A multi-energy power distribution network laboratory protection method

Abstract

The application discloses a kind of multi-energy distribution network laboratory protection methods, it includes: collecting multi-energy distribution network laboratory line connection node current information;Current average value in cycle is calculated, and the current average value is used to calculate the relative extremum of branch two end node current, to calculate branch polarity coefficient, fault coefficient and judge whether fault occurs.No need to accurately measure the accurate value of fault line at line two ends, only the trend of current change and relative numerical relationship, the measurement accuracy of measurement terminal is lower, it is easy to realize, and fault tolerance is higher;Secondly, the method is not only suitable for small resistance grounding fault, but also suitable for broken wire and other high resistance grounding fault;Finally, the method uses time domain data, and does not use frequency domain conversion method, and the calculation rate is high.

Description

Technical Field

[0001] This invention relates to the technical field of multi-energy distribution networks, and more particularly to a laboratory protection method for multi-energy distribution networks. Background Technology

[0002] With the proposal of carbon peaking and carbon neutrality goals, renewable energy has been vigorously developed, and its access and application on the distribution network side are becoming increasingly widespread. The distribution network is gradually transforming from a passive power receiving and distribution network to a multi-energy distribution network, connecting distributed power sources such as photovoltaics, energy storage, and wind power, and actively regulating power. Compared with traditional distribution networks, multi-energy distribution networks have significant differences in steady-state power flow distribution and short-circuit current during faults. In order to study the operating status of multi-energy distribution networks, multi-energy distribution network laboratories have been built in various places to analyze the steady-state and transient characteristics of distribution networks. When a short-circuit fault occurs in the multi-energy distribution network laboratory, it is necessary to quickly clear the fault and protect the operators. However, the level and distribution of short-circuit current are different, which seriously restricts the speed, selectivity, and sensitivity of conventional three-stage current protection.

[0003] Traditional overcurrent protection is limited by the small fault current of the unit, which makes it impossible for the overcurrent relay protection settings to operate effectively. Due to the inherent current-draining characteristics of distributed power sources, directional protection cannot operate effectively when a fault occurs in the downstream line of the distribution network. In addition, differential protection schemes are used, which utilize the direction of the two-phase current at both ends of the line and then compare them to detect internal faults within the protected area.

[0004] Existing protection methods (i.e., frequency domain information-based protection methods) require accurate measurement of the fault line at both ends of the line, which places high demands on the measurement accuracy and acquisition frequency of the measurement terminal, resulting in high costs. Moreover, they are only applicable to low-resistance grounding faults and cannot operate when simulating faults such as open circuits. Existing protection methods (i.e., frequency domain information-based protection methods) extract the required features from the fault current signal through S-transform and Hilbert-Huang transform, which requires high computational resources and cannot meet the protection action time requirements. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the laboratory protection methods for multi-energy distribution networks, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to provide a laboratory protection method for multi-energy distribution networks.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: collecting current information of line connection nodes; Calculate the average current within the cycle, and calculate the relative polarity information of the current at both ends of the branch based on the average current. Then, calculate the branch polarity coefficient, fault coefficient, and determine whether a fault has occurred.

[0009] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, a current acquisition device is arranged at the line connection node of the multi-energy distribution network laboratory, with frequency... f Collect current information; The connection nodes include distributed power connection points, feeder branch nodes, switch nodes, and load nodes.

[0010] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, wherein: the frequency f The current information of the connection nodes of the multi-energy distribution network laboratory line was collected as follows: ; in, t Indicates the number of signal collection points. p Indicates the node number. j The phase represents the information of the nodes at both ends of the line. , s and r Indicates the node numbers at both ends of the branch.

[0011] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, the formula for calculating the average current value within the cycle is: , in, , This represents the mean of the sampled cycles. n This represents a sampling cycle number. n You can choose flexibly based on your computing resources. n Take 100 points.

[0012] As a preferred embodiment of the laboratory protection method for multi-energy distribution networks described in this invention, wherein: the calculation branch s-r Information on the two ends of the node and the relative polarity of the current and ; in, Indicates the polarity of the current at the beginning of the line. This indicates the polarity of the current at the end of the line.

[0013] In a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, the relative polarity information of the node information current is calculated as follows: like ,but =1, =1; like ,but =0, =0; like ,but =-1, =-1; like ,but =1, =-1; like ,but =-1, =1; in, Fault current polarity determination threshold.

[0014] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, the sampling cycles are counted to determine whether they are greater than the set number of cycles.

[0015] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, wherein: the branch is calculated s-r polarity coefficient pc ( s , r The calculation formula is as follows: Where Q represents the number of cycles in the signal acquisition, d Indicates the signal cycle number. Indicates the first d The polarity of the current at the beginning of the line for each signal acquisition cycle. Indicates the first d The polarity of the line end current for each signal acquisition cycle.

[0016] As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, wherein: the branch is calculated s-r Failure coefficient fx The calculation formula is as follows: As a preferred embodiment of the multi-energy distribution network laboratory protection method of the present invention, wherein: judgment Failure coefficient fx The size, if This indicates a malfunction; otherwise, it indicates normal operation. in, This indicates the fault threshold.

[0017] The beneficial effects of this invention are: firstly, it does not require accurate measurement of the faulty line at both ends of the line; only the trend of current change and relative numerical relationship are needed. Secondly, the measurement accuracy requirements of the measurement terminal are low, making it easy to implement and with a high fault tolerance rate. Thirdly, the method is applicable not only to low-resistance grounding faults but also to high-resistance grounding faults such as open circuits. Finally, this method uses time-domain data and does not use frequency-domain conversion methods, resulting in high calculation speed. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Fig. 1 This is a schematic diagram of the overall structure of the multi-energy distribution network laboratory protection method of the present invention.

[0019] Fig. 2 This is a circuit diagram for a power distribution network laboratory.

[0020] Fig. 3 This is a circuit diagram for a power distribution network laboratory. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0025] Example 1 Reference Fig. 1 , Fig. 1 The flowchart of this method is shown below. A laboratory protection method for multi-energy distribution networks includes: S1: Collect connection point current information. Deploy current acquisition devices at the connection nodes of the multi-energy distribution network laboratory lines, using frequency... f Collect current information. It should be noted that: Connection nodes include distributed power connection points, feeder branch nodes, switch nodes, and load nodes; frequency f Collect current information of connection nodes of multi-energy distribution network laboratory lines. .

[0026] in, t Indicates the number of signal collection points. p Indicates the node number. j Indicates phase, including a,b,c The three phases are used to determine which phase is faulty. When phase a is faulty, the current parameters of phase a will change abnormally, forming the node information at both ends of the line. , s and r Indicates the node numbers at both ends of the branch.

[0027] When the laboratory is started up, node data is collected to determine whether there are any faults in each link. During the laboratory's practical application, data can be collected in real time according to the fault frequency to determine whether a fault has occurred.

[0028] S2: Select the sampling cycle number, typically Q is 3-5, and calculate the average current information within that cycle. It should be noted that: The more cycles there are, the higher the accuracy of the judgment, but the more computing resources are required and the longer the calculation time. Therefore, considering accuracy, time and resources, 3 to 5 cycles are selected, and the sampling cycles of voltage and current signals are chosen.

[0029] The formula for calculating the average current within a cycle is: , in, , This represents the mean of the sampled cycles. n This represents a sampling cycle number.n The selection can be flexibly chosen based on computing resources, generally n Take 100 points.

[0030] Generally, we cannot collect voltage and current data from just one point; we need to collect a range of data to facilitate judgment. The voltage and current are at 50Hz, and one cycle is 0.2 seconds. For ease of analysis, we sample the current information within a 0.2s duration, calculate the average value within 0.2s, and then determine the polarity.

[0031] S3: Calculate branch s-r Information on the two ends of the node and the relative polarity of the current and It should be noted that: The relative polarity information of the node current is calculated as follows: like ,but =1, =1; like ,but =0, =0; like ,but =-1, =-1; like ,but =1, =-1; like ,but =-1, =1; in, Indicates the polarity of the current at the beginning of the line. Indicates the polarity of the current at the end of the line. Fault current polarity determination threshold.

[0032] S4: Determine if the cycle number requirement is met. It should be noted that: The number of cycles is the selected cycle in S2. The sampled cycles are counted to determine if they are greater than the set number of cycles. If they are, proceed to the next step. If they are not, repeat S1~S3.

[0033] S5: Calculate branches s-r polarity coefficient pc ( s , r It should be noted that: The calculation formula is as follows: Where Q represents the number of cycles in the signal acquisition, d Indicates the signal cycle number. Indicates the first d The polarity of the current at the beginning of the line for each signal acquisition cycle. Indicates the first d The polarity of the line end current for each signal acquisition cycle.

[0034] S6: Calculate the branch s-r Failure coefficient fx It should be noted that: The calculation formula is as follows: S7: Determine the fault factor fx The size. It should be noted that: like If the signal is positive, it indicates a fault has occurred, triggering a fault warning and isolating the fault; otherwise, it indicates normal operation.

[0035] in, This indicates the fault threshold.

[0036] Example 2 Reference Fig. 2 This embodiment is the second embodiment of the present invention. Unlike the first embodiment, this embodiment provides a verification test of a laboratory protection method for multi-energy distribution networks, and verifies and explains the technical effects used in this method.

[0037] This example will compare and test this method with the frequency domain information-based protection method based on a laboratory circuit of a multi-energy distribution network.

[0038] The frequency domain information protection method uses a zero-sequence current sensor to collect circuit node data. a,b,c Three-phase zero-sequence current is used to extract odd harmonic information through Fourier transform. Considering the information extraction time, odd harmonic current information of the 3rd to 15th orders is generally extracted to obtain the amplitude of the odd harmonic current. The amplitude of the 3rd harmonic current is... Calculate the amplitudes of the 5th to 15th order odd harmonic currents and his Then calculate the amplitude of the third harmonic current and his ratio ， If the ratio is greater than the judgment threshold, a fault is considered to have occurred. The threshold is generally set to 0.2.

[0039] Frequency-domain information-based protection methods rely on odd-order harmonic information. Accurate extraction of odd-order harmonic information requires precise measurement of the zero-sequence current, which places high demands on the measurement accuracy and acquisition frequency of the measurement terminal. If the accurate value of the zero-sequence current cannot be obtained, the odd-order harmonic information will be inaccurate, leading to a deviation in the ratio. Calculation errors can lead to misjudgments or missed judgments, reducing the success rate of identification.

[0040] likeFig. 2 As shown, the laboratory circuit includes three power distribution lines: a cable line, an overhead line, and a cable-overhead hybrid line. The positive sequence resistance, inductance, and capacitance of the overhead line are 0.17 ohms. Ω / km 1.20 mH / km And 0.0097 µF / km The negative sequence resistance, inductance, and capacitance are 0.23. Ω / km 5.48 mH / km And 0.006 µF / km The positive sequence resistance, inductance, and capacitance of the cable line are 0.27 Ω. Ω / km The values ​​are 0.255 mH / km and 0.339 µF / km, respectively; the negative sequence resistance, inductance, and capacitance are 2.7 Ω / km, 1.019 µF / km, and 0.255 mH / km and 0.339 µF / km, respectively. mH / km and 0.28 µF / km Both methods are based on a frequency of 1. kHz This method collects current information from connection nodes in a multi-energy distribution network laboratory, and simulates 50 single-phase low-resistance grounding faults between arbitrary nodes. The fault is determined by directly calculating the current polarity. Calculate the average recognition time and discrimination success rate of this method and the comparison method.

[0041] Table 1.1 kHz Sampling rate comparison results

[0042] Under the same conditions, using frequency 5 kHz acquisition current information, Calculate the average recognition time and discrimination success rate of this method and the comparison method.

[0043] Table 2.5 kHz Sampling rate comparison results

[0044] As can be seen from the comparison of the success rates in Tables 1 and 2, the comparison method requires high signal measurement accuracy. When the frequency of the measurement signal acquisition is reduced (1... kHz The previous comparison method, unable to obtain precise judgment values, led to misjudgments and reduced accuracy. This method uses current polarity for determination, requiring no knowledge of the specific value of the current signal, and achieves a 100% success rate at both sampling rates.

[0045] As can be seen from the comparison of the average time in Tables 1 and 2, the comparison method requires Fourier transform to extract frequency information, resulting in a long calculation time. This method uses current polarity for determination and does not use frequency domain conversion method, resulting in a high calculation speed.

[0046] like Fig. 3As shown, a high-resistance grounding fault is set up by connecting the line to the ground and grass between nodes 7 and 8. This method still uses the above method to determine the fault based on the polarity of the current, and can still accurately determine the fault. The comparison method requires a precise fault current value. Under the condition of high resistance fault, the fault current value is small, which is one-thousandth of that of low resistance fault, and it is in a fluctuating state. Due to the measurement accuracy limit of the acquisition terminal, the traditional method cannot identify weak fault current or has measurement errors, resulting in insufficient fault current value information, failure to determine high resistance fault or low success rate.

[0047] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A laboratory protection method for multi-energy distribution networks, characterized in that: include, Step 1: Collect current information at line connection nodes; Step 2: Select the sampling cycle number and calculate the average current within the cycle; Step 3: Calculate the relative polarity information of the current at both ends of the branch based on the average current value; In step one, the connection nodes include distributed power connection points, feeder branch nodes, switch nodes, and load nodes; Connection node current information is ,in, t Indicates the number of signal collection points. p Indicates the node number. j Indicates phase; The node information at both ends of the line is , s and r Indicates the node numbers at both ends of the branch; In step two, the average current within this cycle is calculated. The formula for calculating the average current within this cycle is: ， in, , This represents the mean of the sampled cycles. n This represents the number of sampling cycles. In step three, calculate the branches. s-r Information on the two ends of the node and the relative polarity of the current and ; The relative polarity information of the node current is calculated as follows: like ,but =1, =1; like ,but =0, =0; like ,but =-1, =-1; like ,but =1, =-1; like ,but =-1, =1; in, Indicates the polarity of the current at the beginning of the line. Indicates the polarity of the current at the end of the line. Fault current polarity determination threshold; Step 4: Count the sampling cycles and determine if it is greater than the set number of cycles. If it is, proceed to the next step; otherwise, repeat steps 1 to 3. Step 5: Calculate the branch s-r polarity coefficient PC ( s , r The calculation formula is as follows: Where Q represents the number of cycles in the signal acquisition, d Indicates the signal cycle number. Indicates the first d The polarity of the current at the beginning of the line for each signal acquisition cycle. Indicates the first d The polarity of the line end current of each signal acquisition cycle; Step 6: Calculate the branch s-r Failure coefficient fx The calculation formula is as follows: Step 7: Determine the fault coefficient fx Size; like If the fault is cleared, it indicates a malfunction and the fault should be isolated; otherwise, it indicates normal operation. in, This indicates the fault threshold.

2. The laboratory protection method for multi-energy distribution networks as described in claim 1, characterized in that: Current acquisition devices are installed at the line connection nodes of the multi-energy distribution network laboratory, at a frequency... f Collect current information.

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