Transformer substation fault detection system based on intelligent monitoring

Abstract

The invention discloses a transformer substation fault detection system based on intelligent monitoring, and relates to the technical field of electric power, the transformer substation fault detection system comprises a monitoring host and a bottom layer module, the bottom layer module comprises a comprehensive measurement module, a battery inspection module, an insulation detection module, a switching value detection module and an AC measurement module; the alternating-current measuring module is used for detecting an alternating-current incoming line state; the comprehensive measurement module is used for collecting the data volume in the direct current system and uploading the data to the monitoring host through an RS485 interface; the battery inspection module is used for collecting single battery data and protecting power equipment; the switching value detection module is used for monitoring switching value signal input; and the insulation detection module is used for detecting bus insulation and branch insulation and carrying out ground fault detection by adopting an improved differential current method and a complex value wavelet detection method. By improving the differential current method, the transformer substation can detect the grounding fault more comprehensively and quickly, and protective measures are taken in time.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to a substation fault detection system based on intelligent monitoring. Background Art

[0002] With the increase in the number of substations in China and the complexity of substation structures, the structure of substations in China has become increasingly complex, and the stable operation of the power system has become more and more important. As an important part of the DC system, the substation provides reliable power supply for various equipment. However, its power supply range is wide, the network is vulnerable to environmental influences, and various problems such as insulation degradation, grounding faults, communication signal loss, motor phase failure, current imbalance, line fault tripping, and unclear fault location are likely to occur. When the DC system cannot quickly find the fault location after a certain point and is grounded, if insulation deterioration or grounding occurs at another point, it may lead to grounding faults in the power system and even accidents, resulting in large-scale power outages.

[0003] In DC system faults, various faults such as insulation degradation, grounding faults, communication signal loss, motor phase failure, current imbalance, line fault tripping, and unclear fault location always affect the stability and safety of the power system and may cause relatively large losses at any time. However, although there are some substation power comprehensive monitoring systems in the prior art, they all simply monitor one of the faults or simply set up some fault detection modules, protection modules, and monitoring modules, and cannot meet the requirement of comprehensive protection for substations. Therefore, it is very necessary to conduct in-depth research on the DC system, realize the identification of various faults and the protection of lines, substations, distribution transformers, and motors, and comprehensively monitor various indicators of the substation, which is of great significance to the safe and stable operation of the power system. Summary of the Invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a substation fault detection system based on intelligent monitoring to solve the technical problems in the prior art that it is impossible to comprehensively and quickly detect various transformer faults, protect power equipment, and comprehensively monitor various indicators of the substation.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A substation fault detection system based on intelligent monitoring, which includes, a monitoring host and a bottom layer module, and the bottom layer module includes a comprehensive measurement module, a battery inspection module, an insulation detection module, a digital input module, and an AC measurement module; The AC measurement module detects the state of the AC incoming line; The comprehensive measurement module collects the data volume in the DC system and uploads the data to the monitoring host through the RS485 interface; The battery inspection module collects the data of individual batteries and protects the power equipment; The digital input detection module monitors the digital input signals; The insulation detection module detects the bus insulation and branch insulation, and uses the improved differential current method and the complex value wavelet detection method to detect the grounding faults.

[0007] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the detection of the AC incoming line status refers to measuring the AC voltage, AC current, active power, active energy, power factor and grid frequency.

[0008] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the data volume refers to AC measurement: detecting 1 three-phase AC voltage, DC measurement: detecting 3 DC voltages, 2 currents, 1 battery temperature and measuring 1 bus insulation, digital input: using opto-isolation to detect 24 digital inputs, 8 digital outputs.

[0009] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the monitoring of the digital input signals refers to detecting 64 digital signals and 8 relay signal outputs, and uploading the data to the monitoring host through the RS485 interface.

[0010] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the collection of the data of individual batteries refers to collecting the voltage of individual batteries, the temperature of the battery pack and the battery current, and uploading the data to the monitoring host through the RS485 interface.

[0011] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the protection of the power equipment refers to protecting the power equipment through the three-stage overcurrent protection element, overload warning element, zero-sequence current protection element, three-phase primary reclosing and post-acceleration element, starting quick-break protection element, negative-sequence current protection element, zero-sequence voltage protection element, overvoltage protection element, undervoltage protection element, loss-of-voltage protection element, open-phase protection element and PT disconnection protection element.

[0012] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the detection of the bus insulation and branch insulation refers to measuring the bus resistance and branch resistance.

[0013] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the improved differential current method specifically includes: By alternately closing switches K1 and K2 to form a first state and a second state, detecting the leakage current in the first state and the second state, and simultaneously measuring the voltage of the positive pole of the bus to the ground and the voltage of the negative pole of the bus to the ground at this time; Calculate the resistance to the ground by combining the leakage current, the voltage of the positive pole of the bus to the ground, and the voltage of the negative pole of the bus to the ground in the first state and the second state.

[0014] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the detection method of complex-valued wavelet specifically includes: Obtain wavelet bases by expanding and translating the wavelet mother function; Use a third-order B-spline wavelet filter for multi-scale decomposition to obtain branch currents; Perform wavelet transform on the branch currents to extract the amplitude and phase of the low-frequency current.

[0015] As a preferred solution of the substation fault detection system based on intelligent monitoring according to the present invention, wherein: the grounding fault detection refers to defining a resistance threshold and preliminarily judging the grounding fault according to the resistance to the ground; Set a fault threshold, calculate the root mean square value of the amplitude of the low-frequency current, and judge the grounding fault.

[0016] The beneficial effects of the present invention are as follows: By improving the differential current method, accurate positioning and rapid response to the grounding faults of the positive and negative poles of the DC system are achieved, the problems of fuzzy positioning and high misjudgment rate are solved, enabling the substation to detect grounding faults more comprehensively and quickly, and taking protection measures in a timely manner, improving the safety and stability of power equipment; Through the complex-valued wavelet detection method, the problem that the detection of low-frequency signals is inaccurate due to excessive harmonic components in the ring network system is solved, achieving rapid and accurate determination of grounding faults, enhancing the sensitivity and real-time performance of fault detection in a complex power grid environment, enabling the substation to detect various faults more comprehensively and quickly, and being able to better protect power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 It is a schematic diagram of a substation fault detection system based on intelligent monitoring; Figure 2It is the operation logic diagram of a three-stage overcurrent protection element; Figure 3 It is the operation logic diagram of an overload warning element; Figure 4 It is the operation logic diagram of a zero-sequence current protection element, where Fig. 4 (a) is the protection tripping operation logic diagram of the zero-sequence current protection element, and Fig. 4 (b) is the protection warning operation logic diagram of the zero-sequence current protection element; Figure 5 It is the operation logic diagram of a three-phase primary reclosing and post-acceleration element; Figure 6 It is the operation logic diagram of a reclosing protection element; Figure 7 It is the operation logic diagram of a post-acceleration element; Figure 8 It is the operation logic diagram of a starting instantaneous protection element; Figure 9 It is the operation logic diagram of a negative-sequence current protection element; Figure 10 It is the operation logic diagram of an overvoltage protection element; Figure 11 It is the operation logic diagram of a zero-sequence voltage protection element, where Figure 11 (a) is the protection tripping operation logic diagram of the zero-sequence voltage protection element, Figure 11 (b) is the protection warning operation logic diagram of the zero-sequence voltage protection element; Figure 12 It is the operation logic diagram of an undervoltage protection element; Figure 13 It is the operation logic diagram of a phase-break protection element, where Figure 13 (a) is the protection warning operation logic diagram of the phase-break protection element, Figure 13 (b) is the protection tripping operation logic diagram of the phase-break protection element; Figure 14 It is the operation logic diagram of a middle PT disconnection protection element; Figure 15 It is the schematic diagram of branch insulation detection for the improved differential current method in the middle; Specific implementation manner

[0019] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific implementation manner of the present invention in detail with reference to the accompanying drawings of the specification.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0021] Second, the "one embodiment" or "embodiment" referred to herein means a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or alternative embodiments that are mutually exclusive with other embodiments.

[0022] Referring to Figures 1 to 15 , a substation fault detection system based on intelligent monitoring is provided, including the following steps: The substation power comprehensive monitoring system for new energy power stations proposed by the substation fault detection system based on intelligent monitoring in this application is code-named: BH-GZG8. The substation power comprehensive monitoring system fully considers the diversity of power system applications. The monitoring host and the underlying data acquisition unit adopt a modular design concept, and the host and the underlying modules can be freely combined. The underlying modules include a comprehensive measurement module, a battery inspection module, an insulation detection module, a digital input module, and an AC measurement module. The monitoring equipment specification table is shown in Table 1.

[0023]

[0024] The AC measurement module (BH-JL-2) completes the detection of the AC incoming line status; the monitor is configured with a comprehensive measurement module (BH-ZH-2) to complete the monitoring of the AC and bus status; the monitor can be optionally equipped with a battery inspection module (BH-XJ-19 or BH-XJ-55) to complete the voltage and status detection of up to 220 batteries; the monitor can be optionally equipped with a digital input module (BH-KG-64), and the user can customize the digital input; the monitor can be optionally equipped with an insulation detection module (BH-JY-64) to complete the detection of bus insulation and branch insulation, and an improved differential current method and a complex-valued wavelet detection method are used for grounding fault detection.

[0025] The monitor supports communication with the UPS, collects UPS data and status; the monitor monitors the AC incoming line status, battery status, bus status, battery charge and discharge status, module status, and UPS status; provides two-way three-phase AC data monitoring; has the functions of bus insulation and branch insulation monitoring. Bus grounding and branch grounding fault alarms; has the function of digital input alarm, and each digital input can be customized. It has switch output dry contacts, preset dry contact closing events, and each dry contact can be freely configured; the upper-level communication has RS232 and RJ45 communication interfaces, and provides two communication protocols, MODBUS and IEC61850 (optional), and can be connected to the power station automation system.

[0026] The following will expand in detail for each module.

[0027] The AC measurement module (BH-JL-2) is a multi-functional AC measurement module designed for systems with a capacity below 1000A. It can measure AC voltage, AC current, active power, active energy, power factor, and grid frequency, and has an RS485 interface for connection to the automation system. AC voltage and DC voltage are prone to interference, so they should be routed separately and not mixed with other data lines. Before connecting, it is still necessary to carefully confirm the wiring to prevent danger. When connecting the secondary wiring of the current transformer for current sampling, it is necessary to ensure that it is carried out under power-off conditions, and disconnection is not allowed during the power-on process. If the CT ratio of the primary current transformer is selected to be below 50:5, the measurement accuracy of JLCL-2 will be reduced. Therefore, it is recommended to use a CT ratio of 50:5 or above. At this time, even when measuring a small current, it will not affect the measurement accuracy. The AC measurement module (BH-JL) is used to measure the current and voltage signals of a three-phase four-wire system, and can also be used to measure the case of a single-phase power supply connection. At this time, attention should be paid to connecting the neutral line for the voltage.

[0028] It should also be noted that: by means of independent wiring, the impact of electromagnetic interference on signal transmission can be reduced, ensuring the accuracy and stability of data. For example, avoiding routing high-current or high-voltage lines parallel to data communication lines can reduce the interference of external electromagnetic fields on the measurement results.

[0029] The comprehensive measurement module (BH-ZH-2) is responsible for collecting data in the DC system, including 1 three-phase AC voltage, 3 DC voltages, 2 currents, 1 battery temperature, and 1 bus insulation, and uploading the data to the monitoring host through the RS485 interface. The main functions of the comprehensive measurement module (BH-ZH-2) are as follows: AC measurement: Detect 1 three-phase AC voltage. DC measurement: Detect 3 DC voltages, 2 currents, 1 battery temperature, and measure 1 bus insulation.

[0030] Digital Input: Detect 24 digital inputs. Digital Output: Provide 8 digital outputs. The digital input detection of the integrated measurement module (BH-ZH-2) uses optocoupler isolation detection technology to detect 24 digital inputs: Each digital input uses independent optocoupler isolation; The pull-up resistor uses a 1kΩ resistor to ensure that the input current ≤ 5mA (the optocoupler input current range: 2~10mA); The optocoupler input voltage range is 12V~24V, and a current-limiting resistor is used to prevent overvoltage damage; The optocoupler output terminal is connected to the GPIO pin of the microcontroller (MCU), and the optocoupler output signal is converted to CMOS level (5V) through a pull-up resistor; A TVS diode is connected in parallel at each input terminal to suppress transient voltage spikes (the maximum clamping voltage ≤ 67V), ensuring that its reverse cut-off voltage ≥ 36V and the peak pulse current ≥ 114A to adapt to the 12~24V optocoupler input current range and protect the optocoupler isolation circuit; A rectifier diode is connected in series to prevent damage to the circuit by reverse voltage at the input terminal; A parallel RC filter (R = 100Ω, C = 0.1μF) is used to eliminate high-frequency noise; Software debouncing of the input signal is performed by the MCU (for example, continuously sample 3 times to confirm the signal stability, and the sampling interval is 2ms); The digital input loop and the main control circuit use independent power supplies, and power isolation is achieved through a DC-DC isolation module (such as LTM8065), and the isolation voltage ≥ 1500V. When the switch is closed, the input current (such as 2~10mA) flows through the light-emitting diode (LED) of the optocoupler, generating an optical signal; The photo-triggered phototransistor conducts (outputs a low level) or cuts off (outputs a high level) to achieve the electro-optical-electrical isolation conversion, and the switch state of the optocoupler transistor on the output side is converted to CMOS level (5V) through a pull-up resistor; An RC filter (R = 100Ω, C = 0.1μF) is used to eliminate high-frequency noise, and mechanical contact jitter is eliminated through multiple samplings (such as 3 consecutive samplings) to ensure signal stability; The CMOS level (5V) is input to the controller (such as a single-chip microcomputer) to complete the digital input detection. The digital input node should be a passive node. The 1st to 24th pins of the wiring terminal marked with "Digital Input" on the integrated measurement module (BH-ZH-2) are the 1st to 24th digital inputs, and the wiring terminal marked with "COM" is the common terminal of the digital input. The integrated measurement module (BH-ZH-2) collects AC voltage and DC voltage. These collected signals are strong and prone to interference. The wiring should be separate and not mixed with other data lines. Although the integrated measurement module (BH-ZH-2) has taken measures to prevent incorrect signal connection during design, it is still necessary to carefully confirm the wiring before connection to prevent danger. When there are other insulation test equipment in the system or when performing equipment withstand voltage test, disconnect the connection between the 32nd pin of the "control bus voltage" sampling terminal and the ground. Before power-on, carefully check the wiring of the current sensor. If it is found that the temperature of the current sensor is high, immediately disconnect the power supply and check the wiring. Pay attention to the direction of the primary current of the current sensor.

[0031] The digital input detection module (BH-KG-64) is responsible for monitoring the input of digital signals and uploading the data to the monitoring host through the RS485 interface. The main functions of the digital input detection module (BH-KG-64) are as follows: detecting 64 digital signals and outputting 8 relay signals.

[0032] It should also be noted that: carefully checking the wiring not only helps prevent electrical faults and equipment damage, but also ensures the safety of operators. For example, before making any electrical connection, appropriate tools and instruments should be used to verify that the circuit is correct, and ensure that all connections are firm and meet safety standards. A 1kΩ pull-up resistor is used to ensure that the input current ≤ 5mA, which can prevent the optocoupler light-emitting diode from burning out due to overcurrent, and at the same time meet the requirements of the normal operating current range of the optocoupler. The maximum clamping voltage of the TVS diode ≤ 67V, and the reverse breakdown voltage ≥ 36V, which can effectively suppress the damage of transient voltage spikes to the input end of the optocoupler and protect the components of the subsequent circuit. The series rectifier diode can prevent the reverse voltage from passing through the input end of the optocoupler and avoid mis-triggering of the optocoupler or damage to the light-emitting diode caused by reverse current. The RC filter (R = 100Ω, C = 0.1μF) can attenuate high-frequency noise and reduce the interference of electromagnetic interference on the optocoupler input signal. The MCU samples continuously for 3 times to confirm that the signal is stable, which can eliminate the mis-triggering caused by mechanical contact jitter and improve the reliability of the digital input signal. The DC-DC isolation module achieves an isolation voltage of ≥ 1500V, which can completely cut off the electrical connection between the input circuit and the main control circuit and prevent high-voltage signals from entering and damaging the control circuit.

[0033] The battery inspection module (BH-XJ-19 / 55) collects data of individual batteries, including battery voltage, battery pack temperature, and battery current, and uploads the data to the monitoring host through the RS485 interface, realizing the functions of protecting the line / substation / distribution transformer / motor and comprehensively monitoring various indicators of the substation. The main functions of the battery inspection module (BH-XJ-19 / 55) are as follows: three-stage overcurrent protection; overload alarm; zero-sequence current protection; three-phase primary reclosing and post-acceleration; starting instantaneous trip protection; negative-sequence current protection; zero-sequence voltage protection; overvoltage protection; undervoltage protection, etc.

[0034] The three-stage current protection realizes the general current protection of conventional lines or components, and all functions can be conveniently switched on and off by the user through the control word. When the line trips due to a fault, the reclosing action occurs and the line recloses on the faulty line or is manually closed on the faulty line, the post-acceleration protection can quickly cut off the faulty line. The action logic diagram of the three-stage overcurrent protection element is as follows Figure 2 As shown in the figure, in the figure, IGLset is the overcurrent protection current setting value; TGLset is the time limit value of the overcurrent protection; IN is the protection current of any phase.

[0035] The action logic diagram of the overload alarm element is asFigure 3 As shown in the figure: In the figure, IGFHset is the over-load protection current setting value; TGFHset is the limit value during over-load protection; IN is the protection current of any phase.

[0036] The operation logic diagram of the zero-sequence current protection element is as Figure 4 shown; in the figure, I0set is the zero-sequence current protection current setting value; TXLset is the limit value during zero-sequence current protection.

[0037] The operation logic diagram of the three-phase primary reclosing and post-acceleration element is as Figure 5 shown; the operation logic diagram of the reclosing protection element is as Figure 6 shown; in order to ensure the reliability and stability of the reclosing, a charging condition is set. Only after the charging condition is met can the reclosing be started. The so-called acceleration means that when a line fails for the first time, the protection acts selectively and then recloses. If the reclosure is on a permanent fault, after the circuit breaker closes, the protection is accelerated to act and the fault is instantaneously cut off, regardless of whether the first action has a time limit. When the line fault protection trips and the reclosing acts, if the fault still exists, at this time the acceleration protection acts as a non-delay protection (acceleration time limit) to instantaneously cut off the fault to avoid the system and equipment from being impacted. The operation logic diagram of the post-acceleration element is as Figure 7 shown; in the figure, IJSset is the acceleration protection current setting value; TJSset is the limit value during acceleration action; IN is the protection current of any phase.

[0038] The operation logic diagram of the starting instantaneous trip protection element is as Figure 8 shown; in the figure, ISDset is the starting instantaneous trip setting value; TSDset is the limit value during starting instantaneous trip; IN is the protection current of any phase; the starting instantaneous trip is designed specifically for motor protection. When the starting instantaneous trip protection is put into operation, the over-current protection and over-load protection are prohibited during the starting time. They are automatically enabled after the starting time ends.

[0039] The operation logic of the negative-sequence current protection element is as Figure 9 shown; for the asymmetric faults occurring inside the motor, it is used to protect the motor's open-phase and current imbalance faults. In the figure, I2set is the negative-sequence current setting value; TFXset is the limit value during the first-stage negative-sequence current protection.

[0040] The function logic diagram of the over-voltage protection element is as Figure 10 shown; in the figure, UGYset is the over-voltage protection voltage setting value; TGYset is the limit value during over-voltage protection; ULN is any line voltage Uab or Ubc. If over-voltage alarm is selected, the switch position is not judged.

[0041] The function logic diagram of the zero-sequence voltage protection element is as Figure 11As shown in the figure; in the figure, ULYset is the setting value of the zero-sequence voltage protection voltage; TLYset is the limit value during zero-sequence voltage protection; U0 is the zero-sequence voltage value; if zero-voltage alarm is selected, the switch position is not judged.

[0042] The logic diagram of the under-voltage protection element is as follows Figure 12 As shown in the figure: in the figure, UDYset is the setting value of the low-voltage protection voltage; TDYset is the limit value during low-voltage protection; ULN is any line voltage Uab or Ubc.

[0043] This device is equipped with loss-of-voltage protection. When both line voltages are less than the setting value of the loss-of-voltage protection, there is no current, and the protection will act after reaching the setting delay. To prevent the loss-of-voltage protection from malfunctioning due to the three-phase loss of voltage on the bus when the device is powered on, the loss-of-voltage protection needs to be charged before starting. The outlet can be selected to trip or alarm. The charging criterion: greater than 10% of the loss-of-voltage protection voltage setting value and maintain for 10 seconds to complete charging.

[0044] This device is equipped with open-phase protection. When any phase voltage is open-phased and reaches the delay, the protection will act. The outlet can be selected to trip or alarm. If the outlet is selected to trip, the outlet criterion adds that the switch position is in the closed position. The logic diagram of the open-phase protection element is as Figure 13 shown; in the figure, TDXset is the limit value during open-phase protection; any line voltage is Uab or Ubc.

[0045] The action logic diagram of the PT disconnection protection element is as Figure 14 shown: in the figure, U1 is the calculated positive-sequence voltage, U2 is the calculated negative-sequence voltage, and IN is the protection current of Ia and Ic. The PT disconnection delay is 10 seconds.

[0046] Input the control loop disconnection control word, and the device will detect whether the control loop is disconnected and upload the remote signal. If it is exited, the detection will not be performed.

[0047] The insulation detection module (BH-JY-64) is responsible for monitoring the bus insulation and branch insulation, and uploading the data to the monitoring host through the RS485 interface. The main functions of the insulation detection module (BH-JY-64) are as follows: Detect the insulation of 2 sections of the bus, and the measurement error of the bus resistance: ≤±5%. Detect the insulation of 64 branches, and the measurement error of the branch resistance: ≤±10%. The inspection time: ≤60S. In the DC system fault, the DC grounding fault is one of the most common and difficult faults at present. In order to detect the grounding fault more accurately, the insulation detection module (BH-JY-64) adopts the improved differential current method and the complex-valued wavelet detection method.

[0048] Among them, the improved differential current method specifically includes: By alternately closing switches K1 and K2, two independent detection states are formed (the first state: K1 closed / K2 open, the second state: K2 closed / K1 open). According to the differential current method of the unbalanced bridge, by judging the polarity of the collected leakage current, it is possible to distinguish whether it is positive grounding, negative grounding or no grounding, and the branch grounding resistance value can be obtained by using the bus voltage and the leakage current values of each branch. The improved differential current method is as Figure 15 shown, where K1 and K2 are the upper and lower arm switches respectively, the positive-to-ground resistance of branch 1 to branch n, is the negative-to-ground resistance from branch 1 to branch n.

[0049] The preliminary detection of the insulation detection module using the improved differential current method includes: judging the polarity of the collected leakage current to distinguish whether it is positive grounding, negative grounding or no grounding, and the branch grounding resistance value can be obtained by using the bus voltage U and the leakage current values of each branch.

[0050] Furthermore, the improved differential current method specifically includes: by grounding the positive and negative of the branch, first closing switch K1 and opening switch K2 to activate the positive pole circuit, forming a differential current path, and detecting the leakage current of the branch at this time , and at the same time, the voltage of the positive pole of the bus to the ground needs to be measured .

[0051] Then open K1 and close K2 to activate the negative pole circuit, form a differential current path and detect the leakage current of the branch at this time , and the partial voltage of the negative pole of the bus to the ground at this time .

[0052] According to the value of the bus voltage , the switch state is automatically switched (from K1 closed to K2 closed or vice versa). When it is detected that the fluctuation of the bus voltage U exceeds ±5% (for example, when the reference voltage is 240V, drops to 228V or rises to 252V), through the relay switching of switches K1 and K2 to disconnect and close, ensuring that the two states are alternately executed.

[0053] It should also be noted that: when the bus voltage fluctuates by more than ±5%, the switch state is automatically switched, which can monitor the development of the grounding fault in real time and ensure that the detection circuit works within the safe voltage range.

[0054] In the first state, the positive pole circuit is formed, and the voltage of the positive pole of the bus to the ground and the voltage of the negative pole of the bus to the ground satisfy: the bus voltage is equal to the sum of the voltage of the positive pole to the ground and the voltage of the negative pole to the ground; in the second state, the negative pole circuit is formed, and the voltage of the positive pole of the bus to the ground and the voltage of the negative pole of the bus to the ground also satisfy: the bus voltage is equal to the sum of the voltage of the positive pole to the ground and the voltage of the negative pole to the ground.

[0055] In the first state, the leakage current of the branch is driven by the voltage of the positive pole of the bus to the ground. Therefore, the relationship that the product of the leakage current and the positive resistance to the ground is equal to the voltage of the positive pole of the bus to the ground is satisfied. In the second state, the leakage current of the branch is driven by the voltage of the negative pole of the bus to the ground. Therefore, the relationship that the product of the leakage current and the negative resistance to the ground is equal to the voltage of the negative pole of the bus to the ground is satisfied. Based on the fact that the bus voltage is equal to the sum of the voltage of the positive pole to the ground and the voltage of the negative pole to the ground, and substituting the product of the leakage current and the positive resistance to the ground equal to the voltage of the positive pole of the bus to the ground according to the voltage division principle, an expression for calculating the resistance to the ground is obtained.

[0056] Combining the leakage current, the voltage of the positive pole of the bus to the ground, and the voltage of the negative pole of the bus to the ground in the first state and the second state to calculate the resistance to the ground, the expression is as follows:

[0057] Wherein, is the positive resistance to the ground of the branch , is the negative resistance to the ground of the branch , is the branch index; In different switch states, after detecting the leakage current of the corresponding branch, the positive voltage of the bus to the ground, and the negative voltage of the bus to the ground, the positive resistance value to the ground and the negative resistance value to the ground of any branch can be calculated.

[0058] Based on the historical positive resistance value to the ground and negative resistance value to the ground, a resistance threshold is defined (such as 600 kΩ). If the positive resistance value to the ground or the negative resistance value to the ground is lower than the resistance threshold, it is preliminarily determined that there is a grounding fault.

[0059] It should also be noted that: setting a 600 kΩ resistance threshold can effectively distinguish normal insulation resistance from faulty grounding resistance, and avoid misjudging faults caused by slight resistance decrease due to environmental humidity changes.

[0060] Furthermore, the detection method of the insulation detection module using complex-valued wavelets specifically includes: the corresponding expressions of the wavelet mother function in the time domain and the frequency domain are:

[0061] In the formula, is the wavelet mother function in the time domain, is the wavelet mother function in the frequency domain, is the normalization constant (usually taking the reciprocal of the square root value of ), is the center frequency (usually taking to ensure zero mean) to control the center frequency position and zero mean of the wavelet, is the complex exponential term, providing oscillation characteristics, is the Gaussian envelope, restricting the time range, is the independent variable of the signal on the time axis, is the width of the Gaussian envelope (usually taking the reciprocal of the center frequency), which affects the frequency domain bandwidth and time domain localization, is the frequency variable, representing the frequency components of the signal; It should also be noted that: the complex-valued wavelet mother function combines the Gaussian envelope with the complex exponential, which can achieve high-resolution analysis in both the time-frequency domain and accurately extract the characteristic frequency components of the signal.

[0062] The wavelet basis is obtained by expanding and translating the wavelet mother function:

[0063] where, is the specific wavelet basis function obtained by scaling and translation , is the scale factor; represents the translation factor; is the time domain wavelet mother function; For a specific frequency , setting , then the wavelet transform of the signal under the component of the specific frequency is:

[0064] where, represents the given frequency of the signal to be extracted; and are integers; is the discrete time series; , are the time points on the discrete time axis; the above formula represents the wavelet transform of the component with frequency at the moment for the sampled signal; the sequence contains all the amplitude and phase information of this component, and the phasor can be obtained from it to extract the characteristics of this component.

[0065] The existence of the loop network significantly increases the harmonic components in the branch current of the DC system, thereby reducing the low-frequency components and lowering the signal-to-noise ratio. Therefore, directly extracting the low-frequency components is challenging and the extraction results are not accurate enough. For this reason, a method of indirectly extracting and eliminating the harmonic components of the branch current can be adopted.

[0066] The branch leakage current is decomposed 3 times at multiple scales using a third-order B-spline wavelet filter, decomposing the signal into 3 layers of scale coefficients and wavelet coefficients. Among them, the first layer corresponds to low frequency (below 0.5 Hz), the second layer corresponds to the fundamental frequency (50 Hz to 60 Hz), and the third layer corresponds to the second harmonic (100 Hz to 120 Hz). The scale coefficients (low-frequency components) are retained and harmonics of the third order and above (such as 150 Hz and 200 Hz) are filtered out. The decomposed signal includes low-frequency current, fundamental frequency components, and second harmonic components. After third-order B-spline wavelet filtering, noise and harmonics of the third order and above are filtered out, and the remaining main components are low-frequency current components and fundamental wave components, which may also contain second harmonic components. Let the branch current be , including the following components:

[0067] Among them, is the low-frequency current, is the fundamental frequency component, is the second harmonic component; The real parts of the fundamental frequency component and the second harmonic component are separated from the branch current through wavelet transform: Set the target frequency, calculate the corresponding wavelet transform coefficients, and retain the target frequency components (the real parts of the fundamental frequency component and the second harmonic component) through threshold truncation (for example, the amplitude threshold is 0.1 A); In this mixed signal is very large, so it is not suitable for directly extracting the relatively weak low-frequency component , the second harmonic component and the fundamental wave component can be extracted first, and the low-frequency current is obtained by subtracting the extracted fundamental frequency component and the second harmonic component from the branch current signal. This method overcomes the inaccuracy of directly extracting low-frequency components when the harmonic content in the branch is too high. The amplitude (i.e., signal strength) and phase (i.e., the relative time difference between the signal and the reference signal) of the extracted low-frequency current can be used to determine whether there is a grounding fault in the DC system: Calculate the root mean square value (RMS) of the amplitude of the low-frequency current, set a fault threshold (for example, 0.05 A) based on the root mean square value (RMS) of the amplitude of the historical low-frequency current. If the root mean square value (RMS) of the low-frequency current is greater than the fault threshold, it is determined that there is a grounding fault; Therefore, the detection method based on complex-valued wavelets can accurately detect the grounding fault in the ring network DC system.

[0068] It should also be noted that: Through the multi-scale decomposition of the third-order B-spline wavelet, the low-frequency, fundamental frequency and harmonic components can be effectively separated, avoiding the interference of high-frequency harmonics in the ring network system on the detection of low-frequency components. Setting an amplitude threshold of 0.1 A can accurately retain the target frequency components, filter out irrelevant noise and high-order harmonics, and improve the signal-to-noise ratio of the grounding fault characteristic signal. By calculating the RMS value of the low-frequency current and comparing it with the threshold of 0.05 A, the degree of grounding fault can be quantitatively judged, avoiding the risk of misjudgment caused by subjective judgment. Adopting a dual verification mechanism of the improved differential current method and complex-valued wavelet detection can improve the accuracy of grounding fault location and reduce the phenomenon of false alarms and missed reports.

[0069] In summary, the present invention realizes the accurate positioning and rapid response of the positive and negative pole grounding faults in the DC system through the improved differential current method, solves the problems of fuzzy positioning and high misjudgment rate, enables the substation to detect the grounding fault more comprehensively and quickly, and takes protection measures in time, improving the safety and stability of power equipment; through the complex-valued wavelet detection method, it solves the problem that the detection of low-frequency signals is inaccurate due to excessive harmonic components in the ring network system, realizes the rapid and accurate determination of grounding faults, improves the sensitivity and real-time performance of fault detection in complex power grid environments, enables the substation to detect various faults more comprehensively and quickly, and can better protect power equipment. In various embodiments, the hardware implementation of the technology can directly adopt existing intelligent devices, including but not limited to industrial control computers, personal computers, smart phones, handheld single machines, floor-standing single machines, etc. Its input device preferably adopts a screen keyboard, its data storage and calculation module adopts existing memories, calculators, and controllers, its internal communication module adopts existing communication ports and protocols, and its remote communication adopts existing GPRS networks, the World Wide Web, etc. Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the above-mentioned division of each functional unit and module is used as an example. In actual applications, the above functions can be allocated to different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of the present application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiment and will not be elaborated here. In each embodiment of the present invention, each functional unit can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes in the above embodiment methods of the present invention, it can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned various method embodiments can be implemented.

[0070] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A substation fault detection system based on intelligent monitoring, characterized in that: include, Monitoring host and bottom-level modules, wherein the bottom-level modules include a comprehensive measurement module, a battery inspection module, an insulation detection module, a switch quantity detection module and an AC measurement module; AC measurement module, detects the status of AC incoming line; The integrated measurement module collects the data volume in the DC system and uploads the data to the monitoring host through the RS485 interface; Battery inspection module collects single battery data and protects power equipment; Switch quantity detection module, monitoring switch quantity signal input; Insulation detection module detects busbar insulation and branch insulation, and uses improved differential current method and complex valued wavelet detection method to perform ground fault detection; The complex-valued wavelet detection method comprises obtaining a wavelet basis by expanding and translating a wavelet mother function, performing multi-scale decomposition using a third-order B-spline wavelet filter to obtain branch currents, and performing wavelet transform on the branch currents to extract the amplitude and phase of the low-frequency current.

2. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The detection of the AC incoming line status refers to measuring the AC voltage, AC current, active power, active electric energy, power factor and grid frequency.

3. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The data volume refers to AC measurement: detection of 1 three-phase AC voltage, DC measurement: detection of 3 DC voltages, 2 currents, 1 battery temperature and measurement of 1 bus insulation, switch input: use optical coupler isolation to detect 24 switch inputs and 8 switch outputs.

4. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The monitoring of switch signal input refers to detecting 64 switch signals and 8 relay signal outputs, and uploading the data to the monitoring host through the RS485 interface.

5. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The collecting of single cell data refers to collecting single cell voltage, battery pack temperature and battery current, and uploading the data to the monitoring host through the RS485 interface.

6. The substation fault detection system based on intelligent monitoring as claimed in claim 5, characterized in that: The protection of power equipment refers to protecting power equipment through three-stage overcurrent protection elements, overload alarm elements, zero-sequence current protection elements, three-phase primary reclosing and post-acceleration elements, starting quick-break protection elements, negative-sequence current protection elements, zero-sequence voltage protection elements, overvoltage protection elements, undervoltage protection elements, loss of voltage protection elements, phase loss protection elements and PT line break protection elements.

7. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The detection of busbar insulation and branch insulation refers to measuring busbar resistance and branch resistance.

8. The substation fault detection system based on intelligent monitoring according to claim 1, characterized in that: The improved differential current method specifically includes: By alternately closing switches K1 and K2, a first state and a second state are formed, leakage currents in the first state and the second state are detected, and the voltage between the positive pole of the bus and the ground and the voltage between the negative pole of the bus and the ground are measured at the same time; The ground resistance is calculated by combining the leakage current in the first state and the second state, the bus positive pole to ground voltage and the bus negative pole to ground voltage.

9. The substation fault detection system based on intelligent monitoring according to claim 8, characterized in that: Conducting ground fault detection means defining a resistance threshold and making a preliminary judgment on the ground fault based on the resistance to ground; Set the fault threshold, calculate the RMS value of the low-frequency current amplitude, and determine the ground fault.

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