Time domain distance protection method and system for connecting photovoltaic power station into same-tower double-circuit line

Abstract

The invention relates to a time domain distance protection method and system for connecting a photovoltaic power station to a same-tower double-circuit line, and the method comprises the steps: building a sequence component fault distance model through considering the influence on the electrical quantity of the same-tower double-circuit line after the photovoltaic power station is connected to the same-tower double-circuit line and the influence on the mutual inductance of the same-tower double-circuit line; the sequence component fault distance model is optimized by using the relation between the zero-sequence current of the fault loop and the fault point current; setting a first related electrical parameter involved in the sequence component fault distance optimization model as a preset fixed value, obtaining a measured value of a second related electrical parameter involved in the sequence component fault distance optimization model, and then performing discretization processing to obtain an actual fault distance; and comparing the actual fault distance with the set distance to judge whether to execute a time domain distance protection action or not. According to the invention, the calculation accuracy of the fault distance is improved, and safe and stable operation of the same-tower double-circuit line under the access of the photovoltaic power station is ensured.

Description

Technical Field

[0001] The present invention relates to the field of power grid fault distance protection, and particularly to a time-domain distance protection method and system for a photovoltaic power station connected to a double-circuit line on the same tower. Background Art

[0002] With the rise of new energy, photovoltaic power stations are widely used in the power grid. However, due to the large uncertainty and volatility of photovoltaic power stations, the power frequency distance protection method cannot accurately judge the location and severity of faults when a photovoltaic power station is connected to a line. Moreover, the intermittent and random volatility of the photovoltaic power station itself makes the fault current difficult to predict. After being connected to a double-circuit line on the same tower, it will change the topological structure of the double-circuit line on the same tower and also affect the changes of parameters such as the amplitude and phase angle of the original electrical quantities in the power grid, thus causing the protection to refuse to operate or malfunction. Therefore, seeking an effective distance protection scheme for a photovoltaic power station connected to a double-circuit line on the same tower, considering the influence of the connection of the photovoltaic power station on the parameters of the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself, is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0003] The present invention provides a time-domain distance protection method and system for a photovoltaic power station connected to a double-circuit line on the same tower to solve at least one of the above technical problems.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: A time-domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower, including: S1, considering the influence of the connection of the photovoltaic power station to the double-circuit line on the same tower on the electrical quantities of the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself, constructing a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; S2, optimizing the sequence component fault distance model by using the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line on the same tower and the fault point current to obtain a sequence component fault distance optimization model; S3, setting the first relevant electrical parameters involved in the sequence component fault distance optimization model to a preset fixed value, and starting the operation of the photovoltaic power station connected to the double-circuit line on the same tower to obtain the measured values of the second relevant electrical parameters involved in the sequence component fault distance optimization model; substituting the preset fixed value of the first relevant electrical parameters and the measured values of the second relevant electrical parameters into the sequence component fault distance optimization model and then performing time-domain discretization processing to obtain the actual fault distance from the protection side of the photovoltaic power station to the fault point under the preset fixed value of the first relevant electrical parameters; S4. Compare the actual fault distance from the photovoltaic power station side protection to the fault point with the set distance under the preset fixed value of the first relevant electrical parameter to determine whether to perform a time-domain distance protection action under the preset fixed value of the first relevant electrical parameter.

[0005] Based on the above technical solutions, the present invention can also be improved as follows.

[0006] Preferably, the S1 is specifically: Construct a fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; Take into account the positive, negative, and zero sequence currents existing in the faulted line of the photovoltaic power station connected to the double-circuit line on the same tower, and substitute them into the fault distance model to obtain the sequence component fault distance model.

[0007] Preferably, the photovoltaic power station connected to the double-circuit line on the same tower includes Circuit I and Circuit II. Assume that Circuit I fails, then the faulted line is Circuit I, and: The fault distance model is expressed as: ; Wherein, represents the voltage on the photovoltaic power station side when the photovoltaic power station is connected to the double-circuit line on the same tower, represents the current on the side of Circuit I close to the photovoltaic power station, represents the zero sequence current on the side of Circuit II close to the photovoltaic power station, and respectively represent the resistance and inductance per unit length of the line on Circuit I, and respectively represent the mutual resistance and mutual inductance per unit length of the line on Circuit I, represents the actual fault distance from the photovoltaic power station side protection to the fault point, represents the fault point current, represents the transition resistance at the fault point, represents time.

[0008] Preferably, the positive, negative, and zero sequence currents existing in the faulted line of the photovoltaic power station connected to the double-circuit line on the same tower are expressed as: ; Wherein, , and respectively represent the zero sequence current, positive sequence current, and negative sequence current on the side of Circuit I close to the photovoltaic power station; The sequence component fault distance model is expressed as: ; Wherein, and respectively represent the zero-sequence resistance and positive-sequence resistance per unit length of the line on the I-th loop, and respectively represent the zero-sequence inductance and positive-sequence inductance per unit length of the line on the I-th loop; in a double-circuit line on the same tower, , , represents the negative-sequence resistance per unit length of the line on the I-th loop, represents the negative-sequence inductance per unit length of the line on the I-th loop.

[0009] Preferably, in the step S2, the relationship between the zero-sequence current of the photovoltaic power station connected to the faulty loop of the double-circuit line on the same tower and the fault point current is expressed as: ; wherein, represents a complex coefficient, and , and respectively represent the real part and the imaginary part; the optimized model of the sequence component fault distance is expressed as: ; wherein, and respectively represent the zero-sequence resistance compensation coefficient and zero-sequence inductance compensation coefficient on the I-th loop, and the zero-sequence resistance compensation coefficient and the zero-sequence inductance compensation coefficient are expressed as: .

[0010] Preferably, in the step S3, the first relevant electrical parameter is ; the second relevant electrical parameters include: , , , , , , , and ; Substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized model of the sequence component fault distance, and then perform discretization processing based on the time domain, specifically: Substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized model of the sequence component fault distance to obtain a simplified model of the sequence component fault distance; the simplified model of the sequence component fault distance is expressed as: ; wherein, , and all represent the coefficients of the sequence component fault distance optimization model, and: ; Using the difference to replace the differential to discretize the sequence component fault distance simplified model based on the time domain, the actual fault distance of the photovoltaic power station side protection to the fault point is obtained under the preset fixed value of the first relevant electrical parameter.

[0011] Preferably, in the step S4, the criterion for executing the time domain distance protection action is: ; where represents the setting distance.

[0012] Preferably, after the step S3, it further includes: S5, changing the preset fixed value of the first relevant electrical parameter multiple times, and executing the step S3 after each change of the preset fixed value of the first relevant electrical parameter, so as to obtain the actual fault distances of the photovoltaic power station side protection to the fault point under multiple different preset fixed values of the first relevant electrical parameter; Comparing the actual fault distances of the photovoltaic power station side protection to the fault point under each different preset fixed value of the first relevant electrical parameter with the setting distance, so as to determine whether to execute the time domain distance protection action under each different preset fixed value of the first relevant electrical parameter, and calculating the error degree between the actual fault distance and the setting distance.

[0013] Preferably, the value range of the preset fixed value of the first relevant electrical parameter is 0 - 300 Ω.

[0014] Based on the above time domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower, the present invention further provides a time domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower.

[0015] The time domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower includes: A modeling module, which is used to consider the influence of the photovoltaic power station connected to the double-circuit line on the same tower on the electrical quantities of the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself, and construct a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; An optimization module, which is used to optimize the sequence component fault distance model by using the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line on the same tower and the current at the fault point, so as to obtain a sequence component fault distance optimization model; A calculation module is configured to set a first relevant electrical parameter involved in the sequence component fault distance optimization model to a preset fixed value, and start the photovoltaic power station to access the double-circuit line on the same tower for operation to obtain the measured value of the second relevant electrical parameter involved in the sequence component fault distance optimization model; substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the sequence component fault distance optimization model, and then perform discretization processing based on time domain to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameter; A protection module is configured to compare the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameter with the setting distance to determine whether to perform the time domain distance protection action under the preset fixed value of the first relevant electrical parameter.

[0016] The beneficial effects of the present invention are as follows: In the time domain distance protection method and system for the photovoltaic power station to access the double-circuit line on the same tower of the present invention, first, the influence of the photovoltaic power station accessing the double-circuit line on the same tower on the line electrical quantity and the mutual inductance of the double-circuit line on the same tower itself are considered to construct the sequence component fault distance model for the photovoltaic power station to access the double-circuit line on the same tower. Then, the relationship between the zero-sequence currents on both sides of the line and the fault point current after the photovoltaic access is used to optimize the sequence component fault distance model. Next, the sequence component fault distance optimization model is discretized by setting and measuring the values of relevant electrical parameters to obtain the actual distance. Finally, it is compared with the setting distance to determine whether to perform the time domain distance protection action; the present invention optimizes the traditional time domain distance protection method, solves the problem that the protection is inaccurate due to the influence of the photovoltaic power station on the line and the mutual inductance of the double-circuit line on the same tower itself after the photovoltaic power station accesses the double-circuit line on the same tower, improves the calculation accuracy of the fault distance, and ensures the safe and stable operation of the double-circuit line on the same tower under the photovoltaic power station access. Description of the Drawings

[0017] Figure 1 It is a flowchart of the time domain distance protection method for the photovoltaic power station to access the double-circuit line on the same tower of the present invention; Figure 2 It is a schematic diagram of the line after the photovoltaic power station accesses the double-circuit line on the same tower; Figure 3 It is a network diagram of the zero-sequence current of the first circuit in the single-phase ground fault after the photovoltaic power station accesses the double-circuit line on the same tower; Figure 4 It is a simulation change diagram of the zero-sequence current amplitude and phase angle on both sides of the double-circuit line on the same tower before and after the photovoltaic power station accesses the double-circuit line on the same tower; Figure 5 It is a schematic diagram of the relationship between the fault point current and the zero-sequence currents on the photovoltaic power station side and the system side; Figure 6This is the structural block diagram of the time-domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower in the present invention. Specific embodiments

[0018] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0019] As Figure 1 shown, the time-domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower includes: S1. Considering the influence of the photovoltaic power station connected to the double-circuit line on the same tower on the electrical quantities of the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself, a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower is constructed; S2. Using the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line on the same tower and the fault point current to optimize the sequence component fault distance model, and obtaining an optimized sequence component fault distance model; S3. Setting the first relevant electrical parameters involved in the optimized sequence component fault distance model to a preset fixed value, and starting the operation of the photovoltaic power station connected to the double-circuit line on the same tower to obtain the measured values of the second relevant electrical parameters involved in the optimized sequence component fault distance model; substituting the preset fixed value of the first relevant electrical parameters and the measured values of the second relevant electrical parameters into the optimized sequence component fault distance model and then performing time-domain discretization processing to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameters; S4. Comparing the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameters with the setting distance to determine whether to perform time-domain distance protection action under the preset fixed value of the first relevant electrical parameters.

[0020] The following is a specific description of each step: In some embodiments, S1 is specifically: Construct a fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; Considering the positive, negative, and zero-sequence currents existing in the faulted line of the photovoltaic power station connected to the double-circuit line on the same tower and substituting them into the fault distance model to obtain the sequence component fault distance model.

[0021] Specifically, the line after the photovoltaic power station is connected to the double-circuit line on the same tower is as Figure 2As shown in the figure. Among them, the photovoltaic power station PV is connected to the double-circuit line on the same tower through a transformer; the connection of the photovoltaic power station to the double-circuit line on the same tower includes Circuit I and Circuit II. The side close to the photovoltaic power station of Circuit I and Circuit II is the M side, and the side close to the system of Circuit I and Circuit II is the N side; on Circuit I, the protection on the photovoltaic power station side is Protection 1, and the protection on the system side is Protection 2. Photovoltaic power station parameter settings: the sampling frequency is 10 kHz, the rated capacity of the photovoltaic power station is 20 MW, the photovoltaic power station is boosted by a transformer and then incorporated into the system. The voltage levels on both the photovoltaic power station side and the system side are set to 220 kV, and the total length of the double-circuit line on the same tower is set to 100 km. Taking Circuit I as an example for analysis, the protection range of Circuit I is 80% of the total line length. Since the total length of the double-circuit line on the same tower with the photovoltaic power station connected is km. Therefore, the set distance is = *80% = 80 km. In this embodiment, taking the A-phase grounding fault on Circuit I as an example, and the transition resistance at the fault point f is (the resistance at the fault point is called the transition resistance); then the faulty circuit in the double-circuit line on the same tower with the photovoltaic power station connected is the said Circuit I, and: The said fault distance model is expressed as: ; (1) Among them, represents the voltage on the photovoltaic power station side when the photovoltaic power station is connected to the double-circuit line on the same tower, is the resistance voltage on Circuit I, is the inductance voltage on Circuit I, is the resistance voltage of the fault point on Circuit I, is the mutual inductance resistance voltage of Circuit II to Circuit I, is the mutual inductance inductance voltage of Circuit II to Circuit I; represents the current on the side close to the photovoltaic power station of the said Circuit I, represents the zero-sequence current on the side close to the photovoltaic power station of the said Circuit II, and respectively represent the resistance and inductance of the line per unit length on the said Circuit I, and respectively represent the mutual inductance resistance and mutual inductance inductance of the line per unit length on the said Circuit I, represents the actual fault distance from the protection on the photovoltaic power station side to the said fault point, represents the fault point current, represents the transition resistance of the said fault point, represents time.

[0022] Furthermore, considering the positive, negative, and zero-sequence currents existing in the faulty line of the photovoltaic power station connected to the double-circuit line on the same tower, the positive, negative, and zero-sequence currents existing in the faulty line of the photovoltaic power station connected to the double-circuit line on the same tower are expressed as: ; (2) Among them, , and respectively represent the zero-sequence current, positive-sequence current, and negative-sequence current on the side of the first circuit near the photovoltaic power station; Substituting Equation (2) into Equation (1) can obtain the sequence-component fault distance model; since this embodiment takes the grounding fault of phase A of the first circuit as an example, this sequence-component fault distance model is specifically the voltage of phase A at the protection 1 near the photovoltaic power station side represented by the sequence components.

[0023] The sequence-component fault distance model is expressed as: ; (3) Among them, and respectively represent the zero-sequence resistance and positive-sequence resistance of the unit length line on the first circuit, and respectively represent the zero-sequence inductance and positive-sequence inductance of the unit length line on the first circuit; in the double-circuit line on the same tower, generally, , , represents the negative-sequence resistance of the unit length line on the first circuit, represents the negative-sequence inductance of the unit length line on the first circuit.

[0024] The network diagram of the zero-sequence current of the first circuit in the single-phase grounding fault after the photovoltaic power station is connected to the double-circuit line on the same tower is as Figure 3 shown; Figure 3 In represents the zero-sequence current on the side of the first circuit near the system side, represents the zero-sequence capacitance of the unit length line on the first circuit, represents the capacitive current at the first end of the first circuit near the photovoltaic power station side, represents the capacitive current at the end of the first circuit near the photovoltaic power station side, represents the capacitive current at the first end of the first circuit near the system side, represents the capacitive current at the end of the first circuit near the system side, represents the unit impedance on the photovoltaic power station side, represents the unit impedance on the system side.

[0025] In some embodiments, for the obtained sequence component fault distance model, by starting the photovoltaic power station to access the same-tower double-circuit line in normal operation and single-phase ground short-circuit fault (i.e., A-phase ground fault) operation, the zero-sequence currents on both sides of the line under the access of the photovoltaic power station are respectively obtained, and the relationship between the zero-sequence current of the I-line and the fault point current in the sequence component is further optimized, thereby optimizing the sequence component fault distance model.

[0026] Since the fault point current cannot be measured, it is necessary to perform equivalent processing on it.

[0027] From Figure 3 it can be seen that: , where the represents the zero-sequence current of the fault point. Thus, it can be known that after the photovoltaic power station is connected to the same-tower double-circuit line, the capacitive current will cause and and there is a phase angle difference between the currents on both sides of the line. Then, the specific situation after the photovoltaic power station is connected to the same-tower double-circuit line can be verified by simulation, and the simulation results are as Figure 4 shown.

[0028] Perform simulations on single-phase ground faults with the photovoltaic power station not connected and connected to the same-tower double-circuit line, and the changes in the line simulation situation can be observed. When the photovoltaic power station is not connected, the current amplitudes and phase angles on both sides of the line are basically the same, but when the photovoltaic power station is connected, it can be clearly observed that the amplitude and phase angle of the zero-sequence current on the photovoltaic power station side change, as Figure 4 shown; among them, Figure 4 in (a) is the simulation change diagram of the zero-sequence current amplitudes on both sides of the same-tower double-circuit line (photovoltaic power station side and system side) after the photovoltaic power station is connected to the same-tower double-circuit line, Figure 4 in (b) is the simulation change diagram of the zero-sequence current amplitudes on both sides of the same-tower double-circuit line when the photovoltaic power station is not connected to the same-tower double-circuit line (i.e., before the photovoltaic power station is connected to the same-tower double-circuit line), Figure 4 in (c) is the simulation change diagram of the zero-sequence current phase angles on both sides of the same-tower double-circuit line after the photovoltaic power station is connected to the same-tower double-circuit line, Figure 4 in (d) is the simulation change diagram of the zero-sequence current phase angles on both sides of the same-tower double-circuit line when the photovoltaic power station is not connected to the same-tower double-circuit line. And according to the relationship between the current changes on the photovoltaic power station side and the system side and the current flowing through the fault point, it can be clearly observed that the current flowing through the fault point is affected by the amplitude and phase angle brought by the connection of the photovoltaic power station, as Figure 5 shown; among them, Figure 5 in (a) is the schematic diagram of the relationship between the zero-sequence current on both sides of the same-tower double-circuit line and the fault current after the photovoltaic power station is connected to the same-tower double-circuit line, Figure 5 in (b) is the schematic diagram of the relationship between the zero-sequence current on both sides of the same-tower double-circuit line and the fault current when the photovoltaic power station is not connected to the same-tower double-circuit line.

[0029] When the photovoltaic power station is not connected and only the double-circuit line on the same tower operates, the zero-sequence network impedance angles on both sides of the fault point are approximately equal, so the zero-sequence currents flowing through both sides of the double-circuit line on the same tower are approximately in the same phase. Therefore, 3 and only differ by a real coefficient , that is and The relationship between them can be expressed as: . Substituting into Equation (1) gives the fault distance optimization model for the double-circuit line on the same tower without the photovoltaic power station connected. The fault distance optimization model for the double-circuit line on the same tower without the photovoltaic power station connected is expressed as: ; (4) When the photovoltaic power station is connected to the double-circuit line on the same tower, due to the weak feed and randomness of the photovoltaic, when a single-phase grounding fault occurs on the double-circuit line on the same tower, the amplitude and phase angle of the zero-sequence currents on both sides of the double-circuit line on the same tower change, resulting in a phase angle difference between the zero-sequence currents on both sides of the double-circuit line on the same tower. At this time, 3 and The relationship between them cannot be represented by the real coefficient , but should be represented by the complex coefficient : ; Substituting and (obtained by transforming in Equation (2)) into Equation (3) gives: ; (5) Since represents a complex coefficient, and , and respectively represent The real part and the imaginary part of The described sequence component fault distance optimization model is expressed as: ; (6) Among them, and respectively represent the zero-sequence resistance compensation coefficient and the zero-sequence inductance compensation coefficient on the I-th line, and the zero-sequence resistance compensation coefficient and the zero-sequence inductance compensation coefficient are expressed as: . (7) In some embodiments, in S3, the first relevant electrical parameter is ; The second relevant electrical parameters include: , , , , , , , and .

[0030] Among them, start the photovoltaic power station to access the double-circuit line on the same tower for operation to obtain the measured values of the second relevant electrical parameters involved in the sequence component fault distance optimization model, specifically: Obtain the voltage and current on the photovoltaic power station side and the inductance and resistance of the double-circuit line on the same tower when the photovoltaic power station accesses the double-circuit line on the same tower for normal operation, and obtain the voltage and current data after the fault of the photovoltaic power station accessing the double-circuit line on the same tower, so as to calculate the zero-sequence current on the photovoltaic power station side and the zero-sequence current on the system side after the fault, and obtain the zero-sequence resistance and zero-sequence inductance of the double-circuit line on the same tower. Calculate the zero-sequence resistance compensation coefficient, zero-sequence inductance compensation coefficient, mutual inductance resistance, and mutual inductance inductance of the II circuit to the I circuit according to the zero-sequence resistance and zero-sequence inductance of the double-circuit line on the same tower.

[0031] Through the simulation of the normal operation of the photovoltaic power station accessing the double-circuit line on the same tower, the present invention can directly obtain the zero-sequence resistance per unit length of the line on the I circuit, the positive-sequence resistance per unit length of the line on the I circuit, the zero-sequence inductance per unit length of the line on the I circuit, the positive-sequence inductance , , , , , Substituting these measured values into Equation (7) can obtain the zero-sequence resistance compensation coefficient and zero-sequence inductance compensation coefficient of the line on the I circuit. Then, when a fault occurs in the double-circuit line on the same tower accessed by the photovoltaic power station, the voltage near the photovoltaic power station side of the I circuit, the current near the photovoltaic power station side of the II circuit, and and can be directly obtained. By analyzing through the FFT element, the zero-sequence current near the photovoltaic power station side of the I circuit and the zero-sequence current Furthermore, after the photovoltaic power station is connected, the actual fault distance when a fault occurs in the double-circuit line on the same tower is calculated. Based on more factors, the accuracy of calculating the fault distance is improved, and the problem of inaccurate protection caused by the influence of the photovoltaic power station on the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself is solved.

[0032] Substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the sequence component fault distance optimization model, and then perform discretization processing based on time domain, specifically: Substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the sequence component fault distance optimization model to obtain a simplified model of the sequence component fault distance; the simplified model of the sequence component fault distance is expressed as: ; (8) Where 、 and all represent the coefficients of the sequence component fault distance optimization model, and: ; (9) Use difference to replace differential to perform discretization processing based on time domain on the simplified model of the sequence component fault distance, and obtain the actual fault distance from the protection on the photovoltaic power station side to the fault point under the preset fixed value of the first relevant electrical parameter.

[0033] Perform discretization processing on Equation (8), that is, use difference to replace differential. According to the three-point differential formula, it can be known that the differential at each sampling moment in the formula can be solved by the difference between the previous sampling moment and the next sampling moment, where is the sampling time interval. According to the three-point differential formula, the discrete-time signal can be expressed as: ; (10) According to Equation (10), the actual fault distance from the protection on the photovoltaic power station side to the fault point under the preset fixed value of the first relevant electrical parameter (transition resistance) can be obtained.

[0034] In some embodiments, in the S4, the criterion for performing time-domain distance protection action is: ; where represents the setting distance.

[0035] Specifically, compare the calculated actual fault distance after fitting with the setting distance . If is satisfied, the protection acts; otherwise, the protection does not act.

[0036] In some embodiments, after the step S3, the method further includes: S5. Changing the preset fixed value of the first relevant electrical parameter multiple times, and after each change of the preset fixed value of the first relevant electrical parameter, executing the step S3 to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under multiple different preset fixed values of the first relevant electrical parameter; Comparing the actual fault distances from the photovoltaic power station side protection to the fault point under each different preset fixed value of the first relevant electrical parameter with the setting distance to determine whether to perform the time-domain distance protection action under each different preset fixed value of the first relevant electrical parameter, and calculating the error degree between the actual fault distance and the setting distance.

[0037] Specifically, according to step S3, when a transition resistance value is set, the corresponding actual fault distance can be calculated. Since the transition resistance of the double-circuit line on the same tower generally ranges from 0 to 300 Ω when a fault occurs, when a single-phase grounding fault occurs on the line, different transition resistance values (0 to 300 Ω) correspond to different fault occurrence positions (0 to 100 km), and the changes in the amplitude, phase angle, and mutual inductance parameters of the relevant electrical quantities of the first circuit and the second circuit; by repeating step S3 for different transition resistance values, multiple corresponding actual fault distances can be calculated, so as to perform the time-domain distance protection determination and calculate the error degree from the setting distance. Multiple data can more accurately reflect that the method has better protection performance.

[0038] Based on the above time-domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower, the present invention further provides a time-domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower.

[0039] As Figure 6 shown, the time-domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower includes: A modeling module, which is used to consider the influence of the connection of the photovoltaic power station to the double-circuit line on the same tower on the electrical quantities of the double-circuit line on the same tower and the influence of the mutual inductance of the double-circuit line on the same tower itself, and construct a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; An optimization module, which is used to optimize the sequence component fault distance model by using the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line on the same tower and the fault point current to obtain a sequence component fault distance optimization model; A calculation module, which is used to set the first relevant electrical parameter involved in the sequence component fault distance optimization model to a preset fixed value, and start the photovoltaic power station to access the double-circuit line on the same tower to obtain the measured value of the second relevant electrical parameter involved in the sequence component fault distance optimization model; substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the sequence component fault distance optimization model, and then perform time-domain discretization processing to obtain the actual fault distance from the protection on the photovoltaic power station side to the fault point under the preset fixed value of the first relevant electrical parameter; A protection module, which is used to compare the actual fault distance from the protection on the photovoltaic power station side to the fault point under the preset fixed value of the first relevant electrical parameter with the setting distance, so as to determine whether to perform time-domain distance protection action under the preset fixed value of the first relevant electrical parameter.

[0040] For the specific functions of each module in the time-domain distance protection system for a photovoltaic power station accessing a double-circuit line on the same tower of the present invention, refer to the specific steps in the time-domain distance protection method for a photovoltaic power station accessing a double-circuit line on the same tower of the present invention, which will not be elaborated here.

[0041] In the time-domain distance protection method and system for a photovoltaic power station accessing a double-circuit line on the same tower of the present invention, first, the influence of the photovoltaic power station accessing the double-circuit line on the same tower on the line electrical quantity and the mutual inductance of the double-circuit line on the same tower itself are considered to construct a sequence component fault distance model for the photovoltaic power station accessing the double-circuit line on the same tower. Then, the sequence component fault distance model is optimized by using the relationship between the zero-sequence currents on both sides of the line and the fault point current after photovoltaic access. Next, the sequence component fault distance optimization model is discretized by setting and measuring the values of relevant electrical parameters to obtain the actual distance. Finally, by comparing with the setting distance, it is determined whether to perform time-domain distance protection action; the present invention optimizes the traditional time-domain distance protection method, solves the problem of inaccurate protection caused by the influence of the photovoltaic power station on the line and the mutual inductance of the double-circuit line on the same tower itself after the photovoltaic power station accesses the double-circuit line on the same tower, improves the calculation accuracy of the fault distance, and ensures the safe and stable operation of the double-circuit line on the same tower under the photovoltaic power station access.

[0042] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Time-domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower, characterized in that, Including: S1, considering the influence of the photovoltaic power station connected to the double-circuit line on the electrical quantities of the double-circuit line and the mutual inductance of the double-circuit line itself, constructing a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line; S2, optimizing the sequence component fault distance model by using the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line and the fault point current to obtain an optimized sequence component fault distance model; S3, setting the first relevant electrical parameter involved in the optimized sequence component fault distance model to a preset fixed value, and starting the operation of the photovoltaic power station connected to the double-circuit line to obtain the measured value of the second relevant electrical parameter involved in the optimized sequence component fault distance model; substituting the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized sequence component fault distance model and performing time-domain discretization processing to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameter; S4, comparing the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameter with the setting distance to determine whether to perform time-domain distance protection action under the preset fixed value of the first relevant electrical parameter.

2. The time-domain distance protection method for a photovoltaic power station connected to a double-circuit line on the same tower according to claim 1, wherein The specific content of S1 is: Constructing a fault distance model for the photovoltaic power station connected to the double-circuit line; Considering the positive, negative, and zero-sequence currents existing in the faulted line of the photovoltaic power station connected to the double-circuit line and substituting them into the fault distance model to obtain the sequence component fault distance model.

3. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 2, characterized in that, The photovoltaic power station connected to the double-circuit line includes Line I and Line II. Assuming that Line I has a fault, then the faulted line is Line I, and: The fault distance model is expressed as: ； Among them, represents the voltage on the PV power station side when the PV power station is connected to a double-circuit line on the same tower, represents the current on the I-th line near the PV power station side, represents the zero-sequence current on the II-th line near the PV power station side, and respectively represent the resistance and inductance per unit length of the I-th line, and respectively represent the mutual resistance and mutual inductance per unit length of the I-th line, represents the actual fault distance from the protection on the PV power station side to the fault point, represents the fault point current, represents the transition resistance of the fault point, represents time.

4. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 3, wherein, The positive, negative, and zero-sequence currents existing in the faulted line of the photovoltaic power station connected to the double-circuit line are expressed as: ； Among them, , and respectively represent the zero-sequence current, positive-sequence current, and negative-sequence current on the side of the I-line close to the PV power station; The sequence component fault distance model is expressed as: ； Among them, and respectively represent the zero-sequence resistance and positive-sequence resistance per unit length of the line on the I circuit; and respectively represent the zero-sequence inductance and positive-sequence inductance per unit length of the line on the I circuit; in a double-circuit line on the same tower, , , represents the negative-sequence resistance per unit length of the line on the I circuit, represents the negative-sequence inductance per unit length of the line on the I circuit.

5. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 4, characterized in that, In S2, the relationship between the zero-sequence current of the faulted line in the photovoltaic power station connected to the double-circuit line and the fault point current is expressed as: ； Among them, represents a complex coefficient, and , and respectively represent the real and imaginary parts of; The optimized sequence component fault distance model is expressed as: ； Among them, and respectively represent the zero-sequence resistance compensation coefficient and the zero-sequence inductance compensation coefficient on the I-line, and the zero-sequence resistance compensation coefficient and the zero-sequence inductance compensation coefficient are expressed as: 。 6. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 5, characterized in that In the S3, the first relevant electrical parameter is ; The second relevant electrical parameter includes: , , , , , , , and ; After substituting the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized sequence component fault distance model and performing time-domain discretization processing, specifically: Substituting the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized sequence component fault distance model to obtain a simplified sequence component fault distance model; the simplified sequence component fault distance model is expressed as: ； Among them, , and all represent the coefficients of the sequence component fault distance optimization model, and: ； Using the difference to replace the differential to perform time-domain discretization processing on the simplified sequence component fault distance model to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under the preset fixed value of the first relevant electrical parameter.

7. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 6, characterized in that In the S4, the criterion for the execution of the time-domain distance protection action is: ; where represents the setting distance.

8. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to claim 6, characterized in that, After S3, it further includes: S5, changing the preset fixed value of the first relevant electrical parameter multiple times, and performing S3 each time after changing the preset fixed value of the first relevant electrical parameter to obtain the actual fault distance from the photovoltaic power station side protection to the fault point under multiple different preset fixed values of the first relevant electrical parameter; Compare the actual fault distance from the photovoltaic power station side protection to the fault point at each different preset fixed value of the first relevant electrical parameter with the setting distance, so as to determine whether to perform a time-domain distance protection action at each different preset fixed value of the first relevant electrical parameter, and calculate the error degree between the actual fault distance and the setting distance.

9. The time-domain distance protection method for a photovoltaic power station to access a double-circuit line on the same tower according to any one of claims 6 to 8, characterized in that, The value range of the preset fixed value of the first relevant electrical parameter is 0 to 300 Ω.

10. A time-domain distance protection system for a photovoltaic power station connected to a double-circuit line on the same tower, characterized in that, It includes: A modeling module, which is used to consider the influence of the photovoltaic power station connected to the double-circuit line on the same tower on the electrical quantities of the double-circuit line on the same tower and the mutual inductance of the double-circuit line on the same tower itself, and construct a sequence component fault distance model for the photovoltaic power station connected to the double-circuit line on the same tower; An optimization module, which is used to optimize the sequence component fault distance model by using the relationship between the zero-sequence current of the faulty line in the photovoltaic power station connected to the double-circuit line on the same tower and the fault point current, and obtain an optimized sequence component fault distance model; A calculation module, which is used to set the first relevant electrical parameter involved in the optimized sequence component fault distance model to a preset fixed value, and start the operation of the photovoltaic power station connected to the double-circuit line on the same tower to obtain the measured value of the second relevant electrical parameter involved in the optimized sequence component fault distance model; substitute the preset fixed value of the first relevant electrical parameter and the measured value of the second relevant electrical parameter into the optimized sequence component fault distance model and perform time-domain discretization processing to obtain the actual fault distance from the photovoltaic power station side protection to the fault point at the preset fixed value of the first relevant electrical parameter; A protection module, which is used to compare the actual fault distance from the photovoltaic power station side protection to the fault point at the preset fixed value of the first relevant electrical parameter with the setting distance, so as to determine whether to perform a time-domain distance protection action at the preset fixed value of the first relevant electrical parameter.

Images