A method for testing the capacitive current of a neutral point ungrounded system

Abstract

This invention discloses a method for testing the capacitive current of a neutral-point ungrounded system, belonging to the field of power safety technology. The method includes the following steps: Step 1: Connect one end of the test lead of the neutral-point capacitive current tester to the neutral point lead of the system under test, and then ground the grounding terminal of the neutral-point capacitive current tester; Step 2: The neutral-point capacitive current tester collects asymmetric voltage and displacement voltage and substitutes them into the capacitive current calculation formula; Step 3: Wirelessly transmit the calculated capacitive current value to the controller; Step 4: Collect vibration velocity and condensation status and transmit the collected information to the controller; Step 5: The controller filters out abnormal capacitive current values; Step 6: Analyze the aging progress of the line; Step 7: Display the filtered capacitive current values ​​and the line aging analysis results. This invention can filter out abnormal capacitive current values ​​based on line vibration velocity, improving the accuracy of the test results.

Description

Technical Field

[0001] This invention relates to the field of power safety technology, specifically a method for testing the capacitive current of a neutral-point ungrounded system. Background Technology

[0002] Cables are widely used in power transmission and distribution systems due to their large transmission capacity and good stability, particularly in ungrounded neutral point systems (10–35 kV). However, power cable transmission lines generally have a large capacitance; empirically, a 10 kV cable transmission line typically has a capacitance of 1.5–2.0 A per kilometer. In ungrounded neutral point systems, excessively high capacitive current values ​​(above 100 A) pose a potential threat to system reliability and stability. Therefore, personnel need to monitor the capacitive current values ​​of ungrounded neutral point systems in real time.

[0003] Common methods for testing capacitance current include the metal grounding method, the external capacitor method, the bias capacitor method, and the signal injection method. Among these, the neutral point capacitance current tester using the external capacitor method is the most common and widely used. This type of neutral point capacitance current tester can measure the asymmetrical voltage U... HC The capacitance current value of the neutral point ungrounded system is obtained by calculating the displacement voltage U0.

[0004] However, existing methods for testing capacitive current have certain drawbacks. They fail to consider the interference of line vibration during the testing process, potentially leading to significant errors in the test results. Therefore, those skilled in the art provide a method for testing the capacitive current of a neutral-point ungrounded system to address the problems mentioned in the background section. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the capacitive current of a neutral-point ungrounded system, which can screen out abnormal capacitive current values ​​based on line vibration velocity, improve the accuracy of test results, and issue graded warnings based on the degree of abnormality, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for testing the capacitive current of a neutral-point ungrounded system includes the following steps:

[0008] Step 1: Connect one end of the test lead of the neutral point capacitance current tester to the neutral point lead-out terminal of the system under test, and then ground the ground terminal of the neutral point capacitance current tester.

[0009] Step 2: The neutral point capacitance current tester collects the asymmetrical voltage U. HC And displacement voltage U0, will voltage U HCSubstituting the displacement voltage U0 into the formula for calculating the capacitor current,

[0010] I C =ω∑C x U φ , where ∑C x Let ∑C be the capacitance being measured. x =C A +C B +C C C A C B C C These are the three-phase capacitances to ground of the system under test, C0 is the external capacitance, U0 is the displacement voltage, i.e., the voltage across the capacitor, and U... HC For three-phase ground asymmetrical voltage, I C U is the capacitive current of the network under test, ω is the angular frequency, and U φ This is the rated phase voltage of the power grid;

[0011] Step 3: Calculate ∑C x with I C Wireless transmission to the controller;

[0012] Step 4: Collect the vibration velocity of the line between the neutral point lead-out terminal and the outdoor power grid using a vibration meter, and detect the condensation state of the environment where the line between the neutral point lead-out terminal and the outdoor power grid is located at night using a dew point meter and a temperature sensor. Then transmit the collected information to the controller. Finally, connect an external single-phase electromagnetic voltage transformer to the neutral point lead-out terminal through an insulated cable, inject a different frequency signal into the secondary side of the single-phase electromagnetic voltage transformer, calculate the capacitive current of the ungrounded system, and wirelessly transmit the calculation result to the controller.

[0013] Step 5: The controller compares the capacitive current measured by the single-phase electromagnetic voltage transformer with the ∑C obtained in Step 3. x with I C Perform a match, matching identical ∑C x with I C Then filter out the abnormal ∑C x with I C And issue graded warnings based on the severity of the anomaly;

[0014] Step Six: The controller analyzes the aging progress of the circuit;

[0015] Step 7: Filter the ∑C x with I C And the results of the line aging analysis are shown.

[0016] As a further aspect of the present invention: in step five, the specific steps for anomaly screening are as follows:

[0017] S401: The vibration velocity at the neutral point outlet is previously labeled Ki, i = 1...n;

[0018] S402: The capacitance previously measured at Ki vibration velocity is denoted as ∑C. x j, j = 1...n, the measured capacitor current is denoted as I. C j, j = 1...n;

[0019] S403: Real-time measurement of the vibration velocity at the neutral point lead-out terminal; the measured capacitance at this vibration velocity is marked as ∑C. x p, the measured capacitor current is marked as I. C p;

[0020] S404: ∑C x p and the ∑C corresponding to the real-time vibration velocity x j is compared, if ∑C x p and any ∑C x If j matches, the output is normal; if ∑C x p is not related to any ∑C x If j matches, the output will be abnormal;

[0021] S405: I C p and the corresponding I of the real-time vibration velocity C j is compared, if I C p and any I C If j matches, the output is normal; if I... C p is not related to any I C If j matches, the output will be abnormal;

[0022] S406: There will be an anomaly in ∑C. x p is filtered out and compared with the normal corresponding ∑C. x j is compared, and I with an anomaly is selected. C p is filtered out and compared with the normal corresponding I. C j is compared;

[0023] S407: Issue tiered warnings based on comparison results.

[0024] As a further aspect of the present invention: in S407, the specific steps for graded early warning are as follows:

[0025] (1): There will be anomalies in ∑C x p and the normal corresponding ∑C x Subtract j from j. If the absolute value of the difference reaches 5uF, it is marked as second class; otherwise, it is marked as first class.

[0026] (2): There will be abnormal IC p and the normal corresponding I C Subtract j from j. If the absolute value of the difference reaches 1A, it is marked as second class; otherwise, it is marked as first class.

[0027] (3): If ∑C x p and ∑C x The absolute value of the difference between j and I C p and I C If the absolute values ​​of the differences in j are both marked as level two, then a level three warning will be output.

[0028] (4): If ∑C x p and ∑C x The absolute value of the difference between j and I C p and I C If any absolute value of the difference between j is marked as second-class, then a level-two warning will be output.

[0029] (5): If ∑C x p and ∑C x The absolute value of the difference between j and I C p and I C If the absolute values ​​of the differences between j are all marked as first-class, then a first-class warning will be output.

[0030] As a further embodiment of the present invention: the controller is connected to an audible and visual warning light. When the controller issues a level 3 warning, the audible and visual warning light turns red and emits an alarm sound; when the controller issues a level 2 warning, the audible and visual warning light turns yellow and emits an alarm sound; when the controller issues a level 3 warning, the audible and visual warning light turns yellow and does not emit an alarm sound.

[0031] As a further aspect of the present invention: in step six, the specific steps for analyzing the aging progress of the circuit are as follows:

[0032] 1): Detect the dew point temperature of the environment between the neutral point lead-out terminal and the outdoor power grid at night using a dew point meter. Compare the dew point temperature with the temperature measured by the temperature sensor. If the temperature measured by the temperature sensor is lower than the dew point temperature, condensation occurs. If condensation occurs, proceed to the next step.

[0033] 2): Detect the vibration velocity at the neutral point lead-out end corresponding to the occurrence of condensation, and mark it as Kp;

[0034] 3): If Kp reaches 5, the duration of condensation at this time is not recorded; if Kp does not reach 5, the duration of condensation at this time Ti is recorded, i = 1...n;

[0035] 4): The cumulative condensation time Ti is denoted as T, i.e., T = T1 + T2 + ... + Tn;

[0036] 5): The preset condensation time threshold is Tm. Let T / Tm = Q%. When Q = 100, the line is old and needs to be replaced.

[0037] As a further aspect of the present invention, the Tm is 1000h.

[0038] As a further aspect of the present invention, the dew point meter includes, but is not limited to, a mirror-type dew point meter, an electrical sensor-type dew point meter, and a dielectric dew point meter.

[0039] As a further aspect of the present invention: the wireless transmission adopts either WIFI or Bluetooth.

[0040] As a further embodiment of the present invention: a high-altitude wiring clamp is provided between one end of the test line and the neutral point lead-out end, and the high-altitude wiring clamp is fixed on one end of the test line to facilitate the connection of one end of the test line to the neutral point lead-out end.

[0041] As a further aspect of the present invention: the controller is connected to a display for displaying the filtered ∑C x with I C And the results of line aging analysis.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1. This application can screen out abnormal capacitive current values ​​based on line vibration velocity, thereby improving the accuracy of test results.

[0044] 2. After screening out abnormal capacitor current values, this application can issue graded warnings based on the degree of abnormality, thereby facilitating staff to understand the degree of abnormality in capacitor current values ​​and to take timely action.

[0045] 3. This application uses the total duration of condensation on the cable to determine the degree of cable aging, thereby promptly reminding staff to replace it in a timely manner.

[0046] 4. This application eliminates the interference of line vibration during the total duration of condensation on the cable, thereby improving the accuracy of the total duration.

[0047] 5. This application uses two methods to measure the capacitive current of an ungrounded system, verifies the results to determine their accuracy, and performs anomaly screening when the two measurement results are the same. This avoids misunderstandings for staff when both measurement methods measure the wrong capacitive current, leading them to mistakenly believe that the results are accurate. Attached Figure Description

[0048] Figure 1 This is a flowchart of a method for testing the capacitive current of a neutral-point ungrounded system. Detailed Implementation

[0049] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0050] Please see Figure 1 In this embodiment of the invention, a method for testing the capacitive current of a neutral-point ungrounded system includes the following steps:

[0051] Step 1: Connect one end of the test lead of the neutral point capacitance current tester to the neutral point lead of the system under test, and then ground the grounding terminal of the neutral point capacitance current tester. The neutral point capacitance current tester uses the external capacitance method to test the capacitance current value. In this embodiment, a high-altitude wiring clamp is provided between one end of the test lead and the neutral point lead, and the high-altitude wiring clamp is fixed on one end of the test lead to facilitate the connection of one end of the test lead to the neutral point lead.

[0052] Step 2: The neutral point capacitance current tester collects the asymmetrical voltage U. HC And displacement voltage U0, will voltage U HC Substituting the displacement voltage U0 into the formula for calculating the capacitor current,

[0053] I C =ω∑C x U φ , where ∑C x Let ∑C be the capacitance being measured. x =C A +C B +C C C A C B C C These are the three-phase capacitances to ground of the system under test, C0 is the external capacitance, U0 is the displacement voltage, i.e., the voltage across the capacitor, and U... HC For three-phase ground asymmetrical voltage, I C U is the capacitive current of the network under test, ω is the angular frequency, and U φ This is the rated phase voltage of the power grid;

[0054] Step 3: Calculate ∑C x with I C The data is transmitted wirelessly to the controller. In this embodiment, the controller model is FPD87326OINSL-0003A, and the wireless transmission uses either WIFI or Bluetooth.

[0055] Step 4: Collect the vibration velocity of the line between the neutral point lead-out terminal and the outdoor power grid using a vibration meter, and detect the condensation state of the environment where the line between the neutral point lead-out terminal and the outdoor power grid is located at night using a dew point meter and a temperature sensor. Then transmit the collected information to the controller. Finally, connect an external single-phase electromagnetic voltage transformer to the neutral point lead-out terminal through an insulated cable, inject a different frequency signal into the secondary side of the single-phase electromagnetic voltage transformer, calculate the capacitive current of the ungrounded system, and wirelessly transmit the calculation result to the controller.

[0056] Step 5: The controller compares the capacitive current measured by the single-phase electromagnetic voltage transformer with the ∑C obtained in Step 3. x with I C Perform a match, matching identical ∑C x with I C Then filter out the abnormal ∑C x with I C And issue graded warnings based on the severity of the anomaly;

[0057] Step Six: The controller analyzes the aging progress of the circuit;

[0058] Step 7: Filter the ∑C x with I C The aging analysis results of the circuit are displayed, allowing staff to directly observe the test results and the aging progress caused by condensation. In this embodiment, the controller is connected to a display to show the filtered ∑C. x with I C And the results of line aging analysis.

[0059] In this embodiment: the specific steps of anomaly screening in step five are as follows:

[0060] S401: The vibration velocity at the neutral point outlet is previously labeled Ki, i = 1...n;

[0061] S402: The capacitance previously measured at Ki vibration velocity is denoted as ∑C. x j, j = 1...n, the measured capacitor current is denoted as I. C j, j = 1...n;

[0062] S403: Real-time measurement of the vibration velocity at the neutral point lead-out terminal; the measured capacitance at this vibration velocity is marked as ∑C. x p, the measured capacitor current is marked as I. C p;

[0063] S404: ∑C x p and the ∑C corresponding to the real-time vibration velocity x j is compared, if ∑C x p and any ∑Cx If j matches, the output is normal; if ∑C x p is not related to any ∑C x If j matches, the output will be abnormal;

[0064] S405: I C p and the corresponding I of the real-time vibration velocity C j is compared, if I C p and any I C If j matches, the output is normal; if I... C p is not related to any I C If j matches, the output will be abnormal;

[0065] S406: There will be an anomaly in ∑C. x p is filtered out and compared with the normal corresponding ∑C. x j is compared, and I with an anomaly is selected. C p is filtered out and compared with the normal corresponding I. C j is compared;

[0066] S407: Issue tiered warnings based on comparison results.

[0067] In this embodiment: In S407, the specific steps for graded early warning are as follows:

[0068] (1): There will be anomalies in ∑C x p and the normal corresponding ∑C x Subtract j from j. If the absolute value of the difference reaches 5uF, it is marked as second class; otherwise, it is marked as first class.

[0069] (2): There will be abnormal I C p and the normal corresponding I C Subtract j from j. If the absolute value of the difference reaches 1A, it is marked as second class; otherwise, it is marked as first class.

[0070] (3): If ∑C x p and ∑C x The absolute value of the difference between j and I C p and I C If the absolute values ​​of the differences in j are both marked as level two, then a level three warning will be output.

[0071] (4): If ∑C x p and ∑C x The absolute value of the difference between j and I C p and I C If any absolute value of the difference between j is marked as second-class, then a level-two warning will be output.

[0072] (5): If ∑C x p and ∑C xThe absolute value of the difference between j and I C p and I C If the absolute values ​​of the differences between j are all marked as first-class, then a first-class warning will be output.

[0073] In this embodiment: the controller is connected to an audible and visual warning light. When the controller issues a level 3 warning, the audible and visual warning light turns red and emits an alarm sound; when the controller issues a level 2 warning, the audible and visual warning light turns yellow and emits an alarm sound; when the controller issues a level 3 warning, the audible and visual warning light turns yellow and does not emit an alarm sound.

[0074] In this embodiment: In step six, the specific steps for analyzing the aging progress of the line are as follows:

[0075] 1): Detect the dew point temperature of the environment between the neutral point lead-out terminal and the outdoor power grid at night using a dew point meter. Compare the dew point temperature with the temperature measured by the temperature sensor. If the temperature measured by the temperature sensor is lower than the dew point temperature, condensation occurs. If condensation occurs, proceed to the next step.

[0076] 2): Detect the vibration velocity at the neutral point lead-out end corresponding to the occurrence of condensation, and mark it as Kp;

[0077] 3): If Kp reaches 5, the duration of condensation at this time is not recorded; if Kp does not reach 5, the duration of condensation at this time Ti is recorded, i = 1...n;

[0078] 4): The cumulative condensation time Ti is denoted as T, i.e., T = T1 + T2 + ... + Tn;

[0079] 5): The preset condensation time threshold is Tm, and T / Tm = Q%. When Q = 100, the line is considered aged and needs to be replaced. In this embodiment, Tm is 1000h.

[0080] The working principle of this invention is as follows: During use, the asymmetrical voltage U is collected using a neutral point capacitance current tester. HC The displacement voltage U0 is used to calculate the capacitive current value of the neutral point ungrounded system. After the capacitive current value is wirelessly transmitted to the controller, the controller filters out the abnormal capacitive current values ​​and issues graded warnings according to the degree of abnormality. The filtered capacitive current values ​​are sent to the display for viewing. In addition, since the presence of condensation can seriously damage the service life of cables, it is necessary to calculate the total duration of condensation on the cables. However, the condensation on the cables may be shaken off by their own vibration. Therefore, it is necessary to set a vibration speed value Kp and remove the cable condensation time that reaches the Kp condition, thereby eliminating vibration interference and accurately calculating the total duration of condensation on the cables. Finally, the total duration T is compared with the preset condensation time threshold Tm to obtain Q%. The larger Q is, the more serious the aging of the line.

[0081] This application employs two methods simultaneously to measure the capacitive current of an ungrounded system, verifying the results against each other to determine accuracy. Furthermore, it performs anomaly screening when both methods yield identical results, preventing misunderstandings caused by both methods simultaneously measuring erroneous capacitive currents, which could lead staff to mistakenly believe the results are accurate. This application can also screen for abnormal capacitive current values ​​based on line vibration velocity, improving the accuracy of test results. After identifying abnormal capacitive current values, it can issue tiered warnings based on the severity of the anomaly, allowing staff to understand the extent of the anomaly and take timely action. This application accumulates the total duration of condensation on cables to determine the degree of cable aging, promptly reminding staff to replace them. The process of accumulating the total duration of condensation on cables eliminates interference from line vibration, further improving the accuracy of the total duration.

[0082] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0083] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method of testing a capacitive current of a neutral ungrounded system, characterized by, The method comprises the following steps: Step one: connect the test line of the neutral point capacitance current tester to the neutral point of the system to be tested, and then connect the ground end of the neutral point capacitance current tester to the ground; Step two: neutral point capacitance current tester collects asymmetric voltage and displacement voltage , voltage and displacement voltage into the capacitance current calculation formula, wherein, C is the measured capacitance, Cp, Cp, Cp are the three phase-to-ground capacitances of the system under test, Cp is the applied capacitance, Up is the displacement voltage, i.e. the terminal voltage over the capacitance, Up is the three phase-to-ground asymmetrical voltage, Ip is the capacitance current of the network under test, ω is the angular frequency, Up is the rated phase voltage of the power grid; Step three: the calculated with wirelessly transmitted to the controller; Step four: collect the vibration speed of the line between the neutral point and the outdoor power grid by the vibration tester, and collect the condensation state of the environment where the line between the neutral point and the outdoor power grid is located at night by the dew point tester and the temperature sensor, then transmit the collected information to the controller, and finally connect the external single-phase electromagnetic voltage transformer to the neutral point through the insulated cable, inject the heterodyne signal at the secondary side of the single-phase electromagnetic voltage transformer, calculate the capacitance current of the ungrounded system, and wirelessly transmit the calculation result to the controller; Step five: the controller matches the measured capacitance current by the single-phase electromagnetic voltage transformer with the result obtained in step three, matches the same With After With And then screens out the abnormal With And issues a graded early warning according to the degree of abnormality; Step six: the controller analyzes the aging progress of the line; Step seven: the filtered with and line aging analysis results are displayed. In the step five, the specific steps of the anomaly screening are as follows: S501: mark the vibration speed of the previous neutral point as Ki, i=1...n; S502: record the measured capacitance at the previous Ki vibration speed as the measured capacitance current as ; S503: measure the vibration velocity of the neutral point lead-out end in real time, mark the measured capacitance under the vibration velocity as , and mark the measured capacitance current as ; S504: Will Corresponding to real-time vibration velocity Perform a comparison, if With any one If it matches, the output will show no anomalies; if it does, the output will show no anomalies. Not with any one If a match is found, the output will be abnormal; S505: comparing the real-time vibration speed with the vibration speed of the normal state corresponding to the real-time vibration speed If the real-time vibration speed matches the vibration speed of the normal state, outputting no abnormality If the real-time vibration speed matches the vibration speed of the normal state, outputting no abnormality If the real-time vibration speed matches the vibration speed of the normal state, outputting no abnormality If the real-time vibration speed matches the vibration speed of the normal state, outputting no abnormality If the real-time vibration speed matches the vibration speed of the normal state, outputting no S506: screen out the abnormal corresponding to normal and compare them, and screen out the abnormal corresponding to normal and compare them, and screen out the abnormal corresponding to normal and compare them, and screen out the abnormal corresponding to normal and compare them, and screen out the abnormal S507: issue a hierarchical early warning according to the comparison result.

2. The method of claim 1, wherein the method comprises: In the S507, the specific steps of the hierarchical early warning are as follows: (1): mark abnormal corresponding to normal Subtract, the absolute value of the difference between the two, if it reaches 5uF mark two, if not, mark one; (2): marking the abnormal corresponding to the normal Subtracting, if the absolute value of the difference reaches 1A, mark two, if not, mark one. (3): If and The absolute value of the difference and If the absolute values ​​of the differences are both marked as level two, then a level three warning will be output. (4): if the absolute value of the difference between the absolute value of the difference between the absolute value of the difference between any one of the two marks is marked as two, output a two-level early warning; (5): if the absolute value of the difference between and and the absolute value of the difference between and are both marked as first class, output a first class early warning.

3. The method of claim 2, wherein the step of determining the capacitance current of the neutral ungrounded system is performed by a method comprising: The controller is connected with a sound and light warning lamp, when the controller issues a three-level early warning, the sound and light warning lamp lights up red and emits an alarm sound; when the controller issues a two-level early warning, the sound and light warning lamp lights up yellow and emits an alarm sound; when the controller issues a three-level early warning, the sound and light warning lamp lights up yellow without emitting an alarm sound.

4. The method of claim 1, wherein the method further comprises: In the step six, the specific analysis steps of the aging progress of the line are as follows: 1) detect the dew point temperature of the environment where the line between the neutral point and the outdoor power grid is located at night by the dew point tester, compare the dew point temperature with the temperature measured by the temperature sensor, if the temperature measured by the temperature sensor is less than the dew point temperature, condensation occurs, and the next step is entered; 2) detect the vibration speed of the neutral point when condensation occurs, and mark it as Kp; 3) if Kp reaches 5, do not record the condensation time at this time, if Kp does not reach 5, record the condensation time Ti, i=1...n; 4) accumulate the condensation time Ti and mark it as T, i.e. T=T1+T2+...+Tn; 5) preset the condensation time threshold Tm, let T / Tm=Q%, when Q=100, the line is aged to the point of replacement.

5. The method of claim 4, wherein the step of determining the capacitance current of the neutral ungrounded system is performed by: The Tm is 1000h.

6. The method of claim 1, wherein, The dew point tester includes but is not limited to a mirror surface type dew point tester, an electric sensor type dew point tester and an electric medium method dew point tester.

7. The method of claim 1, wherein the method further comprises: The wireless transmission adopts one of WIFI or Bluetooth.

8. The method of claim 1, wherein, A high-altitude connecting clamp is arranged between the test line and the neutral point, and the high-altitude connecting clamp is fixed on the test line to facilitate the connection of the test line to the neutral point.

9. The method of claim 1, wherein, The controller is connected with a display to display the screened With and line aging analysis results.

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