A method for detecting phase asymmetric grounding fault

Abstract

The invention discloses a method for detecting a phase asymmetric grounding fault, relates to the technical field of asymmetric grounding fault detection, and solves the technical problem that the prior art only locates the fault interval without performing analysis, resulting in waste of electric power resources; the invention measures the zero-sequence voltage of a three-phase circuit in real time; determines whether to issue an early warning based on the zero-sequence voltage and a preset zero-sequence voltage threshold, and obtains operating data of different three-phase lines; determines whether to issue an early warning based on the operating data and a preset voltage threshold, and calculates the fault phase disconnection time based on the operating data; obtains the real-time temperature of a normal phase, and calculates the normal phase real-time temperature disconnection time based on the real-time temperature; calculates the risk time based on the normal phase real-time temperature disconnection time; calculates the maintenance time based on historical maintenance data; processes the phase asymmetric grounding fault based on the fault phase disconnection time, the risk time, and the maintenance time, and solves the above technical problems.

Description

Technical Field

[0001] The invention belongs to the field of asymmetric grounding fault detection, in particular to a phase asymmetric grounding fault detection method. Background Art

[0002] In the power system, three-phase alternating current is a common power supply method, in which each phase has a certain potential difference with the ground. However, in actual operation, due to various factors such as equipment aging, line damage, external interference, etc., phase asymmetric grounding faults may occur, that is, the insulation performance between one or more phases and the ground is reduced, resulting in abnormal current leakage to the ground, which will not only affect the normal operation of the power system, but also may cause damage to the equipment and even cause safety accidents. Traditional methods usually require manual analysis, which is not only time-consuming but also prone to errors for complex power systems. In addition, traditional methods are also susceptible to external interference, resulting in false alarms or missed alarms.

[0003] The prior art (invention application with publication number CN114113883A) discloses a method for detecting phase asymmetric grounding faults, including deeply integrating the automated intelligent terminal equipment FTU with the small current grounding fast disconnecting device, integrating the grounding detection technology in the FTU with the phase asymmetric grounding detection technology of the small current grounding fast disconnecting device from a technical perspective, utilizing the measurement and summarization of the feeder electrical parameters of the FTU equipment and the communication function with the remote distribution automation terminal and the fault recording and broadcasting of the small current grounding fast disconnecting device, integrating the on-site judgment and action functions, and performing a unified structural design. On the basis of retaining the various functions of the original equipment, the corresponding repeated functions are screened and integrated, thereby further reducing the number of feeder hanging devices and reducing power terminals. The existing technology monitors and controls the information required, including switch status, power parameters, phase-to-phase faults, ground faults and parameters at the time of faults, and executes commands issued by the distribution master station to adjust and control the distribution equipment to achieve functions such as fault location, fault isolation and rapid power restoration in non-fault areas. However, the existing technology only locates the fault interval without performing any analysis. When a phase fails, if all phases are immediately stopped for maintenance, other normally operating phases will be shut down unnecessarily, resulting in a waste of power resources.

[0004] Therefore, the present invention proposes a method for detecting a phase asymmetric grounding fault to solve the above problem. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art; to this end, the present invention proposes a phase asymmetric grounding fault detection method to solve the technical problem that the prior art only locates the fault interval without performing any analysis, and when a phase fails, if all phases are immediately stopped for maintenance, then other normally operating phases will be shut down unnecessarily, resulting in a waste of power resources.

[0006] To achieve the above object, a first aspect of the present invention provides a method for detecting a phase asymmetric grounding fault, comprising:

[0007] Step 1: Measure the zero-sequence voltage of the three-phase circuit in real time; determine whether to perform a phase asymmetric grounding fault warning based on the zero-sequence voltage and the preset zero-sequence voltage threshold; if yes, send a warning message and obtain the operating data of different three-phase lines; if no, continue to detect and judge;

[0008] Step 2: Determine whether to issue an early warning based on the operating data and the preset voltage threshold; if yes, send an early warning message and calculate the fault phase disconnection time based on the operating data; if no, continue to detect and determine;

[0009] Step 3: Obtain the real-time temperature of the normal phase and calculate the real-time temperature breaking time of the normal phase;

[0010] Step 4: Calculate the risk time based on the real-time temperature breaking time of the normal phase; calculate the maintenance time based on the historical maintenance data; and handle the phase asymmetric grounding fault based on the breaking time, risk time and maintenance time of the faulty phase.

[0011] Preferably, the real-time measurement of the zero-sequence voltage of the three-phase circuit includes:

[0012] The zero-sequence voltage of the three-phase circuit is obtained in real time through a voltage transformer; wherein the voltage transformer includes: a three-phase five-column voltage transformer or three single-phase voltage transformers.

[0013] Preferably, judging whether to perform a phase asymmetric grounding fault warning based on the zero-sequence voltage and a preset zero-sequence voltage threshold includes:

[0014] Determine whether the zero-sequence voltage is greater than the preset zero-sequence voltage threshold; if yes, generate phase asymmetric grounding fault warning information; if no, continue to detect and judge; wherein, the preset zero-sequence voltage threshold is set according to the average value of all real-time zero-sequence voltages of the actual three-phase circuit.

[0015] Preferably, the obtaining of operating data of different three-phase lines includes:

[0016] The operating data of each phase of the three-phase line is collected by a data collection device; wherein the operating data includes: real-time current and corresponding real-time voltage.

[0017] Preferably, the determining whether to issue an early warning based on the operating data and a preset voltage threshold includes:

[0018] Determine whether the real-time voltage of each phase in the three-phase line is greater than the preset voltage threshold; if yes, generate ground fault warning information for the corresponding numbered phase; if no, continue monitoring and judgment; wherein, the preset voltage threshold is set according to the average value of all actual three-phase line voltages.

[0019] It should be noted that the corresponding numbered phase refers to a phase in the three-phase line whose real-time voltage is greater than a preset voltage threshold.

[0020] Preferably, the calculating of the fault phase breaking time based on the operating data includes:

[0021] Mark the real-time current of the corresponding phase number as the fault phase current , after linear normalization, the real-time current fluctuation rate of the fault phase is calculated by the formula:

[0022]

[0023] in, is the real-time current fluctuation rate of the fault phase, in A / S, x represents the detection time sequence number of the current or voltage data, and x=1, 2, 3…m, T is the periodic detection period;

[0024] The real-time fault phase breaking time is calculated by the formula :

[0025]

[0026] Where R represents the value of a positive integer that satisfies inequality (1), and the real-time fault phase disconnection time is The unit is seconds, is the breaking current of the circuit breaker, is the fault phase current when x=m.

[0027] It should be noted that because a low-impedance current path is formed between the grounding fault point and the ground, when a single-phase grounding fault occurs, the current in the faulty phase will increase sharply, and the protection equipment of the power system, such as relay protection devices and circuit breakers, will perform a circuit-breaking operation when they detect abnormal current.

[0028] Preferably, the step of obtaining the real-time temperature of the normal phase and calculating the normal phase real-time temperature trip time comprises:

[0029] After the fault phase is disconnected, the real-time temperature of the normal phase is periodically collected through the temperature sensor and marked as ; Among them, the normal phase refers to the remaining two phases except the faulty phase after the faulty phase is disconnected;

[0030] The real-time temperature fluctuation rate of the normal phase is calculated by the formula:

[0031]

[0032] in, is the real-time temperature fluctuation rate, in units of °C / S, b represents the sequence number of the other two phases in the three-phase circuit except the faulty phase, and b=1, 2, y represents the time sequence number of the real-time temperature of the normal phase, y=1, 2, 3…n;

[0033] The real-time temperature trip time is calculated based on the real-time temperature fluctuation rate.

[0034] It should be noted that in the case of a single-phase grounding fault, the circuit breaker usually only disconnects the faulty phase, rather than all phases. This is because a single-phase grounding fault will only affect the faulty phase, while the non-faulty phase can still operate normally. After detecting a single-phase grounding fault, the circuit breaker will quickly cut off the current of the faulty phase to prevent the fault from expanding and protect the safety of the equipment and system. At the same time, the non-faulty phase can still continue to supply power to ensure the stable operation of the system. And the voltage of the non-faulty phase will increase, usually to the line voltage, that is, the root of 3 times the normal phase voltage. This is because after the voltage of the faulty phase decreases, the system will increase the voltage of the non-faulty phase to the line voltage in order to maintain the balance of the three-phase voltage. The current of the non-faulty phase will increase relatively, because their voltage increases, but the load impedance remains unchanged. According to Ohm's law, the current will increase.

[0035] Preferably, the real-time temperature trip time is calculated based on the real-time temperature fluctuation rate, including:

[0036] The normal phase real-time temperature breaking time is calculated by the formula:

[0037]

[0038] Where H represents the value of a positive integer that makes inequality (2) true, and the normal phase real-time temperature circuit breaker time The unit is seconds, Dw is the breaking temperature of the circuit breaker, is the real-time temperature when y=n.

[0039] It should be noted that after a single-phase ground fault breaks the circuit, the voltage and current of the remaining two phases are different from the state before the fault phase, and there are also differences between them, so the phase work is different and the temperature changes are also different.

[0040] Preferably, the risk time is calculated based on the normal phase real-time temperature trip time, including:

[0041] The risk time is calculated by the formula; wherein the risk time includes: the first risk time and the second risk time;

[0042] Mark the first risk time as , specifically: ;

[0043] Mark the second risk time as , specifically: .

[0044] Preferably, the calculation of the maintenance time based on historical maintenance data includes:

[0045] Obtain historical maintenance data of the three-phase circuit through a database, and obtain the average maintenance time of each single-phase grounding fault and the average time from the issuance of an early warning to the start of maintenance; wherein the database stores maintenance time records of historical faults of the three-phase circuit;

[0046] The mean maintenance time is marked as Mw, and the mean time from the issuance of the warning to the start of maintenance is marked as Kj;

[0047] The maintenance time is calculated by a formula; wherein the maintenance time includes: a first maintenance time and a second maintenance time;

[0048] The first maintenance time is marked as Dws, specifically: Dws=Kj+Mw;

[0049] The second maintenance time is marked as Ews, specifically: Ews=Kj+2Mw.

[0050] Preferably, the processing of the phase asymmetric grounding fault based on the fault phase disconnection time, risk time and maintenance time includes:

[0051] when When the fault phase is disconnected, the normal phase is used to continue operation;

[0052] when and When the system is in operation, choose to stop all phases or speed up maintenance;

[0053] when and When the alarm is raised, all phases will be stopped immediately.

[0054] The present invention selects different phase asymmetric grounding fault maintenance strategies by analyzing the real-time fault phase disconnection time, the normal phase real-time temperature disconnection time, the first maintenance time and the second maintenance time, so as to more accurately determine the specific maintenance method, optimize the maintenance plan and reduce unnecessary downtime while ensuring safety, thereby solving the technical problem that the prior art only locates the fault interval without performing analysis, resulting in waste of power resources.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. The present invention measures the real-time zero-sequence voltage of the three-phase circuit. When the real-time zero-sequence voltage exceeds a preset zero-sequence voltage threshold, a phase asymmetric grounding fault warning is issued, and the real-time current and voltage of different three-phase lines are detected. When the real-time voltage of the three-phase line is less than a preset phase voltage threshold, a grounding fault warning of the corresponding numbered phase is issued. The warning can be issued at an early stage of the grounding fault and the faulty phase can be accurately located, so that corresponding measures can be taken more quickly to prevent the fault from expanding or causing more serious consequences.

[0057] 2. After receiving the ground fault warning of the corresponding numbered phase, the present invention obtains the real-time current of the corresponding numbered phase, calculates the real-time current fluctuation rate of the fault phase, and further calculates the real-time fault phase disconnection time, which is helpful to predict the development trend of the fault, take countermeasures in advance, optimize the maintenance plan, reduce potential losses, avoid unnecessary downtime, and improve the availability and reliability of the power system. It solves the technical problem that the prior art only locates the fault interval without analysis. When a phase fails, if all phases are stopped immediately for maintenance, other normally operating phases will be shut down unnecessarily, resulting in a waste of power resources.

[0058] 3. The present invention detects the real-time temperatures of the remaining two phases except the faulty phase after the faulty phase is disconnected, calculates the real-time temperature fluctuation rate of the remaining phases, and further calculates the real-time temperature disconnection time of the remaining phases. This can indirectly understand the operating status of the remaining phases. If the workload and heat dissipation of the non-faulty phases are abnormal, these potential problems can be avoided from further deterioration and the risk of failure can be reduced by taking timely measures.

[0059] 4. The present invention obtains the real-time temperature circuit-breaking time of the remaining phases, calculates the first risk time and the second risk time, and calculates the first maintenance time and the second maintenance time. According to the size relationship between the maintenance time and the risk time, different phase asymmetric grounding fault maintenance strategies are selected, and the specific maintenance method can be determined more accurately. If the risk time is earlier than the maintenance time, it may be necessary to stop the circuit operation in advance to avoid further expansion of the risk. On the contrary, if the maintenance time is earlier than the risk time, the maintenance plan can be optimized to reduce unnecessary downtime while ensuring safety. It helps to optimize the design and operation strategy of the system and improve the performance and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0061] Figure 1 A schematic diagram of the method steps of an embodiment of the present invention;

[0062] Figure 2 A schematic diagram of determining the zero-sequence voltage according to an embodiment of the present invention;

[0063] Figure 3 A schematic diagram of determining operation data according to an embodiment of the present invention. DETAILED DESCRIPTION

[0064] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] See also Figure 1 The first aspect of the present invention provides a method for detecting a phase asymmetric grounding fault, comprising:

[0066] Step 1: Measure the zero-sequence voltage of the three-phase circuit in real time; determine whether to perform a phase asymmetric grounding fault warning based on the zero-sequence voltage and the preset zero-sequence voltage threshold; if yes, send a warning message and obtain the operating data of different three-phase lines; if no, continue to detect and judge;

[0067] Step 2: Determine whether to issue an early warning based on the operating data and the preset voltage threshold; if yes, send an early warning message and calculate the fault phase disconnection time based on the operating data; if no, continue to detect and determine;

[0068] Step 3: Obtain the real-time temperature of the normal phase and calculate the real-time temperature breaking time of the normal phase;

[0069] Real-time measurement of zero-sequence voltage of three-phase circuits, including:

[0070] The zero-sequence voltage of the three-phase circuit is obtained in real time through a voltage transformer; wherein the voltage transformer includes: a three-phase five-column voltage transformer or three single-phase voltage transformers.

[0071] See also Figure 2 , based on the zero-sequence voltage and the preset zero-sequence voltage threshold, it is determined whether to perform a phase asymmetric grounding fault warning, including:

[0072] Determine whether the zero-sequence voltage is greater than the preset zero-sequence voltage threshold; if yes, generate phase asymmetric grounding fault warning information; if no, continue to detect and judge; wherein, the preset zero-sequence voltage threshold is set according to the average value of all real-time zero-sequence voltages of the actual three-phase circuit.

[0073] Get the operating data of different three-phase lines, including:

[0074] The operating data of each phase of the three-phase line is collected by a data collection device; wherein the operating data includes: real-time current and corresponding real-time voltage.

[0075] See also Figure 3 , based on the operating data and the preset voltage threshold, determine whether to issue an early warning, including:

[0076] Determine whether the real-time voltage of each phase in the three-phase line is greater than the preset voltage threshold; if yes, generate ground fault warning information for the corresponding numbered phase; if no, continue monitoring and judgment; wherein, the preset voltage threshold is set according to the average value of all actual three-phase line voltages.

[0077] The fault phase breaking time is calculated based on the operating data, including:

[0078] Mark the real-time current of the corresponding phase number as the fault phase current , after linear normalization, the real-time current fluctuation rate of the fault phase is calculated by the formula:

[0079]

[0080] in, is the real-time current fluctuation rate of the fault phase, in A / S, x represents the detection time sequence number of the current or voltage data, and x=1, 2, 3…m, T is the periodic detection period;

[0081] The real-time fault phase breaking time is calculated by the formula :

[0082]

[0083] Where R represents the value of a positive integer that satisfies inequality (1), and the real-time fault phase disconnection time is The unit is seconds, is the breaking current of the circuit breaker, is the fault phase current when x=m.

[0084] Obtain the real-time temperature of the normal phase and calculate the normal phase real-time temperature circuit breaker time, including:

[0085] After the fault phase is disconnected, the real-time temperature of the normal phase is periodically collected through the temperature sensor and marked as ; Among them, the normal phase refers to the remaining two phases except the faulty phase after the faulty phase is disconnected;

[0086] The real-time temperature fluctuation rate of the normal phase is calculated by the formula:

[0087]

[0088] in, is the real-time temperature fluctuation rate, in units of °C / S, b represents the sequence number of the other two phases in the three-phase circuit except the faulty phase, and b=1, 2, y represents the time sequence number of the real-time temperature of the normal phase, y=1, 2, 3…n;

[0089] The real-time temperature trip time is calculated based on the real-time temperature fluctuation rate.

[0090] The real-time temperature trip time is calculated based on the real-time temperature fluctuation rate, including:

[0091] The normal phase real-time temperature breaking time is calculated by the formula:

[0092]

[0093] Where H represents the value of a positive integer that makes inequality (2) true, and the normal phase real-time temperature circuit breaker time The unit is seconds, Dw is the breaking temperature of the circuit breaker, is the real-time temperature when y=n.

[0094] Example 1: Assume that there is a three-phase circuit system, which is equipped with necessary sensors and monitoring equipment to monitor its operating status in real time. The details are as follows:

[0095] 1. Example settings:

[0096] Preset zero-sequence voltage threshold: 10V;

[0097] Preset voltage threshold: 230V;

[0098] Breaking current of circuit breaker (Dl): 100A;

[0099] Breaking temperature of circuit breaker (Dw): 80℃;

[0100] Periodic detection period (T): 1 second;

[0101] 2. Real-time measurement of zero-sequence voltage of three-phase circuit:

[0102] The zero-sequence voltage of the three-phase circuit is monitored in real time through a three-phase five-column voltage transformer.

[0103] Assume that at a certain moment, the zero-sequence voltage reading is 12V, exceeding the preset zero-sequence voltage threshold of 10V, triggering a phase asymmetric grounding fault warning.

[0104] It should be noted that in an ideal three-phase balanced system, the three-phase voltage and current are symmetrical, so there is no zero-sequence component. However, when a fault occurs in the system, especially when a single-phase grounding occurs, the three-phase voltage and current will become asymmetrical, and the zero-sequence component, i.e., the zero-sequence voltage, can be decomposed. When a ground short circuit occurs in a neutral point direct grounding system (also known as a high-current grounding system), or when a single-phase grounding occurs, a large zero-sequence voltage will appear.

[0105] 3. Obtain the operating data of different three-phase lines:

[0106] When a phase asymmetric ground fault warning is received, the current sensors and voltage sensors installed on different three-phase lines are started to periodically detect the real-time current and voltage of different three-phase lines. Assuming that the voltage of phase A is 240V, which exceeds the preset voltage threshold upper limit of 230V, and the voltages of phases B and C are 230V and 229V respectively, which are within the normal range. Therefore, phase A is marked as a potential fault phase.

[0107] It should be noted that when a single-phase grounding fault occurs, the voltage of the faulty phase will drop significantly, or even drop to zero. This is because the grounding fault forms a low-impedance current path between the phase and the ground, causing the voltage of the faulty phase to be short-circuited or pulled down.

[0108] 4. Calculation of fault phase circuit breaking time:

[0109] Real-time current fluctuation rate of fault phase :Assume that the real-time current fluctuation rate of phase A is is 0.21, is 0.2.

[0110] Real-time fault phase disconnection time :

[0111] Assume that the real-time current of phase A is 50A;

[0112] but

[0113]

[0114] At this time, the value of R can be [61, ∞), then ;

[0115] This means that the circuit breaker operates after 61 seconds.

[0116] 5. Calculation of normal phase real-time temperature circuit-breaking time:

[0117] Assume that after a fault occurs, the real-time temperatures of phase B and phase C are stabilized at 60°C and 61°C respectively, and the circuit breaker's disconnecting temperature Dw is 80°C.

[0118] Real-time temperature fluctuation rate :Assume that the real-time temperature fluctuation rate of phase B is is 0.051, is 0.05.

[0119] Real-time temperature cut-off time :Take phase B as an example;

[0120]

[0121] At this time, the value of H can be [119, ∞), then ;

[0122] This means that when the temperature of phase B reaches 60°C and the fluctuation rate is 0.051, the circuit breaker will operate due to overheating after 119 seconds.

[0123] Through this series of steps and calculations, the system of the present invention can effectively monitor and respond to phase asymmetric grounding faults, disconnect the faulty phase in time, and evaluate the operating status of the non-faulty phase to ensure the safety and stability of the power system.

[0124] Step 4: Calculate the risk time based on the real-time temperature breaking time of the normal phase; calculate the maintenance time based on the historical maintenance data; and handle the phase asymmetric grounding fault based on the breaking time, risk time and maintenance time of the faulty phase.

[0125] The risk time is calculated based on the normal phase real-time temperature circuit breaker time, including:

[0126] The risk time is calculated by the formula; wherein the risk time includes: the first risk time and the second risk time;

[0127] Mark the first risk time as , specifically: ;

[0128] Mark the second risk time as , specifically: .

[0129] The maintenance time is calculated based on historical maintenance data, including:

[0130] Obtain historical maintenance data of the three-phase circuit through a database, and obtain the average maintenance time of each single-phase grounding fault and the average time from the issuance of an early warning to the start of maintenance; wherein the database stores maintenance time records of historical faults of the three-phase circuit;

[0131] The mean maintenance time is marked as Mw, and the mean time from the issuance of the warning to the start of maintenance is marked as Kj;

[0132] The maintenance time is calculated by a formula; wherein the maintenance time includes: a first maintenance time and a second maintenance time;

[0133] The first maintenance time is marked as Dws, specifically: Dws=Kj+Mw;

[0134] The second maintenance time is marked as Ews, specifically: Ews=Kj+2Mw.

[0135] The phase asymmetric grounding fault is handled based on the fault phase disconnection time, risk time and maintenance time, including:

[0136] when When the fault phase is disconnected, the normal phase is used to continue operation;

[0137] when and When the system is in operation, choose to stop all phases or speed up maintenance;

[0138] when and When the alarm is raised, all phases will be stopped immediately.

[0139] Example 2: Assume that there is a three-phase power system, in which phase A has a ground fault, and it is necessary to decide how to handle this fault based on real-time data and historical data. The details are as follows:

[0140] 1. Data acquisition:

[0141] Fault phase disconnection time : The phase-breaking time of phase A fault is 200 seconds.

[0142] Normal phase real-time temperature circuit breaker time : Phase B is 400 seconds and phase C is 500 seconds.

[0143] Historical maintenance data: The average maintenance time is 30 minutes (i.e. 1,800 seconds), and the average time interval from the issuance of an early warning to the start of maintenance is 5 minutes (i.e. 300 seconds).

[0144] 2. Calculate the risk time:

[0145] First risk time : Select the maximum value of the normal phase real-time temperature circuit-breaking time, that is, max(Qwd^n_b)=max(400,500)=500 seconds.

[0146] Second risk time : Select the minimum value of the normal phase real-time temperature circuit-breaking time, that is, min(Qwd^n_b)=min(400,500)=400 seconds.

[0147] 3. Calculate the maintenance time:

[0148] First maintenance time (Dws): maintenance start time plus the mean maintenance time, that is, Kj+Mw=300 seconds+1800 seconds=2100 seconds.

[0149] The second maintenance time (Ews): the maintenance start time plus twice the average maintenance time, that is, Kj+2Mw=300 seconds+2×1800 seconds=3900 seconds.

[0150] 4. Processing based on fault phase disconnection time, risk time and maintenance time:

[0151] Again compare these times to determine the appropriate repair strategy:

[0152] when , it means that after the fault phase is disconnected, the repair can be completed before the remaining phases are disconnected due to overload, and it is not necessary to disconnect all phases. The calculation result is: 2100 seconds < 200 seconds + 400 seconds, which obviously does not meet the conditions, so this situation is not applicable.

[0153] when and , it means that during the maintenance process, one of the remaining phases will be disconnected before the faulty phase is repaired. Calculation shows that: 200 seconds + 400 seconds ≤ 2100 seconds and 3900 seconds < 200 seconds + 500 seconds, the first condition is met (600 seconds ≤ 2100 seconds), but the second condition is not met (3900 seconds > 700 seconds). Therefore, this situation is not completely applicable.

[0154] when and , it means that all other phases will be disconnected before the faulty phase is repaired, and the operation of all phases should be stopped immediately. According to the previous calculation, 200 seconds + 400 seconds ≤ 2100 seconds (satisfied) and 3900 seconds ≥ 200 seconds + 500 seconds (also satisfied). This means that before the maintenance personnel can arrive and start to repair the fault on phase A, both phases B and C may be disconnected due to overload. To avoid this from happening, the safest thing to do is to stop the operation of all phases immediately to prevent further damage or potential safety risks.

[0155] The present invention formulates a more reasonable and timely maintenance strategy based on real-time monitoring data and historical maintenance time, thereby minimizing unnecessary downtime and economic losses while ensuring the safety of the power system.

[0156] Example 3: Assuming a three-phase power system, three single-phase voltage transformers are used to measure the zero-sequence voltage of the three-phase circuit in real time. The preset zero-sequence voltage threshold is 10V, and the preset voltage threshold is 220V. Temperature sensors and data acquisition equipment are installed in the system to monitor the real-time temperature and operation data of each phase.

[0157] Step 1: Real-time measurement of the zero-sequence voltage of the three-phase circuit;

[0158] The zero-sequence voltage of the three-phase circuit is obtained in real time through the voltage transformer, assuming that the measured zero-sequence voltage is 12 V. Since 12 V is greater than the preset zero-sequence voltage threshold of 10 V, a phase asymmetric grounding fault warning information is generated, and the operation data of different three-phase lines are obtained.

[0159] Step 2: Determine whether to issue an early warning based on the operating data and the preset voltage threshold;

[0160] The real-time current and voltage of each phase of the three-phase line are collected through the data acquisition equipment. Assume that the real-time voltage of phase A is 230V, and the real-time voltages of phases B and C are 210V and 215V respectively. Since the real-time voltage of phase A, 230V, is greater than the preset voltage threshold of 220V, the ground fault warning information of phase A is generated, and the fault phase disconnection time is calculated based on the operation data.

[0161] Step 3: Obtain the real-time temperature of the normal phase;

[0162] Assume that after the fault phase is disconnected, the real-time temperatures of phase B and phase C are 50°C and 55°C respectively. The real-time temperature disconnection time of the normal phase is calculated based on the real-time temperature.

[0163] Step 4: Calculate the risk time based on the real-time temperature trip time of the normal phase;

[0164] The risk time is calculated by the formula, assuming that the first risk time The second risk time is 30 minutes For 20 minutes.

[0165] Step 5: Calculate the maintenance time based on historical maintenance data;

[0166] Obtain historical maintenance data from the database, assuming that the average maintenance time is 30 minutes, and the average time from the issuance of the warning to the start of maintenance is 10 minutes. The first maintenance time (Dws) is calculated to be 40 minutes, and the second maintenance time (Ews) is 70 minutes.

[0167] Step 6: Process the phase asymmetric grounding fault based on the fault phase disconnection time, risk time and maintenance time;

[0168] Assuming the fault phase disconnection time 25 minutes;

[0169] because ; It means that after the fault phase is disconnected, maintenance can be completed before the remaining phases are disconnected due to overload. It is not necessary to disconnect all phases. The remaining phases can be used to continue operation after the fault phase is disconnected.

[0170] Part of the data in the above formula is calculated by removing the dimension and taking its numerical value. The formula is a formula closest to the actual situation obtained by software simulation of a large amount of collected data; the preset parameters and preset thresholds in the formula are set by technical personnel in this field according to actual conditions or obtained through simulation of a large amount of data.

[0171] Working principle of the present invention:

[0172] The present invention measures the zero-sequence voltage of a three-phase circuit in real time; determines whether to issue an early warning based on the zero-sequence voltage and a preset zero-sequence voltage threshold, and obtains operating data of different three-phase lines; determines whether to issue an early warning based on the operating data and a preset voltage threshold, and calculates the fault phase disconnection time based on the operating data; obtains the real-time temperature of the normal phase, and calculates the normal phase real-time temperature disconnection time based on the real-time temperature; calculates the risk time based on the normal phase real-time temperature disconnection time; calculates the maintenance time based on historical maintenance data; and processes the phase asymmetric grounding fault based on the fault phase disconnection time, the risk time and the maintenance time, thereby solving the technical problem that the prior art only locates the fault interval without performing analysis, resulting in waste of power resources.

[0173] The above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A method for detecting a phase asymmetric grounding fault, characterized in that: include: Step 1: Real-time measurement of the zero-sequence voltage of the three-phase circuit; Determine whether to issue a phase asymmetric ground fault warning based on the zero-sequence voltage and a preset zero-sequence voltage threshold; If yes, then send warning information and obtain the operation data of the three-phase line; if no, then continue to detect and judge; Step 2: Determine whether to issue an early warning based on the operating data and the preset voltage threshold; If yes, an early warning message is sent, and the fault phase disconnection time is calculated based on the operating data; If not, continue to test and judge; Step 3: Obtain the real-time temperature of the normal phase and calculate the real-time temperature breaking time of the normal phase; Step 4: Calculate the risk time based on the real-time temperature trip time of the normal phase; Calculate the maintenance time based on historical maintenance data; Handle phase asymmetric grounding faults based on fault phase disconnection time, risk time, and repair time; The calculating the fault phase breaking time based on the operation data includes: Mark the real-time current of the corresponding phase number as the fault phase current Gi x , after linear normalization, the real-time current fluctuation rate of the fault phase is calculated by the formula: Among them, Gd m is the real-time current fluctuation rate of the fault phase, in A / S, x represents the detection time sequence number of the current or voltage data, and x = 1, 2, 3...m, T is the periodic detection period; The real-time fault phase breaking time Gsl is calculated by the formula m : Where R represents the value of a positive integer that makes inequality (1) true, and the real-time fault phase disconnection time Gsl m The unit is seconds, Dl is the breaking current of the circuit breaker, Gi m is the fault phase current when x=m; The obtaining of the real-time temperature of the normal phase and calculating the normal phase real-time temperature trip time comprises: After the fault phase is disconnected, the real-time temperature of the normal phase is periodically collected through the temperature sensor and marked as Among them, the normal phase refers to the remaining two phases except the faulty phase after the faulty phase is disconnected; The real-time temperature fluctuation rate of the normal phase is calculated by the formula: in, is the real-time temperature fluctuation rate, in units of °C / S, b represents the sequence number of the other two phases in the three-phase circuit except the faulty phase, and b=1, 2, y represents the time sequence number of the real-time temperature of the normal phase, y=1, 2, 3…n; The real-time temperature trip time is calculated based on the real-time temperature fluctuation rate; The real-time temperature trip time is calculated based on the real-time temperature fluctuation rate, including: The normal phase real-time temperature breaking time is calculated by the formula: Where H represents the value of a positive integer that makes inequality (2) true, and the normal phase real-time temperature circuit breaker time The unit is seconds, Dw is the breaking temperature of the circuit breaker, is the real-time temperature when y=n; The risk time is calculated based on the normal phase real-time temperature breaking time, including: The risk time is calculated by the formula; wherein the risk time includes: the first risk time and the second risk time; Mark the first risk time as Dfs n , specifically: Mark the second risk time as Efs n , specifically: The calculation of the maintenance time based on the historical maintenance data includes: Obtain historical maintenance data of the three-phase circuit through a database, and obtain the average maintenance time of each single-phase grounding fault and the average time from the issuance of an early warning to the start of maintenance; wherein the database stores maintenance time records of historical faults of the three-phase circuit; The mean maintenance time is marked as Mw, and the mean time from the issuance of the warning to the start of maintenance is marked as Kj; The maintenance time is calculated by a formula; wherein the maintenance time includes: a first maintenance time and a second maintenance time; The first maintenance time is marked as Dws, specifically: Dws = Kj + Mw; The second maintenance time is marked as Ews, specifically: Ews=Kj+2Mw.

2. A method for detecting a phase asymmetric grounding fault according to claim 1, characterized in that: The real-time measurement of the zero-sequence voltage of the three-phase circuit includes: The zero-sequence voltage of the three-phase circuit is obtained in real time through a voltage transformer; wherein the voltage transformer includes: a three-phase five-column voltage transformer or three single-phase voltage transformers.

3. The method for detecting a phase asymmetric grounding fault according to claim 1, characterized in that: The determining whether to perform a phase asymmetric grounding fault warning based on the zero-sequence voltage and a preset zero-sequence voltage threshold comprises: Determine whether the zero-sequence voltage is greater than the preset zero-sequence voltage threshold; if yes, generate phase asymmetric grounding fault warning information; if no, continue to detect and judge; wherein, the preset zero-sequence voltage threshold is set according to the average value of all real-time zero-sequence voltages of the actual three-phase circuit.

4. The method for detecting a phase asymmetric grounding fault according to claim 1, characterized in that: The determining whether to issue an early warning based on the operating data and the preset voltage threshold includes: Determine whether the real-time voltage of each phase in the three-phase line is greater than the preset voltage threshold; if yes, generate ground fault warning information for the corresponding numbered phase; if no, continue monitoring and judgment; wherein, the preset voltage threshold is set according to the average value of all actual three-phase line voltages.

5. The method for detecting a phase asymmetric grounding fault according to claim 1, characterized in that: The processing of the phase asymmetric grounding fault based on the fault phase disconnection time, risk time and maintenance time includes: When Dws<Gsl m +Efs n When the fault phase is disconnected, the normal phase is used to continue operation; When Gsl m +Efs n ≤Dws and Ews<Gsl m +Dfs n When the system is in operation, choose to stop all phases or speed up maintenance; When Gsl m +Efs n ≤Dws and Ews≥Gsl m +Dfs n When the alarm is raised, all phases will be stopped immediately.

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