A transient voltage protection method for low voltage DC distribution network based on dynamic threshold principle

Abstract

This invention discloses a method for over-transient voltage protection in low-voltage DC distribution networks based on the dynamic threshold principle, belonging to the field of low-voltage DC distribution networks. The method is as follows: A protection device in the low-voltage DC distribution network collects and monitors the voltage at its location in real time; when the voltage is lower than 90% of the rated voltage, the voltage and voltage change rate at the current time +Δt are obtained as the first voltage and first voltage change rate; and the voltage and voltage change rate at the current time +2Δt are obtained as the second voltage and second voltage change rate, where Δt is the reciprocal of the collection frequency of the protection device; using the second voltage change rate as the dynamic protection threshold, the first voltage change rate and the second voltage change rate are compared. If the first voltage change rate is greater than the second voltage change rate and both are greater than 0, the first measure is taken; otherwise, the second measure is taken. This method is simple and easy to implement, ensures system operational stability, and eliminates the need to set a fixed protection threshold.

Description

Technical Field

[0001] This invention relates to the field of low-voltage DC distribution networks, and specifically to a method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle. Background Technology

[0002] Low-voltage direct current (VDC) distribution networks have been recognized as an effective way to alleviate the pressure on existing power grids. Simultaneously, the rapid development of power electronics technology and the widespread application of low-voltage DC appliances have enabled VDC power supply technology to serve as an auxiliary and alternative to traditional AC power distribution technologies in various areas of "new infrastructure" (such as 5G base stations, data centers, new energy charging piles, DC green buildings, smart homes, industrial internet, rural and remote areas, etc.), prompting existing low-voltage AC distribution networks to evolve towards hybrid AC / DC and DC distribution networks. The energy-saving advantages and enhanced controllability brought by DC distribution technology have been proven by domestic and international demonstration projects. Meanwhile, to promote the wider application of low-voltage DC distribution technology, the International Electrotechnical Commission (IEC) has provided strong support for the development of technical guidelines and standards. However, reliable DC fault protection is considered a key technical challenge to ensure the high stability, high reliability, and high resilience of low-voltage DC distribution systems.

[0003] Existing low-voltage DC high-speed fault protection methods mostly use voltage and current change rates directly to determine protection action. However, due to the rapid changes in DC fault voltage and current signals, existing methods often rely on ultra-high sampling frequency (e.g., 2MHz) signal acquisition equipment to ensure accurate instantaneous current and voltage change rates are obtained and compared with preset protection thresholds for accurate protection action determination. However, large-scale deployment of such equipment in low-voltage distribution networks increases the application cost of low-voltage distribution technology and wastes resources. Furthermore, existing non-unit protection methods often use fixed protection thresholds. Considering the widespread use of low-voltage DC distribution technology, when the signal sampling frequency decreases, the voltage change rate caused by high-impedance faults will be lower than the fixed threshold, leading to protection failure. Summary of the Invention

[0004] To address the problems in the existing technology, this invention proposes a method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle.

[0005] The technical solution adopted in this invention is as follows:

[0006] In a first aspect, this invention discloses a method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle. A protection device is installed on the connecting cables between the main busbar and branch busbars and / or between branch busbars in the low-voltage DC distribution network. The protection device can collect and monitor the voltage at its own location in real time, and control the continuity of the cables. The method includes:

[0007] 1) Monitor the real-time voltage value. When the voltage value is lower than 90% of the rated voltage, proceed to step 2);

[0008] 2) Let t be the time when the voltage value is lower than 90% of the rated voltage. Obtain the voltage and voltage change rate at time t+Δt as the first voltage and first voltage change rate; and obtain the voltage and voltage change rate at time t+2Δt as the second voltage and second voltage change rate; where Δt is the reciprocal of the sampling frequency of the protection device.

[0009] 3) The second voltage change rate is used as the dynamic protection threshold. The first voltage change rate is compared with the second voltage change rate. If the first voltage change rate is greater than the second voltage change rate and both are greater than 0, a fault occurs within the protection area of ​​the protection device, and the protection device takes the first measure. In other cases, a fault occurs outside the protection area of ​​the protection device, and the protection device takes the second measure.

[0010] Furthermore, two protection devices are provided on the cables connecting the main busbar and the branch busbar and / or connecting the branch busbars, respectively, with the two protection devices installed at both ends of the cable.

[0011] Furthermore, each of the protection devices includes a voltage sensor, an auxiliary inductor, a protection relay for protecting the low-voltage DC distribution network, and a circuit breaker. The voltage sensor is used to acquire the voltage of the protection relay in real time and obtain the rate of change of the voltage, as well as to continuously detect the acquired voltage. The auxiliary inductor, voltage sensor, protection relay, and circuit breaker are connected in series. The protection area of ​​the protection relay is isolated between two protection devices through the auxiliary inductor.

[0012] Secondly, the present invention discloses an electronic device, including a processor and a memory, wherein the memory stores machine-executable instructions that can be executed by the processor, and the processor executes the machine-executable instructions to implement the aforementioned method for over-transient voltage protection of low-voltage DC distribution networks based on the dynamic threshold principle.

[0013] Thirdly, the present invention discloses a machine-readable storage medium storing machine-executable instructions, which, when called and executed by a processor, are used to implement the aforementioned method for over-transient voltage protection of low-voltage DC distribution networks based on the dynamic threshold principle.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] This invention proposes an over-transient voltage protection method based on the dynamic threshold principle, effectively solving the problem that existing technologies, which rely on fixed thresholds and transient voltages, struggle to achieve accurate protection under low sampling frequency and high-resistance fault conditions. With the same size auxiliary inductor and sampling frequency, this invention can identify high-resistance faults with approximately four times the resistance of existing technologies; while requiring only about one-quarter of the auxiliary inductor needed to distinguish the same high-resistance faults. This invention significantly improves the fault differentiation capability under low-sampling-frequency voltage sensors, thereby ensuring the protection reliability of low-voltage DC systems. Furthermore, this method drastically reduces the implementation cost of low-voltage DC distribution networks, simplifies the implementation process, and fully guarantees system operational stability. In addition, this invention eliminates the need for preset fixed protection thresholds, demonstrating greater adaptability and flexibility. Attached Figure Description

[0016] Figure 1 This is a simplified system diagram of a low-voltage DC distribution network;

[0017] Figure 2 This is a simplified diagram of a portion of a low-voltage DC distribution network system;

[0018] Figure 3 This is a flowchart of the low-voltage DC distribution network over-transient voltage protection method of the present invention;

[0019] Figure 4 This is the algorithm implementation logic diagram of the low-voltage DC distribution network over-transient voltage protection method of the present invention;

[0020] Figure 5 It is the common connection point PCC and the protection relay R. a1 and protection relay R a2 Time-voltage response diagram for F1 fault;

[0021] Figure 6 It is a protective relay R a1 Time-voltage rate of change response graph for F1 fault;

[0022] Figure 7 It is the common connection point PCC and the protection relay R a1 Time-current response diagram for F1 fault;

[0023] Figure 8 It is a protective relay R a1 The response graph of time-voltage rate of change during F2 fault;

[0024] Figure 9 It is a protective relay Ra1 Response plot of the rate of change of over-transient voltage under different fault resistances and sampling frequencies;

[0025] Figure 10 It is a protective relay R a1 Response graph of transient voltage rate of change amplitude under different fault resistances and sampling frequencies;

[0026] Figure 11 This is a response graph showing the magnitude of the fault resistance when the auxiliary inductor size is different. Detailed Implementation

[0027] The present invention will be further described and illustrated below with reference to specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0028] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0029] The purpose of this invention is to address the shortcomings of current technologies by providing a low-voltage DC distribution network over-transient voltage protection method based on the dynamic threshold principle. This over-transient voltage protection method can effectively distinguish between faults within and outside the protection zone of the protection relay, even at low signal sampling frequencies, and provides a high-stability and high-reliability protection method for low-voltage DC distribution systems.

[0030] This invention is aimed at low-voltage DC distribution networks, such as... Figure 1 As shown, it is a simplified system diagram of a low-voltage DC distribution network. Figure 1 In the diagram, the bolded area marked Bus1 represents the main bus of the low-voltage DC distribution network, while the bolded areas marked Bus2, Bus3, Bus4, and Bus5 represent the branch buses. The main bus is the bus that supplies voltage from the electric field to the user end, and the branch buses are the buses that receive voltage from the main bus and supply voltage to the appliances at the user end. The main bus and branch buses are connected by cables, and the branch buses are connected to each other by cables. Figure 1In this system, two protection devices are installed on the connecting cables between the main busbar and the branch busbar, and between the branch busbars themselves, with each device installed at one end of the cable. Each protection device can collect and monitor the voltage at its location in real time, and control the cable's continuity. Each protection device includes a voltage sensor, an auxiliary inductor, a protection relay for protecting the low-voltage DC distribution network, and a circuit breaker. The protection area of ​​the protection relay is isolated between the two protection devices by the auxiliary inductor. Figure 1 In this context, a1, a2, b1, b2, c1, c2, d1, and d2 all represent protective relays. The area between each protective device and its upstream adjacent protective device is called the upstream protection zone of that protective device, and the area between each protective device and its downstream adjacent protective device is called the downstream protection zone of that protective device. The upstream and downstream protection zones of a protective device constitute the protection area of ​​that protective device, which is also the protection area of ​​the protective relay within that protective device.

[0031] A partial system topology diagram of a low-voltage DC distribution network is shown below. Figure 2 As shown. Since DC protection mainly considers the capacitor discharge stage, fault detection and protection selectivity should be completed before the diode freewheeling stage. During the capacitor discharge stage, the converter can be simplified to a combination circuit of capacitor C, cable resistance R, and inductance L in the fault path. The common junction is the main inverter, whose port capacitance is the main capacitive component in the line because the cable capacitance is much smaller than the main inverter capacitance. Low-voltage DC distribution networks have multiple protection devices, each including a protection relay and a solid-state circuit breaker (i.e., circuit breaker). Figure 2 The circuit breaker and protective relay are drawn together, along with a voltage sensor and an auxiliary inductor. The auxiliary inductor, voltage sensor, protective relay, and circuit breaker are connected in series. The low-voltage DC distribution network area between two adjacent auxiliary inductors forms the protection zone of the two protective relays. The auxiliary inductor, voltage sensor, protective relay, and circuit breaker are connected in series; the auxiliary inductor is used to define the fault boundary, meaning its size affects the resistance value of identifiable high-resistance faults. Figure 2 R in a1 R a2 and R c1 Both indicate a protection relay, to protect relay R a1 For example, when the fault is located in the protective relay R a1 and protection relay R a2 In between, R a1 The circuit should activate. Fault F1 is defined as an inter-pole fault, i.e., the protective relay R... a1 The fault within the protected area (the fault within the protected area) and the protection relay R a2 The fault within the zone, fault F2, is defined as a remote bus fault, i.e., the protection relay Ra2 Fault within the zone, protection relay R a1 For faults outside the designated area, fault F3 is defined as the protection relay R. a1 External faults and protection relay R a2 External faults, such as Figure 2 As shown. The following description is based on the protective relay R. a1 In other words.

[0032] Under normal circumstances, the protection relay R a1 voltage U a Rated voltage U n Its definition is as follows:

[0033]

[0034] Among them, U t It is a protective relay R a1 The voltage near the main inverter terminal, U a It is a protective relay R a1 The voltage at the other end, L a It is a protective relay R a1 The auxiliary inductance I flows through the protective relay R. a1 The current.

[0035] When F1 fault occurs, based on the characteristics of low-voltage DC faults, the protection relay R... a1 Voltage U near the main inverter terminal t and flow through the protection relay R a1 The derivative of the current I can be expressed as formula (2) and formula (3).

[0036]

[0037]

[0038] Wherein, U0 is the initial voltage of the capacitor of the main inverter, L is the inductance, C is the capacitance, s1 and s2 are the roots of the denominator of the Laplace expression of the DC fault characteristics; as shown in formula (4), the cable resistance R, inductance L and capacitance C in the fault circuit are involved.

[0039]

[0040] Where α is the damping coefficient; ω0 is the resonant angular frequency; and R is the cable resistance.

[0041] Substituting formulas (2) and (3) into formula (1), we can obtain the protective relay R. a1 The voltage is expressed as in formula (5).

[0042]

[0043] Taking t=0 and substituting formula (4) into formula (5), we can obtain the protective relay R. a1 The transient voltage is expressed as in formula (6).

[0044]

[0045] Differentiating both sides of equation (5), the protection relay R a1 The voltage derivative is shown in equation (7).

[0046]

[0047] Setting t=0 in this formula, we can obtain the protective relay R. a1 The rate of change of transient voltage is shown in formula (8), where the subscript PT represents transient.

[0048]

[0049] When F1 fault occurs, the protection relay R a1 The transient voltage drops, and after the transient voltage drops, the protective relay R... a1 The rate of change of the transient voltage is positive, and its value is related to the value of the protection relay R in the fault path. a1 It is related to the rated voltage, auxiliary inductance, and cable impedance.

[0050] Furthermore, by taking the derivative of both sides of equation (7) again, the second-order voltage derivative can be expressed as equation (9).

[0051]

[0052] Substituting formula (4) and t=0 into formula (9), we get formula (10). The result is negative, indicating that the rate of change of the transient voltage decreases after the F1 fault occurs.

[0053]

[0054] When F3 malfunction occurs, U a The voltage characteristics at Bus2 are similar to those at Bus2 and can be expressed by formula (2). Meanwhile, by differentiating formula (2), the voltage change rate and second-order change rate at Bus2 are obtained as shown in formulas (11) and (12). Substituting t=0 into the formula, it can be found that during the F3 fault, the protection relay R... a1 The rate of change of voltage is negative, and the rate of change is getting smaller and smaller.

[0055]

[0056]

[0057] Therefore, the protection relay R can be monitored. a1 The positive and negative values ​​of the voltage change rate are used to distinguish downstream faults by comparing the voltage change rates at the second and third points after the fault. In this process, the third point after the fault occurs serves as a dynamic threshold, changing with the location of the fault, and a fixed protection threshold does not need to be set.

[0058] In response to this characteristic, such as Figure 3 As shown, the technical solution of the present invention is as follows:

[0059] Step 1: The voltage sensor collects the voltage U of the protection relay in real time and obtains the rate of change of voltage dU / dt. It also continuously monitors the collected voltage U and the rate of change of voltage dU / dt to ensure that the system status of the low-voltage DC distribution network can be grasped in real time.

[0060] When the voltage value of the protection relay is detected to be lower than 90% of the rated voltage, proceed to step two for further processing; otherwise, continue to step one and continue to acquire and monitor the voltage U and the rate of change of voltage dU / dt in real time.

[0061] Step 2: When the voltage value of the protective relay is lower than the rated voltage U n When the voltage reaches 90%, let time t be the time of the relay. Obtain the voltage U of the protection relay at time t+Δt. (t+Δt) and voltage change rate dU (t+Δt) / d(t+Δt); simultaneously obtain the voltage U of the protection relay at time t+2Δt. (t+2Δt) and voltage change rate dU (t+2Δt) / d(t+2Δt); where Δt is the reciprocal of the sampling frequency of the voltage sensor;

[0062] Step 3: dU (t+2Δt) / d(t+2Δt) is considered as the dynamic protection threshold, and dU (t+Δt) / dt (t+Δt) and dU (t+2Δt) / dt (t+2Δt) Compare, if dU (t+Δt) / dt (t+Δt) Greater than dU (t+2Δt) / d(t+2Δt)anddU (t+Δt) / d(t+Δt) and dU (t+2Δt) If both / d(t+2Δt) are greater than 0, it is determined that a fault has been detected in the protection area of ​​the protection relay. The protection relay sends a disconnect signal to the circuit breaker that shares the protection area with it. The circuit breaker disconnects, cuts off the fault, isolates the fault area, and the cable connection at the current location is disconnected.

[0063] In other cases, it is determined that a fault has occurred outside the protection zone of the protection relay. The protection relay does not send any signal to the circuit breaker, the circuit breaker does not operate, and the cable connection at the current position remains connected.

[0064] In a specific embodiment of the present invention, the formula for calculating the rate of change of voltage dU / dt is as follows:

[0065]

[0066] Among them, U t U is the voltage of the protective relay at time t; (t-Δt) The voltage of the protective relay is at time t-Δt.

[0067] Voltage change rate dU (t+Δt) The formula for calculating / d(t+Δt) is:

[0068]

[0069] Among them, U (t+Δt) Let be the voltage of the protective relay at time t+Δt.

[0070] Voltage change rate dU (t+2Δt) The formula for calculating / d(t+2Δt) is:

[0071]

[0072] Among them, U (t+2Δt) The voltage of the protective relay is at time t+2Δt.

[0073] like Figure 4 The diagram shown is the algorithm implementation logic diagram of the low-voltage DC distribution network over-transient voltage protection method of the present invention. It specifically demonstrates the fault differentiation and fault protection of the low-voltage DC distribution network. That is, the protection relay obtains U and dU / dt, the voltage signal U is compared with 90% of the rated voltage to obtain the fault signal, and the voltage change rate is held by different delays and the "hold" module to obtain the voltage change rate under different delays. The result of the signal comparison is obtained by the comparison module ">" and the logic AND gate is used to judge the logic result.

[0074] exist Figure 2 In the system, when fault F1 occurs, the protection relay R... a1 and R a2 A transient voltage drop was detected, such as Figure 5 As shown, the voltage is below 90% of the rated voltage, therefore a fault is detected; where PCC is the point of common connection. Subsequently, the rate of change of voltage is recorded as follows: Figure 6 As shown, the protective relay R a1The captured transient voltage derivative (i.e., the transient voltage rate of change) dU (t+Δt) / d(t+Δt) is greater than dU (t+2Δt) / d(t+2Δt). Therefore, according to the judgment criteria of the present invention, the fault is identified as being in the protective relay R. a1 Within the downstream protection zone, a trip (disconnection) signal is sent to the relevant circuit breaker, and the fault current is as follows: Figure 7 The interruption was observed. Simultaneously, the protection relay R... a2 It will also be based on the protection relay R a1 The same judgment principle locates fault F1 and issues a trip signal. Once fault F1 is cleared, the voltage at the common junction PCC recovers to its rated voltage within 2 milliseconds. Figure 5 As shown.

[0075] when Figure 2 When the F2 fault occurs, such as Figure 8 As shown, the protective relay R a1 Captured transient voltage change rate dU (t+Δt) / d(t+Δt) is less than dU (t+2Δt) / d(t+2Δt) does not meet the protection triggering condition, therefore the protection relay R a1 It does not operate when F2 fails, thus enabling fault differentiation.

[0076] Regarding the ability to distinguish high-impedance faults, in the case of F1 faults, the response of the proposed dynamic threshold at different sampling frequencies to different fault resistances and sampling frequencies is as follows: Figure 9 As shown. The transient voltage change rate always exceeds the dynamic threshold, thus preventing protection failure. Figure 10 Compared to existing methods based on voltage change rate (where protection fails when the voltage change rate is less than a fixed threshold at approximately 0.25Ω), the over-transient voltage protection method based on the dynamic threshold principle proposed in this invention can cover a fault resistance range from short circuit to 1Ω (the high-resistance fault value that this invention can identify is four times that of existing methods) at a lower sampling frequency of 10kHz. This range is approximately four times that of existing protection methods for low-voltage DC distribution systems based on voltage change rate and fixed threshold. Therefore, this invention can achieve fault protection and fault differentiation in low-voltage DC distribution networks using a low sampling frequency, reducing the implementation cost of low-voltage DC distribution networks. Its implementation method is simple, system stability is guaranteed, and there is no need to set a fixed protection threshold. Figure 11The horizontal axis represents the size of the auxiliary inductance, and the vertical axis represents the ability to detect high-impedance faults using different methods with the current size of the auxiliary inductance. The figure shows that the ability to detect high-impedance faults increases with the increase of the auxiliary inductance. However, for the same ability to detect high-impedance faults, the size of the auxiliary inductance in the method of this invention is one-quarter that of existing methods. In this invention, the inductive reactance of the auxiliary inductance is 10%-20% of the inductive reactance of the cable between the two interconnected protection devices.

[0077] This invention also provides an electronic device, including a memory and a processor;

[0078] The memory is used to store computer programs;

[0079] The processor is used to implement the above-described method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle when executing the computer program.

[0080] This invention also provides a computer-readable storage medium storing a program thereon, which, when executed by a processor, implements the above-described method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle.

[0081] The computer-readable storage medium can be an internal storage unit of any data processing device described in any of the foregoing embodiments, such as a hard disk or memory. The computer-readable storage medium can also be an external storage device of any data processing device, such as a plug-in hard disk, smart media card (SMC), SD card, flash card, etc., equipped on the device. Furthermore, the computer-readable storage medium can include both internal storage units and external storage devices of any data processing device. The computer-readable storage medium is used to store the computer program and other programs and data required by the data processing device, and can also be used to temporarily store data that has been output or will be output.

[0082] Obviously, the embodiments and accompanying drawings described above are merely some examples of this application. Those skilled in the art can apply this application to other similar situations based on these drawings without any creative effort. Furthermore, it is understood that although the work done in this development process may be complex and lengthy, for those skilled in the art, certain design, manufacturing, or production modifications made based on the technical content disclosed in this application are merely conventional technical means and should not be considered as insufficient disclosure of this application. Several modifications and improvements can be made without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle, characterized in that, The low-voltage DC distribution network is equipped with protective devices on the connecting cables between the main bus and branch bus and / or between branch bus and branch bus. These protective devices can collect and monitor the voltage at their location in real time, and control the continuity of the cables. The method includes: 1) Monitor the real-time voltage value. When the voltage value is lower than 90% of the rated voltage, proceed to step 2). 2) Let t be the time when the voltage value is lower than 90% of the rated voltage. Obtain the voltage and voltage change rate at time t+Δt as the first voltage and the first voltage change rate; and obtain the voltage and voltage change rate at time t+2Δt as the second voltage and the second voltage change rate; where Δt is the reciprocal of the sampling frequency of the protection device. 3) The second voltage change rate is used as the dynamic protection threshold. The first voltage change rate is then compared with the second voltage change rate. If the first voltage change rate is greater than the second voltage change rate and both are greater than 0, a fault occurs within the protection area of ​​the protection device, and the protection device takes the first measure. In other cases, a fault occurs outside the protection area of ​​the protection device, and the protection device takes the second measure. Each of the protection devices includes a voltage sensor, an auxiliary inductor, a protection relay, and a circuit breaker. The voltage sensor is used to collect the voltage of the protection relay in real time and obtain the rate of change of the voltage, as well as to continuously detect the collected voltage. The protection relay and the circuit breaker are used to protect the low-voltage DC distribution network. The auxiliary inductor, voltage sensor, protection relay, and circuit breaker are connected in series. The protection area of ​​the protection relay is isolated between two protection devices through the auxiliary inductor. The inductive reactance of the auxiliary inductor is 10%-20% of the inductive reactance of the cable between the two interconnected protection devices; In step 2), the first voltage change rate is The second voltage change rate ;in, for The voltage of the protection relay at all times; for The voltage of the protection relay at all times; for The voltage of the protection relay at all times.

2. The method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle according to claim 1, characterized in that, Two protective devices are installed on the cables connecting the main busbar and the branch busbar and / or connecting the branch busbars, respectively, at both ends of the cable.

3. The method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle according to claim 1, characterized in that, The area between each protection device and its upstream neighboring protection device is called the upstream protection zone of the protection device, and the area between each protection device and its downstream neighboring protection device is called the downstream protection zone of the protection device. The upstream protection zone and the downstream protection zone of a protection device constitute the protection area of ​​the protection device, which is also the protection area of ​​the protection relay within the protection device.

4. The method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle according to claim 1, characterized in that, In step 2), the rated voltage is the rated voltage of the protection relay.

5. The method for protecting low-voltage DC distribution networks from transient voltage based on the dynamic threshold principle according to claim 1, characterized in that, In step 3), the protection device takes a first measure, including: When a fault occurs within the protection area of ​​the protection relay, the protection relay sends a disconnect signal to the circuit breaker, the circuit breaker trips, disconnects the fault, and the cable connection at the current location is broken. The protective device employs a second measure, including: If a fault occurs outside the protection zone of the protection relay, the protection relay will not send any signal to the circuit breaker, the circuit breaker will not trip, and the cable connection at the current location will remain connected.

6. An electronic device, characterized in that, The method includes a processor and a memory, the memory storing machine-executable instructions that can be executed by the processor, the processor executing the machine-executable instructions to implement the low-voltage DC distribution network over-transient voltage protection method based on the dynamic threshold principle as described in any one of claims 1 to 5.

7. A machine-readable storage medium, characterized in that, The machine-readable storage medium stores machine-executable instructions, which, when called and executed by a processor, are used to implement the low-voltage DC distribution network over-transient voltage protection method based on the dynamic threshold principle as described in any one of claims 1 to 5.

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