A Diagnostic Method for Abnormal Neutral Line Wiring of a Low-Voltage Side Three-Phase Four-Wire Metering Device

Abstract

The present invention discloses a diagnostic method for abnormal neutral wire connection of a three-phase four-wire metering device on the low-voltage side, including the steps of: obtaining the daily data curve of the three-phase voltages of a certain three-phase four-wire metering device on the low-voltage side; obtaining the voltage values of each phase at the same moment to obtain a number of voltage data groups; respectively calculating the voltage unbalance degrees of each voltage data group and judging whether the three-phase voltages are balanced; respectively calculating the amplitude differences of the voltages of each phase in each voltage data group and judging whether the three-phase voltages maintain the same amplitude difference at different moments; checking the balance states of other three-phase four-wire metering devices in the same substation area on the same day; and judging whether there is an abnormal neutral wire connection in this three-phase four-wire metering device. Based on the characteristic analysis of the voltage data of the three-phase metering device in the distribution substation area, the present invention realizes the rapid diagnosis of abnormal neutral wire connection of the low-voltage three-phase four-wire metering device. This method is concise and practical, and effectively improves the troubleshooting efficiency of the reasons for the unbalance of the three-phase voltages of the metering device.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric energy calculation, and particularly relates to a diagnosis method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side. Background Art

[0002] Balanced three-phase voltage is the basis for ensuring power quality, saving energy consumption, and maintaining power supply safety. There are many reasons for unbalanced three-phase voltage, including common abnormal reasons such as abnormal meter measurement, serious asymmetry of three-phase loads, and abnormal connection of the neutral line in the electrical circuit. The commonly used troubleshooting method at present is to manually check each metering device that measures unbalanced three-phase voltage item by item from all possible abnormal reasons. This method requires a large amount of human resources and takes a long time. If the ability to automatically judge all or part of the possible abnormal reasons is available, the troubleshooting efficiency of abnormal reasons will be greatly improved. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a diagnosis method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side, and the technical solution adopted is as follows:

[0004] A diagnosis method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side includes the following steps:

[0005] S1. Obtain the daily data curve of the three-phase voltage of a certain three-phase four-wire metering device on the low-voltage side;

[0006] S2. According to the daily data curve of the three-phase voltage, form data groups with the voltage values of each phase at the same moment, and obtain a number of voltage data groups;

[0007] S3. Calculate the voltage unbalance degree of each voltage data group respectively, and judge whether the three-phase voltage is balanced;

[0008] S4. Calculate the amplitude difference of each phase voltage in each voltage data group respectively, and judge whether the three-phase voltage maintains the same amplitude difference at different moments based on this;

[0009] S5. According to S1~S3, check the balance state of other three-phase four-wire metering devices in the same substation area on the same day;

[0010] S6. Comprehensively consider the states of the three-phase four-wire metering devices in the same substation area on the same day, and judge whether there is an abnormal connection of the neutral line in this three-phase four-wire metering device.

[0011] Further, in S2, voltage data groups at 96 different moments are obtained at intervals of 15 minutes, or voltage data groups at 24 different moments are obtained at intervals of 1 hour, and the data groups with incomplete data items or obvious data errors are excluded.

[0012] Further, in S3, if the proportion of the voltage data groups with the voltage unbalance degree within the balance interval is greater than the balance judgment threshold, it is considered that the three-phase voltages of the three-phase four-wire metering device are balanced; otherwise, they are unbalanced. The voltage unbalance degree is calculated by the formula:

[0013] ,

[0014] wherein, and respectively represent the maximum value and the minimum value of the three-phase voltages in the same voltage data group of the three-phase voltages.

[0015] Further, in S4, the amplitude difference includes the amplitude difference between the voltages of phase A and phase B , and the amplitude difference between the voltages of phase A and phase C . The deviations and at adjacent moments and are calculated respectively, and whether the three-phase voltages maintain the same amplitude difference at different moments is judged according to the standard deviations of and .

[0016] Further, in S6, if the three-phase voltages of the three-phase four-wire metering device are unbalanced, the three-phase voltages maintain the same amplitude difference at different moments, and there is at least one three-phase four-wire metering device with balanced three-phase voltages in the same day and the same distribution transformer area, it is determined that there is an abnormal neutral wire connection in the three-phase four-wire metering device.

[0017] Further, the balance interval is [0, 2%], and the balance judgment threshold is 90%.

[0018] Further, if the standard deviations of and both fall within the interval [0, 1V], it is considered that the three-phase voltages of the three-phase four-wire metering device maintain the same amplitude difference at different moments.

[0019] The beneficial effects of the present invention are as follows:

[0020] Based on the characteristic analysis of the voltage data of the three-phase metering devices in the distribution transformer area, the present invention realizes the rapid diagnosis of the abnormal neutral wire connection of the low-voltage three-phase four-wire metering device. This method is concise and practical, and is easy to be converted into a software module algorithm to realize the batch automatic diagnosis of abnormal points, effectively improving the troubleshooting efficiency of the abnormal reasons for the unbalance of the three-phase voltages of the metering device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic flowchart of the method of the present invention;

[0022] Figure 2 This is the voltage curve graph of a three-phase four-wire metering device for low-voltage side metering on a certain day in the embodiment of the present invention;

[0023] Figure 3 This is the voltage curve graph of another three-phase four-wire metering device in the same substation area on the same day. Detailed implementation manners

[0024] Now, the present invention will be further described in detail with reference to the accompanying drawings.

[0025] To achieve rapid diagnosis of abnormal neutral wire connection of a three-phase four-wire metering device on the low-voltage side, the present invention proposes a diagnosis method for abnormal neutral wire connection of a three-phase four-wire metering device on the low-voltage side, as Figure 1 shown, which mainly includes the following steps:

[0026] Step 1: Obtain the three-phase voltage curves of the three-phase four-wire metering device on the low-voltage side from the automated meter reading system , , .

[0027] Step 2: Combine the , , three-phase voltage curves corresponding to each time point to obtain 96 groups of data. Each group of data contains 3 data items (i.e., three-phase voltage values). Check the data group by group, and eliminate the data groups with incomplete data items or data significantly exceeding the reasonable range. Finally, obtain groups of valid data groups. In an automated meter reading system such as the power consumption information collection system, the read meter interval is usually 15 minutes on the distribution transformer side, and the data density of the daily voltage curve record is 96 points; the read meter interval is usually 1 hour for users, and the data density of the daily voltage curve record is 24 points. The number of data groups does not affect the implementation and effect of this method.

[0028] Step 3: Calculate the three-phase voltage unbalance degree of groups of valid data groups group by group. The specific calculation formula is as follows:

[0029] , (1)

[0030] wherein, and respectively represent the maximum and minimum values of the three-phase voltages at the same moment .

[0031] Step 4: Statistically calculate the proportion of the three-phase voltage unbalance degree falling within the interval [0, 2%]. If it is greater than 90%, it is considered that the three-phase voltage is balanced; otherwise, it is unbalanced.

[0032] Step 5: Calculate the amplitude differences between the three-phase voltages at different times for each group to obtain the amplitude differences of each group of voltages, where the voltage amplitude differences include the amplitude difference between the voltage of phase A and that of phase B and the amplitude difference between the voltage of phase A and that of phase C :

[0033] , (2)

[0034] . (3)

[0035] Step 6: Calculate the deviation between adjacent times 、 for each group to obtain the amplitude deviation values of each group. The calculation formula for the deviation value is as follows:

[0036] , (4)

[0037] , (5)

[0038] where and respectively represent 、 the difference between the i th time and the i+ 1st time, and are respectively i at the 、 time of the th time, and i+ are respectively 、 at the

[0039] 1st time.

[0040] Step 7: Calculate the standard deviation of each amplitude deviation value respectively. If the standard deviations all fall within [0, 1V], it is considered that the three-phase voltages maintain the same amplitude difference at different time periods.

[0041] Step 8: According to the above steps, select the data of the same day to check other three-phase four-wire metering devices in this substation area.

[0042] Step 9: If the three-phase voltages of the three-phase four-wire metering device on the low-voltage side are unbalanced, the three-phase voltages maintain the same amplitude difference at different times, and there is at least one three-phase four-wire metering device with balanced three-phase voltages in this substation area, it is determined that the metering device on the low-voltage side is highly suspected of having abnormal wiring of the zero line of the watt-hour meter, such as abnormal wiring of the zero line at the end of the meter when the watt-hour meter is connected to the metering circuit or abnormal connection of the zero line inside the meter.To illustrate the implementation of the present invention in more detail, the following will be described with actual data.

[0043] Obtain the historical daily voltage curve of a certain low-voltage side three-phase four-wire metering device (such as Figure 2 ), and obtain 96 groups of effective data sets. Calculate the three-phase voltage unbalance degree for each group , and the of the 96 groups of data are all about 5%, and the probability of falling within [0, 2%] is 0, determining that the three-phase voltage is unbalanced; calculate the voltage deviation between adjacent moments for each group , , and the standard deviations of the 96 groups , are 0.34V and 0.40V respectively, and both fall within the interval [0, 1V]; randomly select the voltage curve of another three-phase four-wire metering device in the same day in this substation area (such as Figure 3 ), and all 24 groups fall within the interval [0, 2%], determining that the three-phase voltage is balanced. In summary, it is considered that there are highly suspected metering anomalies such as abnormal connection of the neutral wire of the watt-hour meter on the low-voltage side. Through on-site verification, it is found that the neutral wire connection of the low-voltage side watt-hour meter is indeed loose, thus causing metering anomalies.

[0044] The above is only the preferred implementation manner of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A diagnostic method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side, characterized in that, Including the following steps: S1. Obtain the daily data curve of the three-phase voltages of a three-phase four-wire metering device on the low-voltage side; S2. According to the daily data curve of the three-phase voltages, form data groups with the voltage values of each phase at the same moment, and obtain a number of voltage data groups; S3. Calculate the voltage unbalance degrees of each voltage data group respectively, and judge whether the three-phase voltages are balanced; S4. Calculate the amplitude differences of the voltages of each phase in each voltage data group respectively, and judge whether the three-phase voltages maintain the same amplitude difference at different moments based on this; S5. According to S1~S3, check the balance states of other three-phase four-wire metering devices in the same substation area on the same day; S6. Considering comprehensively the states of the three-phase four-wire metering devices in the same substation area on the same day, judge whether there is an abnormal connection of the neutral line in this three-phase four-wire metering device; In S4, the amplitude difference includes the amplitude difference between the voltages of phase A and phase B , and the amplitude difference between the voltages of phase A and phase C . Calculate the deviations and at adjacent moments and respectively, and judge whether the three-phase voltages maintain the same amplitude difference at different moments according to and the standard deviations of In S6, if the three-phase voltages of this three-phase four-wire metering device are unbalanced, the three-phase voltages maintain the same amplitude difference at different moments, and there is at least one three-phase four-wire metering device with balanced three-phase voltages in the same substation area on the same day, it is determined that there is an abnormal connection of the neutral line in this three-phase four-wire metering device.

2. The diagnostic method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side according to claim 1, characterized in that, In S2, obtain 96 voltage data groups at 96 different moments at intervals of 15 minutes, or obtain 24 voltage data groups at 24 different moments at intervals of 1 hour, and eliminate the data groups with incomplete data items or obvious data errors.

3. The diagnostic method for abnormal neutral wire connection of a three-phase four-wire metering device on the low-voltage side according to claim 1, characterized in that, In S3, if the proportion of the voltage data groups with voltage unbalance degrees within the balance interval is greater than the balance judgment threshold, it is considered that the three-phase voltages of the three-phase four-wire metering device are balanced; otherwise, they are unbalanced; the voltage unbalance degree is calculated by the formula: ， Among them, and respectively represent the maximum and minimum values of the three-phase voltages in the same voltage data set. ​ 4. The diagnostic method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side according to claim 3, characterized in that, The balance interval is [0, 2%], and the balance judgment threshold is 90%.

5. The diagnostic method for abnormal connection of the neutral line of a three-phase four-wire metering device on the low-voltage side according to claim 1, characterized in that, If and both have standard deviations falling within the interval [0, 1V], it is considered that the three-phase voltages of this three-phase four-wire metering device maintain the same amplitude difference at different times.

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