Active power distribution network differential protection method, system and device based on phase-to-phase current

Abstract

The application provides an active power distribution network differential protection method, system and device based on phase-to-phase current, relates to the technical field of power system relay protection, and comprises the following steps: when the phase current mutation of three-phase current is greater than a first starting value, according to the steady-state phase quantity of phase-to-phase current before fault and the steady-state phase quantity of phase-to-phase current after fault, the first phase difference of the fault phase and the corresponding phase quantity amplitude are determined; according to the first phase difference of the fault phase, the second phase difference of the fault phase-to-phase is determined; according to the first reliable coefficient, the adaptive braking coefficient, the phase quantity amplitude and the second phase difference, the action quantity and the braking quantity are calculated; the above steps are repeated, if the action quantities of a continuous preset group are all greater than the braking quantity, it is determined that the fault is in the region, and the protection device is triggered to act; the influence of the fault on other regions of the active power distribution network is reduced, and the protection sensitivity and system reliability are improved.

Description

TECHNICAL FIELD

[0001] The present application generally relates to the technical field of power system relay protection, and particularly relates to an active distribution network differential protection method, system and device based on inter-phase current. BACKGROUND

[0002] With the development of urban power grid automation and new energy, the power system is essentially undergoing a profound transformation from a static unidirectional network to a dynamic multi-source interactive system. On the one hand, the topology structure changes frequently due to the automatic reconfiguration technology, which makes it difficult for the traditional time and current step coordination relationship of the stage current protection to cope with the dynamic power grid, resulting in protection coordination difficulties and increased risk of protection mismatch. On the other hand, the active and nonlinear characteristics brought by high penetration of new energy further increase the risk of failure of the fault current direction detection and short-circuit calculation model relied on by the protection. These two problems do not exist in isolation. When the automatic reconfiguration dynamically adjusts the distributed power supply access location, the current limiting characteristics of the inverter and the bidirectional power flow will simultaneously change the fault current amplitude, phase and path, causing the protection setting value mismatch and the direction discrimination failure to superimpose each other, forming a double disturbance of dynamic topology and active equipment.

[0003] To cope with these challenges, differential protection is a common solution. However, the traditional differential protection has high requirements for data synchronization accuracy and communication bandwidth. In the face of the operating environment of frequent access of distributed power supply and dynamic changes of topology in active distribution network, the traditional differential protection has problems of synchronization deviation, communication delay and high operation and maintenance cost. SUMMARY

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide an active distribution network differential protection method, system and device based on inter-phase current to solve the problems of synchronization deviation, communication delay and high operation and maintenance cost.

[0005] In a first aspect, the present application provides an active distribution network differential protection method based on inter-phase current, comprising the following steps:

[0006] Real-time acquisition of three-phase current, when the phase current corresponding to the three-phase current mutation is greater than the first starting value, determining the inter-phase short-circuit fault type according to the size relationship between the three-phase current and the preset threshold value;

[0007] When the inter-phase short-circuit fault type is two-phase inter-phase short-circuit fault or three-phase inter-phase short-circuit fault, obtaining the pre-fault inter-phase current steady-state phase and the post-fault inter-phase current steady-state phase;

[0008] Determining the first phase difference of the fault phase and the phase quantity amplitude corresponding to the first phase difference according to the pre-fault inter-phase current steady-state phase and the post-fault inter-phase current steady-state phase;

[0009] determining a second phase difference between the fault phase and another phase according to the first phase difference;

[0010] obtaining a first reliability coefficient and an adaptive braking coefficient, and calculating an action amount and a braking amount according to the first reliability coefficient, the adaptive braking coefficient, the phasor amplitude and the second phase difference;

[0011] repeating the above steps to obtain the action amount and the braking amount at multiple time points, and determining an in-zone fault and triggering the protection device to act to isolate the fault line if the action amount of a continuous preset group is greater than the braking amount.

[0012] According to the technical scheme provided in the application, the adaptive braking coefficient is determined according to the following steps:

[0013] determining an amplitude factor according to the phasor amplitude;

[0014] constructing multiple amplitude-angle factors according to the amplitude factor and the second phase difference based on an exponential function and a logarithmic function;

[0015] obtaining a margin, and taking the result obtained by dividing the sum of the margin and the minimum value of the amplitude-angle factors by the sum of the minimum value of the amplitude-angle factors and the margin as an adaptive parameter;

[0016] taking the reciprocal of the adaptive parameter as the adaptive braking coefficient.

[0017] According to the technical scheme provided in the application, the method further comprises the following steps:

[0018] monitoring the operation state of the power distribution network in real time after triggering the protection device to act;

[0019] if the operation state meets a preset reconstruction condition, sending a reconstruction instruction to a switching device and a pairing instruction to the protection device; the reconstruction instruction is used to instruct the switching device to switch the on-off state, and the pairing instruction is used to instruct the protection device to establish data interaction with a corresponding end after topology reconstruction.

[0020] According to the technical scheme provided in the application, the first starting value is determined according to the following steps:

[0021] obtaining a phase current amplitude of a previous filtering period and a second reliability coefficient;

[0022] calculating the product of the phase current amplitude and the second reliability coefficient to obtain a first starting value.

[0023] According to the technical scheme provided in the application, the preset threshold value is determined according to the following steps:

[0024] acquire a third reliability coefficient, a self-starting coefficient, a return coefficient and a maximum load current flowing through the protected line;

[0025] multiply the third reliability coefficient, the self-starting coefficient and the maximum load current flowing through the protected line to obtain a first correction value;

[0026] divide the first correction value by the return coefficient to obtain a preset threshold value.

[0027] According to the technical scheme provided in the application, the second phase difference between the fault phase is determined according to the first phase difference, and specifically includes the following steps:

[0028] acquire an initial phase angle of the pre-fault phase-to-phase current phasor;

[0029] take the absolute value of the difference between the first phase difference and the initial phase angle as the second phase difference between the fault phase.

[0030] According to the technical scheme provided in the application, the method further includes the following steps:

[0031] acquire a zero-sequence current in real time;

[0032] when the value of the preset multiple of the zero-sequence current is greater than a second starting value, trigger the protection device to act to isolate the fault line.

[0033] According to the technical scheme provided in the application, the method further includes the following steps:

[0034] monitor the communication condition in real time, and if the communication condition has a communication delay for a preset time length or a packet loss rate exceeds a preset fault tolerance rate, use a sliding time window to calculate the harmonic distortion rate and waveform mutation of the local fault phase-to-phase current;

[0035] if the harmonic distortion rate is greater than a preset distortion rate and the waveform mutation is greater than a preset mutation, determine that it is an abnormal fault, and trigger a tripping action.

[0036] In a second aspect, the application provides an active power distribution network differential protection system based on phase-to-phase current, which includes:

[0037] a data acquisition module, which is used to acquire three-phase current in real time;

[0038] The data processing module is configured to: when a phase current mutation corresponding to the three-phase current is greater than a first starting value, determine a phase-to-phase short-circuit fault type according to a size relationship between the three-phase current and a preset threshold value; when the phase-to-phase short-circuit fault type is a two-phase phase-to-phase short-circuit fault or a three-phase phase-to-phase short-circuit fault, obtain a pre-fault phase-to-phase current steady-state phase quantity and a post-fault phase-to-phase current steady-state phase quantity; determine a first phase difference and a phase quantity amplitude corresponding to the first phase difference according to the pre-fault phase-to-phase current steady-state phase quantity and the post-fault phase-to-phase current steady-state phase quantity; determine a second phase difference between fault phases according to the first phase difference; obtain a first reliable coefficient and an adaptive braking coefficient, and calculate an action quantity and a braking quantity according to the first reliable coefficient, the adaptive braking coefficient, the phase quantity amplitude and the second phase difference; the data processing module is further configured to repeatedly perform the calculation process of the action quantity and the braking quantity to obtain the action quantity and the braking quantity at multiple time points, and if the action quantities of a continuous preset group are all greater than the braking quantity, it is determined that an in-zone fault occurs, and a protection device is triggered to act to isolate a fault line.

[0039] According to the technical scheme provided in the application, the data processing module is further configured to determine an amplitude factor according to the phase quantity amplitude.

[0040] Based on an exponential function and a logarithmic function, a plurality of amplitude and angle factors are constructed according to the amplitude factor and the second phase difference.

[0041] An allowance is obtained, and a result obtained by dividing a sum of the allowance and a minimum value of the amplitude and angle factors by a sum of the minimum value of the amplitude and angle factors and the allowance is taken as an adaptive parameter.

[0042] The reciprocal of the adaptive parameter is taken as the adaptive braking coefficient.

[0043] According to the technical scheme provided in the application, the data acquisition module is further configured to, after triggering the protection device to act, monitor a running state of the power distribution network in real time.

[0044] The data processing module is further configured to, if the running state meets a preset reconstruction condition, send a reconstruction instruction to a switching device and send a pairing instruction to the protection device; the reconstruction instruction is used to instruct the switching device to switch an on-off state, and the pairing instruction is used to instruct the protection device to establish data interaction with a corresponding end after topology reconstruction.

[0045] According to the technical scheme provided in the application, the data processing module is further configured to obtain a phase current amplitude of a previous filtering period and a second reliable coefficient.

[0046] The product of the phase current amplitude and the second reliable coefficient is calculated to obtain the first starting value.

[0047] According to the technical scheme provided in the application, the data processing module is further configured to obtain a third reliability coefficient, a self-starting coefficient, a return coefficient, and a maximum load current flowing through the protected line;

[0048] The product of the third reliability coefficient, the self-starting coefficient, and the maximum load current flowing through the protected line is taken as a first correction value;

[0049] The result obtained by dividing the first correction value by the return coefficient is taken as a preset threshold value.

[0050] According to the technical scheme provided in the application, the data processing module is further configured to obtain an initial phase angle of a pre-fault inter-phase current phasor;

[0051] The absolute value of the difference between the first phase difference and the initial phase angle is taken as a second phase difference of the fault phase inter-phase.

[0052] According to the technical scheme provided in the application, the data acquisition module is further configured to acquire a zero sequence current in real time;

[0053] The data processing module is further configured to trigger the protection device to act when the value of the preset multiple of the zero sequence current is greater than a second starting value, so as to isolate the fault line.

[0054] In a third aspect, the application provides an electronic device, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the active power distribution network differential protection method based on inter-phase current as described above when executing the computer program.

[0055] From the above technical scheme, the application has at least the following beneficial effects:

[0056] The application provides an active power distribution network differential protection method based on inter-phase current, comprising: collecting three-phase currents in real time; when the corresponding phase current mutation of the three-phase current is greater than a first starting value, determining the inter-phase short-circuit fault type according to the size relationship between the three-phase current and a preset threshold value; when the inter-phase short-circuit fault type is two-phase inter-phase short-circuit fault or three-phase inter-phase short-circuit fault, obtaining the pre-fault inter-phase current steady-state phase and the post-fault inter-phase current steady-state phase; determining the first phase difference of the fault phase and the phase amplitude corresponding to the first phase difference according to the pre-fault inter-phase current steady-state phase and the post-fault inter-phase current steady-state phase; determining the second phase difference between the fault phases according to the first phase difference; obtaining the first reliable coefficient and the adaptive braking coefficient, and calculating the action quantity and the braking quantity according to the first reliable coefficient, the adaptive braking coefficient, the phase amplitude and the second phase difference; repeating the above steps to obtain the action quantity and the braking quantity at multiple time points, and if the action quantity of a continuous preset group is greater than the braking quantity, it is determined that it is an internal fault, and the protection device is triggered to act to isolate the fault line.

[0057] The application relies on real-time current collection and multi-dimensional parameter calculation to construct a precise fault discrimination mechanism, and realizes reliable triggering of the protection device by dynamically comparing the action quantity and the braking quantity. Specifically, whether an inter-phase short-circuit fault occurs is determined according to the size relationship between the phase current mutation and the first starting value, and the inter-phase short-circuit fault type is further subdivided according to the relationship between the three-phase current and the preset threshold value, which not only ensures the timeliness of the preliminary fault determination, but also lays a foundation for subsequent targeted calculation. In the fault component and phase difference calculation link, the fault characteristic parameters are accurately captured through the difference and phase analysis of the pre-fault and post-fault inter-phase current steady-state phases, and the first reliable coefficient and the adaptive braking coefficient are introduced to dynamically amplify the difference between internal and external faults, so that the calculation of the action quantity and the braking quantity can adapt to different fault scenarios, and the protection sensitivity and system reliability are significantly improved. Then, the action quantity and the braking quantity at multiple time points are obtained by repeated calculation, and the action quantity of a continuous preset group being greater than the braking quantity is used as the standard for determining the internal fault, which effectively avoids misjudgment caused by single data error and ensures the accuracy of the fault discrimination result. Finally, the protection device is triggered to isolate the fault line, which can quickly cut off the fault source, reduce the influence of the fault on other areas of the active power distribution network, reduce the power outage range and economic loss, and is suitable for fault protection scenarios of various active power distribution networks. BRIEF DESCRIPTION OF DRAWINGS

[0058] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments made with reference to the accompanying drawings.

[0059] Figure 1 The flowchart of the active power distribution network differential protection method based on inter-phase current.

[0060] Figure 2Flow chart for determining adaptive braking coefficient.

[0061] Figure 3 Structure diagram for active power distribution network differential protection system based on phase-to-phase current.

[0062] Figure 4 Result diagram of measured fault phase-to-phase current of protection when data is not synchronized.

[0063] Figure 5 Result diagram of measured fault phase-to-phase current amplitude of protection when data is not synchronized.

[0064] Figure 6 Result diagram of measured fault phase-to-phase current phase of protection when data is not synchronized.

[0065] Figure 7 Fault phase-to-phase short-circuit current phasor diagram measured by protection when data is not synchronized.

[0066] Figure 8 Topological schematic diagram before automatic reconstruction of power distribution network.

[0067] Figure 9 Topological schematic diagram after automatic reconstruction of power distribution network.

[0068] Figure 10 Structure diagram of power grid line with distributed power supply accessing inside the protected line.

[0069] Figure 11 Structure diagram of power grid line with distributed power supply accessing downstream of the protected line.

[0070] Figure 12 Structure diagram of electronic device.

[0071] In the figure, the reference signs are as follows: 1, data acquisition module; 2, data processing module; 500, electronic device; 501, CPU; 502, ROM; 503, RAM; 504, bus; 505, I / O interface; 506, input part; 507, output part; 508, storage part; 509, communication part; 510, driver; 511, detachable medium. DETAILED DESCRIPTION

[0072] The application will be further described below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0073] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0074] For the sake of clear and concise description of the following embodiments, first give a brief introduction of related technology:

[0075] The automatic reconfiguration technology changes the power supply path and topology of the power grid dynamically through remote operation of switches, which fundamentally destroys the two cornerstones on which the stage current protection (represented by three-stage protection) relies for normal operation, namely the fixed short-circuit current level and the preset upstream and downstream coordination relationship. The stage protection relies on the current value and action time pre-set for each circuit breaker, forming a selective protection ladder with step-by-step coordination. When the automatic reconfiguration changes the network topology, the length and equivalent impedance of the line change, causing the short-circuit current value at the same location to deviate from the original setting value, which may cause protection failure or misoperation. More importantly, the reconfiguration completely disrupts the original upstream and downstream logical relationship between circuit breakers, and there is no corresponding coordination value between the new upstream and downstream protections, losing the ability of selective tripping, and a fault can easily trigger multiple circuit breakers to trip out of order, thereby significantly increasing the risk of protection mismatch and power outage range.

[0076] The traditional fault direction detection and short-circuit current calculation model is based on the assumption that the power source in the power grid is a traditional rotating synchronous generator. Rotating synchronous generators will provide a short-circuit current with a huge amplitude (several times the rated current), stable characteristics and mainly at the power frequency when a fault occurs. Photovoltaic, wind power and other new energy sources are connected to the grid through power electronic inverters, and their fault response characteristics are completely different. In order to protect their own equipment, the inverter will perform a low voltage ride through control strategy, actively limiting the output current to within 1.5 times the rated current. This weak, harmonic and phase-controlled fault current makes the traditional overcurrent protection and directional elements that rely on the amplitude of the power frequency current and large phase difference unable to start or judge correctly, resulting in failure or misoperation. At the same time, the traditional short-circuit current calculation method based on the synchronous machine model cannot simulate the current limiting and non-power frequency characteristics of the inverter, and the calculation result is seriously inconsistent with the actual working condition, making the protection setting value set according to it lose its significance.

[0077] Therefore, the automatic reconstruction dynamically adjusts the relative position and role of the distributed generation (DG) in the fault network while changing the physical topology of the power grid. A DG may be located downstream of the fault point before reconstruction, and its weak current has little effect on the upstream protection. After reconstruction, it may become upstream of the fault point, and the injected current, although limited in amplitude, has an abnormal phase, which can pollute the measurement value of the upstream protection, either raising the current to cause overcurrent protection misoperation or causing the directional discrimination element to fail due to the abnormal phase. Therefore, the two failure mechanisms of value mismatch caused by topology change and directional discrimination failure caused by DG power characteristics are triggered simultaneously and superimposed during the reconstruction process, making the protection system face an unprecedented complex situation, and the traditional principle completely loses reliability in this dynamic and active distribution network.

[0078] Therefore, the automatic reconstruction dynamically adjusts the relative position and role of the distributed generation (DG) in the fault network while changing the physical topology of the power grid. A DG may be located downstream of the fault point before reconstruction, and its weak current has little effect on the upstream protection. After reconstruction, it may become upstream of the fault point, and the injected current, although limited in amplitude, has an abnormal phase, which can pollute the measurement value of the upstream protection, either raising the current to cause overcurrent protection misoperation or causing the directional discrimination element to fail due to the abnormal phase. Therefore, the two failure mechanisms of value mismatch caused by topology change and directional discrimination failure caused by DG power characteristics are triggered simultaneously and superimposed during the reconstruction process, making the protection system face an unprecedented complex situation, and the traditional principle completely loses reliability in this dynamic and active distribution network.

[0079] In order to make the active distribution network differential protection method based on inter-phase current provided by the embodiments of the present application more clear and easy to understand, the method will be introduced below in combination with the drawings. As shown in the drawings, the drawings are flowcharts of the active distribution network differential protection method based on inter-phase current provided by the embodiments of the present application, and the method comprises the following steps. Figure 1

[0080] S100, real-time acquisition of three-phase current, when the phase current corresponding to the three-phase current is greater than the first starting value, the type of inter-phase short-circuit fault is determined according to the size relationship between the three-phase current and the preset threshold value. ​

[0081] Three-phase current refers to the continuous measurement of the A, B, and C phase currents on a line by a protection device through a current transformer (CT). Phase A current is the current flowing through the A phase line in a three-phase line, phase B current is the current flowing through the B phase line, and phase C current is the current flowing through the C phase line. All three are currents formed by the directional movement of charge in the corresponding phase lines.

[0082] The phase current surge is used to reflect the degree of drastic instantaneous change in current. Phase current surge = - ;in, The phase current amplitude is calculated based on the current sampling. This represents the phase current amplitude of the previous filtering cycle. For example, the filtering cycle should be 20ms for a full-cycle filtering algorithm and 10ms for a half-cycle filtering algorithm.

[0083] Specifically, the first startup value is determined according to the following steps:

[0084] Obtain the phase current amplitude and the second reliability coefficient of the previous filtering cycle;

[0085] The first starting value is obtained by multiplying the phase current amplitude and the second reliability coefficient.

[0086] Wherein, the first startup value = Here, The second reliability coefficient, The phase current amplitude of the previous filtering cycle is used; the second reliability coefficient is, for example, 0.3.

[0087] To ensure the reliability of protection under various disturbances to the system, the first activation value is set by multiplying the amplitude of each phase current during normal system operation by a second reliability coefficient. The first activation value serves as a threshold for the protection device's activation criterion; its purpose is to prevent frequent false starts due to normal, minor current fluctuations. When the sudden change in phase current exceeds the first activation value, the protection device considers a system fault to have occurred and initiates subsequent fault analysis procedures. If the sudden change in phase current is less than or equal to the first activation value, the criterion is not activated, and the line operates normally.

[0088] When the sudden change in phase current exceeds the first starting value, a phase-to-phase short-circuit fault is determined to have occurred. At this time, the currents of phases A, B, and C in the three phases are compared with preset threshold values. If any phase current exceeds the preset threshold value, that phase is faulty. The phase-to-phase short-circuit fault type is then determined based on the number of faulty phases. If there are no faulty phases, the three-phase current is collected again. If there are two faulty phases, the phase-to-phase short-circuit fault type is a two-phase phase-to-phase short-circuit fault. If there are three faulty phases, the phase-to-phase short-circuit fault type is a three-phase phase-to-phase short-circuit fault.

[0089] There is no case that one faulty phase is judged as phase-to-phase short circuit, which is mainly caused by the physical nature of the fault and the selective configuration of the protection. The definition of phase-to-phase short circuit is the direct short circuit between two or three different phase conductors, whose fault current loop does not flow into the ground. Therefore, to form a phase-to-phase short circuit, at least two phases need to be connected by a low impedance path, which inevitably leads to a sharp increase in the current of at least two phases. If it is monitored that the current of only one phase abnormally increases, it is physically analyzed that the phase current must have found another discharge path, which is most likely the ground, i.e. a single-phase ground fault occurs. If this happens, the current fault analysis program is exited, and the zero sequence current differential protection scheme or the zero sequence overvoltage protection scheme can be used to isolate the faulty line. Here, the zero sequence current differential protection scheme or the zero sequence overvoltage protection scheme is a technology known to those skilled in the art, and will not be described in detail.

[0090] Further, the preset threshold value is determined according to the following steps:

[0091] The third reliability coefficient, the self-starting coefficient, the return coefficient and the maximum load current flowing through the protected line are obtained;

[0092] The product of the third reliability coefficient, the self-starting coefficient and the maximum load current flowing through the protected line is taken as the first correction value;

[0093] The result obtained by dividing the first correction value by the return coefficient is taken as the preset threshold value.

[0094] The preset threshold value can be calculated by the following formula:

[0095] ;

[0096] The preset threshold value is The third reliability coefficient is The self-starting coefficient is The maximum load current flowing through the protected line is The return coefficient is

[0097] The value of the third reliability coefficient is greater than 1; in order to avoid the influence of the factors such as the actual starting value of the current relay may be less than the setting value, the calculation error of short-circuit current, the short-circuit current using the secondary transient current and not taking into account the decay of non-periodic components, the value range of the third reliability coefficient is for example 1.15-1.25. The value of the self-starting coefficient is greater than 1, and its specific value can be determined by the specific wiring of the network and the nature of the load. The value of the return coefficient is less than 1, in order to avoid the vibration of the protection in the action critical situation due to the instability of the short-circuit current, the value range of the return coefficient is for example 0.85-0.95.

[0098] Compared with the traditional differential current composed of the positive sequence components of the currents on both sides of the protected line, the application uses the phase-to-phase current on both sides of the protected line as a component of the differential current and the braking current when a phase-to-phase short-circuit fault occurs, and is less affected by the distributed power supply connected internally and externally to the protected line under the phase-to-phase short-circuit fault condition. Specifically, when a phase-to-phase short-circuit fault occurs upstream of the distributed power supply, the differential current can effectively eliminate the influence of the distributed power supply; when a phase-to-phase short-circuit fault occurs downstream of the distributed power supply, the differential current can significantly reduce the influence of the distributed power supply. Therefore, the application can ensure that the protection correctly operates under an internal fault and does not operate under an external fault.

[0099] S200, when the phase-to-phase short-circuit fault type is a two-phase phase-to-phase short-circuit fault or a three-phase phase-to-phase short-circuit fault, obtaining the corresponding pre-fault phase-to-phase current steady-state phasor and post-fault phase-to-phase current steady-state phasor.

[0100] If the judgment is a BC phase fault, the BC phase-to-phase current is concerned; if it is a three-phase fault, two phases are optionally concerned, such as the AB phase, i.e. the AB phase-to-phase current is concerned. The steady-state phasor refers to the fundamental sine wave of 50 Hz extracted from the original instantaneous sampling value by the protection device using the Fourier algorithm, etc. The steady-state phasor contains amplitude and phase information, which is called a phasor. This step filters out the non-periodic components and high-order harmonics in the fault current, making the calculation more accurate. Before and after the fault refers to the device continuously recording and updating a pre-fault steady-state phasor, which is usually the data of one cycle before the fault is started. After the fault occurs, the post-fault steady-state phasor is calculated. These two phasors are the cornerstone of all subsequent calculations.

[0101] Taking a BC two-phase phase-to-phase short-circuit fault as an example, the pre-fault local BC two-phase phase current steady-state phasor and the pre-fault opposite end BC two-phase phase current steady-state phasor are obtained according to the following formula:

[0102] ;

[0103] ;

[0104] wherein, is the post-fault local BC two-phase phase current steady-state phasor, is the B-phase current phasor measured by the first protection device on one side of the line, is the C-phase current phasor measured by the first protection device on one side of the line, is the post-fault opposite end BC two-phase phase current steady-state phasor, is the B-phase current phasor measured by the second protection device on the opposite side of the first protection device, is the C-phase current phasor measured by the second protection device on the opposite side of the first protection device.

[0105] S300, determining the first phase difference of the fault phase and the phase quantity amplitude corresponding to the first phase difference according to the pre-fault inter-phase current steady-state phase quantity and the post-fault inter-phase current steady-state phase quantity.

[0106] Wherein, the first phase difference of the fault phase includes the phase difference between the local end inter-phase current fault component and the pre-fault inter-phase current and the phase difference between the opposite end inter-phase current fault component and the pre-fault inter-phase current.

[0107] Taking the BC two-phase inter-phase short-circuit fault as an example, based on the fault phase inter-phase current phase quantity before and after the fault, the phase difference between the local end inter-phase current fault component and the pre-fault inter-phase current and the phase difference between the opposite end inter-phase current fault component and the pre-fault inter-phase current are calculated according to the following formula:

[0108] ;

[0109] ;

[0110] Wherein, is the phase difference between the local end inter-phase current fault component and the pre-fault inter-phase current, is the phase difference between the opposite end inter-phase current fault component and the pre-fault inter-phase current, is the post-fault local end BC two-phase phase current steady-state phase quantity, is the post-fault opposite end BC two-phase phase current steady-state phase quantity, is the pre-fault local end inter-phase current steady-state phase quantity, is the pre-fault opposite end inter-phase current steady-state phase quantity.

[0111] In order to verify the synchronization error resistance of the method, a time delay is set in the measuring device on one side of the line, and the difference between the measured electrical quantity information before and after the time delay is observed. When a two-phase inter-phase short-circuit fault occurs at 0.8s, the protection measurement information of one side of the line is shown in Figure 4 , Figure 5 and Figure 6 , and the measured phase quantity information is shown in Figure 7 . In the figure, , are the pre-fault and post-fault current steady-state values measured by the protection without synchronization error, , are the pre-fault and post-fault current steady-state values measured by the protection with 90° synchronization error.

[0112] From Figure 4 , Figure 5 and Figure 6It can be seen that at this time, taking unilateral 90° synchronization error as an example, the fault phase-to-phase current fault steady-state amplitude is the same before and after the synchronization error is set, and the fault phase-to-phase current fault steady-state phase difference is large, so directly using the fault steady-state phase quantity will have a large error. It can be seen that without synchronization error, the first fault component Figure 7 is equal to the first phase of the current steady-state value of the protection measurement after the fault without synchronization error, and the second fault component is equal to the second phase of the current steady-state value of the protection measurement after the fault with 90° synchronization error, so the method is not affected by the synchronization error.

[0113] In order to increase the sensitivity of the scheme, increase the difference between the differential protection action and the braking amount when the fault is in the area, the application changes the traditional current differential protection which directly uses the current phase quantity at both ends of the line to construct the action criterion, and instead uses the amplitude and phase of the fault phase-to-phase current phase quantity at both ends to construct the action quantity.

[0114] Taking BC two-phase-to-phase short-circuit fault as an example, each end calculates the corresponding phase quantity amplitude according to the steady-state phase quantity of the local BC two-phase current after the fault , the steady-state phase quantity of the opposite end BC two-phase current after the fault , , ; wherein, is the corresponding phase quantity amplitude of the steady-state phase quantity of the local BC two-phase current after the fault , is the corresponding phase quantity amplitude of the steady-state phase quantity of the opposite end BC two-phase current after the fault .

[0115] S400, according to the first phase difference, determine the second phase difference between the fault phase-to-phase.

[0116] This step specifically includes:

[0117] Obtain the initial phase angle of the pre-fault phase-to-phase current phase quantity;

[0118] The absolute value of the difference between the first phase difference and the initial phase angle is taken as the second phase difference between the fault phase-to-phase.

[0119] Wherein, the initial phase angle is 180°. Taking BC two-phase-to-phase short-circuit fault as an example, the phase of both ends is exchanged, and the second phase difference between the fault phase-to-phase is obtained according to the following formula:

[0120] ;

[0121] Wherein,​​​ a second phase difference between the fault phase and a second phase, a phase difference between the fault component of the inter-phase current at the local end and the inter-phase current before the fault, a phase difference between the fault component of the inter-phase current at the remote end and the inter-phase current before the fault, the first phase difference of the fault phase including the phase difference between the fault component of the inter-phase current at the local end and the inter-phase current before the fault and the phase difference between the fault component of the inter-phase current at the remote end and the inter-phase current before the fault.

[0122] The information exchanged by the communication device of the application only includes the amplitude of the inter-phase current of the fault phase at both sides of the protected line and the phase of the steady-state phasor difference before and after the fault, which is obtained only by the local information of the protection measurement, without increasing the communication data volume, both of which are numerical values rather than time-tagged sequences, requiring less communication volume and having low requirements for data synchronization.

[0123] S500, obtaining a first reliability coefficient and an adaptive braking coefficient, and calculating an action quantity and a braking quantity according to the first reliability coefficient, the adaptive braking coefficient, the phasor amplitude and the second phase difference.

[0124] The action quantity is used to represent the fault feature strength, and the braking quantity is used to represent the reliability quantity for preventing misoperation. The first reliability coefficient is used to improve the reliability of the action quantity. For example, the first reliability coefficient is . The adaptive braking coefficient changes with the current amplitude and the phase difference, and its value is greater than zero.

[0125] The action quantity and the braking quantity are calculated according to the following formula:

[0126]

[0127]

[0128] wherein, the action quantity is the braking quantity is a second phase difference between the fault phase and a second phase, a steady-state phasor of the BC two-phase phase current at the local end after the fault corresponding phasor amplitude, a steady-state phasor of the BC two-phase phase current at the remote end after the fault corresponding phasor amplitude, a first reliability coefficient, an adaptive braking coefficient.

[0129] Further, as shown in Figure 2 , the adaptive braking coefficient is determined according to the following steps:

[0130] S501, determining an amplitude factor according to the phasor amplitude.

[0131] ​​To overcome the problem that the braking amount gradually increases with the increase of the angle between the line current and the fault component current when the angle is less than 90° <180°, and the influence of the system automatic reconstruction strategy on the protection criterion, an adaptive braking coefficient is set as an adaptive parameter varying with the amplitude and phase of the line current at both ends. First, an amplitude factor is constructed based on the characteristics of the fault-phase current amplitude at both ends of the line to perform the first step of differentiation between internal and external faults, amplify the amplitude change in the internal and external fault characteristics, and make it change with the line parameter change caused by automatic reconstruction.

[0132] The amplitude factor is obtained according to the following formula:

[0133] ;

[0134] wherein, is the amplitude factor, is the steady-state phasor of the BC two-phase current at the local end after the fault corresponding to the phasor amplitude, is the steady-state phasor of the BC two-phase current at the opposite end after the fault corresponding to the phasor amplitude.

[0135] When the line is in normal operation or an external fault occurs, and the amplitude difference is 0, so that is equal to 0; when an internal fault occurs in the line, the fault occurs in the protection zone, which will destroy the distribution of the line current, at this time and the amplitude difference is a non-zero value, resulting in calculated to satisfy 0 <1.

[0136] S502, based on the exponential function and the logarithmic function, an amplitude and phase angle factor is constructed according to the amplitude factor and the second phase difference.

[0137] To accurately distinguish between internal and external faults, an amplitude and phase angle factor based on the fault-phase phasor amplitude and the phase difference is further constructed, which combines the exponential function values of the amplitude factor and the cosine value of 0.5 times the second phase difference between the fault phases , integrates the two variables into the exponential function and the natural logarithmic function which can sensitively respond to variable changes, and then constructs after multiplication and summation. The expression of the amplitude and phase angle factor is as follows:

[0138] ; ​

[0139] wherein, is an amplitude-phase factor, is a second phase difference between fault phases, is an amplitude factor.

[0140] iff is equal to 180° and is equal to 0, is 0; when and any of the variables does not satisfy the above conditions, is greater than 0. In an ideal condition, the minimum value of is 0. Therefore, the amplitude-phase factor will be more sensitive to in-zone faults.

[0141] S503, obtain a margin, divide the sum of the margin and the minimum value of the amplitude-phase factor by the sum of the minimum value of the amplitude-phase factor and the margin, and take the result as the adaptive parameter.

[0142] Due to the existence of the automatic reconstruction strategy, the topology of the system may change, and the relative positions of the distributed power supply and the protection also change. Figure 10 is a power grid line structure diagram in which the distributed power supply is connected inside the protected line, Figure 10 CB0, CB1, CB2 in are circuit breakers in different positions, f 1, f 2, f 3 are possible fault points, which are set in different positions to simulate and analyze the influence on the detection ability of the protection device when the fault occurs upstream, downstream or on the same line of the distributed power supply. Figure 10 A, B, C in respectively represent three-phase line identifiers. Figure 11 is a power grid line structure diagram in which the distributed power supply is connected downstream of the protected line, Figure 11 in f 4, f 5 are possible fault points, which are set in different positions to simulate and analyze the influence on the detection ability of the protection device when the fault occurs upstream, downstream or on the same line of the distributed power supply. Figure 11 A, B in respectively represent two-phase line identifiers.

[0143] When the distributed power supply is connected inside the protected line, as shown in Figure 10 , it affects the amplitude difference of the current on both sides of the line when an inter-phase fault occurs, and may cause the amplitude difference of the current on both sides of the line to decrease under in-zone fault conditions; when the distributed power supply is connected outside the protected line, as shown in Figure 11As shown, it mainly affects the phase difference of the line current on both sides when the phase-to-phase fault occurs, and may cause the phase difference of the line current on both sides to deviate from 180° when the fault occurs in the area. The occurrence of the two distributed power sources caused by the automatic reconstruction strategy will affect the judgment of the differential protection criterion for internal and external faults.

[0144] Therefore, the present application further combines the amplitude and phase angle factors before and after the fault The adaptive braking coefficient is constructed, and when the relative position of the line and the distributed power source changes due to different reconstruction strategies, the amplitude and phase angle factors before the fault The minimum value obtained can fully reflect the amplitude and phase characteristics of the current on both sides of the line during normal operation.

[0145] In order to significantly amplify the difference between internal and external faults of the protected line, and at the same time minimize the impact of the automatic reconstruction strategy of the active distribution network on the differential protection criterion, the adaptive parameter is normalized to form the adaptive parameter , and after each automatic reconstruction strategy is implemented, the adaptive parameter , and are recalculated to reduce the error caused by the change of the line data to the adaptive parameter. The adaptive parameter is calculated according to the following formula:

[0146] ;

[0147] wherein, is the adaptive parameter, is the amplitude and phase angle factor, is the margin. The margin is used to prevent the denominator and the adaptive parameter from being 0, and can be 10 -3 .

[0148] According to the foregoing analysis, is always infinitely close to 180° and infinitely close to 0 when the minimum value of the amplitude and phase angle factor is obtained . Therefore, can always be obtained under normal working conditions (before the fault in the area). And, and will change with the change of the automatic reconstruction strategy of the system, so that the adaptive parameter calculated thereby can effectively adapt to the change of the line parameter and ensure the applicability of the braking coefficient.

[0149] S504, the reciprocal of the adaptive parameter is taken as the adaptive braking coefficient.

[0150] According to the characteristics of the adaptive parameter designed in the foregoing, the adaptive braking coefficient is set as:

[0151] ;

[0152] wherein, is the adaptive braking coefficient, is the adaptive parameter.

[0153] In an ideal condition, when a fault occurs outside the protection zone of the line, is equal to 1, so that is also equal to 1. When a fault occurs inside the protection zone of the line, the value of will become very large, so that will correspondingly become very small. Therefore, when a fault occurs outside the protection zone of the line, the braking current can be maintained at a high level; when a fault occurs inside the protection zone of the line, the value of the braking current will become very small. On this basis, the sensitivity, reliability and adaptability to different line parameters of the line differential protection can be improved.

[0154] S600, repeat the above steps to obtain the action quantity and the braking quantity at multiple moments, if the action quantities of a continuous preset group are all greater than the braking quantity, it is determined that an internal fault occurs, and the protection device is triggered to act to isolate the fault line.

[0155] Here, the preset group is, for example, 3 groups. When the action quantities of the continuous 3 groups are all greater than the braking quantity, it is finally determined that an internal fault occurs, which can effectively avoid the transient process caused by temporary calculation fluctuation, interference or circuit breaker operation, greatly improving the reliability and safety of the protection. Once it is confirmed that an internal fault occurs, the protection device immediately sends a trip signal to drive the circuit breaker to open, thereby isolating the fault line segment and ensuring normal power supply of the non-fault area.

[0156] The application converts the traditional differential protection relying on high-speed synchronous sampling data into exchange of scalar information calculated locally, effectively solving the synchronization and communication bottleneck; at the same time, by focusing on the inter-phase current and introducing the adaptive braking coefficient, the interference brought by the new energy grid connection is effectively resisted, and reliable protection in the high-dynamic active distribution network is realized.

[0157] Further, the method further comprises the following steps:

[0158] After triggering the protection device to act, the running state of the distribution network is monitored in real time;

[0159] If the running state meets the preset reconstruction condition, a reconstruction instruction is sent to the switching device, and a pairing instruction is sent to the protection device; the reconstruction instruction is used to instruct the switching device to switch the on-off state, and the pairing instruction is used to instruct the protection device to establish data interaction with the corresponding end after topology reconstruction.

[0160] It should be noted that the operating state of the power distribution network at least includes whether the area originally supplied by the fault line is in load power shortage, whether other lines are overloaded, whether the output of the inverter distributed power source (photovoltaic, wind power) changes, whether the operating current of the remaining normal lines, and whether the voltage is within the safety threshold, the current on-off state of the inter-station tie switch.

[0161] The preset reconstruction condition is a trigger rule configured in advance by the power distribution network automation master station, for example, load power shortage and / or line overload. When the preset reconstruction condition is met, a reconstruction instruction and a matching instruction are generated; the reconstruction instruction is used to instruct the switching device to switch on or off, thereby controlling the adjustment of the physical structure of the power grid topology, realizing load transfer or power reconnection; the matching instruction is used to instruct the protection device to establish data interaction with the corresponding end after the topology reconstruction, to ensure that the protection of the two ends of the new line can establish data interaction after the topology reconstruction, and realize longitudinal differential protection. Here, the reconstruction instruction and the matching instruction must be generated and sent synchronously to avoid the empty window period when the topology has been reconstructed but the protection has not been matched. If only the reconstruction instruction is executed, the new line has no corresponding differential protection, and once a fault occurs, it cannot be quickly isolated; if only the matching instruction is executed, the protection device is matched, but there is no corresponding topology support, which may lead to incorrect protection criterion calculation.

[0162] In addition, the topology reconstruction mode of the active power distribution network is formulated and perfected by the power distribution automation master station in advance, and each topology reconstruction mode is equipped with a corresponding protection matching scheme. When the master station issues a topology reconstruction instruction, it also issues a new matching instruction for each protection, to ensure that each line of each topology realizes longitudinal differential protection.

[0163] When the automatic reconstruction strategy causes the mutual connection between the lines of the power distribution network to change, the protection at both ends of the line of the power distribution network after automatic reconstruction needs to be matched, and differential protection is used to protect the line after reconstruction. Figure 8 The topology diagram before the automatic reconstruction of the power distribution network is shown in Figure 8 The tie points AB and CA in the figure represent inter-station or inter-section tie switches, which are used to realize load transfer between different power sources or lines; A1 line and A2 line represent different power supply line numbers; A11, A12, and A13 belong to A1 line, and A21, A22, and A23 belong to A2 line. CB1-CB7 represent circuit breakers at different positions, which are used for line protection and control, and cooperate to realize differential protection matching. As shown in Figure 8 Before the implementation of the automatic reconstruction strategy, the tie point AA in the station is not connected, and the power supply of the A12 and A13 lines is realized by the A11 line connecting to the A station, as shown in Figure 8CB1, CB2 cooperate to realize the double-ended differential protection of the line A11, A12, and CB1, CB6 cooperate to realize the double-ended differential protection of the line A11, A13. Similarly, the power supply of the line A22, A23 is realized by the A21 line accessing the A station, as shown in the right side of the line in the figure Figure 8 CB4, CB5 cooperate to realize the double-ended differential protection of the line A21, A22, and CB4, CB7 cooperate to realize the double-ended differential protection of the line A21, A23.

[0164] When the automatic reconstruction strategy is triggered, the load transfer can cause the line topology to change, and the line A12, A13 is connected with the line A23 through the in-station interconnection point AA and is disconnected with the line A11, as shown in the figure Figure 9 All protections in the system will be paired according to the automatic reconstruction strategy of the system. In this case, the power supply of the line A12, A13 is realized by the line A21, A23 accessing the A station, as shown in the line in the figure Figure 9 At this time, CB1 and CB2 are paired to realize the double-ended differential protection of the line A11, and CB3 and CB6 are paired to realize the double-ended differential protection of the line A12, A13, and the protection mode of the line A21, A22 and A23 remains unchanged before the automatic reconstruction strategy is triggered, to ensure the reliability of the power supply of each line after the automatic reconstruction strategy is triggered.

[0165] In addition, the present application considers the line length change caused by the automatic reconstruction of the distribution network and the change of the distributed power access point. When the topology structure of the distribution network changes due to the automatic reconstruction strategy of the power grid and the relative position of the distributed power changes, the present application can effectively act, can adapt to the line fault when the distributed power access point is located inside or outside the protected line, and has wide applicability.

[0166] Further, the method further comprises the following steps:

[0167] Real-time acquisition of zero sequence current;

[0168] When the value of the preset multiple of the zero sequence current is greater than the second starting value, the protection device is triggered to act to isolate the fault line.

[0169] The preset multiple is, for example, three times. In a three-phase alternating current distribution network, the fault types are mainly divided into phase-to-phase short circuit faults and ground faults, such as BC two-phase short circuit and three-phase short circuit, and single-phase grounding and two-phase grounding. The current scheme triggers the corresponding protection scheme by monitoring the zero sequence current, makes up for the insufficient coverage of the foregoing differential protection based on the phase-to-phase current for the ground fault, and forms a complete protection system for phase-to-phase faults and ground faults.

[0170] Specifically, the zero sequence current is collected in real time while the three-phase current is collected in real time, in normal operation, the three-phase current is symmetrical, and the zero sequence current is approximately 0; when a ground fault occurs, the symmetry of the three-phase current is destroyed, and the zero sequence component appears, and the more serious the ground fault, the greater the zero sequence current amplitude. When the three times of the zero sequence current is greater than the second starting value, it is determined that a ground fault occurs, and a zero sequence current differential protection scheme or a zero sequence overvoltage protection scheme is executed to isolate the fault line. Here, the zero sequence current differential protection scheme or the zero sequence overvoltage protection scheme is a technology known to those skilled in the art, and will not be described in detail.

[0171] In addition, the second starting value described above is ;

[0172] wherein, is a fourth reliability coefficient, for example, 1.2; is the maximum unbalanced zero sequence current in the normal operation system, the value of which is determined by the line, for example, the maximum unbalanced zero sequence currents of overhead lines and cable lines are about 0.37A and 0.26A, respectively.

[0173] Further, the method further comprises the following steps:

[0174] Real-time monitoring of communication conditions, if the communication delay of the communication condition is greater than the preset time length or the packet loss rate exceeds the preset fault tolerance rate, the sliding time window is used to calculate the harmonic distortion rate and the waveform mutation of the local fault phase interphase current;

[0175] If the harmonic distortion rate is greater than the preset distortion rate and the waveform mutation is greater than the preset mutation, it is determined that an abnormal fault occurs, and a trip action is triggered.

[0176] Here, the communication condition at least includes the communication time length and the communication packet loss rate. The harmonic distortion rate is used to measure the degree of deviation of the current waveform from the sine wave, which will significantly increase due to the response of power electronic equipment in the event of a fault. The waveform mutation is used to measure the degree of mutation of the current in a short time, which will far exceed the normal range due to the sudden increase of the current amplitude in the event of a fault. The preset time length, the preset fault tolerance rate, the preset distortion rate and the preset mutation are all set according to the actual situation.

[0177] First, the communication condition of the protection device at both ends of the line is monitored in real time, if the delay is greater than the preset time length or the packet loss rate exceeds the preset fault tolerance rate, the backup protection is started immediately; secondly, the local fault phase interphase current data is intercepted by using the sliding time window, the fundamental wave and the harmonic are decomposed by fast Fourier transform (FFT), the harmonic distortion rate is calculated, and the waveform mutation is obtained by comparing the current instantaneous value of the current window with the previous window; finally, the double index and logic are used to determine the fault, only when the harmonic distortion rate is greater than the preset distortion rate and the waveform mutation is greater than the preset mutation, it is determined that an abnormal fault occurs, and a trip action is triggered.

[0178] The scheme can cover the communication failure scene, make up for the defects of traditional differential protection relying on communication, and still reliably identify faults through local data even if the main protection fails due to fiber interruption, electromagnetic interference and the like, so as to avoid fault expansion; and adapt to new power grid features, and use harmonic distortion rate and waveform mutation as criteria in view of the characteristics of more harmonics and waveform distortion when the inverter type distributed power source fails, so that the scheme is more suitable for the fault characteristics of new energy distribution network than the traditional current amplitude criterion; the first feature calculation is completed within 40 ms after the fault through the sliding time window, and the logic avoids single index misjudgment, such as excluding normal harmonic overproof or load mutation interference, so as to realize the balance between rapid tripping and accurate protection, and provide double security for new energy high penetration and topology frequent change distribution network.

[0179] In order to further improve the adaptability and reliability of the scheme of the application after the automatic reconstruction of the distribution network, the influence of the protection pairing scheme change under different topological structures on the protection criterion is considered. Specifically, when the distribution automation master station issues an instruction to change the power grid topology and re-pairs the protection devices at both ends of the line, the data processing module 2 also executes the following adaptive parameter optimization process:

[0180] The distribution automation master station pre-configures a corresponding set of reference parameters for each possible topological reconstruction scheme and corresponding protection pairing scheme. The reference parameter set at least includes the typical minimum value reference of the amplitude and phase angle factor of the line under normal operation and the recommended reference value of the margin under the topological working condition; when the distribution automation master station confirms that the new protection pairing relationship takes effect, it will issue the reference parameter set corresponding to the new pairing scheme to the related protection devices. The protection devices receive and load the new reference parameter set as the initial reference for calculating adaptive parameters, replacing the parameter settings before reconstruction, so as to quickly adapt to the new network structure.

[0181] During a short learning period after the topological reconstruction is completed, for example, several power frequency periods, the protection device continuously monitors and calculates the actual amplitude and phase angle factor under the premise that the line is in normal operation. The data processing module 2 compares the actual value calculated in real time with the expected reference value issued by the distribution automation master station. If a significant and continuous deviation is found between the two, it is determined that the pre-stored reference parameters do not completely match the actual electrical characteristics under the new working condition. At this time, the data processing module 2 will start the parameter fine-tuning program, and use the weighted smoothing algorithm to slowly integrate the actual value calculated in real time into the reference parameters, so as to online fine-tune the minimum reference of the amplitude and phase angle factor and the margin reference, so that the calculation of adaptive parameters can more accurately reflect the true characteristics of the current line.

[0182] After the online fine-tuning is completed, the protection device will use the optimized new parameter set to calculate the adaptive braking coefficient until the next topology reconstruction occurs; this process ensures that the main parameters of the differential protection criterion can be dynamically optimized to follow changes in the power grid topology and protection pairing relationship, effectively avoiding the problem of reduced protection performance caused by fixed parameters that cannot adapt to all operating modes, and significantly improving the overall reliability of the system under dynamic operating conditions.

[0183] By introducing the adaptive parameter optimization process, the differential protection method not only can cope with topology changes, but also can actively adapt to the changed electrical characteristics, which is an important part of realizing high-reliability protection for active distribution networks.

[0184] As shown in Figure 3 The present application provides an active distribution network differential protection system based on inter-phase current, comprising:

[0185] A data acquisition module 1, the data acquisition module 1 is used for real-time acquisition of three-phase current;

[0186] A data processing module 2, the data processing module 2 is used for determining the inter-phase short-circuit fault type according to the size relationship between the three-phase current and the preset threshold value when the phase current abruptness corresponding to the three-phase current is greater than the first starting value; obtaining the corresponding pre-fault inter-phase current steady-state phasor and post-fault inter-phase current steady-state phasor when the inter-phase short-circuit fault type is two-phase inter-phase short-circuit fault or three-phase inter-phase short-circuit fault; determining the first phase difference and the phasor amplitude corresponding to the first phase difference according to the pre-fault inter-phase current steady-state phasor and the post-fault inter-phase current steady-state phasor; determining the second phase difference of the fault phase inter-phase according to the first phase difference; obtaining the first reliable coefficient and the adaptive braking coefficient, and calculating the action quantity and the braking quantity according to the first reliable coefficient, the adaptive braking coefficient, the phasor amplitude and the second phase difference; the data processing module 2 is also used for repeatedly executing the calculation process of the action quantity and the braking quantity to obtain the action quantity and the braking quantity at multiple time points, and if the action quantity of the continuous preset group is greater than the braking quantity, it is determined as an internal fault, and the protection device is triggered to act to isolate the fault line.

[0187] The system converts the traditional differential protection relying on high-speed synchronous sampling data into local scalar information exchange, effectively solving the synchronization and communication bottleneck; at the same time, by focusing on the inter-phase current and introducing the adaptive braking coefficient, the interference brought by the grid-connected new energy is effectively resisted, and reliable protection in the high-dynamic active distribution network is realized.

[0188] The present application provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the active distribution network differential protection method based on inter-phase current as described in the above embodiments.

[0189] Among them, such as Figure 12 As shown, the electronic device 500 includes a CPU 501, which can perform various appropriate actions and processes according to a program stored in ROM 502 or a program loaded from storage section 508 into RAM 503.

[0190] RAM 503 also stores various programs and data required for system operation. CPU 501, ROM 502, and RAM 503 are interconnected via bus 504. I / O interface 505 is also connected to bus 504.

[0191] The following components are connected to I / O interface 505: an input section 506 including a keyboard, mouse, etc.; an output section 507 including a cathode ray tube (CRT), liquid crystal display (LCD), etc., and speakers, etc.; a storage section 508 including a hard disk, etc.; and a communication section 509 including a network interface card such as a LAN card, modem, etc. The communication section 509 performs communication processing via a network such as the Internet. A drive 510 is also connected to I / O interface 505 as needed. A removable medium 511, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., is installed on drive 510 as needed so that computer programs read from it can be installed into storage section 508 as needed.

[0192] Specifically, according to embodiments of this application, the above reference flow Figure 1 The described process can be implemented as a computer software program.

[0193] For example, this application includes a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network via communication section 509, and / or installed from removable medium 511. When the computer program is executed by CPU 501, it performs the functions defined in the system of this application.

[0194] It should be noted that the computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium or any combination thereof. The computer-readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a computer-readable storage medium can include, but are not limited to, the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a RAM (Random Access Memory), a ROM (Read-Only Memory), an erasable programmable ROM (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0195] In this application, a computer readable storage medium can be any tangible medium that can retain, store, or maintain the program for use by or in connection with an instruction execution system, apparatus, or device. In this application, a computer readable signal medium can include a computer readable program code, propagated by any means, including but not limited to wireless, wire line, optical fiber, RF, etc. The computer readable medium discussed in this application can be transitory or non-transitory computer readable medium.

[0196] The flow diagrams and the block diagrams in the drawings are illustrations of the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flow diagrams or block diagrams can represent a module, a segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

[0197] It also should be noted that in some alternative implementations, the functions noted in the blocks can occur in a different order than that described in the figures. For example, two blocks noted in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustrations, and combinations thereof, can be implemented by special purpose hardware-based systems that perform the specified functions or operations, or combinations of special purpose hardware and computer instructions.

[0198] The units described in the embodiments of the present application can be implemented in the form of software, or can be implemented in the form of hardware, and the described units can also be arranged in a processor. In some cases, the names of the units do not constitute a limitation on the units themselves. The described units or modules can also be arranged in a processor.

[0199] The above description is merely the preferred embodiments of the present application and the explanation of the technical principles used. It should be understood by those skilled in the art that the scope of the application disclosed in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by the combinations of the above technical features or equivalent features without departing from the inventive concept. For example, the technical solutions formed by the mutual replacement of the above features and the technical features disclosed in the present application (but not limited to) having similar functions.

Claims

1. An active power distribution network differential protection method based on interphase current, characterized in that, The method comprises the following steps: Real-time acquisition of three-phase currents, when the corresponding phase current mutation of the three-phase currents is greater than a first starting value, determining the phase-to-phase short-circuit fault type according to the size relationship between the three-phase currents and a preset threshold value; When the phase-to-phase short-circuit fault type is a two-phase phase-to-phase short-circuit fault or a three-phase phase-to-phase short-circuit fault, obtaining the pre-fault phase-to-phase current steady-state phase sequence and the post-fault phase-to-phase current steady-state phase sequence; According to the pre-fault phase-to-phase current steady-state phase sequence and the post-fault phase-to-phase current steady-state phase sequence, determining the first phase difference of the fault phase and the phase sequence amplitude corresponding to the first phase difference; According to the first phase difference, determining the second phase difference between the fault phases; Obtaining a first reliable coefficient and an adaptive braking coefficient, and calculating the action amount and the braking amount according to the first reliable coefficient, the adaptive braking coefficient, the phase sequence amplitude and the second phase difference; Repeating the above steps to obtain the action amount and the braking amount at multiple time points, if the action amount of a continuous preset group is greater than the braking amount, it is determined that it is an intra-zone fault, and the protection device is triggered to act to isolate the fault line; The adaptive braking coefficient is determined according to the following steps: According to the phase sequence amplitude, determining an amplitude factor; Based on the exponential function and the logarithmic function, constructing a plurality of amplitude phase angle factors according to the amplitude factor and the second phase difference; Obtaining a margin, and taking the result obtained by dividing the sum of the margin and the minimum value of the amplitude phase angle factor by the sum of the minimum value of the amplitude phase angle factor and the margin as an adaptive parameter; Taking the reciprocal of the adaptive parameter as the adaptive braking coefficient; According to the first phase difference, determining the second phase difference between the fault phases, specifically comprising the following steps: Obtaining the initial phase angle of the pre-fault phase-to-phase current phase sequence; Taking the absolute value of the difference between the first phase difference and the initial phase angle as the second phase difference between the fault phases.

2. A method for phase current based active power distribution network differential protection as claimed in claim 1 wherein, The method further comprises the following steps: After triggering the protection device to act, real-time monitoring of the operating state of the power distribution network; If the operating state meets the preset reconstruction condition, a reconstruction instruction is sent to the switch device, and a matching instruction is sent to the protection device; the reconstruction instruction is used to instruct the switch device to switch the on-off state, and the matching instruction is used to instruct the protection device to establish data interaction with the corresponding end after topology reconstruction.

3. The method of claim 1, wherein the method is characterized by: The first starting value is determined according to the following steps: Obtaining the phase current amplitude of the previous filtering period and a second reliable coefficient; Calculating the product of the phase current amplitude and the second reliable coefficient to obtain the first starting value.

4. The method of claim 1, wherein the method is based on interphase current of the power distribution network. The preset threshold value is determined according to the following steps: Obtaining a third reliable coefficient, a self-starting coefficient, a return coefficient and a maximum load current flowing through the protected line; Taking the product of the third reliable coefficient, the self-starting coefficient and the maximum load current flowing through the protected line as a first correction value; Taking the result obtained by dividing the first correction value by the return coefficient as the preset threshold value.

5. The method of claim 1, wherein the method is based on interphase current of the power distribution network. The method further comprises the following steps: Real-time acquisition of zero sequence currents; When the value of the preset multiple of the zero sequence current is greater than a second starting value, the protection device is triggered to act to isolate the fault line.

6. The method of claim 1, wherein the method is based on interphase current of the power distribution network. The method further comprises the following steps: Real-time monitoring of communication, if the communication exists communication delay preset length or packet loss rate exceeds the preset fault tolerance, then use the sliding time window, calculate the local fault phase intercurrent harmonic distortion rate and waveform mutation; If the harmonic distortion rate is greater than the preset distortion rate and the waveform mutation is greater than the preset mutation, it is determined as an abnormal fault, and a trip action is triggered.

7. An active power distribution network differential protection system based on interphase current, characterized by, Comprise: Data acquisition module, the data acquisition module is used for real-time acquisition three-phase current; Data processing module, the data processing module is used for when the phase current corresponding to the three-phase current mutation is greater than the first starting value, according to the size relation of the three-phase current and the preset threshold value, the type of phase-to-phase short circuit fault is determined;When the phase-to-phase short circuit fault type is two-phase phase-to-phase short circuit fault or three-phase phase-to-phase short circuit fault, the corresponding pre-fault phase-to-phase current steady-state phase and post-fault phase-to-phase current steady-state phase are obtained;According to the pre-fault phase-to-phase current steady-state phase and the post-fault phase-to-phase current steady-state phase, the first phase difference and the phase quantity amplitude corresponding to the first phase difference are determined; According to the first phase difference, the second phase difference of the fault phase is determined; Get the first reliable coefficient and the adaptive braking coefficient, and according to the first reliable coefficient, the adaptive braking coefficient, the phase quantity amplitude and the second phase difference, the action quantity and the braking quantity are calculated;The data processing module is also used for repeatedly executing the calculation process of the action quantity and the braking quantity to obtain the action quantity and the braking quantity at multiple times, if the action quantity of the continuous preset group is greater than the braking quantity, it is determined as an intra-zone fault, and the protection device is triggered to act to isolate the fault line; Wherein, the data processing module is also used for determining the amplitude factor according to the phase quantity amplitude;Based on the exponential function and the logarithmic function, according to the amplitude factor and the second phase difference, a plurality of amplitude angle factors are constructed;Get the margin, the sum of the margin and the minimum value of the amplitude angle factor divided by the sum of the minimum value of the amplitude angle factor and the margin is used as the adaptive parameter;The reciprocal of the adaptive parameter is used as the adaptive braking coefficient; The data processing module is also used for obtaining the initial phase angle of the pre-fault phase-to-phase current phase quantity;The absolute value of the difference between the first phase difference and the initial phase angle is used as the second phase difference of the fault phase.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, The processor executes the computer program to realize the steps of the phase-to-phase current based active power distribution network differential protection method in any one of claims 1 to 6.

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