Active power distribution network adaptive current differential protection method based on time domain waveform
By adopting an adaptive current differential protection method based on time domain waveform in the active distribution network, the difficulty of setting parameters and operation delay problems of traditional protection methods under multi-terminal power supply and high distributed power permeability are solved, and the protection effect of high sensitivity and transition resistance resistance resistance is achieved.
Patent Information
- Application Number
- CN202411510133.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-28
- Publication Date
- 2025-02-25
AI Technical Summary
The traditional active distribution network protection method has problems such as difficulty in setting parameters, long operation delay and poor selectivity when multi-end power supply and distributed power supply are high, and it is difficult to adapt to the operating state of the island.
Adaptive current differential protection method based on time domain waveforms is adopted, by collecting three-phase currents in real time on the protection device, calculating positive sequence current components using discrete full-circumference algorithm and symmetric component method, constructing waveform difference index, adaptively adjusting the differential protection braking coefficient, and achieving accurate judgment of faults in the region.
This method can effectively solve the protection refusal problem when the transition resistance is large and the traversing current is dominant. It has high sensitivity and ability to withstand transition resistance, is not affected by DG permeability and synchronization error, has a small amount of data transmission and strong anti-noise ability.
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Figure CN119518626A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of active distribution network relay protection, and in particular to an active distribution network adaptive current differential protection method based on time domain waveform. Background Art
[0002] With the shortage of fossil energy, the development of power electronics technology and the increase in the national economy's demand for electricity, more and more clean energy is connected to the distribution network in the form of distributed generation (DG), which makes the traditional distribution network change from a radial distribution network powered by a single power source to an active distribution network powered by multiple terminals. The load current under normal operation and the short-circuit current after a fault may flow in both directions under different operating modes. At the same time, different types of DGs present different fault characteristics. Affected by the inverter control strategy, the fault current output by the inverter-interfaced distributed generator (IIDG) presents the characteristics of limited current amplitude and controllable phase angle. The short-circuit current that the motor type distributed generator (MTDG) can provide is relatively large, with a maximum value of about 6 to 10 times the rated current. Considering these factors, traditional overcurrent protection has problems such as difficult parameter setting, long action delay and poor selectivity. More seriously, if the DG is disconnected from the grid after a fault, the change in the distribution network topology will also have an adverse effect on traditional protection methods. Therefore, with the continuous increase in DG penetration in distribution networks, traditional protection methods have become difficult to apply, and new methods that are more sensitive and reliable are urgently needed.
[0003] At present, the protection methods for active distribution networks can be roughly divided into two categories. One is single-end protection. The prior art proposes an adaptive current protection scheme, which improves the existing three-stage current protection by adding directional elements, intelligent electronic devices, etc. However, the topological structure and operation mode of the active distribution network are complex and changeable. When the DG penetration rate is high, the protection delay and setting coordination between the segments are still difficult. In addition, the existing improved protection scheme cannot be applied to the island operation state, and still needs to be coordinated with other protection methods to realize the protection of the distribution network containing DG.
[0004] The prior art proposes an improved overcurrent protection scheme, which requires the use of communication to transmit the parameter information of the DG to the protection device so as to adaptively adjust the overcurrent criterion. In this sense, it can be considered that the protection method is gradually transitioning from a single-ended quantity to a double-ended quantity.
[0005] Compared with the protection method based on single-end quantities, the longitudinal protection method based on electrical quantities at both ends of the line requires the addition of additional data channels, but it has more superior "four properties" of action in multi-power supply networks.
[0006] The prior art proposes a protection method based on comparison of voltage fault components. According to the ratio of the estimated value of the positive-sequence voltage fault component to the measured value, the faults inside and outside the zone are identified. The protection requirements of the active distribution network in different fault scenarios such as short circuit fault and line break fault are taken into account. The method has the advantages of not being affected by unmeasurable branches, not being affected by the penetration rate of distributed power sources, and having strong tolerance to transition resistance. However, three-phase voltage transformers are generally not installed on the feeders of the actual distribution network.
[0007] The prior art proposes a current sequence component comparison protection containing DG feeders. For asymmetric faults, a negative sequence current phase comparison protection criterion is constructed based on the phase difference of the negative sequence current on both sides of the protection area. For symmetrical faults, a positive sequence current amplitude comparison protection criterion is constructed based on the difference in the magnitude of the short-circuit current provided by the system side and the DG side. However, the protection process is relatively complicated and the influence of the T-connected branch is not considered.
[0008] The existing technology introduces the waveform similarity principle and proposes a dual / multi-terminal line differential protection method based on the dynamic time bending algorithm. The DTW algorithm is used to calculate the Euclidean distance between the current sequence sampling points at both ends of the line, but the processing of waveform amplitude normalization weakens the perception of the waveform "amplitude difference". At the same time, it relies on a large amount of simulation data testing and field operation experience to set the protection setting, which makes it difficult to select the setting and it is difficult to give full play to the advantages of waveform similarity protection.
[0009] It can be seen that there is no reliable method in the existing active distribution network protection methods that does not require the additional installation of voltage transformers, is not affected by factors such as DG penetration and unmeasurable load switching, and has low requirements for communication and data synchronization.
[0010] In view of this, an adaptive current differential protection method for active distribution networks based on time domain waveform is needed. Summary of the invention
[0011] In view of the problems existing in the prior art, the present invention provides an adaptive current differential protection method for active distribution network based on time domain waveform, which can adaptively adjust the differential protection braking coefficient based on the difference in the time domain waveform of the positive sequence current on both sides of the protection, and can effectively solve the problem of protection refusal in the time zone where the transition resistance is large and the through current is dominant. At the same time, the proposed method has the advantages of small amount of data transmission and no influence from DG weak feed. The specific technical scheme is as follows:
[0012] An active distribution network adaptive current differential protection method based on time domain waveform, comprising:
[0013] Install protection devices on each feeder of the node to collect the three-phase current of each feeder in real time;
[0014] The protection device uses the phase current mutation as the starting criterion for detecting whether a fault has occurred. When the bus phase current mutation is lower than the threshold value, the subsequent protection process begins.
[0015] Record the current sampling value when the fault occurs, and use the discrete full-cycle Fourier algorithm to calculate the three-phase current phasors;
[0016] The positive-sequence fault component of the current is calculated using the symmetrical component method, and the time-domain expression of the positive-sequence component is obtained according to the amplitude and phase of the positive-sequence component of the current;
[0017] The difference of positive sequence current waveforms on both sides of the protection under different fault conditions is explored, and the waveform difference index S is constructed by Riemann integral formula. K , calculate the differential protection factor K res , construct the current differential criterion;
[0018] The current differential criterion is used to determine whether an internal fault has occurred. If so, a trip command is sent, otherwise it is considered that no internal fault has occurred.
[0019] Preferably, the protection device uses the phase current mutation as a starting criterion for detecting whether a fault occurs, and enters a subsequent protection process when the bus phase current mutation is lower than a threshold value, specifically:
[0020] ||i(t)-i(tN)|-|i(tN)-i(t-2N)||>I set
[0021] Where i(t) represents the phase current sampling value at the tth sampling point, N is the number of sampling points in one power frequency cycle, and I set is the starting threshold value.
[0022] Preferably, the current positive sequence fault component is calculated by using the symmetrical component method, specifically:
[0023]
[0024] In the formula, represents the positive sequence fault current component, e j is the rotation factor, They are the three-phase current components respectively.
[0025] Preferably, the time domain expression of the positive sequence fault component is obtained according to the amplitude and phase of the positive sequence fault component, specifically:
[0026] The positive-sequence fault component of the current is calculated using the symmetrical component method. According to the amplitude and phase of the positive-sequence component, the time-domain expression of the positive-sequence component is obtained. Specifically, the three-phase current components are first obtained using the full-cycle Fourier algorithm, and then the current fault component is obtained using the symmetrical component method. At the same time, only two data points, amplitude and phase, need to be transmitted to the other end. The specific formula is as follows:
[0027]
[0028] Where A represents the amplitude of the positive sequence current component, Represents the phase angle of the positive sequence current component.
[0029] Preferably, the difference in the positive sequence current waveforms on both sides of the protection under different fault conditions is explored to construct a waveform difference index SK, which is specifically:
[0030] Extend the Riemann integral to the current waveform and calculate S using the Riemann integral formula L , S M , S K , using the waveform difference index S K Comprehensively measure the difference in signal amplitude and phase angle, and quantitatively describe the difference in current waveform at both ends. K It represents the waveform difference index, which comprehensively measures the difference in amplitude and phase angle of the signal. L represents the positive sequence current i at both ends of the line MN. M + (t), -i N + (t) The area of the graph enclosed in the data window, S M Indicates the positive sequence current i at both ends of line MN M + (t), -i N + (t) The area of the graph enclosed by the x-axis in the data window and S M .
[0031] Preferably, the calculation of the differential protection coefficient K res , construct the current differential criterion, specifically:
[0032] Taking the critical minimum area ratio a as the base, S K As the independent variable, a logarithmic function is introduced to amplify the difference in current waveforms at both ends.
[0033] An active distribution network adaptive current differential protection system based on time domain waveform, applied to the method, comprises a data acquisition module, a current mutation detection module, a mutation point three-phase current phasor calculation module, a time domain expression acquisition module, a peer information acquisition module, a current differential criterion construction module and an intra-area fault judgment module;
[0034] The data acquisition module is used to obtain current information on both sides of the protected line;
[0035] The sudden change detection module is used to detect the sudden change of current of the protected line;
[0036] The current mutation detection module is used to detect whether a fault occurs and make a judgment;
[0037] The three-phase current phasor calculation module at the mutation point uses a full-cycle Fourier algorithm to calculate the three-phase current components;
[0038] The time domain expression acquisition module is used to obtain the time domain expression of the positive sequence component;
[0039] The peer information acquisition module is used to send fault information to the peer and request peer information;
[0040] The current differential criterion constructing module is used to construct a current differential criterion;
[0041] The in-zone fault judgment module is used to judge whether a fault occurs within the protection zone.
[0042] A computer-readable storage medium includes a stored program, wherein when the program is executed, the device where the computer-readable storage medium is located is controlled to execute the method described.
[0043] A processor is used to run a program, wherein the method is executed when the program is run.
[0044] Compared with the prior art, the present invention has the following beneficial effects:
[0045] (1) The present invention only uses the current data at both ends, and does not require additional voltage transformers or power distribution master station equipment.
[0046] (2) The present invention constructs a waveform difference index to quantitatively describe the difference between the current waveforms at both ends, and amplifies this difference through a logarithmic function, thereby adaptively changing the differential protection braking coefficient K. res , which makes this method have higher sensitivity and tolerance to transition resistance.
[0047] (3) The present invention only needs to transmit two data points, amplitude and phase, to the other end. The amount of transmitted data is small and economical. At the same time, it improves the problems of packet loss and bit error in the traditional waveform similarity algorithm and has good anti-noise ability and engineering applicability.
[0048] (4) The present invention is not affected by synchronization errors. When an out-of-zone fault occurs, the synchronization errors on both sides of the protection are the same. When an in-zone fault occurs, as the synchronization error increases, the waveform difference also increases, and the protection tends to have a more reliable operation.
[0049] (5) The present invention is not affected by factors such as fault type, fault location and DG random output. BRIEF DESCRIPTION OF THE DRAWINGS
[0050] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.
[0051] Figure 1 The figure is the overall flow chart of the protection method.
[0052] Figure 2 This is a schematic diagram of the active distribution network topology.
[0053] Figure 3 Schematic diagram of Riemann integral.
[0054] Figure 4 Schematic diagram of the positive sequence current waveform during out-of-zone fault.
[0055] Figure 5 This is a schematic diagram of the positive sequence current waveform during a fault in the area.
[0056] Figure 6 This is a schematic diagram of the positive sequence current waveform when a high resistance fault occurs in the area.
[0057] Figure 7 Schematic diagram of the change of differential protection braking coefficient.
[0058] Figure 8 It is a distribution network model.
[0059] Fig. 9 The protection performance of each algorithm under different transition resistances is compared.
[0060] Fig.10 This is the protection action characteristic mentioned in this description.
[0061] Fig.11 This is a schematic diagram of the positive sequence current waveform during DG weak feeding. DETAILED DESCRIPTION
[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0063] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.
[0064] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.
[0065] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
[0066] Example 1
[0067] See also Figure 1-11 , an active distribution network adaptive current differential protection method based on time domain waveform, comprising:
[0068] Install protection devices on each feeder of the node to collect the three-phase current of each feeder in real time;
[0069] The protection device uses the phase current mutation as the starting criterion for detecting whether a fault has occurred. When the bus phase current mutation is lower than the threshold value, the subsequent protection process begins.
[0070] Record the current sampling value when the fault occurs, and use the discrete full-cycle Fourier algorithm to calculate the three-phase current phasors;
[0071] The positive-sequence fault component of the current is calculated using the symmetrical component method, and the time-domain expression of the positive-sequence component is obtained according to the amplitude and phase of the positive-sequence component of the current;
[0072] The difference of positive sequence current waveforms on both sides of the protection under different fault conditions is explored, and the waveform difference index S is constructed by Riemann integral formula. K , calculate the differential protection factor K res , construct the current differential criterion;
[0073] The current differential criterion is used to determine whether an internal fault has occurred. If so, a trip command is sent, otherwise it is considered that no internal fault has occurred.
[0074] As a further embodiment, the protection device uses the phase current mutation amount as a starting criterion for detecting whether a fault occurs. When the bus phase current mutation amount is lower than the threshold value, the subsequent protection process is entered, specifically:
[0075] ||i(t)-i(tN)|-|i(tN)-i(t-2N)||>I set
[0076] Where i(t) represents the phase current sampling value at the tth sampling point, N is the number of sampling points in one power frequency cycle, and I set is the starting threshold value.
[0077] As a further embodiment, the current positive sequence fault component is calculated by using the symmetrical component method, specifically:
[0078]
[0079] In the formula, represents the positive sequence fault current component, e j is the rotation factor, They are the three-phase current components respectively.
[0080] As a further embodiment, the time domain expression of the positive sequence fault component is obtained according to the amplitude and phase of the positive sequence fault component, which is specifically:
[0081] The positive-sequence fault component of the current is calculated using the symmetrical component method. According to the amplitude and phase of the positive-sequence component, the time-domain expression of the positive-sequence component is obtained. Specifically, the three-phase current component is first obtained using the full-cycle Fourier algorithm, and then the current fault component is obtained using the symmetrical component method. At the same time, only two data points, amplitude and phase, need to be transmitted to the other end; this not only greatly reduces the communication volume, but also reduces the impact of packet loss, bit error, and noise. The specific formula is as follows:
[0082]
[0083] Where A represents the amplitude of the positive sequence current component, Represents the phase angle of the positive sequence current component.
[0084] As a further embodiment, the difference of positive sequence current waveforms on both sides of the protection under different fault conditions is explored to construct a waveform difference index S K , specifically:
[0085] Extend the Riemann integral to the current waveform and calculate S using the Riemann integral formula L , S M , S K , using the waveform difference index S K Comprehensively measure the difference in signal amplitude and phase angle, and quantitatively describe the difference in current waveform at both ends. The specific principles are as follows:
[0086] The Riemann integral is defined as the area S enclosed by the non-negative function f(x) and the X-axis on a given interval (a, b). Its mathematical expression is If f(x) has a negative value, the corresponding area value S is negative. For the convenience of actual calculation, this paper adopts the infinite approximation difference form, as shown below:
[0087]
[0088] Its geometric meaning is Figure 2 As shown in the figure, when the rectangular area division is more "fine", the sum of the rectangular areas is closer to the Riemann integral S.
[0089] Extend the definition of Riemann integral to the time domain current waveform and define the positive sequence current signal at both ends of the line MN The area of the figure enclosed in the data window is S L , the sampling rate of the device is known to be f s , so the subinterval length x i+1 -x i Fixed to 1 / f s ,f(x i+1 ) is the sampling point x i+1 The corresponding positive sequence current value i at both ends + (t Mi+1 ),-i + (t Ni+1 ), so S L The mathematical definition of is as follows:
[0090]
[0091] Define the current signal at both ends The maximum area of the graph enclosed in the data window is S M , its mathematical definition is as follows:
[0092]
[0093] Where: T C is the sampling interval of the device, T is the period of the current signal at both ends, and n is the total number of sampling points in one period.
[0094] Normalize the area of the graph enclosed by the current signals at both ends and define the waveform difference index S as shown in the following formula: K , which can comprehensively measure the difference in signal amplitude and phase angle, and quantitatively describe the difference in current waveform at both ends.
[0095]
[0096] exist Figure 2 In the simple active distribution network shown in the figure, the feeder segment MN is taken as the protected segment, R M and R N They are protection devices on both sides of the protected section, f1 and f2 are respectively the fault outside the zone and the fault inside the zone, and DG is an inverter-type distributed generation (IBDG). When the system is operating normally or a three-phase short circuit occurs at the fault point f2 outside the zone, the influence of the line capacitance current can be ignored due to the short distribution network feeder. In theory, the positive sequence current on both sides is The phase difference is 180°, so and will completely overlap, S L , is close to 0 at this time, such as Figure 4 shown.
[0097] When a three-phase short circuit occurs at the fault point f1 in the area, the positive sequence current flowing through both ends of the line MN is no longer equal, and the current waveforms are significantly different. L , S K Will remain non-zero, such as Figure 5 shown.
[0098] When a non-metallic ground fault occurs in the line area, with the increase of transition resistance or the decrease of DG capacity, a through current may occur, and the positive sequence current on both sides The phase difference gradually becomes smaller. Figure 6 As shown in the figure, a two-phase ground short circuit fault with a 100Ω transition resistor is set at the fault point f1. At this time, the positive sequence current signals on both sides are Similar but not completely overlapping, S L With S K The sizes tend to 0 but are not 0.
[0099] Therefore, in order to solve the impact of through current on traditional differential protection, the critical minimum area ratio a is taken as the base and SK is taken as the independent variable. A logarithmic function is introduced to amplify the difference in current waveforms at both ends to ensure that when there is a fault outside the zone, the braking coefficient increases and the protection reliability improves; when there is a fault inside the zone, the braking coefficient decreases and the protection sensitivity improves, and it is not affected by the dominant through current when the transition resistance is large.
[0100] The calculation of differential protection coefficient K res , construct the current differential criterion, specifically:
[0101] Taking the critical minimum area ratio a as the base, S K As the independent variable, a logarithmic function is introduced to amplify the difference in current waveforms at both ends. The specific principle is as follows:
[0102] definition:
[0103] K res =log a S K
[0104] In the formula, K res is the braking coefficient of the adaptive differential protection, to ensure normal operation and out-of-zone faults (S K ≈0), K res The larger value is taken, and the critical minimum area ratio a is defined as 1×10 -5 , S K When the actual calculation result is less than or equal to a, S is takenK =a, so that K res Take 1 for both.
[0105] Figure 7 K is the differential protection braking coefficient res Waveform Difference Index S K The schematic diagram of the change shows that K res Follow S K Monotonically decreasing, when the system is operating normally or an out-of-zone fault occurs, as shown by the black point in the figure, K res Take 1. At the same time S K ≈a, the derivative of the function approaches infinity, K res The descent speed is extremely fast, S K A slight increase in K res Therefore, when a fault occurs in the system and there is a through current, as shown by the red dot in the figure, K res A smaller value can still be obtained to ensure that the protection can operate correctly. K >>a), as shown by the green dot in the figure, K res The value is close to 0.
[0106] In addition, the adaptive current differential protection criterion is:
[0107]
[0108] I dif >I res
[0109] Where: I dif is the differential current, I res is the braking current, I op is the starting threshold, take a smaller value.
[0110] by Figure 1 Taking the simple active distribution network shown as an example for analysis, when an internal fault occurs (f2), the differential protection criterion is not met; when an external fault occurs (f1), the differential protection criterion is met, and it can be considered that an internal fault occurs in the protected section.
[0111] The active distribution network model is built by electromagnetic transient simulation software PSCAD / EMTDC, and the adaptive current differential protection method for active distribution network based on time domain waveform proposed in this invention is simulated and verified:
[0112] 1) Build the model
[0113] The simulation model of active distribution network is as follows Figure 8As shown. The system voltage level is 10kV, and the neutral point is not grounded. The capacity of DG1 is 1MW, which is a PQ-controlled inverter DG with low voltage ride-through capability. The positive sequence impedance of feeder 1 is (0.17+j0.34)Ω / km, the length of feeder B1B2 is 3km, and the length of feeder B2B3 is 6km; the capacity of load L1 is 6MVA, and the fault points f1 and f2 are located at the midpoints of feeder sections B1B2 and B2B3 respectively.
[0114] 2) Simulation analysis
[0115] a) Simulation results under fault conditions inside and outside the zone
[0116] In order to verify the effectiveness of the adaptive current differential protection method for active distribution network based on time domain waveform proposed in this invention, three-phase short circuit, two-phase short circuit and two-phase ground short circuit through 1Ω and 100Ω transition resistors are set at the fault points f1 and f2 respectively. This section mainly takes the feeder segment B2B3 between R3 and R4 as the research object. The fault time is 2s. The simulation results of the proposed method are shown in Table 1.
[0117] Table 1 Simulation results when faults occur inside and outside the zone
[0118]
[0119] It can be seen from Table 1 that no matter what type of fault occurs and what the size of the transition resistance is, the braking coefficient increases when there is an out-of-zone fault, and decreases when there is an in-zone fault. The protection always ensures that there is no false operation for an out-of-zone fault and no refusal to operate for an in-zone fault.
[0120] b) Simulation results under different noise interference
[0121] There will be certain noise in the measurement current of the protection device due to electromagnetic interference. In order to study whether the proposed method is applicable when there is noise, a three-phase metallic short circuit with a fault resistance of 1Ω is set at different fault points, and Gaussian white noise with signal-to-noise ratios of 50dB, 40dB and 30dB are superimposed respectively. The simulation results are shown in Table 2.
[0122] Table 2 Simulation results when unmeasurable load is put into use
[0123]
[0124] The protection method proposed in this paper only needs to transmit two data points, amplitude and phase, to the other end. At the same time, the discrete full-cycle Fourier algorithm itself has a certain noise resistance, which reduces the impact of noise on the protection action from the source. As can be seen from Table 2, under the influence of different degrees of noise, the protection can correctly identify faults inside and outside the zone.
[0125] c) Comparative analysis with existing protection principles
[0126] When two-phase ground short circuit fault is set at fault point f2 with different transition resistances, the action performance of Pearson algorithm, DTW algorithm and positive sequence fault component differential protection algorithm are as follows: Figure 8 As shown. Among them, the Euclidean distance coefficient is a positive indicator, and the protection is activated when its value is greater than the threshold; the Pearson correlation coefficient is a negative indicator, and the protection is activated when its value is less than the threshold. The positive sequence fault component differential protection algorithm constant is set to 0.5, and the protection is activated when the braking coefficient is greater than 0.5.
[0127] Depend on Fig. 9 It can be seen that when a non-metallic grounding fault occurs in the line area, as the transition resistance increases, the amplitude and phase differences of the current waveforms on both sides are no longer obvious, the sensitivity of the traditional waveform similarity algorithm and the positive-sequence fault component differential protection algorithm is greatly reduced, and both have the risk of refusal to operate.
[0128] like Fig.10 As shown in the figure, the proposed protection can adaptively adjust the differential protection coefficient, and the action time is within 2ms. It can identify faults sensitively, reliably and quickly, which has obvious advantages over other algorithms.
[0129] d) Simulation results of DG weak feed
[0130] To verify the effectiveness of the proposed method when the load side is weakly fed, the DG at the end of feeder 1 is disconnected and a three-phase short circuit fault is set at point f2. In the non-fault section, the protection can be correctly not operated. In the fault section, the current waveform flowing through the protection on both sides is as follows: Fig.10 shown.
[0131] Depend on Fig.11 It can be seen that S L With S M Similar, waveform difference index S K Approaching 1, the differential protection braking coefficient K res When the value approaches 0, the protection can operate correctly. In principle, this method solves the problem of numerical robustness caused by the sampling value of DG side being zero, without any auxiliary judgment criteria, and has higher reliability.
[0132] The simulation results verify the effectiveness of the proposed method. Compared with the existing protection algorithm, the proposed method has the advantages of less transmitted data, strong resistance to transition resistance and less influence by through current.
[0133] Aiming at the problem of the degradation of the performance of the traditional longitudinal differential protection caused by the weak fault characteristics of the inverter-type distributed power supply and the fault-through current of the system, the present invention analyzes the difference in amplitude and phase of the positive-sequence current at both ends of the line after the fault inside and outside the area, and proposes an adaptive current differential protection method for active distribution network based on time domain waveform. The method first installs protection devices on each feeder of the node, collects the three-phase current of each feeder in real time, and uses the full-cycle Fourier algorithm to calculate the three-phase current components, and uses the symmetrical component method to calculate the positive-sequence fault component of the current; then, according to the amplitude and phase of the positive-sequence component, the time-domain expression of the positive-sequence component is obtained, and the S is calculated by the Riemann integral formula. L、 S M、 S K , and further calculate the differential protection coefficient K res ; Finally, if the differential protection criterion is met, it is considered that an in-zone fault has occurred and a trip command is sent. The PSCAD simulation results show that when various faults occur in the active distribution network, the protection method proposed in the present invention can reliably identify the fault section. Compared with the traditional differential protection and waveform similarity algorithm, the protection proposed in the present invention has the advantages of less transmission data, strong resistance to transition resistance, and no influence from DG weak feed, and the sensitivity and speed of the protection are greatly improved.
[0134] Example 2
[0135] An active distribution network adaptive current differential protection system based on time domain waveform, applied to the method, comprises a data acquisition module, a current mutation detection module, a mutation point three-phase current phasor calculation module, a time domain expression acquisition module, a peer information acquisition module, a current differential criterion construction module and an intra-area fault judgment module;
[0136] The data acquisition module is used to obtain current information on both sides of the protected line;
[0137] The sudden change detection module is used to detect the sudden change of current of the protected line;
[0138] The current mutation detection module is used to detect whether a fault occurs and make a judgment;
[0139] The three-phase current phasor calculation module at the mutation point uses a full-cycle Fourier algorithm to calculate the three-phase current components;
[0140] The time domain expression acquisition module is used to obtain the time domain expression of the positive sequence component;
[0141] The peer information acquisition module is used to send fault information to the peer and request peer information;
[0142] The current differential criterion constructing module is used to construct a current differential criterion;
[0143] The in-zone fault judgment module is used to judge whether a fault occurs within the protection zone.
[0144] Example 3
[0145] A computer-readable storage medium includes a stored program, wherein when the program is executed, the device where the computer-readable storage medium is located is controlled to execute the method described.
[0146] Example 4
[0147] A processor is used to run a program, wherein the method is executed when the program is run.
[0148] Those of ordinary skill in the art will appreciate that the units of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition of each example has been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.
[0149] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical function division, and there may be other division methods in actual implementation, for example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.
[0150] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.
[0151] 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 this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-0nlyMemory), random access memory (RAM, RandomAccessMemory), mobile hard disk, magnetic disk or optical disk, etc., which can store program code.
[0152] Finally, it should be noted that 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.
Claims
1. An adaptive current differential protection method for active distribution network based on time domain waveform, characterized in that: include: Install protection devices on each feeder of the node to collect the three-phase current of each feeder in real time; The protection device uses the phase current mutation as the starting criterion for detecting whether a fault has occurred. When the bus phase current mutation is lower than the threshold value, the subsequent protection process begins. Record the current sampling value when the fault occurs, and use the discrete full-cycle Fourier algorithm to calculate the three-phase current phasors; The positive-sequence fault component of the current is calculated using the symmetrical component method, and the time-domain expression of the positive-sequence component is obtained according to the amplitude and phase of the positive-sequence component of the current; The difference of positive sequence current waveforms on both sides of the protection under different fault conditions is explored, and the waveform difference index S is constructed by Riemann integral formula. K , calculate the differential protection factor K res , construct the current differential criterion; The current differential criterion is used to determine whether an internal fault has occurred. If so, a trip command is sent, otherwise it is considered that no internal fault has occurred.
2. The method for adaptive current differential protection of active distribution network based on time domain waveform according to claim 1 is characterized in that: The protection device uses the phase current mutation as the starting criterion for detecting whether a fault has occurred. When the bus phase current mutation is lower than the threshold value, the subsequent protection process is entered, specifically: ||i(t)-i(t-N)|-|i(t-N)-i(t-2N)||>I set Where i(t) represents the phase current sampling value at the tth sampling point, N is the number of sampling points in one power frequency cycle, and I set is the starting threshold value.
3. The method for adaptive current differential protection of active distribution network based on time domain waveform according to claim 2 is characterized in that: The current positive sequence fault component is calculated by using the symmetrical component method, specifically: In the formula, represents the positive sequence fault current component, e j is the rotation factor, They are the three-phase current components respectively.
4. The method for adaptive current differential protection of active distribution network based on time domain waveform according to claim 3 is characterized in that: The time domain expression of the positive sequence fault component is obtained according to the amplitude and phase of the positive sequence fault component, which is specifically: The positive-sequence fault component of the current is calculated using the symmetrical component method. According to the amplitude and phase of the positive-sequence component, the time-domain expression of the positive-sequence component is obtained. Specifically, the three-phase current components are first obtained using the full-cycle Fourier algorithm, and then the current fault component is obtained using the symmetrical component method. At the same time, only two data points, amplitude and phase, need to be transmitted to the other end. The specific formula is as follows: Where A represents the amplitude of the positive sequence current component, Represents the phase angle of the positive sequence current component.
5. The method for adaptive current differential protection of active distribution network based on time domain waveform according to claim 4 is characterized in that: The differences in the positive sequence current waveforms on both sides of the protection under different fault conditions are explored, and the waveform difference index SK is constructed, which is: The Riemann integral is extended to the current waveform, and SL, SM, and SK are calculated using the Riemann integral formula. The waveform difference index SK is used to comprehensively measure the difference in amplitude and phase angle of the signal, and quantitatively describe the difference in current waveforms at both ends. K It represents the waveform difference index, which comprehensively measures the difference in amplitude and phase angle of the signal. L represents the positive sequence current i at both ends of the line MN. M + (t), -i N + (t) The area of the graph enclosed in the data window, S M Indicates the positive sequence current i at both ends of line MN M + (t), -i N + (t) The area of the graph enclosed by the x-axis in the data window and S M .
6. The method for adaptive current differential protection of active distribution network based on time domain waveform according to claim 5, characterized in that: The calculation of differential protection coefficient K res , construct the current differential criterion, specifically: Taking the critical minimum area ratio a as the base, S K As the independent variable, a logarithmic function is introduced to amplify the difference in current waveforms at both ends.
7. An active distribution network adaptive current differential protection system based on time domain waveform, characterized in that: The method applied to any one of claims 1 to 6 comprises a data acquisition module, a current mutation detection module, a mutation point three-phase current phasor calculation module, a time domain expression acquisition module, a peer information acquisition module, a current differential criterion construction module and an intra-area fault judgment module; The data acquisition module is used to obtain current information on both sides of the protected line; The sudden change detection module is used to detect the sudden change of current of the protected line; The current mutation detection module is used to detect whether a fault occurs and make a judgment; The three-phase current phasor calculation module at the mutation point uses a full-cycle Fourier algorithm to calculate the three-phase current components; The time domain expression acquisition module is used to obtain the time domain expression of the positive sequence component; The peer information acquisition module is used to send fault information to the peer and request peer information; The current differential criterion constructing module is used to construct a current differential criterion; The in-zone fault judgment module is used to judge whether a fault occurs within the protection zone.
8. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein: When the program is running, the device where the computer-readable storage medium is located is controlled to execute the method according to any one of claims 1 to 6.
9. A processor, characterized in that: The processor is used to run a program, wherein the program executes the method according to any one of claims 1 to 6 when running.