Direction discrimination element-based intra-region fault discrimination method and system

Abstract

The invention relates to an internal fault discrimination method and system based on a direction discrimination element, and belongs to the field of new energy. The judgment method comprises the following steps: when a differential protection starting criterion is met, judging whether the differential protection starting criterion is in a low-value ratio differential action region or not; if yes and the fault duration is smaller than the preset fault duration, a direction judgment element is entered for fault direction judgment; if not, ending the judgment; when each side direction distinguishing element meets the positive direction criterion, judging whether a low-voltage criterion is met or not; and when the low-voltage criterion is met, the judgment result of the direction judgment element is kept until the positive direction criterion of the direction judgment element lasts for a plurality of sampling periods, and an internal fault is judged. The efficiency of the protection action of the protection device can be improved, so that the safe and stable operation of a power grid is improved.

Description

Technical Field

[0001] The invention relates to a method and system for distinguishing faults within a region based on a direction distinguishing element, and belongs to the field of new energy. Background Art

[0002] Under the strategic goal of "dual carbon", accelerating the promotion of new energy power generation to replace traditional fossil 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 peak and carbon neutrality". After large-scale new energy power generation, the voltage is usually raised by a step-up transformer and then connected to the high-voltage AC power grid. Therefore, the fast and reliable fault removal of the step-up transformer is crucial for the safe and stable operation of new energy sites.

[0003] At present, the step-up transformer of large-scale new energy power supply includes longitudinal current differential protection device 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. When a fault occurs outside the step-up transformer, the longitudinal current differential protection device does not operate reliably.

[0004] However, in the process of the step-up transformer transmitting electricity from the low-voltage side to the high-voltage side (i.e., forward transmission), when a fault occurs inside the step-up transformer, the fault current at the low-voltage side protection installation of the step-up transformer is provided by the new energy power source. Its fault current has the characteristics of limited amplitude and large harmonic content, which may meet the saturation locking criteria of the current transformer (TA), resulting in delayed action or even no action of the differential protection, which will seriously threaten the safe and stable operation of the power grid. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for distinguishing faults within a zone based on a direction distinguishing element, so as to solve the problem in the prior art that when a step-up transformer has an internal fault during forward power transmission, the differential protection is delayed or even does not act.

[0006] To achieve the above object, the solution of the present invention includes:

[0007] The present invention provides a method for distinguishing faults within a zone based on a direction distinguishing element, comprising: when the judgment criteria for starting differential protection are met, judging whether the zone is located in a low-value ratio differential action zone;

[0008] When it is located, and the fault duration is less than the preset fault duration, the direction determination component is entered to determine the fault direction; when it is not located, the determination is terminated;

[0009] When the direction discrimination elements on each side meet the positive direction criterion, it is determined whether the low-voltage criterion is met;

[0010] When the low-voltage criterion is met, the judgment result of the direction discrimination element is maintained until the positive direction criterion of the direction discrimination element lasts for several sampling cycles, and then it is judged as an in-zone fault.

[0011] Furthermore, when the direction discriminating elements on each side do not all 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 the direction discriminating elements on each side satisfy the positive direction criterion, a positive direction criterion flag is also set;

[0013] In the low-value ratio differential action area, when the fault duration is greater than or equal to the preset fault duration, determining whether there is a positive direction criterion flag bit;

[0014] When the positive direction criterion flag is present and the low voltage criterion is met, the judgment result of the direction judgment element is maintained until the positive direction criterion of the direction judgment element lasts for several sampling cycles, and then it is judged as an in-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 the positive direction criterion flag is present but the low voltage criterion is not satisfied, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

[0017] Furthermore, the current transformer saturation blocking criterion is used to determine whether it is an internal fault, including:

[0018] If the current transformer saturation blocking criterion persists for several sampling cycles, it is judged as an in-zone fault.

[0019] Furthermore, when the maximum value of the three-phase differential current is greater than the differential current starting setting value, the differential protection is started.

[0020] The system for distinguishing faults within a zone based on a direction distinguishing element of the present invention comprises a processor, and the processor is used to execute the above-mentioned method for distinguishing faults within a zone based on a direction distinguishing element when calling a computer program.

[0021] The beneficial effects of the present invention are as follows: as a pioneering invention, the present invention determines whether it is located in the low-value ratio differential action zone when the start differential protection criterion is met; when it is located, and when the fault duration is less than the preset fault duration, the direction discrimination element is entered to judge the fault direction; when it is not located, the discrimination is terminated; when the direction discrimination elements on each side meet the positive direction criterion, it is simultaneously judged whether the low-voltage criterion is met; 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 several sampling cycles, and it is judged as an in-zone fault. By adding a direction discrimination element to judge the fault direction, when the fault direction belongs to a forward fault, it can be directly judged whether the fault is located in the zone, and when it is located in the zone, the protection device directly acts. Since there is no need to use the current transformer saturation lockout criterion, it can be directly judged whether the forward fault is located in the zone, and when it is located in the zone, the protection device directly acts, which improves the efficiency of the protection action of the protection device, thereby improving the safe and stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a typical new energy station delivery system provided by an embodiment of the present invention;

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

[0024] Figure 3 It is a flow chart of a method for determining an intra-area fault based on a direction determining element provided by an embodiment of the present invention;

[0025] Figure 4 It is a specific flow chart of a method for determining an intra-area fault based on a direction determining element provided by an embodiment of the present invention;

[0026] Figure 5 yes Figure 1 When an in-zone fault occurs on the high-voltage side of the step-up transformer, a schematic diagram of a calculated voltage drop and a measured voltage drop waveform is obtained by using the fault identification method provided by an embodiment of the present invention;

[0027] Figure 6 yes Figure 1 When an out-of-zone fault occurs on the high-voltage side of the step-up transformer, a schematic diagram of a calculated voltage drop and a measured voltage drop waveform is obtained by using the fault identification method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0029] Figure 1 is a schematic diagram of a typical new energy station delivery system provided by an embodiment of the present invention. Figure 1 As shown in the figure, the wind farm is connected to the external system through the transmission line. The wind farm mainly includes double-fed wind turbines, box transformers, collectors and station main transformers. s is the equivalent voltage source of the external system. Among them, the station main transformer is a step-up transformer. M is the high-voltage side protection installation location of the step-up transformer, and N is the low-voltage side protection installation location of the step-up transformer.

[0030] When a phase-to-phase fault with transition resistance occurs at F3 inside the low-voltage side of the step-up transformer, the second and third harmonic proportions of the fault phase current at the M 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 fixed value. If the existing current transformer saturation blocking criterion is used, the differential protection will be delayed or even not acted, which will seriously threaten the safe and stable operation of the power grid.

[0031] In order to solve the problem in the prior art that the differential protection delays or even does not act when a step-up transformer has an in-zone fault during forward power transmission, the concept of the present invention is to determine the fault direction by adding a direction discrimination element. When the fault direction belongs to a forward fault, it can be directly determined whether the fault is located in the zone. When it is located in the zone, the protection device acts directly. Since there is no need to use the current transformer saturation lockout criterion, it can be directly determined whether the forward fault is located in the zone. When it is located in the zone, the protection device acts directly, which improves the efficiency of the protection action of the protection device and thereby improves the safe and stable operation of the power grid.

[0032] An embodiment of a method for determining faults within a region based on a direction determining element:

[0033] Combine the following Figure 3 and Figure 4 The working principle of an intra-zone fault identification method based on a direction identification element provided by an embodiment of the present invention is specifically described.

[0034] Figure 3 is a flow chart of a method for determining an intra-area fault based on a direction determining element provided by an embodiment of the present invention. Figure 4 FIG. 1 is a specific flow chart of a method for determining an intra-area fault based on a direction determining element provided by an embodiment of the present invention. Figure 3 and Figure 4 As shown, the discrimination method comprises the following steps:

[0035] S10, when the differential protection start-up criterion is met, determine whether it is in the low-ratio differential action area. If it is, execute step S20; otherwise, end.

[0036] Specifically, it can be determined first whether the start differential protection criterion is met. If so, it means that a fault has occurred. In order for the protection device of the step-up transformer to take action, it is necessary to further determine whether it is in the low-value ratio differential action area. If not, it means that no fault has occurred.

[0037] The judgment of whether the start differential protection criterion is met includes: the first step is to calculate 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 The start differential protection criterion is met if 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, For A, B, C three phases, then I dA Represents the differential current of phase A, I dB Represents the differential current of phase B, I dC Represents the differential current of phase C; represents the current on each side of the step-up transformer, m represents the number of windings of the step-up transformer, and the following explanation is given by taking the case where the number of windings m of the step-up transformer is 2 as an example.

[0041] When m=2, i is 1 or 2. Taking phase A as an example: then I 1A Indicates the current of phase A on the high voltage side, I 2A Indicates the current of phase A on the low voltage side.

[0042] As an optional implementation, the voltage and current on each side of the step-up transformer can be collected in real time through a voltage transformer and a current transformer respectively, and then used after filtering.

[0043] As another optional implementation, the voltage and current on each side of the step-up transformer may be collected in advance and stored in a memory for subsequent retrieval.

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

[0045] The steady-state ratio differential protection criterion includes 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 Indicates the ratio braking coefficient setting value, the value range is (0.2, 0.75), and the embodiment of the present invention is based on K b1 =0.5 as an example for illustration.

[0048] Among them, the single-phase braking current It can be calculated by 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), and then the comparison condition of the largest single-phase braking current is determined according to the relationship between the braking current and the rated current. If the largest single-phase braking current is greater than the corresponding comparison condition in formula (2), it is considered that the largest single-phase differential current is in the low-value ratio differential action area, and step S20 needs to be executed; if the largest single-phase braking current is greater than the corresponding comparison condition in formula (3), it is considered that the largest single-phase differential current is in the high-value ratio differential action area, and the judgment is terminated.

[0051] S20, determine whether the fault duration is less than the preset fault duration. If so, execute step S30; otherwise, execute step S70.

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

[0053] The preset fault duration may be set according to actual conditions, and the present invention does not impose any particular limitation thereto. The following description will be given hereinafter by taking the preset fault duration of 40 milliseconds (ms) as an example for illustrative explanation.

[0054] When t-tq<40ms, the direction discrimination element is valid, and the 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 invalid, and step S60 is executed.

[0055] S30, judging whether all the lateral direction elements satisfy the positive criterion. If yes, executing step S40; otherwise, executing step S60.

[0056] After entering the direction determination 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; furthermore, the waveform correlation coefficient between the calculated voltage drop value and the measured voltage drop value in the data window needs to be obtained; finally, it is determined whether the waveform correlation coefficient is greater than or equal to the set value of the waveform correlation coefficient. If it is greater than or equal to, it is considered that a forward fault has occurred, otherwise a reverse fault has occurred.

[0058] Specifically, taking the high-voltage side directional element judgment criterion when the A phase of the high-voltage side of the double-winding transformer with Yd11 connection is single-phase grounding fault as an example, the principle 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 They 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 impedance of the line respectively; i MA (t) represents the instantaneous current value of phase A at the high voltage side protection installation location; i MB (t) represents the instantaneous value of the current of phase B at the high-voltage side protection installation location; i MC (t) represents the instantaneous value of the current of phase C at the high voltage side protection installation location.

[0062] The measured 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 of phase A at the high-voltage side protection installation location; u MA (t) represents the instantaneous value of the voltage of phase A at the high-voltage side protection installation location; i MAf (t-nT) represents the current memory of phase A at the high-voltage side protection installation location; i MBf (t-nT) represents the current memory 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 Substitute the following formula (7) to calculate the waveform correlation coefficient r in the data window: u1MA，u2MA :

[0066]

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

[0068] Take phase A as an example: It represents the average value of the calculated voltage drop value of phase A in a fixed time window. represents the mean value of the voltage drop measured on phase A in a fixed time window, u 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 setting value r of the waveform correlation coefficient? setM .

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

[0071] Among them, for the setting value r of the waveform correlation coefficient setM It can be set according to the actual situation. In the embodiment of the present invention, r setM The data window length may be set according to actual conditions, and the embodiment of the present invention takes W=10 ms as an example for exemplary description.

[0072] It should be noted that for those skilled in the art, if the transformer winding is a double winding, after knowing the principle explanation of the high-voltage side direction element judgment criterion when the high-voltage side A phase single-phase grounding fault occurs, when other phases on the high-voltage side have single-phase grounding faults, how to judge whether it is a forward fault, the principle is similar, and it will not be repeated here. Similarly, when a single-phase grounding fault occurs on the low-voltage side, how to judge whether it is a forward fault, the principle is similar, and it will not be repeated here.

[0073] It should be noted that, for those skilled in the art, if the transformer winding is other windings, after knowing the principle description of the high-voltage side directional element criterion when there is a single-phase grounding fault on phase A on the high-voltage side, how to judge whether it is a forward fault, the principle is similar to that on the high-voltage side, and will not be repeated here.

[0074] After all side direction elements meet the positive criterion, the positive direction criterion flag Dir is set. The positive direction criterion flag Dir=1 or the positive direction criterion flag Dir=0. The present invention does not make any special limitation on this. The following explanation will be given by taking the positive direction criterion flag Dir=1 as an example.

[0075] S40, determine whether the low voltage criterion is met. If yes, execute step S50; otherwise, clear the positive criterion flag and end the determination.

[0076] Among them, the following formula (8) can be used to judge the low voltage criterion:

[0077]

[0078] If it is less than U dset , it is considered that the low-voltage criterion is met, and step S50 can be continued; if it is greater than or equal to U dset , it is considered that the low-voltage criterion is not met, and the positive criterion flag needs to be cleared to end the judgment.

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

[0080] N can be set according to actual conditions, and the present invention does not make any special restrictions on this. In this embodiment, N is 80 as an example for exemplary description; Δt can be set according to actual conditions, and the present invention does not make any special restrictions on this. In this embodiment, Δt is 0.25ms as an example for exemplary description; U dset The setting can be set according to the actual situation, and the present invention does not make any special limitation on this. dset Taking 10% of the rated voltage as an example, an exemplary description is given.

[0081] S50, the determination result of the direction determination element is maintained until the positive determination criterion of the direction determination element lasts for several sampling cycles, and then it is determined to be an in-zone fault.

[0082] As an optional implementation, it is possible to determine whether it is an in-zone fault by sampling multiple times continuously after the fault and determining whether the total time length during which the positive criterion of the direction determination element is satisfied exceeds a set sampling time length.

[0083] As another optional implementation, after the fault occurs, the positive direction criterion of the direction discriminating element is counted by continuous sampling for multiple times, and then it is determined whether the accumulated number of times exceeds the set number to determine whether it is an in-zone fault. The following is an example of counting the positive direction criterion of the direction discriminating element and determining whether the accumulated number of times exceeds the set number.

[0084] like Figure 4 As shown, after the low-voltage criterion is met, the direction discrimination element is sampled once every sampling interval, and then accumulated until the total number is greater than or equal to the preset number t set When t set The setting can be set according to the actual situation, and the present invention does not make any special limitation on this. In this embodiment, t set Take 10 as an example for illustration.

[0085] S60. Determine whether the fault is within the zone by using the current transformer saturation blocking criterion.

[0086] When the direction discrimination elements on each side do not all meet the positive direction criterion, it indicates that there is a reverse fault. Then the current transformer saturation blocking criterion can be used to determine whether it is an internal fault.

[0087] Before using the current transformer saturation blocking criterion to determine whether it is an internal fault, it is necessary to clear the positive direction criterion flag bit and set the sampling number t when using the directional element criterion l1 It is also cleared to increase the accuracy of judging whether it is an in-zone fault using the current transformer saturation blocking criterion.

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

[0089]

[0090] in, represents the second harmonic in the phase current; Represents the third harmonic in the phase current; Indicates the fundamental wave in the phase current; and are all certain proportional constants.

[0091] for The value of can be set according to the actual situation, and the present invention does not make any special restrictions on this. Taking 0.15 as an example, an exemplary description is given; The value of can be set according to the actual situation, and the present invention does not make any special restrictions on this. Take 0.2 as an example for illustration.

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

[0093] As an optional implementation, under open conditions, multiple consecutive samplings are performed to determine whether the total time for which the current transformer saturation blocking criterion is satisfied exceeds a set sampling time to determine whether it is an in-zone fault.

[0094] As another optional implementation, under open conditions, continuous sampling is performed for multiple times, the current transformer saturation blocking criteria are counted, and then it is determined whether the fault is within the zone by judging whether the accumulated number exceeds the set number. The following is a time description by taking the counting of the current transformer saturation blocking criteria and judging whether the accumulated number exceeds the set number as an example.

[0095] When the above formula (9) is satisfied, it means that it is not in the open condition (i.e., the blocking condition). At this time, the sampling number t of the current transformer saturation blocking criterion will be used. l2 After clearing, the judgment ends.

[0096] like Figure 4 As shown, under open conditions, every sampling interval, a sample is collected to meet the current transformer saturation blocking criterion until the total number is greater than or equal to the preset number t set When t l2 Clear to zero and then end the judgment.

[0097] S70, determine whether there is a positive criterion flag. If yes, execute step S80; if not, execute step S60.

[0098] When the fault duration is greater than or equal to the preset fault duration, the direction determination element fails. At this time, it is necessary to determine whether it is a forward fault by judging whether there is a forward judgment flag bit.

[0099] When there is a positive judgment flag, it means that the fault is still a positive fault. When the low voltage judgment is met, the positive judgment of the direction discrimination element can be continued, that is, step S80 can be executed. When there is no positive judgment flag, it means that the fault is a reverse fault, and the positive judgment of the direction discrimination element cannot be continued. It is necessary to use the current transformer saturation blocking judgment, that is, step S60 is executed.

[0100] S80, determine whether the low voltage criterion is met. If so, execute step S50; if not, execute step S60.

[0101] The low-voltage criterion can refer to the above formula (8), which will not be described in detail here.

[0102] Combine the following Figure 5 and Figure 6 The accuracy of the intra-zone fault identification method based on the direction identification element provided in this embodiment is proved.

[0103] Figure 5 yes Figure 1 When an in-area fault occurs on the high-voltage side of the step-up transformer in the embodiment, the fault identification method provided by the embodiment of the present invention is used to obtain a schematic diagram of the calculated voltage drop and the measured voltage drop waveform, as shown in FIG. Figure 5 As shown, at this time, the calculated voltage drop and the measured voltage drop have basically the same change trend, and the waveform similarity is approximately 1, which can reflect that when the intra-zone fault discrimination method based on the direction discrimination element provided by the embodiment of the present invention is applied, the accuracy is relatively high.

[0104] Figure 6 yes Figure 1 When an out-of-zone fault occurs on the high-voltage side of the step-up transformer in the embodiment, the fault identification method provided by the embodiment of the present invention is used to obtain a schematic diagram of the calculated voltage drop and the measured voltage drop waveform, as shown in FIG. Figure 6 As shown, at this time, the calculated voltage drop and the measured voltage drop have opposite changing trends, and the waveform similarity is approximately -1, which can reflect that when the intra-zone fault discrimination method based on the direction discrimination element provided by the embodiment of the present invention is applied, the accuracy is relatively high.

[0105] The method for distinguishing faults within the zone based on the direction distinguishing element provided by the embodiment of the present invention determines whether it is located in the low-value ratio differential action zone when the start differential protection criterion is met; when it is located and the fault duration is less than the preset fault duration, the direction distinguishing element is entered to judge the fault direction; when it is not located, the distinction is terminated; when the direction distinguishing elements on each side meet the positive direction criterion, it is simultaneously determined whether the low voltage criterion is met; when the low voltage criterion is met, the distinction result of the direction distinguishing element is maintained until the positive direction criterion of the direction distinguishing element lasts for several sampling cycles, and it is judged as an in-zone fault. By adding a direction distinguishing element to judge the fault direction, when the fault direction belongs to a forward fault, it can be directly determined whether the fault is located within the zone, and when it is located within the zone, the protection device directly acts. Since there is no need to use the current transformer saturation lockout criterion, it can be directly determined whether the forward fault is located within the zone, and when it is located within the zone, the protection device directly acts, thereby improving the efficiency of the protection action of the protection device, thereby improving the safe and stable operation of the power grid.

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

[0107] An embodiment of the present invention provides an intra-zone fault determination system based on a direction determination element, comprising a processor, wherein the processor is used to execute the intra-zone fault determination method based on a direction determination element as described above when calling a computer program.

[0108] The intra-zone fault determination system based on a direction determination element provided in the embodiment of the present invention can achieve the same beneficial effects as the aforementioned intra-zone fault determination method based on a direction determination element, which will not be described in detail here.

Claims

1. A method for determining faults within a zone based on a direction determining element, characterized in that: Including: when the start differential protection criterion is met, judging whether it is in the low value ratio differential action area; When it is located, and the fault duration is less than the preset fault duration, the direction determination component is entered to determine the fault direction; when it is not located, the determination is terminated; When the direction discrimination elements on each side meet the positive direction criterion, it is determined whether the low-voltage criterion is met; When the low voltage criterion is met, the determination result of the direction determination element is maintained until the positive direction criterion of the direction determination element lasts for several sampling cycles, and then it is determined to be an in-zone fault.

2. The method for determining faults within a zone based on a direction determining element according to claim 1, characterized in that: When the direction discrimination elements on each side do not all meet the positive direction criterion, the current transformer saturation blocking criterion is used to determine whether it is an internal fault.

3. The method for determining faults within a zone based on a direction determining element according to claim 1, characterized in that: When the direction discrimination elements on each side meet the positive direction criterion, a positive direction criterion flag is also set; When the low-value ratio differential action area is located and the fault duration is greater than or equal to the preset fault duration, determining whether the positive direction criterion flag exists; When the positive direction criterion flag is present and the low voltage criterion is met, the determination result of the direction determination element is maintained until the positive direction criterion of the direction determination element lasts for several sampling cycles, and then it is determined to be an in-zone fault.

4. The method for determining faults within a zone based on a direction determining element according to claim 3, characterized in that: When the positive direction criterion flag does not exist, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

5. The method for determining faults within a zone based on a direction determining element according to claim 3, characterized in that: When the positive direction criterion flag is present but the low voltage criterion is not satisfied, the current transformer saturation blocking criterion is used to determine whether it is an intra-zone fault.

6. The method for determining faults within a zone based on a direction determining element according to claim 2, 4 or 5, characterized in that: The method of using the current transformer saturation blocking criterion to determine whether it is an internal fault includes: If the current transformer saturation blocking criterion lasts for several sampling cycles, it is judged as an in-zone fault.

7. The method for determining faults within a zone based on a direction determining element according to claim 1, characterized in that: When the maximum value of the three-phase differential current is greater than the differential current starting setting value, the differential protection is started.

8. An intra-area fault identification system based on a direction identification element, characterized in that: It comprises a processor, and the processor is used to execute the method for distinguishing intra-zone faults based on a direction distinguishing element as described in any one of claims 1 to 7 when calling a computer program.

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