Adaptive enhanced pilot protection method considering the operating status of smart distribution network

Abstract

The present invention proposes an adaptive enhanced longitudinal protection method taking into account the operating status of an intelligent distribution network, comprising: configuring protection devices at both ends of a protected line to measure the local three-phase current in real time; when the measured current of any phase meets the fault detection criterion, the protection device enters an adaptive longitudinal protection process: the protection device calculates the three-phase current phasor through a real-time rolling data window; the protection devices at both ends communicate with each other to calculate the three-phase current phasor; after the communication is completed, the amplitude ratio and phase difference of the three-phase current phasor at both ends are calculated; the enhancement coefficient is adaptively adjusted according to the amplitude ratio of the current phasor at both ends; the action amount of the adaptive longitudinal protection is calculated by multiplying the enhancement coefficient by the current amplitude ratio; the braking amount of the adaptive longitudinal protection is calculated according to the phase difference function of the current phasor at both ends; whether an in-zone fault occurs is determined according to the action amount and the braking amount, and if the action amount of any phase current is greater than the braking amount, it is considered that an in-zone fault has occurred.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection for distribution networks, and in particular relates to an adaptive enhanced pilot protection method taking into account the operating status of an intelligent distribution network. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Compared with traditional distribution networks, smart distribution networks have higher power supply reliability and better new energy absorption capacity, and are a key link in new power systems. In addition to the traditional radial open-loop operation mode, smart distribution networks can also supply power to loads through a complex closed-loop network consisting of two or more terminals, resulting in the direction of short-circuit current in the feeder no longer being determined. In addition, with the large-scale grid connection of distributed generation (DG) such as distributed photovoltaics, the impact of DG on the fault characteristics of distribution network feeders cannot be ignored. Since conventional distribution network feeder current protection designed for radial networks is difficult to adapt to smart distribution networks with diverse operating conditions and complex fault characteristics, experts have conducted research on new protection principles suitable for smart distribution networks in recent years.

[0004] The prior art proposes an adaptive directional overcurrent protection based on the adjustment of the constant value in the operating state of the smart distribution network. The method first installs directional elements at each protection installation location, then designs two sets of current protection constant values ​​for the open-loop operating state and closed-loop operating state of the distribution network, and finally adaptively adjusts the selected protection constant value according to the operating state of the distribution network. Although this type of protection takes into account the different operating states of the smart distribution network, it is difficult to take into account the changes in the output of distributed power sources. Since the output of distributed power sources such as photovoltaics and wind power fluctuates greatly with weather changes, adaptive directional overcurrent protection may not be applicable when the penetration rate of distributed power sources in the smart distribution network is high.

[0005] Prior art has proposed a directional longitudinal protection method for distribution networks. This type of method requires the installation of directional elements at both ends of the protected section. After a fault occurs, the fault direction is first determined, and then the protection devices at both ends transmit fault direction information to each other through the communication network. When both ends are determined to be a forward fault, the protected section is identified as a fault section. Directional longitudinal protection is less affected by changes in the operating state of the distribution network, but the current mainstream fault direction criteria such as power direction and impedance direction are all designed for synchronous power sources, and most distributed power sources connected to the distribution network are inverter power sources. When the penetration rate of inverter power sources is high, the reliability of directional longitudinal protection will be affected.

[0006] The prior art proposes a distributed current differential protection method for active distribution networks. This method takes into account the complex fault characteristics caused by the access of a large number of distributed power sources, and introduces the current differential used in high-voltage transmission lines into the distribution network feeder protection. Compared with the overcurrent protection constructed using only single-end quantity information, it has higher reliability. However, the current differential protection uses the phase sum of the currents at both ends as the protection action quantity. When a fault with a certain transition resistance occurs in the distribution network, the amplitude of the short-circuit current is low, and there is a problem that the differential current cannot exceed the braking threshold, resulting in false protection.

[0007] Prior art proposes a longitudinal protection based on the comparison of the current amplitudes measured at both ends. Since most distributed power sources such as distributed photovoltaics connected to the distribution network are inverter-type power sources, the short-circuit current provided by the downstream distributed power source in the section after a fault occurs is much smaller than the short-circuit current provided by the upstream system power source, so the amplitude difference of the current at both ends of the fault section is large. However, the longitudinal protection based on current amplitude comparison can only be applied to open-loop networks. When the distribution network is closed-loop operated, the current amplitude ratio at both ends of the fault section and the non-fault section may be similar. Therefore, it cannot be applied to smart distribution networks with variable operating states.

[0008] The inventors have discovered that existing feeder protection methods for smart distribution networks do not adequately consider changes in network operating status and are unable to effectively identify faults involving transition resistance in scenarios with high penetration of distributed power generation. There is no feeder protection method that is not affected by changes in network operating status and distributed power generation access. Summary of the invention

[0009] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides an adaptive enhanced longitudinal protection method taking into account the operating state of the intelligent distribution network. The method uses the difference in current amplitude at both ends to construct the action amount of the protection criterion, and improves the sensitivity during high-resistance faults through an adaptive enhancement coefficient; in addition, the protection braking amount is constructed through the current phase difference function at both ends to improve the reliability of protection under closed-loop operation.

[0010] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0011] A first aspect of the present invention provides an adaptive enhanced pilot protection method taking into account the operating state of a smart distribution network, comprising:

[0012] Configure protection devices at both ends of the protected line and measure the local three-phase current in real time;

[0013] When the measured current of any phase meets the fault detection criteria, it is considered that a fault has occurred in the system, and the protection device enters the adaptive longitudinal protection process;

[0014] After entering the adaptive longitudinal protection process, the protection device calculates the three-phase current phasors through a real-time rolling data window;

[0015] The three-phase current phasors calculated by the protection devices at both ends communicating with each other;

[0016] After the communication is completed, the amplitude ratio and phase difference of the three-phase current phasors at both ends are calculated;

[0017] Adaptively adjust the enhancement factor according to the amplitude ratio of the current phasors at both ends;

[0018] The action amount of the adaptive longitudinal protection is calculated by multiplying the enhancement coefficient and the current amplitude ratio;

[0019] Calculate the braking amount of the adaptive pilot protection according to the phase difference function of the current phasors at both ends;

[0020] Whether an internal fault has occurred is determined based on the action amount and braking amount of the adaptive longitudinal protection. If the action amount of any phase current is greater than the braking amount, it is considered that an internal fault has occurred.

[0021] Furthermore, a fault detection criterion based on the phase current mutation amount is adopted, and the calculation result of the absolute value of the current current sampling value minus the sampling value one cycle ago is subtracted from the calculation result of the absolute value of the sampling value one cycle ago minus the sampling value two cycles ago. When the amplitude of the calculation results of three consecutive sampling points is greater than the fault detection threshold, it is regarded as a fault occurring, and the protection device enters the subsequent protection process.

[0022] Furthermore, the protection device calculates the three-phase current phasors through a real-time rolling data window including:

[0023] The full-cycle discrete Fourier algorithm is used to calculate the current phasor. For each phase current, the current phasor at the current moment is calculated using the data of the previous cycle at the current sampling point, and then the data window is rolled back to calculate the current phasor at the next moment.

[0024] Furthermore, the protection devices at both ends collect the three-phase current phasors for a set time period, and centrally communicate the three-phase current phasors within the set time period;

[0025] The protection device converts each current phasor into real and imaginary parts for transmission.

[0026] Furthermore, according to the current phasor measured by the protection devices at both ends and The amplitude ratio of the maximum and minimum current phasors in the adaptive adjustment is used to set the enhancement factor , when the amplitude ratio is close to 1 Take the smaller one first When the amplitude ratio is far from 1 Take the larger second Values, as follows:

[0027] ,

[0028] and They are the current phasors measured by the protection devices at both ends respectively.

[0029] Furthermore, the current phasor measured by the protection devices at both ends and The current amplitude ratio of the maximum and minimum current phases in the current phase is multiplied by the enhancement coefficient to calculate the action amount of the adaptive longitudinal protection. for:

[0030] ,

[0031] Amount of action It is understood as a per-unit current based on the smaller value of the current amplitude at both ends. is the adaptive enhancement coefficient, and They are the current phasors measured by the protection devices at both ends respectively.

[0032] Furthermore, the braking amount of the adaptive pilot protection is calculated according to the phase difference function of the current phasors at both ends, specifically:

[0033] ,

[0034] In the formula, is the reliability coefficient, the value of the reliability coefficient is greater than 2. is the phase difference function, is the phase difference of the current phasors at both ends.

[0035] The second aspect of the present invention provides an adaptive enhanced longitudinal protection device taking into account the operating status of an intelligent distribution network, comprising: at least one processing unit, the processing unit, a storage unit, a collection unit and a communication unit are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the adaptive enhanced longitudinal protection method taking into account the operating status of the intelligent distribution network is implemented.

[0036] The above technical solution has the following beneficial effects:

[0037] The present invention utilizes the current amplitude ratio at both ends and the phase difference of the enhancement coefficient that can be adjusted adaptively to construct the action amount of the protection criterion. When no fault occurs in the zone, the action amount is very small, and when a fault occurs in the zone, the action amount is very large, so that the adaptive longitudinal protection has higher reliability and sensitivity, and has higher ability to resist transition resistance.

[0038] The present invention utilizes the phase difference of the current at both ends to construct the braking amount. In the scenario where the smart distribution network is in closed-loop operation or the protected line downstream contains a synchronous power supply, the braking amount when an in-zone fault occurs is very small, much smaller than the protection action amount, thereby ensuring that the protection can operate reliably and sensitively.

[0039] In the adaptive longitudinal protection proposed in the present invention, the action amount and the braking amount are adaptively changed according to the current measured at both ends. There is no need to obtain information such as the operating status of the distribution network, the output of distributed power sources, the load size, etc., and there is no need to protect the voltage information at the installation site, which is easy to implement.

[0040] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0042] Figure 1 A schematic diagram of feeder protection configuration for a smart distribution network according to an embodiment of the present invention;

[0043] Figure 2 It is a schematic diagram of a fault equivalent network in a feeder area during open-loop operation of a smart distribution network according to an embodiment of the present invention;

[0044] Figure 3 A schematic diagram of a fault equivalent network in a feeder area during closed-loop operation of a smart distribution network according to an embodiment of the present invention;

[0045] Figure 4 A schematic diagram of a smart distribution network simulation model according to an embodiment of the present invention;

[0046] Figure 5 It is the action and braking amount variation curve of the three-phase short circuit fault at point f4 in the inverter type distributed power supply network in the open-loop operation state;

[0047] Figure 6 It is the action and braking amount variation curve of the BC two-phase short circuit fault at point f4 in the open-loop operation state and inverter-type distributed power supply network;

[0048] Figure 7 It is the action and braking amount variation curve of the CA two-phase grounding fault at point f4 in the inverter-type distributed power supply network in the open-loop operation state;

[0049] Figure 8 It is the action and braking amount variation curve of the open-loop operation state and the occurrence of a three-phase short-circuit fault at point f2 in a power grid containing a synchronous distributed power source;

[0050] Fig. 9 It is the action and braking amount variation curve of the open-loop operation state and the BC two-phase short circuit fault at point f2 in the power grid containing synchronous distributed power generation;

[0051] Fig.10 It is the action and braking change curve of the open-loop operation state and the CA two-phase grounding fault at point f2 in the power grid containing synchronous distributed power generation;

[0052] Fig.11 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f4 through a 50Ω transition resistor;

[0053] Fig.12 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f4 through a 100Ω transition resistance;

[0054] Fig.13 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f2 through a 50Ω transition resistor;

[0055] Fig.14 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f2 through a 100Ω transition resistance;

[0056] Fig.15 It is the action and braking amount variation curve of the three-phase short circuit fault at point f4 during closed-loop operation;

[0057] Fig.16 It is the action and braking amount variation curve of BC two-phase short circuit fault at point f4 during closed-loop operation;

[0058] Fig.17 It is the action and braking amount variation curve when a CA two-phase grounding fault occurs at point f4 through a 100Ω transition resistance during closed-loop operation;

[0059] Fig.18 It is an overall flow chart of the adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network according to an embodiment of the present invention;

[0060] Fig.19 It is a schematic diagram of an adaptive enhanced longitudinal protection device taking into account the operating status of a smart distribution network according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0062] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0063] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0064] Based on the description of the background technology, Figure 1 The smart distribution network feeder shown is taken as an example to describe the limitations of existing protection methods in the smart distribution network.

[0065] The two important features that distinguish smart distribution networks from traditional distribution networks are that they allow closed-loop operation and have a large number of distributed power sources, which lead to greater uncertainty in the direction and magnitude of feeder fault currents. When traditional feeder protection methods are applied to smart distribution networks, there are risks of difficulty in setting, poor selectivity, reduced sensitivity, and even false operation and refusal to operate.

[0066] In the feeder protection of intelligent distribution network, upgrading the current protection of traditional distribution network to adaptive directional overcurrent protection is the most common solution in field operation. This method first installs directional elements at each protection installation location. Figure 1 In the figure, it is represented by a black rectangle, and then two sets of current protection settings are designed for the open-loop operation state and closed-loop operation state of the distribution network. Finally, the selected protection settings are adaptively adjusted according to the operation state of the distribution network. Although this method takes into account the different operation states of the smart distribution network, it requires the distribution master station to monitor the system operation state in real time and send the information to each protection device. When the master station or its communication system fails, the protection performance of the entire network will be reduced. In addition, this method is difficult to take into account the changes in the output of distributed power sources. When the penetration rate of distributed power sources is high and the output of distributed power sources such as photovoltaics and wind power fluctuates greatly with weather changes, the adaptive directional overcurrent protection may not be applicable.

[0067] With the rapid development of smart distribution network communication networks, feeder current differential protection has been introduced in some core urban distribution networks that have high requirements for power supply reliability. The current differential protection uses the phase sum and phase difference amplitudes of the current at both ends of the protected line as the protection action and braking amount, respectively. It is not affected by changes in the operating state of the distribution network and has high reliability. However, when the fault point contains a certain transition resistance, the current amplitude at both ends decreases, and the action amount of the current differential protection cannot exceed the fixed action threshold, resulting in protection refusal to operate.

[0068] The longitudinal protection based on the comparison of the current amplitudes measured at both ends is a new feeder protection principle specifically proposed for active distribution networks. Since most distributed power sources such as distributed photovoltaics connected to the distribution network are inverter-type power sources, the short-circuit current provided by the downstream distributed power source in the section after the fault occurs is much smaller than the short-circuit current provided by the upstream system power source. Therefore, the amplitude difference of the current at both ends of the fault section is large. The longitudinal protection based on the comparison of current amplitudes is to identify the faults inside and outside the area through this feature. However, this method can only be applied to open-loop networks. When the distribution network is closed-loop, the current amplitude ratio at both ends of the fault section and the non-fault section may be similar. Therefore, it cannot be applied to smart distribution networks with variable operating states.

[0069] The overall idea proposed by the present invention is:

[0070] The present invention first configures protection devices at both ends of the protected line, and the protection devices measure the local three-phase current in real time; when the measured current of any phase meets the fault detection criterion, it is regarded as a fault in the system, and the protection device enters the adaptive longitudinal protection process: the protection device calculates the three-phase current phasor through a real-time rolling data window, and the devices at both ends communicate with each other to calculate the three-phase current phasor; after the communication is completed, the amplitude ratio and phase difference of the three-phase current phasor at both ends are calculated, and the enhancement coefficient and the action amount of the longitudinal protection are adaptively adjusted according to the amplitude ratio of the current phasor at both ends, and the braking amount of the longitudinal protection is calculated according to the phase difference function of the current phasor at both ends; finally, it is judged whether an in-zone fault occurs according to the action amount and braking amount of the adaptive longitudinal protection, and if the action amount of any phase current is greater than the braking amount, it is regarded that an in-zone fault occurs.

[0071] Embodiment 1

[0072] like Fig.18 As shown, this embodiment discloses an adaptive enhanced pilot protection method taking into account the operating state of the smart distribution network, which specifically includes the following steps:

[0073] Step 1: Configure protection devices at both ends of the protected line, and the protection devices measure the local three-phase current in real time.

[0074] Step 2: When the measured current of any phase meets the fault detection criterion, it is considered that a fault has occurred in the system, and the protection device enters the adaptive longitudinal protection process.

[0075] Specifically, in order to ensure the sensitivity of fault detection and the ability to resist system frequency deviation, a fault detection criterion based on the phase current mutation is adopted, and the calculation result of the absolute value of the current current sampling value minus the sampling value one cycle ago is subtracted from the calculation result of the absolute value of the sampling value one cycle ago minus the sampling value two cycles ago. For each phase current, the fault detection criterion is as follows:

[0076] ,

[0077] In the formula, i φ ( k )express φ Phase current in the k The sampling value of the sampling point, N is the number of sampling points of the protection device in one power frequency cycle, K S is the fault detection threshold coefficient, I N is the rated current amplitude.

[0078] In order to eliminate the interference of factors such as noise, when the amplitude of the calculation results of three consecutive sampling points of any phase current is greater than the fault detection threshold, it is considered that a fault has occurred and the protection device enters the adaptive longitudinal protection process.

[0079] Step 3: After entering the adaptive longitudinal protection process, the protection device calculates the three-phase fault current phasors through a real-time rolling data window.

[0080] Specifically, the process of real-time calculation of three-phase fault current phasors is:

[0081] To ensure the calculation accuracy, the full-cycle discrete Fourier algorithm is used to calculate the current phasor. For each phase current, the current phasor at this moment is calculated based on the data of the previous cycle of the current sampling point, and then the data window is rolled back to calculate the current phasor at the next moment.

[0082] Step 4: The protection devices at both ends communicate with each other to calculate the three-phase current phasors.

[0083] Specifically, in the process of communicating current phasors, in order to reduce the amount of communication data, each current phasor is converted into the form of real and imaginary parts for transmission; in addition, in order to reduce the space occupied by the frame header, frame tail, address bit, control bit, and check bit information in each frame of communication data, the protection devices at both ends collect the three-phase current phasors of the set time length, and the three-phase current phasors within the set time length are communicated collectively. For example, the current phasor data is sent every 5 milliseconds.

[0084] Step 5: Calculate the adaptive enhancement coefficient based on the amplitude ratio of the current phasors at both ends .

[0085] Specifically, the adaptive enhancement coefficient The function of is to take a larger value when a fault occurs in the zone to increase the protection action and improve the protection sensitivity; take a smaller value in normal operation or out-of-zone fault to reduce the protection action and improve the protection safety. Since the currents measured at both ends are the same through current when no fault occurs in the zone, the current amplitude ratio is close to 1, and when a fault occurs in the zone, the current amplitude at one end is often much larger than that at the other end. Therefore, the adaptive enhancement coefficient is constructed according to the amplitude ratio of the currents at both ends. .by Figure 1 The feeder segment MN in the smart distribution network shown in the figure is taken as an example to be protected. When the system is in open-loop operation, f When a fault occurs at a point, a fault equal value network is constructed as follows Figure 2 shown.

[0086] Figure 2 middle, and are the current phasors measured by the protection devices at both ends. The direction from the busbar to the line is the positive direction. and are the potential of the main grid equivalent power source and the short-circuit current provided by the distributed power source, Z ML and Z NR are the equivalent impedances on the left side of busbar M and on the right side of busbar N, Z MF and Z NF are the equivalent impedances from busbar M and busbar N to the fault point, Z f Add impedance to the fault.

[0087] In the area f After a point failure occurs, The size is determined by the system power supply, which can be several times or even dozens of times the load current. The size of is determined by the distributed power supply. Since the inverter has limited ability to withstand large currents, the upper limit of the short-circuit current that the distributed power supply can output is 1.2 times its rated current, resulting in the fault current on this side being much smaller than that on the system side. Therefore, according to the current phasor measured by the protection devices at both ends and The amplitude ratio of the maximum and minimum current phasors in the adaptive adjustment is used to set the enhancement factor , when the amplitude ratio is close to 1 Take the smaller one first When the amplitude ratio is far from 1 Take the larger second To simplify the processing of the protection device, when the current amplitude ratio at both ends is greater than 2, Take the larger second value, this application takes 1; when the amplitude ratio is less than or equal to 2, Take the smaller one first The value is 0.1 in this application, as shown below:

[0088] ,

[0089] and They are the current phasors measured by the protection devices at both ends respectively.

[0090] Step 6: Current phasors measured by the protection devices at both ends and The action amount of the adaptive longitudinal protection is calculated by multiplying the current amplitude ratio of the maximum and minimum current phases by the enhancement coefficient.

[0091] Specifically, the action amount of the adaptive pilot protection for:

[0092] ,

[0093] Amount of action It is understood as a per-unit current based on the smaller value of the current amplitude at both ends. When there is no fault in the zone, the current amplitude ratio at both ends is close to 1. Take the smaller value and multiply the two to get the action amount When a fault occurs in the area, the current amplitude at both ends is relatively large in most cases. Take the larger value and multiply the two to get Very large, the protection can act reliably and sensitively.

[0094] It should be noted that when the smart distribution network is in a closed-loop operation state, f When a fault occurs at a point, both ends of the system power supply provide a large short-circuit current, such as Figure 3 At this time, the current amplitudes at both ends are close, and the fault section cannot be determined using only the amplitude information. Therefore, it is necessary to use the phase relationship of the currents at both ends to adaptively reduce the braking amount of the protection to prevent the protection from failing to operate. The braking amount will be introduced in detail in the subsequent step 7.

[0095] Step 7: Calculate the braking amount of the adaptive longitudinal protection according to the phase difference function of the current phasors at both ends.

[0096] Specifically, the braking amount of the adaptive longitudinal protection I res is the multiplication of the reliability coefficient and the phase difference function, as shown below:

[0097] ,

[0098] In the formula, is the reliability coefficient, the value of the reliability coefficient is greater than 2. is the phase difference of the current phasors at both ends.

[0099] When no fault occurs within the area, the same through current flows through both ends of the feeder, and the phase difference The value is 180°, the phase difference function The value of is 1, and The braking amount after multiplication Much larger than the amount of action , the protection will not malfunction. When an internal fault occurs, if the distribution network is in closed-loop operation or the protected line downstream contains a synchronous power supply, the phase difference The value of is small, the phase difference function The value is close to 0, the braking amount The value of is extremely small, even if the current amplitudes at both ends are close, the protection can still operate correctly; if the distribution network is in closed-loop operation and the downstream only contains inverter-type distributed power sources, the phase difference The situation may be close to 180°, and the braking amount The value is close to value, but at this time the current amplitude at both ends is extremely large, the action Much greater than the braking , the protection can still operate correctly.

[0100] Step 8: Determine whether an internal fault has occurred based on the operating and braking quantities of the adaptive longitudinal protection. If the operating quantity of any phase current is Greater than the braking amount It is considered that an intra-area fault has occurred.

[0101] Verification Example

[0102] PSCAD / EMTDC simulation software was used to build a smart distribution network model with switchable operating states. Faults were set in the distribution lines and the fault simulation data were processed using MATLAB software. The adaptive enhanced longitudinal protection method considering the operating state of the smart distribution network proposed in the present invention was verified.

[0103] 1) Simulation model

[0104] The simulation model structure is as follows Figure 4As shown. The simulation model is a medium-voltage distribution network with a voltage level of 10 kV, and the neutral point is ungrounded. In the simulation model, B represents the bus; L represents the load, and the specific parameters are shown in Table 1; R represents the protection device, which collects the current information at the corresponding load switch; DG represents the distributed power source, among which DG1 is a diesel generator with a rated power of 1 MW (simulating a synchronous distributed power source), and DG2 and DG3 are photovoltaic power sources with rated powers of 1 MW and 4 MW respectively (simulating an inverter distributed power source); f Indicates the fault point, and each point is located at the midpoint of the section. The simulation model controls the operation state of the distribution network through the tie switch. In the default state, the tie switch is disconnected, that is, open-loop operation. The specific parameters of the distribution line are shown in Table 2.

[0105] Table 1 Load parameters

[0106]

[0107] Table 2 Line parameters

[0108]

[0109] 2) Simulation verification

[0110] a) Verify the effectiveness of the proposed adaptive longitudinal protection method in open-loop operation with inverter-type distributed power sources downstream:

[0111] Since most of my country's smart distribution networks are in open-loop operation most of the time, and most of the distributed power sources connected to the distribution network are inverter-type distributed power sources, different types of faults are first set at point f4, including three-phase short circuit, two-phase short circuit and two-phase grounding. The feeder segment B4B5 is taken as the protected segment. The action and braking amount change curves of the proposed adaptive longitudinal protection method are shown in Figure 2. Figure 5 , Figure 6 and Figure 7 As shown. Among them, Figure 5 The curves of the action and braking amount change when a three-phase short circuit fault occurs at point f4 in an inverter-type distributed power supply network in an open-loop operation state. Figure 6 The curves of the action and braking amount change when a BC two-phase short circuit fault occurs at point f4 in an inverter-type distributed power supply network in an open-loop operation state are shown in Figure 2. Figure 7 It is the action and braking change curve of the open-loop operation state and the CA two-phase grounding fault at point f4 in the inverter-type distributed power supply network.

[0112] Depend on Figure 5 , Figure 6 and Figure 7It can be seen that before the fault occurs, the action amount of this method is maintained at about 1 and the braking amount is maintained at about 3 (the reliability coefficient is 3), which is consistent with the theoretical analysis and will not cause false operation. After the fault occurs in the area, no matter what type of fault it is, the protection action amount will quickly increase to a larger value, and the stable value is about 100, which is much larger than the braking amount. Therefore, the proposed adaptive longitudinal protection method can act reliably, sensitively and quickly.

[0113] In the protected area B 4 B 5 Upstream and downstream failure points f 3 , f 5 Set different types of faults, and the protected zone B after the fault 4 B 5 The values ​​of the action and braking amounts are basically consistent with those before the fault, and the protection is reliable and will not malfunction.

[0114] b) Verification of the effectiveness of the proposed adaptive pilot protection method in open-loop operation with synchronous distributed power sources downstream:

[0115] Although most distributed power sources in smart distribution networks are inverter-type distributed power sources, there may also be a small number of synchronous distributed power sources, such as diesel generators and compressed air energy storage. Therefore, different types of faults are set at point f2, including three-phase short circuit, two-phase short circuit and two-phase grounding. The feeder segment B2B3 is taken as the protected segment. The action and braking amount change curves of the proposed adaptive longitudinal protection method are shown in Figure 2. Figure 8 , Fig. 9 and Fig.10 shown. Figure 8 The curve of the action and braking amount changes when a three-phase short circuit fault occurs at point f2 in an open-loop operation state and a synchronous distributed power grid. Fig. 9 The curves of the action and braking amount change when a BC two-phase short circuit fault occurs at point f2 in an open-loop operation state and a synchronous distributed power grid are shown in Figure 1. Fig.10 It is the action and braking change curve of the open-loop operation state when a CA two-phase grounding fault occurs at point f2 in a power grid containing synchronous distributed power generation.

[0116] Depend on Figure 8 , Fig. 9 and Fig.10 It can be seen that before the fault occurs, the action amount of this method is maintained at about 1 and the braking amount is maintained at about 3, and the protection is reliable and will not malfunction. After the fault occurs in the area, no matter what type of fault it is, the protection action amount will quickly increase to a larger value, and the stable value is about 15, which is lower than Figure 5However, since the short-circuit current phase characteristics provided by the synchronous distributed power supply downstream of the fault point are similar to those of the system power supply, the phase difference between the two currents is small, and the braking amount of the protection drops rapidly after the fault. Therefore, the proposed adaptive longitudinal protection method can still operate reliably, sensitively and quickly.

[0117] In the protected area B 2 B 3 Upstream failure point f 1 Set different types of faults, and the protected zone B after the fault 2 B 3 The values ​​of the action and braking amounts are basically consistent with those before the fault, and the protection is reliable and will not malfunction.

[0118] c) When the fault point contains a large transition resistance, that is, a high-resistance fault, the effectiveness of the proposed adaptive longitudinal protection method is verified:

[0119] The proposed adaptive longitudinal protection method can overcome the problem of insufficient protection performance of current differential protection when the fault contains large transition resistance. In order to verify this advantage, two-phase grounding faults with large transition resistance (50Ω and 100Ω) are set at points f4 and f2 respectively, and feeder segments B4B5 and feeder segments B2B3 are used as protected sections respectively. The action and braking amount change curves of the proposed adaptive longitudinal protection method are shown in Figure 2. Fig.11 , Fig.12 , Fig.13 and Fig.14 shown. Fig.11 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f4 through a 50Ω transition resistor. Fig.12 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f4 through a 100Ω transition resistance. Fig.13 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f2 through a 50Ω transition resistor. Fig.14 The curve of the action and braking amount changes when a CA two-phase grounding fault occurs at point f2 through a 100Ω transition resistance.

[0120] Depend on Fig.11 , Fig.12 , Fig.13 and Fig.14It can be seen that after the fault occurs in the area with large transition resistance, the protection action amount can quickly exceed the braking amount. Although the action amount is temporarily lower than the braking amount in some cases, this situation only exists in the transient process within 5ms after the fault. After that, the protection action amount can be significantly greater than the braking amount. The proposed adaptive longitudinal protection method can operate reliably. In contrast, the conventional longitudinal current differential protection will refuse to operate when the transition resistance is 20Ω, so the proposed protection scheme has a stronger ability to resist transition resistance.

[0121] d) Verification of the effectiveness of the proposed adaptive pilot protection method during closed-loop operation of the distribution network:

[0122] The biggest advantage of the proposed adaptive longitudinal protection method is that it can be applied to both open-loop and closed-loop distribution networks. In order to verify the effectiveness of this method in closed-loop distribution network operation, the tie switch in the simulation model is closed and different types of faults are set at each fault point again. The adaptive longitudinal protection can correctly judge the faults inside and outside the area. The faults include: three-phase short circuit at the fault point f4, two-phase short circuit of BC, and two-phase grounding of CA through a 100Ω transition resistor. The change curves of the action amount and the braking amount are shown in the figure. Fig.15 , Fig.16 and Fig.17 shown. Fig.15 This is the curve of the action and braking amount changes when a three-phase short circuit fault occurs at point f4 during closed-loop operation. Fig.16 This is the curve of the action and braking amount changes when a BC two-phase short circuit fault occurs at point f4 during closed-loop operation. Fig.17 This is the curve of the change of the action and braking amount when a CA two-phase grounding fault occurs at point f4 through a 100Ω transition resistance during closed-loop operation.

[0123] Depend on Fig.15 , Fig.16 and Fig.17 It can be seen that after different types of intra-area faults occur in the closed-loop distribution network, the protection action amount increases rapidly, the braking amount decreases rapidly, and the action amount rapidly exceeds and is much greater than the braking amount. Therefore, the proposed adaptive longitudinal protection method in the closed-loop distribution network can operate reliably, sensitively, and quickly, and has a high ability to resist transition resistance.

[0124] The simulation verification results based on PSCAD-MATLAB show that the adaptive enhanced longitudinal protection method taking into account the operating status of the intelligent distribution network proposed in the present invention is applicable to both open-loop and closed-loop distribution networks. It can ensure that the feeder protection has high reliability, sensitivity and speed without obtaining the distribution network status information, and has high resistance to transition resistance.

[0125] Embodiment 2

[0126] like Fig.19 As shown, the second aspect of the present invention provides an adaptive enhanced longitudinal protection device taking into account the operating status of the smart distribution network, comprising: at least one processing unit, the processing unit, the storage unit, the acquisition unit and the communication unit are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the adaptive enhanced longitudinal protection method taking into account the operating status of the smart distribution network is implemented.

[0127] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0128] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. An adaptive enhanced pilot protection method taking into account the operating status of a smart distribution network, characterized in that: include: Configure protection devices at both ends of the protected line and measure the local three-phase current in real time; When the measured current of any phase meets the fault detection criteria, it is considered that a fault has occurred in the system, and the protection device enters the adaptive longitudinal protection process and executes: The protection device calculates the three-phase current phasors through a real-time rolling data window; The three-phase current phasors calculated by the protection devices at both ends communicating with each other; After the communication is completed, the amplitude ratio and phase difference of the three-phase current phasors at both ends are calculated; The enhancement factor is adaptively adjusted according to the amplitude ratio of the maximum and minimum current phases in the current phase measured by the protection devices at both ends. When the amplitude ratio is close to 1, Take the smaller one first When the amplitude ratio is far from 1 Take the larger second value; The action amount of the adaptive pilot protection is calculated by multiplying the enhancement coefficient and the current amplitude ratio, where the braking amount of the adaptive pilot protection is I res is the multiplication of the reliability coefficient and the phase difference function, as shown below: , where is the reliability coefficient, the value of the reliability coefficient is greater than 2. is the phase difference function, is the phase difference of the current phasors at both ends; Whether an internal fault has occurred is determined based on the action amount and braking amount of the adaptive longitudinal protection. If the action amount of any phase current is greater than the braking amount, it is considered that an internal fault has occurred.

2. The adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network as claimed in claim 1 is characterized in that: A fault detection criterion based on the phase current mutation is adopted. The calculation result of the absolute value of the current sampling value minus the sampling value one cycle ago is subtracted from the calculation result of the absolute value of the sampling value one cycle ago minus the sampling value two cycles ago. When the amplitude of the calculation results of three consecutive sampling points is greater than the fault detection threshold, it is considered that a fault has occurred and the protection device enters the subsequent protection process.

3. The adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network as claimed in claim 1, characterized in that: The protection device calculates the three-phase current phasors through a real-time rolling data window, including: The full-cycle discrete Fourier algorithm is used to calculate the current phasor. For each phase current, the current phasor at the current moment is calculated using the data of the previous cycle at the current sampling point, and then the data window is rolled back to calculate the current phasor at the next moment.

4. The adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network as claimed in claim 1, characterized in that: The protection devices at both ends collect the three-phase current phasors for a set time period, and centrally communicate the three-phase current phasors within the set time period; The protection device converts each current phasor into real and imaginary parts for transmission.

5. The adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network as claimed in claim 1, characterized in that: When the amplitude ratio is close to 1 Take the smaller one first When the amplitude ratio is far from 1 Take the larger second Values ​​as follows: ， and They are the current phasors measured by the protection devices at both ends respectively.

6. The adaptive enhanced pilot protection method taking into account the operating status of the smart distribution network as claimed in claim 1, characterized in that: The current phasor measured by the protection device at both ends and The current amplitude ratio of the maximum and minimum current phases in the current phase is multiplied by the enhancement coefficient to calculate the action amount of the adaptive longitudinal protection. for: ， Amount of action It is understood as a per-unit current based on the smaller value of the current amplitude at both ends. is the adaptive enhancement coefficient, and They are the current phasors measured by the protection devices at both ends respectively.

7. An adaptive enhanced longitudinal protection device taking into account the operating status of a smart distribution network, characterized in that it comprises: At least one processing unit, the processing unit, the storage unit, the collection unit and the communication unit are interconnected through a bus unit, the storage unit stores a computer program, and when the computer program is executed by the processing unit, the adaptive enhanced longitudinal protection method taking into account the operating status of the smart distribution network as described in any one of claims 1-6 is implemented.

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