Distance Adaptive Protection Method and System of Phase-Shifting Transformer in Active Distribution Network

Abstract

A distance adaptive protection method and system for a phase-shifting transformer in an active distribution network, including: based on the equivalent impedance model of the phase-shifting transformer, determining the input-output voltage relationship, analyzing the changes in the network operation mode caused by connecting to the distribution network, and then calculating the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power supply under different fault types. Based on the fault current characteristics, correcting the positive-sequence, negative-sequence, and zero-sequence branch coefficients of the distance protection of the distribution network, combining with the equivalent impedance of the phase-shifting transformer, calculating the initial value of the setting impedance in the second stage of the distance protection, and establishing the corresponding relationship between it and the equivalent impedance of the phase-shifting transformer. By real-time monitoring the phase angle difference on both sides of the closed-loop point of the distribution network, dynamically adjusting the tap position on the secondary side of the excitation transformer, making the equivalent impedance of the phase-shifting transformer change accordingly, and real-time updating the distance protection setting impedance value, realizing the adaptive setting of protection parameters, and improving the fault recognition accuracy and protection reliability.

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 the modern power system. 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 protection maloperation or refusal to operate. 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, 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 fixed-setting methods. 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 the 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 technologies, 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:

[0008] 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;

[0009] 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 sources in the distribution network under different fault types according to the changes in the network operation mode;

[0010] According to the current characteristics of the distributed inverter power sources 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;

[0011] 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, 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;

[0012] 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 to achieve the adaptive setting of the protection parameters.

[0013] 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:

[0014] 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;

[0015] According to 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:

[0016]

[0017] 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:

[0018]

[0019] 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 shunt transformer respectively; represents the equivalent impedance of the internal winding of the series transformer; represents the equivalent exciting impedance of the phase-shifting transformer.

[0020] Preferably, determining the changes in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network includes:

[0021] 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 by the following formula:

[0022]

[0023] Calculate the change in the line voltage phase before and after the connection of the phase-shifting transformer by the following formula:

[0024]

[0025] 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 by the following formula:

[0026]

[0027] 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.

[0028] 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 change in the network operation mode includes:

[0029] Based on the change 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 grounding fault and two-phase interphase fault respectively;

[0030] According to the composite sequence network, determine the fault characteristic parameters under two-phase interphase fault and the fault characteristic parameters under single-phase grounding fault , , including:

[0031] Calculate the fault characteristic parameters of a two-phase inter-phase fault with the following formula :

[0032]

[0033] Calculate the fault characteristic parameters of a single-phase ground fault with the following formula :

[0034]

[0035] The fault characteristic parameters of a single-phase ground fault with the following formula :

[0036]

[0037] 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 combined equivalent impedance of the zero sequence components of the distribution network; represents the distributed inverter power supply voltage.

[0038] Preferably, perform real-time identification of the fault type, including:

[0039] Obtain the equivalent impedance model of the phase-shifting transformer and determine the network operation mode change. During the fault, collect the amplitude and phase information of the three-phase voltage and three-phase current;

[0040] 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 ground discrimination threshold, the asymmetric fault discrimination threshold, and the phasor difference threshold; Determine the fault type according to the following rules:

[0041] 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 at the same time, it is determined as a two-phase ground fault, otherwise it is a single-phase ground fault;

[0042] When the amplitude of the zero-sequence component is lower than the grounding discrimination threshold, while the amplitude of the negative-sequence component exceeds the asymmetric fault discrimination threshold, the fault is determined to be a two-phase interphase fault;

[0043] When the amplitude of the zero-sequence component is lower than the grounding discrimination threshold and the negative-sequence component is lower than the asymmetric fault discrimination threshold, and the phasor difference between the three-phase voltages and currents is not greater than the phasor difference threshold, the fault is determined to be a three-phase symmetrical short circuit.

[0044] Preferably, the positive-sequence branch coefficient, negative-sequence branch coefficient, and zero-sequence branch coefficient used for recalculating and correcting the distance protection of the distribution network include:

[0045] After determining the fault type, introduce the fault characteristic parameters of the inverter power supply and , and the relationship between the output current and the grid connection point voltage of the inverter power supply fault operating point is expressed as follows:

[0046]

[0047] In the formula, represents the fault current output by the inverter power supply; represents the grid connection point voltage of the inverter power supply;

[0048] When the inverter power supply triggers low-voltage ride-through or current-limiting operation and the actual output current reaches the maximum allowable value, replace the limit value with to reflect the upper limit of the fault current that the inverter power supply can output;

[0049] 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 distribution network line impedance and the equivalent impedance of the phase-shifting transformer to obtain the corrected branch coefficient .

[0050] Preferably, calculate the branch coefficient of the single-phase grounding fault with the following formula:

[0051]

[0052] Calculate the branch coefficient of the two-phase interphase fault with the following formula:

[0053]

[0054] 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 phase C voltage.

[0055] Preferably, the initial value of the setting impedance for 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:

[0056] Combining the branch coefficient with the equivalent impedance model to calculate the initial value of the setting impedance according to the following formula :

[0057]

[0058] 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.

[0059] Preferably, establishing 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 includes:

[0060] According to the initial value of the setting impedance and the equivalent impedance of the phase-shifting transformer , constructing the mapping relationship of the setting impedance changing with the equivalent impedance of the phase-shifting transformer according to the following formula:

[0061]

[0062] Wherein, represents a setting impedance adjustment function obtained by fitting based on grid operation data.

[0063] Preferably, the method for 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 on both sides of the closed-loop point of the distribution network includes:

[0064] Obtain the phase voltages on the left and right sides of the closed-loop point of the distribution network and , calculate the voltage phase angles and on both sides, and calculate the real-time phase angle difference according to the following formula :

[0065]

[0066] Compare the real-time phase angle difference with the preset threshold :

[0067] If , then select a tap with a winding turn ratio greater than the current winding turn ratio and .

[0068] If , then select a tap with a winding turn ratio less than the current winding turn ratio and .

[0069] Preferably, the method for updating the setting impedance value of the second-stage protection of the distance protection in real time by using the correspondence between the setting impedance and the equivalent impedance of the phase-shifting transformer includes:

[0070] 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 ;

[0071] When the tap position changes, obtain the new winding turn ratios and , and calculate the updated equivalent impedance of the phase-shifting transformer according to the following formula:

[0072]

[0073] Calculate the updated setting impedance value of the second stage of the distance protection according to the established correspondence between the setting impedance and the equivalent impedance:

[0074]

[0075] Wherein, Represents the updated equivalent impedance of the phase-shifting transformer; Represents the equivalent impedance calculation function of the phase-shifting transformer; Represents the new turns ratio of the parallel transformer windings; Represents the new turns ratio of the series transformer windings; Represents the winding resistance of the series transformer; Represents the winding impedance of the parallel transformer; Represents the set impedance value of the second stage of distance protection after update.

[0076] 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 set impedance calculation module, and an adaptive setting module;

[0077] 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;

[0078] 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 source in the distribution network under different fault types according to this change;

[0079] 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 source under different fault types;

[0080] The set impedance calculation module is used to calculate the initial value of the set impedance of the second-stage protection of the distance protection by using the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients, combined with the equivalent impedance of the current operating state of the phase-shifting transformer, and establish a corresponding relationship between the set 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 set impedance;

[0081] 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 in the phase angle difference, so that the equivalent impedance of the phase-shifting transformer is adjusted accordingly; further, using the corresponding relationship between the set impedance and the equivalent impedance of the phase-shifting transformer, the set 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.

[0082] Compared with the prior art, the beneficial effects of the present invention at least include:

[0083] 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 positive-sequence, negative-sequence, and zero-sequence branch coefficients, improves the accuracy of distance protection setting, enables it to 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 actions; by 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 can be adjusted, and accordingly, the distance protection setting parameters are dynamically updated to realize the adaptive optimization of 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 inverter power supplies, maintains high protection performance in power grids with high new energy penetration rates, and meets the protection requirements of smart distribution networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] 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;

[0085] Figure 2 is a schematic diagram of power system fault analysis provided according to an embodiment of the present invention;

[0086] Figure 3 is a composite sequence network diagram during a two-phase interphase fault on a line provided according to an embodiment of the present invention;

[0087] Figure 4 is a composite sequence network diagram during a single-phase grounding fault on a line provided according to an embodiment of the present invention;

[0088] Figure 5 is a power grid structure diagram of the influence of the phase-shifting transformer on the short-circuit current provided according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0089] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0090] 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.

[0091] 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:

[0092] 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;

[0093] Preferably, step 1 includes:

[0094] 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;

[0095] According to the above turns ratio 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:

[0096]

[0097] Step 1.2, 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:

[0098]

[0099] 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 exciting impedance of the phase-shifting transformer.

[0100] Specifically, analyze the fault ride-through characteristics of the distributed inverter power supply and the influence analysis of the distributed inverter power supply on the operating characteristics of distance protection. Traditional relay protection has many deficiencies in the distribution network with new energy access. 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 facing the loop closing problem, the original protection scheme may no longer be applicable.

[0101] Before closing the loop, 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 causes the continuous change of the branch factor, thus causing the change of the setting of the second stage of distance protection. Therefore, it is necessary to recalculate the branch coefficient.

[0102] 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 known as 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.

[0103] It should be noted that the structure of the active distribution network changes during the grid closing process or when the opening and closing of the current source 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 grid 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 grid closing process of the active distribution network. Therefore, due to the characteristic that the 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.

[0104] 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 power 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 .

[0105] As Figure 2 shown, it is the traditional distance protection boosting line diagram. If the setting calculation is carried out according to the traditional distance protection setting method. The branch coefficient in the active distribution network is calculated according to the boosting coefficient. The branch coefficient can be expressed as:

[0106]

[0107] 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.

[0108] According to the expression of the branch coefficient, the branch coefficient of the power grid with an inverter power source connected to the 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.

[0109] To ensure the accuracy and sensitivity of the distance II-section protection operation, 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 perform the setting calculation of the distance II-section protection according to the corrected branch coefficients.

[0110] 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.

[0111] Preferably, determining the change in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network includes:

[0112] Step 2.1: 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 with the following formula:

[0113]

[0114] Calculate the change in the line voltage phase before and after the connection of the phase-shifting transformer with the following formula:

[0115]

[0116] Step 2.2: 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 with the following formula:

[0117]

[0118] 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.

[0119] Step 2.3: Based on the change in the network operation mode after the connection of the phase-shifting transformer to the distribution network, construct a composite sequence network containing the phase-shifting transformer and the distributed inverter power supply in the distribution network under single-phase ground fault and two-phase interphase fault respectively.

[0120] Step 2.4: Determine the fault characteristic parameters for two-phase interphase faults and single-phase ground faults based on the composite sequence network 、 , including:

[0121] As Figure 3 shown, it is the composite sequence network diagram for two-phase interphase faults on the line. Calculate the fault characteristic parameters for two-phase interphase faults using the following formula :

[0122]

[0123] As Figure 4 shown, it is the composite sequence network diagram for single-phase interphase faults on the line. Calculate the fault characteristic parameters for single-phase ground faults using the following formula :

[0124]

[0125] Calculate the fault characteristic parameters for single-phase ground faults using the following formula :

[0126]

[0127] 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 source to the fault point S section; represents the negative-sequence impedance from the fault point PQ to the distributed inverter power source; represents the positive-sequence impedance from the distributed inverter power source to the fault point S section; represents the positive-sequence impedance from the fault point PQ to the distributed inverter power source; represents the zero-sequence impedance from the phase-shifting transformer to the fault point QM section; represents the combined equivalent impedance of the zero-sequence component of the distribution network; represents the voltage of the distributed inverter power source.

[0128] 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 source under different fault types;

[0129] Preferably, Step 3 includes:

[0130] Based on the composite sequence network diagrams of various types of faults, the external network characteristics of the inverter power source as shown can be obtained. Combining the external network characteristics of the inverter power source with the fault characteristics of the inverter power source can determine the fault operating point.

[0131] 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 inverter power supply at the fault operating point as follows:

[0132]

[0133] In the formula, represents the fault current output by the inverter power supply; represents the grid connection point voltage of the inverter power supply;

[0134] Specifically, the characteristic parameters a and b refer to the slope and intercept of the dotted line, and they affect the intersection position of the external network characteristics and the fault characteristics of the distributed inverter power supply at the same time, so the output current of the inverter power supply will be different.

[0135] 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 the differences of a and b. After obtaining the branch coefficient and substituting it into the second section distance protection setting value formula at the protection location, the setting value of the second section distance protection at the protection location can be calculated.

[0136] 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;

[0137] 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 .

[0138] Preferably, when a single-phase ground fault occurs:

[0139]

[0140] For a single-phase ground fault that occurs on a line connected with a phase shifter, after a distributed power source is connected to bus B:

[0141]

[0142]

[0143]

[0144] If a two-phase interphase fault occurs, substitute the current of the two-phase interphase fault . Then the new branch coefficient can be obtained.

[0145]

[0146] 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.

[0147] Preferably, the fault type is identified in real time, including:

[0148] After obtaining the equivalent impedance model of the phase-shifting transformer and determining the change in the network operation mode, during the fault, the amplitude and phase information of the three-phase voltage and three-phase current are collected;

[0149] 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:

[0150] 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 at the same time, it is determined as a two-phase grounding fault, otherwise it is a single-phase grounding fault;

[0151] When the amplitude of the zero-sequence component is lower than the ground discrimination threshold, while 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;

[0152] When the amplitude of the zero-sequence component is lower than the ground discrimination threshold and 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.

[0153] When a phase-shifting transformer is connected to an 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.

[0154] In a normal distribution network line, such as Figure 5 shown, the formula for the branch coefficient is:

[0155]

[0156] 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.

[0157] 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 of 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.

[0158] 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 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;

[0159] Preferably, step 4 includes:

[0160] Step 4.1: Combine the branch coefficient with the equivalent impedance model to calculate the initial value of the setting impedance as follows :

[0161]

[0162] 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.

[0163] Specifically, the setting impedance of the second stage of distance protection should be calculated separately according to specific conditions, 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 exciting transformer of the phase-shifting transformer to meet the closed-loop requirements. This adjustment will change the number of winding turns in the connecting line, thereby affecting the impedance of the phase-shifting transformer.

[0164] 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, therefore, selecting the minimum value between and is equivalent to comparing the magnitudes of

[0165] 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.

[0166] 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:

[0167]

[0168] In the formula, represents the setting impedance adjustment function fitted based on the power grid operation data.

[0169] 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 exciting 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.

[0170] Preferably, step 5 includes:

[0171] 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 of both sides, and calculate the real-time phase angle difference as follows:

[0172]

[0173] Step 5.2, compare the real-time phase angle difference with the preset threshold as follows:

[0174] If , select the tap with a winding turn ratio greater than the current winding turn ratio and .

[0175] If , select the tap with a winding turn ratio less than the current winding turn ratio and .

[0176] 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 ;

[0177] 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:

[0178]

[0179] Step 5.5, according to the established corresponding relationship between the setting impedance and the equivalent impedance, calculate the updated distance protection second-stage setting impedance value:

[0180]

[0181] 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.

[0182] 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;

[0183] 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;

[0184] The network operation mode analysis module is used to analyze the change of 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;

[0185] 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;

[0186] 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 current operating state of the phase-shifting transformer, 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;

[0187] 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, 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 realize the adaptive setting of the protection parameters.

[0188] The beneficial effects of the present invention at least include:

[0189] 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 actions; by 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 to realize 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, and enhance the stability and security of the system. It is especially suitable for complex power grid environments containing distributed inverter power supplies, maintains high protection performance in power grids with high penetration of new energy, and meets the protection requirements of smart distribution grids.

[0190] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer-readable storage medium having thereon computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0191] 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 It includes 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 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 source in the distribution network under different fault types based on the change in the network operation mode; According to the current characteristics of the distributed inverter power source 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 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; 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 to achieve the adaptive setting of protection parameters.

2. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: The determination of the relationship between the input and output voltages of the phase-shifting transformer and the establishment of an 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: 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: Wherein, 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-side and secondary-side winding impedances of the parallel transformer respectively; represents the equivalent impedance of the internal winding of the series transformer; represents the equivalent magnetizing impedance of the phase-shifting transformer.

3. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: The determination of the change in the network operation mode caused by the connection of the phase-shifting transformer to the distribution network includes: Based on the equivalent impedance model of the phase-shifting transformer, calculate the change amount of the line equivalent impedance before and after the connection of the phase-shifting transformer as follows: Calculate the change amount of the line voltage phase before and after the connection of the phase-shifting transformer as follows: According to the change in the equivalent impedance of the line and the change in the voltage phase , the power flow distribution matrix before and after the connection of the phase-shifting transformer is as follows: In the formula, represents the change in 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 amount 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.

4. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: The analysis of the positive-sequence, negative-sequence, and zero-sequence current characteristics of the distributed inverter power source in the distribution network under different fault types according to the change in the network operation mode includes: Based on the change 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 source under single-phase ground fault and two-phase interphase fault respectively; Determine the fault characteristic parameters under two-phase interphase faults and the fault characteristic parameters under single-phase grounding faults according to the composite sequence network and , including: Calculate the fault characteristic parameters of a two-phase interphase fault using the following formula : Calculate the fault characteristic parameters of single-phase grounding faults using the following formula : Fault characteristic parameters for single-phase grounding faults in the following formula :[[]]END]] Wherein, represents the positive sequence impedance from the phase-shifting transformer to the QM section of the fault point; represents the negative sequence impedance from the phase-shifting transformer to the QM section of the fault point; represents the negative sequence impedance from the distributed inverter power source to the S section of the fault point; represents the negative sequence impedance from the PQ section of the fault point to the distributed inverter power source; represents the positive sequence impedance from the distributed inverter power source to the S section of the fault point; represents the positive sequence impedance from the PQ section of the fault point to the distributed inverter power source; represents the zero sequence impedance from the phase-shifting transformer to the QM section of the fault point; represents the combined equivalent impedance of the zero sequence component of the distribution network; represents the distributed inverter power source voltage.

5. A distance adaptive protection method for a phase-shifting transformer in an active distribution network according to claim 4, characterized in that: The real-time identification of the fault type includes: After obtaining the equivalent impedance model of the phase-shifting transformer and determining the change in the network operation mode, the amplitudes and phase information of the three-phase voltages and three-phase currents are collected during the fault period; The three-phase voltages and currents are decomposed into positive-sequence, negative-sequence, and zero-sequence components, and are respectively compared with preset discrimination thresholds, including a ground discrimination threshold, an asymmetric fault discrimination threshold, and a 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, while 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 amplitude of the zero-sequence component is lower than the ground 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 voltages and currents is not greater than the phasor difference threshold, the fault is determined as a three-phase symmetrical short circuit.

6. The distance adaptive protection method of 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 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 , 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: 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-limited operation and the actual output current reaches the maximum allowable value, the limit value will be substituted , to reflect the upper limit of the fault current that the inverter power supply can output; Incorporate the positive-sequence, negative-sequence, and zero-sequence current components of the corrected 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 .

7. The distance adaptive protection method of a phase-shifting transformer in an active distribution network according to claim 6, characterized in that: The branch coefficient for a single-phase grounding fault is calculated by the following formula: The branch coefficient for a two-phase interphase fault is calculated by the following formula: 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 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 phase C voltage.

8. The distance adaptive protection method of a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: Using the corrected positive-sequence, negative-sequence, and zero-sequence branch coefficients, combined with the equivalent impedance of the current operating state of the phase-shifting transformer, to determine the initial value of the setting impedance for the second-stage protection of the distance protection, including: Combine the branch coefficient with the equivalent impedance model to calculate the initial value of the setting impedance as follows : Wherein, 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.

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

10. The distance adaptive protection method of a phase-shifting transformer in an active distribution network according to claim 1, characterized in that: According to the real-time change of the phase angle difference between both sides of the closed-loop point of the distribution network, dynamically changing the tap position of the secondary side of the excitation transformer of the phase-shifting transformer, including: Obtain the phase voltages on the left and right sides of the closed-loop point of the distribution network and , calculate the voltage phase angles on both sides and , and calculate the real-time phase angle difference according to the following formula : Compare the real-time phase angle difference with a preset threshold as follows: If , select a tap with a winding turn ratio greater than the current winding turn ratio and ; If , then select a tap with a winding turns ratio smaller than the current winding turns ratio and .

11. The distance adaptive protection method of a phase-shifting transformer in an active distribution network according to claim 1 or 10, characterized in that: Using the corresponding relationship between the setting impedance and the equivalent impedance of the phase-shifting transformer to real-time update the setting impedance value of the second-stage protection of the distance protection, including: Obtaining the tap configuration of the current excitation transformer includes that multiple taps are provided on the secondary side of the excitation transformer, and each tap corresponds to a different winding turns 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: According to the established corresponding relationship between the setting impedance and the equivalent impedance, calculating the updated setting impedance value for the second-stage distance protection: In the formula, represents the updated equivalent impedance of the phase-shifting transformer; represents the calculation function of the equivalent impedance of the phase-shifting transformer; represents the new turns ratio of the parallel transformer winding; represents the new turns ratio of the series transformer winding; represents the winding resistance of the series transformer; represents the winding impedance of the parallel transformer; represents the set impedance value of the second stage of the distance protection after update.

12. A distance adaptive protection system of a phase-shifting transformer in an active distribution network, comprising: 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; characterized in that: 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 with the equivalent impedance of the current operating state of the phase-shifting transformer, 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; 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, 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 realize the adaptive setting of the protection parameters.

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