Surge protection coordination and optimization method for communication power supply system

Abstract

This invention discloses a surge protection coordination and optimization method for communication power supply systems, relating to the field of lightning protection technology. The method includes the following steps: selecting appropriate surge protection devices (SPDs) based on the composition of the communication power supply system for simulation experiments, and constructing an SPD model; analyzing overvoltage and energy standards based on the constructed SPD model; recognizing that the waveform of the fault traveling wave reaching the upstream SPD changes with the lightning strike location, and performing time-domain and frequency-domain analysis on this change; identifying factors affecting the overvoltage waveform reaching the load and the overvoltage waveform reaching each level of SPD, and deriving reasonable optimization and coordination suggestions; addressing the protection problem of communication power supply systems when subjected to lightning surges, this invention proposes a method to optimize the coordination between multiple levels of SPDs and between SPDs and protected devices. By progressively attenuating lightning surges and rationally configuring the starting voltage, energy absorption capacity, and overvoltage level of each level of SPD, the lightning withstand capability and reliability of the communication power supply system are improved.

Description

Technical Field

[0001] This invention relates to the field of lightning protection technology, specifically to a method for coordinating and optimizing surge protection in communication power systems. Background Technology

[0002] Lightning conductors and surge arresters in transmission lines effectively prevent direct lightning strikes. However, when a lightning strike occurs, the phase conductors can experience strong electromagnetic interference, leading to induced lightning surges that reach the power supply system and affect power stability. To achieve lightning surge protection, multi-stage surge protectors (SPDs) are typically required, depending on the overvoltage category of the protected equipment and the wiring of the electrical installations. In such cases, effective SPD coordination should be checked to prevent downstream SPDs from being overloaded, while also limiting overvoltage levels to below the withstand voltage of the protected equipment.

[0003] In recent years, research on surge protection devices (SPDs) and their coordination in various systems has yielded some positive results. However, in reality, power outages and communication short circuits caused by lightning strikes are frequent occurrences in communication power systems. Therefore, a significant amount of effort is still needed to refine and improve surge protection for communication power systems. In multi-level protection designs for communication power systems, SPDs are commonly used as core protection components. By rationally selecting different types and rated voltages of SPDs and achieving coordinated operation across multiple levels, progressive attenuation of lightning surges can be effectively achieved. This application utilizes an efficient coordination and optimization method to address the aforementioned issues. Summary of the Invention

[0004] The purpose of this invention is to provide a method for coordinating and optimizing surge protection in communication power systems, so as to solve the problems existing in the prior art as described in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for coordinating and optimizing surge protection in communication power systems includes the following steps:

[0007] S1: Select a suitable SPD based on the composition of the communication power supply system, conduct simulation experiments, and construct an SPD model;

[0008] S2: Analyze overvoltage and energy standards based on the constructed SPD model;

[0009] S3: The waveform of the fault traveling wave reaching the upstream SPD will change with the location of the lightning strike. Time domain and frequency domain analysis is performed on this change.

[0010] S4: The factors that affect the overvoltage waveform reaching the load and the overvoltage waveform reaching each stage of SPD were investigated through simulation experiments in electromagnetic transient software, and reasonable optimization and coordination suggestions were derived.

[0011] Preferably, in S2, the upstream SPD generally operates before the downstream SPD to absorb a larger inrush current. When the fault voltage is insufficient to activate the upstream SPD, it is necessary to consider whether the line wave impedance and the load impedance are equal, whether the traveling wave is reflected, what conditions the line parameters must meet to enable the upstream SPD to start first, and to determine the impact of the load condition on it.

[0012] Preferably, the specific optimization process of the SPD is as follows:

[0013] The steepness of the lightning surge current is calculated, and the upstream surge protection device (SPD) is prioritized for activation based on the matching relationship between line impedance and load impedance. The transmission line lengths between SPDs are adjusted to ensure that the voltage protection coordination between SPDs conforms to the lightning surge energy transfer law. During the SPD configuration process, load characteristics are considered to ensure that the surge voltage level at the equipment end is within a safe range. Finally, by comparing the success or failure of energy coordination under different loads, the corresponding overvoltage standards are studied.

[0014] Preferably, the specific analysis steps in S2 are as follows:

[0015] S21: Since the line impedance is usually much greater than the line resistance, for ease of analysis, the influence of the line resistance is ignored here. Assume the line is a lossless uniform transmission line, with line length *l*, unit inductance *L0*, and unit capacitance *R0*. The line impedance... speed of propagation The time required for a wave to travel from point A to point B is τ = l / v, and Z... C τ=lL0;

[0016] The rising edge of the applied impulse current can be approximated as a slanted wave, i.e., I g =at, assuming the current starts from point A at time 0, and after time τ, the wavefront of the current wave reaches point B. Before the upstream SPD is turned on, the voltage U on the upstream SPD is... A for:

[0017]

[0018] When the current wave reaches point B, according to U A Is it greater than the startup voltage U of the upstream SPD? 1-1ma This needs to be discussed in two separate cases;

[0019] S22: When U A ≥U 1-1maIf the upstream SPD has already turned on before the current wave reaches point B, then the general formula for determining whether the upstream SPD acts before the downstream SPD is:

[0020] Line length l or line surge impedance Z C When is known, the rising slope 'a' of the impulse current wave satisfies

[0021]

[0022] When the steepness 'a' of the applied impulse waveform is known, the line length or the line wave impedance satisfies

[0023]

[0024] As can be seen from equations (2) and (3), under the action of steep or large-amplitude inrush current, the upstream SPD is likely to act before the downstream SPD. Increasing the transmission line length between the two-stage protectors can make the upstream SPD act before the downstream SPD.

[0025] S23: When U A ≤U 1-1ma When considering the influence of the load on the current reflection and refraction, it is necessary to discuss the load and the line impedance value.

[0026] S24: When Z l =Z C When the load impedance equals the line surge impedance, the current wave does not reflect at point B and is entirely refracted into the load. After the current wave reaches point B, the voltage on the downstream SPD must reach the starting voltage U. 2-1ma The time required is t1:

[0027]

[0028] For the upstream SPD to activate before the downstream SPD, the line parameters must meet the following requirements:

[0029]

[0030] S25: When Z l ≠Z C When the load impedance is not equal to the line wave impedance, the current wave is reflected at point B, and the current I entering the load... L for:

[0031]

[0032] The voltage on the load must reach U 2-1ma The value, and the time required t2, is:

[0033]

[0034] For the upstream SPD to activate before the downstream SPD, the line parameters must meet certain conditions, where H(w) is the refractive index and K(w) is the reflection index.

[0035]

[0036]

[0037] Preferably, the specific analysis steps of S3 are as follows:

[0038] S31: According to the superposition principle, any fault on the line can be decomposed into normal operation component and fault component. The fault component can be regarded as a transient mechanism added to the voltage source. The fault-added voltage source will generate a broadband traveling wave signal with step, which is generated from the fault point and refracted and reflected along the line wave impedance discontinuity.

[0039] S32: Lightning surge voltage is an external fault. From the perspective of frequency domain analysis, the fault traveling wave has a wide frequency band. The wave impedance, transmission function and refraction and reflection coefficient are all functions of frequency, as shown in equations (9) to (13). Due to the influence of factors such as transmission function and refraction and reflection coefficient, the amplitude attenuation and phase change of each frequency component of the traveling wave are different during the transmission process.

[0040]

[0041] A(w)=e -γx (26)

[0042] In the formula: A(w) is the transfer function, α(w) and β(w) are the attenuation coefficients respectively, and R0, L0, C0 and G0 are the line distribution parameters. When the lightning strike location is far away, the surge traveling wave will exhibit a large attenuation of the high-frequency components, which will lead to a reduction in the surge steepness and amplitude reaching the SPD, thereby affecting the energy coordination between SPDs. The impact on the energy coordination of the two SPDs is tested by changing the surge location generated by the lightning strike and the cable length between the SPDs.

[0043] Preferably, the specific steps in S4 are as follows:

[0044] S41: When only the influence of lightning amplitude is considered, an experiment was conducted on different distances between two series-connected SPDs using a surge generator that can generate 8 / 20us direct lightning current. The energy coordination of the two-stage surge protectors was studied using SPD1 rated voltage of 660V and SPD2 rated voltage of 330V as examples. Lightning surge intrusion was studied using lightning surge peak voltages of 10kV, 20kV and 50kV.

[0045] S42: Taking four lightning strike locations as examples, namely 20m, 100m, 500m and 1km, the energy absorption of the two-stage SPD is compared, and the inter-stage cable is appropriately extended for energy coordination.

[0046] S43: When the equipment is subjected to different loads, the system analyzes the electrical characteristics under three different loads, namely resistive, capacitive and resistive-capacitive loads, and makes optimization and coordination suggestions based on the analysis results.

[0047] Preferably, the present invention also includes experimental investigations into whether there is a correlation and influence between overvoltage and energy standards, providing a basis for whether the implementation of the two coordinated standards can be carried out separately.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] 1. This invention addresses the protection problem of communication power supply systems when subjected to lightning surges. It proposes a method to optimize the coordination between multiple levels of SPDs and between SPDs and protected devices. By attenuating lightning surges step by step and rationally configuring the start-up voltage, energy absorption capacity, and overvoltage level of each level of SPD, the lightning withstand capability and reliability of the communication power supply system are improved.

[0050] 2. This invention also considers the impact of different load conditions and lightning strike locations on the coordination of SPDs. Through simulation and experimental verification, specific optimization suggestions are proposed to ensure the coordination effect of SPDs under various complex conditions. At the same time, the independence of the two coordination standards is obtained through this method, which not only improves the overall lightning resistance performance of the system, but also reduces resource waste and provides a reliable guarantee for the stable operation of the communication power supply system. Attached Figure Description

[0051] Figure 1 This is a schematic diagram showing the installation location of the SPD for multi-level protection in a communication power supply system.

[0052] Figure 2 This is the wiring diagram for the two-stage voltage-limiting surge protector of the present invention.

[0053] Figure 3 This is a diagram showing the arrival times of various surge harmonics in this invention.

[0054] Figure 4 This is a time-domain difference diagram showing the different lightning strike locations according to the present invention.

[0055] Figure 5 This is a frequency domain difference diagram showing the different lightning strike locations according to the present invention.

[0056] Figure 6 This diagram illustrates the relationship between the energy coordination, voltage magnitude, and inter-stage cable length of the two-stage surge protection system of this invention.

[0057] Figure 7 This is a comparison diagram of the energy absorbed by cables between different stages of the two-stage SPD at different lightning strike locations according to the present invention.

[0058] Figure 8 The above diagram shows the overvoltage waveforms for different resistive loads according to the present invention.

[0059] Figure 9 The above diagram shows the overvoltage waveforms for different capacitive loads according to the present invention.

[0060] Figure 10 The above diagram shows the overvoltage waveforms of different resistive-capacitive loads according to the present invention.

[0061] Figure 11 This is a comparison diagram of the energy absorbed by the two-stage SPD under different conditions when the load is a resistor.

[0062] Figure 12 This is a comparison diagram of the energy absorbed by the two-stage SPD under different conditions when the load of the present invention is a capacitor. Detailed Implementation

[0063] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0064] Please see Figure 1-12 The present invention provides the following technical solutions:

[0065] Since most lightning interference or damage to communication power systems is caused by intrusion into the power distribution system, surge protection measures for communication power systems typically employ secondary and tertiary protection for the low-voltage power distribution system and install surge protectors (SPDs) with different surge current ratings to improve the lightning withstand capability of the communication power system. A diagram showing the installation locations of multi-level protection SPDs in the power system of a certain communication station is shown below. Figure 1 As shown.

[0066] (1) Level 1 protection: voltage around 6kV; input terminals of 220 / 380VAC low-voltage main distribution panel and main generator conversion panel.

[0067] (2) Secondary protection: The voltage is around 4kV, AC power distribution panel input terminal, UPS switching power supply input terminal, and rectifier used in the communication building communication equipment room.

[0068] (3) Level 3 protection: The voltage is around 1kV. The input terminals of the AC power distribution cabinet of the communication equipment in the central computer room, the power input terminals of the communication air conditioner, and other locations including the power input terminals of the outdoor 3G / 4G / 5G base station power system.

[0069] There are two common types of transient voltage suppressor (SPDs): voltage-switching SPDs and voltage-limiting SPDs. In practical applications, they are mostly installed in parallel or Kelvin-connected configurations at various input ports of low-voltage power distribution systems. Transient voltage suppressor diodes have fast response times but low current carrying capacity, and in practical applications, they often need to be used in conjunction with gas discharge tubes. Due to their small parasitic capacitance, they are widely used in signal lines. However, for switching SPDs, arcing is unavoidable, and there is also a follow current problem, which still poses a threat to downstream protected equipment. Voltage-limiting SPDs are generally varistors, with even faster response times, stronger protection levels, and the ability to be equipped with monitoring interfaces for monitoring. Therefore, voltage-limiting SPDs were chosen to construct the experimental model.

[0070] Typical wiring for a two-stage voltage-limiting SPD is as follows: Figure 2 As shown, the total energy of the input system increases with the increase of the impulse voltage. The operating sequence of the SPD is closely related to the energy coordination of the cascaded SPDs. When the surge current impacts the upstream SPD and the amplitude of the surge current is large, the upstream SPD can start discharging first. The terminal voltage of the upstream SPD is equal to the sum of the terminal voltage of the downstream SPD and the voltage drop induced by the inductance of the leads connecting the upstream and downstream SPDs. The inductance of each pair of parallel leads is approximately 0.5 μH / m to 1 μH / m.

[0071] The coordination of SPDs (Supply-Protected Devices) must strictly adhere to two core principles: energy distribution and voltage protection. Regarding energy distribution, upstream SPDs should handle more energy dissipation to ensure the overall protection effectiveness of the system. In terms of voltage protection, downstream SPDs, being closer to the protected equipment, should have a voltage protection threshold no higher than that of upstream SPDs to provide more precise overvoltage protection. Simultaneously, when downstream SPDs start up, it is essential to ensure that the overvoltage value experienced by the equipment does not exceed its rated protection level to guarantee safe operation of the equipment.

[0072] The overvoltage and energy standards are analyzed based on the constructed SPD model. The upstream SPD generally operates before the downstream SPD to absorb the larger inrush current. When the fault voltage is insufficient to activate the upstream SPD, it is necessary to consider whether the line surge impedance is equal to the load impedance, whether the traveling wave is reflected, what conditions the line parameters must meet to enable the upstream SPD to start first, and to determine the impact of the load conditions on it.

[0073] The specific optimization process of SPD is as follows: calculate the steepness of the lightning surge current, and based on the matching relationship between line impedance and load impedance, prioritize the activation of upstream SPDs; adjust the transmission line length between SPDs to ensure that the voltage protection coordination between SPDs conforms to the lightning surge energy transfer law; during the SPD configuration process, consider the load characteristics to ensure that the surge voltage level at the equipment end is within a safe range; finally, by comparing the success or failure of energy coordination under different loads, study the corresponding overvoltage standards.

[0074] The steps for analyzing overvoltage and energy standards are as follows:

[0075] (1) Since the line impedance is usually much greater than the line resistance, for ease of analysis, the influence of the line resistance is ignored here. It is assumed that the line is a lossless uniform transmission line, with a line length of l, a unit inductance of L0, a unit capacitance of R0, and a line impedance of L0. speed of propagation The time required for a wave to travel from point A to point B is τ = l / v, and Z... C τ=lL0;

[0076] The rising edge of the applied impulse current can be approximated as a slanted wave, i.e., I g =at, assuming the current starts from point A at time 0, and after time τ, the wavefront of the current wave reaches point B. Before the upstream SPD is turned on, the voltage U on the upstream SPD is... A for:

[0077]

[0078] When the current wave reaches point B, according to U A Is it greater than the startup voltage U of the upstream SPD? 1-1ma This needs to be discussed in two separate cases;

[0079] (2)When U A ≥U 1-1ma If the upstream SPD has already turned on before the current wave reaches point B, then the general formula for determining whether the upstream SPD acts before the downstream SPD is:

[0080] Line length l or line surge impedance Z C When is known, the rising slope 'a' of the impulse current wave satisfies

[0081]

[0082] When the steepness 'a' of the applied impulse waveform is known, the line length or the line wave impedance satisfies

[0083]

[0084] As can be seen from equations (2) and (3), under the action of steep or large-amplitude inrush current, the upstream SPD is likely to act before the downstream SPD. Increasing the transmission line length between the two-stage protectors can make the upstream SPD act before the downstream SPD.

[0085] (3)When U A ≤U 1-1ma When considering the influence of the load on the current reflection and refraction, it is necessary to discuss the load and the line impedance value.

[0086] (4) When Z l =Z C When the load impedance equals the line surge impedance, the current wave does not reflect at point B and is entirely refracted into the load. After the current wave reaches point B, the voltage on the downstream SPD must reach the starting voltage U. 2-1ma The time required is t1:

[0087]

[0088] For the upstream SPD to activate before the downstream SPD, the line parameters must meet the following requirements:

[0089]

[0090] S25: When Z l ≠Z C When the load impedance is not equal to the line wave impedance, the current wave is reflected at point B, and the current I entering the load... L for:

[0091]

[0092] The voltage on the load must reach U 2-1ma The value, and the time required t2, is:

[0093]

[0094] For the upstream SPD to activate before the downstream SPD, the line parameters must meet certain conditions, where H(w) is the refractive index and K(w) is the reflection index.

[0095]

[0096]

[0097] In practical engineering, the load impedance at the load end cannot always be equal to the line surge impedance. As can be seen from equations (9) and (10), it is necessary to discuss the influence of different load conditions on it. The experiment will be divided into resistive load, capacitive load and resistive-capacitive load, and the influence of different values ​​on the overvoltage magnitude will be tested respectively.

[0098] The waveform of the fault traveling wave reaching the upstream SPD changes with the location of the lightning strike. Time-domain and frequency-domain analyses are performed on this change; the specific analysis steps are as follows:

[0099] (1) According to the superposition principle, any fault on the line can be decomposed into normal operation component and fault component. The fault component can be regarded as a transient mechanism added to the voltage source. The fault-added voltage source will generate a broadband traveling wave signal with step, which is generated from the fault point and refracted and reflected along the line wave impedance discontinuity.

[0100] From a time-domain perspective Figure 3 This describes the time-domain reflection and refraction of each traveling wave surge within a certain time window. Refraction is often more complex. Taking refraction at point M as an example, the refraction of different surge harmonics varies. If the fault location is different, the traveling wave propagation path will be different, leading to different refraction, reflection processes and wavefront arrival times. Figure 4 As shown, there are significant differences in the traveling wave waveforms at the detection points.

[0101] (2) Lightning surge voltage is an external fault. From the perspective of frequency domain analysis, the fault traveling wave has a wide frequency band. The wave impedance, transmission function and refraction and reflection coefficient are all functions of frequency, such as Equation (9) to Equation (13). Due to the influence of factors such as transmission function and refraction and reflection coefficient, the amplitude attenuation and phase change of each frequency component of the traveling wave are different during the transmission process.

[0102]

[0103] A(w)=e -γx (39)

[0104] In the formula: A(w) is the transfer function, α(w) and β(w) are the attenuation coefficients respectively, and R0, L0, C0 and G0 are the line distribution parameters. When the lightning strike location is far away, the surge traveling wave will exhibit a large attenuation of the high-frequency components, which will lead to a reduction in the surge steepness and amplitude reaching the SPD, thereby affecting the energy coordination between SPDs. The impact on the energy coordination of the two SPDs is tested by changing the surge location generated by the lightning strike and the cable length between the SPDs.

[0105] The factors affecting the overvoltage waveform reaching the load and the overvoltage waveform reaching each stage of the SPD were investigated through simulation experiments using electromagnetic transient software, and reasonable optimization and coordination suggestions were derived. The specific steps are as follows:

[0106] (1) When only the influence of lightning amplitude is considered, an experiment was conducted on different distances between two series-connected SPDs using a surge generator that can generate 8 / 20us direct lightning current. The energy coordination of the two-stage surge protectors was studied using the rated voltage of SPD1 (660V) and SPD2 (330V) as examples. Lightning surge intrusion was studied using peak lightning surge voltages of 10kV, 20kV and 50kV.

[0107] The energy absorbed by SPD1 and SPD2 is as follows Figure 6 As shown in the figure, the energy absorption of upstream and downstream SPDs under different surge voltages is compared. According to the analysis in Section 1, when two SPDs cooperate, the upstream SPD should absorb more energy than the downstream SPD. When a lightning surge below 10kV is injected and the distance between the two SPDs is less than 3m, the downstream SPD absorbs more energy than the upstream SPD, indicating that energy coordination between the two SPDs fails. However, when the distance between the two SPDs is greater than 3m, the energy is mainly concentrated in the upstream SPD, and energy coordination is achieved. This rule also applies to other surge voltage conditions; the larger the surge voltage, the shorter the critical cable length, meaning fewer inter-stage cables are required. This also indicates that if a protection module consists of multiple SPDs, the rated voltage of the upstream SPD should not be too low, otherwise it will lead to severe overvoltage attenuation. Careful distribution is needed; otherwise, the energy coordination effect of subsequent SPDs will be weakened or even ineffective.

[0108] (2) The different lightning strike locations are also the cause of energy coordination failure. Taking four lightning strike locations as examples, namely 20m, 100m, 500m and 1km, the energy absorption of the two-stage SPD is compared, and the inter-stage cable is appropriately extended for energy coordination.

[0109] like Figure 7 As shown, a comprehensive analysis of the four figures leads to the following conclusions: As the distance of the lightning strike current increases, the energy absorbed by the two SPD stages gradually decreases. When the inter-stage cable is short, the energy absorption of SPD1 is much lower than that of SPD2, which may lead to an imbalance in energy distribution. This can cause SPD1 to fail during surge protection, while SPD2 may overheat and fail due to absorbing too much energy. Further analysis shows that if the lightning strike point is close, for example, 20 meters, the inter-stage cable length only needs to be about 4 meters to ensure that SPD1 absorbs more energy than SPD2; however, when the lightning strike point distance reaches 1 kilometer, the inter-stage cable length needs to be over 100 meters.

[0110] In general, as the distance from the lightning strike point increases, the required inter-stage cable length also increases significantly. This increase leads to changes in the energy distribution between the two SPDs, thus affecting their overall performance. In this case, it is advisable to use an inductor or resistor instead of a longer cable. The purpose is to increase the voltage drop, allowing SPD1 to be triggered and turned on in time when a surge current passes through, thereby sharing some of the surge energy and reducing the energy burden on the secondary SPD.

[0111] (3) When the equipment is used as different loads, the system analyzes the electrical characteristics of three different loads, namely resistive, capacitive and resistive-capacitive loads, and makes optimization and coordination suggestions based on the analysis results.

[0112] like Figure 7 As shown, the maximum overvoltage amplitude on 1Ω, 10Ω, 50Ω, and 100Ω resistive loads was compared with the distance between the SPD and the load; Figure 8 As shown, the maximum overvoltage amplitude on 0.1nF, 1nF, 10nF, and 100nF capacitive loads was compared with the distance between the SPD and the load; Figure 9 As shown, the maximum overvoltage amplitude on 10Ω / 10pF, 20Ω / 10pF and 50Ω / 10pF resistive-capacitive loads was compared with the distance between the SPD and the load.

[0113] Furthermore, based on the second standard for SPD coordination, the cable lengths between resistive and capacitive loads were tested when the downstream SPD operated, determining the shortest effective protection distance. Taking a resistive load with a protection distance of 100m as an example, the peak values ​​of the overvoltage changes in the load and the downstream SPD were recorded after the downstream SPD operated. For the capacitive load, the overvoltage value at the point of maximum difference between the overvoltages of the two loads was recorded by adjusting the protection cable length. Specific data are shown in Tables 1 and 2. These analytical results provide important reference for optimizing SPD configuration and load protection.

[0114] Table 1 Effect of Resistive Load

[0115]

[0116] The results show that if the equipment is considered as a resistive load, the overvoltage value will only exhibit a small steepness when the load impedance is sufficiently small. When the load impedance exceeds 50Ω, the overvoltage peak value remains almost unchanged, but the steepness still increases with the increase of load impedance. When the resistive load is less than the characteristic impedance of the connecting cable (84.5Ω), the load voltage will not spike, indicating that the SPD can effectively protect the equipment, and the effective protection distance is unlimited. If the resistive load is greater than the characteristic impedance of the cable, the load voltage will spike shortly after the SPD activates. When the resistive load is greater than 120Ω, the spike overvoltage value will exceed the SPD overvoltage, and the effective protection distance will decrease rapidly, generally within 10m. In this case, the final-stage SPD protection must be close to the protected device to prevent the final-stage SPD from failing to provide protection or even affecting the normal operation of the equipment.

[0117] Table 2 Impact of Capacitive Load

[0118]

[0119] If the equipment is treated as a capacitive load, the voltage across the load will oscillate, and this oscillation can cause severe damage to the protected equipment. For example... Figure 8 As shown, the frequency and amplitude of the oscillation change with the capacitance value; the larger the capacitance value, the smaller the oscillation frequency and the larger the amplitude; conversely, the smaller the capacitance value, the larger the oscillation frequency and the smaller the amplitude. In the experiment, multiple adjustments to the capacitance value and the length of the protective cable failed to eliminate the oscillation. Table 2 shows that reducing the length of the protective cable effectively reduces the overvoltage oscillation amplitude, while higher capacitance values ​​require shorter protective cables. Therefore, in such cases, it is recommended that the secondary protection be placed closer to the equipment or connected in series with a resistor to reduce the impact of the oscillation.

[0120] If the device is considered as a resistive-capacitive load, such as Figure 9 As shown, similar to a capacitive load, oscillations will occur at both ends of the load. The oscillation frequency and amplitude change with the capacitance value. However, due to the damping effect of the resistor, the amplitude is also affected by the resistance value. The larger the resistance value, the smaller the amplitude; the smaller the resistance value, the larger the amplitude.

[0121] This invention also includes experimental investigations to explore the correlation and influence between overvoltage and energy standards, providing a basis for whether the implementation of the two coordinated standards can be separated. When both coordinated standards of the two-stage SPD are met, the protection effect is maximized. However, whether the implementation of the two coordinated standards can be separated is also worthy of attention in practical applications. Therefore, in addition to this, this invention also explores whether there is any mutual influence. Comparative experiments were conducted on the energy coordination of the two-stage SPD and the two lightning strike amplitudes for both resistive and capacitive load conditions, comparing whether the overvoltage standard was met. Here, E1 represents the secondary SPD overvoltage, and E2 represents the load overvoltage. The results are as follows: Figure 11 and Figure 12 As shown.

[0122] Because the overvoltage curves for different types of loads are similar and difficult to observe when the load is resistive, a scatter plot is used, mainly observing the YZ projection direction, such as... Figure 11 As shown, comparing the same overvoltage with the same surge amplitude reveals that the overvoltages of those without successful energy matching are all higher than those with successful matching. Different surge amplitudes have little impact on overvoltages with or without energy matching. However, for different overvoltages with the same surge amplitude, regardless of whether energy matching is successful, the load overvoltage does not exceed the overvoltage of the secondary SPD. This indicates that overvoltage matching is not directly related to whether energy matching is successful.

[0123] Depend on Figure 12 It is evident that the surge amplitude significantly impacts the overvoltage amplitude. Under a high-surge lightning strike, uncoordinated two-stage SPDs exhibit higher secondary overvoltages, and consequently, higher load overvoltages. Under the same surge amplitude, without successful energy coordination, the load overvoltage of the two-stage SPDs exhibits greater voltage fluctuations than with successful coordination, and the larger the surge amplitude, the more pronounced the voltage fluctuations. This demonstrates that overvoltage coordination directly influences the success of energy coordination.

[0124] In summary, the present invention aims to solve the coordination problem of multi-stage surge protectors in communication power systems, thereby avoiding the failure of protection modules, unnecessary waste of resources, and even impact on equipment power supply.

[0125] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for coordinating and optimizing surge protection in a communication power supply system, characterized in that, Includes the following steps: S1: Select a suitable SPD based on the composition of the communication power supply system, conduct simulation experiments, and construct an SPD model; S2: Analyze the overvoltage and energy standards based on the constructed SPD model; the specific analysis steps in S2 are as follows: S21: Since the line impedance is usually much greater than the line resistance, for ease of analysis, the influence of the line resistance is ignored. We assume the line is a lossless uniform transmission line, and the line length is given as... The unit inductance is The unit capacitance is C0, and the line surge impedance is... speed of spread The time it takes for a wave to travel from point A to point B And there are ; The rising edge of the applied impulse current can be approximated as a slanted wave, i.e. = Suppose that the current starts from point A at time 0, and after time... When the current wavefront reaches point B, before the upstream SPD turns on, the voltage across the upstream SPD is... for: (2) When the current wave reaches point B, according to Is it greater than the startup voltage of the upstream SPD? This needs to be discussed in two separate cases; S22: When If the upstream SPD has already turned on before the current wave reaches point B, then the general formula for determining whether the upstream SPD acts before the downstream SPD is: Line length l or line surge impedance When the rise slope of the impulse current wave is known, satisfy (3) Added shock waveform steepness When known, the line length or line surge impedance satisfies (4) As can be seen from equations (2) and (3), under the action of steep or large-amplitude inrush current, the upstream SPD is likely to act before the downstream SPD. Increasing the transmission line length between the two-stage protectors can make the upstream SPD act before the downstream SPD. S23: When When considering the influence of the load on the current reflection and refraction, it is necessary to discuss the load and the line impedance value. S24: When Z L =Z C When the load impedance equals the line surge impedance, the current wave does not reflect at point B and is entirely refracted into the load. After the current wave reaches point B, the voltage on the downstream SPD must reach the starting voltage. It will take time. for: (5) For the upstream SPD to activate before the downstream SPD, the line parameters must meet the following requirements: (6) S25: When Z L ≠Z C When the load impedance is not equal to the line wave impedance, the current wave is reflected at point B, and the current entering the load... for: (7) The voltage on the load must reach Value, requires time for: (8) For the upstream SPD to activate before the downstream SPD, the line parameters must meet certain conditions, including The refractive index is 1. K Reflection coefficient (9) (10) (11) S3: The waveform of the fault traveling wave reaching the upstream SPD will change with the location of the lightning strike. Time domain and frequency domain analysis is performed on this change. S4: The factors that affect the overvoltage waveform reaching the load and the overvoltage waveform reaching each stage of SPD were investigated through simulation experiments in electromagnetic transient software, and reasonable optimization and coordination suggestions were derived.

2. The surge protection coordination and optimization method for a communication power supply system according to claim 1, characterized in that, In S2, the upstream SPD should activate before the downstream SPD to absorb a larger inrush current. When the fault voltage is insufficient to activate the upstream SPD, it is necessary to consider whether the line wave impedance and the load impedance are equal, whether the traveling wave is reflected, what conditions the line parameters must meet to enable the upstream SPD to activate first, and to determine the impact of the load condition on it.

3. The surge protection coordination and optimization method for a communication power supply system according to claim 2, characterized in that, The specific optimization process of the SPD is as follows: The steepness of the lightning surge current is calculated, and the upstream surge protection device (SPD) is prioritized for activation based on the matching relationship between line impedance and load impedance. The transmission line lengths between SPDs are adjusted to ensure that the voltage protection coordination between SPDs conforms to the lightning surge energy transfer law. During the SPD configuration process, load characteristics are considered to ensure that the surge voltage level at the equipment end is within a safe range. Finally, by comparing the success or failure of energy coordination under different loads, the corresponding overvoltage standards are studied.

4. The surge protection coordination and optimization method for a communication power supply system according to claim 1, characterized in that, The specific analysis steps for S3 are as follows: S31: According to the superposition principle, any fault on the line can be decomposed into normal operation component and fault component. The fault component can be regarded as a transient mechanism added to the voltage source. The fault-added voltage source will generate a broadband traveling wave signal with step, which is generated from the fault point and refracted and reflected along the line wave impedance discontinuity. S32: Lightning surge voltage is an external fault. From the perspective of frequency domain analysis, the fault traveling wave has a wide frequency band. The wave impedance, transmission function and refraction and reflection coefficient are all functions of frequency, as shown in equation (9) to equation (13). Due to the influence of transmission function and refraction and reflection coefficient, the amplitude attenuation and phase change of each frequency component of the traveling wave are different during transmission. (12) (13) (13) In the formula: For transfer functions, and These are the attenuation coefficients, , , , As a line distribution parameter, when the lightning strike location is far away, the surge traveling wave will exhibit a large attenuation of high-frequency components, which will lead to a reduction in the surge steepness and amplitude reaching the SPD, thereby affecting the energy coordination between SPDs. The impact on the energy coordination of the two SPDs is tested by changing the surge location generated by the lightning strike and the cable length between the SPDs.

5. The surge protection coordination and optimization method for a communication power supply system according to claim 1, characterized in that, The specific steps in S4 are as follows: S41: When only the influence of lightning amplitude is considered, an experiment was conducted on different distances between two series-connected SPDs using a surge generator that can generate 8 / 20 μs direct lightning current. The energy coordination of the two-stage surge protectors was studied using SPD1 rated voltage of 660V and SPD2 rated voltage of 330V as examples. Lightning surge intrusion was studied using lightning surge peak voltages of 10kV, 20kV and 50kV. S42: Taking four lightning strike locations as examples, namely 20m, 100m, 500m and 1km, the energy absorption of the two-stage SPD is compared, and the inter-stage cable is appropriately extended for energy coordination. S43: When the equipment is subjected to different loads, the system analyzes the electrical characteristics under three different loads, namely resistive, capacitive and resistive-capacitive loads, and makes optimization and coordination suggestions based on the analysis results.

6. The surge protection coordination and optimization method for a communication power supply system according to claim 1, characterized in that, It also includes experiments to explore whether there is a correlation and influence between overvoltage and energy standards, providing a basis for whether the implementation of the two coordinated standards can be carried out separately.

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