Secondary current loop two-point grounding early warning method and system based on holographic voltage acquisition

Abstract

The invention discloses a secondary current loop two-point grounding early warning method and system based on holographic voltage acquisition. The method comprises the following steps: acquiring holographic voltage of a permanent grounding point; when the number of times that the holographic voltage sampling value is not smaller than the starting voltage threshold value is not smaller than the sampling voltage continuous over-limit number of times threshold value, opening logic judgment time, setting a plurality of judgment periods in the logic judgment time, and obtaining a holographic voltage sequence collected in each judgment period in real time; constructing a voltage steady-state criterion to judge whether steady-state holographic voltage abnormity exists or not, and constructing a voltage positive increment criterion and a voltage negative increment criterion to judge whether dynamic holographic voltage abnormity exists or not; and if at least one of the voltage steady-state criterion, the voltage positive increment criterion or the voltage negative increment criterion is met in any one judgment period, giving a secondary current loop two-point grounding alarm. According to the invention, real-time monitoring and early warning of the two-point grounding condition of the secondary current loop are realized, and maloperation of a relay protection device is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of operation and maintenance of secondary substation systems, and more specifically, relates to a two-point grounding warning method and system for secondary current circuits in holographic voltage acquisition. Background Art

[0002] When a fault occurs in the power system, the relay protection device obtains and analyzes the fault-related information, and then operates to trip, so as to isolate the fault within the smallest range and ensure the stability of the power grid and the safety of the equipment. However, its own reliability has also become the focus of research. Especially for the problem of misoperation of protection devices caused by two-point grounding of the secondary current circuit, relevant research is of great significance.

[0003] At present, the research on two-point grounding of secondary current circuits still stays in the principle analysis, and there is little research on the monitoring and discrimination methods for two-point grounding of secondary current circuits.

[0004] The existing two-point grounding monitoring and discrimination methods are mainly daily substation operation and maintenance inspections. Through daily inspection work in the station, the visual method is used to judge whether there are foreign objects on the terminal blocks of the current circuit inside devices such as terminal boxes and protection panels, so as to prevent two-point grounding of the secondary current circuit. The deficiencies of the existing technology are as follows:

[0005] 1) Lack of real-time performance. Since daily operation and maintenance inspections are usually carried out at fixed intervals, the frequency generally does not exceed 2 times a day. The inspection time for a certain switch cabinet accumulates to more than ten minutes a day, and the remaining time can basically not be taken into account. Coupled with the large randomness of the occurrence of two-point grounding events in the secondary current circuit, it is impossible to monitor in real time.

[0006] 2) Insufficient prevention of accidental events. Relying solely on daily operation and maintenance inspections, the efficiency and timeliness of discovering problems are insufficient. Due to the accidental nature of the two-point grounding problem, the proportion discovered through daily inspection means is relatively low, and it is easy to leave hidden dangers of misoperation of protection devices.

[0007] 3) The severity cannot be quantified. When discovering relevant hidden dangers through daily operation and maintenance means, due to the influence of the subjective judgment of operation and maintenance personnel, it is impossible to quantitatively analyze the impact caused by the hidden dangers. Summary of the Invention

[0008] To solve the deficiencies existing in the prior art, the present invention provides a two-point grounding warning method and system for secondary current circuits in holographic voltage acquisition, which realizes real-time monitoring and warning of two-point grounding of secondary current circuits in substations.

[0009] The present invention adopts the following technical solutions.

[0010] The first aspect of the present invention provides a two-point grounding warning method for secondary current circuits in holographic voltage acquisition, including the following steps:

[0011] Step 1, collect the holographic voltage of the permanent grounding point in the secondary current circuit;

[0012] Step 2, when the number of times the sampled value of the holographic voltage is not less than the starting voltage threshold is not less than the threshold of the continuous over-limit times of the sampled voltage, proceed to Step 3; otherwise, return to Step 1;

[0013] Step 3, after the starting criterion is met, open the logic discrimination time, set multiple discrimination periods within the logic discrimination time, and obtain the holographic voltage sequence collected in each discrimination period in real time; construct a voltage steady-state criterion based on the holographic voltage sequence to determine whether there is an abnormal steady-state holographic voltage, and construct a voltage positive increment criterion and a voltage negative increment criterion based on the holographic voltage sequence to determine whether there is an abnormal dynamic holographic voltage;

[0014] Step 4, in any one of the discrimination periods, if at least one of the voltage steady-state criterion, the voltage positive increment criterion, or the voltage negative increment criterion is satisfied, issue an alarm for two-point grounding in the secondary current circuit.

[0015] Preferably, in Step 1, use the sampling resistor R installed at the permanent grounding point of the secondary current circuit t to collect the holographic voltage, set the sampling frequency f of the holographic voltage to 200*n Hz, where n is an integer ≥ 20, and R t ≤0.1Ω.

[0016] Preferably, in Step 2, the starting criterion is satisfied when the following relational expression holds:

[0017]

[0018] In the formula:

[0019] S set1 is the threshold of the continuous over-limit times of the sampled voltage;

[0020] is the absolute value of the j-th sampled value of the holographic voltage;

[0021] U set1 is the starting voltage threshold.

[0022] Preferably, the threshold S of the continuous over-limit times of the sampled voltage set1 is set to 6, and the starting voltage threshold U set1 is set to 0.003V.

[0023] Preferably, in Step 3, the voltage steady-state criterion is expressed by the following formula:

[0024] m1≥S set2 , when m1 = m1 + 1

[0025] In the formula:

[0026] m1 represents the cumulative number of times of voltage over - limit, which is initialized to 0 at the beginning of each discrimination period;

[0027] S set2 is the threshold value of the number of times of steady - state voltage over - limit;

[0028] is the absolute value of the i - th sampling value in the holographic voltage sequence within the same discrimination period;

[0029] U set2 is the steady - state voltage set value.

[0030] Preferably, the threshold value S of the number of times of steady - state voltage over - limit set2 is set to 6, and the steady - state voltage set value U set2 is set to 0.0135V.

[0031] Preferably, in step 3, the voltage positive - increment criterion is expressed by the following formula:

[0032] m2≥S set3 , when then m2 = m2 + 1

[0033]

[0034] In the formula:

[0035] f represents the sampling frequency;

[0036] is the i - th sampling value in the holographic voltage sequence within the same discrimination period;

[0037] m2 represents the cumulative number of times of voltage positive - increment over - limit, which is initialized to 0 at the beginning of each discrimination period;

[0038] S set3 is the threshold value of the number of times of voltage change rate over - limit;

[0039] k set1 is the set value of the adjacent sampling voltage change rate;

[0040] q + is the sampling voltage subscript when m2 = 1, and p + is the sampling voltage subscript when m2 = S set3 , and p + -q + ≥S set3 ;

[0041] k set2 is the set value of the average change rate of the head - and - tail voltages.

[0042] Preferably, in step 3, the voltage negative increment criterion is expressed by the following formula:

[0043] m3≥S set3 When m3 = m3 + 1

[0044]

[0045] Wherein:

[0046] f represents the sampling frequency;

[0047] m3 represents the cumulative number of times the voltage negative increment exceeds the limit, and is initialized to 0 at the start of each discrimination period;

[0048] is the i-th sampling value in the holographic voltage sequence within the same discrimination period;

[0049] S set3 is the threshold value of the number of times the voltage change rate exceeds the limit;

[0050] k set1 is the set value of the adjacent sampling voltage change rate;

[0051] q' - is the sampling voltage subscript when m3 = 1, and p' - is the sampling voltage subscript when m3 = S set3 p' - -q' - ≥S set3 ;

[0052] k set2 is the set value of the average change rate of the head and tail voltages.

[0053] Preferably, the threshold value S of the number of times the voltage change rate exceeds the limit set3 is set to 6, the set value k of the adjacent sampling voltage change rate set1 is set to 4V / s, and the set value k of the average change rate of the head and tail voltages set2 is set to 4.2V / s.

[0054] The second aspect of the present invention provides a two-point grounding warning system for the secondary current loop of holographic voltage acquisition, which operates the two-point grounding warning method for the secondary current loop of holographic voltage acquisition, including: a sampling resistor and a logic judgment module 32;

[0055] Among them, the sampling resistor is used to collect the holographic voltage of the permanent grounding point 5 of the secondary current loop;

[0056] The logic judgment module 32 includes a starting element 321, a voltage steady-state element 322, a voltage positive increment element 323, and a voltage negative increment element 324;

[0057] The starting element 321 is used to determine whether the starting criterion is met. If so, it opens the logic discrimination time and activates the voltage steady-state element 322, the voltage positive increment element 323, and the voltage negative increment element 324.

[0058] The voltage steady-state element 322 is used to send an alarm signal when the voltage steady-state criterion is met.

[0059] The voltage positive increment element 323 is used to send an alarm signal when the voltage positive increment criterion is met.

[0060] The voltage negative increment element 324 is used to send an alarm signal when the voltage negative increment criterion is met.

[0061] Compared with the prior art, the beneficial effects of the present invention at least include:

[0062] 1) By collecting the holographic voltage of the sampling resistance of the permanent grounding point of the current loop in real time, the real-time monitoring and early warning of the two-point grounding situation of the secondary current loop are realized, so as to detect the two-point grounding of the secondary current loop in time and effectively avoid the misoperation of the relay protection device.

[0063] 2) By combining multiple criteria as the early warning criteria, the steady-state and dynamic situations are more comprehensively discriminated, which not only improves the reliability of the two-point grounding early warning of the secondary current loop, but also ensures the rapidity of the early warning discrimination, effectively preventing the occasional occurrence of the two-point grounding problem of the secondary current loop, thereby improving the detection efficiency of the two-point grounding of the secondary current loop.

[0064] 3) The early warning criteria have clear quantitative standards, avoiding the lack of unified standards or subjective judgment errors of the operation and maintenance personnel. Brief Description of the Drawings

[0065] Figure 1 is a schematic diagram of the two-point grounding of the secondary current loop provided according to the embodiment of the present invention;

[0066] Figure 2 is a schematic diagram of the structure of the logic judgment module of the two-point grounding early warning system of the secondary current loop provided according to the embodiment of the present invention;

[0067] Figure 3 is a schematic diagram of testing the performance of the two-point grounding early warning system provided according to the application example of the present invention;

[0068] In the figure: 1. Rheological terminal box; 2. Protection panel; 21. Protection device; 3. Two-point grounding warning system for secondary current circuit; 31. Two-point grounding equivalent power supply; 32. Logic judgment module; 321. Starting element; 322. Voltage steady-state element; 323. Positive voltage increment element; 324. Negative voltage increment element; 4. Temporarily generated grounding point; 5. Permanent grounding point of secondary current circuit; 61. Cable trench; 62. Cable; 7. Simulation line. Specific implementation mode

[0069] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0070] Embodiment 1 of the present invention provides a two-point grounding warning method for a secondary current circuit for holographic voltage acquisition, including the following steps:

[0071] Step 1, collect the holographic voltage of the permanent grounding point in the secondary current circuit.

[0072] The schematic diagram of two-point grounding of the secondary current circuit is as Figure 1 shown. In the figure, the secondary current circuit from the rheological terminal box 1 to the protection panel 2 is taken as an example. The two-point grounding equivalent power supply 31 includes a potential difference voltage source ΔU and its internal resistance R. The grounding points of the secondary current circuit include the temporarily generated grounding point 4 and the permanent grounding point 5 of the secondary current circuit.

[0073] In a preferred but non-limiting implementation mode of the present invention, a sampling resistor R t ≤0.1 Ω is installed at the position of the permanent grounding point 5 of the secondary current circuit for collecting the holographic voltage The sampling frequency of the holographic voltage is f = 200 * n Hz, where n is an integer ≥ 20.

[0074] In a further exemplary but non-limiting implementation mode, R t is set to 0.1 Ω and f is set to 4000 Hz.

[0075] It can be understood that, ideally, if there is only one grounding point in the current circuit, the holographic voltage collected in the sampling resistor is always zero.

[0076] Step 2, construct the starting criteria. Specifically, in order to avoid the impact of electromagnetic interference on the circuit during actual operation of the substation, the fault judgment calculation is started only when the holographic voltage sampling value reaches the set threshold value for multiple consecutive times, and then continue to step 3, otherwise return to step 1.

[0077] In a preferred but non-limiting embodiment of the present invention, the start criterion is expressed as follows:

[0078]

[0079] Where:

[0080] S set1 The threshold value of the number of times the sampling voltage exceeds the limit continuously;

[0081] is the absolute value of the jth sampling value of the holographic voltage;

[0082] U set1 is the starting voltage threshold.

[0083] In a further exemplary but non-limiting embodiment, the sampling voltage exceeds the threshold value S for consecutive times. set1 Set to 6, the starting voltage threshold value U set1 Set to 0.003V.

[0084] Step 3: When the start criteria are met, the logic is opened for a short time to determine the time T. d Perform fault discrimination calculations and calculate the fault at the logic discrimination time T d Set multiple judgment cycles T p , obtain each judgment cycle T in real time p Holographic voltage sequence collected internally A voltage steady-state criterion is constructed based on the holographic voltage sequence to determine whether there is a steady-state holographic voltage anomaly, and a voltage positive increment criterion and a voltage negative increment criterion are constructed based on the holographic voltage sequence to determine whether there is a dynamic holographic voltage anomaly.

[0085] It is worth noting that after entering a new judgment cycle, the values of the holographic voltage sequence need to be updated in sequence, where the initial value of the holographic voltage sequence in the new judgment cycle is is the end value of the holographic voltage sequence in the previous judgment cycle

[0086] In an exemplary but non-limiting embodiment of the present invention, T d Set to 100ms, T p Set to 10ms.

[0087] In a preferred but non-limiting embodiment of the present invention, step 3 comprises:

[0088] Step 3.1, set the voltage steady-state criterion. Specifically, within a discrimination period, determine whether the holographic voltage sampling values reach the steady-state voltage setting value cumulatively for multiple times. The voltage steady-state criterion is expressed by the following formula:

[0089] m1≥S set2 When m1 = m1 + 1

[0090] In the formula:

[0091] m1 represents the cumulative number of voltage overlimit times, which is initialized to 0 at the beginning of each discrimination period;

[0092] S set2 is the threshold of the number of steady-state voltage overlimit times;

[0093] is the absolute value of the i-th sampling value in the holographic voltage sequence within the same discrimination period;

[0094] U set2 is the steady-state voltage setting value.

[0095] In a further exemplary but non-limiting embodiment, S set2 is set to 6, and U set2 is set to 0.0135V.

[0096] Step 3.2, set the voltage positive increment criterion. Specifically, within a discrimination period, determine whether the cumulative change rate of adjacent sampling voltages is greater than or equal to the set value of the change rate of adjacent sampling voltages for multiple times, and at the same time, the average change rate of the first and last voltages is greater than or equal to the set value of the average change rate of the first and last voltages. The voltage positive increment criterion is expressed by the following formula:

[0097] m2≥S set3 When m2 = m2 + 1

[0098]

[0099] In the formula:

[0100] f represents the sampling frequency;

[0101] is the i-th sampling value in the holographic voltage sequence within the same discrimination period;

[0102] m2 represents the cumulative number of voltage positive increment overlimit times, which is initialized to 0 at the beginning of each discrimination period;

[0103] S set3 is the threshold of the number of voltage change rate overlimit times;

[0104] k set1Set the value for the rate of change of adjacent sampling voltages;

[0105] q + is the sampling voltage subscript when m2=1, p + m2=S set3 The sampling voltage subscript when p + -q + ≥S set3 ;

[0106] k set2 The average change rate of the voltage at the beginning and end is set, that is, the value from the first voltage positive increment exceeding the limit to the Sth set3 The voltage change rate from the time when the voltage positive increment exceeds the limit to the time when the voltage negative increment exceeds the limit set3 The threshold value of the voltage change rate when the voltage negative increment exceeds the limit, where k set1 、k set2 All are set values greater than zero.

[0107] In a further exemplary but non-limiting embodiment, S set3 Set to 6, k set1 Set to 4V / s, k set2 Set to 4.2V / s.

[0108] Step 3.3, set the voltage negative increment judgment criterion. Specifically, within a judgment cycle, determine whether the adjacent sampling voltage change rate is cumulatively less than or equal to the inverse of the adjacent sampling voltage change rate set value in step 3.2 for multiple times, and at the same time, the average change rate of the first and last two voltages is less than or equal to the inverse of the average change rate of the first and last voltages set value in step 3.2. The voltage negative increment judgment criterion is expressed as the following formula:

[0109] m3≥S set3 ,when When m3=m3+1

[0110]

[0111] Where:

[0112] m3 represents the cumulative number of times the voltage negative increment exceeds the limit, which is initialized to 0 at the beginning of each judgment cycle;

[0113] q' - is the sampling voltage subscript when m3=1, p' - m3=S set3 The sampling voltage subscript when , and

[0114] p' - -q' - ≥S set3 .

[0115] Step 4, within any discrimination period, if at least one of the voltage steady-state criterion, voltage positive increment criterion, or voltage negative increment criterion is satisfied, a warning of two-point grounding in the secondary current circuit is issued.

[0116] It can be understood that by only opening the logic discrimination time briefly after the start criterion is satisfied, the CPU resources of the system can be effectively saved, preventing the device from being in the fault discrimination calculation state for a long time, and enhancing the system stability. By setting the voltage steady-state criterion and introducing the voltage positive increment criterion and voltage negative increment criterion simultaneously, the monitoring under different characteristic waveforms such as high-amplitude holographic voltage stability and low-amplitude time-varying can be realized, so as to more comprehensively discriminate the situation of two-point grounding in the secondary current circuit, improve the recognition accuracy rate, and achieve the reliability and rapidity of the discrimination of two-point grounding in the secondary current circuit.

[0117] Embodiment 2 of the present invention provides a two-point grounding warning system for a secondary current circuit with holographic voltage acquisition, which operates the two-point grounding warning method for a secondary current circuit with holographic voltage acquisition described in Embodiment 1, and includes a sampling resistor R t , a potential difference voltage source ΔU, its internal resistance R, and a logic judgment module 32.

[0118] Among them, the sampling resistor R t is used to collect the holographic voltage of the permanent grounding point in the secondary current circuit;

[0119] The structure of the logic judgment module 32 is as Figure 2 shown, and includes: a starting element 321, a voltage steady-state element 322, a voltage positive increment element 323, and a voltage negative increment element 324.

[0120] The starting element 321 is used to judge whether the start criterion is satisfied. If so, it opens the logic discrimination time and activates the voltage steady-state element 322, the voltage positive increment element 323, and the voltage negative increment element 324;

[0121] The voltage steady-state element 322 is used to issue an alarm signal when the voltage steady-state criterion is satisfied;

[0122] The voltage positive increment element 323 is used to issue an alarm signal when the voltage positive increment criterion is satisfied

[0123] The voltage negative increment element 324 is used to issue an alarm signal when the voltage negative increment criterion is satisfied.

[0124] Preferably, by adjusting the potential difference voltage source ΔU, the performance of the starting element 321, the voltage steady-state element 322, the voltage positive increment element 323, and the voltage negative increment element 324 is tested.

[0125] Preferably, the early warning system is also equipped with a waveform display module for displaying the waveforms and values of the potential difference voltage source and the holographic voltage acquisition. By comparing the waveforms, the effectiveness of the holographic voltage acquisition can be verified, and the severity of the two-point grounding can be quantitatively analyzed based on the magnitude of the acquired voltage.

[0126] Application example:

[0127] Combined with the actual rheological terminal box and protection panel, configure the two-point grounding early warning system for the secondary current loop of holographic voltage acquisition as described in Embodiment 2 to achieve the application example as Figure 3 shown. Among them, the protection panel 2 contains a protection device 21. The cable 62 from the rheological terminal box 1 in the cable trench 61 to the protection panel 2 is the secondary current loop. The two-point grounding early warning system 3 of the secondary current loop is respectively connected to the rheological terminal box 1 and the protection panel 2 through the simulation line 7. The permanent grounding point resistance R t , the potential difference voltage source ΔU and its internal resistance R are built into the two-point grounding early warning system 3 of the secondary current loop to achieve the acquisition of the holographic voltage and the adjustment of the two-point grounding voltage difference. The system changes the magnitude of the potential difference voltage source ΔU in real time to test the reliability and rapidity of the two-point grounding early warning criterion.

[0128] When the potential difference voltage source ΔU is too high or changes violently, the system can correctly issue an early warning, and the reliability and rapidity of the early warning system and the early warning criterion can be verified. After reliable operation, the system displays the waveform of ΔU and the holographic voltage acquisition waveform of R t to test the effectiveness of the holographic voltage acquisition.

[0129] Compared with the prior art, the beneficial effects of the present invention at least include:

[0130] 1) By real-time collecting the holographic voltage of the sampling resistance at the permanent grounding point of the current loop, the real-time monitoring and early warning of the two-point grounding situation of the secondary current loop are realized, so as to timely detect the two-point grounding of the secondary current loop and effectively avoid the misoperation of the relay protection device.

[0131] 2) By combining multiple criteria as the early warning criterion, the steady-state and dynamic situations are more comprehensively discriminated, which not only improves the reliability of the two-point grounding early warning of the secondary current loop, but also ensures the rapidity of the early warning discrimination, effectively preventing the occasional occurrence of the two-point grounding problem of the secondary current loop, thereby improving the detection efficiency of the two-point grounding of the secondary current loop.

[0132] 3) The early warning criterion has a clear quantitative standard, avoiding the lack of a unified standard or subjective judgment errors of the operation and maintenance personnel.

[0133] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer-readable storage medium having thereon computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific embodiments of the present invention, and any modification or equivalent substitution that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A warning method for two-point grounding of the secondary current circuit in holographic voltage acquisition, characterized in that, It includes the following steps: Step 1, collect the holographic voltage of the permanent grounding point in the secondary current loop; Step 2, when the number of times the sampled value of the holographic voltage is not less than the starting voltage threshold value is not less than the threshold value of the continuous over-limit times of the sampled voltage, continue to execute Step 3, otherwise return to Step 1; Step 3, when the starting criterion is met, open the logical discrimination time, set multiple discrimination periods within the logical discrimination time, and obtain the holographic voltage sequence collected in each discrimination period in real time; construct a voltage steady-state criterion based on the holographic voltage sequence to judge whether there is an abnormal steady-state holographic voltage, and construct a voltage positive increment criterion and a voltage negative increment criterion based on the holographic voltage sequence to judge whether there is a dynamic holographic voltage abnormality; Step 4, within any one discrimination period, if at least one of the voltage steady-state criterion, the voltage positive increment criterion, or the voltage negative increment criterion is satisfied, issue an alarm for two-point grounding in the secondary current loop.

2. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 1, characterized in that: In Step 1, a sampling resistor R installed at the permanent grounding point of the secondary current loop is used t to collect holographic voltage. Set the sampling frequency f of the holographic voltage to f = 200*n Hz, where n is an integer ≥ 20, and R t ≤ 0.1 Ω.

3. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 1, characterized in that: In Step 2, the starting criterion is satisfied when the following relational expression holds: In the formula: S set1 is the threshold value of the continuous over-limit times of the sampling voltage; is the absolute value of the j-th sampled value of the holographic voltage; U set1 is the starting voltage threshold value.

4. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 3, characterized in that: Sampling voltage continuous overlimit times threshold S set1 Set to 6, starting voltage threshold U set1 Set to 0.003V.

5. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 1, characterized in that: In Step 3, the voltage steady-state criterion is expressed by the following formula: m1≥S set2 When occurs, m1 = m1 + 1 In the formula: m1 represents the cumulative number of voltage over-limit times, which is initialized to 0 at the start of each discrimination period; S set2 is the threshold value of the number of times of steady-state voltage overrun; is the absolute value of the i-th sampled value in the holographic voltage sequence within the same discrimination period; U set2 is the steady-state voltage setpoint.

6. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 5, characterized in that: Steady-state voltage overlimit times threshold S set2 is set to 6, and the steady-state voltage set value U set2 is set to 0.0135V.

7. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 1, characterized in that: In Step 3, the voltage positive increment criterion is expressed by the following formula: m2≥S set3 When occurs, m2 = m2 + 1 In the formula: f represents the sampling frequency; is the i-th sampled value in the holographic voltage sequence within the same discrimination period; m2 represents the cumulative number of voltage positive increment over-limit times, which is initialized to 0 at the start of each discrimination period; S set3 is the threshold of the number of times of over-limit voltage change rate; k set1 is the set value of the change rate of adjacent sampling voltages; q + Sampling voltage subscript when m2 = 1, p + For m2 = S set3 Sampling voltage subscript at that time, p + -q + ≥S set3 ; k set2 It is the set value of the average change rate of the head and tail voltages.

8. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 1, characterized in that: In Step 3, the voltage negative increment criterion is expressed by the following formula: m3≥S set3 When occurs, m3 = m3 + 1 In the formula: f represents the sampling frequency; m3 represents the cumulative number of voltage negative increment over-limit times, which is initialized to 0 at the start of each discrimination period; is the i-th sampling value in the holographic voltage sequence within the same discrimination period; S set3 is the threshold value of the number of times of over-limit voltage change rate; k set1 is the set value of the change rate of adjacent sampling voltages; q' - Sampling voltage subscript when m3 = 1, p' - Sampling voltage subscript when m3 = S set3 Sampling voltage subscript when m3 = S, p'--q' - ≥S set3 ; k set2 It is the set value of the average change rate of the head and tail voltages.

9. The method for early warning of two-point grounding in a secondary current loop with holographic voltage acquisition according to claim 7 or 8, characterized in that: Threshold S for the number of times of over-limit voltage change rate set3 Set to 6, set value k of adjacent sampling voltage change rate set1 Set to 4 V / s, set value k of average change rate of head and tail voltages set2 Set to 4.2 V / s.

10. The two-point grounding warning system for the secondary current loop of holographic voltage acquisition operates according to the two-point grounding warning method for the secondary current loop of holographic voltage acquisition as described in any one of claims 1-9, characterized in that, It includes: A sampling resistor and a logic judgment module (32); Among them, the sampling resistor is used to collect the holographic voltage of the permanent grounding point (5) in the secondary current loop; The logic judgment module (32) includes a starting element (321), a voltage steady-state element (322), a voltage positive increment element (323), and a voltage negative increment element (324); The starting element (321) is used to judge whether the starting criterion is met. If so, it opens the logical discrimination time and activates the voltage steady-state element (322), the voltage positive increment element (323), and the voltage negative increment element (324); The voltage steady-state element (322) is used to issue an alarm signal when the voltage steady-state criterion is met; The positive voltage increment element (323) is used to issue an alarm signal when the positive voltage increment criterion is met; The negative voltage increment element (324) is used to issue an alarm signal when the negative voltage increment criterion is met.

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