Method and system for analyzing the action of unbalanced voltage protection of 10kV shunt capacitor device

Abstract

This invention discloses a method and system for analyzing the unbalanced voltage protection action of a 10kV parallel capacitor bank, relating to the field of unbalanced voltage protection technology. The method includes analyzing the tripping situation of the capacitor bank; conducting on-site test diagnosis and calculating the three-phase unbalanced voltage; and performing simulation analysis of the three-phase unbalanced protection action. By systematically analyzing the tripping situation of the 10kV parallel capacitor bank, combined with on-site tests and precise three-phase unbalanced voltage calculations, this invention accurately identifies the root cause—the non-short-circuiting of the neutral point and the discharge coil neutral point—effectively avoiding false tripping, significantly improving the reliability of the protection device, reducing equipment maintenance costs, and extending its service life. It also provides clear operational guidance for maintenance personnel, ensuring the stable operation and continuous power supply of the power system. When conducting fault analysis and diagnosis, primary equipment should be analyzed from the outside in to ensure comprehensiveness.

Description

Technical Field

[0001] This invention relates to the field of unbalanced voltage protection technology, and in particular to a method and system for analyzing the operation of unbalanced voltage protection for 10kV parallel capacitor banks. Background Technology

[0002] The primary function of parallel capacitors is to improve the power factor by providing capacitive reactive power, thereby reducing losses and increasing system voltage. This study addresses an incident where a three-phase unbalanced voltage protection system tripped during the switching process of a 10kV parallel capacitor bank. Through experimental diagnosis and theoretical calculations, a comprehensive analysis determined that the protection tripped because the neutral points of the capacitors and the discharge coil were not short-circuited. PSCAD was used to simulate the unbalanced voltage values ​​under both short-circuited and non-short-circuited conditions. The simulation results under the non-short-circuited condition were largely consistent with the protection waveform data, reproducing the protection tripping process. The simulation also showed that a short-circuit condition would not trigger the protection trip. Based on the simulation results, relevant conclusions and recommendations are provided.

[0003] Currently, most primary equipment used in AC power systems is inductive, such as transformers, reactors, and voltage transformers. This makes the entire power system inductive, consuming a large amount of reactive power and reducing the system's power factor. To improve the power factor, the most common approach is to connect capacitor banks in parallel on the low-voltage busbars of substations. This compensates for reactive power, thereby improving the load's power factor and voltage quality. Therefore, the safe and reliable operation of capacitor banks is a crucial aspect of substation operation and maintenance, especially in key substations or areas with special power quality requirements. However, with the widespread adoption of parallel capacitor banks, the occurrence of abnormal tripping of capacitor banks is also increasing.

[0004] This invention addresses a "tripping immediately upon activation" incident involving a 10kV parallel capacitor bank. It conducts a detailed fault diagnosis and analysis of the tripping situation, incorporating protection waveform recordings, background SOE files, on-site inspections, and electrical equipment test analysis results. Simulation verification was performed using electromagnetic transient PSCAD software, ultimately determining the cause of the capacitor bank tripping and providing a reference for handling abnormal tripping issues in parallel capacitor banks. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the problem to be solved by this invention is: how to analyze the accident situation of "tripping immediately upon connection" in 10kV parallel capacitor devices.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for analyzing the unbalanced voltage protection action of a 10kV parallel capacitor bank, including analyzing the tripping situation of the capacitor bank; performing on-site test diagnosis and three-phase unbalanced voltage calculation; and performing simulation analysis of the three-phase unbalanced protection action.

[0008] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor bank described in this invention, the analysis of capacitor bank tripping includes the case where the 10kV parallel capacitor bank trips immediately upon activation. By retrieving the SOE file from the substation's backend, the operating status of the parallel capacitor bank before tripping is checked. If it shows that the parallel capacitor bank was in normal operation before tripping, then it is checked whether the integrated automation upgrade work has modified the primary components. If not, on-site testing and diagnosis are performed.

[0009] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor device described in this invention, the on-site test diagnosis includes analysis based on the wiring diagram of the parallel capacitor device. The causes of the three-phase voltage imbalance tripping fault include internal capacitor faults causing large capacitance deviations, internal winding faults in the discharge coil, and reactor faults. If the tripping upon activation is not caused by internal capacitor faults causing large capacitance deviations, internal winding faults in the discharge coil, or reactor faults, then a three-phase unbalanced voltage calculation analysis is performed to determine the cause of the tripping upon activation.

[0010] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor bank described in this invention, the three-phase unbalanced voltage calculation includes, after initially determining that the capacitor tripping is not caused by primary equipment parameters, analyzing the cause of the three-phase unbalanced voltage action of the capacitor bank, and calculating and verifying the three-phase unbalanced voltage value under actual operating conditions using the equipment parameters within the bank, the bus voltage value, and the three-phase unbalanced voltage protection principle. The initial unbalanced voltage is expressed as:

[0011]

[0012] Among them, U P For the initial unbalanced voltage, U O U is the neutral point offset voltage. A U B U C For the three-phase voltage of the 10kV bus, Y A Y B Y C This is the admittance value of the three-phase capacitor.

[0013] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor bank described in this invention, the three-phase unbalanced voltage calculation further includes importing the actual bus voltage value and capacitance admittance value into the calculation U. P The unbalanced voltage value is calculated based on the transformation ratio of the discharge coil. It is then determined whether the unbalanced voltage value exceeds the protection setting value. If the unbalanced voltage value does not exceed the protection setting value, a simulation analysis of the three-phase unbalanced protection action is performed to analyze the cause of the tripping immediately upon activation.

[0014] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor bank described in this invention, the three-phase unbalanced protection action simulation analysis includes: if the cause of the immediate tripping situation cannot be found through on-site test diagnosis and three-phase unbalanced voltage calculation, then checking whether the neutral point of the capacitor and the neutral point of the discharge coil are short-circuited, measuring the primary impedance value of the three-phase discharge coil, calculating the initial unbalanced voltage based on the impedance value, converting the measured discharge coil impedance value into an admittance value, and simultaneously substituting it into the initial unbalanced voltage formula along with the bus voltage value to obtain the initial unbalanced voltage U. P Determine the initial unbalanced voltage U P The relationship between the unbalanced voltage value within the protection recording and the initial unbalanced voltage U P If the unbalanced voltage value is greater than the value recorded in the protection waveform, the tripping accident is caused by the protection action due to the failure to short-circuit the neutral points of the two circuits.

[0015] As a preferred embodiment of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor device described in this invention, the three-phase unbalanced protection action simulation analysis further includes clarifying the cause of protection tripping and using electromagnetic transient PSCAD software to perform simulation modeling analysis under two operating conditions: the capacitor neutral point and the discharge coil neutral point are not short-circuited and short-circuited.

[0016] Another objective of this invention is to provide a system for analyzing the unbalanced voltage protection operation of a 10kV parallel capacitor bank. This system solves the problem of analyzing the unbalanced voltage protection operation of a 10kV parallel capacitor bank by constructing such an analysis system.

[0017] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a 10kV parallel capacitor bank unbalanced voltage protection action analysis system, comprising a trip analysis module, a diagnostic module, and a simulation analysis module; the trip analysis module is used to analyze the tripping situation of the capacitor bank; the diagnostic module is used to perform on-site test diagnosis and three-phase unbalanced voltage calculation; and the simulation analysis module is used to perform three-phase unbalanced protection action simulation analysis.

[0018] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the unbalanced voltage protection action analysis method for a 10kV parallel capacitor device as described above.

[0019] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method for analyzing the unbalanced voltage protection action of a 10kV parallel capacitor bank.

[0020] The beneficial effects of this invention are as follows: The 10kV parallel capacitor bank unbalanced voltage protection action analysis method provided by this invention, through systematic analysis of the tripping situation of the 10kV parallel capacitor bank, combined with field tests and accurate three-phase unbalanced voltage calculations, accurately identifies the root cause as the neutral point and discharge coil neutral point not being short-circuited. This effectively avoids false tripping, significantly improves the reliability of the protection device, reduces equipment maintenance costs and extends service life, and provides clear operational guidance for maintenance personnel, ensuring the stable operation and continuous power supply of the power system. This invention, through field comparison and simulation calculations, determines that the protection malfunction is caused by incorrect primary wiring of the capacitor bank. When the discharge coil and capacitor neutral point are not short-circuited, the zero-sequence voltage mainly reflects the impedance imbalance of the primary winding of the discharge coil, making it impossible to monitor the capacitor's operating status. Only when the discharge coil and capacitor neutral point are short-circuited, because the capacitor impedance is much smaller than that of the discharge coil, and after being connected in parallel with the discharge coil, the zero-sequence voltage mainly reflects the capacitor capacitance imbalance. Therefore, in order to detect internal defects in the capacitor equipment in advance, it is necessary to short-circuit the neutral points of both. Even when the discharge coil and capacitor neutral point are short-circuited, the zero-sequence voltage increases with the greater the impedance imbalance of the discharge coil. Therefore, when selecting a discharge coil, in addition to conducting tests on turns ratio and volt-ampere characteristics, three-phase discharge coils with relatively small impedance deviations should be selected for use to reduce the initial unbalanced voltage of the capacitor bank. Regarding this tripping incident, the equipment still tripped immediately upon being switched on, even without changing the primary capacitor wiring and ensuring correct secondary wiring during the integrated automation upgrade. Therefore, when conducting fault analysis and diagnosis, primary equipment should be analyzed systematically from the outside in to ensure comprehensiveness. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The flowchart shows the unbalanced voltage protection action analysis method for a 10kV parallel capacitor device provided in the first embodiment of the present invention.

[0023] Figure 2 Wiring diagram of the parallel capacitor device for the unbalanced voltage protection action analysis method of the 10kV parallel capacitor device provided in the first embodiment of the present invention.

[0024] Figure 3 The diagram shows the three-phase unbalanced voltage protection principle of the 10kV parallel capacitor device unbalanced voltage protection action analysis method provided in the first embodiment of the present invention.

[0025] Figure 4 The diagram shows an incorrect wiring diagram of a field parallel capacitor device for the unbalanced voltage protection action analysis method of a 10kV parallel capacitor device provided in the first embodiment of the present invention.

[0026] Figure 5 This is a structural diagram of the unbalanced voltage protection action analysis system for a 10kV parallel capacitor device provided in the second embodiment of the present invention.

[0027] Figure 6 The PSCAD simulation model diagram of the unbalanced voltage protection action analysis method for a 10kV parallel capacitor device provided in the third embodiment of the present invention is shown.

[0028] Figure 7 The waveform diagram of three-phase unbalanced voltage under short-circuit condition for the unbalanced voltage protection action analysis method of 10kV parallel capacitor device provided in the third embodiment of the present invention.

[0029] Figure 8 The waveform diagram of the three-phase unbalanced voltage under the non-short-circuit condition of the unbalanced voltage protection action analysis method for the 10kV parallel capacitor device provided in the third embodiment of the present invention. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Example 1

[0033] Reference Figures 1-4This is the first embodiment of the present invention, which provides a method for analyzing the unbalanced voltage protection action of a 10kV parallel capacitor bank, including: analyzing the tripping situation of the capacitor bank; performing on-site test diagnosis and three-phase unbalanced voltage calculation; and performing simulation analysis of the three-phase unbalanced protection action.

[0034] S1. Analyze the tripping situation of the capacitor bank.

[0035] A 35kV substation underwent a comprehensive protection automation upgrade. After the on-site work was completed, maintenance personnel encountered an immediate tripping issue when activating the 10kV parallel capacitor bank. On-site protection messages indicated a three-phase voltage imbalance protection trip. Protection waveform recordings showed a three-phase voltage imbalance value of 18V, while the protection device's three-phase voltage imbalance setting was 9V with a timing delay of 0.2s. Reviewing the substation's SOE (System on Equip) files revealed that the parallel capacitor bank had been operating normally before the tripping. Furthermore, this automation upgrade only addressed the secondary equipment wiring and did not modify the primary circuitry.

[0036] If the parallel capacitor bank was operating normally before the trip, and the primary circuit was not modified during the integrated automation upgrade, then an on-site test and diagnosis should be performed.

[0037] S2. Conduct on-site testing and diagnosis, and calculate the three-phase unbalanced voltage.

[0038] S2.1 On-site test diagnosis.

[0039] The 10kV parallel capacitor bank, model TBB10-450 / 450-AKW, includes a reactor, surge arrester, discharge coil, and capacitors, with the capacitors connected in a single star configuration. The wiring diagram for the parallel capacitor bank is shown below. Figure 2 As shown.

[0040] Based on the wiring diagram of the parallel capacitor bank, the main possible causes of the "three-phase voltage imbalance trip" fault are as follows: 1) Internal capacitor faults causing large capacitance deviations; 2) Faults in the internal windings of the discharge coil, such as winding breakdown or damage; 3) Reactor faults, such as winding short circuits, open circuits, or insulation damage. All of these situations can lead to significant changes in the secondary voltage detected by the discharge coil, causing the open delta voltage to exceed the set value, thus triggering the three-phase voltage imbalance protection and ultimately tripping the capacitor bank. In addition, external damage to the primary equipment or incorrect wiring may also cause the protection device to trip.

[0041] Therefore, after the incident, in order to investigate the specific cause of the tripping accident, the maintenance personnel first inspected the appearance of the parallel capacitor bank upon arrival at the site, and no obvious fault points were found. Subsequently, high-voltage tests were conducted on each piece of equipment within the system, and the diagnostic results are shown in Tables 1 to 5.

[0042] Table 1. Capacitance test values ​​(μF)

[0043]

[0044] Table 2. Test values ​​of DC resistance of reactors (mΩ)

[0045]

[0046] Table 3 Reactor Reactance Values ​​(mH)

[0047]

[0048] Table 4 Discharge Coil Turns Ratio

[0049]

[0050] Table 5. Overall Insulation and Withstand Voltage Tests for Three-Phase A, B, and C

[0051]

[0052]

[0053] If the cause of "tripping immediately upon activation" is unrelated to the parameters of the primary equipment, then a three-phase unbalanced voltage calculation and analysis should be performed to determine the cause of the tripping immediately upon activation.

[0054] According to the test data in Tables 1 to 5, the test data of each device in the parallel capacitor bank all meet the requirements of relevant national, industry, and enterprise standards, including GB 50150-2016 "Standard for Acceptance Testing of Electrical Equipment in Electrical Installation Engineering", DL / T596-2021 "Preventive Testing Procedures for Power Equipment", and Q / CSG1206007-2017 "Maintenance Testing Procedures for Power Equipment". Therefore, it can be preliminarily determined that the reason for the "immediate tripping upon activation" of the capacitor bank in this tripping incident is unrelated to the parameters of the primary equipment.

[0055] S2.2 Calculation of three-phase unbalanced voltage.

[0056] After initially determining that the capacitor tripping was not caused by primary equipment parameters, in order to further analyze the cause of the three-phase unbalanced voltage action of the capacitor bank, the three-phase unbalanced voltage value under actual operating conditions was calculated and verified by using the equipment parameters and bus voltage values ​​of the bank, combined with the three-phase unbalanced voltage protection principle.

[0057] The schematic diagram of three-phase unbalanced voltage protection in GB / T11024.3-2019 "Parallel capacitors for AC power systems with nominal voltage above 1000V - Part 3: Protection of parallel capacitors and parallel capacitor banks" is as follows. Figure 3 As shown.

[0058] The capacitor is connected in an ungrounded star configuration, with a discharge coil connected in parallel across the capacitor terminals. Their secondary sides are connected in an open delta configuration. When a capacitor fails, its capacitance changes, causing an imbalance in the capacitance of related parts of the capacitor bank. This capacitance imbalance leads to a neutral point shift, resulting in an unbalanced voltage output through the open delta. Ideally (when the bus voltage, three-phase reactance, and capacitance values ​​are identical), the open delta voltage is 0V. When a capacitor or discharge coil fails, the open delta voltage increases, exceeding the set value and triggering the protection system. This protection is called open delta unbalanced voltage protection. It is simple to wire, highly sensitive, and has strong phase indication capabilities, clearly identifying the faulty phase, facilitating rapid fault location and handling, and effectively protecting the capacitor bank. However, because the three-phase bus voltage and capacitor parameters can differ, the setting value must consider the initial voltage imbalance caused by the three-phase system and equipment parameters to avoid malfunctions. According to the literature "Estimation of Initial Unbalance Value for Parallel Capacitor Bank Protection", the initial unbalance voltage UP, which is equal to 3 times the neutral point offset voltage U0, can be calculated using the following formula (1):

[0059]

[0060] Among them, U P For the initial unbalanced voltage, U O U is the neutral point offset voltage. A U B U C U is the three-phase voltage of the 10kV bus. A =10.8×10 3 ∠0°V, U B =10.2×10 3 ∠241°V, U C =10.2×10 3 ∠119°V, Y A Y B Y C Y is the admittance value of the three-phase capacitor. A =jωC A Y B =jωC B Y C =jωC C Three-phase capacitor value C A C B CC See Table 1.

[0061] By importing the actual bus voltage and capacitance admittance values ​​into the calculation U P The unbalanced voltage value is calculated based on the transformation ratio of the discharge coil. It is then determined whether the unbalanced voltage value exceeds the protection setting value. If the unbalanced voltage value does not exceed the protection setting value, a simulation analysis of the three-phase unbalanced protection action is performed to analyze the cause of the "tripping immediately upon activation" situation.

[0062] By importing the actual bus voltage and capacitor admittance values ​​into the calculation, UP is approximately equal to 188V. Based on the turns ratio of the discharge coil, the unbalanced voltage is calculated to be 2.96V, which does not exceed the protection setting value (9V).

[0063] S3. Perform simulation analysis of three-phase unbalanced protection actions.

[0064] Through experimental diagnosis of each primary device within the capacitor bank and theoretical calculation of the unbalanced voltage value, no related cause was found. Therefore, a more detailed investigation was conducted on the primary and secondary wiring of the parallel capacitor bank. By comprehensively comparing the on-site wiring of the parallel capacitor bank with the unbalanced voltage protection schematic diagram, it was found that the actual on-site primary wiring did not short-circuit the neutral point of the capacitor and the neutral point of the discharge coil, as follows: Figure 4 As shown.

[0065] According to the capacitor wiring diagram, when the neutral point of the capacitor and the neutral point of the discharge coil are not short-circuited, the open delta voltage detected on the secondary side of the discharge coil is not affected by the imbalance of the three-phase capacitor values, but is related to the primary impedance value of the discharge coil.

[0066] To verify whether the tripping incident was caused by the failure to short-circuit the neutral points of the capacitor and the discharge coil, the primary impedance of the three-phase discharge coil was first measured, and the initial unbalanced voltage was calculated based on the impedance values. The discharge coil impedance values ​​are shown in Table 6. The measured discharge coil impedance values ​​were converted into admittance values, and then substituted into equation (1) along with the bus voltage value for calculation. The initial unbalanced voltage UP was found to be 22V, which is slightly greater than the unbalanced voltage value (18V) recorded in the protection waveform. Therefore, it was initially suspected that the tripping incident was caused by the failure to short-circuit the neutral points of the capacitor and the discharge coil, resulting in the protection action.

[0067] Table 6. Discharge coil impedance test values ​​(mΩ)

[0068]

[0069] Example 2

[0070] Reference Figure 5This is the second embodiment of the present invention, which differs from the previous embodiment in that it provides a 10kV parallel capacitor device unbalanced voltage protection action analysis system, including: a trip analysis module 100, a diagnostic module 200 and a simulation analysis module 300.

[0071] The trip analysis module 100 is used to analyze the tripping situation of the capacitor bank.

[0072] The diagnostic module 200 is used for on-site test diagnosis and three-phase unbalanced voltage calculation.

[0073] The simulation analysis module 300 is used to perform simulation analysis of three-phase unbalanced protection actions.

[0074] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0075] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0076] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0077] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0078] Example 3

[0079] Reference Figures 6-8 The third embodiment of the present invention differs from the first two embodiments in that it is used to verify and explain the technical effects adopted in the present invention, so as to verify the real effect of the method.

[0080] To further clarify the cause of the protection trip, simulation modeling and analysis were conducted using electromagnetic transient PSCAD software under two operating conditions: no short circuit and short circuit between the capacitor neutral point and the discharge coil neutral point. Based on... Figure 1 Build a model of the parallel capacitor bank and import the relevant parameters of the reactor, capacitor, discharge coil, and other equipment, such as... Figure 6 As shown.

[0081] The capacitor and discharge coil neutral point are short-circuited.

[0082] In the simulation model, Ea, Eb, and Ec are used to monitor the voltage across the discharge coil, respectively. The three-phase unbalanced voltage (3 times the zero-sequence voltage 3U0) is calculated using the vector summation of the three-phase voltages. The vector summation of Ea, Eb, and Ec is calculated using the built-in Summing / DifferencingJunctions component in PSCAD, and the effective value of the three-phase unbalanced voltage E0 is calculated using the RMS component. The final simulation waveform is shown below. Figure 7As shown.

[0083] In the simulation, the circuit breaker's closing time was set to 0.1s. The simulation waveform shows that 0.1s after the circuit breaker closes, the unbalanced voltage reaches its peak due to harmonics or inrush current. After 0.2s, the unbalanced voltage stabilizes at around 149V. Based on the discharge coil turns ratio, the three-phase unbalanced voltage 3U0 is calculated to be 2.34V, which is basically consistent with the theoretical calculation value (2.96V). Simultaneously, the waveform shows that after the capacitor is switched on, neither the unbalanced voltage value nor the fluctuation time exceeds the protection's setting value and timing limit. Therefore, under this operating condition, the protection will not trip.

[0084] Furthermore, the impedance of the primary coil of the discharge coil was varied to investigate whether its imbalance would cause protection operation. With the capacitor and the neutral point of the discharge coil short-circuited, simulations were performed with the impedance values ​​of the B-phase discharge coil set to 5000Ω and 6000Ω, yielding calculated unbalanced voltage values ​​of 3.5V and 4.35V. These results show that the imbalance of the discharge coil does indeed affect the unbalanced voltage value, but the impact is limited and will not cause protection operation under normal wiring and with sufficient margin in the protection settings. However, to further reduce the impact of the discharge coil on the unbalanced voltage, an impedance test of the primary coil should be performed when selecting the discharge coil, and three-phase discharge coils with similar impedances should be selected for use in combination.

[0085] The capacitor and discharge coil neutral points are not short-circuited.

[0086] After short-circuiting the neutral points of the capacitor and discharge coil in the model, a simulation of the un-short-circuited operating condition was performed. Without changing other parameter settings, the waveform of the effective value E0 of the three-phase unbalanced voltage was obtained as follows: Figure 8 As shown.

[0087] The unbalanced voltage value is stable at around 1187V from the simulation waveform. According to the discharge coil turns ratio, 3U0 is about 18.7V, which is close to the data (18V) monitored by the protection waveform and the actual calculated value (22V).

[0088] Therefore, through simulation analysis of the two operating conditions, the protection waveform recorded under the actual field conditions basically matches the simulation calculation results, verifying the correctness of the aforementioned conjecture and confirming that the tripping accident was caused by the failure to short-circuit the neutral point of the capacitor and the neutral point of the discharge coil. Simulation also verified that short-circuiting the neutral point of the capacitor and the neutral point of the discharge coil would not trigger the protection operation.

[0089] Based on the diagnostic analysis of the causes of capacitor bank protection actions, the following conclusions were drawn:

[0090] The main purpose of three-phase unbalanced voltage protection is to detect faults in equipment such as capacitors, reactors, and discharge coils in a timely manner. After the protection is activated, the relevant equipment in the device should be tested and diagnosed first.

[0091] The invention ultimately determined, through on-site comparison and simulation calculations, that the malfunction of the protection system was caused by incorrect primary wiring of the capacitor bank. When the discharge coil and capacitor neutral point are not short-circuited, the zero-sequence voltage primarily reflects the impedance imbalance of the primary winding of the discharge coil, making it impossible to monitor the capacitor's operating status. Only when the discharge coil and capacitor neutral point are short-circuited, because the capacitor's impedance is much smaller than that of the discharge coil, and it is connected in parallel with the discharge coil, does the zero-sequence voltage primarily reflect the capacitance imbalance of the capacitor. Therefore, to detect internal defects in the capacitor bank in advance, it is necessary to short-circuit the neutral points of both components during operation.

[0092] Even when the discharge coil and capacitor neutral point are short-circuited, the zero-sequence voltage will increase as the impedance imbalance of the discharge coil increases. Therefore, when selecting a discharge coil, in addition to conducting tests on turns ratio and volt-ampere characteristics, three-phase discharge coils with small impedance deviations should be selected as much as possible to reduce the initial unbalanced voltage of the capacitor device.

[0093] Regarding this tripping incident, the equipment still tripped immediately upon being switched on, even though the primary wiring of the capacitors was not changed and the secondary wiring was ensured to be correct during the integrated automation upgrade. Therefore, when conducting fault analysis and diagnosis, primary equipment should be analyzed one by one from the outside in to ensure comprehensiveness.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of analyzing the operation of an unbalanced voltage protection of a 10 kV shunt capacitor device, characterized by: include, Analyze the tripping situation of the capacitor bank; Perform on-site testing and diagnosis, and calculate three-phase unbalanced voltage. Simulation analysis of three-phase unbalanced protection action was performed. The on-site test diagnosis includes analysis based on the wiring diagram of the parallel capacitor device. The causes of the three-phase voltage imbalance tripping fault include internal capacitor faults causing large capacitance deviations, faults in the internal windings of the discharge coil, and reactor faults. If the immediate tripping upon activation is not caused by an internal capacitor fault leading to a large capacitance deviation, a fault in the internal winding of the discharge coil, or a fault in the reactor, then a three-phase unbalanced voltage calculation and analysis should be performed to determine the cause of the immediate tripping upon activation. The three-phase unbalanced voltage calculation includes, after initially determining that the capacitor tripping was not caused by primary equipment parameters, analyzing the reasons for the three-phase unbalanced voltage action of the capacitor bank, and calculating and verifying the three-phase unbalanced voltage value under actual operating conditions using equipment parameters, bus voltage values, and the three-phase unbalanced voltage protection principle. The initial unbalanced voltage is expressed as follows: in, U P The initial unbalanced voltage, U O This is the neutral point offset voltage. U A 、U B 、U C This refers to the three-phase voltage of the 10kV bus. Y A 、Y B 、 Y C This is the admittance value of the three-phase capacitor; The three-phase unbalanced voltage calculation also includes importing the actual bus voltage value and capacitance admittance value into the calculation. U P The unbalanced voltage value is calculated based on the turns ratio of the discharge coil. It is then determined whether the unbalanced voltage value exceeds the protection setting value. If the unbalanced voltage value does not exceed the protection setting value, a simulation analysis of the three-phase unbalanced protection action is performed to analyze the cause of the tripping immediately upon activation. The simulation analysis of the three-phase unbalanced protection action includes, if the cause of the immediate tripping issue cannot be found through on-site testing and three-phase unbalanced voltage calculation, checking whether the neutral point of the capacitor and the neutral point of the discharge coil are short-circuited, measuring the primary impedance value of the three-phase discharge coil, calculating the initial unbalanced voltage based on the impedance value, converting the measured discharge coil impedance value into an admittance value, and simultaneously substituting it into the initial unbalanced voltage formula along with the bus voltage value to obtain the initial unbalanced voltage. U P Determine the initial unbalanced voltage U P The relationship between the unbalanced voltage value in the protection recording and the initial unbalanced voltage... U P If the unbalanced voltage value is greater than the value recorded in the protection waveform, the tripping accident is caused by the protection action due to the failure to short-circuit the neutral points of the two circuits.

2. The 10 kV shunt capacitor device unbalanced voltage protection action analysis method of claim 1, wherein: The analysis of capacitor bank tripping situations includes cases where a 10kV parallel capacitor bank trips immediately upon activation. By retrieving the SOE file from the substation's backend, the operating status of the parallel capacitor bank before the trip is checked. If the parallel capacitor bank was in normal operation before the trip, it is checked whether the integrated automation upgrade work has modified the primary components. If not, on-site testing and diagnosis are conducted.

3. The 10 kV shunt capacitor device unbalanced voltage protection action analysis method of claim 2, wherein: The simulation analysis of the three-phase unbalanced protection action also includes identifying the cause of the protection trip and using electromagnetic transient PSCAD software to perform simulation modeling analysis under two operating conditions: the capacitor neutral point and the discharge coil neutral point are not short-circuited and are short-circuited.

4. A system for analyzing the operation of an unbalanced voltage protection of a 10 kV shunt capacitor device according to any one of claims 1 to 3, characterized in that: It includes a trip analysis module (100), a diagnostic module (200), and a simulation analysis module (300). The trip analysis module (100) is used to analyze the tripping situation of the capacitor bank; The diagnostic module (200) is used for on-site test diagnosis and three-phase unbalanced voltage calculation; The simulation analysis module (300) is used to perform simulation analysis of three-phase unbalanced protection actions.

5. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the method for analyzing the unbalanced voltage protection action of a 10kV parallel capacitor device as described in any one of claims 1 to 3.

6. A computer readable storage medium having stored thereon a computer program, characterized in that: When the computer program is executed by the processor, it implements the steps of the method for analyzing the unbalanced voltage protection action of the 10kV parallel capacitor device as described in any one of claims 1 to 3.

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