Low-voltage power supply line neutral line breakage fault identification method, device and system

Abstract

The invention relates to the technical field of power fault diagnosis, in particular to a low-voltage power supply line neutral line breakage fault identification method, device and system, and the method comprises the steps: obtaining the line information of a low-voltage power supply line measured at the current moment; judging whether a neutral line breaking risk exists in the low-voltage power supply line or not based on the neutral line current value and the module value of the three-phase current; if yes, calculating a load voltage deviation value based on a load impedance value recorded at a historical moment; and when the load voltage deviation value is greater than the voltage deviation threshold value, determining that a neutral line breaking fault exists in the low-voltage power supply line. According to the neutral line current condition, the operation data are updated and stored, the data are obtained from the long-term real-time operation data of the power supply line and are closer to the actual operation condition of the line, and when the neutral line breaking risk occurs, the breaking fault criterion is based on the stored data, so that the judgment accuracy is better; the method is more suitable for operation conditions of engineering sites.

Description

Technical Field

[0001] The present application relates to the technical field of power fault diagnosis, and in particular to a method, device and system for identifying a neutral line break fault in a low-voltage power supply line. Background Art

[0002] With the continuous growth of electricity demand in modern society, the reliability and safety of low-voltage power supply lines, as an important part of the power grid directly connected to power users, are particularly important. Low-voltage power supply lines generally use three-phase four-wire system to transmit electric energy. Among them, the neutral line, as an important part of the current loop, bears the key responsibility of balancing the load. However, due to long-term use, environmental factors and equipment aging, neutral line disconnection failures occur from time to time. Such faults not only affect the normal operation of the power system, but may also cause problems such as overvoltage on the load side and accidental electrification of the user's equipment casing. In turn, it is easy to cause serious safety hazards, such as equipment damage, electrical fires and personal safety accidents. Therefore, it is particularly important to detect neutral line disconnection failures in a timely and accurate manner.

[0003] Traditional fault detection methods usually rely on regular inspections and manual monitoring. Although this method can detect problems to a certain extent, it has defects such as slow response, low efficiency, and high risk of missed detection. Summary of the invention

[0004] The present application aims to at least solve one of the technical problems existing in the prior art or related art that traditional fault detection methods usually rely on regular inspections and manual monitoring. Although this method can detect problems to a certain extent, it has defects such as slow response, low efficiency, and high risk of missed detection.

[0005] To this end, the present application provides a method for identifying a neutral line break fault in a low-voltage power supply line. According to the neutral line current, the load impedance data, voltage modulus deviation data, and angle deviation data of each phase are updated and stored. These data are obtained from the long-term real-time operation data of the power supply line, which is closer to the actual operation of the line. When there is a risk of neutral line break, the line break fault judgment criterion is based on the stored data, so that the judgment is more accurate and more adapted to the operation conditions of the project site.

[0006] The present application also provides a low-voltage power supply line neutral line break fault identification device and system including this method.

[0007] According to the first aspect of the present application, a method for identifying a neutral line break fault in a low-voltage power supply line is provided, comprising:

[0008] Obtaining line information of the low-voltage power supply line measured at the current moment, the line information at least including: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value and the phase angle of the three-phase current;

[0009] Based on the neutral current value and the modulus value of the three-phase current, determine whether there is a risk of neutral line disconnection in the low-voltage power supply line;

[0010] If so, the load voltage deviation value is calculated based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment;

[0011] When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line;

[0012] If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

[0013] Optionally, the step of judging whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current includes:

[0014] Determining whether the neutral line current value is greater than a first current threshold;

[0015] If not, the current modulus deviation is calculated based on the modulus values ​​of the three-phase currents;

[0016] When the current modulus deviation is less than or equal to the first current threshold, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line;

[0017] When the current modulus deviation is greater than the first current threshold, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line;

[0018] If yes, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line.

[0019] Optionally, the step of calculating the current modulus deviation based on the modulus of the three-phase current includes:

[0020] Based on the modulus values ​​of the three-phase currents, the difference between the currents of each phase is calculated to obtain a first current intermediate value;

[0021] Taking the absolute value of the first current intermediate value to obtain the second current intermediate value;

[0022] The maximum value among the second current intermediate values ​​is taken as the current modulus deviation.

[0023] Optionally, the steps of recording the load impedance value include:

[0024] When there is no risk of neutral line disconnection in the low-voltage power supply line, the load impedance value is calculated based on the phasor values ​​of the three-phase voltage and the phasor values ​​of the three-phase current measured in real time;

[0025] Record the load impedance value.

[0026] Optionally, the step of calculating the load voltage deviation value based on the load impedance value recorded at the historical moment includes:

[0027] Calculate the phasor value of the three-phase load voltage based on the load impedance value recorded at the historical moment and the phasor value of the three-phase current measured in real time;

[0028] According to the phasor value of the three-phase load voltage, the modulus value of the three-phase load voltage is obtained;

[0029] Based on the modulus values ​​of the three-phase load voltages, the load voltage deviation value is calculated.

[0030] Optionally, the method for identifying a neutral line disconnection fault in a low-voltage power supply line further includes:

[0031] When there is a risk of neutral line disconnection in the low-voltage power supply line, the load phase angle deviation value is calculated based on the phasor value of the three-phase load voltage;

[0032] When the load phase angle deviation value is greater than the phase angle deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line.

[0033] Optionally, the step of calculating the load phase angle deviation value according to the phasor value of the three-phase load voltage includes:

[0034] According to the phasor value of the three-phase load voltage, the phase angle of the three-phase load voltage is obtained;

[0035] Based on the phase angle of the three-phase load voltage, the difference between the phase angles of each phase is calculated to obtain the load phase angle deviation value.

[0036] Optionally, the step of determining the voltage deviation threshold includes:

[0037] The voltage deviation threshold is determined based on the maximum voltage deviation value recorded at the historical moment and the voltage experience threshold; the maximum voltage deviation value is the maximum value of the three-phase voltage deviation values ​​recorded when there is no risk of neutral line break in the low-voltage power supply line.

[0038] A second aspect of the present application provides a device for identifying a neutral line break fault in a low-voltage power supply line, comprising:

[0039] An acquisition module is used to acquire line information of the low-voltage power supply line measured at the current moment, the line information at least including: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value and the phase angle of the three-phase current;

[0040] A judgment module, used to judge whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current;

[0041] The analysis module is used to calculate the load voltage deviation value based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment;

[0042] When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line;

[0043] If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

[0044] Optionally, the judging module can be used to judge whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current, and the steps include:

[0045] Determining whether the neutral line current value is greater than a first current threshold;

[0046] If not, the current modulus deviation is calculated based on the modulus values ​​of the three-phase currents;

[0047] When the current modulus deviation is less than or equal to the first current threshold, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line;

[0048] When the current modulus deviation is greater than the first current threshold, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line;

[0049] If yes, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line.

[0050] Optionally, the judging module may be used to calculate the current modulus deviation based on the modulus of the three-phase current, and the steps include:

[0051] Based on the modulus values ​​of the three-phase currents, the difference between the currents of each phase is calculated to obtain a first current intermediate value;

[0052] Taking the absolute value of the first current intermediate value to obtain the second current intermediate value;

[0053] The maximum value among the second current intermediate values ​​is taken as the current modulus deviation.

[0054] Optionally, the judging module may be used to record the load impedance value in the following steps:

[0055] When there is no risk of neutral line disconnection in the low-voltage power supply line, the load impedance value is calculated based on the phasor values ​​of the three-phase voltage and the phasor values ​​of the three-phase current measured in real time;

[0056] Record the load impedance value.

[0057] Optionally, the analysis module can be used to calculate the load voltage deviation value based on the load impedance value recorded at the historical moment, including the following steps:

[0058] Calculate the phasor value of the three-phase load voltage based on the load impedance value recorded at the historical moment and the phasor value of the three-phase current measured in real time;

[0059] According to the phasor value of the three-phase load voltage, the modulus value of the three-phase load voltage is obtained;

[0060] Based on the modulus values ​​of the three-phase load voltages, the load voltage deviation value is calculated.

[0061] Optionally, an analysis module may be used to calculate the load phase angle deviation value based on the phasor value of the three-phase load voltage when there is a risk of a neutral line disconnection in the low-voltage power supply line;

[0062] When the load phase angle deviation value is greater than the phase angle deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line.

[0063] Optionally, the analysis module can be used to calculate the load phase angle deviation value according to the phasor value of the three-phase load voltage, including the following steps:

[0064] According to the phasor value of the three-phase load voltage, the phase angle of the three-phase load voltage is obtained;

[0065] Based on the phase angle of the three-phase load voltage, the difference between the phase angles of each phase is calculated to obtain the load phase angle deviation value.

[0066] Optionally, the analysis module may be used to determine the voltage deviation threshold value by the steps of:

[0067] The voltage deviation threshold is determined based on the maximum voltage deviation value recorded at the historical moment and the voltage experience threshold; the maximum voltage deviation value is the maximum value of the three-phase voltage deviation values ​​recorded when there is no risk of neutral line break in the low-voltage power supply line.

[0068] A third aspect of the present application provides a low-voltage power supply line neutral line disconnection fault identification system, comprising:

[0069] A collection unit is configured to collect three-phase voltage, three-phase current and neutral line current flowing through the low-voltage power supply line;

[0070] The controller is configured to execute a method for identifying a neutral line break fault in a low-voltage power supply line as described in the first aspect or in each of its implementations.

[0071] The fourth aspect of the present application provides a computer-readable storage medium for storing a computer program, wherein the computer program enables a computer to execute the method in the first aspect or its various implementations.

[0072] One of the above technical solutions has at least the following advantages or beneficial effects:

[0073] For a method for identifying a neutral line break fault in a low-voltage power supply line in an embodiment of the present application, the method includes: obtaining line information of the low-voltage power supply line measured at the current moment, the line information at least including: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value of the three-phase voltage and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value of the three-phase current and the phase angle of the three-phase current; based on the neutral line current value and the modulus value of the three-phase current, judging whether there is a neutral line break risk in the low-voltage power supply line; if so, calculating the load voltage deviation value based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment; when the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line; if not, it is determined that there is no neutral line break fault in the low-voltage power supply line. According to the neutral line current, the load impedance data, voltage modulus deviation data, and angle deviation data of each phase are updated and stored. These data are obtained from the long-term real-time operation data of the power supply line, which is closer to the actual operation of the line. When there is a risk of neutral line disconnection, the disconnection fault judgment criteria are based on the stored data, making the judgment more accurate and more adaptable to the operation conditions of the project site.

[0074] A low-voltage power supply line neutral line break fault identification device and system provided in an embodiment of the present application is provided with the method described above. Since the method has the above-mentioned technical effect, a low-voltage power supply line neutral line break fault identification device and system provided with the method should also have corresponding technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 One of the flow charts of a method for identifying a neutral line break fault in a low-voltage power supply line provided in an embodiment of the present application is shown;

[0076] Figure 2 A second flow chart of a method for identifying a neutral line break fault in a low-voltage power supply line provided in an embodiment of the present application is shown;

[0077] Figure 3 A schematic diagram of a low-voltage power supply line model provided in an embodiment of the present application is shown;

[0078] Figure 4 The waveform diagram of the three-phase voltage provided by the embodiment of the present application is shown;

[0079] Figure 5 The waveform diagram of the three-phase current provided by the embodiment of the present application is shown;

[0080] Figure 6 shows a waveform diagram of the neutral line current provided by an embodiment of the present application;

[0081] Figure 7 A schematic diagram of a neutral line break fault identification device for a low-voltage power supply line provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0082] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0083] As mentioned above, low-voltage power supply lines refer to power lines with a rated voltage of 1kV and below. The general wiring widely adopts the three-phase four-wire system of AC 220 / 380V, of which three are phase lines, representing phases A, B, and C respectively, and the other is the neutral line N. If the neutral point on the power supply side of the circuit is grounded, the neutral line is also called the zero line.

[0084] When a neutral line break occurs in a low-voltage power supply line, the neutral point will shift, causing the neutral point voltage to increase to the ground. The three-phase circuit will no longer be balanced, which will cause current and voltage fluctuations. Specifically, the phase voltage with a small load will increase, while the phase voltage with a large load will decrease. This may cause the electrical equipment connected to this phase to be damaged due to excessive voltage, or to fail to work properly due to too low voltage.

[0085] Traditional fault detection methods usually rely on regular inspections and manual monitoring. Although this method can detect problems to a certain extent, it has defects such as slow response, low efficiency, and high risk of missed detection.

[0086] In order to solve at least one of the technical problems existing in the prior art or related technology, the present application provides a method, device and system for identifying a neutral line break fault in a low-voltage power supply line, the method comprising: obtaining line information of the low-voltage power supply line measured at the current moment, the line information comprising at least: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value of the three-phase voltage and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value of the three-phase current and the phase angle of the three-phase current; based on the neutral line current The load impedance value and the modulus value of the three-phase current are used to determine whether there is a risk of neutral line disconnection in the low-voltage power supply line; if so, the load voltage deviation value is calculated based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment; when the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line disconnection fault in the low-voltage power supply line; if not, it is determined that there is no neutral line disconnection fault in the low-voltage power supply line. According to the neutral line current situation, the load impedance data, voltage modulus deviation data, and angle deviation data of each phase are updated and stored. These data are obtained from the long-term real-time operation data of the power supply line, which is closer to the actual operation of the line. When there is a risk of neutral line disconnection, the disconnection fault judgment criterion is based on the stored data, so that the judgment is more accurate and more suitable for the operation conditions of the project site.

[0087] The following describes, with reference to the accompanying drawings, a method, device, and system for identifying a neutral line break fault in a low-voltage power supply line according to some embodiments provided by the present application.

[0088] See also Figures 1 to 7 The first aspect of the present application provides a method for identifying a neutral line disconnection fault in a low-voltage power supply line, comprising:

[0089] S100: Obtain the line information of the low-voltage power supply line measured at the current moment, the line information including at least: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value and the phase angle of the three-phase current.

[0090] The acquisition unit can measure the vector value of the three-phase voltage, the vector value of the three-phase current and the neutral line current value of the low-voltage power supply line in real time, thereby obtaining the modulus value of the three-phase voltage. 、 The phase angle of three-phase voltage and the modulus of three-phase current 、 The phase angle of the three-phase current.

[0091] The modulus is also called the effective value, which means that the average heat generated by AC in one cycle is equal to the heat generated by a certain DC in the same period of time. For AC with a sinusoidal waveform, there is a fixed relationship between its effective value and peak value. Therefore, if the peak value of the three-phase voltage is measured, its effective value can be calculated.

[0092] The phase angle, also known as the angle of argument, indicates the phase difference of the voltage or current waveform relative to the reference waveform (such as the starting point of a sine wave). In a three-phase AC system, the phase angles of the three-phase voltage and current usually differ by 120°, which is determined by the symmetry and phase relationship of the three-phase AC system.

[0093] S200: Based on the neutral line current value and the modulus values ​​of the three-phase currents, determine whether there is a risk of neutral line disconnection in the low-voltage power supply line.

[0094] In an illustrative embodiment, Figure 2 As shown, based on the neutral line current value and the modulus value of the three-phase current, the steps of judging whether there is a neutral line disconnection risk in the low-voltage power supply line include:

[0095] S210: Determine whether the neutral line current value is greater than a first current threshold.

[0096] The neutral line is mainly used to provide a current loop so that the current of each phase can flow in a balanced manner. Ideally, if the three-phase load is completely balanced, the current on the neutral line should be zero, because the currents of each phase are equal in magnitude and opposite in direction, and they cancel each other out on the neutral line. However, in practical applications, it is impossible for the three-phase load to be completely balanced, so the current on the neutral line is often not zero. When there is current on the neutral line, that is, the neutral line current value is greater than the first current threshold, it means that the neutral line is not broken. The first current threshold can be determined based on the maximum error when the acquisition unit measures the current. For example, the first current threshold is set to 10 times the maximum error, which is expressed by the following formula:

[0097] (1)

[0098] In formula (1), I N is the neutral current measured by the acquisition unit, I err is the maximum error when the acquisition unit measures current, I err It can be obtained by referring to the instruction manual of the measuring component in the acquisition unit. n 1 is the empirical coefficient and the value is 5-15.

[0099] S220: If yes, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line.

[0100] When the neutral line current value is greater than the first current threshold, formula (1) is satisfied, which means that there is current on the neutral line. Therefore, there is no risk of disconnection on the neutral line.

[0101] S230: If not, calculate the current modulus deviation based on the modulus of the three-phase current;

[0102] When the neutral line current value is less than or equal to the first current threshold, that is, formula (1) is not satisfied, it means that there is no current on the neutral line. There are two situations in which there is no current on the neutral line. One is that the neutral line is broken, and the other is that there is no power supply on the three-phase line. Therefore, it is also necessary to calculate the current modulus deviation to determine whether there is current on the three-phase line.

[0103] In an exemplary embodiment, the step of calculating the current modulus deviation based on the modulus of the three-phase current includes:

[0104] Based on the modulus values ​​of the three-phase currents, the difference between the currents of each phase is calculated to obtain a first current intermediate value;

[0105] Taking the absolute value of the first current intermediate value to obtain the second current intermediate value;

[0106] The maximum value among the second current intermediate values ​​is taken as the current modulus deviation.

[0107] S240: Determine whether the current modulus deviation is greater than the first current threshold, expressed as:

[0108] (2)

[0109] In formula (2), To find the maximum value among them; I A , I B , I C are the modulus values ​​of the three-phase currents A, B, and C, respectively. n 1 is the empirical coefficient and the value is 5-15.

[0110] When the current modulus deviation is less than or equal to the first current threshold, it is determined that there is no neutral line disconnection risk in the low-voltage power supply line. Failure to satisfy formula (2) indicates that there is no power supply on the three-phase line, resulting in no current on the neutral line, and there is no neutral line disconnection risk at this time.

[0111] When the current modulus deviation is greater than the first current threshold, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line. If formula (2) is satisfied, it means that there is power supply on the three-phase line, but there is no current on the neutral line. In this case, there is a risk of neutral line disconnection.

[0112] S300: If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

[0113] When there is no risk of neutral line disconnection in the low-voltage power supply line, it means that the low-voltage power supply line is operating normally. At this time, it can be determined that there is no neutral line disconnection fault in the low-voltage power supply line. At the same time, it is necessary to record, update and store the operation data, which at least includes: load impedance value, maximum voltage deviation value, and maximum amplitude deviation value. These operation data are obtained from the long-term real-time operation data of the power supply line, which is closer to the actual operation of the line. When there is a risk of neutral line disconnection, the disconnection fault judgment criteria are based on the stored data, which makes the judgment more accurate and more adaptable to the operation conditions of the project site.

[0114] S310: Record the load impedance value, including:

[0115] When there is no risk of neutral line disconnection in the low-voltage power supply line, the load impedance value is calculated based on the phasor values ​​of the three-phase voltage and the phasor values ​​of the three-phase current measured in real time; the load impedance value is recorded.

[0116] The formula is:

[0117] (3)

[0118] In formula (3), They are the phasor values ​​of the three-phase voltages A, B and C measured in real time by the acquisition unit; are the phase values ​​of the three-phase currents A, B, and C measured in real time by the acquisition unit; Z PA is the load impedance value of phase A, Z PB is the load impedance value of phase B, Z PC is the C phase load impedance value.

[0119] S320: Record the maximum voltage deviation value.

[0120] When there is no risk of neutral line disconnection in the low-voltage power supply line, the difference between the phase voltages is calculated based on the modulus values ​​of the three-phase voltages measured in real time to obtain the three-phase voltage deviation value;

[0121] Determine whether the three-phase voltage deviation value difference obtained at the current moment is greater than the maximum voltage deviation value recorded at the historical moment;

[0122] If so, the three-phase voltage deviation value obtained at the current moment is updated and recorded as the maximum voltage deviation value.

[0123] If not, the original maximum voltage deviation value is maintained.

[0124] The formula for calculating the three-phase voltage deviation value is:

[0125] (4)

[0126] In formula (4), To find the maximum value among them; U A , U B , U C are the modulus values ​​of the three-phase voltages A, B, and C, respectively. U SP is the three-phase voltage deviation value.

[0127] if U SP Greater than the maximum voltage deviation value stored U P , then U SP The value of U P , and update the storage U P Otherwise keep the original U P constant.

[0128] S330: Record the maximum angular deviation value.

[0129] When there is no risk of neutral line disconnection in the low-voltage power supply line, the difference between the phase angles of each phase is calculated based on the phase angles of the three-phase voltage measured in real time to obtain the three-phase phase angle deviation value;

[0130] Determine whether the three-phase phase angle deviation value obtained at the current moment is greater than the maximum phase angle deviation value recorded at the historical moment;

[0131] If so, update and record the three-phase angular deviation value obtained at the current moment as the maximum angular deviation value.

[0132] If not, keep the original maximum angular deviation value.

[0133] The formula for calculating the three-phase phase angle deviation is:

[0134] (5)

[0135] In formula (5), , , ,in, are the phase angles of the three-phase voltages A, B, and C, respectively. is the three-phase angular deviation value. It should be noted that To be within the range of -180° to 180°, if the If any value of is greater than 180°, subtract 360° from it to make it less than 180°; if the value obtained is If any value in is less than -180°, add 360° to it so that it is greater than -180°.

[0136] if Greater than the maximum stored angle deviation value , then The value of , and update the storage Otherwise keep the original constant.

[0137] S400: If yes, then the load voltage deviation value is calculated based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment.

[0138] When there is a risk of neutral line disconnection in the low-voltage power supply line, the neutral point will be offset, causing the neutral point voltage to increase, and the three-phase circuit will no longer be balanced. Specifically, the phase voltage with a small load will increase, while the phase voltage with a large load will decrease. Therefore, it is possible to determine whether a neutral line disconnection fault has occurred based on whether the three-phase load voltage has deviated.

[0139] In an exemplary embodiment, the step of calculating the load voltage deviation value based on the load impedance value recorded at a historical moment includes:

[0140] S410: Calculate the phasor value of the three-phase load voltage based on the load impedance value recorded at the historical moment and the phasor value of the three-phase current measured in real time.

[0141] The three-phase load voltage refers to the difference between the voltage of each phase at the meter box and the voltage at the neutral point of the load. According to the definition of the three-phase load voltage, the following formula can be obtained:

[0142] (6)

[0143] In formula (6), They are the phasor values ​​of the three-phase voltages A, B and C measured in real time by the acquisition unit; is the phasor value of the voltage at the neutral point of the load, is the phasor value of the A-phase load voltage, is the phasor value of the B-phase load voltage, is the phasor value of the C phase load voltage.

[0144] but, Only when the neutral line is not broken can it be directly measured by the acquisition unit. If the neutral line is broken, it cannot be directly measured. Figure 3 As shown in Figure 6, when the neutral line is not broken, the voltage at the measuring point n is the load neutral point voltage. However, when the neutral line is broken, the load neutral point voltage cannot be measured. Therefore, it is impossible to calculate the load neutral point voltage according to formula (6). , , , the following formula needs to be listed according to the circuit principle:

[0145] (7)

[0146] In formula (7), are the phase values ​​of the three-phase currents A, B, and C measured in real time by the acquisition unit; Z PA , Z PB , Z PC They are respectively the A-phase load impedance value, the B-phase load impedance value, and the C-phase load impedance value stored in step S310.

[0147] By combining formula (6) and formula (7), we can get the following formula:

[0148] (8)

[0149] In formula (8), , , is the phasor value of the three-phase load voltage, are the phase values ​​of the three-phase currents A, B, and C measured in real time by the acquisition unit; Z PA , Z PB , Z PC They are the load impedance value of phase A, phase B, and phase C stored in step S310. The phasor value of the three-phase load voltage can be calculated by formula (8).

[0150] S420: Obtaining the modulus value of the three-phase load voltage according to the phasor value of the three-phase load voltage.

[0151] S430: Calculate the load voltage deviation value based on the modulus value of the three-phase load voltage.

[0152] The steps for calculating the load voltage deviation value are the same as those for calculating the three-phase voltage deviation value, and will not be repeated here.

[0153] In an exemplary embodiment, the step of determining the voltage deviation threshold comprises:

[0154] The voltage deviation threshold is determined based on the maximum voltage deviation value recorded at the historical moment and the voltage experience threshold; the maximum voltage deviation value is the maximum value of the three-phase voltage deviation values ​​recorded when there is no risk of neutral line break in the low-voltage power supply line.

[0155] The formula is as follows:

[0156] (9)

[0157] In formula (9), They are , , the modulus value; U P is the maximum voltage deviation value stored in step 320; U SET is the voltage experience threshold, which can be 0.1 U N -0.3 U N , U N is the rated value of the line voltage, n 2 is the empirical coefficient with a value of 0.9-1.3.

[0158] S500: When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line. That is, formula (9) is satisfied, indicating that the three-phase circuit has lost balance, the phase voltage with a small load has increased, and the phase voltage with a large load has decreased. Therefore, it can be determined that there is a neutral line break fault in the low-voltage power supply line.

[0159] When the load voltage deviation value is less than or equal to the voltage deviation threshold, formula (9) is not satisfied. In this case, it is necessary to make a judgment based on the load amplitude angle deviation value.

[0160] S600: When there is a risk of neutral line disconnection in the low-voltage power supply line, the load phase angle deviation value is calculated based on the phasor values ​​of the three-phase load voltage.

[0161] In an illustrative embodiment, the step of calculating the load phase angle deviation value according to the phasor value of the three-phase load voltage includes:

[0162] According to the phasor value of the three-phase load voltage, the phase angle of the three-phase load voltage is obtained;

[0163] Based on the phase angle of the three-phase load voltage, the difference between the phase angles of each phase is calculated to obtain the load phase angle deviation value.

[0164] The formula is as follows:

[0165] (10)

[0166] In formula (10), is the maximum argument deviation value stored in step 330; is the empirical threshold of the argument angle, which can be 25°-35°; , , ,in, They are , , It should be noted that To be within the range of -180° to 180°, if the If any value of is greater than 180°, subtract 360° from it to make it less than 180°; if the value obtained is If any value in is less than -180°, add 360° to it so that it is greater than -180°.

[0167] When the load phase angle deviation value is greater than the phase angle deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line. That is, formula (10) is satisfied, which also means that the three-phase circuit has lost balance. Therefore, it can be determined that there is a neutral line break fault in the low-voltage power supply line.

[0168] When neither formula (9) nor formula (10) is satisfied, it is determined that there is no neutral line break fault in the low-voltage power supply line.

[0169] For example, MATLAB / Simulink software was used to build Figure 3 The low voltage power supply line model shown in the figure. The rated voltage of each phase of the line is 220V, the rated value is the effective value, and its modulus is the effective value. times. In order to simulate the difference in three-phase voltages during operation, the effective values ​​of the three-phase voltages A, B, and C are set to 220V, 225V, and 215V, respectively; the initial angles of the three-phase voltages are intentionally set to be not strictly symmetrical, and are set to 0°, -123°, and 118°, respectively; the resistance of the three-phase load is set to 3Ω, 4Ω, and 5Ω, respectively, and the inductance of the three-phase load is set to 0.5mH, 0.3mH, and 0.1mH, respectively. No line break fault is set at the beginning of the simulation, and a line break fault is set at 0.1 seconds. The waveform of the three-phase voltage signal obtained by simulation is shown in the figure below: Figure 4 As shown in the figure, the three-phase current signal waveform obtained by simulation is as follows Figure 5 As shown in the figure, the simulated neutral line current signal waveform is as follows Figure 6 shown.

[0170] The test results before 0.1 seconds are as follows:

[0171] Since the neutral line current satisfies formula (1), that is, there is no risk of line disconnection on the neutral line, it is determined that there is no neutral line disconnection fault in the low-voltage power supply line, and the operation data is updated and stored: the phasor values ​​of the three-phase voltages A, B, and C are measured in real time according to the acquisition unit. Their moduli are 311.080V, 318.150V, and 304.010V, respectively, and their angular angles are 90°, -33°, and -152°, respectively; the phasor values ​​of the three-phase currents A, B, and C are measured in real time. Their moduli are 103.451A, 79.521A, and 60.859A, respectively, and their angular angles are 87.034°, -34.412°, and -152.325°, respectively.

[0172] In step S310, the load impedance value Z of phase A is updated and stored in real time by calculating formula (3). PA , B phase load impedance value Z PB , C phase load impedance value Z PC , they are also phasor values, their moduli are 3.007Ω, 4.001Ω, 4.995Ω, and their arguments are 2.966°, 1.412°, 0.325°.

[0173] In step S320, the three-phase voltage deviation value is calculated by formula (4): U SP The three-phase voltage deviation value obtained is 15.554V, and it is updated and stored as the maximum voltage deviation value U P .

[0174] In step S330, the three-phase phase angle deviation value is calculated by formula (5): , the obtained three-phase phase angle deviation value 3°, and update and store it as the maximum angle deviation value .

[0175] The test results after 0.1 seconds are as follows:

[0176] Since the neutral line current does not satisfy formula (1), it is determined that there may be a risk of a neutral line break in the low-voltage power supply line, and the process proceeds to step S210 for further determination.

[0177] Step S210: The acquisition unit re-measures the phasor values ​​of the three-phase currents A, B, and C in real time to determine whether they satisfy formula (2). At this time, the phasor values ​​of the three-phase currents A, B, and C are measured in real time, and their modulus values ​​are 90.689A, 81.293A, and 68.352A, respectively, and their angles are 91.371°, -42.191°, and -148.153°, respectively. Since formula (2) is satisfied, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line, and the process goes to step S400.

[0178] Step S400: By combining equations (6) and (7), equation (8) is obtained. By using equation (8), , , , at this time, the , , The modulus values ​​are 272.703V, 325.242V, and 341.437V, and the angles are 94.337°, -40.779°, and -147.828°, respectively.

[0179] Step S500: Since the obtained , , Formula (9) is satisfied, so it is determined that there is a neutral line break fault in the low-voltage power supply line, and the line break identification system sends an alarm signal.

[0180] Step S600: At the same time, , , Formula (10) is also satisfied, so it is determined that there is a neutral line break fault in the low-voltage power supply line, and the line break identification system sends an alarm signal.

[0181] The method provided in the present application can perform adaptive patrols. If it is determined that there is no neutral line break fault based on the neutral line current situation, the operating data is updated and stored, including: load impedance value, maximum voltage deviation value, and maximum angle deviation value. After the system is put into operation for a long time, these data are obtained from the long-term real-time operation data of the power supply line, which is closer to the actual operation of the line. The subsequent line break fault judgment criteria not only take into account the manually set empirical threshold, but also take into account the data updated and stored in the adaptive patrol. Such a design makes the method more reliable and more adaptable to the operating conditions of the project site.

[0182] The three-phase load voltage in this application refers to the difference between the voltage of each phase at the meter box and the voltage at the neutral point of the load. In fact, traditional technology cannot measure the voltage at the neutral point of the load, and thus cannot measure the voltage of each phase load, making it difficult to achieve neutral line break detection and identification from this aspect. However, this application performs adaptive patrols, acquires, updates and stores the impedance value of each phase load in real time, and indirectly measures the load voltage of each phase through the load impedance value and its calculation formula, achieving effective neutral line break detection and identification. Compared with signal injection detection methods, this application requires less hardware equipment and is convenient for engineering implementation.

[0183] A second embodiment of the present application provides a device for identifying a neutral line break fault in a low-voltage power supply line, such as Figure 7 As shown, including:

[0184] The acquisition module 71 is used to obtain the line information of the low-voltage power supply line measured at the current moment, and the line information at least includes: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value and the phase angle of the three-phase current;

[0185] A judgment module 72 is used to judge whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current;

[0186] Analysis module 73, for calculating the load voltage deviation value based on the load impedance value recorded at the historical moment; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment;

[0187] When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line;

[0188] If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

[0189] In some embodiments of the present application, the judging module 72 can be used to judge whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current, including:

[0190] Determining whether the neutral line current value is greater than a first current threshold;

[0191] If not, the current modulus deviation is calculated based on the modulus values ​​of the three-phase currents;

[0192] When the current modulus deviation is less than or equal to the first current threshold, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line;

[0193] When the current modulus deviation is greater than the first current threshold, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line;

[0194] If yes, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line.

[0195] In some embodiments of the present application, the judging module 72 may be used to calculate the current modulus deviation based on the modulus of the three-phase current, and the steps include:

[0196] Based on the modulus values ​​of the three-phase currents, the difference between the currents of each phase is calculated to obtain a first current intermediate value;

[0197] Taking the absolute value of the first current intermediate value to obtain the second current intermediate value;

[0198] The maximum value among the second current intermediate values ​​is taken as the current modulus deviation.

[0199] In some embodiments of the present application, the judgment module 72 may be used to record the load impedance value in the following steps:

[0200] When there is no risk of neutral line disconnection in the low-voltage power supply line, the load impedance value is calculated based on the phasor values ​​of the three-phase voltage and the phasor values ​​of the three-phase current measured in real time;

[0201] Record the load impedance value.

[0202] In some embodiments of the present application, the analysis module 73 may be used to calculate the load voltage deviation value based on the load impedance value recorded at a historical moment, and the steps include:

[0203] Calculate the phasor value of the three-phase load voltage based on the load impedance value recorded at the historical moment and the phasor value of the three-phase current measured in real time;

[0204] According to the phasor value of the three-phase load voltage, the modulus value of the three-phase load voltage is obtained;

[0205] Based on the modulus values ​​of the three-phase load voltages, the load voltage deviation value is calculated.

[0206] In some embodiments of the present application, the analysis module 73 may be used to calculate the load phase angle deviation value according to the phasor value of the three-phase load voltage when there is a risk of a neutral line disconnection in the low-voltage power supply line;

[0207] When the load phase angle deviation value is greater than the phase angle deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line.

[0208] In some embodiments of the present application, the analysis module 73 may be used to calculate the load phase angle deviation value according to the phasor value of the three-phase load voltage, including the following steps:

[0209] According to the phasor value of the three-phase load voltage, the phase angle of the three-phase load voltage is obtained;

[0210] Based on the phase angle of the three-phase load voltage, the difference between the phase angles of each phase is calculated to obtain the load phase angle deviation value.

[0211] In some embodiments of the present application, the analysis module 73 may be used to determine the voltage deviation threshold value, including the following steps:

[0212] The voltage deviation threshold is determined based on the maximum voltage deviation value recorded at the historical moment and the voltage experience threshold; the maximum voltage deviation value is the maximum value of the three-phase voltage deviation values ​​recorded when there is no risk of neutral line break in the low-voltage power supply line.

[0213] A third aspect of the present application provides a low-voltage power supply line neutral line disconnection fault identification system, comprising:

[0214] A collection unit is configured to collect three-phase voltage, three-phase current and neutral line current flowing through the low-voltage power supply line;

[0215] The controller is configured to execute a method for identifying a neutral line break fault in a low-voltage power supply line in the first aspect or in each of its implementations.

[0216] The controller can be a mobile phone, tablet computer, desktop computer, laptop computer, server, industrial computer, single-chip microcomputer, PLC (Programmable Logic Controller), DSP (digital signal processor), FPGA (Field Programmable Gate Array), ASIC (Application-specific integrated circuit) and other devices with storage and computing functions, and the embodiments of the present application do not limit this.

[0217] Since the low-voltage power supply line neutral line break fault identification system provided in this embodiment has the low-voltage power supply line neutral line break fault identification method provided in any of the above embodiments, the low-voltage power supply line neutral line break fault identification system has all the beneficial effects of the low-voltage power supply line neutral line break fault identification method provided in any of the above embodiments, which will not be repeated here.

[0218] The fourth aspect of the present application also provides a computer storage medium on which a computer program is stored, and when the computer program is executed by a computer, the computer can perform the method of the above method embodiment. In other words, an embodiment provided by the present application also provides a computer program product containing instructions, and when the instructions are executed by a computer, the computer can perform the method of the above method embodiment.

[0219] When software is used for implementation, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instruction is loaded and executed on a computer, the process or function according to the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instruction can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instruction can be transmitted from a website site, a computer, a server or a data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (Digital Subscriber Line, DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or a data center that includes one or more available media integration. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a digital video disc (Digital Video Disc, DVD)), or a semiconductor medium (e.g., a solid-state drive (SSD)), etc.

[0220] It should be noted that the terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0221] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "embodiment", "exemplary embodiment", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0222] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for identifying a neutral line break fault in a low-voltage power supply line, characterized in that: include: Acquire the line information of the low-voltage power supply line measured at the current moment, the line information at least including: the phasor value of the three-phase voltage, the phasor value of the three-phase current and the neutral line current value, wherein the phasor value of the three-phase voltage is composed of the modulus value and the phase angle of the three-phase voltage, and the phasor value of the three-phase current is composed of the modulus value and the phase angle of the three-phase current; Based on the neutral line current value and the modulus value of the three-phase current, judging whether there is a neutral line disconnection risk in the low-voltage power supply line; If so, then based on the load impedance value recorded at the historical moment, the load voltage deviation value is calculated; the load voltage deviation value is the modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at the historical moment; When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line; If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

2. A method for identifying a neutral line break fault in a low-voltage power supply line according to claim 1, characterized in that: The step of judging whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current includes: Determining whether the neutral line current value is greater than a first current threshold; If not, calculating the current modulus deviation based on the modulus of the three-phase current; When the current modulus deviation is less than or equal to the first current threshold, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line; When the current modulus deviation is greater than the first current threshold, it is determined that there is a risk of neutral line disconnection in the low-voltage power supply line; If yes, it is determined that there is no risk of neutral line disconnection in the low-voltage power supply line.

3. A method for identifying a neutral line break fault in a low-voltage power supply line according to claim 2, characterized in that: The step of calculating the current modulus deviation based on the modulus of the three-phase current comprises: Based on the modulus values ​​of the three-phase currents, calculating the difference between the currents of each phase to obtain a first current intermediate value; Taking an absolute value of the first current intermediate value to obtain a second current intermediate value; The maximum value among the second current intermediate values ​​is taken as the current modulus deviation.

4. A method for identifying a neutral line break fault in a low-voltage power supply line according to claim 1, characterized in that: The steps for recording load impedance values ​​include: When there is no risk of neutral line disconnection in the low-voltage power supply line, the load impedance value is calculated based on the phasor values ​​of the three-phase voltage and the phasor values ​​of the three-phase current measured in real time; The load impedance value is recorded.

5. A method for identifying a neutral line break fault in a low voltage power supply line according to claim 1, characterized in that: The step of calculating the load voltage deviation value based on the load impedance value recorded at the historical moment includes: Calculate the phasor value of the three-phase load voltage based on the load impedance value recorded at the historical moment and the phasor value of the three-phase current measured in real time; Obtaining a modulus value of the three-phase load voltage according to the phasor value of the three-phase load voltage; Based on the modulus values ​​of the three-phase load voltages, a load voltage deviation value is calculated.

6. A method for identifying a neutral line break fault in a low voltage power supply line according to claim 5, characterized in that: Also includes: When there is a risk of neutral line disconnection in the low-voltage power supply line, the load phase angle deviation value is calculated according to the phasor value of the three-phase load voltage; When the load phase angle deviation value is greater than the phase angle deviation threshold, it is determined that a neutral line break fault exists in the low-voltage power supply line.

7. A method for identifying a neutral line break fault in a low voltage power supply line according to claim 6, characterized in that: The step of calculating the load phase angle deviation value according to the phasor value of the three-phase load voltage comprises: Obtaining the phase angle of the three-phase load voltage according to the phasor value of the three-phase load voltage; Based on the phase angles of the three-phase load voltage, the difference between the phase angles of each phase is calculated to obtain the load phase angle deviation value.

8. A method for identifying a neutral line break fault in a low voltage power supply line according to claim 1, characterized in that: The steps to determine the voltage deviation threshold include: The voltage deviation threshold is determined based on the maximum voltage deviation value recorded at a historical moment and the voltage experience threshold; the maximum voltage deviation value is the maximum value of the three-phase voltage deviation values ​​recorded when there is no risk of neutral line break in the low-voltage power supply line.

9. A device for identifying a neutral line break fault in a low-voltage power supply line, characterized in that: include: An acquisition module is used to acquire line information of a low-voltage power supply line measured at the current moment, wherein the line information at least includes: a phasor value of a three-phase voltage, a phasor value of a three-phase current, and a neutral line current value, wherein the phasor value of the three-phase voltage is composed of a modulus value and an angle of the three-phase voltage, and the phasor value of the three-phase current is composed of a modulus value and an angle of the three-phase current; A judgment module, used for judging whether there is a risk of neutral line disconnection in the low-voltage power supply line based on the neutral line current value and the modulus value of the three-phase current; An analysis module is used to calculate a load voltage deviation value based on the load impedance value recorded at a historical moment; the load voltage deviation value is a modulus deviation of the three-phase load voltage; the load impedance value is calculated based on the phasor value of the three-phase voltage and the phasor value of the three-phase current recorded at a historical moment; When the load voltage deviation value is greater than the voltage deviation threshold, it is determined that there is a neutral line break fault in the low-voltage power supply line; If not, it is determined that there is no neutral line break fault in the low-voltage power supply line.

10. A low voltage power supply line neutral line disconnection fault identification system, characterized in that: include: A collection unit is configured to collect three-phase voltage, three-phase current and neutral line current flowing through the low-voltage power supply line; A controller is configured to execute a method for identifying a neutral line break fault in a low-voltage power supply line according to any one of claims 1 to 8.

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