Method and device for analyzing applicability of 90-degree wiring direction element in active power distribution network

Abstract

The invention provides a method and a device for analyzing the applicability of a 90-degree wiring direction element in an active power distribution network, and the method comprises the steps: firstly constructing an equivalent composite sequence network after a fault for a power distribution network connected with an IIDG; and then, considering the IIDG influence, quantitatively calculating the voltage and current phase difference range measured by elements in all directions under different faults, and evaluating element actions and sensitivity changes according to the voltage and current phase difference range to obtain a conventional fault scene applicability result. And the misjudgment condition of the element under the transition resistor is evaluated, and the applicability during short circuit through the transition resistor is determined. And finally, constructing a multi-scene example simulation model, and verifying the result, thereby comprehensively evaluating the applicability of the directional element. According to the method, the output characteristics of the inverter type distributed power supply with the low voltage ride-through capability are accurately analyzed, a composite sequence network model is constructed, the measured voltage and current phase difference of each directional element is quantitatively calculated, and the applicability of the 90-degree wiring power directional element under the conditions of conventional faults of an active power distribution network and short circuit through a transition resistor is comprehensively evaluated.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection in power systems, and particularly relates to a method and device for analyzing the applicability of a 90° wiring direction element in an active distribution network. Background Art

[0002] In recent years, with the advancement of energy transformation, a large number of distributed generations (DGs) have been connected to the distribution network in a multi-point and decentralized manner in the form of inverter-interfaced distributed generations (IIDGs), which has promoted the transformation of the distribution network from a traditional passive network to an active distribution network. In an active distribution network, due to the connection of IIDGs, when a fault occurs in the system, multiple IIDGs may inject short-circuit currents into the fault point simultaneously, making it difficult to accurately predict the magnitude and direction of the fault current.

[0003] To address the challenges of active distribution network protection, the currently widely adopted solution is to add a direction element on the basis of traditional current protection, or to adopt distance protection or pilot protection formed based on fault direction discrimination information. Among them, the direction element plays a crucial role in the protection scheme, and correct direction discrimination is the key to ensuring the correct operation of the protection. Traditional direction elements, such as 90° wiring power direction elements, perform well in traditional power grids with a single power source type and relatively stable operating modes. In such a power grid environment, the phasor relationship between voltage and current during a fault is relatively fixed, and the 90° wiring power direction element can accurately judge the fault direction according to the preset phase relationship, thus ensuring the reliable operation of relay protection.

[0004] However, in an active distribution network, due to the strong coupling and nonlinear relationship between the grid connection point voltage of IIDGs and their output currents, the phasor characteristics of voltage and current after a system fault are significantly affected by it, which may lead to a decline in the performance of 90° wiring power direction elements and there are adaptability problems. Currently, the research on the adaptability of 90° wiring power direction elements in active distribution networks mainly focuses on qualitative analysis. Researchers have proposed the possibility of misoperation of the direction element under specific conditions through theoretical derivation and simulation, and concluded that the 90° wiring direction element is not suitable for active distribution networks based on simulation data. However, this research method lacks quantitative research on the misoperation problem of the power direction element. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method and device for analyzing the applicability of a 90° wiring direction element in an active distribution network to solve the above problems existing in the prior art.

[0006] To achieve the above object, the technical solutions provided by the present invention are as follows:

[0007] In a first aspect, the present invention provides a method for analyzing the applicability of a 90° wiring direction element in an active distribution network, including the following steps:

[0008] For a distribution network with inverter-type distributed generation (IIDG) connected, construct an equivalent composite sequence network;

[0009] Combined with the equivalent composite sequence network, for each direction element at different relative positions to the fault point in the distribution network, based on the influence of IIDG connection, quantitatively calculate the range of the phase difference between the measured voltage and current of each direction element under different types of faults;

[0010] Evaluate the operation status and sensitivity change of each direction element according to the range of the voltage-current phase difference, and obtain the first applicability analysis result of the direction element in the conventional fault scenario according to the operation status and sensitivity change;

[0011] Based on the situation of a short-circuit fault occurring through a transition resistance in the system, update the line impedance parameters, and substitute the line impedance parameters into the quantitative calculation of the measured data of each direction element under different types of faults, and judge the misjudgment situation of the direction element according to the calculation result, so as to obtain the second applicability analysis result of the direction element when short-circuiting through a transition resistance;

[0012] Verify the first applicability analysis result and the second applicability analysis result, so as to complete the applicability analysis of the direction element in the active distribution network.

[0013] Further, in constructing the equivalent composite sequence network:

[0014] If the distribution network with IIDG connected is simplified and includes a system power source and buses M, N, and O connected in sequence starting from the system power source, where the direction elements at each position are the direction element 1 downstream of bus M, the direction element 2 upstream of bus N, the direction element 3 downstream of bus N, and the direction element 4 upstream of bus O;

[0015] Assume that the fault occurs between direction element 3 and direction element 4, denoted as the fault point f. Then, in the equivalent composite sequence network, the system power source is equivalent to a constant voltage source and an equivalent impedance in series, is the equivalent impedance of the MN section line, the line impedance from bus N to the fault point is equivalent to , the line impedance from bus O to the fault point is equivalent to , the load impedance is ; the inverter-type distributed power source is equivalent to a voltage-controlled current source, and its connection point voltage is , and the output current is ; The positive-sequence current flowing through the upstream line of the fault is , and the equivalent negative-sequence impedance at the fault point is .

[0016] Furthermore, when a three-phase short-circuit fault occurs in the system, the equivalent negative-sequence impedance at the fault point equals zero. At this time, if the IIDG connection point is at the downstream bus O of the fault point, the measured phase differences of the directional elements at different positions satisfy the following conditions:

[0017] For the directional elements 1 and 3 upstream of the fault point, it satisfies:

[0018]

[0019] In the formula, is the measured line voltage phasor between phase B and phase C; is the measured current phasor of phase A; is the internal angle of the directional element; is the line impedance angle;

[0020] At this time, the directional elements 1 and 3 can correctly reflect the fault direction and ideally operate in the most sensitive state;

[0021] For the directional element 2 upstream of the fault point, it satisfies:

[0022]

[0023] At this time, the directional element 2 can correctly reflect the fault direction and ideally operate in the most sensitive state;

[0024] For the directional element 4 downstream of the fault point, it satisfies:

[0025]

[0026] In the formula, is the phase angle by which the output current of the inverter-type distributed power source lags behind the grid connection point voltage;

[0027] At this time, if , the directional element 4 can correctly reflect the fault direction, otherwise it will make a misjudgment.

[0028] Furthermore, when a BC two-phase short-circuit fault occurs in the system and the IIDG connection point is at the downstream bus O of the fault point, the measured phase differences of the directional elements at different positions satisfy the following conditions:

[0029] For the directional elements 1 and 3 at different positions upstream of the fault point, it satisfies:

[0030]

[0031] In the formula, is the measured line voltage phasor between phase C and phase A; is the measured current phasor of phase B; is the measured line voltage phasor between phase A and phase B; is the measured current phasor of phase C; is the internal angle of the directional element; is the line impedance angle;

[0032] At this time, directional elements 1 and 3 can correctly reflect the fault direction;

[0033] For the directional element 2 upstream of the fault point, it satisfies:

[0034]

[0035] At this time, the directional element 2 will judge a reverse-direction fault and will not misjudge, but the sensitivity decreases;

[0036] For the directional element 4 downstream of the fault point, it satisfies:

[0037]

[0038] At this time, if the shunt of the IIDG output current on the upstream branch is less than the shunt of the short-circuit current provided by the system on this branch, the directional element 4 will surely misjudge.

[0039] Furthermore, when a BC two-phase short-circuit fault occurs in the system, four boundary conditions need to be considered for the applicability analysis of the directional element, as follows:

[0040] One is that the voltage at the parallel connection point in the composite sequence network is about 0.5 times the rated voltage range, then the IIDG output current lags behind the voltage at the parallel connection point by about range;

[0041] Two is that when the IIDG penetration rate at the parallel connection point is 100% and its maximum output current is less than 1.5 times the rated current, the voltage drop of the IIDG output current on line fO does not exceed 10.5% of the voltage at the parallel connection point;

[0042] Three is the line impedance angle ;

[0043] Four is that the shunt of the IIDG output current on its upstream branch is greater than the shunt of the short-circuit current provided by the system on this branch.

[0044] Furthermore, when the IIDG access point is at the upstream bus N of the fault point, if a three-phase short-circuit fault occurs in the system, the operating characteristics of the directional elements upstream of the fault point remain unchanged, and the directional elements downstream of the fault point will not start.

[0045] Further, when the IIDG access point is located on the upstream bus N of the fault point, if a BC two-phase short circuit occurs in the system, the upstream direction elements 1 and 2 at the IIDG connection point operate in a sensitive state;

[0046] For the direction element 3, when the fault point is located at the outlet of bus N, the B-phase and C-phase relays of the direction element 3 satisfy:

[0047]

[0048] In the formula, is the measured line voltage phasor between the C-phase and the A-phase; is the measured current phasor of the B-phase; is the measured line voltage phasor between the A-phase and the B-phase; is the measured current phasor of the C-phase; is the internal angle of the direction element; is the line impedance angle;

[0049] If the fault point is at a certain distance from bus N and the measured negative sequence voltage of the bus is zero, the B-phase and C-phase relays of the direction element 3 satisfy:

[0050]

[0051] At this time, the B-phase and C-phase relays in the direction element 3 can correctly reflect the fault direction, but the sensitivity decreases;

[0052] The downstream direction element 4 at the fault point will not operate.

[0053] Further, the first applicability analysis results of the direction element in the conventional fault scenario are as follows:

[0054] When there is an IIDG access at the downstream bus O of the fault point, if the fault is a three-phase short circuit, the upstream and downstream direction elements at the fault point can both operate correctly, but the sensitivity will decrease; if the fault is a two-phase interphase short circuit, the upstream direction elements at the fault point can all operate correctly. When the fault is close and the line impedance angle is at this time, the downstream direction element at the fault point may misjudge;

[0055] When there is an IIDG access at the upstream bus N of the fault point, if the fault is a three-phase short circuit, the upstream direction elements at the fault point are not affected; if the fault is a two-phase interphase short circuit, the upstream direction elements at the IIDG connection point can all operate correctly, but the sensitivity decreases.

[0056] Further, when a short circuit fault occurs in the system and the transition resistance needs to be considered, the relevant parameters are updated according to the quantization characteristics of the line equivalent impedance in the equivalent composite sequence network. Specifically:

[0057] When a short - circuit fault occurs in the system and the transition resistance needs to be considered, the equivalent impedance of the line in the equivalent composite sequence network is resistive. At this time, update the relevant parameters to the line impedance angle 。

[0058] In a second aspect, the present invention provides an analysis device for the applicability of a 90° wiring direction element in an active distribution network, including:

[0059] An equivalent composite sequence network construction module, configured to construct an equivalent composite sequence network for a distribution network with inverter - type distributed generation (IIDG) connected;

[0060] A phase - difference calculation module, configured to combine the equivalent composite sequence network, and for each direction element with different relative positions to the fault point in the distribution network, based on the influence of IIDG connection, quantitatively calculate the range of the phase difference between the measured voltage and current of each direction element under different types of faults;

[0061] A first applicability analysis module, configured to evaluate the operation conditions and sensitivity changes of each direction element according to the range of the voltage - current phase difference, and obtain the first applicability analysis result of the direction element in a conventional fault scenario according to the operation conditions and sensitivity changes;

[0062] A second applicability analysis module, configured to update the line impedance parameters based on the situation of a short - circuit fault occurring in the system through a transition resistance, substitute the line impedance parameters into the quantitative calculation of the measured data of each direction element under different types of faults, and judge the misjudgment situation of the direction element according to the calculation result, so as to obtain the second applicability analysis result of the direction element when short - circuiting through a transition resistance;

[0063] A verification module, configured to verify the first applicability analysis result and the second applicability analysis result, so as to complete the applicability analysis of the direction element in the active distribution network.

[0064] In summary, the present invention provides a method and device for analyzing the applicability of a 90° wiring direction element in an active distribution network, including constructing an equivalent composite sequence network for a distribution network with inverter-type distributed generation (IIDG) access; for each 90° wiring power direction element with different relative positions to the fault point in the distribution network, considering the influence of IIDG access, quantitatively calculating the range of the phase difference between the measured voltage and current of each direction element under different types of faults; evaluating the operating conditions and sensitivity changes of each direction element based on the range of the voltage and current phase difference, and obtaining the applicability analysis results of the direction element in a conventional fault scenario according to the operating conditions and sensitivity changes; when a short-circuit fault occurs in the system and the transition resistance needs to be considered, updating relevant parameters according to the quantization characteristics of the line equivalent impedance in the equivalent composite sequence network, substituting the measured data of each direction element in different scenarios for calculation, and judging the misjudgment situation of the direction element, so as to determine the applicability analysis results of the 90° wiring power direction element when short-circuiting through the transition resistance; verifying the applicability analysis results, thereby completing the applicability analysis of the 90° wiring direction element in the active distribution network. By accurately analyzing the output characteristics of the inverter-type distributed generation with low voltage ride-through ability, constructing a composite sequence network model and quantitatively calculating the phase difference between the measured voltage and current of each direction element, the present invention comprehensively evaluates the applicability of the 90° wiring power direction element in the conventional fault and short-circuit scenarios through the transition resistance in the active distribution network. Description of the Drawings

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0066] Figure 1 It is a flowchart of a method for analyzing the applicability of a 90° wiring direction element in an active distribution network provided by an embodiment of the present invention;

[0067] Figure 2 It is a 10kV distribution network diagram with IIDG grid connection provided by an embodiment of the present invention;

[0068] Figure 3 It is an equivalent composite sequence network diagram when IIDG is connected downstream of the fault point provided by an embodiment of the present invention;

[0069] Figure 4 It is an equivalent composite sequence network diagram when IIDG is connected upstream of the fault point provided by an embodiment of the present invention;

[0070] Figure 5 It is a phasor diagram of electrical quantities downstream of the fault point provided by an embodiment of the present invention;

[0071] Figure 6 The phasor diagrams of phase components and sequence components at the near fault point during two-phase short circuit between phases provided by the embodiments of the present invention;

[0072] Figure 7 The phasor diagrams of phase components and sequence components at the far fault point during two-phase short circuit between phases provided by the embodiments of the present invention;

[0073] Figure 8 The phasor diagrams of phase components and sequence components downstream of the fault point during long-distance faults when the IIDG capacity in the embodiments of the present invention is large;

[0074] Figure 9 The phasor diagrams of phase components and sequence components downstream of the fault point during short-distance faults provided by the embodiments of the present invention;

[0075] Figure 10 The phasor diagrams of phase components and sequence components at the near fault point when the IIDG capacity in the embodiments of the present invention is small;

[0076] Figure 11 The phasor diagrams of phase components and sequence components at the near fault point when the IIDG capacity in the embodiments of the present invention is large;

[0077] Figure 12 The phasor diagrams of phase components and sequence components at the far fault point when the IIDG capacity in the embodiments of the present invention is small;

[0078] Figure 13 The phasor diagrams of phase components and sequence components at the far fault point when the IIDG capacity in the embodiments of the present invention is large;

[0079] Figure 14 The block diagram of the composition of a computer device provided by the embodiments of the present invention. Detailed implementation manners

[0080] To make the objectives, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0081] Please refer to Figure 1 , the embodiments of the present invention provide a method for analyzing the applicability of a 90° wiring direction element in an active distribution network, including the following steps:

[0082] S1: For the distribution network with the access of inverter-type distributed generation (IIDG), construct an equivalent composite sequence network.

[0083] It should be noted that the equivalent composite sequence network is a network formed by decomposing a three-phase system into positive-sequence, negative-sequence, and zero-sequence networks according to the symmetrical component method when analyzing asymmetrical faults in a power system, and then connecting the sequence networks according to the fault type for analyzing the relationship of electrical quantities after the fault.

[0084] S2: Combining the equivalent composite sequence network, for each directional element with different relative positions to the fault point in the distribution network, based on the influence of the access of IIDG, quantitatively calculate the range of the phase difference between the measured voltage and current of each directional element under different types of faults.

[0085] It should be noted that in this step, based on the equivalent composite sequence network, the influence of the access of inverter-type distributed generation on the electrical quantities of the distribution network is considered. For different types of faults (such as when there is a three-phase short circuit, the clamping effect of the large power grid on the voltage phase and the angular relationship between the current and voltage; when there is a two-phase interphase short circuit, combining multiple boundary conditions such as the grid-connected point voltage and the lagging phase of the IIDG output current), using circuit principles and phasor analysis methods, calculate the range of the phase difference between the measured voltage and current of each 90° wiring power direction element.

[0086] S3: Evaluate the operating conditions and the change in sensitivity of each directional element based on the range of the phase difference between the voltage and current, and obtain the first applicability analysis result of the directional element in the conventional fault scenario according to the operating conditions and the change in sensitivity.

[0087] It should be noted that according to the range of the phase difference between the voltage and current calculated in step S2, based on the operating criterion of the power direction relay (such as the magnitude relationship between the cosine quantity corresponding to the input voltage and current of the power direction relay and zero, and considering factors such as measurement errors), judge the operating conditions of each directional element (whether it can correctly reflect the fault direction). Compare the operating state of the power direction relay under ideal conditions, analyze the change in the sensitivity of the directional element under different fault scenarios, and thus obtain the first applicability analysis result of the directional element in the conventional fault scenario.

[0088] S4: Based on the situation of a short circuit fault occurring in the system through a transition resistance, update the line impedance parameters, and substitute the line impedance parameters into the quantitative calculation of the measured data of each directional element under different types of faults, and judge the misjudgment situation of the directional element according to the calculation result, so as to obtain the second applicability analysis result of the directional element when short-circuiting through a transition resistance.

[0089] It should be noted that the transition resistance is the resistance existing at the fault point when a short circuit fault occurs in the power system. It will affect the magnitude and phase of the short-circuit current, and thus affect the operation of the relay protection device.

[0090] When a short - circuit fault occurs in the system and there is a transition resistance, the equivalent impedance of the line will exhibit quantization characteristics (such as being resistive). According to this characteristic, the line impedance parameters in the equivalent composite sequence network are updated. Substitute the updated parameters into the measured data of each directional element under different scenarios for calculation, and judge whether the directional element will misjudge according to the calculation results, so as to determine the second applicability analysis result of the 90° connection power - direction element when short - circuiting through a transition resistance.

[0091] S5: Verify the first applicability analysis result and the second applicability analysis result, so as to complete the applicability analysis of the directional element in the active distribution network.

[0092] It should be noted that in the verification process, a simulation model can be constructed according to the parameters of the actual distribution network, and parameters such as the positive - sequence impedance per unit length of each line segment, the maximum load current of the line under normal operating conditions, and the current threshold for the directional element to start judging the fault direction are set. Set various scenarios such as different grid - connection positions of inverter - type distributed generation, fault types, transition resistances, and IIDG penetration rates for case analysis. Compare the measured values and action conditions of each directional element obtained from the simulation with the applicability analysis results obtained from the theoretical analysis in the previous steps to verify its accuracy.

[0093] The applicability analysis method provided in this embodiment is based on constructing an equivalent composite sequence network, analyzes the electrical quantity characteristics of the distribution network after the access of inverter - type distributed generation under different fault scenarios (including conventional faults and short - circuit faults through transition resistances), quantitatively calculates the phase difference between the voltage and current measured by the 90° connection power - direction element, evaluates the action conditions and sensitivity changes of the directional element according to the action criterion of the power - direction relay, so as to judge its applicability in the active distribution network, and verifies the analysis results using a simulation model.

[0094] The following combines Figure 2 to introduce the distribution network with the access of the inverter - type distributed generation IIDG of the present invention.

[0095] First, the output characteristics analysis of the IIDG with low - voltage ride - through ability is as follows:

[0096] (1) The fault output characteristics of the IIDG with low - voltage ride - through ability are determined by its control strategy and current - limiting technology. The steady - state output current of the IIDG is a current source controlled by the positive - sequence voltage at the connection point, does not contain negative - sequence components, and the phase angle between the positive - sequence voltage at its connection point and the positive - sequence output current satisfies: If the amplitude of the output current is limited within then .

[0097] (2) The voltage phase at the IIDG grid connection point is related to the fault location. Upstream of the fault point, due to the clamping effect of the system voltage, the voltage phase at the IIDG grid connection point changes little before and after the fault; downstream of the fault point, the voltage phase at the grid connection point may mutate after the fault, which is related to the fault type, line impedance, transition resistance, fault location, and distributed power output, etc., and has uncertainty. However, the phase difference between the grid connection point voltage and the IIDG output current is within a certain range.

[0098] In one embodiment, in constructing the equivalent composite sequence network, if the distribution network connected with the inverter-type distributed power source IIDG is simplified as Figure 2 shown, including a system power source and, starting from the system power source, successively connected bus M, bus N, and bus O. Among them, the directional elements at each position are the directional element 1 downstream of bus M, the directional element 2 upstream of bus N, the directional element 3 downstream of bus N, and the directional element 4 upstream of bus O. When a fault occurs at point f between protection 3 and protection 4, and bus O and bus N are respectively connected with IIDG, explore the influence of the relative position between the IIDG connection point and the fault point on the 90° wiring power direction element.

[0099] In establishing the positive and negative sequence equivalent networks after the fault and forming the composite sequence network, the system power source can be equivalent to a constant voltage source and the equivalent impedance in series. is the equivalent impedance of the MN section line, the line impedance from bus N to the fault point is equivalent to and the line impedance from bus O to the fault point is equivalent to , the load impedance is . The inverter-type distributed power source is equivalent to a voltage-controlled current source, its grid connection point voltage is , and the output current is . The positive sequence current flowing through the upstream line of the fault is , and the equivalent negative sequence impedance at the fault point is . Since is usually much larger than the line impedance, the current flowing to the load after the fault can be ignored. According to the sequence component boundary conditions of the phase-to-phase short-circuit fault, the positive and negative sequence voltages at the fault point are equal, forming a composite sequence network, as shown in Figure 3 and Figure 4 . If a three-phase short circuit occurs in the system, in the figure is equal to zero; if a two-phase phase-to-phase short circuit occurs in the system, is slightly smaller than the sum of the equivalent impedances of the upstream system and line of the fault point. At this time, the positive sequence voltage at the IIDG grid connection point is slightly smaller than .

[0100] The following is based on the distribution network shown in Figure 2 to introduce some other embodiments of the present invention.

[0101] In a further embodiment, when the IIDG access point is located on bus O (the bus downstream of the fault point), due to the clamping effect of the large power grid on the network upstream of the fault point f, the positive-sequence voltage phases of each bus before and after the fault are not much different. The current flows from the power source end to the fault point, and the angle by which the current lags behind the voltage is the line impedance angle. If the fault type is a three-phase short circuit, the directional elements at different positions satisfy:

[0102] For the directional elements 1 and 3 upstream of the fault point,

[0103] (1)

[0104] Wherein, is the measured line voltage phasor between phase B and phase C; is the measured current phasor of phase A; is the internal angle of the directional relay, usually equal to , and is the line impedance angle. Considering the influence of measurement errors, etc., the cosine quantity corresponding to the input voltage and current of the power direction relay at this time is between , that is, the output power is positive, and the directional element can correctly reflect the fault direction. Ideally, the cosine quantity is 1, and the directional element works in the most sensitive state.

[0105] For the directional element 2 upstream of the fault point,

[0106] (2)

[0107] The cosine quantity corresponding to the input voltage and current of the power direction relay is between , that is, the output power is negative, and the directional element can correctly reflect the fault direction. Ideally, it works in the most sensitive state.

[0108] For the directional element 4 downstream of the fault point, since the downstream voltage is much lower than , the output current of the IIDG will lag behind the voltage , therefore,

[0109] (3)

[0110] Wherein, is the phase angle by which the output current of the inverter-type distributed power source lags behind the grid connection point voltage, is determined by the degree of distributed power source amplitude limiting. When the maximum amplitude of the distributed power source output current is limited to , it is . Therefore, when , the output power of the directional element is positive and can correctly reflect the fault direction, otherwise it will misjudge.

[0111] In a further embodiment, when the IIDG access point is located on bus O (the downstream bus of the fault point), if the system fault type is a BC two-phase short circuit, considering four boundary conditions, one is that since the voltage at the parallel connection point in the composite sequence network is about 0.5 times the rated voltage, the output current of the IIDG lags behind the voltage at the parallel connection point by about ; the second is that when the IIDG penetration rate at the parallel connection point is 100% and its maximum output current is less than 1.5 times the rated current, the voltage drop of the IIDG output current on line fO does not exceed 10.5% of the voltage at the parallel connection point; the third is the line impedance angle ; the fourth is that the shunt of the IIDG output current on its upstream branch is greater than the shunt of the short-circuit current provided by the system on this branch, that is, the direction of the short-circuit current in line fO is towards the fault point.

[0112] Based on the boundary conditions of the foregoing embodiments, in a further embodiment, phasor diagrams of various electrical quantities downstream of the fault point are drawn, as shown in Figure 5 . Using the cosine theorem, it can be obtained that lags behind by about , that is, the phase shift of the positive-sequence voltages upstream and downstream of the fault point is small, and the negative-sequence voltage is not affected by the IIDG.

[0113] Therefore, the positive-sequence and negative-sequence voltages of the non-faulty phase A at the fault point are equal, while the positive-sequence voltage is larger and the negative-sequence voltage is smaller at positions farther from the fault point upstream of the fault point. The magnitude of the positive-sequence voltage at any point will be greater than or equal to the negative-sequence voltage. Using the symmetrical component method for analysis, boundary values of the voltage-current phase difference will appear when measuring voltage and current at a position near the fault point (where the positive-sequence and negative-sequence voltages are equal) and at a position far from the fault point (where the negative-sequence voltage is almost zero). The sequence component and phasor relationships in the two cases are respectively as shown in Figure 6 and 7 . Therefore, for the directional elements 1 and 3 at different positions upstream of the fault point, it can be obtained that

[0114] (4)

[0115] In the formula, is the measured line voltage phasor between phase C and phase A; is the measured current phasor of phase B; is the measured line voltage phasor between phase A and phase B; is the measured current phasor of phase C.

[0116] When considering a certain measurement error, the directional elements 1 and 3 can still correctly reflect the fault direction, but the sensitivity will decrease.

[0117] For the component 2 in the upstream direction of the fault point, since the phase of the positive and negative sequence measured currents is opposite to that of the actual current, it is equivalent to the interchange of the positive and negative sequence currents in the figure. It can be obtained that the measured currents of phase B and phase C are exactly opposite to those in the figure. Therefore, the measured phase difference of the directional component satisfies Equation (5), and the directional component 2 will determine a reverse-direction fault without misjudgment, but the sensitivity decreases.

[0118] (5)

[0119] The negative sequence current component downstream of the fault point can be ignored, and the measured current is the positive sequence current output by the IIDG, which lags behind the positive sequence voltage of the bus by about , and the positive sequence voltage at the fault point is equal to the negative sequence voltage. Then, the positive sequence voltage of the bus affected by the IIDG will be greater than or equal to the negative sequence voltage, but not more than 2 times at most. Therefore, according to the two boundaries that the positive sequence voltage of phase A of the bus is equal to the negative sequence voltage and the positive sequence voltage is equal to twice the negative sequence voltage, the vector relationships of each phase in the two cases are respectively drawn as Figure 8 and 9 shown. Therefore, for the directional component 4 downstream of the fault point, it can be obtained that,

[0120] (6)

[0121] When the line impedance angle , the output power of the phase B directional component is positive, but when the fault is close and the line impedance angle is , the output power of the phase C directional component may be negative, and the directional component will misjudge.

[0122] In actual operation, the greater the IIDG penetration rate at the grid connection point, the greater the voltage drop of the IIDG output current on the line fO, the greater the phase shift of the system positive sequence voltage, and at the same time, the negative sequence voltage and the positive and negative sequence currents in the system will also change greatly, and the possibility of misjudgment of the directional components upstream and downstream of the fault point will increase. In addition, if the capacity of the IIDG is small, the shunt of its output current on its upstream branch is less than the shunt of the short-circuit current provided by the system on this branch, that is, the direction of the short-circuit current in the line fO is towards the load side, then the directional component 4 will surely misjudge.

[0123] In a further embodiment, when the IIDG access point is located at the bus N (upstream of the fault point), if a three-phase short-circuit fault occurs in the system, due to the clamping effect of the large power grid, the phase shift of the voltage upstream of the fault point is small, and the current provided by the IIDG is also much smaller than the short-circuit current provided by the system. Therefore, the operating characteristics of the directional component are hardly affected; there is no IIDG access downstream of the fault point, and the short-circuit current can be ignored, and the directional component will not start.

[0124] In a further embodiment, when the IIDG access point is located on bus N (upstream of the fault point), if a BC two-phase short circuit occurs in the system, the phase jump of the system voltage is relatively small. The upstream direction elements 1 and 2 of the IIDG connection point can operate in a more sensitive state. For direction element 3, since the positive-sequence voltage at the POC is greater than , the phase of the IIDG output current lags behind the phase of the positive-sequence voltage at the connection point by less than . Superimposed on the positive-sequence short-circuit current provided by the system side lagging behind the positive-sequence voltage by , the phase of the positive-sequence current flowing through protection 3 will lag behind the positive-sequence voltage by approximately . The farther the fault point is from bus N and the larger the IIDG capacity, the closer the phase of the positive-sequence current lags behind the positive-sequence voltage is to . Considering two cases to analyze the boundary of the measured phase difference: one is that the fault point is located at the outlet of bus N, then the positive-sequence voltage of phase A of the bus is equal to the negative-sequence voltage. As shown in the electrical quantities such as Figure 10 and 11 , it can be obtained that the B-phase and C-phase relays of direction element 3 satisfy

[0125] (7)

[0126] In the formula, is the measured line voltage phasor between phase C and phase A; is the measured current phasor of phase B; is the measured line voltage phasor between phase A and phase B; is the measured current phasor of phase C.

[0127] The second is that the distance between bus N and the fault point is relatively far. At this time, the measured negative-sequence voltage of the bus is almost zero. As shown in the electrical quantities such as Figure 12 and 13 , it can be obtained that the B-phase and C-phase relays of direction element 3 satisfy

[0128] (8)

[0129] From the above conclusions, it can be seen that the B-phase and C-phase relays in direction element 3 can also correctly reflect the fault direction, but the sensitivity is greatly reduced. The downstream of the fault point is a passive network, and direction element 4 will not operate.

[0130] In a further embodiment, summarizing the above analysis results, when there is an IIDG access downstream of the fault point (bus O), if the fault is a three-phase short circuit, the upstream and downstream direction elements of the fault point can all operate correctly, but the sensitivity will decrease; if the fault is a two-phase interphase short circuit, the upstream direction elements of the fault point can all operate correctly. When the fault is close and the line impedance angle is When a fault occurs, the downstream direction element of the fault point may misjudge. When there is an IIDG connected upstream of the fault point (N bus), if the fault is a three-phase short circuit, the upstream direction element of the fault point is basically not affected; if the fault is a two-phase short circuit between phases, the upstream direction elements at the IIDG connection point can all operate correctly, but the sensitivity drops significantly. Therefore, when a metallic short circuit fault occurs, The overall sensitivity of the wiring direction element will decrease to varying degrees, and may misjudge in extreme cases. Considering factors such as measurement errors, the probability of misjudgment is extremely high.

[0131] In a further embodiment, regarding the influence of the transition resistance on the 90° wiring power direction element, when a short circuit fault occurs in the system and the transition resistance is large, the line equivalent impedance in the system composite sequence network can be considered resistive, which is equivalent to the above analysis . In the measurement data analysis results of each direction element in different scenarios, Still equal to Subtracting the normal line impedance angle, taken as , substituting It can be seen that misjudgment will occur in the scenarios corresponding to equations (3), (4), (5) and equation (8). Therefore, when the system has a short circuit through the transition resistance, The applicability of the wiring direction element is even worse.

[0132] The following is introduced in combination with a specific example.

[0133] According to Figure 2 The shown 10kV distribution network is used to build a simulation model to verify the proposed conclusion. An inverter-type distributed power source is connected to each of the N and O buses, and the positive sequence impedance per unit length of each line is (0.13 + j0.35) Ω / km. Under normal operating conditions, the maximum load current of the line is about 70A. When the fault current measured at the protection installation location is greater than 140A, the direction element starts to judge the fault direction.

[0134] (1) Operating conditions when the IIDG penetration rate is 100%

[0135] Four scenarios are designed according to the grid connection position of IIDG, fault type and transition resistance. Scenario 1: The grid connection capacity of IIDG upstream of the fault point is 1.2 MVA, and three-phase and BC two-phase metallic short circuits occur at point f respectively. Scenario 2: The grid connection capacity of IIDG upstream of the fault point is 1.2 MVA, and three-phase and BC two-phase short circuits through a 10 Ω transition resistance occur at point f respectively. Scenario 3: The grid connection capacity of IIDG downstream of the fault point is 1.2 MVA, and three-phase and BC two-phase metallic short circuits occur at point f respectively. Scenario 4: The grid connection capacity of IIDG downstream of the fault point is 1.2 MVA, and three-phase and BC two-phase short circuits through a 10 Ω transition resistance occur at point f respectively. The simulation results of Scenarios 1 and 2 are shown in Table 4.1, and the simulation results of Scenarios 3 and 4 are shown in Table 4.2.

[0136] Table 4.1 Measured values and operating conditions of directional elements in Scenarios 1 and 2 with 100% IIDG penetration

[0137]

[0138] Table 4.2 Measured values and operating conditions of directional elements in Scenarios 3 and 4 with 100% IIDG penetration

[0139]

[0140] (2)Operating conditions when the IIDG penetration is 170%

[0141] Similarly, four scenarios are designed according to the grid connection position of IIDG, fault type and transition resistance. Scenario 1: The grid connection capacity of IIDG upstream of the fault point is 2.06 MVA, and three-phase and BC two-phase metallic short circuits occur at point f respectively. Scenario 2: The grid connection capacity of IIDG upstream of the fault point is 2.06 MVA, and three-phase and BC two-phase short circuits through a 10 Ω transition resistance occur at point f respectively. Scenario 3: The grid connection capacity of IIDG downstream of the fault point is 2.06 MVA, and three-phase and BC two-phase metallic short circuits occur at point f respectively. Scenario 4: The grid connection capacity of IIDG downstream of the fault point is 2.06 MVA, and three-phase and BC two-phase short circuits through a 10 Ω transition resistance occur at point f respectively. The simulation results of Scenarios 1 and 2 are shown in Table 4.3, and the simulation results of Scenarios 3 and 4 are shown in Table 4.4.

[0142] Table 4.3 Measured values and operating conditions of directional elements in Scenarios 1 and 2 with 170% IIDG penetration

[0143]

[0144] Table 4.4 Measured values and operating conditions of directional elements in Scenarios 3 and 4 with 170% IIDG penetration

[0145]

[0146] Combined with the simulation results in Tables 4.1 to 4.4, it can be seen that when a metallic phase-to-phase short-circuit fault occurs in the system, the wiring power direction element can correctly judge the fault direction under the simulated scenarios, but the sensitivity may decrease. Especially when the distributed power source is downstream of the fault point and the penetration rate is relatively high, the sensitivity of the direction element decreases significantly; in the case of a short circuit through a transition resistor, the increase of the transition resistor will cause more offset of the line impedance angle, thus having a greater impact on the result of direction discrimination, and the probability of misjudgment of the direction element increases significantly. This simulation result further confirms the theoretical analysis result.

[0147] The present invention takes into account the strong coupling non-linear relationship between the terminal voltage and the output current of the IIDG with low-voltage ride-through capability, and analyzes the phase characteristics relationship of the voltage and current of each protection in the distribution network when a fault occurs upstream or downstream of the connection point of the inverter-type distributed power source. By setting different scenarios, the influences of different fault positions, different fault types, different line impedances, etc. on the traditional power direction element with 90° wiring are studied. Through analysis, it is concluded that in the scenario of a metallic fault occurring on the line, the sensitivity of the direction relay with 90° wiring decreases to varying degrees, which is related to factors such as the distributed power source penetration rate, grid connection position, and fault position, and may be misjudged in extreme cases; when short-circuiting through a transition resistor, the direction element will be misjudged in multiple scenarios, and the 90° wiring direction element is no longer applicable to the protection of active distribution networks.

[0148] Combined with the above embodiments, it can be seen that the present invention has the following advantages:

[0149] 1. This method analyzes the output characteristics of the inverter-type distributed power source with low-voltage ride-through capability under different current-limiting measures, and calculates the boundary range of the phase of its output current lagging behind the voltage at the connection point.

[0150] 2. Based on the fault output characteristics of the inverter-type distributed power source, different IIDG access positions, different fault positions and fault types are set, a composite sequence network model is established, and the phase characteristics of the system voltage and current are calculated and analyzed by using the constraint conditions under various working conditions, especially the boundary values of the line voltage containing the fault phase and the fault-phase current, and further the boundary values of the cosine of the phase difference between the measured voltage and current of the 90° wiring direction element are obtained to determine the action situation of the 90° wiring direction element, and the quantitative analysis process is detailed and accurate.

[0151] 3. Based on the analysis results of the boundary values, it can be seen that the sensitivity of the 90° wiring power direction element will decrease to varying degrees when applied in the distribution network with IIDG access. According to the influence of the existence of the transition resistor on the phase of the measured electrical quantity, the tolerance ability of the direction element to the transition resistor is further analyzed, and the conclusion that the 90° wiring power direction element is not applicable to the direction protection of active distribution networks is obtained. The overall process is complete and detailed, and the scenario setting is reasonable.

[0152] Based on the same inventive concept, an embodiment of the present application further provides an applicability analysis device for a 90° wiring direction element in an active distribution network for implementing the applicability analysis method of the 90° wiring direction element involved above in the active distribution network. The solution provided by this device for solving problems is similar to the solution described in the above method. Therefore, the specific limitations in the embodiment of the applicability analysis device for the 90° wiring direction element in the active distribution network provided below can refer to the limitations on the applicability analysis method of the 90° wiring direction element in the active distribution network in the above text, and will not be repeated here.

[0153] An embodiment of the present invention further provides an applicability analysis device for a 90° wiring direction element in an active distribution network, including:

[0154] An equivalent composite sequence network construction module, configured to construct an equivalent composite sequence network for a distribution network with inverter-type distributed generation (IIDG) access;

[0155] A phase difference calculation module, configured to combine the equivalent composite sequence network, and for each direction element with different relative positions to the fault point in the distribution network, quantitatively calculate the range of the phase difference between the measured voltage and current of each direction element under different types of faults based on the influence of IIDG access;

[0156] A first applicability analysis module, configured to evaluate the operation situation and the change in sensitivity of each direction element based on the range of the voltage-current phase difference, and obtain a first applicability analysis result of the direction element in a conventional fault scenario according to the operation situation and the change in sensitivity;

[0157] A second applicability analysis module, configured to update the line impedance parameters based on the situation of a short-circuit fault occurring through a transition resistance in the system, substitute the line impedance parameters into the quantitative calculation of the measured data of each direction element under different types of faults, and judge the misjudgment situation of the direction element according to the calculation result, so as to obtain a second applicability analysis result of the direction element when short-circuiting through a transition resistance;

[0158] A verification module, configured to verify the first applicability analysis result and the second applicability analysis result, thereby completing the applicability analysis of the direction element in the active distribution network.

[0159] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above division of each functional unit and module is used as an example. In actual applications, the above functions can be allocated to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of each functional unit and module are only for the convenience of mutual distinction and do not limit the protection scope of this application. The specific working processes of the units and modules in the above system can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0160] Referring to Figure 14 , an embodiment of the present invention further provides a computer device, including: a memory, a processor, and a computer program stored on the memory. When the computer program is executed on the processor, it implements the applicability analysis method of the 90° wiring direction element in the active distribution network as described in any one of the above methods.

[0161] The computer device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The computer device may include, but is not limited to, a processor and a memory. Those skilled in the art can understand that Figure 14 this is only an example of a computer device and does not constitute a limitation on the computer device. It may include more or fewer components than shown in the figure, or combine some components, or different components. For example, it may also include input / output devices, network access devices, etc.

[0162] The so-called processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0163] In some embodiments, the memory may be an internal storage unit of the computer device, such as the hard disk or memory of the computer device. In other embodiments, the memory may also be an external storage device of the computer device, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, etc. equipped on the computer device. Further, the memory may also include both the internal storage unit and the external storage device of the computer device. The memory is used to store an operating system, application programs, a BootLoader, data, and other programs, such as the program code of the computer program. The memory may also be used to temporarily store data that has been output or is to be output.

[0164] An embodiment of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is run by a processor, it implements the applicability analysis method of the 90° wiring direction element in an active distribution network as described in any one of the above methods.

[0165] In this embodiment, if the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, to implement all or part of the processes in the above embodiment methods of the present application, a computer program can be used to instruct relevant hardware to complete. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above various method embodiments. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, an executable file, or some intermediate form, etc. The computer-readable medium can at least include: any entity or device that can carry the computer program code to the photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. For example, a USB flash drive, a mobile hard disk, a magnetic disk, or an optical disc, etc. In some jurisdictions, according to legislation and patent practice, the computer-readable medium may not be an electrical carrier signal and a telecommunication signal.

[0166] In the above embodiments, the descriptions of the various embodiments have their own emphases. For the parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0167] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. A professional technician can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0168] In the embodiments disclosed in this application, it should be understood that the disclosed device / terminal device and method can be implemented in other ways. For example, the device / terminal device embodiments described above are merely illustrative. For example, the division of the modules or units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection to each other can be through some interfaces. The indirect coupling or communication connection of the device or unit can be in an electrical, mechanical or other form.

[0169] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0170] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing the applicability of 90° wiring direction elements in active distribution networks, characterized in that: The steps include: For the distribution network connected to the inverter-type distributed generation IIDG, an equivalent composite sequence network is constructed; Combined with the equivalent composite sequence network, for the directional elements in different relative positions to the fault point in the distribution network, based on the influence of IIDG access, the range of the voltage and current phase difference measured by the directional elements under different types of faults is quantitatively calculated; Evaluate the action status and sensitivity change of each directional element according to the range of the voltage and current phase difference, and obtain a first applicability analysis result of the directional element in a conventional fault scenario according to the action status and the sensitivity change; Based on the situation that the system has a short circuit fault through the transition resistor, the line impedance parameters are updated, and the line impedance parameters are substituted into the quantitative calculation of the measurement data of each directional element under different types of fault conditions, and the misjudgment of the directional element is judged according to the calculation results, so as to obtain the second applicability analysis result of the directional element when the directional element is short-circuited through the transition resistor; The first suitability analysis result and the second suitability analysis result are verified, thereby completing the suitability analysis of the directional element in the active power distribution network.

2. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 1 is characterized in that: In constructing an equivalent composite sequence network: If the distribution network to which the inverter-type distributed generation IIDG is connected is simplified, it includes a system power supply and bus M, bus N and bus O connected in sequence from the system power supply, wherein the directional elements at each position are directional element 1 downstream of bus M, directional element 2 upstream of bus N, directional element 3 downstream of bus N and directional element 4 upstream of bus O; Assuming that the fault occurs between directional element 3 and directional element 4, denoted as fault point f, then in the equivalent composite sequence network, the system power supply is equivalent to a constant voltage source and equivalent impedance The series connection, is the equivalent impedance of the MN section line, and the line impedance from bus N to the fault point is equivalent to , the line impedance from bus O to the fault point is equivalent to , the load impedance is ; The inverter-type distributed power source is equivalent to a voltage-controlled current source, and its grid-connected point voltage is , the output current is ; The positive sequence current flowing through the fault upstream line is , the equivalent negative sequence impedance at the fault point is .

3. The method for analyzing the applicability of the 90° wiring direction element in the active distribution network according to claim 2 is characterized in that: If a three-phase short circuit fault occurs in the system, the equivalent negative sequence impedance of the fault point =0. At this time, if the IIDG access point is located at the bus O downstream of the fault point, the phase difference measured by the directional elements at different positions meets the following conditions: For directional elements 1 and 3 upstream of the fault point, the following conditions are satisfied: In the formula, is the measured line voltage phasor between phase B and phase C; Measure the current phasor for phase A; is the interior angle of the directional element; is the line impedance angle; At this point, directional elements 1 and 3 can correctly reflect the fault direction and ideally work in the most sensitive state; For the upstream directional element 2 of the fault point, the following conditions are satisfied: At this point, directional element 2 can correctly reflect the fault direction and ideally works in the most sensitive state; For the downstream directional element 4 of the fault point, the following conditions are satisfied: In the formula, It is the phase angle of the inverter type distributed power supply output current lagging behind the grid connection point voltage; At this time, if When , directional element 4 can correctly reflect the fault direction, otherwise it will be misjudged.

4. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 2 is characterized in that: If a BC two-phase short circuit fault occurs in the system, and the IIDG access point is located at the bus O downstream of the fault point, the phase difference measured by the directional elements at different positions meets the following conditions: For directional elements 1 and 3 at different locations upstream of the fault point, the following conditions are satisfied: In the formula, is the measured line voltage phasor between phase C and phase A; Measure the current phasor for phase B; is the measured line voltage phasor between phase A and phase B; Measure the current phasor for phase C; is the interior angle of the directional element; is the line impedance angle; At this time, directional elements 1 and 3 can correctly reflect the fault direction; For the upstream directional element 2 of the fault point, the following conditions are satisfied: At this time, directional element 2 will judge the reverse direction fault and will not make a false judgment, but the sensitivity will decrease; For the downstream directional element 4 of the fault point, the following conditions are satisfied: At this time, if the current split by the IIDG output current on the upstream branch is smaller than the current split by the short-circuit current provided by the system on the branch, the directional element 4 will certainly make a wrong judgment.

5. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 4 is characterized in that: When a BC two-phase short circuit fault occurs in the system, four boundary conditions need to be considered when analyzing the applicability of the directional element, as follows: First, the grid connection point voltage in the composite sequence network is about 0.5 times the rated voltage range, so the IIDG output current lags behind the grid connection point voltage phase by about scope; Second, when the IIDG penetration rate at the grid connection point is 100% and its maximum output current is less than 1.5 times the rated current, the voltage drop of the IIDG output current on the line fO does not exceed 10.5% of the grid connection point voltage; The third is the line impedance angle ; Fourth, the diversion of the IIDG output current on its upstream branch is greater than the diversion of the short-circuit current provided by the system on this branch.

6. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 2 is characterized in that: When the IIDG access point is located at the bus N upstream of the fault point, if a three-phase short circuit fault occurs in the system, the action characteristics of the components in each direction upstream of the fault point remain unchanged, and the components in the direction downstream of the fault point will not start.

7. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 2, characterized in that: When the IIDG access point is located at the upstream bus N of the fault point, if a two-phase short circuit occurs in the system, the directional elements 1 and 2 upstream of the IIDG grid connection point work in the sensitive state; For directional element 3, if the fault point is located at the busbar N outlet, the B-phase and C-phase relays of directional element 3 meet the following requirements: In the formula, is the measured line voltage phasor between phase C and phase A; Measure the current phasor for phase B; is the measured line voltage phasor between phase A and phase B; Measure the current phasor for phase C; is the interior angle of the directional element; is the line impedance angle; If the fault point is a certain distance from the busbar N and the negative sequence voltage measured on the busbar is zero, the B-phase and C-phase relays of the directional element 3 satisfy: At this time, the B-phase and C-phase relays in directional element 3 can correctly respond to the fault direction, but the sensitivity is reduced; Directional element 4 downstream of the fault point will not operate.

8. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 2 is characterized in that: The first applicability analysis results of the directional element in common fault scenarios are as follows: When the IIDG is connected to the downstream bus O of the fault point, if the fault is a three-phase short circuit, the upstream and downstream direction components of the fault point can operate correctly, but the sensitivity will be reduced; if the fault is a two-phase short circuit, the upstream direction components of the fault point can operate correctly. When the fault point is in the downstream direction, the component may misjudge; When the bus N upstream of the fault point is connected with IIDG, if the fault is a three-phase short circuit, the upstream directional elements of the fault point will not be affected; if the fault is a two-phase short circuit, the upstream directional elements of the IIDG grid-connected point can operate correctly, but the sensitivity is reduced.

9. The method for analyzing the applicability of the 90° wiring direction element in the active power distribution network according to claim 2, characterized in that: When a short circuit fault occurs in the system and the transition resistance needs to be considered, the quantitative characteristics of the line equivalent impedance in the equivalent composite sequence network are updated with relevant parameters, specifically: When a short circuit occurs in the system and the transition resistance needs to be considered, the line equivalent impedance in the equivalent composite sequence network is resistive. At this time, the relevant parameters are updated as the line impedance angle. .

10. A device for analyzing the applicability of a 90° wiring direction element in an active distribution network, characterized in that: include: The equivalent composite sequence network construction module is used to construct an equivalent composite sequence network for the distribution network connected to the inverter-type distributed power source IIDG; A phase difference calculation module is used to combine the equivalent composite sequence network and, for each directional element in a distribution network with a different relative position to the fault point, quantitatively calculate the range of the voltage and current phase difference measured by each directional element under different types of faults based on the influence of IIDG access; A first applicability analysis module, used to evaluate the action status and sensitivity change of each directional element according to the range of the voltage and current phase difference, and obtain a first applicability analysis result of the directional element in a conventional fault scenario according to the action status and the sensitivity change; A second suitability analysis module is used to update the line impedance parameters based on the situation that the system has a short circuit fault through the transition resistor, and substitute the line impedance parameters into the quantitative calculation of the measurement data of each directional element under different types of fault conditions, and judge the misjudgment of the directional element according to the calculation result, so as to obtain the second suitability analysis result of the directional element when the directional element is short-circuited through the transition resistor; The simulation verification module is used to verify the first suitability analysis result and the second suitability analysis result, thereby completing the suitability analysis of the directional element in the active power distribution network.

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