Distance adaptive protection method and system for phase-shifting transformer in active power distribution network

Abstract

The invention discloses a distance adaptive protection method and system for a phase-shifting transformer in an active power distribution network, and the method comprises the steps: determining an input and output voltage relation based on an equivalent impedance model of the phase-shifting transformer, and analyzing the network operation mode change caused by the access to the power distribution network, and calculating positive sequence, negative sequence and zero sequence current characteristics of the distributed inverter power supply under different fault types. Based on fault current characteristics, positive sequence, negative sequence and zero sequence branch coefficients of distance protection of the power distribution network are corrected, equivalent impedance of the phase-shifting transformer is combined, a setting impedance initial value of a second stage of distance protection is calculated, and a corresponding relation between the setting impedance initial value and the equivalent impedance of the phase-shifting transformer is established. The phase angle difference between the two sides of a closed-loop point of the power distribution network is monitored in real time, the tap position of the secondary side of the exciting transformer is dynamically adjusted, the equivalent impedance of the phase-shifting transformer is changed accordingly, the distance protection setting impedance value is updated in real time, self-adaptive setting of protection parameters is achieved, and the fault recognition precision and the protection reliability are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of transmission line distance protection setting, and more specifically, relates to a distance adaptive protection method and system for a phase-shifting transformer in an active distribution network. Background Art

[0002] With the continuous increase in the proportion of new energy access, the active distribution network containing distributed inverter power supplies has gradually become an important part of modern power systems. However, due to the power electronic interface characteristics of distributed inverter power supplies, their fault current characteristics are significantly different from those of traditional synchronous generators, making it difficult for traditional distance protection methods based on short-circuit current characteristics to adapt to complex power grid environments, which may lead to misoperation or refusal of protection. In addition, as an important device for improving power flow distribution and suppressing circulating current, the access of a phase-shifting transformer will change the equivalent impedance and phase characteristics of the distribution network, thereby affecting the distribution of fault current and making it difficult for traditional fixed-setting distance protection schemes to ensure protection accuracy and reliability.

[0003] Existing technologies usually configure distance protection by using a fixed-setting method. However, in an active distribution network containing a phase-shifting transformer and distributed inverter power supplies, due to the influence of the winding parameters of the phase-shifting transformer, the control strategies of distributed power sources, and the network topology structure on fault current, fixed-setting protection is difficult to take into account different operating conditions, and the setting parameters often require manual intervention and cannot achieve adaptive adjustment. Some studies have proposed methods based on impedance calculation or branch coefficient correction to optimize distance protection, but these methods usually do not consider the dynamic characteristics of the phase-shifting transformer or fail to establish the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer, resulting in insufficient adaptability of the protection scheme in actual operation.

[0004] Therefore, for an active distribution network containing a phase-shifting transformer, there is an urgent need for a distance protection method that can adaptively adjust protection parameters to ensure accurate fault identification under different operating conditions, optimize protection setting, and improve the safety and stability of the distribution network. Summary of the Invention

[0005] To solve the deficiencies in the existing technology, the present invention provides a distance adaptive protection method and system for a phase-shifting transformer in an active distribution network.

[0006] The present invention adopts the following technical solutions.

[0007] The first aspect of the present invention provides a distance adaptive protection method for a phase-shifting transformer in an active distribution network, including the following steps: Determine the relationship between the input and output voltages of the phase-shifting transformer and establish an equivalent impedance model of the phase-shifting transformer; According to the equivalent impedance model of the phase-shifting transformer, determine the changes in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network, and analyze the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types according to the changes in the network operation mode; According to the current characteristics of the distributed inverter power supply under different fault types, recalculate and correct the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient adopted by the distance protection of the distribution network; Using the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients, combined with the equivalent impedance of the current operation state of the phase-shifting transformer, determine the initial value of the setting impedance of the second-stage protection of the distance protection, and establish the corresponding relationship between the setting impedance of the second-stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer based on the initial value of the setting impedance; According to the real-time change of the phase angle difference on both sides of the closed-loop point of the distribution network, dynamically change the tap position of the secondary side of the excitation transformer of the phase-shifting transformer, so that the equivalent impedance of the phase-shifting transformer changes accordingly, and use the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer to update the setting impedance value of the second-stage protection of the distance protection in real time, so as to realize the adaptive setting of the protection parameters.

[0008] Preferably, the determination of the relationship between the input and output voltages of the phase-shifting transformer and the establishment of the equivalent impedance model of the phase-shifting transformer include: According to the structure of the double-core symmetric phase-shifting transformer composed of a series transformer and a parallel transformer, determine the turns ratio of the parallel transformer and the turns ratio of the series transformer; According to the above turns ratio and the winding impedance parameters of the series transformer and the parallel transformer respectively, construct the input voltage and output voltage of the phase-shifting transformer as follows:

[0009] According to the input voltage and output voltage of the phase-shifting transformer, construct the equivalent impedance model of the phase-shifting transformer as follows:

[0010] In the formula, and are the output voltage and input voltage respectively; and are the turns ratio of the parallel transformer and the turns ratio of the series transformer respectively; represents the output current; represents the equivalent impedance of the phase-shifting transformer; and are the primary and secondary winding impedances of the parallel transformer respectively; represents the equivalent impedance of the internal winding of the series transformer; represents the equivalent excitation impedance of the phase-shifting transformer.

[0011] Preferably, determining the changes in the network operation mode caused by the connection of the phase-shifting transformer includes: Based on the equivalent impedance model of the phase-shifting transformer, calculate the change in the equivalent impedance of the line before and after the connection of the phase-shifting transformer using the following formula:

[0012] Calculate the change in the line voltage phase before and after the connection of the phase-shifting transformer using the following formula:

[0013] According to the change in the equivalent impedance of the line and the change in the voltage phase , calculate the power flow distribution matrix before and after the connection of the phase-shifting transformer using the following formula:

[0014] In the formula, represents the change in the equivalent impedance caused by the connection of the phase-shifting transformer; represents the equivalent impedance of the line after the connection of the phase-shifting transformer; represents the equivalent impedance of the line before the connection of the phase-shifting transformer; represents the change in the voltage phase caused by the phase-shifting transformer; represents the voltage phase angle of the line after the connection of the phase-shifting transformer; represents the voltage phase angle of the line before the connection of the phase-shifting transformer; represents the power flow distribution matrix after the connection of the phase-shifting transformer; represents the power flow distribution matrix before the connection of the phase-shifting transformer.

[0015] Preferably, analyzing the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types according to the changes in the network operation mode includes: Based on the changes in the network operation mode after the connection of the phase-shifting transformer to the distribution network, construct a composite sequence network of the distribution network containing the phase-shifting transformer and the distributed inverter power supply under single-phase ground fault and two-phase interphase fault respectively; According to the composite sequence network, determine the fault characteristic parameters under two-phase interphase fault and the fault characteristic parameters under single-phase ground fault 、 , including: Calculate the fault characteristic parameters of the two-phase interphase fault using the following formula :

[0016] Calculate the fault characteristic parameters of the single-phase ground fault using the following formula :

[0017] The fault characteristic parameters of single-phase grounding fault in the following formula :

[0018] In the formula, represents the positive-sequence impedance from the phase-shifting transformer to the fault point QM section; represents the negative-sequence impedance from the phase-shifting transformer to the fault point QM section; represents the negative-sequence impedance from the distributed inverter power supply to the fault point S section; represents the negative-sequence impedance from the fault point PQ to the distributed inverter power supply; represents the positive-sequence impedance from the distributed inverter power supply to the fault point S section; represents the positive-sequence impedance from the fault point PQ to the distributed inverter power supply; represents the zero-sequence impedance from the phase-shifting transformer to the fault point QM section; represents the synthetic equivalent impedance of the zero-sequence component of the distribution network; represents the voltage of the distributed inverter power supply.

[0019] Preferably, the fault type is identified in real time, including: After obtaining the equivalent impedance model of the phase-shifting transformer and determining the change in the network operation mode, collect the amplitude and phase information of the three-phase voltage and three-phase current during the fault; Decompose the three-phase voltage and current into positive-sequence, negative-sequence, and zero-sequence components, and compare them with the preset discrimination thresholds respectively. The discrimination thresholds include the grounding discrimination threshold, the asymmetric fault discrimination threshold, and the phasor difference threshold; judge the fault type according to the following rules: When the amplitude of the zero-sequence component exceeds the corresponding grounding discrimination threshold, it is determined that the fault includes a grounding factor; if the amplitude of the negative-sequence component also exceeds the asymmetric fault discrimination threshold at the same time, it is determined as a two-phase grounding fault, otherwise it is a single-phase grounding fault; When the amplitude of the zero-sequence component is lower than the grounding discrimination threshold and the amplitude of the negative-sequence component exceeds the asymmetric fault discrimination threshold, it is determined that the fault is a two-phase interphase fault; When the amplitude of the zero-sequence component is lower than the grounding discrimination threshold, the amplitude of the negative-sequence component is lower than the asymmetric fault discrimination threshold, and the phasor difference between the three-phase voltage and current is not greater than the phasor difference threshold, it is determined that the fault is a three-phase symmetrical short circuit.

[0020] Preferably, the recalculation and correction of the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient adopted by the distance protection of the distribution network include: After determining the fault type, introduce the fault characteristic parameters of the inverter power supply and to represent the relationship between the output current and the grid connection point voltage of the fault operation point of the inverter power supply in the following formula

[0021] Wherein, represents the output fault current of the inverter power supply; represents the grid connection point voltage of the inverter power supply; When the inverter power supply triggers low voltage ride through or current limiting operation and the actual output current reaches the maximum allowable value, the limit value is substituted for to reflect the upper limit of the fault current that the inverter power supply can output; The corrected positive sequence, negative sequence and zero sequence current components of the inverter power supply are respectively incorporated into the composite sequence network, and combined with the line impedance of the distribution network and the equivalent impedance of the phase-shifting transformer to obtain the corrected branch coefficient .

[0022] Preferably, the branch coefficient of the single-phase grounding fault is calculated by the following formula:

[0023] The branch coefficient of the two-phase interphase fault is calculated by the following formula:

[0024] Wherein, represents the reference branch current; represents the fault branch current; represents the equivalent impedance of the phase-shifting transformer; represents the impedance from path S to 1; represents the impedance from path S to 2; represents the impedance from the fault point to the power supply; represents the impedance between two phases; represents the phase displacement factor of the phase-shifting transformer; represents the positive sequence impedance of the section from the phase-shifting transformer to the fault point QM; represents the negative sequence impedance of the section from the phase-shifting transformer to the fault point QM; represents the negative sequence impedance of the section from the distributed inverter power supply to the fault point S; represents the negative sequence impedance from the fault point PQ to the distributed inverter power supply; represents the positive sequence impedance of the section from the distributed inverter power supply to the fault point S; represents the positive sequence impedance from the fault point PQ to the distributed inverter power supply; represents the voltage of the distributed inverter power supply; represents the voltage of phase C.

[0025] Preferably, the initial setting impedance value of the second-stage protection of the distance protection is determined by using the corrected positive sequence, negative sequence and zero sequence branch coefficients and combining with the equivalent impedance of the current operating state of the phase-shifting transformer, including: Combine the branch coefficient with the equivalent impedance model to calculate the initial value of the setting impedance as follows :

[0026] In the formula, represents the initial value of the setting impedance; and represent the protection setting coefficients in different time intervals; represents the fixed reference impedance of the protection device; represents the setting impedance of the first-stage protection; represents the corrected branch coefficient; represents the equivalent impedance of the phase-shifting transformer; represents the time after the fault occurs; represents the preset time threshold.

[0027] Preferably, establishing the correspondence relationship between the setting impedance of the second-stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer based on the initial value of the setting impedance includes: According to the initial value of the setting impedance and the equivalent impedance of the phase-shifting transformer , construct the mapping relationship of the setting impedance changing with the equivalent impedance of the phase-shifting transformer as follows:

[0028] In the formula, represents the setting impedance adjustment function fitted based on the power grid operation data.

[0029] Preferably, dynamically changing the tap position of the secondary side of the excitation transformer of the phase-shifting transformer according to the real-time change of the phase angle difference between both sides of the closed-loop point of the distribution network includes: Obtain the phase voltages and on the left and right sides of the closed-loop point of the distribution network, calculate the voltage phase angles and on both sides, and calculate the real-time phase angle difference as follows:

[0030] Compare the real-time phase angle difference with the preset threshold : If , then select the tap with a winding turn ratio greater than the current winding turn ratio and ; If , then select a tap with a winding turn ratio smaller than the current winding turn ratio and of the tap.

[0031] Preferably, the method for real-time updating the setting impedance value of the second-stage protection of the distance protection by using the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer includes: Obtain the tap configuration of the current excitation transformer, including that there are multiple taps on the secondary side of the excitation transformer, and each tap corresponds to a different winding turn ratio and ; When the tap position changes, obtain the new winding turn ratio and , and calculate the updated equivalent impedance of the phase-shifting transformer as follows:

[0032] According to the established corresponding relationship between the setting impedance and the equivalent impedance, calculate the updated setting impedance value of the second stage of the distance protection:

[0033] In the formula, represents the updated equivalent impedance of the phase-shifting transformer; represents the equivalent impedance calculation function of the phase-shifting transformer; represents the new winding turn ratio of the parallel transformer; represents the new winding turn ratio of the series transformer; represents the winding resistance of the series transformer; represents the winding impedance of the parallel transformer; represents the updated setting impedance value of the second stage of the distance protection.

[0034] The second aspect of the present invention provides a distance adaptive protection system for a phase-shifting transformer in an active distribution network, including: an equivalent impedance calculation module, a network operation mode analysis module, a branch coefficient correction module, a setting impedance calculation module, and an adaptive setting module; The equivalent impedance calculation module is used to determine the relationship between the input and output voltages of the phase-shifting transformer and establish an equivalent impedance model of the phase-shifting transformer based on this relationship; The network operation mode analysis module is used to analyze the change in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network based on the equivalent impedance model of the phase-shifting transformer, and calculate the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types according to this change; The branch coefficient correction module is used to recalculate and correct the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient adopted by the distance protection of the distribution network based on the current characteristics of the distributed inverter power supply under different fault types; The setting impedance calculation module is used to calculate the initial value of the setting impedance of the second-stage protection of the distance protection by using the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients and combining the equivalent impedance of the phase-shifting transformer in the current operating state, and based on the initial value of the setting impedance, establish the corresponding relationship between the setting impedance of the second-stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer; The adaptive setting module is used to monitor the phase angle difference on both sides of the closed-loop point of the distribution network in real time, and dynamically adjust the tap position of the secondary side of the excitation transformer of the phase-shifting transformer according to the change of the phase angle difference, so that the equivalent impedance of the phase-shifting transformer is adjusted accordingly; further utilize the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer to update the setting impedance value of the second-stage protection of the distance protection in real time, so as to realize the adaptive setting of the protection parameters.

[0035] Compared with the prior art, the beneficial effects of the present invention at least include: Based on the equivalent impedance model of the phase-shifting transformer and combined with the fault current characteristics of the distributed inverter power supply, the present invention realizes the correction of the positive-sequence, negative-sequence, and zero-sequence branch coefficients, improves the accuracy of the distance protection setting, makes it adapt to different operating conditions, and avoids misoperation or refusal to operate; by establishing the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer and making adaptive adjustments based on real-time monitoring data, the setting impedance can match the system operating state, ensuring the accuracy of fault discrimination and the reliability of protection action; adopting the method of adjusting the tap position of the secondary side of the excitation transformer in real time based on the phase angle difference, the equivalent impedance of the phase-shifting transformer is adjustable, and the distance protection setting parameters are dynamically updated accordingly, realizing the adaptive optimization of the protection parameters; the present invention can effectively improve the power flow distribution of the distribution network, reduce the influence of the access of the phase-shifting transformer on the network operation mode, enhance the stability and security of the system, is especially suitable for complex power grid environments containing distributed inverter power supplies, maintains high protection performance in power grids with high new energy penetration rates, and meets the protection requirements of intelligent distribution networks. Description of the Drawings

[0036] Figure 1 is a schematic flow chart of the differential protection method for a single-core asymmetric phase-shifting transformer provided according to an embodiment of the present invention; Figure 2 is a schematic diagram of power system fault analysis provided according to an embodiment of the present invention; Figure 3 is a composite sequence network diagram during a two-phase interphase fault of a line provided according to an embodiment of the present invention; Figure 4 is a composite sequence network diagram during a single-phase ground fault of a line provided according to an embodiment of the present invention; Figure 5 It is a power grid structure diagram showing the influence of a phase-shifting transformer on short-circuit current provided according to an embodiment of the present invention. Specific Embodiments

[0037] Next, the accompanying drawings in the embodiments of the present invention will be combined to clearly and completely describe the technical solutions in the embodiments of the present invention.

[0038] It should be understood that the step numbers used in the text are only for convenient description and do not limit the execution order of the steps. As Figure 1 shown, Example 1 of the present invention provides a distance adaptive protection method for a phase-shifting transformer in an active distribution network, including the following steps: Step 1, determine the relationship between the input and output voltages of the phase-shifting transformer and establish an equivalent impedance model of the phase-shifting transformer; Preferably, Step 1 includes: Step 1.1, according to the structure of the dual-core symmetric phase-shifting transformer composed of a series transformer and a parallel transformer, determine the turns ratio of the parallel transformer and the turns ratio of the series transformer; Based on the above turns ratios and the respective winding impedance parameters of the series transformer and the parallel transformer, construct the input voltage and output voltage of the phase-shifting transformer as follows:

[0039] Step 1.2, according to the input voltage and output voltage of the phase-shifting transformer, construct an equivalent impedance model of the phase-shifting transformer as follows:

[0040] In the formula, and are the output voltage and the input voltage respectively; and are the turns ratio of the parallel transformer and the turns ratio of the series transformer respectively; represents the output current; represents the equivalent impedance of the phase-shifting transformer; and are the primary and secondary winding impedances of the parallel transformer respectively; represents the equivalent impedance of the internal winding of the series transformer; represents the equivalent excitation impedance of the phase-shifting transformer.

[0041] Specifically, analyze the fault ride-through characteristics of distributed inverters and the impact of distributed inverters on the operating characteristics of distance protection. Traditional relay protection has many deficiencies in the distribution network with the access of new energy. Traditional distance protection adopts different wiring methods according to different fault types, calculates the branch coefficients of different wiring methods, and formulates protection setting schemes. However, when distributed power sources and phase-shifting transformers are connected to the distribution network and there is a loop closing problem, the original protection scheme may no longer be applicable.

[0042] Before loop closing, the phase angle difference at the loop closing point is not fixed, and the tap position of the phase-shifting transformer needs to change with the change of the phase angle difference. This change leads to the continuous change of the branch factor, which in turn leads to the change of the setting of the second stage of distance protection. Therefore, it is necessary to recalculate the branch coefficient.

[0043] According to the recalculated branch coefficient, determine the distance adaptive protection method of the phase-shifting transformer in the active distribution network. The double-core symmetric phase-shifting transformer is mainly composed of a series transformer and a parallel transformer (also called an exciting transformer). The parallel transformer is used to extract the voltage from the line. By changing the tap position of the secondary winding of the parallel transformer, the extracted voltage can be changed. Then the series transformer reinjects the changed voltage into the line and superimposes it on the original line voltage to generate a new voltage with an unchanged amplitude but a changed phase angle. Therefore, by adjusting the tap position of the parallel transformer, the phase angle of the symmetric double-core phase-shifting transformer can be changed.

[0044] It should be noted that the structure of the active distribution network changes during the grid loop closing process or when the connection and disconnection of current sources in the grid occur, and the access of the phase-shifting transformer will also cause changes in the network operation mode. If a fault occurs during the loop closing process, the direction and magnitude of the current will be significantly different from those in the traditional distribution network. The current protection used in the traditional distribution network will have problems during the loop closing process of the active distribution network. Therefore, due to the characteristic that distance protection is not affected by the operation mode, it is considered to be used for the relay protection of the closed-loop network of the distribution system.

[0045] The branch coefficient in distance protection is an important parameter in power system protection, which is used to measure the distance between the fault location and the protection device location. The branch coefficient is mainly divided into two types: the boosting coefficient and the out-drawing coefficient. The boosting coefficient refers to the coefficient when there is a boosting power source in the branch circuit during a fault in the electrical network. Under normal circumstances 。The out-drawing coefficient refers to the coefficient when a fault occurs in the network with an out-drawing branch line. Under normal circumstances 。

[0046] Such as Figure 2As shown, it is a traditional distance protection aiding line diagram. If the setting calculation is carried out according to the traditional distance protection setting method. In the active distribution network, the branch coefficient is calculated according to the aiding coefficient. The branch coefficient can be expressed as:

[0047] When a three-phase short-circuit fault and a two-phase interphase fault occur in the system, the fault-phase voltage or the voltage between the two fault-phases at the short-circuit point is 0, and the fault voltage measured at the protection installation location.

[0048] According to the expression of the branch coefficient, the branch coefficient of the power grid with an inverter power supply connected to a phase-shifting transformer must be different from that calculated according to the traditional setting method, which directly affects the setting value of the upstream distance II-section protection. Therefore, if the setting calculation is carried out according to the traditional setting method, the distance protection may have insufficient sensitivity or misoperation.

[0049] In order to ensure the accuracy and sensitivity of the distance II-section protection action, it is necessary to recalculate and correct the positive-sequence, negative-sequence, and zero-sequence branch coefficients of the protection according to the fault characteristics of the inverter power supply, and carry out the setting calculation of the distance II-section protection according to the corrected branch coefficient.

[0050] Step 2: According to the equivalent impedance model of the phase-shifting transformer, determine the change in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network, and analyze the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types according to the change in the network operation mode; Preferably, determining the change in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network includes: Step 2.1: Based on the equivalent impedance model of the phase-shifting transformer, calculate the change in the line equivalent impedance before and after the connection of the phase-shifting transformer as follows:

[0051] Calculate the change in the line voltage phase before and after the connection of the phase-shifting transformer as follows:

[0052] Step 2.2: According to the change in the line equivalent impedance and the change in the voltage phase , calculate the power flow distribution matrix before and after the connection of the phase-shifting transformer as follows:

[0053] In the formula, represents the change in the equivalent impedance caused by the connection of the phase-shifting transformer; represents the line equivalent impedance after the connection of the phase-shifting transformer; represents the line equivalent impedance before the connection of the phase-shifting transformer; represents the voltage phase change caused by the phase-shifting transformer; represents the voltage phase angle of the line after the phase-shifting transformer is connected; represents the voltage phase angle of the line before the phase-shifting transformer is connected; represents the power flow distribution matrix after the phase-shifting transformer is connected; represents the power flow distribution matrix before the phase-shifting transformer is connected.

[0054] Step 2.3: According to the change in the network operation mode after the phase-shifting transformer is connected to the distribution network, construct a composite sequence network of the distribution network with a phase-shifting transformer and a distributed inverter under single-phase ground fault and two-phase interphase fault respectively; Step 2.4: Determine the fault characteristic parameters under two-phase interphase fault and single-phase ground fault according to the composite sequence network 、 , including: As Figure 3 shown, it is the composite sequence network diagram during two-phase interphase fault of the line. Calculate the fault characteristic parameters of two-phase interphase fault with the following formula :

[0055] As Figure 4 shown, it is the composite sequence network diagram during single-phase interphase fault of the line. Calculate the fault characteristic parameters of single-phase ground fault with the following formula :

[0056] The fault characteristic parameters of single-phase ground fault are calculated with the following formula :

[0057] In the formula, represents the positive sequence impedance from the phase-shifting transformer to the fault point QM section; represents the negative sequence impedance from the phase-shifting transformer to the fault point QM section; represents the negative sequence impedance from the distributed inverter to the fault point S section; represents the negative sequence impedance from the fault point PQ to the distributed inverter; represents the positive sequence impedance from the distributed inverter to the fault point S section; represents the positive sequence impedance from the fault point PQ to the distributed inverter; represents the zero sequence impedance from the phase-shifting transformer to the fault point QM section; represents the synthetic equivalent impedance of the zero sequence component of the distribution network; represents the voltage of the distributed inverter.

[0058] Step 3: Recalculate and correct the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient used in the distance protection of the distribution network according to the current characteristics of the distributed inverter power supply under different fault types. Preferably, Step 3 includes: According to the composite sequence network diagrams of various types of faults, the external network characteristics of the inverter power supply as shown can be obtained. By combining the external network characteristics of the inverter power supply with its fault characteristics, the fault operating point can be determined.

[0059] After determining the fault type, introduce the fault characteristic parameters of the inverter power supply and , and express the relationship between the output current and the grid connection point voltage of the fault operating point of the inverter power supply as follows:

[0060] In the formula, represents the fault current output by the inverter power supply; represents the grid connection point voltage of the inverter power supply; Specifically, the characteristic parameters a and b refer to the slope and intercept of the dotted line, which simultaneously affect the intersection position of the external network characteristics and the fault characteristics of the distributed inverter power supply, and thus the output current of the inverter power supply will be different.

[0061] The characteristic parameter a will change according to different fault states, and the value of b will be relatively fixed. The corresponding positive-sequence branch coefficient also changes with different values of a and b. After obtaining the branch coefficient, substituting it into the setting value formula of the second-section distance protection at the protection location, the setting value of the second-section distance protection at the protection location can be calculated.

[0062] When the inverter power supply triggers low-voltage ride-through or current-limiting operation and the actual output current reaches the maximum allowable value, substitute the limit value for to reflect the upper limit of the fault current that the inverter power supply can output; Incorporate the corrected positive-sequence, negative-sequence, and zero-sequence current components of the inverter power supply into the composite sequence network respectively, and combine the line impedance of the distribution network and the equivalent impedance of the phase-shifting transformer to obtain the corrected branch coefficient .

[0063] Preferably, when a single-phase grounding fault occurs:

[0064] For a single-phase grounding fault that occurs on a line connected to a phase shifter, after a distributed power source is connected to bus B:

[0065]

[0066]

[0067] When a two-phase interphase fault occurs, the current of the two-phase interphase fault is substituted. Then the new branch coefficient can be obtained.

[0068]

[0069] In the formula, represents the reference branch current; represents the fault branch current; represents the equivalent impedance of the phase-shifting transformer; represents the impedance from path S to 1; represents the impedance from path S to 2; represents the impedance from the fault point to the power source; represents the impedance between two phases; represents the phase displacement factor of the phase-shifting transformer; represents the positive-sequence impedance of the section from the phase-shifting transformer to the fault point QM; represents the negative-sequence impedance of the section from the phase-shifting transformer to the fault point QM; represents the negative-sequence impedance of the section from the distributed inverter power source to the fault point S; represents the negative-sequence impedance from the fault point PQ to the distributed inverter power source; represents the positive-sequence impedance of the section from the distributed inverter power source to the fault point S; represents the positive-sequence impedance from the fault point PQ to the distributed inverter power source; represents the voltage of the distributed inverter power source; represents the voltage of phase C.

[0070] Preferably, the fault type is identified in real time, including: After obtaining the equivalent impedance model of the phase-shifting transformer and determining the change in the network operation mode, the amplitude and phase information of the three-phase voltage and three-phase current are collected during the fault; The three-phase voltage and current are decomposed into positive-sequence, negative-sequence, and zero-sequence components, and compared with the preset discrimination thresholds respectively. The discrimination thresholds include the ground discrimination threshold, the asymmetric fault discrimination threshold, and the phasor difference threshold; The fault type is discriminated according to the following rules: When the amplitude of the zero-sequence component exceeds the corresponding ground discrimination threshold, it is determined that the fault includes a grounding factor; If the amplitude of the negative-sequence component also exceeds the asymmetric fault discrimination threshold, it is determined as a two-phase grounding fault, otherwise it is a single-phase grounding fault; When the amplitude of the zero-sequence component is lower than the ground discrimination threshold and the amplitude of the negative-sequence component exceeds the asymmetric fault discrimination threshold, the fault is determined as a two-phase interphase fault; When the zero-sequence component amplitude is lower than the grounding discrimination threshold, the negative-sequence component is lower than the asymmetric fault discrimination threshold, and the phasor difference between the three-phase voltage and current is not greater than the phasor difference threshold, the fault is determined to be a three-phase symmetrical short circuit.

[0071] When a phase-shifting transformer is connected to the active distribution network system, the phase-shifting transformer will change the phase angle of the current in the distribution network, and also change the applicable range of the protection. Therefore, it also needs to be corrected.

[0072] In a normal distribution network line, such as Figure 5 shown, the formula for the branch coefficient is:

[0073] where is the phase angle changed by the phase-shifting transformer. Where is the equivalent setting impedance of the phase-shifting transformer, , are both the equivalent impedances of the external power supplies in the distribution network. , are both the equivalent impedances of the lines in the distribution network.

[0074] Therefore, when a distributed power source is connected to the distribution network with a phase-shifting transformer and it becomes an active distribution network, the fault characteristics of the distributed inverter power source make the setting calculation of the distance protection for the line containing the inverter power source, especially the calculation of the setting value of the second section of the distance protection, more complex and difficult. The present invention fully considers the fault characteristics of the distributed inverter power source and the influence of the phase-shifting transformer on the action characteristics of the second section of the distance protection of the power grid, and corrects the branch coefficient of the second section of the distance protection.

[0075] Step 4: Use the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients, and combine with the equivalent impedance of the current operating state of the phase-shifting transformer to determine the initial value of the setting impedance of the second-stage protection of the distance protection, and establish a corresponding relationship between the setting impedance of the second-stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer based on the initial value of the setting impedance; Preferably, step 4 includes: Step 4.1: Combine the branch coefficient with the equivalent impedance model to calculate the initial value of the setting impedance as follows :

[0076] In the formula, represents the initial value of the setting impedance; and represent the protection setting coefficients in different time intervals; represents the fixed reference impedance of the protection device; represents the setting impedance of the first-stage protection; represents the corrected branch coefficient; represents the equivalent impedance of the phase-shifting transformer; represents the time after the fault occurs; represents the preset time threshold.

[0077] Specifically, the setting impedance of the second stage of the distance protection should be calculated separately according to the specific situation, and the smaller value should be selected. When the phase angle difference between both sides of the closed-loop point changes, it is necessary to adjust the tap position of the secondary side of the excitation transformer of the phase-shifting transformer to meet the closed-loop requirements. This adjustment will change the number of winding turns in the connected line, thereby affecting the impedance of the phase-shifting transformer.

[0078] Assume that the equivalent impedances of the two power sources are equal, and the difference in line length can be ignored. Since the impedance of the phase-shifting transformer is variable, selecting the minimum value between and is equivalent to comparing and in terms of magnitude.

[0079] When a fault occurs on line BC, the protection setting range is calculated using the branch coefficient Kb. The tapped turns correspond to the setting of the tap-changer position. Considering the minimum number of tap turns, the equivalent impedance of the phase-shifting transformer is significantly reduced. Therefore, when the branch line is not considered, the setting of the second stage protection is determined as the lower limit.

[0080] Step 4.2, according to the initial value of the setting impedance and the equivalent impedance of the phase-shifting transformer , construct the mapping relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer as follows:

[0081] In the formula, represents the setting impedance adjustment function fitted based on the power grid operation data.

[0082] Step 5, according to the real-time change of the phase angle difference between both sides of the closed-loop point of the distribution network, dynamically change the tap position of the secondary side of the excitation transformer of the phase-shifting transformer, so that the equivalent impedance of the phase-shifting transformer changes accordingly, and use the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer to update the setting impedance value of the second stage protection of the distance protection in real time, so as to realize the adaptive setting of the protection parameters.

[0083] Preferably, step 5 includes: Step 5.1, obtain the phase voltages and on the left and right sides of the closed-loop point of the distribution network, calculate the voltage phase angles and on both sides, and calculate the real-time phase angle difference as follows:

[0084] Step 5.2, compare the real-time phase angle difference with the preset threshold : If , select the tap with a winding turn ratio greater than the current winding turn ratio and ; If , select the tap with a winding turn ratio less than the current winding turn ratio and .

[0085] Step 5.3, obtain the tap configuration of the current excitation transformer, including that there are multiple taps on the secondary side of the excitation transformer, and each tap corresponds to a different winding turn ratio and ; Step 5.4, when the tap position changes, obtain the new winding turn ratio and , and calculate the updated equivalent impedance of the phase-shifting transformer as follows:

[0086] Step 5.5, according to the established correspondence between the setting impedance and the equivalent impedance, calculate the updated distance protection second-stage setting impedance value:

[0087] In the formula, represents the updated equivalent impedance of the phase-shifting transformer; represents the equivalent impedance calculation function of the phase-shifting transformer; represents the new winding turn ratio of the shunt transformer; represents the new winding turn ratio of the series transformer; represents the winding resistance of the series transformer; represents the winding impedance of the shunt transformer; represents the updated distance protection second-stage setting impedance value.

[0088] Example 2 of the present invention provides a distance adaptive protection system for a phase-shifting transformer in an active distribution network, including: an equivalent impedance calculation module, a network operation mode analysis module, a branch coefficient correction module, a setting impedance calculation module, and an adaptive setting module; The equivalent impedance calculation module is used to determine the relationship between the input and output voltages of the phase-shifting transformer and establish an equivalent impedance model of the phase-shifting transformer based on this relationship; A network operation mode analysis module, which is used to analyze the change of the network operation mode caused by the connection of a phase-shifting transformer to the distribution network based on the equivalent impedance model of the phase-shifting transformer, and calculate the positive-sequence, negative-sequence, and zero-sequence current characteristics of distributed inverters in the distribution network under different fault types according to this change; A branch coefficient correction module, which is used to recalculate and correct the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient adopted by the distance protection of the distribution network based on the current characteristics of distributed inverters under different fault types; A setting impedance calculation module, which is used to calculate the initial value of the setting impedance of the second-stage protection of the distance protection by using the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients and combining with the equivalent impedance of the current operation state of the phase-shifting transformer, and establish the corresponding relationship between the setting impedance of the second-stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer based on the initial value of the setting impedance; An adaptive setting module, which is used to monitor the phase angle difference on both sides of the closed-loop point of the distribution network in real time, and dynamically adjust the tap position of the secondary side of the excitation transformer of the phase-shifting transformer according to the change of the phase angle difference, so that the equivalent impedance of the phase-shifting transformer is adjusted accordingly; further, by using the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer, the setting impedance value of the second-stage protection of the distance protection is updated in real time to achieve the adaptive setting of the protection parameters.

[0089] The beneficial effects of the present invention at least include: Based on the equivalent impedance model of the phase-shifting transformer and combined with the fault current characteristics of distributed inverters, the present invention realizes the correction of the positive-sequence, negative-sequence, and zero-sequence branch coefficients, improves the accuracy of distance protection setting, makes it adapt to different operating conditions, and avoids misoperation or refusal to operate; by establishing the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer and making adaptive adjustments based on real-time monitoring data, the setting impedance can match the system operation state, ensuring the accuracy of fault discrimination and the reliability of protection actions; adopting the method of real-time adjusting the tap position of the secondary side of the excitation transformer based on the phase angle difference, the equivalent impedance of the phase-shifting transformer is adjustable, and the distance protection setting parameters are dynamically updated accordingly to achieve the adaptive optimization of the protection parameters; the present invention can effectively improve the power flow distribution of the distribution network, reduce the impact of the connection of the phase-shifting transformer on the network operation mode, enhance the stability and security of the system, is particularly suitable for complex power grid environments containing distributed inverters, maintains high protection performance in power grids with high new energy penetration, and meets the protection requirements of smart distribution networks.

[0090] The present disclosure can be a system, a method, and / or a computer program product. The computer program product can include a computer-readable storage medium having computer-readable program instructions thereon for causing a processor to implement various aspects of the present disclosure.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent replacements, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A distance adaptive protection method for a phase-shifting transformer in an active distribution network, characterized in that: The following steps are involved: Determine the relationship between the input and output voltages of the phase-shifting transformer and establish an equivalent impedance model of the phase-shifting transformer; According to the equivalent impedance model of the phase-shifting transformer, the changes in the network operation mode caused by the phase-shifting transformer connected to the distribution network are determined. According to the changes in the network operation mode, the positive-sequence, negative-sequence and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types are analyzed; According to the current characteristics of the distributed inverter under different fault types, the positive sequence branch coefficient, negative sequence branch coefficient and zero sequence branch coefficient used in the distribution network distance protection are recalculated and corrected; The corrected positive-sequence, negative-sequence and zero-sequence branch coefficients are used in combination with the equivalent impedance of the current operating state of the phase-shifting transformer to determine the initial value of the setting impedance of the second stage of distance protection. The corresponding relationship between the setting impedance of the second stage of distance protection and the equivalent impedance of the phase-shifting transformer is established based on the initial value of the setting impedance. According to the real-time change of the phase angle difference on both sides of the closed-loop point of the distribution network, the tap position on the secondary side of the phase-shifting transformer excitation transformer is dynamically changed to change the equivalent impedance of the phase-shifting transformer accordingly. The corresponding relationship between the set impedance and the equivalent impedance of the phase-shifting transformer is used to update the set impedance value of the second stage protection of the distance protection in real time to realize the adaptive setting of the protection parameters.

2. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 is characterized in that: The determining of the relationship between the input and output voltages of the phase-shifting transformer and establishing an equivalent impedance model of the phase-shifting transformer includes: According to the structure of the double-core symmetrical phase-shifting transformer consisting of a series transformer and a parallel transformer, the turns ratio of the parallel transformer and the turns ratio of the series transformer are determined; According to the above turns ratio and the winding impedance parameters of the series transformer and the parallel transformer, the input voltage and output voltage of the phase-shifting transformer are constructed as follows: According to the input voltage and output voltage of the phase-shifting transformer, the equivalent impedance model of the phase-shifting transformer is constructed as follows: In the formula, and are the output voltage and input voltage respectively; and are the turns ratio of the parallel transformer and the turns ratio of the series transformer respectively; Indicates the output current; It represents the equivalent impedance of the phase-shifting transformer; and are the primary and secondary winding impedances of the parallel transformer respectively; It represents the equivalent impedance of the internal winding of the series transformer; Represents the equivalent excitation impedance of the phase-shifting transformer.

3. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 is characterized in that: Determine the changes in network operation mode caused by the phase-shifting transformer connected to the distribution network, including: Based on the equivalent impedance model of the phase-shifting transformer, the change in line equivalent impedance before and after the phase-shifting transformer is connected is calculated as follows: The phase change of the line voltage before and after the phase-shifting transformer is connected is calculated as follows: According to the change of line equivalent impedance And the voltage phase change , the power flow distribution matrix before and after the phase-shifting transformer is connected is as follows: In the formula, Indicates the change in equivalent impedance caused by the connection of the phase-shifting transformer; Indicates the equivalent impedance of the line after the phase-shifting transformer is connected; Indicates the equivalent impedance of the line before the phase-shifting transformer is connected; Indicates the voltage phase change caused by the phase-shifting transformer; Indicates the voltage phase angle of the line after the phase-shifting transformer is connected; Indicates the voltage phase angle of the line before the phase-shifting transformer is connected; Represents the power flow distribution matrix after the phase-shifting transformer is connected; Represents the power flow distribution matrix before the phase-shifting transformer is connected.

4. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 is characterized in that: The method of analyzing the positive sequence, negative sequence and zero sequence current characteristics of distributed inverter power supplies in the distribution network under different fault types according to changes in the network operation mode includes: According to the change of network operation mode after the phase-shifting transformer is connected to the distribution network, a composite sequence network containing phase-shifting transformers and distributed inverters is constructed under single-phase grounding fault and two-phase interphase fault. According to the composite sequence network, the fault characteristic parameters under two-phase phase-to-phase fault and single-phase grounding fault are determined. , ,include: The fault characteristic parameters of two-phase interphase fault are calculated as follows: : The fault characteristic parameters of a single-phase ground fault are calculated as follows: : The fault characteristic parameters of a single-phase grounding fault are as follows: : In the formula, It represents the positive sequence impedance of the phase-shifting transformer to the fault point QM section; It represents the negative sequence impedance of the phase-shifting transformer to the fault point QM section; It represents the negative sequence impedance of the S segment from the distributed inverter to the fault point; Represents the negative sequence impedance from the fault point PQ to the distributed inverter power supply; It represents the positive sequence impedance of the S segment from the distributed inverter to the fault point; Represents the positive sequence impedance from the fault point PQ to the distributed inverter power supply; It represents the zero-sequence impedance of the phase-shifting transformer to the fault point QM section; It represents the synthetic equivalent impedance of the zero-sequence component of the distribution network; Indicates the distributed inverter power supply voltage.

5. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 4 is characterized in that: Real-time identification of fault types, including: After obtaining the equivalent impedance model of the phase-shifting transformer and determining the change in the network operation mode, the amplitude and phase information of the three-phase voltage and three-phase current are collected during the fault period; The three-phase voltage and current are decomposed into positive sequence, negative sequence and zero sequence components, and compared with the preset discrimination thresholds, which include grounding discrimination threshold, asymmetric fault discrimination threshold and phasor difference threshold. The fault type is judged according to the following rules: When the amplitude of the zero-sequence component exceeds the corresponding grounding judgment threshold, it is determined that the fault includes the grounding factor; if the amplitude of the negative-sequence component exceeds the asymmetric fault judgment threshold at the same time, it is determined to be a two-phase grounding fault, otherwise it is a single-phase grounding fault; When the amplitude of the zero-sequence component is lower than the grounding judgment threshold, and the amplitude of the negative-sequence component exceeds the asymmetric fault judgment threshold, the fault is judged to be a two-phase phase-to-phase fault; When the amplitude of the zero-sequence component is lower than the grounding judgment threshold and the negative-sequence component is lower than the asymmetric fault judgment threshold, and the phasor difference between the three-phase voltage and current is not greater than the phasor difference threshold, the fault is determined to be a three-phase symmetrical short circuit.

6. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 or 5, characterized in that: The recalculation and correction of the positive sequence branch coefficient, negative sequence branch coefficient and zero sequence branch coefficient used in the distribution network distance protection include: After determining the fault type, the fault characteristic parameters of the inverter power supply are introduced. and , the relationship between the output current and the grid connection point voltage at the inverter fault operation point is expressed as follows: In the formula, Indicates the inverter power supply output fault current; Indicates the grid-connected voltage of the inverter power supply; When the inverter triggers low voltage ride-through or current limiting operation and the actual output current reaches the maximum allowable value, the limit value is replaced , to reflect the upper limit of the fault current that the inverter power supply can output; The corrected positive sequence, negative sequence and zero sequence current components of the inverter power supply are respectively incorporated into the composite sequence network, and the corrected branch coefficient is obtained by combining the distribution network line impedance and the equivalent impedance of the phase-shifting transformer. .

7. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 6 is characterized in that: The branching factor of a single-phase ground fault is calculated as follows: The branching coefficient of a two-phase phase-to-phase fault is calculated as follows: In the formula, Indicates the reference branch current; Indicates the fault branch current; Represents the equivalent impedance of the phase-shifting transformer; represents the impedance of the path S to 1; represents the impedance of the path S to 2; Indicates the impedance from the fault point to the power supply; Represents the impedance between two phases; Represents the phase shift factor of the phase-shifting transformer; It represents the positive sequence impedance of the phase-shifting transformer to the fault point QM section; It represents the negative sequence impedance of the phase-shifting transformer to the fault point QM section; It represents the negative sequence impedance of the S segment from the distributed inverter to the fault point; Represents the negative sequence impedance from the fault point PQ to the distributed inverter power supply; It represents the positive sequence impedance of the S segment from the distributed inverter to the fault point; Represents the positive sequence impedance from the fault point PQ to the distributed inverter power supply; Indicates the voltage of distributed inverter power supply; Indicates the C phase voltage.

8. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 is characterized in that: The method uses the corrected positive-sequence, negative-sequence and zero-sequence branch coefficients and the equivalent impedance of the current operating state of the phase-shifting transformer to determine the initial value of the set impedance of the second stage of distance protection, including: The branching coefficient With the equivalent impedance model Combined with the following formula, the initial value of the impedance setting is calculated : In the formula, Indicates the initial value of the setting impedance; and Indicates the protection setting coefficient in different time intervals; Indicates the fixed reference impedance of the protection device; Indicates the setting impedance of the first stage protection; represents the corrected branching coefficient; It represents the equivalent impedance of the phase-shifting transformer; Indicates the time after the fault occurs; Indicates the preset time threshold.

9. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 8 is characterized in that: The corresponding relationship between the setting impedance of the second stage protection of the distance protection and the equivalent impedance of the phase-shifting transformer is established based on the initial value of the setting impedance, including: According to the initial value of impedance And the equivalent impedance of the phase-shifting transformer , the mapping relationship between the set impedance and the equivalent impedance of the phase-shifting transformer is constructed as follows: In the formula, It represents the set impedance adjustment function obtained by fitting based on the grid operation data.

10. The distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: The method dynamically changes the tap position of the secondary side of the phase-shifting transformer excitation transformer according to the real-time change of the phase angle difference on both sides of the closed-loop point of the distribution network, including: Get the phase voltage on the left and right sides of the closed-loop point of the distribution network and , calculate the voltage phase angle on both sides and , the real-time phase angle difference is calculated as follows : The real-time phase angle difference With preset threshold For comparison: like , then select a winding turns ratio greater than the current winding turns ratio and The tap; like , then select a winding turns ratio that is smaller than the current winding turns ratio and The tap.

11. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1 or 10, characterized in that: The corresponding relationship between the set impedance and the equivalent impedance of the phase-shifting transformer is used to update the set impedance value of the second stage of distance protection in real time, including: Get the tap configuration of the current excitation transformer, including multiple taps on the secondary side of the excitation transformer, each tap corresponds to a different winding turns ratio and ; When the tap position changes, get the new winding turns ratio and , the updated equivalent impedance of the phase-shifting transformer is calculated as follows: According to the established correspondence between the setting impedance and the equivalent impedance, the updated second-stage setting impedance value of the distance protection is calculated: In the formula, represents the updated equivalent impedance of the phase-shifting transformer; It represents the calculation function of equivalent impedance of phase-shifting transformer; It represents the turns ratio of the new parallel transformer windings; represents the new series transformer winding turns ratio; Represents the winding resistance of the series transformer; Represents the winding impedance of the parallel transformer; Indicates the updated second-stage setting impedance value of distance protection.

12. A distance adaptive protection system for a phase-shifting transformer in an active distribution network, comprising: Equivalent impedance calculation module, network operation mode analysis module, branch coefficient correction module, setting impedance calculation module and adaptive setting module; characterized by: An equivalent impedance calculation module is used to determine the relationship between the input and output voltages of the phase-shifting transformer and to establish an equivalent impedance model of the phase-shifting transformer based on the relationship; The network operation mode analysis module is used to analyze the changes in network operation mode caused by the phase-shifting transformer being connected to the distribution network based on the equivalent impedance model of the phase-shifting transformer, and calculate the positive-sequence, negative-sequence and zero-sequence current characteristics of the distributed inverter power supply in the distribution network under different fault types according to the changes; A branch coefficient correction module is used to recalculate and correct the positive sequence branch coefficient, negative sequence branch coefficient and zero sequence branch coefficient used in the distribution network distance protection based on the current characteristics of the distributed inverter under different fault types; The setting impedance calculation module is used to calculate the initial value of the setting impedance of the second stage of distance protection by using the corrected positive-sequence, negative-sequence and zero-sequence branch coefficients and the equivalent impedance of the current operating state of the phase-shifting transformer, and to establish the corresponding relationship between the setting impedance of the second stage of distance protection and the equivalent impedance of the phase-shifting transformer based on the initial value of the setting impedance; The adaptive setting module is used to monitor the phase angle difference on both sides of the closed-loop point of the distribution network in real time, and dynamically adjust the tap position of the secondary side of the phase-shifting transformer excitation transformer according to the change of the phase angle difference, so that the equivalent impedance of the phase-shifting transformer is adjusted accordingly; further, the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer is used to update the setting impedance value of the second stage protection of the distance protection in real time to realize the adaptive setting of the protection parameters.

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