A method and system for discriminating an in-zone fault based on a direction discrimination element

Abstract

This invention relates to a method and system for intra-zone fault identification based on a direction discrimination element, belonging to the field of new energy. The identification method includes: when the differential protection activation criterion is met, determining whether the fault is located in a low-value ratio differential operation zone; if so, and if the fault duration is less than a preset fault duration, entering the direction discrimination element to determine the fault direction; if not, ending the identification process; when all direction discrimination elements on both sides meet the positive direction criterion, determining whether the low-voltage criterion is met; if the low-voltage criterion is met, maintaining the identification result of the direction discrimination element until the positive direction criterion of the direction discrimination element persists for a certain number of sampling cycles, then determining it as an intra-zone fault. This invention can improve the efficiency of protection device operation, thereby improving the safe and stable operation of the power grid.

Description

Technical Field

[0001] This invention relates to a method and system for intra-area fault detection based on a direction discrimination element, belonging to the field of new energy. Background Technology

[0002] Under the "dual-carbon" strategic goal, accelerating the replacement of traditional fossil fuel power generation with new energy power generation and building a new power system with a gradually increasing proportion of new energy has become the main direction of China's power system development. New energy power generation is an important supporting technology for achieving the goal of "carbon peaking and carbon neutrality". After large-scale new energy power generation, the voltage is usually stepped up by step-up transformers and then centrally connected to the high-voltage AC grid. Therefore, the rapid and reliable fault isolation of step-up transformers is crucial for the safe and stable operation of new energy power plants.

[0003] Currently, the step-up transformers of large-scale new energy power sources include longitudinal current differential protection devices as the main protection. Theoretically, when a fault occurs inside the step-up transformer, the longitudinal current differential protection device has absolute selectivity and can operate quickly and reliably. However, when a fault occurs outside the step-up transformer, the longitudinal current differential protection device will not operate reliably.

[0004] However, during the process of power transmission from the low-voltage side to the high-voltage side of the step-up transformer (i.e., forward power transmission), when a fault occurs inside the step-up transformer, the fault current at the low-voltage side protection installation point of the step-up transformer is provided by the new energy power source. Its fault current exhibits characteristics such as limited amplitude and high harmonic content, which may meet the current transformer (TA) saturation blocking criterion, leading to delayed operation or even non-operation of differential protection, which in turn seriously threatens the safe and stable operation of the power grid. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for intra-zone fault identification based on a direction discrimination element, in order to solve the problem in the prior art that differential protection delays or even fails to operate when an intra-zone fault occurs in a step-up transformer during forward power transmission.

[0006] To achieve the above objectives, the present invention includes:

[0007] The present invention provides a method for intra-zone fault discrimination based on a direction discrimination element, comprising: determining whether the differential protection is located in a low-value ratio differential operation zone when the differential protection activation criterion is met;

[0008] When the fault is located and the fault duration is less than the preset fault duration, the fault direction determination element is activated to determine the fault direction; when the fault is not located, the determination ends.

[0009] When all the directional discrimination elements meet the positive direction criterion, determine whether the low-voltage criterion is met;

[0010] When the low-pressure criterion is met, the discrimination result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for a certain number of sampling cycles, then it is judged as an intra-zone fault.

[0011] Furthermore, when not all directional discrimination elements meet the positive direction criterion, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

[0012] Furthermore, when all lateral direction discrimination elements meet the positive direction criterion, a positive direction criterion flag is also set;

[0013] When the fault is in the low-value ratio differential operation zone and the fault duration is greater than or equal to the preset fault duration, determine whether there is a positive direction criterion flag.

[0014] When a positive direction criterion flag is present and the low-voltage criterion is met, the criterion result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for several sampling cycles, then it is judged as an intra-zone fault.

[0015] Furthermore, when there is no positive direction criterion flag, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

[0016] Furthermore, when a positive direction criterion flag is present but the low voltage criterion is not met, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

[0017] Furthermore, using the current transformer saturation blocking criterion to determine whether it is an intra-zone fault includes:

[0018] If the current transformer saturation blocking criterion is maintained for several sampling cycles, it is determined to be an intra-zone fault.

[0019] Furthermore, when the maximum value of the three-phase differential current exceeds the differential current start-up setting value, the differential protection is activated.

[0020] The present invention provides an intra-area fault discrimination system based on a direction discrimination element, comprising a processor, which is used to execute the discrimination method for intra-area fault discrimination based on a direction discrimination element as described above when a computer program is invoked.

[0021] The beneficial effects of this invention are as follows: As a pioneering invention, this invention determines whether the fault is located in the low-value ratio differential operation zone when the differential protection activation criterion is met; if it is located in the zone, and the fault duration is less than a preset fault duration, the fault direction is determined by the direction discrimination element; if it is not located in the zone, the discrimination ends; when all the direction discrimination elements on both sides meet the positive direction criterion, the low-voltage criterion is also determined; when the low-voltage criterion is met, the discrimination result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for a certain number of sampling cycles, then it is determined to be a fault within the zone. By adding a direction discrimination element to determine the fault direction, when the fault direction is a positive fault, it can be directly determined whether the fault is located within the zone, and if it is located within the zone, the protection device operates directly. Since it is not necessary to rely on the current transformer saturation blocking criterion to directly determine whether a positive fault is located within the zone, and the protection device operates directly when it is located within the zone, the efficiency of the protection device's protection operation is improved, thereby improving the safe and stable operation of the power grid. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a typical new energy power station power transmission system provided in an embodiment of the present invention;

[0023] Figure 2 yes Figure 1 A schematic diagram showing the proportion of second and third harmonics in the fault phase current flowing through the low-voltage side protection installation point when a high-resistance fault occurs in the low-voltage side zone of the step-up transformer.

[0024] Figure 3 This is a flowchart illustrating an intra-area fault detection method based on a direction discrimination element provided in an embodiment of the present invention;

[0025] Figure 4 This is a schematic flowchart illustrating a method for intra-area fault detection based on a direction discrimination element provided in an embodiment of the present invention.

[0026] Figure 5 yes Figure 1 When a fault occurs on the high-voltage side of the step-up transformer in the circuit, the fault discrimination method provided in this embodiment of the invention is used to obtain a schematic diagram of the calculated voltage drop and the measured voltage drop waveform.

[0027] Figure 6 yes Figure 1 When an external fault occurs on the high-voltage side of the step-up transformer, the fault discrimination method provided in this embodiment of the invention is used to obtain a schematic diagram of the calculated voltage drop and the measured voltage drop waveform. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 This is a schematic diagram of a typical new energy power station power transmission system provided in an embodiment of the present invention, such as... Figure 1 As shown, the wind farm is connected to the external system via transmission lines. The wind farm mainly includes doubly-fed induction generators, transformer substations, collector lines, and the main transformer of the wind farm. s This serves as the equivalent voltage source for the external system. The main transformer at the station is a step-up transformer. M represents the installation location for the high-voltage side protection of the step-up transformer, and N represents the installation location for the low-voltage side protection of the step-up transformer.

[0030] When a phase-to-phase fault with transition resistance occurs at point F3 inside the low-voltage side of the step-up transformer, the proportions of the second and third harmonics of the fault phase current at the M-phase protection installation point on the low-voltage side of the step-up transformer are as follows: Figure 2 As shown, it can be seen that the proportion of the second and third harmonics of the fault phase current exceeds the set value. If the existing current transformer saturation blocking criterion is used, the differential protection will be delayed or even not operated, which will seriously threaten the safe and stable operation of the power grid.

[0031] To address the problem in existing technologies where differential protection experiences delayed operation or even fails to operate when a fault occurs within the fault zone of a step-up transformer during forward power transmission, this invention proposes adding a direction-determining element to determine the fault direction. When the fault direction is forward, it can be directly determined whether the fault is within the fault zone. If it is, the protection device operates directly. Since it eliminates the need for current transformer saturation blocking criteria, it directly determines whether a forward fault is within the fault zone, and the protection device operates directly when it is, thus improving the efficiency of the protection device's operation and consequently enhancing the safe and stable operation of the power grid.

[0032] An embodiment of an intra-regional fault detection method based on a direction-discriminating element:

[0033] The following is combined with Figure 3 and Figure 4 This invention provides a detailed explanation of the working principle of an intra-area fault discrimination method based on a direction discrimination element, as provided in this embodiment.

[0034] Figure 3 This is a flowchart illustrating an intra-area fault detection method based on a direction discrimination element provided in an embodiment of the present invention. Figure 4 This is a schematic flowchart illustrating a method for intra-area fault detection based on a direction discrimination element provided in an embodiment of the present invention. Figure 3 and Figure 4 As shown, the discrimination method includes the following steps:

[0035] S10. If the differential protection activation criterion is met, determine whether it is in the low-value ratio differential operation zone. If it is, proceed to step S20; otherwise, end.

[0036] Specifically, you can first determine whether the differential protection activation criteria are met. If they are met, it means that a fault has occurred. In order for the protection device of the step-up transformer to operate, it is necessary to further determine whether it is in the low-value ratio differential operation zone. If it is not met, it means that no fault has occurred.

[0037] The criteria for determining whether the differential protection is activated include: First, calculating the differential current of each phase of the step-up transformer. The second step is to compare the differential currents of each phase and select the maximum value. The third step is to determine the maximum value. Is it greater than the differential current starting setting value I? cdqd ,if Then the differential protection activation criterion is met, if Then the differential protection criterion is not met.

[0038] The three-phase differential current of the step-up transformer can be calculated using the following formula (1).

[0039]

[0040] in, If it is a three-phase system consisting of phases A, B, and C, then I dA I represents the differential current of phase A. dB I represents the differential current of phase B. dC This represents the differential current of phase C; This represents the current on each side of the step-up transformer, and m represents the number of windings of the step-up transformer. The following example uses a step-up transformer with 2 windings as an example for illustration.

[0041] When m = 2, i takes values ​​of 1 and 2. Taking phase A as an example: then I 1A I represents the current in phase A of the high-voltage side. 2A This indicates the current in phase A on the low-voltage side.

[0042] As an alternative implementation, the voltage and current on each side of the step-up transformer can be acquired in real time through voltage transformers and current transformers, and then filtered before use.

[0043] As an alternative implementation, the voltage and current on each side of the step-up transformer can be collected in advance and stored in a memory for later retrieval.

[0044] The determination of whether it is in the low-value ratio differential operation zone is made using the steady-state ratio differential protection criterion.

[0045] The steady-state ratio differential protection criteria include the following formula (2) and the following formula (3):

[0046]

[0047] in, Indicates single-phase braking current; I e Indicates the rated current of the step-up transformer; K b1 This represents the ratio braking coefficient setting value, which ranges from (0.2, 0.75). In this embodiment of the invention, K is used as the value. b1 Taking 0.5 as an example, we will provide an illustrative explanation.

[0048] Among them, single-phase braking current It can be calculated using the following formula (4):

[0049]

[0050] After selecting the largest single-phase differential current, the braking current of the corresponding phase is calculated according to formula (3). Then, based on the relationship between the braking current and the rated current, the comparison condition of the largest single-phase braking current is determined. If the largest single-phase braking current is greater than the comparison condition in formula (2), it is considered that the largest single-phase differential current is in the low-value ratio differential operation zone, and step S20 needs to be executed. If the largest single-phase braking current is greater than the comparison condition in formula (3), it is considered that the largest single-phase differential current is in the high-value ratio differential operation zone, and the judgment ends.

[0051] S20. Determine whether the fault duration is less than the preset fault duration. If it is less, proceed to step S30; otherwise, proceed to step S70.

[0052] As an optional implementation, the fault duration can be the difference between the sampling time t and the differential protection activation criterion tq.

[0053] The preset fault duration can be set according to the actual situation. This invention does not impose any special limitation on it. The following example uses a preset fault duration of 40 milliseconds (ms) as an example for illustrative explanation.

[0054] When t-tq < 40ms, the direction discrimination element is effective, and the fault direction discrimination element can be entered to perform fault direction discrimination, and step S30 is executed; when t-tq ≥ 40ms, the direction discrimination element is ineffective, and step S60 is executed.

[0055] S30. Determine whether all directional elements satisfy the positive criterion. If yes, proceed to step S40; otherwise, proceed to step S60.

[0056] After entering the direction discrimination element, the electrical quantity data near the zero crossing point is used to quickly determine the fault direction using a short window algorithm, that is, to determine whether the fault direction is a forward fault or a reverse fault.

[0057] First, the calculated voltage drop value of the faulty phase needs to be obtained; then, the measured voltage drop value of the faulty phase needs to be obtained; next, the waveform correlation coefficient between the calculated voltage drop value and the measured voltage drop value within the data window needs to be obtained; finally, it is determined whether the waveform correlation coefficient is greater than or equal to the waveform correlation coefficient setting value. If it is greater than or equal to, a forward fault is considered to have occurred; otherwise, a reverse fault has occurred.

[0058] Specifically, taking the single-phase grounding fault of phase A on the high-voltage side of a Yd11 connected double-winding transformer as an example, the principle of the high-voltage side directional element judgment criterion is explained:

[0059] The voltage drop value u of phase A can be obtained using the following formula (5). 1MA :

[0060]

[0061] Among them, L S L M R S R M These represent the self-inductance, mutual inductance, self-resistance, and mutual resistance between the equivalent impedance of the opposite AC system and the sum of the equivalent impedances of the lines, respectively; MA (t) represents the instantaneous current value of phase A at the high-voltage side protection installation location; i MB (t) represents the instantaneous current value of phase B at the high-voltage side protection installation location; i MC (t) represents the instantaneous current value of phase C at the high-voltage side protection installation location.

[0062] The voltage drop u of phase A can be obtained using the following formula (6). 2MA :

[0063]

[0064] Among them, u MAf (t-nT) represents the voltage memory value of phase A at the high-voltage side protection installation location; u MA (t) represents the instantaneous voltage value of phase A at the high-voltage side protection installation location; i MAf (t-nT) represents the current memory value of phase A at the high-voltage side protection installation location; i MBf (t-nT) represents the current memory value of phase B at the high-voltage side protection installation location; i MCf (t-nT) represents the current memory of phase C at the high-voltage side protection installation location; T is the power frequency period, and n is 2.

[0065] will u 1MAand u 2MA Substituting into the following formula (7), the waveform correlation coefficient r within the data window is calculated. u1MA，u2MA :

[0066]

[0067] in, Represents the waveform correlation coefficient. This represents the average value of the calculated voltage drop over a fixed time window. This represents the average value of the single-phase measured voltage drop over a fixed time window. This indicates the real-time calculated voltage drop value for a single phase. This represents the real-time measured voltage drop value for a single phase, and W represents the data window length.

[0068] Taking phase A as an example: This represents the average calculated voltage drop value of phase A over a fixed time window. u represents the average value of the measured voltage drop of phase A within a fixed time window. 1MA (t) represents the real-time calculated voltage drop value of phase A, u 2MA (t) represents the real-time measured voltage drop value of phase A.

[0069] Determine the waveform correlation coefficient r u1MA，u2MA Is it greater than or equal to the waveform correlation coefficient setting value r? setM .

[0070] If r u1MA，u2MA ≥r setM If r u1MA，u2MA <r setM If so, it is determined that a reverse fault has occurred on the high-voltage side of the step-up transformer.

[0071] Among them, the tuning value r of the waveform correlation coefficient setM It can be set according to the actual situation. In the embodiments of the present invention, r is used. setM The example given is 0.5; the data window length can be set according to the actual situation. In this embodiment of the invention, W=10ms is used as an example for illustrative purposes.

[0072] It should be noted that, for those skilled in the art, if the transformer winding is a double winding, after understanding the principle of the high-voltage side directional element criterion in the case of a single-phase ground fault on phase A of the high-voltage side, the principle for determining whether a single-phase ground fault on other phases of the high-voltage side is a forward fault is similar, and will not be repeated here. Similarly, the principle for determining whether a single-phase ground fault on the low-voltage side is a forward fault is similar, and will not be repeated here.

[0073] It should be noted that, for those skilled in the art, if the transformer windings are other windings, after understanding the principle of the high-voltage side directional element criterion in the case of a single-phase ground fault on phase A of the high-voltage side, the principle of how to determine whether it is a positive fault is similar to that on the high-voltage side, and will not be repeated here.

[0074] After all directional elements satisfy the positive criterion, a positive criterion flag Dir is set. The positive criterion flag Dir can be set to 1 or 0. This invention does not make any special limitation on this. The following description will take the positive criterion flag Dir=1 as an example.

[0075] S40. Determine whether the low-voltage criterion is met. If yes, proceed to step S50; otherwise, clear the positive criterion flag and end the judgment.

[0076] The low-pressure criterion can be determined using the following formula (8):

[0077]

[0078] If less than U dset If the low-pressure criterion is met, then step S50 can continue; if it is greater than or equal to U... dset If the low-voltage criterion is not met, the positive criterion flag needs to be cleared to zero, and the discrimination process ends.

[0079] Among them, u MA (t) represents the voltage sampling value of phase A at the high-voltage side protection installation location; u MB (t) represents the voltage sampling value of phase B at the high-voltage side protection installation location; u MC (t) represents the voltage sampling value of phase C at the high-voltage side protection installation location; N represents the number of sampling points of the protector within one power frequency cycle; Δt represents the sampling interval; U dset This indicates a low voltage threshold.

[0080] The setting of N can be adjusted according to actual conditions, and this invention does not impose any particular limitation on it. This embodiment uses N=80 as an example for illustrative purposes. The setting of Δt can also be adjusted according to actual conditions, and this invention does not impose any particular limitation on it. This embodiment uses Δt=0.25ms as an example for illustrative purposes. Regarding U... dset The settings can be configured according to actual conditions, and this invention does not impose any particular limitations on them. This embodiment uses U... dset The following example illustrates the use of 10% of the rated voltage.

[0081] S50. The discrimination result of the direction discrimination element is maintained until the positive criterion of the direction discrimination element continues for a certain number of sampling cycles, then it is judged as an in-zone fault.

[0082] As an optional implementation, it can be determined whether it is an in-zone fault by taking multiple consecutive samples after a fault and judging whether the total duration of the positive criterion of the direction discrimination element exceeds the set sampling duration.

[0083] As another alternative implementation, after a fault occurs, the positive criteria of the direction discrimination element can be counted multiple times consecutively. The fault type can then be determined by checking if the accumulated count exceeds a predetermined number. The following explanation will use the example of counting the positive criteria of the direction discrimination element and checking if the accumulated count exceeds a predetermined number.

[0084] like Figure 4 As shown, after the low-voltage criterion is met, a sample is taken once using the direction discrimination element at every sampling interval, and then the results are accumulated until the total number of samples is greater than or equal to the preset number t. set At that time, it was considered a fault within the region. Specifically, for t... set The setting can be adjusted according to the actual situation. This invention does not impose any special limitations on it. In this embodiment, t is used. set Let's take 10 as an example to illustrate this.

[0085] S60. Use the current transformer saturation blocking criterion to determine whether it is an intra-zone fault.

[0086] If not all directional discrimination elements meet the positive direction criterion, it indicates a reverse fault. In this case, the current transformer saturation blocking criterion can be used to determine whether it is an intra-zone fault.

[0087] Before using the current transformer saturation blocking criterion to determine whether it is an in-zone fault, the positive direction criterion flag needs to be cleared to zero, and the sampling number t when using the direction element criterion needs to be set. l1 Resetting the current transformer to zero can increase the accuracy of determining whether a fault is within the zone using the current transformer saturation blocking criterion.

[0088] The current transformer saturation blocking criterion is determined using the following formula (9):

[0089]

[0090] in, This represents the second harmonic in the phase current; This represents the third harmonic in the phase current; This represents the fundamental wave in the phase current; and All of them are a certain proportionality constant.

[0091] for The value of can be set according to the actual situation. This invention does not impose any special limitations on this. This embodiment uses . Taking 0.15 as an example, we will provide an illustrative explanation; for The value of can be set according to the actual situation. This invention does not impose any special limitations on this. This embodiment uses . Taking 0.2 as an example, we will provide an illustrative explanation.

[0092] The TA saturation discrimination element works under open conditions. Therefore, if the above formula (9) is not met, it means that the TA saturation discrimination element is under open conditions. At this time, the discrimination result is maintained, and then the current transformer saturation blocking criterion is continued for several sampling cycles, and then it is judged as an intra-zone fault.

[0093] As an optional implementation, under open conditions, multiple consecutive samples are taken to determine whether the total duration of the current transformer saturation blocking criterion exceeds the set sampling duration, thereby determining whether it is an intra-zone fault.

[0094] As an alternative implementation, under open conditions, multiple consecutive samples are taken to count the current transformer saturation blocking criteria. Then, by determining whether the accumulated count exceeds a set number, it is determined whether it is an in-zone fault. The following explanation will use the example of counting the current transformer saturation blocking criteria and determining whether the accumulated count exceeds a set number for time-related explanation.

[0095] If the above formula (9) is satisfied, it indicates that the condition is not open (i.e., the condition is blocked). In this case, the sampling number t when the current transformer saturation blocking criterion is used will be adopted. l2 After clearing to zero, the judgment process ends.

[0096] like Figure 4 As shown, under open conditions, the current transformer saturation blocking criterion is sampled once every sampling interval until the total number of samples is greater than or equal to the preset number t. set At that time, it was considered a fault within the zone. Under the interlocking condition, t l2 Clear to zero, then end the discrimination process.

[0097] S70. Determine if there is a positive criterion flag. If yes, proceed to step S80; otherwise, proceed to step S60.

[0098] If the fault duration is greater than or equal to the preset fault duration, the direction discrimination element fails. In this case, it is necessary to determine whether it is a positive fault by checking whether there is a positive criterion flag.

[0099] When the positive criterion flag is present, it indicates that the fault is still a positive fault. If the low-voltage criterion is met, the positive criterion of the direction discrimination element can continue to be used, i.e., step S80 can be executed. When the positive criterion flag is absent, it indicates that the fault is a reverse fault. In this case, the positive criterion of the direction discrimination element cannot continue to be used, and the current transformer saturation blocking criterion needs to be used, i.e., step S60 should be executed.

[0100] S80. Determine whether the low-voltage criterion is met. If it is met, proceed to step S50; otherwise, proceed to step S60.

[0101] The low-pressure criterion can be found in the above formula (8), which will not be elaborated here.

[0102] The following is combined with Figure 5 and Figure 6 This demonstrates the accuracy of the intra-regional fault discrimination method based on direction discrimination elements provided in this embodiment.

[0103] Figure 5 yes Figure 1 When a fault occurs on the high-voltage side of the step-up transformer, the fault discrimination method provided in this embodiment of the invention yields a schematic diagram of the calculated voltage drop and the measured voltage drop waveform, as shown in the figure. Figure 5 As shown, the calculated voltage drop and the measured voltage drop change trends are basically consistent, and the waveform similarity is approximately 1. This reflects that the accuracy is relatively high when applying the fault discrimination method based on the direction discrimination element provided in this embodiment of the invention.

[0104] Figure 6 yes Figure 1 When an external fault occurs on the high-voltage side of the step-up transformer, the fault discrimination method provided in this embodiment of the invention is used to obtain schematic diagrams of the calculated voltage drop and the measured voltage drop waveforms, as shown in the figure. Figure 6 As shown, the calculated voltage drop and the measured voltage drop show opposite trends, and the waveform similarity is approximately -1. This reflects that the accuracy is relatively high when applying the fault discrimination method based on the direction discrimination element provided in this embodiment of the invention.

[0105] The intra-zone fault identification method based on a direction discrimination element provided in this invention determines whether the fault is located in a low-ratio differential operation zone when the differential protection activation criterion is met. If it is located in the zone and the fault duration is less than a preset fault duration, the method initiates fault direction determination using a direction discrimination element. If the fault is not located in the zone, the determination process ends. When all direction discrimination elements on both sides meet the positive direction criterion, the method simultaneously determines whether the low-voltage criterion is met. If the low-voltage criterion is met, the determination result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element persists for a certain number of sampling cycles, at which point the fault is determined to be within the zone. By adding a direction discrimination element to determine the fault direction, when the fault direction is a positive fault, it can be directly determined whether the fault is located within the zone. If the fault is located within the zone, the protection device operates directly. Since it is not necessary to rely on the current transformer saturation blocking criterion to directly determine whether a positive fault is located within the zone, and the protection device operates directly when the fault is located within the zone, the efficiency of the protection device's operation is improved, thereby enhancing the safe and stable operation of the power grid.

[0106] An embodiment of an intra-area fault detection system based on a direction-discriminating element:

[0107] The present invention provides an intra-area fault discrimination system based on a direction discrimination element, comprising a processor, which is used to execute the discrimination method for intra-area fault discrimination based on a direction discrimination element as described above when calling a computer program.

[0108] The intra-area fault discrimination system based on direction discrimination element provided in this embodiment of the invention can achieve the same beneficial effects as the aforementioned intra-area fault discrimination method based on direction discrimination element, and will not be repeated here.

Claims

1. A method for intra-area fault detection based on a direction-discriminating element, characterized in that, This includes: determining whether the differential protection is in the low-ratio differential operation zone when the differential protection activation criteria are met; When the fault is located and the fault duration is less than the preset fault duration, the fault direction determination element is activated to determine the fault direction; when the fault is not located, the determination ends. When all directional discrimination elements meet the positive direction criterion, a positive direction criterion flag is set, and it is determined whether the low voltage criterion is met; when not all directional discrimination elements meet the positive direction criterion, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault. When the low-voltage criterion is met, the discrimination result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for a certain number of sampling cycles, then it is determined to be an in-zone fault; when the low-voltage criterion is not met, the positive criterion flag is cleared. When the fault is in the fault position and the fault duration is greater than or equal to the preset fault duration, determine whether there is a positive criterion flag bit; When there is a positive criterion flag, it is determined whether the low voltage criterion is met; if it is met, the discrimination result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for several sampling cycles, then it is determined to be an intra-zone fault; if it is not met, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault. When there is no positive criterion flag, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

2. The intra-area fault discrimination method based on a direction discrimination element according to claim 1, characterized in that, The method of using the current transformer saturation blocking criterion to determine whether it is an intra-zone fault includes: If the current transformer saturation blocking criterion is maintained for several sampling cycles, it is determined to be a fault within the zone.

3. The intra-area fault discrimination method based on a direction discrimination element according to claim 1, characterized in that, When the maximum value of the three-phase differential current is greater than the differential current start-up setting value, the differential protection is activated.

4. An intra-area fault detection system based on a direction-discriminating element, characterized in that, Includes a processor, which is configured to execute, when a computer program is invoked, the intra-area fault discrimination method based on a direction discrimination element as described in any one of claims 1-3.

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