detecting the fault based on the at least one phase angle during the power fluctuation includes detecting the fault based on the rate of change of the at least one phase angle with respect to time during the power fluctuation. The method described in C1. [C9] During the aforementioned power fluctuation, detecting the fault based on the rate of change of the at least one phase angle with respect to time is: For each of the at least one phase angle, the rate of change of each phase angle with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the at least one phase angle. The failure is determined when the duration of any of the at least one of the phase angles within the predetermined range exceeds the respective time threshold. including, The method described in C8. [C10] Determining the rate of change of each of the aforementioned phase angles with respect to time is: This includes determining the instantaneous rate of change of each phase angle with respect to time, in accordance with the fact that each of the phase angles falls within the aforementioned predefined range. Method used at C9. [C11] Determining the rate of change of each of the aforementioned phase angles with respect to time is: The process includes determining the average rate of change of each phase angle with respect to time in the most recent cycle of the power fluctuation, in such cases that each phase angle falls within the predetermined range. The most recent cycle of the power fluctuation includes the period from the time it previously entered the predetermined range to the time it is currently in the predetermined range. Method used at C9. [C12] During the aforementioned power fluctuation, detecting the fault based on the rate of change of the at least one phase angle with respect to time is: For each of the at least one phase angle, the instantaneous rate of change of each phase angle with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. The failure is determined when the instantaneous rate of change of any of the at least one of the phase angles exceeds a predetermined threshold. including, The method described in C8. [C13] Estimating the voltage at the second location of the transmission line is The process includes calculating the voltage at the second location of the transmission line in the time domain based on the measured amount of electricity, The method described in C1. [C14] At least one processor unit, The at least one memory connected to the at least one processor unit and storing instructions that can be executed by the at least one processor unit, Equipped with, If the instruction is executed by the at least one processor unit, the method described in any one of the C1 to C13 items is performed. electronic equipment. [C15] Equipped with distance relays used in power systems, The electronic device described in C14. [C16] A computer-readable storage medium storing computer-readable program instructions, wherein, when executed by a processor unit, the computer-readable program instructions cause the processor unit to perform the method described in any one of C1 to C13. Computer-readable storage medium.

Claims

[Claim 1] A method for determining a fault in a power system, The method of estimating the voltage at a second location of a transmission line based on the measured amount of electricity at a first location of the transmission line within the power system and the impedance of the transmission line, wherein the measured amount of electricity is expressed in terms of the three phases of the power system and includes the voltage and current at the first location of the transmission line. Determining the phase angle between the voltage at the first position and the estimated voltage at the second position, wherein the determination is This includes determining a first phase angle between the phase voltage of the first phase at the first position and the estimated phase voltage of the first phase at the second position, and determining a second phase angle between the interphase voltage of the second to the third phase at the first position and the estimated interphase voltage of the second to the third phase at the second position. Detecting the fault based on the change in phase angle during power fluctuations, wherein the detection is The process includes detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, and detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, For each of the aforementioned phase angles, the rate of change of each of the aforementioned phase angles with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the phase angles. The process includes determining a fault when the duration of any of the phase angles within the predetermined range exceeds the respective time threshold, including, method. [Claim 2] A method for determining a fault in a power system, The method of estimating the voltage at a second location of a transmission line based on the measured amount of electricity at a first location of the transmission line within the power system and the impedance of the transmission line, wherein the measured amount of electricity is expressed in terms of the three phases of the power system and includes the voltage and current at the first location of the transmission line. Determining the phase angle between the voltage at the first position and the estimated voltage at the second position, wherein the determination is The process includes determining the phase angle between the phase voltage of each of the three phases at the first position and the estimated phase voltage of the same phase at the second position. Detecting the fault based on the change in phase angle during power fluctuations, wherein the detection is The process includes detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, and detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, For each of the aforementioned phase angles, the rate of change of each of the aforementioned phase angles with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the phase angles. The process includes determining a fault when the duration of any of the phase angles within the predetermined range exceeds the respective time threshold, including, method. [Claim 3] A method for determining a fault in a power system, The method of estimating the voltage at a second location of a transmission line based on the measured amount of electricity at a first location of the transmission line within the power system and the impedance of the transmission line, wherein the measured amount of electricity is expressed in terms of the three phases of the power system and includes the voltage and current at the first location of the transmission line. Determining the phase angle between the voltage at the first position and the estimated voltage at the second position, wherein the determination is For each of the three two-phase combinations, the process includes determining the phase angle between the phase voltage of each two-phase combination at the first position and the estimated phase voltage of the same two-phase combination at the second position. Detecting the fault based on the change in phase angle during power fluctuations, wherein the detection is The process includes detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, and detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, For each of the aforementioned phase angles, the rate of change of each of the aforementioned phase angles with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the phase angles. The process includes determining a fault when the duration of any of the phase angles within the predetermined range exceeds the respective time threshold, including, method. [Claim 4] A method for determining a fault in a power system, The method of estimating the voltage at a second location of a transmission line based on the measured amount of electricity at a first location of the transmission line within the power system and the impedance of the transmission line, wherein the measured amount of electricity is expressed in terms of the three phases of the power system and includes the voltage and current at the first location of the transmission line. Determining the phase angle between the voltage at the first position and the estimated voltage at the second position, wherein the determination is The method includes determining a first phase angle for each of the three phases between the phase voltage of each phase at the first position and the estimated phase voltage of the same phase at the second position; determining a second phase angle for each of the three two-phase combinations between the phase voltage of each two-phase combination at the first position and the estimated phase voltage of the same two-phase combination at the second position; and determining the average angle based on the first phase angle of the three phases and the second phase angle of the three two-phase combinations as the phase angle. Detecting the fault based on the change in phase angle during power fluctuations, wherein the detection is The process includes detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, and detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, For each of the aforementioned phase angles, the rate of change of each of the aforementioned phase angles with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the phase angles. The process includes determining a fault when the duration of any of the phase angles within the predetermined range exceeds the respective time threshold, including, method. [Claim 5] A method for determining a fault in a power system, The method of estimating the voltage at a second location of a transmission line based on the measured amount of electricity at a first location of the transmission line within the power system and the impedance of the transmission line, wherein the measured amount of electricity is expressed in terms of the three phases of the power system and includes the voltage and current at the first location of the transmission line. Determining the phase angle between the voltage at the first position and the estimated voltage at the second position, wherein the determination is This includes determining the phase angle between the positive-sequence component of the phase voltage of one of the three phases at the first position and the positive-sequence component of the estimated phase voltage of the same phase at the second position. Detecting the fault based on the change in phase angle during power fluctuations, wherein the detection is The process includes detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, and detecting the fault during power fluctuations based on the rate of change of the phase angle with respect to time, For each of the aforementioned phase angles, the rate of change of each of the aforementioned phase angles with respect to time is determined in accordance with the fact that each phase angle falls within a predetermined range. Based on the determined rate of change and the predefined range, a time threshold is determined for each of the phase angles. The process includes determining a fault when the duration of any of the phase angles within the predetermined range exceeds the respective time threshold, including, method. [Claim 6] Determining the rate of change of each of the aforementioned phase angles with respect to time is: This includes determining the instantaneous rate of change of each phase angle with respect to time, in accordance with the fact that each of the phase angles falls within the aforementioned predefined range. The method according to any one of claims 1 to 5. [Claim 7] Determining the rate of change of each of the aforementioned phase angles with respect to time is: The process includes determining the average rate of change of each phase angle with respect to time in the most recent cycle of power fluctuations, in such cases that each phase angle falls within the aforementioned predefined range. The most recent cycle of the power fluctuation includes the period from the time it previously entered the predetermined range to the time it is currently in the predetermined range. The method according to any one of claims 1 to 5. [Claim 8] Estimating the voltage at the second position of the transmission line is This includes calculating the voltage at the second position of the transmission line in the time domain based on the amount of electricity sampled at the first position, The method according to any one of claims 1 to 5. [Claim 9] At least one processor unit, A memory connected to the at least one processor unit, which stores instructions that can be executed by the at least one processor unit, Equipped with, If the instruction is executed by the at least one processor unit, the method according to any one of claims 1 to 8 is performed. electronic equipment. [Claim 10] Equipped with distance relays used in power systems, The electronic device according to claim 9. [Claim 11] A computer-readable storage medium that stores computer-readable program instructions, When the computer-readable program instruction is executed by a processor unit, it causes the processor unit to execute the method according to any one of claims 1 to 8. Computer-readable storage medium.

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