A longitudinal differential protection method suitable for unmeasurable load branch of power distribution network

Abstract

The application provides a longitudinal differential protection method suitable for an unmeasurable load branch of a power distribution network, and relates to the technical field of the power distribution network, which comprises the following steps: collecting a first voltage and current at a measuring point of a protected line under normal operation, and converting the first voltage and current into a first positive sequence component; starting protection devices at both ends of the protected line based on the first positive sequence component, collecting a second voltage and current at the measuring point after a fault, and converting the second voltage and current into a second positive sequence component; calculating a pseudo-unbalanced power and a setting value based on the first positive sequence component and the second positive sequence component; and if the pseudo-unbalanced power is greater than the setting value, the protection devices at both sides of the protected line cut off the fault line at the same time. The application can naturally shield the influence of the access of the unmeasurable branch on the difficult setting of the line protection, the pseudo-unbalanced power obviously changes when an internal fault occurs in the line, the pseudo-unbalanced power is obviously smaller than the setting value for an external fault, and the external fault can be avoided without misoperation.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and specifically to a longitudinal differential protection method applicable to unmeasurable load branches in power distribution networks. Background Technology

[0002] Currently, the large-scale integration of distributed power sources and numerous unmeasurable load branches into distribution networks has resulted in complex network structures and diverse operating modes. Traditional three-stage current protection suffers from problems such as difficulty in setting, narrow protection range, and misjudgment of fault direction, making it difficult to balance sensitivity and speed of protection. With the development of communication technology, longitudinal protection, due to its advantages of fast action speed and high sensitivity, provides a new approach for distribution network protection research.

[0003] Existing longitudinal differential protection mainly compares the current phase and amplitude on both sides of the line. When the line is operating normally, the current characteristics at both ends are the same; when a fault occurs, a significant differential current appears at both ends of the line, and the protection trips when it exceeds the set value. However, traditional longitudinal differential protection is only applicable to a single line. After an unmeasurable load branch is connected to the grid via a T-connection, differential current will be detected at both ends of the distribution line during normal operation and during faults outside the zone, leading to a decrease in the sensitivity and reliability of the differential protection. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a longitudinal differential protection method applicable to unmeasurable load branches in distribution networks, which provides protection against faults both within and outside the protection zone.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first voltage and current at the measurement point under normal operation is collected in the protected line, and the first voltage and current are converted into the first positive sequence component. Based on the first positive sequence component, the protection devices at both ends of the protected line are activated, and the second voltage and current at the measurement point after the fault are collected and converted into the second positive sequence component. The pseudo-unbalanced power and setting value are calculated based on the first positive sequence component and the second positive sequence component. If the unbalanced power exceeds the set value, the protection devices on both sides of the protected line will simultaneously disconnect the faulty line.

[0006] In some embodiments, the step of acquiring the first voltage and current at the measurement point under normal operation in the protected line and converting the first voltage and current into a first positive sequence component includes: Several measuring points are set at both ends and in the middle of the protected line; The voltage and current signals are simultaneously collected at each measurement point using a voltage transformer, and the sum is used to obtain the first voltage and current. The first voltage and current are converted into a first positive sequence component using the symmetrical component method, and the first positive sequence component is sent to the protection device.

[0007] In some embodiments, the process of activating the protection devices at both ends of the protected line based on the first positive sequence component includes: If the first positive sequence component is less than the preset start value, the voltage and current at all measurement points under normal operation will be re-acquired. In response to the first positive sequence component being greater than a preset start value, the protection device activates the protection at both ends of the protected line.

[0008] In some embodiments, the process of acquiring the second voltage and current at the measurement point after the fault and converting the second voltage and current into a second positive sequence component includes: The voltage and current signals at each measurement point after a fault are collected by a voltage transformer, and the sum is used to obtain the second voltage and current. The second voltage and current are converted into a second positive sequence component using the symmetrical component method, and the second positive sequence component is sent to the protection device.

[0009] In some embodiments, the process of calculating the pseudo-unbalanced power and setting value based on the first positive sequence component and the second positive sequence component includes: The quasi-unbalanced power is calculated based on the line impedance, the first positive sequence component, and the second positive sequence component. The set value is greater than the historical maximum pseudo-unbalanced power during normal line operation and less than the historical minimum pseudo-unbalanced power during line faults.

[0010] In some embodiments, if the unbalanced power is less than the set value, the protection devices on both sides of the protected line are locked, and the first voltage and current at the measurement point under normal operation are collected again in the protected line, and the first voltage and current are converted into the first positive sequence component.

[0011] In some embodiments, the formula for the pseudo-unbalanced power is as follows: ; In the formula, The positive sequence voltage component represents the measurement point i before the fault. This represents the positive sequence voltage component at measurement point i after the fault. This represents the positive sequence current component at measurement point i before the fault. This represents the positive sequence current component at measurement point i after the fault.

[0012] This invention proposes a longitudinal differential protection system for unmeasurable load branches, comprising: The circuit includes several measurement points, several protection devices, and a distributed photovoltaic power source; Measurement points are set on both sides of the protected line. One end of each measurement point is connected to the protection device, and the other end is connected to the protected line. A separate measurement point is set up between the distributed photovoltaic power source and the protected line.

[0013] This invention proposes a computer device, comprising: At least one processor; and a memory storing a computer program executable on the processor, wherein the processor, when executing the program, performs the steps of the longitudinal differential protection method applicable to unmeasurable load branches in a distribution network.

[0014] This invention proposes a computer-readable storage medium storing a computer program that, when executed by a processor, performs the steps of a longitudinal differential protection method applicable to unmeasurable load branches in a distribution network.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a longitudinal differential protection method applicable to unmeasurable load branches in distribution networks. The method includes: collecting the first voltage and current at the measurement point under normal operation in the protected line, and converting the first voltage and current into a first positive sequence component; activating the protection devices at both ends of the protected line based on the first positive sequence component, collecting the second voltage and current at the measurement point after the fault, and converting the second voltage and current into a second positive sequence component; calculating the pseudo-unbalanced power and setting value based on the first and second positive sequence components; if the pseudo-unbalanced power is greater than the setting value, the protection devices on both sides of the protected line simultaneously disconnect the faulty line.

[0016] This invention can naturally shield the impact of unmeasurable branch access on the difficulty of setting line protection, and has a certain resistance to transition resistance. When an internal fault occurs in the line, the pseudo-unbalanced power changes significantly, much greater than the setting value, and has better sensitivity than other traditional protection schemes; for external faults, the pseudo-unbalanced power is significantly less than the setting value, and can avoid false tripping due to external faults. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0018] Figure 1 The present invention provides a flowchart of a longitudinal differential protection method applicable to unmeasurable load branches in a distribution network.

[0019] Figure 2 The power distribution system diagram of the longitudinal differential protection system for unmeasurable load branches provided by the present invention.

[0020] Figure 3 A schematic diagram of the structure of an embodiment of the computer device provided by the present invention.

[0021] Figure 4 This is a schematic diagram of an embodiment of the computer-readable storage medium provided by the present invention.

[0022] Figure 5 The positive sequence equivalent network diagram of the longitudinal differential protection system for unmeasurable load branches provided by the present invention.

[0023] Figure 6 The equivalent circuit diagram of the linear constant impedance model of the longitudinal differential protection system for the unmeasurable load branch provided by this invention.

[0024] Figure 7 The equivalent circuit diagram of the fault system within the zone of the longitudinal differential protection system for the unmeasurable load branch provided by the present invention.

[0025] Figure 8 This is a logic diagram of an embodiment of a longitudinal differential protection method for unmeasurable load branches in a distribution network provided by the present invention.

[0026] Figure 9 The simulation verification diagram of the external fault of the longitudinal differential protection system for the unmeasurable load branch provided by the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.

[0028] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0029] This invention proposes a longitudinal differential protection method applicable to unmeasurable load branches in distribution networks. Please refer to [link / reference]. Figure 1 ,include: The first voltage and current at the measurement point under normal operation is collected in the protected line, and the first voltage and current are converted into the first positive sequence component. Based on the first positive sequence component, the protection devices at both ends of the protected line are activated, and the second voltage and current at the measurement point after the fault are collected and converted into the second positive sequence component. The pseudo-unbalanced power and setting value are calculated based on the first positive sequence component and the second positive sequence component. If the unbalanced power exceeds the set value, the protection devices on both sides of the protected line will simultaneously disconnect the faulty line.

[0030] When the protected line is in normal operation, the first voltage and current data will be collected at the measurement point to ensure that the acquired data truly reflects the normal operation of the line. The collected first voltage and current data is then converted into the first positive sequence component, which presents the electrical characteristics of the line under normal operating conditions.

[0031] When a line fault occurs, the second voltage and current after the fault are quickly collected at the measurement point. The electrical parameters change, and the second voltage and current data record these abnormal conditions, converting them into a second positive-sequence component. By comparing this second positive-sequence component with the first positive-sequence component, the differences in the electrical characteristics of the line before and after the fault are revealed.

[0032] The simulated unbalanced power reflects the degree of power imbalance caused by a fault in the line; the setting value is a pre-set safety threshold and an important standard for judging the severity of the fault.

[0033] In some embodiments, please refer to Figure 1 The step of acquiring the first voltage and current at the measurement point under normal operation in the protected line and converting the first voltage and current into a first positive sequence component includes: Several measuring points are set at both ends and in the middle of the protected line; The voltage and current signals are simultaneously collected at each measurement point using a voltage transformer, and the sum is used to obtain the first voltage and current. The first voltage and current are converted into a first positive sequence component using the symmetrical component method, and the first positive sequence component is sent to the protection device.

[0034] Voltage transformers accurately capture and convert the complex voltage and current information in a line into measurable signals. By summing the signals collected from various measurement points, the first voltage and current are obtained, which comprehensively reflect the overall electrical characteristics of the line during normal operation.

[0035] After obtaining the initial voltage and current, the complex initial voltage and current can be decomposed into positive-sequence, negative-sequence, and zero-sequence components using the symmetrical component method, from which the first positive-sequence component is extracted. The first positive-sequence component reflects the electrical characteristics of the symmetrical portion of the line during normal operation and is an important basis for judging whether the line is in a healthy state. Finally, the converted first positive-sequence component is promptly sent to the protection device, allowing the device to understand the normal operating parameters of the line in advance. This enables the device to quickly and accurately judge and act in the event of a subsequent fault, ensuring the safe and stable operation of the power system.

[0036] In some embodiments, please refer to Figure 1 The process of activating the protection devices at both ends of the protected line based on the first positive sequence component includes: If the first positive sequence component is less than the preset start value, the voltage and current at all measurement points under normal operation will be re-acquired. In response to the first positive sequence component being greater than a preset start value, the protection device activates the protection at both ends of the protected line.

[0037] After obtaining the first positive sequence component, it is carefully compared with the preset start-up value. This preset start-up value is determined after extensive experimentation and verification using actual operating data, taking into account factors such as the line's rated parameters, operating environment, and various possible operating conditions. It is a crucial threshold for determining whether the line needs to activate the protection device. The start-up value must be greater than the maximum load current fluctuation that the line may experience during normal operation to avoid erroneous activation of the protection device due to load fluctuations. The current change start-up value is generally set to 0.2 times the rated current. For lines with drastic load changes, the setting value can be appropriately increased, with a range of 0.1 to 0.5 times the rated current. For protection devices involving zero-sequence current, the start-up value must be greater than the maximum zero-sequence unbalanced current that the line may experience during normal operation, with a setting range of 0.1 to 0.5 times the rated zero-sequence current.

[0038] If the first positive sequence component is less than the preset starting value, this indicates that the line is currently in normal operation and there are no abnormal conditions that could cause a fault. At this time, the voltage and current at all measurement points under normal operation are re-acquired. The re-acquisition process is a reconfirmation of the line's operating status. By comparing and analyzing multiple sets of data, the possibility of an abnormality in the first positive sequence component due to errors in individual measurement point data or temporary interference can be further eliminated, ensuring that the judgment of the line status is accurate.

[0039] When the first positive sequence component exceeds the preset activation value, an abnormal situation occurs that affects the safe operation of the line. At this time, the protection device will quickly activate the protection at both ends of the protected line. The simultaneous activation of the protection at both ends is like setting up a double blockade for the faulty line, which can quickly cut off the fault current, prevent the fault from spreading further, avoid more serious damage to the line equipment, and effectively ensure the stable operation of the entire power system, reducing the scope and duration of power outages caused by local faults.

[0040] In some embodiments, please refer to Figure 1 The process of acquiring the second voltage and current at the measurement point after the fault and converting the second voltage and current into a second positive sequence component includes: The voltage and current signals at each measurement point after a fault are collected by a voltage transformer, and the sum is used to obtain the second voltage and current. The second voltage and current are converted into a second positive sequence component using the symmetrical component method, and the second positive sequence component is sent to the protection device.

[0041] When a fault occurs in the protected line, the voltage and current signals collected from various measurement points after the fault are summarized to obtain the second voltage and current, which comprehensively reflects the overall electrical characteristics of the line after the fault occurs. It is significantly different from the data during normal operation and contains key information such as the fault type and location.

[0042] After obtaining the second voltage and current, the symmetrical component method is used to convert them. The symmetrical component method extracts the second positive-sequence component. After conversion, the system quickly sends the second positive-sequence component to the protection device. Upon receiving the second positive-sequence component, the protection device combines it with previously acquired information such as the first positive-sequence component during normal operation to perform comprehensive analysis and judgment, quickly determine the nature and location of the fault, and then take corresponding protective actions to disconnect the faulty line, prevent the fault from escalating, and ensure the safe and stable operation of the power system.

[0043] In some embodiments, please refer to Figure 1 The process of calculating the pseudo-unbalanced power and setting value based on the first positive sequence component and the second positive sequence component includes: The quasi-unbalanced power is calculated based on the line impedance, the first positive sequence component, and the second positive sequence component. The set value is greater than the historical maximum pseudo-unbalanced power during normal line operation and less than the historical minimum pseudo-unbalanced power during line faults.

[0044] When calculating the pseudo-unbalanced power, line impedance reflects the line's resistance to current flow and is related to factors such as line material, length, and cross-sectional area. Using the first positive-sequence component during normal operation and the second positive-sequence component after a fault, combined with the line impedance, the pseudo-unbalanced power is calculated. This reflects the degree of power imbalance before and after the fault and directly reflects the magnitude of the fault's impact on the line. When a short-circuit fault occurs, the impedance at the fault point decreases sharply, leading to a sharp increase in current and consequently a significant rise in the pseudo-unbalanced power. Calculating this power allows for an accurate assessment of the fault's severity.

[0045] Setting a setting value provides a clear operating threshold for the protection device. The setting value must comprehensively consider the pseudo-unbalanced power during normal line operation and fault conditions. It should be greater than the historical maximum pseudo-unbalanced power during normal line operation to avoid maloperation of the protection device during normal operation fluctuations and ensure the stable operation of the power system. Simultaneously, the setting value should be less than the historical minimum pseudo-unbalanced power during line faults to ensure that the protection device can operate promptly and reliably when a fault occurs, quickly disconnecting the faulty line and preventing the fault from escalating. In long-term operation monitoring of a certain line, the maximum pseudo-unbalanced power during normal operation was found to be 110 kW, while the minimum pseudo-unbalanced power during a fault was 500 kW. The setting value is set between 110 kW and 500 kW. This avoids power fluctuations during normal operation and allows for rapid response during faults, ensuring the safe and reliable operation of the power system.

[0046] In some embodiments, please refer to Figure 1 If the unbalanced power is less than the set value, the protection devices on both sides of the protected line will be locked, and the first voltage and current at the measurement point under normal operation will be collected again in the protected line, and the first voltage and current will be converted into the first positive sequence component.

[0047] In power system protection mechanisms, when the simulated unbalanced power is calculated based on the first and second positive sequence components, if the simulated unbalanced power is less than the set value, it indicates that the line may not actually have experienced a serious fault requiring disconnection. In this case, locking the protection devices on both sides of the protected line is a crucial measure. Locking the protection devices means temporarily suppressing their operation, avoiding the disconnection of normal lines or lines with only minor anomalies due to misjudgment, and ensuring the continuity of power supply.

[0048] After the lockout, the system will restart the acquisition of the first voltage and current at the measurement points under normal operating conditions of the protected line. This process is similar to the initial acquisition. Using high-precision voltage and current transformers, high-precision measurement points are strategically placed at both ends and the middle of the line to simultaneously acquire the voltage and current signals at each measurement point. For example, on a 110kV distribution line, the calculated pseudo-unbalanced power is 80 kW, while the preset setting value is 120 kW. Since 80 kW is less than 120 kW, the protection devices on both sides of the line are locked out. Subsequently, the voltage and current at the measurement points under normal operating conditions are reacquired, and the first positive sequence component is obtained after conversion. By continuously monitoring and analyzing this data, the operating status of the line can be more accurately grasped, ensuring that the protection devices can act quickly and accurately in the event of a real fault, thus guaranteeing the safe and stable operation of the power system.

[0049] When an internal fault occurs on the line, the pseudo-unbalanced power changes significantly, much greater than the set value, and has better sensitivity than other traditional protection schemes; for external faults, the pseudo-unbalanced power is significantly less than the set value, and can avoid false tripping due to external faults.

[0050] In some embodiments, please refer to Figure 1 The formula for the pseudo-unbalanced power is as follows: ; In the formula, This represents the positive sequence voltage component at measurement point i before the fault. This represents the positive sequence voltage component at measurement point i after the fault. This represents the positive sequence current component at measurement point i before the fault. This represents the positive sequence current component at measurement point i after the fault.

[0051] The positive-sequence voltage component at the measurement point before the fault represents the symmetrical voltage component at that point during normal line operation. Different types of faults have different effects on voltage; short-circuit faults cause a sharp drop in voltage. Comparing the voltage before and after the fault helps determine the location and type of the fault.

[0052] The positive-sequence voltage component at the measurement point after a fault visually demonstrates the change in the symmetrical voltage component at the measurement point after the fault occurs. Faults cause changes in voltage amplitude and phase, and these changes can be accurately captured. Before the fault, the normal current component at the measurement point is stable and conforms to the line load characteristics. By comparing it with the current after the fault, it can be determined whether the fault caused an abnormal increase or decrease in current.

[0053] The positive-sequence current component at the measurement point after the fault, along with the voltage parameters after the fault and the current parameters before the fault, are used in the calculation of the pseudo-unbalanced power. The calculated pseudo-unbalanced power is an important basis for the protection device to determine whether to operate, and directly affects the reliability and sensitivity of the protection device.

[0054] When the simulated unbalanced power is less than the set value, the line is in normal operation or an external fault has occurred, and the protection on both sides is blocked and does not operate. When the simulated unbalanced power is greater than the set value, it indicates that an internal fault has occurred in the line, and the protection on both sides of the protected line will operate to disconnect the faulty line.

[0055] This invention proposes a longitudinal differential protection system for unmeasurable load branches. Please refer to [link / reference]. Figure 2 ,include: The circuit includes several measurement points, several protection devices, and a distributed photovoltaic power source; Measurement points are set on both sides of the protected line. One end of each measurement point is connected to the protection device, and the other end is connected to the protected line. A separate measurement point is set up between the distributed photovoltaic power source and the protected line.

[0056] Network topology diagram as follows Figure 2 As shown in the figure, the measurement points are 1, 2, and 3, the protection devices CB1 and CB2 at both ends of the protected line, the unmeasurable load branches, and the distributed photovoltaic power source.

[0057] Measuring points 1 and 2 are located on both sides of the protected line, with one end connected to the protection device and the other end connected to the main line. They are used to measure the voltage and current at the protection installation point before and after the fault, convert them into positive-sequence components, and send them to the protection device. Measuring point 3 is connected to the distributed power source at one end and to the main line via line T at the other end. It is used to measure the voltage and current at the distributed power source access point before and after the fault, convert them into positive-sequence components, and send them to the protection devices on both sides.

[0058] One end of protection CB1 is connected to measuring point 1, and the other end is connected to the power grid. One end of protection CB2 is connected to measuring point 2, and the other end is connected to the power line through the power supply line. When a possible fault is detected in the system, the two protections receive the corresponding information from the measuring points and calculate the pseudo-unbalanced power. When the operating equation is satisfied, the two protections operate.

[0059] In some embodiments, please refer to Figure 2 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9This invention provides an illustrative example. Tellegen's second theorem, also known as the quasi-power conservation law, is only affected by the topology. If all unmeasurable load branches within the protected line's range are linear impedances, the two sides of the protected line and the distributed power source are equivalent to network ports. Figure 2 The power distribution system shown can be represented by the equivalent network ports on both sides of the line and the distributed power sources according to Tellegen's second theorem, resulting in the positive-sequence equivalent network of the system, as shown below. Figure 5 As shown: According to Tellegen's second law, for two circuits with n nodes, b branches, identical topologies but different parameters, under the condition that the voltage and current of each branch take the associated reference direction, the following conditions are satisfied: ; In the formula: , and , These represent the voltage and current components of each corresponding branch of the two circuits.

[0060] For example Figure 2 The distribution network wiring diagram shown, after considering the unmeasurable branches as a linear constant impedance model, has the following equivalent circuit diagram: Figure 6 As shown.

[0061] For a protected line, when an external fault occurs, the topology of the internal system of the protected line remains unchanged before and after the fault. According to the positive sequence components, Tellegen's second law can be used as follows: ; ; In the formula: and These are the positive sequence components of voltage and current at measurement point i before the fault; and These are the positive sequence components of voltage and current of the line / branch before the fault; and These are the positive sequence components of voltage and current at measurement point i after the fault; and These are the positive sequence components of voltage and current of the line / branch after the fault.

[0062] For the equivalent linear impedance branches of lines and branches, the following exists: ; Further deduction: ; When an internal fault occurs in the circuit, the equivalent circuit diagram of the system is as follows: Figure 7 As shown, if we consider the fault point as an equivalent branch with infinite impedance before the fault, ensuring that the line topology is consistent before and after the fault, Tellegen's second theorem can still be applied: ; ; have: ; After a fault occurs within the protected area, the internal topology of the protected line changes. This is no longer true, and a certain difference will occur between its left and right ends, such as... As shown. The physical meaning of this difference is a pseudo-power, but it differs from the traditional definition of power. It can be defined as pseudo-unbalanced power, that is... ,at this time The larger size allows for the differentiation between faults within and outside the zone, and can be used to address the pseudo-unbalanced power. This study investigates its application as a criterion for differential protection operation.

[0063] Furthermore, by treating distributed power sources as measurable inputs, only the input and output values ​​of this equivalent multi-port element need to be considered, greatly reducing the logical complexity of protection actions and thus achieving precise protection operation. This paper will focus on the improved Tellegen's Second Theorem to study a new longitudinal differential protection scheme. Tellegen's Second Theorem treats the line as an equivalent multi-port element, considering only the impact of changes in the system topology after a fault on the electrical quantities of the ports, which can naturally shield the impact of the access of unmeasurable branches on the difficulty of line protection setting.

[0064] In this embodiment, when the protection devices on both sides of the protected line determine that differential protection is required, the protection devices on both sides will operate simultaneously to disconnect the faulty line from the system.

[0065] This application provides a longitudinal differential protection method suitable for unmeasurable load branches in a new type of power distribution system, the method comprising: The voltage and current at measuring points 1, 2, and 3 under normal operation are collected, converted into positive sequence components, and sent to the protection device for storage. When the positive sequence current at measuring point 1 is detected When a sudden increase exceeding a certain value indicates a potential fault in the system, the voltage and current at points 1, 2, and 3 after the fault are detected are collected and converted into positive-sequence components, which are then sent to the protection device. Upon receiving all the information, the protection device establishes its operating equations based on Tellegen's second theorem. ; In the formula, This is the proposed unbalanced power setting value; The differential protection will operate based on the operating equation. When the pseudo-unbalance power on the left is less than the setting value, the line is in normal operation or an external fault has occurred, and the protections on both sides are blocked from operating. When the pseudo-unbalance power is greater than the setting value, it indicates an internal fault has occurred on the line, and the protections on both sides of the protected line will operate to disconnect the faulty line.

[0066] The logical structure diagram of this method is as follows: Figure 8 As shown. Detailed implementation method: Determine if a fault has occurred in the system and activate the operating current threshold of the protection at both ends. It should be increased to at least 1.25 times the rated current, that is K is set to 1.25.

[0068] This method requires calculating the quasi-unbalanced power, and the specific formula is as follows: ; In the formula This represents the positive sequence voltage component at measurement point i before the fault. This represents the positive sequence voltage component at measurement point i after the fault. This represents the positive sequence current component at measurement point i before the fault. This represents the positive sequence current component at measurement point i after the fault.

[0069] When a fault occurs within the line area In the formula The fault point is the node voltage before the fault, which is close to the voltages at each measured point before the fault, and has the following characteristics: Then there is There is a set value .

[0070] This setting principle ensures that the differential protection will not maloperate under the three types of unmeasurable loads, and that the protection has high sensitivity.

[0071] When the simulated unbalanced power is greater than the set value, it is determined that a fault has occurred inside the distribution network line containing unmeasurable branches, and the protection on both sides of the line will operate simultaneously to disconnect the faulty line from the system.

[0072] When the simulated unbalanced power is not greater than the set value, it is determined that the line is operating normally or an external fault has occurred. The protection on both sides of the line is locked and does not operate, and the system status continues to be monitored.

[0073] example: according to Figure 2 The power distribution line wiring method shown is used. Different types of faults occur at fault point f at 0.5s. The relationship between Pr and Pset before and after the fault occurs is compared to analyze whether the protection devices on both sides of the line will operate correctly. Simulation verification is performed, as shown in Table 1.

[0074] Table 1 Fault Type Verification Table When a three-phase fault occurs outside the zone, the relationship between Pr and Pset is as follows: Figure 9 .

[0075] It is evident that under normal operating conditions or when an external fault occurs, the protection does not operate when the pseudo-unbalance power is less than the set value. However, when a fault occurs within the line, and different types of faults occur at fault point f, the pseudo-unbalance power exceeds the set value at the instant the fault occurs, causing the protections on both sides of the line to operate simultaneously and disconnect the fault. This proves that the protection can operate correctly under this operating criterion and play its role in protecting the line.

[0076] The system's resistance to transition resistance under this tuning principle is shown in Table 2 below.

[0077] Table 2. Resistance to Transition Resistance As the transition resistance increases, the sensitivity of the protection will gradually decrease until the transition resistance reaches 45 ohms, which is close to the protection action boundary. Therefore, it can be seen that the longitudinal differential protection action principle meets certain requirements for resistance to transition resistance.

[0078] Simulation experiments demonstrate that the novel longitudinal differential protection scheme derived from the improved Tellegen's second theorem can naturally shield against the influence of unmeasurable branch connections on the difficulty of setting line protection, and also possesses a certain resistance to transition resistance. When an internal fault occurs on the line, the pseudo-unbalanced power changes significantly, far exceeding the set value, exhibiting better sensitivity than other traditional protection schemes. For external faults, the pseudo-unbalanced power is significantly less than the set value, effectively avoiding false tripping due to external faults. This scheme is not only theoretically innovative but also demonstrates significant advantages in practical applications, effectively improving the safety and reliability of power systems.

[0079] Based on the same inventive concept, according to another aspect of the present invention, such as Figure 3 As shown, an embodiment of the present invention also provides a computer device 30, which includes a processor 310 and a memory 320. The memory 320 stores a computer program 321 that can be run on the processor. When the processor 310 executes the program, it performs the steps of the method described above.

[0080] Based on the same inventive concept, according to another aspect of the present invention, such as Figure 4 As shown, embodiments of the present invention also provide a computer-readable storage medium 40, which stores a computer program 410 that, when executed by a processor, performs the methods described above.

[0081] Embodiments of the present invention may also include a corresponding computer device. The computer device includes a memory, at least one processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes any of the methods described above when executing the program.

[0082] The memory, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules, such as program instructions / modules in the embodiments of this application. The processor executes various functional applications and data processing of the device by running the non-volatile software programs, instructions, and modules stored in the memory, thereby implementing the above-described method.

[0083] The memory may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the device. Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In embodiments, the memory may optionally include memory remotely located relative to the processor, which can be connected to the local module via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0084] Finally, it should be noted that those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The storage medium for the program can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc. The above computer program embodiments can achieve the same or similar effects as any of the corresponding foregoing method embodiments.

[0085] Those skilled in the art will also understand that the various exemplary logic blocks, modules, circuits, and algorithm steps described in conjunction with the disclosure herein can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability between hardware and software, the functionality of various illustrative components, blocks, modules, circuits, and steps has been generally described. Whether this functionality is implemented as software or as hardware depends on the specific application and the design constraints imposed on the system as a whole. Those skilled in the art can implement the functionality in various ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the embodiments disclosed herein.

[0086] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. The sequence numbers of the disclosed embodiments of this invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0087] It should be understood that, as used herein, the singular form “a” is intended to include the plural form as well, unless the context clearly supports an exception. It should also be understood that, as used herein, “and / or” refers to any and all possible combinations of one or more of the associated listed items.

[0088] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A longitudinal differential protection method applicable to unmeasurable load branches in a distribution network, characterized in that, include: The circuit includes several measurement points, several protection devices, and a distributed photovoltaic power source; measurement points are set on both sides of the protected line, with one end of each measurement point connected to the protection device and the other end connected to the protected line; a separate measurement point is set between the distributed photovoltaic power source and the protected line; the distributed photovoltaic power source is connected to the grid via a T-connection. The first voltage and current at the measurement point under normal operation is collected in the protected line, and the first voltage and current are converted into the first positive sequence component. Based on the first positive sequence component, the protection devices at both ends of the protected line are activated, and the second voltage and current at the measurement point after the fault are collected and converted into the second positive sequence component. The pseudo-unbalanced power and setting value are calculated based on the first and second positive sequence components; wherein, the setting value is set to be greater than the historical maximum pseudo-unbalanced power during normal line operation and less than the historical minimum pseudo-unbalanced power during line faults; the formula for the pseudo-unbalanced power is as follows: ； In the formula, This represents the positive sequence voltage component at measurement point i before the fault. This represents the positive sequence voltage component at measurement point i after the fault. This represents the positive sequence current component at measurement point i before the fault. This represents the positive sequence current component at measurement point i after the fault. If the unbalanced power exceeds the set value, the protection devices on both sides of the protected line will simultaneously disconnect the faulty line.

2. The longitudinal differential protection method for unmeasurable load branches in a distribution network according to claim 1, characterized in that, The step of acquiring the first voltage and current at the measurement point under normal operation in the protected line and converting the first voltage and current into a first positive sequence component includes: Several measuring points are set at both ends and in the middle of the protected line; The voltage and current signals are simultaneously collected at each measurement point using a voltage transformer, and the sum is used to obtain the first voltage and current. The first voltage and current are converted into a first positive sequence component using the symmetrical component method, and the first positive sequence component is sent to the protection device.

3. The longitudinal differential protection method for unmeasurable load branches in a distribution network according to claim 1, characterized in that, The process of activating the protection devices at both ends of the protected line based on the first positive sequence component includes: If the first positive sequence component is less than the preset start value, the voltage and current at all measurement points under normal operation will be re-acquired. In response to the first positive sequence component being greater than a preset start value, the protection device activates the protection at both ends of the protected line.

4. The longitudinal differential protection method for unmeasurable load branches in a distribution network according to claim 1, characterized in that, The process of acquiring the second voltage and current at the measurement point after the fault and converting the second voltage and current into a second positive sequence component includes: The voltage and current signals at each measurement point after a fault are collected by a voltage transformer, and the sum is used to obtain the second voltage and current. The second voltage and current are converted into a second positive sequence component using the symmetrical component method, and the second positive sequence component is sent to the protection device.

5. A longitudinal differential protection method for unmeasurable load branches in a distribution network according to claim 1, characterized in that, If the unbalanced power is less than the set value, the protection devices on both sides of the protected line will be locked, and the first voltage and current at the measurement point under normal operation will be collected again in the protected line, and the first voltage and current will be converted into the first positive sequence component.

6. A computer device, comprising: At least one processor; The processor also includes a memory storing a computer program that can run on the processor, characterized in that the processor executes the program by performing the steps of a longitudinal differential protection method for unmeasurable load branches in a distribution network as described in any one of claims 1 to 4.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it performs the steps of a longitudinal differential protection method for unmeasurable load branches in a distribution network as described in any one of claims 1 to 4.

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