Relay protection method for single-loop distribution network with distributed power supply based on 5G communication

Abstract

The application provides a single-loop power distribution network relay protection method containing a distributed power supply based on 5G communication. When the abrupt variable starting element of the line local differential protection starts, data transmission requests are sent to the opposite side through the 5G communication network, and four shape similar distance values of the two-side current data in one cycle are calculated. If all the four values are higher than the floating threshold, it is determined that the ring network trunk line is faulty, the local protection outlet is tripped and a trip signal is sent to the opposite device. If not, it is determined that the fault is outside the area, and the protection does not act. Based on the single-loop power distribution network protection method, the shortcomings of the traditional three-section current protection as the main protection of the ring network trunk line, such as the difficulty in setting cooperation, can be effectively made up, and the defects of the traditional current protection as the bus backup protection, such as the insufficient sensitivity, can be improved, so that the single-loop power distribution network relay protection method has good practical application value.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection, specifically relating to a main protection method for a single-ring distribution network containing distributed power sources based on 5G communication technology. Background Technology

[0002] To address global climate change and achieve carbon neutrality, large-scale grid integration of renewable energy is an indispensable part of achieving emission reduction targets. With the continuous development of new energy technologies, their penetration rate in power systems is increasing, and the power supply model is gradually shifting from large-scale centralized power supply to a combination of centralized and distributed power supply. However, after distributed renewable energy is integrated into the grid, the original single-source network becomes a multi-source network, making the grid structure increasingly complex and affecting the power flow direction of the power system. Simultaneously, because the output of renewable energy gradually changes with environmental conditions, it may contribute to or divert fault currents during power system faults, adversely affecting the reliability, sensitivity, selectivity, and speed of relay protection. For single-source ring networks, traditional three-stage current protection inherently suffers from setting difficulties; the integration of renewable energy makes the coordination of protection settings a critical issue.

[0003] Differential protection, as the main protection, can protect the entire length of the line, requiring neither time coordination nor setting coordination. Using it as the main protection in distribution networks is a solution to the shortcomings of traditional three-stage protection. However, communication is one of the necessary conditions for the correct operation of line differential protection. Traditional differential protection requires laying optical fibers at both ends of the line as a fast information transmission channel, but the cost of laying optical cables over a large area in distribution systems is too high, making it difficult to widely promote in distribution networks. Traditional wireless transmission modes suffer from excessive time delay and low reliability, making it difficult to meet the speed requirements of differential protection.

[0004] 5G communication technology boasts advantages such as low latency, low power consumption, and high reliability. The large-scale deployment of 5G base stations provides favorable conditions for implementing differential protection in distribution networks based on 5G communication. However, similar to other wireless communication methods, the current sampling sequence transmitted via 5G communication is also susceptible to latency jitter and data packet loss, leading to current waveform distortion. Furthermore, the sampling times on both sides may be inconsistent. These issues negatively impact differential protection criteria directly based on Kirchhoff's current law. Therefore, further research is needed on data processing algorithms for differential protection to eliminate the adverse effects of communication latency jitter and data packet loss. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the defects of the existing three-stage current protection and provide a relay protection method for a single-ring distribution network with distributed power sources based on 5G communication, which solves the problems of difficulty in setting and coordinating the three-stage current protection of the single-ring network after the grid connection of new energy and the problem of fast operation of the main protection of the distribution line.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a relay protection method for a single-ring distribution network with distributed power sources based on 5G communication, comprising the following steps:

[0007] The protection device calculates the current surge of each line in real time;

[0008] If the sudden change in current exceeds the starting setting value, the line differential protection and bus differential protection will be activated.

[0009] The line differential protection determines whether the current fault is a fault within the line area; if it determines that a fault within the line area has occurred, the protection output on this side trips the circuit breaker on this side and simultaneously sends a trip signal to the line protection device on the opposite side to disconnect the faulty line.

[0010] The bus differential protection determines whether the current fault is a fault within the bus zone; if it is determined to be a fault within the bus zone, the protection device sends a trip command to trip the circuit breakers of the incoming and outgoing lines on the bus.

[0011] After the differential protection of the line issues a trip command, it continuously monitors the current sampling values ​​on both sides of the line and starts a timer. If the current sampling value on this side fails to reach the specified value within t... set The current drops to 0 within a time period, while the sampled current value on the opposite side is at t. set If the value drops to 0 within a certain time, the adjacent circuit breaker will trip.

[0012] After the bus differential protection issues a trip command, it immediately checks the current sampling values ​​of all incoming and outgoing lines of the bus and starts a timer. If the current sampling value of any line fails to reach the specified time, the timer will continue to operate. set If the value drops to 0 within a certain time, the circuit breaker on the opposite side of the line will trip, thus isolating the fault.

[0013] Furthermore, the formula for calculating the current surge is as follows:

[0014]

[0015] Where, Δi k This refers to the sudden change in current, i k Let N be the k-th current sample value, and N be the number of sampling points per 50Hz power frequency cycle. For the first One current sample value, i k-N This is the (kN)th current sample value;

[0016] The starting setting value ranges from 0.1 to 0.2 times the rated current value.

[0017] Furthermore, the line differential protection adopts a principle based on morphological similarity distance, specifically including:

[0018] The local protection device sends a message to the remote protection device, requesting the remote device to transmit the remote current information to the local device in real time via the 5G communication network; the remote current information includes: the current sampling value collected by the remote device and the corresponding sampling time data;

[0019] After receiving the current information from the other side, this side determines whether there is any missing data. If so, it uses interpolation to correct and fill in the missing data to ensure that the number of data points per cycle is N.

[0020] The data window length is set to one power frequency sampling period. Each wave data window is divided into four smaller data windows. The current sampling value and sampling time data in each smaller data window are standardized.

[0021] Based on the standardized data, calculate the morphological similarity distance values ​​d1, d2, d3 and d4 of the waveforms on both sides within each small data window;

[0022] The calculated waveform morphology similarity distance is compared with the similarity distance threshold. When all four distance values ​​are greater than the similarity distance threshold, it is determined that the fault is within the main line area. The protection on this side sends a trip signal to the protection on the other side. After receiving the signal, the protection on the other side will take action without delay. Conversely, if at least one of the morphology similarity distance values ​​in the four small data windows does not exceed the similarity distance threshold, the protection on this side will not trip and will not send a trip command to the protection device on the other side of the line.

[0023] Furthermore, the method of using interpolation to correct and fill in missing data specifically includes:

[0024] The protection device acquires the k-th sampled value of the opposite side current information through the 5G communication network; if the sampled value arrives at the protection device, it is stored in the sampled value buffer; if the sampled value does not arrive, it waits for a short time interval t. wait , t wait If the sampled value is still not reached, then the information i of the unreachable sampled value is calculated using interpolation. k There are two possible scenarios:

[0025] a. The next sample value has not yet arrived: i k =2i k-1 -i k-2 ;

[0026] btk+1 The sampled value arrives at time i k =(i k-1 +i k+1 ) / 2.

[0027] Furthermore, the standardization process for the current sample values ​​and sampling time data within each small data window is as follows:

[0028] The maximum and minimum values ​​of the local current sampled value and the sampling time data in each small data window are respectively denoted as i. max.p and i min.p Where p = 1, 2, 3, 4, representing the p-th data point out of four data points; the maximum and minimum time values ​​in each small data window are denoted as t. max.p and t min.p The standardized current sample value and sampling time are as follows:

[0029]

[0030]

[0031] Furthermore, after standardization, the time and current sampling values ​​for the local and opposite sides of the line within each small data window are I... 1.p {(t′ 1.(p-1)N / 4 ,i′ 1.(p-1)N / 4 ),···,(t′ 1.j ,i′ 1.j ),···,(t′ 1.pN / 4 ,i′ 1.pN / 4 )} and I 2.p {(t′ 2.(p-1)N / 4 ,i′ 2.(p-1)N / 4 ),···,(t′ 2.j ,i′ 2.j ),···,(t′ 2.pN / 4 ,i′ 2.pN / 4 )}, where t′ 1.j This is the j-th value of the time sampled values ​​after per-unit processing on this side of the line; i′ 1.j The j-th value of the current sample after per-unit processing on this side of the line; t′ 2.j The j-th value of the time sampled value after the line side has been per-unitized; i′ 2.j is the j-th value of the current sampled value after per-unit processing on the opposite side of the line; p = 1, 2, 3, 4, representing the p-th data in the four data sets; N is the number of sampling points in each 50Hz power frequency cycle.

[0032] Furthermore, the calculation of the morphological similarity distance value between the waveforms on both sides within each small data window based on the standardized data specifically includes:

[0033] The morphological similarity distance between the two sequences is:

[0034] d p =D ep ×(2-ASD p / SAD p Equation (4)

[0035] Where, d p D represents the morphological similarity distance. ep Let ASD be the Euclidean distance between two waveforms in the p-th small data window. p SAD represents the Manhattan distance between two waveforms in the p-th small data window. p It is the absolute value of the sum of the differences between the two waveform data in the p-th small data window.

[0036] Furthermore, in formula (4)

[0037]

[0038]

[0039]

[0040] get:

[0041]

[0042] Furthermore, the similarity distance threshold adopts a floating threshold, and the calculation formula for the floating threshold within each small data window is as follows:

[0043]

[0044] Furthermore, the step of "if at least one of the similarity distance values ​​in the four small data windows does not exceed the similarity distance threshold, then the local protection will not trip and will not send a trip command to the protection device on the other side of the line" further includes: continuously sliding the data window and continuously detecting for two power frequency cycles; if all four distance values ​​are detected to be greater than the similarity distance threshold within the two power frequency cycles, then the local protection will trip and send a trip signal to the protection on the other side; otherwise, the protection will not send a trip signal but will send a signal to the other side and stop real-time data transmission.

[0045] Furthermore, the bus differential protection determines whether the current fault is a fault within the bus zone, specifically including:

[0046] After the bus differential protection is activated, the sum of the current sampling values ​​of all incoming and outgoing lines of the bus is calculated;

[0047] The sum of the current sampled values ​​is compared with the braking threshold value of the bus differential protection; if the sum of the current sampled values ​​is greater than the braking threshold value, it is judged as a bus fault; otherwise, it is judged as an external fault, and the protection does not operate.

[0048] Furthermore, the bus differential protection determines whether the current fault is a fault within the bus zone, specifically including:

[0049] After the bus differential protection is activated, the sum of the current sampling values ​​of all incoming and outgoing lines of the bus is calculated;

[0050] The sum of the current sampled values ​​is compared with the braking threshold value of the bus differential protection. If the sum of the current sampled values ​​is greater than the braking threshold value, it is determined to be a bus fault. Otherwise, the data window is continuously slid to continuously detect for two power frequency cycles. If the sum of the current sampled values ​​is detected to be greater than the braking threshold value within two power frequency cycles, it is determined to be a bus fault and the bus differential protection operates. Otherwise, it is determined to be an external fault and the protection does not operate.

[0051] Furthermore, after the line differential protection or bus differential protection issues a trip command, if the circuit breaker fails to operate, a trip signal is sent through the station communication or 5G network to trip other circuit breakers on the opposite side of the line connected to the circuit breaker that failed to operate or on the connected bus, thus completing the fault isolation.

[0052] Compared with the prior art, the beneficial effects of the present invention are: the technical solution of the present invention is based on 5G communication technology, realizes the real-time transmission of power data on both sides of the power distribution line, and can trip adjacent circuit breakers without relying on power information in the event of bus protection failure, thereby achieving fault isolation. It not only solves the problem of difficult coordination of single-ring three-stage current protection settings after new energy grid connection, but also realizes the full-line fast operation of the main protection of the power distribution line. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of a relay protection method for a single-ring distribution network with distributed power sources based on 5G communication technology, according to an embodiment of the invention.

[0054] Figure 2 This is a simulation model diagram of a single-ring distribution network according to an embodiment of the present invention;

[0055] Figure 3 This is a logic diagram of the single-ring distribution network protection system of the present invention;

[0056] Figure 4 This is the tripping signal of each circuit breaker in the case of a fault in the L1 area of ​​line 1 according to the present invention;

[0057] Figure 5 This is the tripping signal of each circuit breaker in the case of a fault in busbar B2 area of ​​Example 2 according to the present invention;

[0058] Figure 6 This invention provides the tripping signals of each circuit breaker in the case of a fault in the L1 area of ​​line 1 but circuit breaker 3 refusing to operate.

[0059] Figure 7 This is the tripping signal of each circuit breaker in the case of a fault in the busbar B2 area of ​​Example 1, but the circuit breaker 3 fails to operate. Detailed Implementation

[0060] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0061] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0062] The main network of a single-ring distribution network can be divided into two parts according to function: the trunk line and the busbar. The current acquisition devices for the busbar differential protection are located in the same substation, and fault identification can be achieved without data transmission; therefore, the traditional busbar differential protection method is used. The protection devices at both ends of the trunk line are located in different substations. The implementation of its differential protection requires the transmission of electrical sampling information via 5G communication technology; therefore, this line adopts differential protection based on the principle of morphological similarity as the main protection.

[0063] Figure 1 The diagram illustrates a relay protection method for a single-ring distribution network with distributed power sources based on 5G communication technology according to an embodiment of the present invention, comprising the following steps:

[0064] S100: The protection device calculates the current surge of each line in real time;

[0065] S200: If the current surge exceeds the start-up setting value, then the line differential protection and bus differential protection will be started.

[0066] S300: The line differential protection determines whether the current fault is a fault within the line area; if it determines that a fault within the line area has occurred, the protection output on this side trips the circuit breaker on this side and simultaneously sends a trip signal to the line protection device on the opposite side to disconnect the faulty line.

[0067] S400: The bus differential protection determines whether the current fault is a fault within the bus zone; if it is determined that the current fault is within the bus zone, the protection device sends a trip command to trip the circuit breakers of the incoming and outgoing lines on the bus.

[0068] S500: After the line differential protection issues a trip command, it continuously monitors the current sampling values ​​on both sides of the line and starts a timer. If the current sampling value on this side fails to reach the specified value within t... set The current drops to 0 within a time period, while the sampled current value on the opposite side is at t. setIf the value drops to 0 within a certain time, the adjacent circuit breaker will trip.

[0069] S600: After the bus differential protection issues a trip command, it immediately checks the current sampling values ​​of all incoming and outgoing lines of the bus and starts a timer. If the current sampling value of any line fails to reach the specified value within t... set If the value drops to 0 within a certain time, the circuit breaker on the opposite side of the line will trip, thus isolating the fault.

[0070] Among them, the setting time t set The calculation method is as follows:

[0071] t set =t act +t t +Δt (8)

[0072] Among them, t act The time from when the protection device issues a trip command to when the circuit breaker tripping mechanism starts; t t The tripping time is the inherent tripping time of the circuit breaker, and Δt is the time range, which is taken as 0.2s to 0.5s.

[0073] In a preferred embodiment, after the line differential protection or bus differential protection issues a trip command, if the circuit breaker fails to operate, a trip signal is sent through the station communication or 5G network to trip other circuit breakers on the opposite side of the line connected to the circuit breaker that failed to operate or on the connected bus, thereby completing fault isolation.

[0074] The above scheme can effectively make up for the shortcomings of the traditional three-stage current protection when used as the main protection of the ring network trunk line, which is difficult to coordinate. At the same time, it can also improve the shortcomings of the traditional current protection as the backup protection of the busbar, which is insufficient in sensitivity, and has good practical application value.

[0075] In a preferred embodiment, the formula for calculating the current surge is:

[0076]

[0077] Where, Δi k This refers to the sudden change in current, i k Let N be the k-th current sample value, and N be the number of sampling points per 50Hz power frequency cycle. For the first One current sample value, i k-N This is the (kN)th current sample value.

[0078] Setting value Δi k.set The value range is 0.1 to 0.2 times the rated current.

[0079] If Δi k It exceeds Δi k.setIf the condition is met, the line differential protection criteria and bus differential protection criteria will be activated; otherwise, the protection will not be activated.

[0080] This method significantly reduces the adverse effects of system frequency variations and DC components on the calculation of abrupt changes, and the data length it uses is only one cycle.

[0081] In a preferred embodiment, the line differential protection adopts the principle of morphological similarity distance, specifically including:

[0082] S301: The local protection device sends a message to the remote protection device, requesting the remote device to transmit the remote current information to the local device in real time through the 5G communication network; the remote current information includes: the current sampling value collected by the remote device and the corresponding sampling time data;

[0083] S302: After receiving the current information from the other side, this side determines whether there is any missing data. If so, it uses interpolation to correct and fill in the missing data to ensure that the number of data points per cycle is N.

[0084] S303: Select a data window length of one power frequency sampling period, divide each wave data window into 4 small data windows, and standardize the current sampling value and sampling time data in each small data window;

[0085] S304: Calculate the morphological similarity distance values ​​d1, d2, d3 and d4 of the waveforms on both sides within each small data window based on the standardized data;

[0086] S305: Compare the calculated waveform morphology similarity distance with the similarity distance threshold value; when all four distance values ​​are greater than the similarity distance threshold value, it is determined that the fault is in the main line area, and the protection on this side sends a trip signal to the protection on the other side. After receiving the signal, the protection on the other side will take action without delay; otherwise, if at least one of the morphology similarity distance values ​​in the four small data windows does not exceed the similarity distance threshold value, the protection on this side will not trip and will not send a trip command to the protection device on the other side of the line.

[0087] The effect of adopting the above steps is that, for faults outside the zone accompanied by CT saturation, the current transformer is in a desaturated state for at least 1 / 4 of the cycle time in each cycle, and at least one of the four distance values ​​is less than the setting threshold. Therefore, CT saturation will not cause protection malfunction.

[0088] Preferably, in step S302, the method of using interpolation to correct and fill in missing data specifically includes:

[0089] The protection device acquires the k-th sampled value of the opposite side current information through the 5G communication network; if the sampled value arrives at the protection device, it is stored in the sampled value buffer; if the sampled value does not arrive, it waits for a short time interval t. wait , t wait If the sampled value is still not reached, then the information i of the unreachable sampled value is calculated using interpolation. k There are two possible scenarios:

[0090] a. The next sample value has not yet arrived: i k =2i k-1 -i k-2 ;

[0091] bt k+1 The sampled value arrives at time i k =(i k-1 +i k+1 ) / 2.

[0092] t wait It can be set to approximately 2 to 3 sampling intervals (e.g., for a 4800Hz sampling frequency, t wait It can be set from 0.417ms to 0.625ms.

[0093] In a preferred embodiment, in step S303, the data window length is selected as one power frequency sampling period, and it is divided into four equal small data windows. To reduce the influence of waveform amplitude on the morphological similarity distance calculation results, and to eliminate the adverse effects of inconsistent time and current dimensions on distance calculation, the collected current and time information are standardized. The specific process is as follows:

[0094] The maximum and minimum values ​​of the local current sampled value and the sampling time data in each small data window are respectively denoted as i. max.p and i min.p Where p = 1, 2, 3, 4, representing the p-th data point out of four data points; the maximum and minimum time values ​​in each small data window are denoted as t. max.p and t min.p The standardized current sample value and sampling time are as follows:

[0095]

[0096]

[0097] Where i k ′ and t k ′ represents the standardized current sample value and sampling time.

[0098] After standardization, the time and current sample values ​​for the local and opposite sides of the line within each small data window are I, respectively.1.p {(t′ 1.(p-1)N / 4 ,i′ 1.(p-1)N / 4 ),···,(t′ 1.j ,i′ 1.j ),···,(t′ 1.pN / 4 ,i′ 1.pN / 4 )} and I 2.p {(t′ 2.(p-1)N / 4 ,i′ 2.(p-1)N / 4 ),···,(t′ 2.j ,i′ 2.j ),···,(t′ 2.pN / 4 ,i′ 2.pN / 4 )}, where t′ 1.j This is the j-th value of the time sampled values ​​after per-unit processing on this side of the line; i′ 1.j The j-th value of the current sample after per-unit processing on this side of the line; t′ 2.j The j-th value of the time sampled value after the line side has been per-unitized; i′ 2.j is the j-th value of the current sampled value after per-unit processing on the opposite side of the line; p = 1, 2, 3, 4, representing the p-th data in the four data sets; N is the number of sampling points in each 50Hz power frequency cycle.

[0099] In a preferred embodiment, step S304, calculating the morphological similarity distance value of the waveforms on both sides within each small data window based on the standardized data, specifically includes:

[0100] The morphological similarity distance between the two sequences is:

[0101] d p =D ep ×(2-ASD p / SAD p Equation (4)

[0102] Where, d p D represents the morphological similarity distance. ep Let ASD be the Euclidean distance between two waveforms in the p-th small data window. p SAD represents the Manhattan distance between two waveforms in the p-th small data window. p It is the absolute value of the sum of the differences between the two waveform data in the p-th small data window.

[0103] In the formula (4)

[0104]

[0105]

[0106]

[0107] get:

[0108]

[0109] In a preferred embodiment, in step S305, the similarity distance threshold is a floating threshold, and the formula for calculating the floating threshold within each small data window is as follows:

[0110]

[0111] In an optional embodiment, step S305 employs the following strategy: comparing the calculated waveform morphology similarity distance with a similarity distance threshold value; when all four distance values ​​are greater than the similarity distance threshold value, it is determined that the fault is within the main line area, and the local protection sends a trip signal to the opposite protection. After receiving the signal, the opposite protection operates without delay; conversely, if at least one of the morphology similarity distance values ​​in the four small data windows does not exceed the similarity distance threshold value, the local protection does not trip and does not send a trip command to the protection device on the opposite side of the line. The process further includes: continuously sliding the data window and continuously detecting for two power frequency cycles; if all four distance values ​​are detected to be greater than the similarity distance threshold value within the two power frequency cycles, the local protection trips and simultaneously sends a trip signal to the opposite protection; otherwise, the protection does not send a trip signal but sends a signal to the opposite side and stops real-time data transmission.

[0112] In a preferred embodiment, the bus differential protection employs the following steps:

[0113] S401: After the bus differential protection is activated, calculate the sum of the current sampling values ​​of all incoming and outgoing lines of the bus, I. sum ;

[0114]

[0115] Among them, I m is the current sampling value of the m-th line of the busbar, with the direction of flow to the busbar being positive. h is the total number of incoming and outgoing lines.

[0116] S402: Sum the current sample values ​​and add them to the braking threshold value I of the bus differential protection. set Compare; if the sum of the current sample values ​​is greater than the braking threshold value, i.e.: I sum >I set If the fault is found, it is judged as a busbar fault; otherwise, it is judged as an external fault and the protection will not operate.

[0117] Setting value I set =K rel ×0.1I kw.max / K CT K rel The reliability coefficient is taken as 1.2 to 1.3; I kw.maxThe maximum short-circuit current flowing through the primary side of the differential protection current transformer when a short circuit occurs outside the busbar protection range; K CT The transformation ratio of the current transformer used for busbar protection.

[0118] In a preferred embodiment, the bus differential protection may also employ the following steps:

[0119] S411: After the bus differential protection is activated, calculate the sum of the current sampling values ​​of all incoming and outgoing lines of the busbar;

[0120] S412: Compare the sum of the current sampled values ​​with the braking threshold value of the bus differential protection; if the sum of the current sampled values ​​is greater than the braking threshold value, it is judged as a bus fault; otherwise, continuously slide the data window and continuously detect for two power frequency cycles. If the sum of the current sampled values ​​is detected to be greater than the braking threshold value within two power frequency cycles, it is judged as a bus fault and the bus differential protection operates; otherwise, it is judged as an external fault and the protection does not operate.

[0121] The following is combined with Figures 2-7 The method of this invention is described in the context of a specific single-ring distribution network.

[0122] Figure 2 This is a schematic diagram of a single-ring distribution network simulation model built on the PSCAD simulation platform. The ring network voltage is 20kV, and the internal resistance of the power supply G is 0.1H. Transformers T1, T2, and T3 all have a turns ratio of 20 / 10kV, using a Δ / Y connection, with the low-voltage side grounded via a 3Ω small resistor. The four main lines are all 10km long, with a resistance per unit length of 0.02Ω / km and an inductance per unit length of 0.4Ω / km. The three loads are all (100+j20)MVA. Each blue area represents a substation, and both the lines and busbars are equipped with the line differential protection and busbar differential protection proposed in this invention.

[0123] According to the appendix Figure 3 The flowchart shown focuses on the operating conditions of main line L1 fault and busbar B2 fault, and the corresponding protection actions are analyzed as follows:

[0124] Example 1: Main line L1 fault.

[0125] After a fault occurs on the main line L1, the integrated protection devices on both sides of line L1 detect sudden changes in currents I2 and I3, Δi. k Exceeding the setting threshold Δi k.set Therefore, the differential protection of line L1 is activated, and the differential protection of busbars B1 and B2 is activated.

[0126] According to the appendix Figure 3As shown in the diagram, after the differential protection of line L1 is activated, the integrated protection devices on both sides send signals to the other side via the 5G network, requesting the other side to transmit the current sampling value and sampling time information to their own side in real time. Upon receiving the data transmission request, both sides immediately transmit the current sampling value and corresponding sampling time information collected on their own side to the other side via the 5G communication network.

[0127] After receiving the current time sampling information from the other side, both sides of the line determine whether there are any missing real-time data received on their own side. If there are any missing data, the data is filled and corrected.

[0128] Subsequently, the current-time data within each small data window were standardized using formulas (2) and (3), and the morphological similarity distance d between the current waveforms on both sides of the four small data windows was calculated using formulas (5) and (6). p and the corresponding floating threshold d p.set .

[0129] The four morphological similarity distance values ​​d within a one-cycle data window were determined. 1,2,3,4 All are greater than the corresponding d set The protection on this side trips and sends a trip signal to the protection on the opposite side. The faulty line is disconnected without delay, and at the same time, the protection sends a stop data transmission signal to the opposite side.

[0130] Simultaneously with the activation of the line differential protection, the bus protection criteria were also assessed. (According to Appendix...) Figure 3 The logic is that the protection devices on both sides calculate the sum of the incoming and outgoing currents I of busbars B1 and B2 respectively. 1sum and I 2sum Since the L1 fault on line is an external fault for both busbars at this time, the sum of the currents is approximately 0, which is less than the setting threshold value of the busbar protection. Therefore, the protection does not send a trip command and returns after continuous monitoring for 2 cycles.

[0131] After the line protection device sends a trip signal, the sampled values ​​of the current flowing through circuit breakers 2 and 3 are detected at t. set The value drops to 0 within a certain time period, at which point this judgment is complete.

[0132] The trip signals received by each circuit breaker are shown in the attached table. Figure 4 As shown, circuit breakers 2 and 3 tripped without delay, disconnecting the faulty line L1.

[0133] Example 2: Busbar B2 fault

[0134] After a fault occurs on busbar B2, the protection devices on both sides of line L1 detect currents I2, I3, I4, and I... 10 When a sudden change occurs, the amount of the change exceeds the setting threshold, so the differential protection of line L1 and bus B1 and B2 is activated.

[0135] After the differential protection of line L is activated, similar to the operation process in Example 1, the protection devices on both sides first send a data transmission request signal to the other end and process the received current sample value and the corresponding sampling time information. Subsequently, the current time information of the four small data windows in the data window is standardized, and the similarity distance value of the four waveforms is calculated.

[0136] Since the fault is outside the line area, the similarity distance values ​​of the four waveforms are all less than the corresponding floating threshold. After continuous monitoring for 2 cycles, the protection returns without sending a trip signal, and at the same time sends a signal to the protection on the other side to stop real-time data transmission.

[0137] While the line differential protection is making a judgment, the differential protection of bus B1 and B2 is also judging the nature of the fault. For bus B1, the sum of the collected incoming and outgoing current sampling values ​​is less than the threshold value, so the protection does not operate and returns after 2 cycles. For bus B2, the sum of the incoming and outgoing current sampling values ​​is greater than the setting threshold, so the protection operates, trips circuit breakers 3, 4 and 10, and clears the fault.

[0138] After the bus protection issues a trip signal, if the sampled current values ​​flowing through circuit breakers 3, 4, and 10 drop to 0 within the set range, it indicates that the fault has been successfully cleared, and this judgment is complete.

[0139] After the criteria are activated, the trip signals received by each circuit breaker are as follows: Figure 5 As shown, circuit breakers 3, 4 and 10 tripped without delay, successfully disconnecting the faulty bus B2.

[0140] Example 3: Line L1 is faulty and circuit breaker 3 fails to operate.

[0141] If, in Example 1, the line differential protection issues a trip signal but fails to clear the fault in time due to the failure of circuit breaker 3, then the operation steps of protection devices 1 and 2 are as follows: Protection device 1 detects that I3 fails to drop to 0 within the set time, and then sends a trip signal to the protection device on the other side through the 5G communication network, requesting the tripping of all circuit breakers on other incoming and outgoing lines of bus B2; Protection device 2 also detects that the current I3 fails to drop to 0 within the set time, and directly sends a trip command to the circuit breakers on other incoming and outgoing lines of bus B2.

[0142] The trip signals received by each circuit breaker are shown in the attached table. Figure 6 As shown, after circuit breaker 2 successfully trips, circuit breakers 4 and 10 trip with a delay of t. set The circuit breaker tripped, successfully disconnecting the faulty line L1.

[0143] Example 4: Busbar B2 fault and circuit breaker 3 fails to operate

[0144] If, in Example 2, the bus differential protection issues a trip signal but fails to clear the fault in time due to the failure of circuit breaker 3, then the operation steps of protection device 2 are as follows: protection device 2 detects that the current I3 fails to drop to 0 within the set time, and sends a trip signal to the protection device on the other side through the 5G communication network.

[0145] The trip signals received by each circuit breaker are shown in the attached table. Figure 7 As shown, the delay t after circuit breakers 4 and 10 trip. set Circuit breaker 2 tripped, disconnecting the faulty busbar B2.

[0146] In summary, this embodiment verifies the correctness and feasibility of the DC grounding fault protection method for DC hybrid distribution networks submitted in this invention.

[0147] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A relay protection method for a single-ring distribution network with distributed power sources based on 5G communication, characterized in that, Includes the following steps: The protection device calculates the current surge of each line in real time; If the sudden change in current exceeds the starting setting value, the line differential protection and bus differential protection will be activated. The line differential protection determines whether the current fault is a fault within the line area; If a fault is detected within the line area, the protection output on this side will trip the circuit breaker on this side and simultaneously send a trip signal to the line protection device on the opposite side to disconnect the faulty line. The bus differential protection determines whether the current fault is a fault within the bus zone; if it is determined to be a fault within the bus zone, the protection device sends a trip command to trip the circuit breakers of the incoming and outgoing lines on the bus. After the differential protection of the line issues a trip command, it continuously monitors the current sampling values ​​on both sides of the line and starts a timer. If the current sampling value on this side fails to reach the specified value, the protection will continue to monitor the current sampling values ​​on both sides of the line. t set The current drops to 0 within a time period while the current sampling value on the opposite side is within... t set If the value drops to 0 within a certain time, the adjacent circuit breaker will trip. After the bus differential protection issues a trip command, it immediately checks the current sampling values ​​of all incoming and outgoing lines of the bus and starts a timer. If the current sampling value of any line fails to reach the specified value, the protection will take action. t set If the temperature drops to 0 within a certain time, the circuit breaker on the opposite side of the line will trip to isolate the fault. The line differential protection adopts the principle of morphological similarity distance, specifically including: the local protection device sends a signal to the remote protection device, requesting the remote device to transmit the remote current information to the local device in real time via a 5G communication network; the remote current information includes: the current sampling value collected by the remote device and the corresponding sampling time data; after receiving the remote current information, the local device determines whether there is any data missing. If so, interpolation is used to correct and fill in the missing data to ensure that the number of data points per cycle is [missing information]. N The data window length is selected as one power frequency sampling period. Each wave data window is divided into four smaller data windows. The current sampling value and sampling time data in each smaller data window are standardized. Based on the standardized data, the morphological similarity distance values ​​d1, d2, d3, and d4 of the waveforms on both sides in each smaller data window are calculated. The calculated waveform morphological similarity distances are compared with the similarity distance threshold. When all four distance values ​​are greater than the similarity distance threshold, it is determined that there is a fault in the main line area. The protection on this side sends a trip signal to the protection on the other side. After receiving the signal, the protection on the other side will take action without delay. Conversely, if at least one of the morphological similarity distance values ​​in the four smaller data windows does not exceed the similarity distance threshold, the protection on this side will not trip and will not send a trip command to the protection device on the other side of the line. The bus differential protection determines whether the current fault is within the bus zone by: after the bus differential protection is started, calculating the sum of the current sampling values ​​of all incoming and outgoing lines of the bus; comparing the sum of the current sampling values ​​with the braking threshold value of the bus differential protection; if the sum of the current sampling values ​​is greater than the braking threshold value, it is judged as a bus fault; otherwise, it is judged as a fault outside the bus zone, and the protection does not operate.

2. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that, The formula for calculating the current surge is: Equation (1) in, This refers to the sudden change in current. For the first k One current sample value, N The number of sampling points per 50Hz power frequency cycle. For the ( ) current sampling values, For the ( ) current sample values; The starting setting value ranges from 0.1 to 0.2 times the rated current value.

3. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that, The method of using interpolation to correct and fill in missing data specifically includes: The protection device obtains the opposite side current information through the 5G communication network. k A sample value is taken; if the sample value reaches the protection device, it is stored in the sample value buffer; if the sample value does not reach the protection device, a short time interval is waited. t wait , t wait If the sampled value is still not reached, then the information of the unreachable sampled value is calculated using interpolation. i k There are two possible scenarios: a. The next sample value has not yet arrived: ; b. t k+1 The sampled value arrives at time: .

4. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that, The standardization process for the current sample values ​​and sampling time data within each small data window is as follows: The maximum and minimum values ​​of the local current sampled value and the data at the sampling time in each small data window are respectively denoted as: and ,in, , indicating the fourth of the four data sets p Each data window contains a set of data points; the maximum and minimum time values ​​within each small data window are denoted as follows: and The standardized current sample value and sampling time are as follows: Equation (2) Equation (3).

5. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that: After standardization, the time and current sample values ​​for the local and opposite sides of the line within each small data window are as follows: and In the formula, The first time sampled value after the line side has been per-unitized j One value; The first current sample value after per-unit processing on this side of the line. j One value; The first time sampled value after the line side is per-unitized j One value; The first current sample value after per-unit processing on the opposite side of the line. j One value; , indicating the fourth of the four data sets p share; N This represents the number of sampling points per 50Hz power frequency cycle.

6. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 5, characterized in that: The calculation of the morphological similarity distance value of the waveforms on both sides within each small data window based on the standardized data specifically includes: The morphological similarity distance between the two sequences is: Equation (4) in, d p The distance is the morphological similarity distance. D ep For the first p The Euclidean distance between two waveforms in a small data window, ASD p For the first p Manhattan distance between two waveforms in a small data window, SAD p For the first p The absolute value of the sum of the differences between two waveform data in a small data window.

7. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 6, characterized in that: In the formula (4) get: Equation (5).

8. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 5, characterized in that: The similarity distance threshold adopts a floating threshold, and the formula for calculating the floating threshold within each small data window is as follows: Equation (6).

9. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that: The statement that if at least one of the similarity distance values ​​in the four small data windows does not exceed the similarity distance threshold, the local protection will not trip and will not send a trip command to the protection device on the other side of the line. This is followed by: continuously sliding the data window and continuously detecting for two power frequency cycles; if all four distance values ​​are detected to be greater than the similarity distance threshold within the two power frequency cycles, the local protection will trip and simultaneously send a trip signal to the protection device on the other side; otherwise, the protection will not send a trip signal but will send a signal to the other side and stop real-time data transmission.

10. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that: The bus differential protection determines whether the current fault is a fault within the bus zone, specifically including: After the bus differential protection is activated, the sum of the current sampling values ​​of all incoming and outgoing lines of the bus is calculated; The sum of the current sampled values ​​is compared with the braking threshold value of the bus differential protection. If the sum of the current sampled values ​​is greater than the braking threshold value, it is determined to be a bus fault. Otherwise, the data window is continuously slid to continuously detect for two power frequency cycles. If the sum of the current sampled values ​​is detected to be greater than the braking threshold value within two power frequency cycles, it is determined to be a bus fault and the bus differential protection operates. Otherwise, it is determined to be an external fault and the protection does not operate.

11. The relay protection method for a single-ring distribution network with distributed power sources based on 5G communication according to claim 1, characterized in that: If a circuit breaker fails to operate after the line differential protection or bus differential protection issues a trip command, a trip signal is sent through the station communication or 5G network to trip other circuit breakers on the opposite side of the line connected to the circuit breaker that failed to operate or on the connected bus, thus completing the fault isolation.

Images