Traveling wave slope criterion adaptive setting protection method based on fault condition information pre-recognition

Abstract

The application discloses a protection method of self-adapting setting of a travelling wave slope criterion based on pre-recognition of fault condition information, and specifically comprises the following steps: after protection is started and it is determined that a forward fault occurs, the characteristics of voltage and current measurement values are used to pre-recognize the fault condition of the most serious out-of-zone fault that is likely to occur, and then the setting value of the slope criterion is self-adaptively adjusted according to the recognition result. The application can improve the sensitivity of the protection while retaining the high-speed performance and reliability of the traditional slope protection, so that the protection can better adapt to the performance requirements of the flexible DC power transmission system on the protection.

Description

Technical Field

[0001] This invention belongs to the field of protection technology for flexible DC transmission systems, specifically relating to an adaptive setting protection method based on traveling wave slope criterion pre-identification of fault condition information. Background Technology

[0002] Flexible DC transmission systems place higher demands on the rapid, reliable, and sensitive identification of faults. Due to the low system inertia of DC systems, faults develop rapidly and can damage the system in a short time. Therefore, the speed of protection is extremely important; for example, the Zhangbei Flexible DC Transmission System requires protection to operate within 3 ms. Traditional slope-type traveling wave protection has the advantages of high speed and reliability, but its setting criteria are based on the principle of ensuring that it does not erroneously when the most severe case of all external faults occurs. The resulting setting values ​​are relatively large, which makes traditional protection less sensitive to high-resistivity faults within the protection zone. Summary of the Invention

[0003] The purpose of this invention is to provide an adaptive setting protection method based on the traveling wave slope criterion for pre-identification of fault condition information, which solves the problem of poor sensitivity in traditional slope-based traveling wave protection.

[0004] To achieve the above objectives, the technical solution adopted in this invention is: an adaptive setting protection method based on the traveling wave slope criterion for fault condition information pre-identification. After the protection is started and identified as a positive fault, the fault conditions of the most severe external fault that may occur are identified and predicted in advance by the characteristics of voltage and current measurement values. Then, the setting value of the slope criterion is adaptively adjusted according to the identification results.

[0005] The technical solution of the present invention also has the following characteristics: The adaptive setting protection method based on traveling wave slope criterion for fault condition information pre-identification of the present invention is implemented according to the following steps: Step 1: Protection Startup; Step 2: Determine the direction of the fault; Step 3: Calculate the absolute value Δ of the first-mode voltage reverse traveling wave fault component after phase-mode transformation. u 1.b The calculation formula is as follows: (1) In the formula: Z c1 The impedance is a known constant when the parameters of the flexible DC transmission system are fixed. u p , u n and i p , i nThese represent the positive and negative voltages and currents, respectively. u 1. i 1 represents the voltage and current of the circuit after the fault. u 1.normal , i 1.normal This represents the voltage and current of a module under normal conditions. In addition, the Δ value of the first five points in the data window after the fault traveling wave reaches the protection installation location should be calculated. u 1.b sum S front ,Right now: (2) In the formula: T n Indicates the sampling interval; Simultaneously search for Δ within the data window. u 1.b The maximum value Δ u 1.b.max ; Step 4: Determine if there is S front > S front.set.low ,in S front.set.low To protect the low setting value, so as to avoid the most serious external faults in the next section of the line; Step 5: Determine if there is a Δ u 1.b.max >Δ u 1.b.max.ref , where Δ u 1.b.max.ref For Δ u 1.b.max The reference value is larger as the noise level increases; Step 6: Fault type identification; Step 7: Waveform feature recognition; Step 8: Based on the fault type identification results in Step 6 and the waveform category identification results in Step 7, adopt the corresponding tuning strategy and adaptively select the tuning value.

[0006] In step 2: if the fault direction is determined to be a reverse fault, the protection will not operate; if the fault direction is determined to be a forward fault, then proceed to step 3.

[0007] In step 4: If S front ≤ S front.set.low This indicates that the fault may occur in the next section of the line, and the protection will not operate in this case; if S front > Sfront.set.low Then proceed to step 5.

[0008] In step 5: if Δ u 1.b.max ≤Δ u 1.b.max.ref If the waveform amplitude is too small, noise will significantly interfere with the results, and the reliability of subsequent judgments will be low. In this case, the protection will not activate. u 1.b.max >Δ u 1.b.max.ref If the result is positive, the reliability of the subsequent steps will be considered high, and the process will proceed to step 6.

[0009] In step 6: the fault types are positive grounding fault, negative grounding fault, and inter-electrode fault.

[0010] In step 7: the waveform characteristics of each fault type are divided into three categories.

[0011] In step 8: Each category corresponds to a tuning strategy.

[0012] The beneficial effects of the present invention are as follows: The present invention provides an adaptive setting protection method based on the traveling wave slope criterion for fault condition information pre-identification. While retaining the advantages of high speed and reliability of traditional slope-type protection, this protection method can improve its sensitivity, making the protection more adaptable to the performance requirements of flexible DC transmission systems. Attached Figure Description

[0013] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of an adaptive setting protection method for traveling wave slope criterion based on fault condition information pre-identification according to the present invention.

[0014] Figure 2 This is a topology diagram of a typical four-terminal MMC DC transmission system. Figure 3 This is the waveform diagram of the F1 fault within 1ms.

[0015] Figure 4 It is the waveform of the first wave of the f2 fault at a certain point within 1ms.

[0016] Figure 5 This is the waveform diagram of the f3 fault within 1ms.

[0017] Figure 6 This is the waveform diagram of the f4 fault within 1ms.

[0018] Figure 7This is the waveform diagram of the F5 fault within 1ms.

[0019] Figure 8 It is the waveform of the first line of the f6 fault at a certain point within 1ms.

[0020] Figure 9 It is a waveform diagram of a near-end fault within 1ms.

[0021] Figure 10 It is a waveform diagram of a fault at the other end within 1ms.

[0022] Figure 11 It includes the fault conditions and waveform characteristics of Category 1.

[0023] Figure 12 It includes the fault conditions and waveform characteristics of Category 2.

[0024] Figure 13 It includes the fault conditions and waveform characteristics of Category 3.

[0025] Figure 14 This is a diagram showing the tuning strategy and simulation results under category 1.

[0026] Figure 15 This is a diagram showing the tuning strategy and simulation results under category 2.

[0027] Figure 16 This is a diagram showing the tuning strategy and simulation results under category 3.

[0028] Figure 17 These are simulation results under 123 fault conditions. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1 The present invention provides an adaptive setting protection method based on traveling wave slope criterion for fault condition information pre-identification. After the protection is started and identified as a positive fault, the most severe external fault conditions that may occur are identified and predicted in advance by the characteristics of voltage and current measurement values. Then, the setting value of the slope criterion is adaptively adjusted according to the identification results.

[0031] The present invention provides an adaptive setting protection method based on traveling wave slope criterion for fault condition information pre-identification. This protection method retains the advantages of high speed and reliability of traditional slope-based protection while improving its sensitivity, making the protection more adaptable to the performance requirements of flexible DC transmission systems.

[0032] Example 2 like Figure 1As shown in Example 2, the adaptive setting protection method for traveling wave slope criterion based on fault condition information pre-identification according to the present invention is implemented according to the following steps: Step 1: Protection Startup; Step 2: Fault direction determination: If the fault direction is determined to be a reverse fault, the protection will not operate; if the fault direction is determined to be a forward fault, proceed to step 3. Step 3: Calculate the absolute value Δ of the first-mode voltage reverse traveling wave fault component after phase-mode transformation. u 1.b The calculation formula is as follows: (1) In the formula: Z c1 The impedance is a known constant when the parameters of the flexible DC transmission system are fixed. u p , u n and i p , i n These represent the positive and negative voltages and currents, respectively. u 1. i 1 represents the voltage and current of the circuit after the fault. u 1.normal , i 1.normal This represents the voltage and current of a module under normal conditions. In addition, the Δ value of the first five points in the data window after the fault traveling wave reaches the protection installation location should be calculated. u 1.b sum S front ,Right now: (2) In the formula: T n Indicates the sampling interval; Simultaneously search for Δ within the data window. u 1.b The maximum value Δ u 1.b.max ; Step 4: Determine if there is S front > S front.set.low ,in S front.set.low To protect the low setting value, so as to avoid the most serious external faults in the next section of the line; like S front ≤ S front.set.lowThis indicates that the fault may occur in the next section of the line, and the protection will not operate in this case; if S front > S front.set.low Then proceed to step 5; Step 5: Determine if there is a Δ u 1.b.max >Δ u 1.b.max.ref , where Δ u 1.b.max.ref For Δ u 1.b.max The reference value is larger as the noise level increases; If Δ u 1.b.max ≤Δ u 1.b.max.ref If the waveform amplitude is too small, noise will significantly interfere with the results, and the reliability of subsequent judgments will be low. In this case, the protection will not activate. u 1.b.max >Δ u 1.b.max.ref If so, the results obtained in the subsequent steps are considered to be highly reliable, and the process proceeds to step 6. Step 6: Fault type identification; Step 7: Waveform feature recognition; Step 8: Based on the fault type identification results in Step 6 and the waveform category identification results in Step 7, adopt the corresponding tuning strategy and adaptively select the tuning value.

[0033] Example 3 Unlike Example 2, in Example 3, the adaptive setting protection method of traveling wave slope criterion based on fault condition information pre-identification of the present invention identifies the fault types as positive ground fault, negative ground fault, and inter-pole fault, and identifies which type of fault it is.

[0034] Example 4 Unlike Example 3, in Example 4, the waveform characteristics of each fault type are divided into three categories, namely Category 1, Category 2 and Category 3.

[0035] Example 5 Unlike Example 4, in Example 5, the adaptive setting protection method of traveling wave slope criterion based on fault condition information pre-identification of the present invention provides a setting strategy for each category.

[0036] in: Positive grounding faults are categorized into three types: 1, 2, and 3, which correspond to setting strategies 1, 2, and 3, respectively. Inter-pole faults are classified into categories 1, 2, and 3, which correspond to tuning strategies 4, 5, and 6, respectively. The categories 1, 2, and 3 of negative grounding faults correspond to setting strategies 7, 8, and 9, respectively.

[0037] Example 6 Example 6 uses a typical four-terminal MMC DC transmission system to perform simulation tests of the present invention.

[0038] Table 1 shows the fault settings in the simulation of this invention.

[0039] The absolute value Δ of the voltage reverse traveling wave fault component is then discussed below. u 1.b It is simply referred to as "mode voltage".

[0040] Figure 2 This is a topology diagram of a typical four-terminal MMC DC transmission system. In this diagram, f1, f3, f5, and f8 represent line faults at the MMC outlet, f4 and f7 represent bus faults, and f2, f6, and f9 represent faults at any location on the line other than the MMC outlet. F1 to f6 are forward faults, and the rest are reverse faults. Only f1 to f3 are in-zone faults. Since there are mature technologies for identifying reverse faults, the focus of this invention is on distinguishing between forward faults inside and outside the zone. Based on this topology, a simulation model is built in PSCAD, and the current-limiting reactor inductor... L b =0.1H, and the fault settings are shown in Table 1. f1, f3, and f5 are line end faults, and their fault locations are uniquely determined; f2 and f6 are line non-end faults, which can represent an infinite number of fault locations. For example, f6 in Table 1 represents 8 fault locations, that is, faults 10, 30, ..., 300 km away from f5. For f6, each fault location corresponds to 3 types of transition resistance, so f6 contains 8 × 3 = 24 different fault conditions. Table 1 contains a total of 123 different fault conditions, which cover all common fault conditions. It should be noted that since the traveling wave waveform characteristics are similar under positive grounding faults, negative grounding faults, and inter-pole faults, and the design ideas of the protection principle are exactly the same, only positive grounding faults will be discussed.

[0041] Combination Figures 3 to 10 It can analyze the characteristics of the reverse traveling wave within 1ms under various fault conditions: (1) F1 fault waveform: such as Figure 3 As shown, the waveform rises rapidly at first, then rises slowly, showing an overall monotonic trend, and the amplitude is negatively correlated with the transition resistance.

[0042] (2) Fault waveform of f2 (unsuperimposed reflective traveling wave): such as Figure 4 As shown, under different transition resistances, the waveforms all rise rapidly at first and then tend to flatten out, with an overall monotonic trend. The maximum value of the waveform is negatively correlated with the transition resistance. Fault waveforms f3, f4, and f5: as shown Figures 5 to 7 As shown, the fault waveforms f3, f4, and f5 exhibit similar characteristics: they monotonically increase at low resistance and initially increase then decrease at high resistance. Furthermore, the larger the transition resistance, the more pronounced the downward trend at the end of the waveform. The maximum waveform value is negatively correlated with the transition resistance.

[0043] (3) F6 fault waveform (unsuperimposed reflective traveling wave): such as Figure 8 As shown, the wavefront slope and amplitude all rise first and then fall under different transition resistances. The wavefront slope and amplitude are significantly smaller than those of faults f1 to f4 in this circuit.

[0044] (4) Waveforms of near-end fault and near-opposite-end fault of f2: as shown Figure 9 and Figure 10 As shown, the fault condition is an f2 fault near the line boundary. Due to the influence of the fault point or boundary reflection, the waveform has significant singularities.

[0045] The waveform of fault f6 near the line boundary: Under the effect of reflection, the waveform has a significant singularity, and the wavefront slope and amplitude are significantly smaller than those of faults f1 to f4 on this line.

[0046] Based on the similarities and differences in waveform characteristics under various fault conditions, the waveform characteristics are divided into three categories. Each category includes fault conditions and waveform examples. Figures 11-13 As shown, the common characteristics of the waveforms in the three categories and the fault conditions they include are as follows: 1) Category 1: Significant singularities exist in the waveform. Fault conditions exhibiting this waveform characteristic include: f2 and f6 faults near the MMC boundary. For example... Figure 11 As shown.

[0047] 2) Category 2: The waveform shows a trend of first rising and then falling. Fault conditions exhibiting this waveform characteristic include: f6 faults that are far from the MMC and non-metallic f3, f4, and f5 faults, such as... Figure 12 As shown.

[0048] 3) Category 3: Overall monotonically rising waveform. Fault conditions exhibiting this waveform characteristic include: f1 fault, f2 fault located far from the MMC, and low-impedance f3, f4, and f5 faults. For example... Figure 13 As shown.

[0049] The traditional traveling wave slope criterion is set to ensure that it does not malfunction when the most severe case of all external faults occurs (i.e., when an f4 metallic fault occurs). However, because the wavefront slope of an f4 fault is relatively large, its... Sfront The calculation results are large, so the setting value of the traditional method is also large, resulting in poor sensitivity of the traditional protection to high-resistivity faults within the zone. The protection principle proposed in this invention, after a fault occurs, first determines the category of the fault waveform, and then sets the setting value based on the most severe external fault within that category. Since the most severe external fault in each category is not necessarily an f4 metallic fault, the setting value for the most severe external fault... S front The calculation results will decrease, so the setting value can be set smaller to improve the sensitivity of the protection.

[0050] The following are the tuning strategies designed for each fault category: 1) Tuning Strategy 1: If the waveform characteristics of a certain fault match the description in Category 1, then the only possible fault conditions for this fault are... Figure 11 One of them, at this time the set value only needs to avoid Figure 11 The most severe external fault condition is sufficient; therefore, the protection criterion setting value is: (3) In the formula K rel For reliability coefficient, S ref As a reference value for setting, f5 metallic faults can be considered the most severe type of fault outside the included area in this category; therefore, the reference value for setting is... S ref For metallic f5 conditions S front In this invention, the setting value for avoiding f5 metallic faults is denoted as... S front.set.low Since this category does not include f4 metallic faults, the setting value is lower than that of traditional protection, thus improving the protection's sensitivity. This applies to faults in the above 123 groups of fault conditions whose theoretical waveform characteristics belong to category 1. S front Arranged in descending order, and summarized as follows: Figure 14 As can be seen, the new tuning strategy has a smaller tuning value than the traditional tuning value (that is, the traditional tuning value that avoids f4 metallic faults) and can distinguish between faults inside and outside the zone.

[0051] 2) Tuning Strategy 2: If the waveform characteristics of a certain fault match the description in Category 2, then the only possible fault conditions for this fault are... Figure 12 One of them. As can be seen from the foregoing analysis, the objective of this invention is to make the slope criterion setting value as small as possible compared to the traditional setting value while ensuring reliability, thereby improving the sensitivity of the protection. To this end, this invention uses the maximum waveform value Δ within 1ms. u 1.b.maxTo estimate the magnitude of the transition resistance, and to set the maximum waveform value as Δ u 1.b.max The f4 fault is considered the most serious possible out-of-area fault, according to the Δ u 1.b.max F4 malfunction S front To select the tuning value. To further explain the principle of this method, Figure 15 With Δ u 1.b.max As the x-axis, with S front Using the vertical axis as the ordinate, the fault conditions whose waveform characteristics belong to category 2 among the 123 sets of fault conditions mentioned above are plotted on the coordinate (Δ). u 1.b.max , S front The values ​​are plotted as scatter points, and a broken line is used to distinguish the setting values ​​for faults inside and outside the fault zone. For Δ in the figure... u 1.b.max <Δ u 1.b.max.A The part that must be avoided is the most serious fault in the next section of the line, that is, in equation (3). S ref Take f5 metallic fault S front Therefore, the set value at this time is S front.set.low For Δ in the figure u 1.b.max >Δ u 1.b.max.B The part that needs to be avoided is the most serious fault on this line, that is, in formula (3). S ref Take f4 metallic fault S front This invention will avoid the f4 metallic fault. S front Record S front.set.high When Δ u 1.b.max.A ≤Δ u 1.b.max ≤Δ u 1.b.max.B When adjusting, the reference value can be written as: (4) Using the f4 fault data from the 80Ω and 100Ω transition resistors, it can be determined that... k and b The value of Δ. u 1.b.max.A Δ u 1.b.max.BThe oblique lines represented by equations (3) and (4) S front.set.low , S front.set.high The x-coordinate of the intersection point. If we assume the setting value for traditional slope-type protection is... S front.set.high Then we can draw the following conclusion: Because S front.set.high , S front.set.low The values ​​of (4) are both less than or equal to the traditional setting values, thus improving the sensitivity of the protection.

[0052] 3) Tuning Strategy 3: If the waveform characteristics of a certain fault match the description in Category 3, then the only possible fault conditions for this fault are... Figure 13 One of them, from Figure 13 It can be seen that the faults outside the zone only include low-resistance f4 and low-resistance f5 faults. All fault conditions belonging to category 3 in the above 123 sets of fault conditions are plotted using coordinates (Δ). u 1.b.max , S front Plot in scatter form Figure 16 It can be seen that the Δ of faults f4 and f5 is... u 1.b.max and S front All show significant differences, therefore, if Δ u 1.b.max If the value is too small, the possibility that the most serious fault outside the protection zone is the low resistance fault f4 can be directly ruled out, and the most serious fault outside the protection zone can be considered to be the low resistance fault f5. The setting value can then be reduced to improve the protection sensitivity. Figure 16 In the middle, with Δ u 1.b.max =Δ u dividing As the dividing line, when Δ u 1.b.max >Δ u dividing In equation (3) S ref = S front.set.high When Δ u 1.b.max ≤Δ u dividing In equation (3) S ref = S front.set.low .

[0053] The above has been introduced Figure 1The tuning strategies 1 to 3 are as follows, while the design ideas for tuning strategies 4 to 9 are exactly the same, and will not be elaborated here.

[0054] The protection principle proposed in this invention first extracts the waveform characteristics of the reverse traveling wave of the single-mode voltage within a 1ms data window after a fault occurs, determines which category the waveform belongs to, and then adopts the appropriate setting strategy for that category.

[0055] The following is a brief description of a feasible method for extracting fault waveform features: First, perform waveform trend analysis to see if there is a downward trend in the latter half of the waveform; if there is no downward trend in the tail, the waveform may be category 1 or category 3. Then, perform singularity detection. If there is a singularity, it is category 1; otherwise, it is category 3. If there is a downward trend in the tail, it may be category 1 or category 2. At this time, perform singularity detection again. If there is a singularity, it is category 1; otherwise, it is category 2.

[0056] The simulation results under the above 123 sets of fault conditions are summarized as follows: Figure 17 The figure illustrates faults outside the protection zone and faults within the zone identified by different waveform categories, along with the setting values. As can be seen from the figure, the setting values ​​effectively distinguish between faults inside and outside the protection zone, with no false tripping occurring. Considering a 1000Ω transition resistance, the protection failed to operate under only two fault conditions, demonstrating high reliability and sensitivity of the protection principle. If the setting values ​​of traditional protection were set to... S front.set.high In the traditional method, S front < S front.set.high If none of the points operate, then there are 12 sets of fault conditions where operation fails, thus indicating that the sensitivity of the method proposed in this invention is significantly higher than that of the traditional method.

[0057] The foregoing description illustrates and describes several preferred embodiments of the invention. However, as previously stated, it should be understood that the invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. An adaptive setting protection method based on traveling wave slope criterion for fault condition information pre-identification, characterized in that, After the protection is activated and identified as a positive fault, the fault conditions of the most serious external fault that may occur are identified and predicted in advance by the characteristics of voltage and current measurement values. Then, the setting value of the slope criterion is adaptively adjusted according to the identification results. The specific steps are as follows: Step 1: Protection Startup; Step 2: Determine the direction of the fault; Step 3: Calculate the absolute value Δ of the first-mode voltage reverse traveling wave fault component after phase-mode transformation. u 1.b The calculation formula is as follows: （1） In the formula: Z c1 The impedance is a known constant when the parameters of the flexible DC transmission system are fixed. u p , u n and i p , i n These represent the positive and negative voltages and currents, respectively. u 1. i 1 represents the voltage and current of the circuit after the fault. u 1.normal , i 1.normal This represents the voltage and current of a module under normal conditions. In addition, the Δ value of the first five points in the data window after the fault traveling wave reaches the protection installation location should be calculated. u 1.b sum S front ,Right now: （2） In the formula: T n Indicates the sampling interval; Simultaneously search for Δ within the data window. u 1.b The maximum value Δ u 1.b.max ; Step 4: Determine if there is S front > S front.set.low ,in S front.set.low To protect the low setting value, so as to avoid the most serious external faults in the next section of the line; Step 5: Determine if there is a Δ u 1.b.max >Δ u 1.b.max.ref , where Δ u 1.b.max.ref For Δ u 1.b.max The reference value is larger as the noise level increases; Step 6: Fault type identification: The fault types are positive grounding fault, negative grounding fault, and inter-pole fault; Step 7: Waveform Feature Identification: The waveform features of each fault type are divided into three categories, denoted as Category 1, Category 2, and Category 3, respectively; Step 8: Based on the fault type identification results in Step 6 and the waveform category identification results in Step 7, adopt the corresponding setting strategy and adaptively select the setting value. Specifically: Category 1, Category 2 and Category 3 of positive grounding faults correspond to setting strategy 1, setting strategy 2 and setting strategy 3 respectively; Category 1, Category 2 and Category 3 of inter-pole faults correspond to setting strategy 4, setting strategy 5 and setting strategy 6 respectively; Category 1, Category 2 and Category 3 of negative grounding faults correspond to setting strategy 7, setting strategy 8 and setting strategy 9 respectively.

2. The adaptive setting protection method for traveling wave slope criterion based on fault condition information pre-identification according to claim 1, characterized in that, In step 2: if the fault direction is determined to be a reverse fault, the protection will not operate; If the fault direction is determined to be a forward fault, proceed to step 3.

3. The adaptive setting protection method based on traveling wave slope criterion for fault condition information pre-identification according to claim 2, characterized in that, In step 4: if S front ≤ S front.set.low This indicates that the fault may occur in the next section of the line, and the protection will not operate in this case; if S front > S front.set.low Then proceed to step 5.

4. The adaptive setting protection method for traveling wave slope criterion based on fault condition information pre-identification according to claim 3, characterized in that, In step 5: if Δ u 1.b.max ≤Δ u 1.b.max.ref If the waveform amplitude is too small, noise will significantly interfere with the results, and the reliability of subsequent judgments will be low. In this case, the protection will not activate. u 1.b.max >Δ u 1.b.max.ref If the result is positive, the reliability of the subsequent steps will be considered high, and the process will proceed to step 6.

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