Ratio-adaptive power failure phase judgment method

Abstract

The invention discloses a ratio self-adaptive power fault phase judgment method, which comprises the following steps of: acquiring voltage and current sampling values of a cycle before and after a fault point for a to-be-judged line and a sudden change point; according to the voltage and current sampling values, calculating a fundamental wave effective value ratio of a next cycle wave to a front cycle wave of the three-phase voltage fault abrupt change point; if the fundamental wave effective value ratio of the next cycle wave to the previous cycle wave of the i-phase fault mutation point is greater than 1, replacing the next sampling value with the normal value of the sampling value before the fault, and setting the fundamental wave effective value ratio of the i-phase as 1; otherwise, keeping unchanged; fault phase judgment is carried out according to the comprehensive ratio, and if the ratio of the fundamental wave effective values of the next cycle wave and the front cycle wave of the i-phase fault mutation point is lower than the comprehensive ratio, the i phase is the fault phase. According to the scheme, defects caused by too large or too small thresholds and defects caused by zero sequence abnormity are effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and specifically relates to a fault phase determination method based on an adaptive ratio, and in particular to a method capable of quickly and accurately determining the type of power grounding or short circuit fault. The method obtains an adaptive unified determination ratio according to the ratios of each phase reduced after a voltage fault, and distinguishes the details of two-phase faults in combination with the phase difference of the fault phase. Background Art

[0002] Fault phase selection is a key link in relay protection. Its rapid and accurate phase selection has positive significance for ensuring the safety of transmission lines and the stability of power systems. Phase selection is also an important part of accurate fault distance measurement.

[0003] Existing fault recording devices and protection devices require fault type judgment and distance analysis for power faults. Accurate fault phase determination is the prerequisite for fault location. At present, the fault phase determination algorithm mainly adopts power frequency phase current difference sudden change quantity phase selection and sequence component phase selection, which is mainly effective for high-voltage transmission lines; for medium and low voltage systems, the voltage and current changes are irregular, which does not conform to the classic high-voltage system power model, so it is difficult to accurately select the phase.

[0004] The sudden phase selection is due to abnormal voltage or weak power supply side causing voltage increase and current abnormality. The phase cannot be judged through the current line, the voltage of the non-fault phase increases or partially decreases, and it is also impossible to accurately judge. The sequence method is due to the increase of voltage or decrease of current in the non-fault phase, resulting in inaccurate sequence analysis value and phase, and the correct result cannot be obtained.

[0005] In addition, when ground faults are judged using zero-sequence, they are affected by the ground resistance. The zero-sequence variation range has no unified judgment threshold, or the opposite extreme situation occurs, which can easily lead to misjudgment.

[0006] In the prior art, an invention patent with the publication number CN100388581 C discloses a phase differential current method for preventing transformer differential protection from malfunctioning. The three-phase differential currents Ida, Idb, and Idc in the transformer differential protection respectively form a ratio braking element with the zero-sequence current 3Io on the Y0 side of the transformer. When the ratio value is less than the setting value K, the corresponding phase differential current is judged to be the error current caused by the fault outside the zone, and the corresponding phase ratio differential protection is braked to prevent the transformer differential protection from malfunctioning. The invention can completely avoid the transformer differential protection malfunction caused by the ground fault outside the zone on the Y0 side, and does not affect the correct operation of the differential protection under the fault condition inside the zone.

[0007] Another invention patent with the publication number CN1614849A discloses a method for braking the zero-sequence fault component of the phase-converting to prevent the transformer protection from malfunctioning. The three-phase current fault component on the Y0 side of the transformer without the zero-sequence fault component is used to form a ratio braking element with the zero-sequence current fault component on this side. When the ratio value is less than the set value, the braking signal of the corresponding phase is output to brake the transformer ratio differential protection. The application of this scheme can completely avoid the transformer differential protection malfunction caused by the ground fault outside the Y0 side when the errors of the three-phase current transformers are inconsistent, and can also prevent the transformer differential protection malfunction caused by the differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions.

[0008] Although the above scheme mentions that the three-phase current fault components on the Y0 side of the transformer minus the zero-sequence component are used to form ratio braking elements with the zero-sequence current fault components on that side, in the above scheme, the ratio used for the transformer differential protection is obtained by dividing the zero-sequence current fault component on that side. Therefore, the disadvantages caused by the zero-sequence abnormality cannot be avoided. Summary of the invention

[0009] A brief summary of embodiments of the present invention is provided below to provide a basic understanding of certain aspects of the present invention. It should be understood that the following summary is not an exhaustive summary of the present invention. It is not intended to identify key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to provide certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0010] In order to solve the above technical problems, the idea adopted by the present invention is to realize an automatic judgment method based on the ratio of the effective value of the voltage before and after the fault and the phase difference: an adaptive unified judgment ratio is obtained according to the ratio of each phase reduced after the voltage fault, and the data abnormality is pre-processed in advance to make the ratio more effective, and the details of the two-phase ground short circuit are distinguished in combination with the phase difference of the fault phase. Through this scheme, the defects of the mutation phase selection and the sequence method can be effectively avoided, and the results are more accurate. This scheme is not only applicable to high-voltage systems, but also to medium and low-voltage systems.

[0011] Specifically, the present invention provides a ratio adaptive power fault phase determination method, which includes:

[0012] Step 1: For the line and mutation point to be judged, obtain the voltage and current sampling values ​​of one cycle before and after the fault point;

[0013] Step 2: Determine the voltage and current change ratio based on the voltage and current sampling values, as follows:

[0014] Calculate the ratio of the fundamental effective value of the cycle after the three-phase voltage fault mutation point to the previous cycle rmsRat i :

[0015] rmsRat i =rms i _after / rms i _before;

[0016] Where i is a natural number, representing the three phases A, B, and C, rmsRat i It is the ratio of the fundamental effective value of the cycle after the fault mutation point of phase i to the fundamental effective value of the cycle before the fault, rms i _after is the effective value of the fundamental wave of one cycle after the fault mutation point, rms i _before is the effective value of the fundamental wave of the cycle before the fault mutation point. Phase i refers to one of the three-phase electricity, and the three-phase electricity is usually marked as phases A, B, and C. Therefore, the ratio of the effective value of the fundamental wave of the cycle after the three-phase voltage fault mutation point to the previous cycle is recorded as rmsRatA, rmsRatB, and rmsRatC respectively; rmsRat i That is, the ratio of voltage and current change;

[0017] Step 3: Data Preprocessing:

[0018] If the fundamental effective value ratio of the cycle after the fault mutation point of phase i to the cycle before is rmsRat i >1, indicating that the voltage increases abnormally after the fault, the normal value of the sampling value before the fault is used to replace the subsequent sampling value, and the fundamental effective value ratio of the i phase is set to 1; to prevent the abnormal voltage increase from interfering with the unified ratio, the procedure is as follows:

[0019] If rmsRat i >1.02, then rms i _after=rms i _before,rmsRat i =1; otherwise unchanged.

[0020] After data preprocessing, the calculation interference of abnormally large ratios is effectively eliminated, making the comprehensive ratio more accurate and effective.

[0021] Step 4: Calculate the adaptive comprehensive ratio rmsRatAvg as the average of the phase ratios:

[0022] rmsRatAvg=(rmsRatA+rmsRatB+rmsRatC) / 3.

[0023] The comprehensive ratio can be regarded as the average of the three-phase ratios. The phase below the average is the fault phase, which can adapt to various fault conditions.

[0024] Step 5: According to the comprehensive ratio rmsRatAvg in step 4, the fault phase is judged. If the ratio of the fundamental effective value of the cycle after the fault mutation point of phase i to the fundamental effective value of the cycle before is lower than the comprehensive ratio rmsRatAvg, then phase i is the fault phase.

[0025] Furthermore, the step 5 performs fault phase determination according to the comprehensive ratio rmsRatAvg of step 4, including:

[0026] Step 51: First, three-phase fault determination is performed. The specific determination method for voltage three-phase fault is: rmsRat per phase i <(rmsRatAvg+0.99) / 2. Three-phase fault is a rare fault type in the power system, so it is judged and processed first.

[0027] Step 52: Compare the ratio of the fundamental effective value of each phase with rmsRatAvg. If it is less than rmsRatAvg, it is one of the fault phases; mark the fault phase, and statistically determine whether it is a single-phase fault or a two-phase fault.

[0028] As an implementation scheme, the step 52 marks the fault phase and statistically determines whether it is a single-phase fault or a two-phase fault, specifically including:

[0029] If it is a two-phase fault, calculate whether the phase difference between the two phases is within 35 degrees. If so, it is a two-phase short circuit, otherwise it is a two-wire grounding fault, which can avoid misjudgment by using the zero-sequence threshold;

[0030] If it is a single-phase fault, it is a single-phase grounding fault;

[0031] If there is no fault phase, the output is fault-free.

[0032] In particular, if it is a reclosing point fault judgment, the voltage and current before the fault mutation point can be replaced with the voltage and current during the normal period, and then according to the above judgment method, the correct reclosing fault phase can be obtained. Specifically, for the reclosing point fault judgment, the data preprocessing process of step 3 is modified as follows:

[0033] If the fundamental effective value ratio of the cycle after the fault mutation point of phase i to the cycle before is rmsRat i >1, the voltage and current before the fault mutation point are replaced by the voltage and current values ​​in the normal period afterwards, and the fundamental effective value ratio of the i phase is set to 1.

[0034] The other steps are the same as those of the above ratio adaptive power fault phase determination method.

[0035] The solution of the present invention can be applied to various voltage levels to obtain accurate fault types. Through data preprocessing, the influence of the voltage single-phase ratio on the comprehensive ratio is avoided; an adaptive three-phase unified ratio is adopted to automatically form a judgment comparison standard, and the comparison value will automatically float with the severity of the fault, and the ratio situation is automatically judged to obtain accurate fault phase difference. For two-phase faults, by comparing the phase difference after the fault, the defect of setting an inappropriate threshold value for judging two-phase grounding short circuit by zero sequence is effectively avoided, and grounding and short circuit situations are effectively distinguished.

[0036] In summary, the present invention adopts the above scheme to implement a ratio-adaptive power fault phase judgment method. After data preprocessing through a single-phase ratio, an adaptive unified judgment ratio is established. Each phase ratio is compared with the unified ratio to determine whether the phase is a faulty phase. Finally, the phase difference between the two phases after the fault is used instead of the zero sequence to distinguish between grounding and short circuit faults, effectively avoiding the defects caused by various thresholds that are too large or too small and the disadvantages caused by zero-sequence abnormalities. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention may be better understood by referring to the following description in conjunction with the accompanying drawings, wherein the same or similar reference numerals are used throughout the drawings to represent the same or similar components. The accompanying drawings, together with the following detailed description, are incorporated in and form a part of this specification and are used to further illustrate the preferred embodiments of the present invention and to explain the principles and advantages of the present invention.

[0038] In the figure:

[0039] Figure 1 FIG. 4 is a flow chart of fault phase determination according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] Embodiments of the present invention will be described below with reference to the accompanying drawings. Elements and features described in one drawing or one embodiment of the present invention may be combined with elements and features shown in one or more other drawings or embodiments. It should be noted that for the purpose of clarity, the representation and description of components and processes that are not related to the present invention and are known to those of ordinary skill in the art are omitted in the drawings and descriptions.

[0041] See also Figure 1 The present invention provides a ratio-adaptive power fault phase determination method, which automatically determines the fault phase based on the voltage effective value ratio and phase difference before and after the fault. Specifically, it includes:

[0042] 1. For the line and mutation point to be judged, obtain the voltage and current sampling values ​​of one cycle before and after the fault point (obtain the voltage and current sampling values ​​before and after the three-phase fault point of the line, and calculate the effective value phase of the three-phase before and after);

[0043] 2. Determine the voltage and current change ratio rmsRati :

[0044] Calculate the ratio of the fundamental effective value of the cycle after the three-phase voltage fault mutation point to the previous cycle rmsRat i :rmsRat i =rms i _after / rms i _before;

[0045] i is a natural number, representing the three phases A, B, and C. The ratio of the fundamental effective value of the cycle after the voltage fault mutation point to the previous cycle of the three phases A, B, and C is recorded as rmsRatA, rmsRatB, and rmsRatC respectively;

[0046] 3. Data preprocessing:

[0047] If the voltage increases abnormally after a fault (rmsRat i >1), the normal value sampled before the fault is used to replace the subsequent sampled value, and the new ratio of this phase is set to 1 to prevent the abnormal voltage increase from interfering with the uniform ratio.

[0048] If rmsRat i >1.02, then rms i _after=rms i _before,rmsRat i =1; otherwise unchanged.

[0049] 4. Calculate the adaptive comprehensive comparison ratio rmsRatAvg, rmsRatAvg is the average value of the three-phase ratio rmsRat:

[0050] After data preprocessing, the calculation interference of abnormally large ratios is effectively eliminated, making the comprehensive ratio more accurate and effective. The comprehensive ratio can be regarded as the average line of the three-phase ratios. The phase below the average line is the fault phase, which can adapt to various fault conditions.

[0051] rmsRatAvg=(rmsRatA+rmsRatB+rmsRatC) / 3;

[0052] 5. Determine whether it is a three-phase fault:

[0053] Voltage three phases reduced simultaneously (rmsRat per phase i <(rmsRatAvg+0.99) / 2), it is a three-phase fault; three-phase fault is a rare fault type in the power system, so it should be judged and processed first.

[0054] 6. Fault phase determination

[0055] Each phase ratio is compared with rmsRatAvg. If it is less than rmsRatAvg, it is one of the fault phases; mark the fault phase, and statistically determine whether it is a single-phase fault or a two-phase fault:

[0056] If it is a two-phase fault, calculate whether the phase difference between the two phases is within 35 degrees. If so, it is a two-phase short circuit, otherwise it is a two-wire grounding fault, which can avoid misjudgment by using the zero-sequence threshold;

[0057] If it is a single-phase fault, it is a single-phase grounding fault;

[0058] If there is no fault phase, the output is fault-free.

[0059] In particular, if it is a reclosing point fault judgment, the voltage and current before the fault mutation point can be replaced with the voltage and current during the normal period, and then the correct reclosing fault phase can be obtained according to the above judgment method.

[0060] In various wave recording, ranging or phase determination devices, after obtaining the line fault mutation point, the original fault phase determination method is replaced by this solution, which can more accurately obtain the corresponding fault phase, and then perform the original process processing, such as ranging processing, to avoid subsequent ranging and fault processing errors caused by phase determination errors.

[0061] For different fault conditions, the phase judgment examples are as follows:

[0062]

[0063] From the above situations, combined with the two-phase fault phase difference to determine the short circuit and grounding types, the fault types can be accurately distinguished, which fully demonstrates the effectiveness and rationality of this method.

[0064] The voltage and current of the present invention only need to use single-side voltage and current data to determine the phase, while the prior art (such as the transformer differential protection scheme mentioned in the background technology) uses data from both sides for difference processing. Therefore, the present invention has wider applicability.

[0065] In addition, the ratio mentioned in the prior art is obtained by dividing the zero-sequence current fault component on that side, while the ratio of the present invention is divided by the effective value of the voltage cycle before the fault, thereby completely avoiding the disadvantages caused by zero-sequence abnormality. Therefore, the present application can effectively avoid the disadvantages caused by zero-sequence abnormality, and does not need to set the threshold in advance, avoiding the defects caused by the setting value being too large or too small, so the adaptive unified judgment ratio is more effective and accurate.

[0066] In addition, the ratio mentioned in the prior art is compared with the set value K, while the present invention is compared with the adaptive unified judgment ratio, which does not require the threshold to be set in advance, and completely avoids the defects caused by the set value being too large or too small. Therefore, there is no need to set the threshold in advance, and the defects caused by the user setting the value too large or too small are avoided, so the adaptive unified judgment ratio is more practical and accurate.

[0067] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0068] Although the present invention has been disclosed above by describing specific embodiments of the present invention, it should be understood that all the above embodiments and examples are exemplary rather than restrictive. Those skilled in the art may design various modifications, improvements or equivalents of the present invention within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included in the protection scope of the present invention.

Claims

1. A ratio adaptive power fault phase determination method, characterized in that: include: Step 1: For the line and mutation point to be judged, obtain the voltage and current sampling values ​​of one cycle before and after the fault point; Step 2: Calculate the rmsRat ratio of the fundamental wave of the cycle after the three-phase voltage fault mutation point to the fundamental wave of the cycle before the fault mutation point based on the voltage and current sampling values. i : rmsRat i =rms i _after / rms i _before; Where i is a natural number, representing the three phases A, B, and C, rmsRat i It is the ratio of the fundamental effective value of the cycle after the fault mutation point of phase i to the fundamental effective value of the cycle before the fault, rms i _after is the effective value of the fundamental wave of one cycle after the fault mutation point, rms i _before is the effective value of the fundamental wave of the cycle before the fault mutation point; the ratio of the effective value of the fundamental wave of the cycle after the three-phase voltage fault mutation point to the previous cycle is recorded as rmsRatA, rmsRatB, and rmsRatC respectively; Step 3: Data Preprocessing: If the fundamental effective value ratio of the cycle after the fault mutation point of phase i to the cycle before is rmsRat i >1, the normal value of the sampling value before the fault is used to replace the subsequent sampling value, and the fundamental effective value ratio of the i phase is set to 1; otherwise, it remains unchanged; Step 4: Calculate the adaptive comprehensive ratio rmsRatAvg as the average of the phase ratios: rmsRatAvg=(rmsRatA+rmsRatB+rmsRatC) / 3; Step 5: According to the comprehensive ratio rmsRatAvg in step 4, the fault phase is judged. If the ratio of the fundamental effective value of the cycle after the fault mutation point of phase i to the fundamental effective value of the cycle before is lower than the comprehensive ratio rmsRatAvg, then phase i is the fault phase.

2. A ratio adaptive power fault phase determination method according to claim 1, characterized in that: The step 5 of performing fault phase determination according to the comprehensive ratio rmsRatAvg of step 4 includes: Step 51: First, perform three-phase fault identification. When each phase rmsRat i <(rmsRatAvg+0.99) / 2, it is a three-phase fault.

3. A ratio adaptive power fault phase determination method according to claim 2, characterized in that: The step 5 also includes: Step 52: Compare the ratio of the fundamental effective value of each phase with rmsRatAvg. If it is less than rmsRatAvg, it is one of the fault phases; mark the fault phase, and statistically determine whether it is a single-phase fault or a two-phase fault.

4. A ratio adaptive power fault phase determination method according to claim 3, characterized in that: In step 52, the fault phase is marked and statistics are performed to determine whether it is a single-phase fault or a two-phase fault, specifically including: if it is a two-phase fault, calculating whether the phase difference between the two phases of the fault is within 35 degrees, if so, it is a two-phase short circuit, otherwise it is a two-wire grounding fault; If it is a single-phase fault, it is a single-phase grounding fault; If there is no fault phase, the output is fault-free.

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