A CT saturation fault identification method and system

Abstract

The invention relates to the technical field of relay protection of electric power system, and discloses a CT saturation fault identification method and system. When a transformer has an in-zone fault, the original differential current and the original braking current of each sampling point of the fault phase are calculated, and the number of sampling points with positive original braking current modulus in the total number of sampling points of each cycle is counted; the ratio of the original differential current to the original braking current is calculated, and different fault types are judged and identified. After the differential protection is started, the discrimination is put into use, which can not only identify the type of CT saturation, but also the differential protection can reliably act for the working condition of in-zone fault accompanied by CT saturation, and the differential protection can also reliably not act for the working condition of out-of-zone fault accompanied by CT saturation, thereby improving the reliability of transformer differential protection.

Description

Technical Field

[0001] The invention belongs to the technical field of power system relay protection, and in particular relates to a CT saturation fault identification method and system. Background Art

[0002] As the scale of grid-connected renewable energy power generation continues to expand, the role of transformers as key equipment connecting renewable energy and large power grids has become increasingly important, carrying the mission of transmitting renewable energy power to large power grids. When a transformer has an in-zone fault or an out-of-zone to in-zone fault and is accompanied by CT saturation, the differential current waveform will be severely distorted under CT saturation, and the power frequency quantity algorithm will calculate a large second harmonic. For the transformer longitudinal differential protection locked by the second harmonic, the fault cannot be quickly and reliably removed, threatening the safety and stability of the transformer equipment and the power system.

[0003] For example, the Chinese invention patent application document with application publication number CN 106207995 A discloses a differential protection method, device and CT saturation identification method and device. The scheme uses the relationship between the absolute value of each differential differential current sampling point and the maximum sampling point in a single cycle to find a certain number of distortion points to identify the presence of CT saturation in the fault current. Then, by further comparing the characteristic relationship between the original differential current and the braking current sampling value, it is identified whether the CT saturation type is CT saturation for an out-of-zone fault or CT saturation for an in-zone fault, and the differential protection is locked or opened accordingly. Although it can solve part of the steady-state CT saturation problem, when CT transient saturation occurs and is accompanied by an in-zone fault, the transformer differential protection is affected by the secondary harmonic. Since the patented technology does not involve the identification of CT saturation and excitation surge current, the differential protection will be delayed or refused to operate.

[0004] And the Chinese invention patent application document with application publication number CN 105140893 A discloses a differential protection CT saturation identification method, which mainly identifies CT saturation and faults through the original braking current sampling value information and the relationship between the original differential current and the original braking current sampling value. However, this scheme cannot identify the type of CT saturation, and this technology cannot solve the problem of fast and reliable action when the transformer differential protection has CT transient saturation and is accompanied by an in-zone fault. Summary of the invention

[0005] The present invention provides a CT saturation fault identification method and system, which are used to solve the problem that the prior art cannot identify the CT transient saturation of the transformer differential protection and the accompanying faults in the zone.

[0006] In order to solve the above technical problems, the technical solutions included in the present invention and the beneficial effects corresponding to the technical solutions are as follows:

[0007] The present invention provides a technical solution for a CT saturation fault identification method. When a transformer has an in-zone fault, the original differential current and the original braking current of each sampling point of the fault phase are calculated, and the number of sampling points with positive original braking current modulus values ​​in the total number of sampling points of each cycle is counted; the ratio of the original differential current to the original braking current is calculated, and the following judgment is performed:

[0008] (1) When the ratio is greater than a first set parameter, a first sampling point number at which the ratio is greater than the first set parameter is counted, and when the first sampling point number is greater than the set value, it is identified as a serious in-zone fault;

[0009] (2) If the ratio is not greater than the first setting parameter, and the ratio is greater than the second setting parameter, the number of second sampling points at which the ratio is greater than the second setting parameter is counted, and when the second sampling point number is greater than the setting value, it is identified as a slight in-zone fault; the second setting parameter is less than the first setting parameter;

[0010] When any of the above judgments is met and the number of sampling points with positive original braking current modulus values ​​is less than a certain proportion of the total number of sampling points, it is identified as CT saturation of the fault within the occurrence zone; otherwise, it is identified as CT saturation of the fault outside the occurrence zone.

[0011] The beneficial effects of the above technical solution are as follows: the CT saturation fault identification method of the present invention, when put into judgment after the differential protection is started, can not only identify the type of CT saturation, but also the differential protection can reliably operate for the working condition of the fault in the zone accompanied by CT saturation, and can reliably not operate for the working condition of the fault outside the zone accompanied by CT saturation, thereby improving the reliability of the transformer differential protection.

[0012] Furthermore, a method for determining whether a transformer has an in-zone fault is as follows: calculating the effective value of the differential current of each phase among the three phases A, B, and C of the differential current, and determining whether the effective value of the differential current of each phase is greater than a starting current setting threshold; when the effective value of the differential current of any phase is greater than the starting current setting threshold, an in-zone fault occurs in the transformer, and the phase is a faulty phase.

[0013] Furthermore, when a serious zone fault is identified, the differential protection is immediately opened.

[0014] Furthermore, when a minor fault is identified within the zone, the differential protection is opened with a delay of one sampling period.

[0015] Furthermore, the first setting parameter is between 1 and 2, and the second setting parameter is between 0.3 and 0.9; the setting value is the smaller value between the number of sampling points with positive original braking current modulus value and 5 / 6 of the total number of sampling points.

[0016] First, set the parameters within a larger range, identify the serious faults within the zone, and then continue to narrow the range to more accurately identify the minor faults within the zone, and then combine the set values ​​to determine whether the CT is saturated within the zone or outside the zone. This solution identifies the fault type more accurately and improves the accuracy of differential protection.

[0017] The present invention also provides a technical solution for a CT saturation fault identification system, comprising a processor, wherein the processor is used to calculate the original differential current and the original braking current of each sampling point of the fault phase when judging that a fault occurs in the transformer area, and to count the number of sampling points with positive original braking current modulus values ​​in the total number of sampling points of each cycle; calculate the ratio of the original differential current to the original braking current, and perform the following judgment:

[0018] (1) When the ratio is greater than a first set parameter, a first sampling point number at which the ratio is greater than the first set parameter is counted, and when the first sampling point number is greater than the set value, it is identified as a serious in-zone fault;

[0019] (2) If the ratio is not greater than the first setting parameter, and the ratio is greater than the second setting parameter, the number of second sampling points at which the ratio is greater than the second setting parameter is counted, and when the second sampling point number is greater than the setting value, it is identified as a slight in-zone fault; the second setting parameter is less than the first setting parameter;

[0020] When any of the above judgments is met and the number of sampling points with positive original braking current modulus values ​​is less than a certain proportion of the total number of sampling points, it is identified as CT saturation of the fault within the occurrence zone; otherwise, it is identified as CT saturation of the fault outside the occurrence zone.

[0021] The beneficial effects of the above technical solution are as follows: the CT saturation fault identification method of the present invention, when put into judgment after the differential protection is started, can not only identify the type of CT saturation, but also the differential protection can reliably operate for the working condition of the fault in the zone accompanied by CT saturation, and can reliably not operate for the working condition of the fault outside the zone accompanied by CT saturation, thereby improving the reliability of the transformer differential protection.

[0022] Furthermore, a method for determining whether a transformer has an in-zone fault is as follows: calculating the effective value of the differential current of each phase among the three phases A, B, and C of the differential current, and determining whether the effective value of the differential current of each phase is greater than a starting current setting threshold; when the effective value of the differential current of any phase is greater than the starting current setting threshold, an in-zone fault occurs in the transformer, and the phase is a faulty phase.

[0023] Furthermore, when a serious zone fault is identified, the differential protection is immediately opened.

[0024] Furthermore, when a minor fault is identified within the zone, the differential protection is opened with a delay of one sampling period.

[0025] Furthermore, the first setting parameter is between 1 and 2, and the second setting parameter is between 0.3 and 0.9; the setting value is the smaller value between the number of sampling points with positive original braking current modulus value and 5 / 6 of the total number of sampling points.

[0026] First, set the parameters within a larger range, identify the serious faults within the zone, and then continue to narrow the range to more accurately identify the minor faults within the zone, and then combine the set values ​​to determine whether the CT is saturated within the zone or outside the zone. This solution identifies the fault type more accurately and improves the accuracy of differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the CT saturation fault identification method of the present invention. DETAILED DESCRIPTION

[0028] The basic concept of the present invention is to improve the reliability of the ratio differential protection action when the transformer fails and is accompanied by CT saturation in the scenario of renewable energy power generation grid connection. According to the characteristics of the step-up transformer naturally having a double-sided power supply in the scenario of renewable energy power generation grid connection, the present invention proposes a CT saturation fault identification method and system by constructing the action equation of differential current and braking current to identify the characteristic relationship between the differential current sampling value and the braking current sampling value when the transformer fails in the area.

[0029] First, the original differential current and the original braking current are calculated using the time domain information of the current on each side of the transformer, and the number of sampling points N in a cycle sampling point N where the original braking current modulus value is greater than 0 is counted. Ir ; Secondly, the ratio of the original differential current to the original braking current is greater than k1 (k1∈(1,2)) and the number of sampling points that meet the requirement is greater than When , it is identified as a serious fault in the zone, and the differential protection is instantly opened; otherwise, if the ratio of the corresponding original differential current to the original braking current is greater than k2 (k2∈(0.3, 0.9)) and the number of sampling points that meet the requirements is greater than When it is identified as a minor fault in the area, after a delay of T Delay Finally, if any of the above ratios is satisfied, continue to compare to satisfy N Ir Less than When CT saturation occurs, it is identified as an in-zone fault. Otherwise, if the above relationship is met at the same time, it is identified as an out-zone fault.

[0030] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0031] Method Example:

[0032] like Figure 1The CT saturation fault identification method flow chart shown in the figure has the following specific implementation steps:

[0033] 1) Calculate the effective value of the differential current of each phase in phases A, B, and C Determine whether the effective value of each phase differential current is greater than the starting current setting threshold I op ;

[0034] 2) When the effective value of the differential current of any phase is greater than the starting current setting threshold, calculate the original differential current i of each sampling point of the phase cd (k) and the original braking current i r (k), and count the total number of sampling points N in each cycle in real time, and calculate the original braking current modulus value |i r (k)|N number of sampling points greater than 0 Ir ;

[0035] 3) Compare and count the number of sampling points n whose ratio of the original differential current modulus value and the original braking current modulus value corresponding to the phase and the cycle is greater than k1 k1 , and the number of sampling points n k1 When it is greater than the preset value a, it is identified as a serious zone fault and the differential protection is instantly opened.

[0036] 4) If step 3) is not satisfied, continue to compare and count the number of sampling points n whose ratio of the original differential current modulus value and the original braking current modulus value corresponding to the phase and the cycle is greater than k2 k2 , when the number of sampling points n k2 When it is greater than the preset value a, it is identified as a minor fault within the area. Delay After the differential protection is opened, T Delay The value is 1 sampling period.

[0037] 5) By comparing N Ir and The relationship between CT saturation type is used to identify the CT saturation type. If step 3) or step 4) is met at the same time, it is identified as CT saturation in the fault zone; if When both step 3) and step 4) are not satisfied, it is identified as an out-of-zone fault CT saturation.

[0038] System Example:

[0039] The implementation method of the CT saturation fault identification system of the present invention has been clearly introduced in the CT saturation fault identification method embodiment and will not be repeated here.

[0040] The CT saturation fault identification method and system of the present invention not only effectively solves the problem that when a fault occurs in the boost transformer in the new energy grid-connected scenario and is accompanied by CT saturation, the differential protection is affected by the harmonics introduced by CT saturation, thereby improving the performance of the differential protection, but is also applicable to differential protection of high-voltage level interconnection and step-down transformer equipment. The method has a simple principle and a wide range of engineering applications.

[0041] The specific implementation methods of the present invention are given above, but the present invention is not limited to the described implementation methods. Under the idea given by the present invention, the technical means in the above-mentioned embodiments are transformed, replaced, and modified in a way that is easy for a person skilled in the art to think of, and the effect is basically the same as the corresponding technical means in the present invention, and the purpose of the invention is basically the same. The technical solution formed in this way is formed by fine-tuning the above-mentioned embodiments, and this technical solution still falls within the protection scope of the present invention.

Claims

1. A CT saturation fault identification method, characterized in that: When a transformer has an in-zone fault, the original differential current and original braking current of each sampling point of the fault phase are calculated, and the number of sampling points with positive original braking current modulus values ​​in the total number of sampling points in each cycle is counted; the ratio of the original differential current to the original braking current is calculated, and the following judgment is made: (1) When the ratio is greater than a first set parameter, a first sampling point number at which the ratio is greater than the first set parameter is counted, and when the first sampling point number is greater than the set value, it is identified as a serious in-zone fault; (2) If the ratio is not greater than the first setting parameter, and the ratio is greater than the second setting parameter, the number of second sampling points at which the ratio is greater than the second setting parameter is counted, and when the second sampling point number is greater than the setting value, it is identified as a slight in-zone fault; the second setting parameter is less than the first setting parameter; When any of the above judgments is met and the number of sampling points with positive original braking current modulus values ​​is less than a certain proportion of the total number of sampling points, it is identified as CT saturation of the fault within the occurrence zone; otherwise, it is identified as CT saturation of the fault outside the occurrence zone.

2. The CT saturation fault identification method according to claim 1, characterized in that: The method for determining whether a transformer has an in-zone fault is as follows: calculate the effective value of the differential current of each phase among the three phases A, B, and C, and determine whether the effective value of the differential current of each phase is greater than the starting current setting threshold. When the effective value of the differential current of any phase is greater than the starting current setting threshold, the transformer has an in-zone fault and the phase is the fault phase.

3. The CT saturation fault identification method according to claim 1, characterized in that: When a serious zone fault is identified, the differential protection is immediately opened.

4. The CT saturation fault identification method according to claim 3, characterized in that: When a minor fault is identified within the zone, the differential protection is opened with a delay.

5. The CT saturation fault identification method according to claim 4, characterized in that: The first setting parameter is between 1 and 2, and the second setting parameter is between 0.3 and 0.9; the setting value is the smaller value between the number of sampling points with positive original braking current modulus value and 5 / 6 of the total number of sampling points.

6. A CT saturation fault identification system, characterized in that: The invention comprises a processor, wherein the processor is used to calculate the original differential current and the original braking current of each sampling point of the fault phase when judging that a fault occurs in the transformer area, and count the number of sampling points with positive original braking current modulus in the total number of sampling points of each cycle; calculate the ratio of the original differential current to the original braking current, and make the following judgment: (1) When the ratio is greater than a first set parameter, a first sampling point number at which the ratio is greater than the first set parameter is counted, and when the first sampling point number is greater than the set value, it is identified as a serious in-zone fault; (2) If the ratio is not greater than the first setting parameter, and the ratio is greater than the second setting parameter, the number of second sampling points at which the ratio is greater than the second setting parameter is counted, and when the second sampling point number is greater than the setting value, it is identified as a slight in-zone fault; the second setting parameter is less than the first setting parameter; When any of the above judgments is met and the number of sampling points with positive original braking current modulus values ​​is less than a certain proportion of the total number of sampling points, it is identified as CT saturation of the fault within the occurrence zone; otherwise, it is identified as CT saturation of the fault outside the occurrence zone.

7. The CT saturation fault identification system according to claim 6, characterized in that: The method for determining whether a transformer has an in-zone fault is as follows: calculate the effective value of the differential current of each phase among the three phases A, B, and C, and determine whether the effective value of the differential current of each phase is greater than the starting current setting threshold. When the effective value of the differential current of any phase is greater than the starting current setting threshold, the transformer has an in-zone fault and the phase is the fault phase.

8. The CT saturation fault identification system according to claim 7, characterized in that: When a serious zone fault is identified, the differential protection is immediately opened.

9. The CT saturation fault identification system according to claim 7, characterized in that: When a minor fault is identified within the zone, the differential protection is opened with a delay.

10. The CT saturation fault identification system according to claim 9, characterized in that: The first setting parameter is between 1 and 2, and the second setting parameter is between 0.3 and 0.9; the setting value is the smaller value between the number of sampling points with positive original braking current modulus value and 5 / 6 of the total number of sampling points.

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