Active power distribution network symmetric fault differential protection method considering T-connection unmeasurable branches
By collecting line currents in active distribution networks and calculating the fault current amplitude ratio characteristics, the problem of reduced sensitivity and reliability of traditional differential protection methods in T-connected unmeasurable branches is solved, enabling accurate identification and differentiation of symmetrical faults and improving the selectivity and reliability of protection devices.
Patent Information
- Application Number
- CN202510820961.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-19
- Publication Date
- 2025-10-31
AI Technical Summary
Traditional differential protection methods suffer from reduced sensitivity and reliability in active distribution networks with unmeasurable T-connected branches, and cannot effectively distinguish between faults inside and outside the zone.
By collecting the current at the beginning and end of the distribution network line, calculating the fault current amplitude ratio characteristics, and using the preset differential protection strategy to carry out symmetrical fault differential protection, the fault scenario can be judged to distinguish between faults inside and outside the zone.
It improves the adaptability of the distribution network to complex fault scenarios, ensures that the protection device does not malfunction when there is a fault outside the area, and enhances selectivity and reliability.
Smart Images
Figure CN120879482A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of differential protection for symmetrical faults in active distribution networks, and specifically to a method for differential protection of symmetrical faults in active distribution networks that takes into account unmeasurable branches connected by T-connections. Background Technology
[0002] The proportion of distributed generation (DG) in distribution networks is gradually increasing. Taking China as an example, as of June 2023, the installed capacity of distributed photovoltaic (PV) power generation in China reached 198 million kW, accounting for approximately 7.3% of the total installed capacity. Especially in some receiving-end power grids in China, the proportion of distributed PV and other new energy sources connected to the grid is rapidly increasing. On the one hand, DG can improve the power supply quality and flexibility of the distribution network; on the other hand, the connection of DG changes the original fault current distribution of the distribution network, rendering traditional staged current protection ineffective. Furthermore, the fault characteristics of DG are increasingly affected by power electronic devices, placing higher demands on the rapid response capability of protection systems. To ensure the safe and stable operation of the distribution network after large-scale DG integration, it is required to configure full-line fast-acting protection. Lines connected to DG typically require differential current protection as the main protection. However, distribution network feeders often contain a large number of loads connected in a T-connection configuration and inverter-type DG, significantly reducing the sensitivity and reliability of traditional differential protection. Therefore, it is urgent to conduct research on new differential protection methods for distribution networks containing unmeasurable T-connected branches. Summary of the Invention
[0003] To address the problem that in existing active distribution networks with unmeasurable T-connected branches, the T-connected distributed generation still supplies current to the line during a symmetrical fault, affecting the setting process of differential protection methods based on the head-to-end current amplitude ratio, this invention proposes a differential protection method for symmetrical faults in active distribution networks considering unmeasurable T-connected branches, comprising:
[0004] Collect the line-start current I of the target line in the distribution network Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system.
[0005] Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
[0006] Preferably, based on the line start-up current I Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is performed according to a preset differential protection strategy, including:
[0007] Based on the current I at the beginning of the line Mx and the line end current I Nx Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio1 Based on the current I at the beginning of the line Mx and short-circuit current value Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 ;
[0008] Determine the ratio of the fault current amplitude at the beginning and end of the line to characteristic I. ratio1 Characteristic II: Ratio of Fault Current Amplitude at the Beginning and End of the Line ratio2 Does it meet the criteria for symmetrical fault scenarios?
[0009] If so, a fault is confirmed to exist within the area, and protection actions are performed on the target line.
[0010] If not, then an external fault is identified, and the protection is locked.
[0011] Preferably, the amplitude of the fault current at the beginning and end of the line is greater than that of characteristic I. ratio1 Determine using the following formula:
[0012]
[0013] Preferably, the ratio of the fault current amplitude at the beginning and end of the line to characteristic II is... ratio2 Determine using the following formula:
[0014]
[0015] Preferably, the symmetric fault scenario criterion is satisfied when the following two equations are both true:
[0016]
[0017] In the formula, K rel For reliability coefficient, γ is the ratio of minimum current amplitude at the beginning and end of the line, and σ is the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value.
[0018] Preferably, the minimum amplitude ratio γ of the current at the beginning and end of the line is determined by the following formula:
[0019]
[0020] In the formula, ε is a constant that is preset to 0.
[0021] Preferably, the characteristic of the ratio of fault current amplitude at the beginning and end of the line is I.ratio2 The minimum value σ is determined by the following formula:
[0022]
[0023] Based on the same inventive concept, the present invention also provides an active distribution network symmetrical fault differential protection system considering T-connected unmeasurable branches, characterized in that it includes: a data acquisition module and a protection module;
[0024] The data acquisition module is used to collect the line-start current I of the target line in the distribution network. Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system.
[0025] The protection module is used to base the line head current I... Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
[0026] Preferably, the protection module is used for:
[0027] Based on the current I at the beginning of the line Mx and the line end current I Nx Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio1 Based on the current I at the beginning of the line Mx and short-circuit current value Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 ;
[0028] Determine the ratio of the fault current amplitude at the beginning and end of the line to characteristic I. ratio1 Characteristic II: Ratio of Fault Current Amplitude at the Beginning and End of the Line ratio2 Does it meet the criteria for symmetrical fault scenarios?
[0029] If so, a fault is confirmed to exist within the area, and protection actions are performed on the target line.
[0030] If not, then an external fault is identified, and the protection is locked.
[0031] Preferably, the amplitude of the fault current at the beginning and end of the line in the protection module is higher than that of characteristic I. ratio1 Determine using the following formula:
[0032]
[0033] Preferably, the amplitude of the fault current at the beginning and end of the line in the protection module is greater than that of characteristic I.ratio2 Determine using the following formula:
[0034]
[0035] Preferably, the symmetric fault scenario criterion in the protection module is satisfied when the following two equations are both true:
[0036]
[0037] In the formula, K rel For reliability coefficient, γ is the ratio of minimum current amplitude at the beginning and end of the line, and σ is the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value.
[0038] Preferably, the ratio γ of the minimum amplitude of the line start and end currents in the protection module is determined by the following formula:
[0039]
[0040] In the formula, ε is a constant that is preset to 0.
[0041] Preferably, the protection module contains a characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value σ is determined by the following formula:
[0042]
[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0044] This invention provides a differential protection method for symmetrical faults in an active distribution network considering unmeasurable branches with T-connections. The method is characterized by including: acquiring the line-start current I of the target line in the distribution network. Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system. Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is performed according to a preset differential protection strategy. This invention analyzes the relationship between the current at the beginning and end of the line and the minimum short-circuit current at the end of the line when a symmetrical fault occurs in the upstream and downstream areas of the distribution network, and proposes a three-phase short-circuit identification criterion based on the amplitude ratio characteristic, thereby improving the adaptability of the distribution network to complex fault scenarios. Attached Figure Description
[0045] Figure 1 The flowchart of the active distribution network symmetrical fault differential protection method considering the T-connected unmeasurable branch is shown in the present invention.
[0046] Figure 2 This invention provides a diagram of a 10kV distribution network with a neutral point grounded by a small resistor, which is part of the symmetrical fault differential protection method for active distribution networks considering T-connected unmeasurable branches in this invention.
[0047] Figure 3 This invention provides a schematic diagram showing the relationship between the protection criteria and setting values when a symmetrical short circuit occurs on line NO downstream of line MN in an active distribution network with an unmeasurable branch connected to a T-connection.
[0048] Figure 4 This invention provides a schematic diagram showing the relationship between the protection criteria and setting values when a symmetrical short circuit occurs on line NO downstream of line MN in an active distribution network with an unmeasurable branch connected to a T-connection.
[0049] Figure 5 This is a schematic diagram of the active distribution network symmetrical fault differential protection system considering the unmeasurable branch of the T-connection according to the present invention. Detailed Implementation
[0050] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.
[0051] Example 1
[0052] This invention provides a method for differential protection of symmetrical faults in active distribution networks considering unmeasurable branches connected in a T-connection, as shown in the flowchart below. Figure 1 As shown:
[0053] S1. Collect the line-start current I of the target line in the distribution network. Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system.
[0054] S2, Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
[0055] Step S2 specifically includes:
[0056] Assume that there are T-connected unmeasurable loads and distributed generation sources within the MN section of the distribution network, see Figure 2 , Figure 2 This is a diagram of a distribution network with a neutral point grounded through a small resistor. The system-side power supply voltage is 10kV, and L, M, N, and O are the busbars, R... nThe neutral point grounding resistor has a resistance of 10Ω. L1, L2, and L3 are loads connected to the busbar. TL is a T-type load, and its current is denoted as I. TL IIDG1 and IIDG2 are inverter-type distributed generation sources connected to the bus, and TDG is a T-type inverter-type distributed generation source, whose current is denoted as I. TDG When a symmetrical fault occurs on the line, the voltage drop is severe, and the non-induction motor load exhibits a constant impedance model, with I... TL ≈0. Therefore, only the effects of IIDG and induction motor load on fault characteristics need to be considered.
[0057] The minimum short-circuit current that occurs when a three-phase short circuit occurs at the end of line MN of this level is denoted as . Define the method for calculating the current amplitude ratio:
[0058]
[0059] In the formula, x represents the phase, I Mx I Nx I represents the current at both ends of the line. ratio1 I ratio2 These are the two defined current amplitude ratios.
[0060] For the ratio of the current amplitude at the beginning and end of the line, I ratio1 When the fault occurs within the MN section of the line, the short-circuit current I on the M side... Mx The sum of the system short-circuit current and the short-circuit current output by IIDG1 is relatively large; the short-circuit current I on the N side... Nx This is the short-circuit current output by IIDG2 and its downstream distributed power sources, and its amplitude is relatively small. At this time, I Mx I Nx The amplitude ratio satisfies:
[0061]
[0062] Specifically, when the downstream line of MN contains a large-capacity induction motor load, at the moment of a fault, the induction motor load will feed a large short-circuit current into the line, at which time I Nx The amplitude will increase significantly, and equation (2) may not hold true at the moment the fault occurs.
[0063] When a three-phase short-circuit fault occurs in the upstream section of line MN, the fault current I at terminal M... Mx The fault current at terminal N is the sum of the short-circuit current at T-connected IIDG; while the fault current at terminal N is I Nx This is the sum of the short-circuit currents of IIDG2 and the downstream IIDG, i.e.:
[0064]
[0065] Specifically, when there is no IIDG downstream of line MN, I Nx ≈0, at this time the fault current I at terminal M is 0. Mx With the fault current I at the N terminal Nx The amplitude ratio will be much greater than 1, as shown in equation (2). This equation still holds even if there is a large-capacity induction motor load downstream of line MN.
[0066] When a three-phase short-circuit fault occurs in the downstream section of line MN, the fault current I at terminal M... Mx The fault current I at terminal N is the sum of the system short-circuit current and the short-circuit current of IIDG1. Nx Given the sum of the fault current at terminal M and the short-circuit current at T-connected IIDG, we have:
[0067]
[0068] Even if there is a large-capacity induction motor load downstream of line MN, equation (4) still holds true.
[0069] In summary, the ratio of fault current amplitude at the beginning and end of the fault can be used to distinguish between downstream faults outside the fault zone and faults within the fault zone, but it cannot accurately distinguish between faults within the fault zone and upstream faults outside the fault zone.
[0070] The ratio of the current at the beginning of the line to the minimum short-circuit current amplitude at the end of the line during a three-phase short circuit is I. ratio2 When the fault occurs within the MN section of the line, there is always I Mx It will not be significantly smaller than Right now:
[0071]
[0072] In the formula, Zs refers to the equivalent impedance of the system; Z LN This refers to the impedance of line LN; This is the equivalent electromotive force of the system power supply.
[0073] When a three-phase short circuit occurs in the upstream section of line MN, I Mx The sum of short-circuit currents from the downstream IIDG is ∑I DG Since the short-circuit capacity of the IIDG does not exceed 67% of the system's short-circuit capacity, therefore:
[0074]
[0075] As can be seen from equations (5) and (6), by determining a suitable ratio k, I ratio2 There will be significant differences between faults within the zone and upstream faults outside the zone, which can ensure that the protection does not malfunction when there is a fault outside the zone and improve selectivity.
[0076] For the characteristic I of the fault current amplitude ratio at the beginning and end of line MN ratio1 I Nx It will not exceed 67% of the system short-circuit current, therefore the minimum amplitude γ of the current at the beginning and end of the line is:
[0077]
[0078] In the formula, ε is a constant close to 0, which is to prevent numerical overflow caused by the short-circuit current on the N side approaching 0.
[0079] The characteristic I of the ratio of the fault current at the M-end of the line to the current amplitude when a three-phase short circuit occurs at the end of the line. ratio2 When an upstream fault occurs outside the zone, I Mx The short-circuit current from IIDG, this ratio does not exceed 0.67, while during intra-zone faults, this ratio will not be significantly less than 1. In order to meet the selectivity of the protection, I ratio2 The minimum value is set as follows:
[0080]
[0081] In summary, the protection criteria for symmetrical fault scenarios are as follows:
[0082]
[0083] Among them, K rel For reliability coefficient, it can generally be taken as 1.1. When considering the load of the T-connected unmeasurable induction motor, since its short-circuit current rapidly decays to the steady-state level in a short time, equation (9) still holds.
[0084] Regarding this criterion Figure 3 This indicates the relationship between the protection criterion and the setting value when a symmetrical short circuit occurs on the upstream line LM of line MN. The setting value I is... set1 The size is 1.5kA;
[0085] Figure 4 This indicates the relationship between the protection criterion and the setting value when a symmetrical short circuit occurs on line NO downstream of line MN. The setting value I is... set2 The current is 0.7kA. As can be seen, the protection system reliably does not operate when a symmetrical fault occurs outside the protection zone.
[0086] Example 2
[0087] Based on the same inventive concept, this invention also provides an active distribution network symmetrical fault differential protection system that considers unmeasurable branches connected in a T-connection, such as... Figure 5 As shown, it includes: a data acquisition module and a protection module;
[0088] The data acquisition module is used to collect the line-start current I of the target line in the distribution network. Mxand the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system.
[0089] The protection module is used to base the line head current I... Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
[0090] Preferably, the protection module is used for:
[0091] Based on the current I at the beginning of the line Mx and the line end current I Nx Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio1 Based on the current I at the beginning of the line Mx and short-circuit current value Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 ;
[0092] Determine the ratio of the fault current amplitude at the beginning and end of the line to characteristic I. ratio1 Characteristic II: Ratio of Fault Current Amplitude at the Beginning and End of the Line ratio2 Does it meet the criteria for symmetrical fault scenarios?
[0093] If so, a fault is confirmed to exist within the area, and protection actions are performed on the target line.
[0094] If not, then an external fault is identified, and the protection is locked.
[0095] Preferably, the amplitude of the fault current at the beginning and end of the line in the protection module is higher than that of characteristic I. ratio1 Determine using the following formula:
[0096]
[0097] Preferably, the amplitude of the fault current at the beginning and end of the line in the protection module is greater than that of characteristic I. ratio2 Determine using the following formula:
[0098]
[0099] Preferably, the symmetric fault scenario criterion in the protection module is satisfied when the following two equations are both true:
[0100]
[0101] In the formula, K relFor reliability coefficient, γ is the ratio of minimum current amplitude at the beginning and end of the line, and σ is the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value.
[0102] Preferably, the ratio γ of the minimum amplitude of the line start and end currents in the protection module is determined by the following formula:
[0103]
[0104] In the formula, ε is a constant that is preset to 0.
[0105] Preferably, the protection module contains a characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value σ is determined by the following formula:
[0106]
[0107] In summary, this invention provides a differential protection method for symmetrical faults in an active distribution network that considers unmeasurable branches connected in a T-connection. The method is characterized by including: acquiring the line-start current I of the target line in the distribution network. Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system. Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is performed according to a preset differential protection strategy. This invention analyzes the relationship between the current at the beginning and end of the line and the minimum short-circuit current at the end of the line when a symmetrical fault occurs in the upstream and downstream areas of the distribution network, and proposes a three-phase short-circuit identification criterion based on the amplitude ratio characteristic, thereby improving the adaptability of the distribution network to complex fault scenarios.
[0108] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0109] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.
[0110] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.
[0111] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0112] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.
Claims
1. A differential protection method for symmetrical faults in an active distribution network considering unmeasurable branches with T-connections, characterized in that, include: Collect the line-start current I of the target line in the distribution network Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system. Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
2. The method according to claim 1, characterized in that, Based on the current I at the beginning of the line Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is performed according to a preset differential protection strategy, including: Based on the current I at the beginning of the line Mx and the line end current I Nx Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio1 Based on the current I at the beginning of the line Mx and short-circuit current value Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 ; Determine the ratio of the fault current amplitude at the beginning and end of the line to characteristic I. ratio1 Characteristic II: Ratio of Fault Current Amplitude at the Beginning and End of the Line ratio2 Does it meet the criteria for symmetrical fault scenarios? If so, a fault is confirmed to exist within the area, and protection actions are performed on the target line. If not, then an external fault is identified, and the protection is locked.
3. The method as described in claim 2, characterized in that, The characteristic of the ratio of fault current amplitude at the beginning and end of the line is I. ratio1 Determine using the following formula:
4. The method as described in claim 2, characterized in that, Characteristic II: Fault Current Amplitude Ratio at the Beginning and End of the Line ratio2 Determine using the following formula:
5. The method as described in claim 2, characterized in that, The symmetric fault scenario criterion is satisfied when both of the following equations are true: In the formula, K rel For reliability coefficient, γ is the ratio of minimum current amplitude at the beginning and end of the line, and σ is the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value.
6. The method as described in claim 5, characterized in that, The minimum amplitude ratio γ of the current at the beginning and end of the line is determined by the following formula: In the formula, ε is a constant that is preset to 0.
7. The method as described in claim 5, characterized in that, The above refers to the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 The minimum value σ is determined by the following formula:
8. An active distribution network symmetrical fault differential protection system considering unmeasurable branches connected in a T-connection, characterized in that, include: Data acquisition module, protection module; The data acquisition module is used to collect the line-start current I of the target line in the distribution network. Mx and the current I at the end of the line Nx Calculate the short-circuit current value at the end of the line when a three-phase short circuit occurs under the minimum operating mode of the distribution network system. The protection module is used to base the line head current I... Mx The current I at the end of the line Nx and short-circuit current value Differential protection for symmetrical faults in the distribution network is carried out according to the preset differential protection strategy.
9. The system according to claim 8, characterized in that, The protection module is used for: Based on the current I at the beginning of the line Mx and the line end current I Nx Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio1 Based on the current I at the beginning of the line Mx and short-circuit current value Calculate the characteristic of the ratio of fault current amplitude at the beginning and end of the line. ratio2 ; Determine the ratio of the fault current amplitude at the beginning and end of the line to characteristic I. ratio1 Characteristic II: Ratio of Fault Current Amplitude at the Beginning and End of the Line ratio2 Does it meet the criteria for symmetrical fault scenarios? If so, a fault is confirmed to exist within the area, and protection actions are performed on the target line. If not, then an external fault is identified, and the protection is locked.
10. The system as described in claim 9, characterized in that, The characteristic I is the ratio of the fault current amplitude at the beginning and end of the line in the protection module. ratio1 Determine using the following formula: