An alternating current line protection method, system, storage medium and electronic device

Abstract

The application discloses an alternating current line protection method and system, a storage medium and an electronic device. The method comprises the following steps: acquiring a power grid fault type; when the fault type indicates that a symmetric fault occurs in the power grid, acquiring phase voltage measurement values and phase current measurement values of any phase of a line measurement point, performing coordinate transformation to acquire phase voltage components and phase current components, judging whether the phase voltage components and the phase current components satisfy a first preset criterion, and when the first preset criterion is satisfied, determining that an in-zone fault occurs and a protection action is performed; if none of the first preset criterion is satisfied, it is determined that an out-of-zone fault occurs and the protection action is not performed; when the fault type indicates that an asymmetric fault occurs in the power grid, acquiring line voltage measurement values and line current measurement values of any two phases of the line measurement point, performing coordinate transformation to acquire line voltage components and line current components, judging whether the line voltage components and the line current components satisfy a second preset criterion, and when the second preset criterion is satisfied, the protection action is performed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system protection, and more particularly, to a protection method and system for an alternating current line, a storage medium, and an electronic device. BACKGROUND

[0002] Safe operation is an important foundation and prerequisite for building a new power system, and relay protection is crucial as the "first line of defense" for safe and stable operation. However, in the new power system, power electronic devices such as new energy power sources and flexible DC converter stations have completely changed the system fault characteristics, and the traditional backup relay protection principle relying on synchronous power source characteristics is threatened. The main manifestations are as follows: after the power grid fails, power electronic devices will quickly change control strategies and related parameters, the fault current, voltage and sequence component characteristics are quite different from traditional synchronous motor systems, the amplitude is limited, the phase angle is controlled, and other characteristics result in a serious decline in protection reliability.

[0003] To adapt to the fault characteristics of new power systems, the research on the distance protection of the outgoing line of the new energy station has made certain progress. In view of the problem of large calculation error of power frequency impedance, some scholars based on digital low-pass filtering and fault point voltage reconstruction proposed a differential equation solving algorithm for iterative calculation of fault distance, constructed a distance protection scheme suitable for the outgoing line of the wind farm and carried out simulation verification. Some scholars analyzed the fault transient voltage of the doubly-fed wind turbine, and based on the difference coefficient of the memory voltage drop and the actual voltage drop under different fault conditions, proposed a time-domain distance protection algorithm that can still quickly identify the fault direction under zero voltage fault condition. The calculation accuracy of the above time-domain distance protection scheme is not affected in theory by the fault current characteristics of new energy, and it can be well applied to new energy outgoing lines. However, the above related schemes do not fully consider the model error caused by the neglect of distributed capacitance in the concentrated parameter model of the line, that is, they do not analyze the adaptability of the time-domain distance protection to the length of the transmission line. With the continuous expansion of the scale of new energy in China, the consumption of new energy through ultra-high voltage and long-distance transmission has gradually become a reality, so the error caused by neglecting the distributed capacitance of the line will become more and more important. Some scholars pointed out that due to the constantly changing measured impedance trajectory, distance protection cannot be used as a remote backup for lower-level lines. At the same time, the literature proposes an improved permissive pilot protection strategy to solve this problem. Some scholars allow the distance protection at the station side to delay action, and let the system side circuit breaker trip first, at which time the weak feedback effect disappears and the distance protection at the station side can act correctly, but this method increases the fault isolation time. In addition, some scholars change the setting value of the power frequency variation distance protection to prevent the protection from malfunctioning when the reverse direction fault occurs under the condition that the back impedance is capacitive, but the impedance characteristics of new energy change with factors such as control strategy and fault condition, so the method of modifying the setting value is difficult to apply to new energy outgoing lines.

[0004] Therefore, based on the above analysis, it can be seen that the existing distance protection for new energy outgoing lines needs to be improved. Therefore, it is necessary to develop a new protection principle with good performance.

[0005] Therefore, a new protection method for alternating current lines is needed. SUMMARY

[0006] The present application provides an alternating current line protection method, system, storage medium and electronic device to solve the problem of how to efficiently protect alternating current lines.

[0007] In order to solve the above problems, according to one aspect of the present application, an alternating current line protection method is provided, the method comprising:

[0008] acquiring a fault type of a power grid;

[0009] when the fault type indicates that the power grid has a symmetric fault, acquiring phase voltage measurement values and phase current measurement values of any phase of a line measurement point, performing coordinate transformation on the phase voltage measurement values and phase current measurement values to acquire phase voltage components and phase current components, judging whether the phase voltage components and phase current components satisfy a first preset criterion, and when the first preset criterion is satisfied, determining that it is an in-zone fault and performing protection; if none of them is satisfied, determining that it is an out-of-zone fault and not performing protection;

[0010] when the fault type indicates that the power grid has an asymmetric fault, acquiring line voltage measurement values and line current measurement values of any two phases of a line measurement point, performing coordinate transformation on the line voltage measurement values and line current measurement values to acquire line voltage components and line current components, judging whether the line voltage components and line current components satisfy a second preset criterion, and when the second preset criterion is satisfied, performing protection.

[0011] Preferably, wherein the coordinate transformation on the phase voltage measurement values and phase current measurement values to acquire phase voltage components and phase current components comprises:

[0012] acquiring the phase voltage measurement values as d-axis components in a d-axis reference coordinate system with the phase voltage phase of the any phase as the d-axis reference coordinate system, as the phase voltage components;

[0013] acquiring the phase current measurement values as d-axis components in a d-axis reference coordinate system with the phase current phase of the any phase as the d-axis reference coordinate system, as the phase current components.

[0014] Preferably, wherein judging whether the phase voltage components and phase current components satisfy the first preset criterion, and when the first preset criterion is satisfied, performing protection, comprises:

[0015] judging whether the phase voltage components and phase current components satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, determining that it is an in-zone fault and performing protection; if none of them is satisfied, determining that it is an out-of-zone fault and not performing protection;

[0016] wherein, u d is the phase voltage component; I d is the phase current component; R set is a first preset setting value; X set is a second preset setting value; θ1 is a phase angle difference of the phase voltage measurement values and the phase current measurement values.

[0017] Preferably, wherein the coordinate transformation on the line voltage measurement values and line current measurement values to acquire line voltage components and line current components comprises:

[0018] the line voltage measurement value is taken as a d-axis component in a d-axis reference coordinate system with the phase-to-phase voltage phase of the arbitrary two phases as the d-axis reference coordinate system, as a line voltage component;

[0019] the line current measurement value is taken as a d-axis component in a d-axis reference coordinate system with the phase-to-phase current phase of the arbitrary two phases as the d-axis reference coordinate system, as a line current component.

[0020] Preferably, the line voltage component and the line current component are judged whether to satisfy the second preset criterion, and when the second preset criterion is satisfied, the protection action includes:

[0021] the phase voltage component and the phase current component are judged whether to satisfy a third preset sub-criterion or a fourth preset sub-criterion and when the third preset sub-criterion or the fourth preset sub-criterion is satisfied, it is determined as an internal fault, and the protection action is performed; if neither is satisfied, it is determined as an external fault, and the protection action is not performed.

[0022] wherein u dX is the line voltage component; I dX is the line current component; R set is the first preset setting value; X set is the second preset setting value; and θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

[0023] According to another aspect of the present application, there is provided a protection system for an AC line, the system comprising:

[0024] a fault type acquisition unit, configured to acquire a power grid fault type;

[0025] a first protection unit, configured to, when the fault type indicates that the power grid has a symmetrical fault, acquire a phase voltage measurement value and a phase current measurement value of an arbitrary phase at a line measurement point, perform coordinate transformation on the phase voltage measurement value and the phase current measurement value to acquire a phase voltage component and a phase current component, judge whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, determine an internal fault and perform a protection action; if neither is satisfied, determine an external fault and not perform the protection action.

[0026] a second protection unit, configured to, when the fault type indicates that the power grid has an asymmetrical fault, acquire a line voltage measurement value and a line current measurement value of an arbitrary two phases at the line measurement point, perform coordinate transformation on the line voltage measurement value and the line current measurement value to acquire a line voltage component and a line current component, judge whether the line voltage component and the line current component satisfy a second preset criterion, and when the second preset criterion is satisfied, perform a protection action.

[0027] Preferably, the first protection unit, in order to obtain the phase voltage component and the phase current component, performs coordinate transformation on the phase voltage measurement and the phase current measurement, comprising:

[0028] obtaining the phase voltage measurement as a d-axis component in a d-axis reference coordinate system with the phase voltage phase of the any phase as the d-axis reference;

[0029] obtaining the phase current measurement as a d-axis component in a d-axis reference coordinate system with the phase current phase of the any phase as the d-axis reference.

[0030] Preferably, the first protection unit, in order to determine whether the phase voltage component and the phase current component satisfy the first preset criterion, and when the first preset criterion is satisfied, performing the protection action, comprising:

[0031] determining whether the phase voltage component and the phase current component satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, determining as an internal fault, and performing the protection action; if neither is satisfied, determining as an external fault, and not performing the protection action;

[0032] wherein, u d is the phase voltage component; I d is the phase current component; R set is the first preset setting value; X set is the second preset setting value; and θ1 is the phase angle difference between the phase voltage measurement and the phase current measurement.

[0033] Preferably, the second protection unit, in order to obtain the line voltage component and the line current component, performs coordinate transformation on the line voltage measurement and the line current measurement, comprising:

[0034] obtaining the line voltage measurement as a d-axis component in a d-axis reference coordinate system with the phase-to-phase voltage phase of the any two phases as the d-axis reference;

[0035] obtaining the line current measurement as a d-axis component in a d-axis reference coordinate system with the phase-to-phase current phase of the any two phases as the d-axis reference.

[0036] Preferably, the second protection unit, in order to determine whether the line voltage component and the line current component satisfy the second preset criterion, and when the second preset criterion is satisfied, performing the protection action, comprising:

[0037] determining whether the phase voltage component and the phase current component satisfy a third preset sub-criterion or a fourth preset sub-criterion When the third preset sub-criterion or the fourth preset sub-criterion is satisfied, the fault is determined as an intra-zone fault, and the protection is operated; if neither of the two is satisfied, the fault is determined as an extra-zone fault, and the protection is not operated.

[0038] wherein, u dX is a line voltage component; I dX is a line current component; R set is a first preset setting value; X set is a second preset setting value; and θ2 is a phase angle difference between the line voltage measurement value and the line current measurement value.

[0039] Based on another aspect of the present application, the present application provides a computer readable storage medium having a computer program stored thereon, the program being executed by a processor to implement the steps of any one of the protection methods for an AC line.

[0040] Based on another aspect of the present application, the present application provides an electronic device comprising:

[0041] the computer readable storage medium described above; and

[0042] one or more processors configured to execute the program in the computer readable storage medium.

[0043] The present application provides a protection method, system, storage medium and electronic device for an AC line, the method comprising: obtaining a power grid fault type; when the fault type indicates that a symmetric fault occurs in the power grid, obtaining a phase voltage measurement value and a phase current measurement value of any phase at a line measurement point, performing coordinate transformation on the phase voltage measurement value and the phase current measurement value to obtain a phase voltage component and a phase current component, determining whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, determining that the fault is an intra-zone fault and the protection is operated; if neither of the two is satisfied, determining that the fault is an extra-zone fault and the protection is not operated; when the fault type indicates that an asymmetric fault occurs in the power grid, obtaining a line voltage measurement value and a line current measurement value of any two phases at the line measurement point, performing coordinate transformation on the line voltage measurement value and the line current measurement value to obtain a line voltage component and a line current component, determining whether the line voltage component and the line current component satisfy a second preset criterion, and when the second preset criterion is satisfied, the protection is operated. The method of the present application is suitable for various scenarios of new energy power supply access and sending, has high reliability, has important engineering significance for future high-proportion new energy power electronic system, and can provide premise and guarantee for further development of high-proportion new energy power electronic system in the future. BRIEF DESCRIPTION OF DRAWINGS

[0044] The exemplary embodiments of the present application can be more completely understood in reference to the following drawings:

[0045] Figure 1Flow chart of the protection method 100 for AC line according to the embodiment of the present application;

[0046] Figure 2 Schematic diagram of the simulation verification model of the protection principle PSCAD according to the embodiment of the present application;

[0047] Figure 3 Schematic diagram of the simulation result of the fault voltage and current dq components at 5km according to the embodiment of the present application;

[0048] Figure 4 Schematic diagram of the simulation result of the R, X at the fault at 5km according to the embodiment of the present application;

[0049] Figure 5 Schematic diagram of the simulation result of the voltage and current dq components at the external fault according to the embodiment of the present application;

[0050] Figure 6 Schematic diagram of the simulation result of the R, X at the fault at 100km according to the embodiment of the present application;

[0051] Figure 7 Schematic diagram of the structure of the protection system 700 for AC line according to the embodiment of the present application. DETAILED DESCRIPTION

[0052] Reference will now be made to the exemplary embodiments of the present application with reference to the accompanying drawings, however, the present application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art. The terminology used in the description of the exemplary embodiments presented herein is not intended to be limiting in scope, but is intended to be illustrative of the present application. In the drawings, like numerals refer to like elements through.

[0053] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

[0054] New energy power supply, flexible DC converter station and other power electronic devices have completely changed the system fault characteristics. The traditional backup relay protection principle relying on the characteristics of synchronous power supply is threatened, mainly reflected in that: after the power grid fails, the power electronic device will quickly change the control strategy and related parameters, the fault current, voltage and sequence component characteristics are greatly different from the traditional synchronous motor system, the amplitude is limited, the phase angle is controlled, and other characteristics cause the protection reliability to seriously decrease. Therefore, the present application provides a new principle of AC line protection based on decoupling of electrical quantities, and provides an AC line protection method, which is mainly characterized by cutting in from the perspective of new energy control system, rotating coordinate system transformation (dq0 transformation) of the measured current and voltage of the outgoing line, then using the correlation between active power, reactive power and line parameters to form a protection principle, and realizing reliable judgment and distinction between internal and external faults. The method only uses local measurement information, solves the problem of traditional power frequency distance protection caused by limited amplitude, non-power frequency, controlled phase angle, unstable internal impedance after new energy failure, and the problems of refusal and misoperation.

[0055] Figure 1 A flowchart of the AC line protection method 100 according to the embodiment of the present application. As shown in Figure 1 The AC line protection method provided by the embodiment of the present application is suitable for a variety of new energy power supply access to outgoing scenes, has high reliability, has important engineering significance for future high proportion of new energy consumption and safe operation of power grid, and can provide premise and protection for further development of high proportion of new energy power electronic system in the future. The AC line protection method 100 provided by the embodiment of the present application starts from step 101, in step 101, the type of power grid fault is obtained.

[0056] In step 102, when the fault type indicates that a symmetrical fault occurs in the power grid, the phase voltage measurement value and the phase current measurement value of any phase of the line measurement point are obtained, the phase voltage measurement value and the phase current measurement value are coordinate transformed to obtain phase voltage components and phase current components, whether the phase voltage components and the phase current components satisfy a first preset criterion is judged, and when the first preset criterion is satisfied, a protection action is performed.

[0057] Preferably, wherein the coordinate transformation of the phase voltage measurement value and the phase current measurement value to obtain the phase voltage component and the phase current component comprises:

[0058] The phase voltage measurement value is obtained as a d-axis component in a d-axis reference coordinate system with the phase voltage phase of the any phase as the d-axis reference coordinate system, as the phase voltage component;

[0059] The phase current measurement value is obtained as a d-axis component in a d-axis reference coordinate system with the phase current phase of the any phase as the d-axis reference coordinate system, as the phase current component.

[0060] Preferably, the method comprises judging whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, the protection action comprises:

[0061] judging whether the phase voltage component and the phase current component satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, determining that the fault is an internal fault, and the protection action is performed; if neither of the first preset sub-criterion and the second preset sub-criterion is satisfied, determining that the fault is an external fault, and the protection action is not performed.

[0062] wherein u d is the phase voltage component; I d is the phase current component; R set is a first preset setting value; X set is a second preset setting value; and θ1 is a phase angle difference between the measured phase voltage and the measured phase current.

[0063] When a symmetrical fault occurs in the power grid, the new energy is usually controlled by power decoupling to realize low-voltage ride through, that is, the active and reactive power outputs of the new energy power supply during the fault are determined by the control system. Therefore, from the perspective of the control system, the measured current and voltage can be transformed in the rotating coordinate system (dq0 transformation), and then the correlation between the active power, the reactive power and the line parameters is used to form the protection principle. Therefore, according to the instantaneous power balance, the active power can be:

[0064]

[0065] wherein u d , i d are the measured phase voltage and the measured phase current of the line measurement point, respectively, and the d-axis component in the d-axis reference coordinate system with the phase voltage phase of any phase as the reference coordinate system. I d is the measured phase current of the line measurement point, and the d-axis component in the d-axis reference coordinate system with the phase current phase of phase A as the reference coordinate system; R represents the resistance component of the line impedance, that is, R can be expressed as:

[0066]

[0067] Therefore, in the rotating coordinate system, i d = I d cosθ, and θ is the phase angle difference between the measured voltage and the measured current of the line measurement point, so it can be simplified as:

[0068]

[0069] When the system is in normal operation, θ is the power factor angle, i.e. R is very large, which can be regarded as the resistance component of the load impedance when the system is in normal operation. When a fault occurs in the forward protection range, then 0≤R≤R set set =0.8×R1, which is the protection I segment value. R1 is the positive sequence resistance value of the whole length of the protected line, i.e. after the fault, it can be expressed as:

[0070]

[0071] Simplifying, the first preset protection sub-criterion can be obtained:

[0072]

[0073] Similarly, the reactive power under symmetrical fault can be:

[0074]

[0075] i q is the q-axis component of the measured phase current of the line measurement point in the d-axis reference coordinate system with the A-phase voltage phase as the reference, and I d is the d-axis component of the measured phase current of the line measurement point in the d-axis reference coordinate system with the A-phase current phase as the reference. X represents the reactance component of the line impedance, i.e. X can be expressed as:

[0076]

[0077] Therefore, in the rotating coordinate system, i q =I d sinθ, and θ is the phase angle difference between the measured voltage and the measured current of the line measurement point, so it can be simplified as:

[0078]

[0079] When the system is in normal operation, θ can be understood as the power factor angle, i.e. X is very large, which can be regarded as the reactance component of the load impedance when the system is in normal operation. When a fault occurs in the forward protection range, then 0≤X≤X set . X set =0.8×X1, which is the protection I segment value. X1 is the positive sequence reactance value of the whole length of the protected line, i.e. after the fault, it can be expressed as:

[0080]

[0081] Simplifying, the second preset protection sub-criterion can be obtained:

[0082]

[0083] ​Therefore, in the application, when the fault type indicates that a symmetrical fault occurs in the power grid, firstly, phase voltage measurement values and phase current measurement values of any phase of a line measurement point are obtained; then, the phase voltage measurement values and the phase current measurement values are subjected to coordinate transformation to obtain a d-axis component of the phase voltage measurement values under a d-axis reference coordinate system with a phase voltage phase of the any phase as the d-axis reference coordinate system, as a phase voltage component, and to obtain a d-axis component of the phase current measurement values under the d-axis reference coordinate system with a phase current phase of the any phase as the d-axis reference coordinate system, as a phase current component; finally, it is judged whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, a protection action is performed. Specifically, it includes judging whether the phase voltage component and the phase current component satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, it is determined that an in-zone fault occurs, and the protection action is performed; otherwise, if neither of the first preset sub-criterion and the second preset sub-criterion is satisfied, it is determined that an out-of-zone fault occurs, and the protection action is not performed.

[0084] In step 103, when the fault type indicates that an asymmetrical fault occurs in the power grid, line voltage measurement values and line current measurement values of any two phases of a line measurement point are obtained, the line voltage measurement values and the line current measurement values are subjected to coordinate transformation to obtain line voltage components and line current components, it is judged whether the line voltage components and the line current components satisfy a second preset criterion, and when the second preset criterion is satisfied, a protection action is performed.

[0085] Preferably, the coordinate transformation of the line voltage measurement values and the line current measurement values to obtain the line voltage components and the line current components includes:

[0086] obtaining a d-axis component of the line voltage measurement values under a d-axis reference coordinate system with an inter-phase voltage phase of the any two phases as the d-axis reference coordinate system, as a line voltage component;

[0087] obtaining a d-axis component of the line current measurement values under the d-axis reference coordinate system with an inter-phase current phase of the any two phases as the d-axis reference coordinate system, as a line current component.

[0088] Preferably, the judgment of whether the line voltage components and the line current components satisfy the second preset criterion and the protection action performed when the second preset criterion is satisfied include:

[0089] judging whether the phase voltage component and the phase current component satisfy a third preset sub-criterion or a fourth preset sub-criterion and when the third preset sub-criterion or the fourth preset sub-criterion is satisfied, it is determined that an in-zone fault occurs, and the protection action is performed; otherwise, if neither of the third preset sub-criterion and the fourth preset sub-criterion is satisfied, it is determined that an out-of-zone fault occurs, and the protection action is not performed.

[0090] wherein, u dX is a line voltage component; I dXis the line current component; R set is the first preset setting value; X set is the second preset setting value; θ2is the phase angle difference of the line voltage measurement value and the line current measurement value.

[0091] When the power grid has an asymmetric fault, there are frequency multiplication components after direct dq0 transformation, which is not applicable to distance protection construction, so a virtual rotating coordinate system method is proposed to re-construct a spatial rotating symmetric system to facilitate dq0 transformation, that is, the method of virtual construction is used for calculation under asymmetric fault. The line voltage (current) of the line measurement point is taken as the reference to construct three-phase symmetric systems, that is, there are three groups of three-phase symmetric components in the calculation process, and the instantaneous value functions of the voltage and the current can be respectively:

[0092]

[0093] In the formula, * represents a virtual phase, U and I represent the amplitude of the function, cos is the cosine function, w represents the angular frequency, t represents time, and φ represents the phase angle difference. Therefore, U m = U mab = U mbc = U mca , I m = I mab = I mbc = I mca From the formula, it can be seen that the frequency multiplication component is eliminated at this time, and the energy conservation is still satisfied. Therefore, according to the instantaneous power balance, the active power and the reactive power under asymmetric fault can be:

[0094]

[0095]

[0096] In the calculation process, three groups of symmetric components are calculated respectively due to the existence of the virtual phase. Therefore, i dX may be the d-axis component of the two-phase current difference (i.e., the line current) of the line measurement point under the d-axis reference coordinate system with the AB, BC, or CA phase-to-phase voltage phase as the reference. u dX may be the d-axis component of the line voltage of the line measurement point under the d-axis reference coordinate system with the AB, BC, or CA phase-to-phase voltage phase as the reference. i qX may be the q-axis component of the two-phase current difference (i.e., the line current) of the line measurement point under the d-axis reference coordinate system with the AB, BC, or CA phase-to-phase voltage phase as the reference. Therefore, I dX may be the d-axis component of the two-phase current difference (i.e., the line current) of the line measurement point under the d-axis reference coordinate system with the AB, BC, or CA phase-to-phase current phase as the reference. That is, R, X can be expressed as:

[0097]

[0098] Therefore, in the rotating coordinate system, i dX = I dX cos θ, i qX = I dX sin θ, θ is the phase angle difference between the measured voltage (line voltage) and the measured current of the line measurement point, so it can be simplified as:

[0099]

[0100] During normal operation, θ can be understood as the power factor angle, that is, R is large, which can be regarded as the resistance component of the load impedance during normal operation of the system. X is large, which can be regarded as the reactance component of the load impedance during normal operation of the system.

[0101] When a fault occurs in the forward protection range, then 0≤R≤R set , 0≤X≤X set . Wherein the I section fixed value R set = 0.8×R1, R1 is the positive sequence resistance value of the full length of the protected line, the I section fixed value X set = 0.8×X1, X1 is the positive sequence reactance value of the full length of the protected line, that is, after the fault, it can be expressed as:

[0102]

[0103] Simplifying can obtain the third preset protection sub-criterion:

[0104]

[0105] The fourth preset protection sub-criterion can be obtained:

[0106]

[0107] Therefore, in the present application, when the fault type indicates that the power grid is subjected to an asymmetric fault, first, the line voltage measurement value and the line current measurement value of any two phases of a line measurement point are obtained; then, the line voltage measurement value and the line current measurement value are subjected to coordinate transformation, the d-axis component of the line voltage measurement value under the d-axis reference coordinate system with the phase-to-phase voltage phase of the two phases as the reference is obtained as the line voltage component, and the d-axis component of the line current measurement value under the d-axis reference coordinate system with the phase-to-phase current phase of the two phases as the reference is obtained as the line current component; finally, it is judged whether the line voltage component and the line current component satisfy the second preset criterion, and when the second preset criterion is satisfied, the protection is actuated. Specifically, it includes: judging whether the phase voltage component and the phase current component satisfy the third preset sub-criterion or the fourth preset sub-criterion When the third preset sub-criterion or the fourth preset sub-criterion is satisfied, the fault is determined as an intra-zone fault, and the protection is operated; otherwise, if neither of the two sub-criteria is satisfied, the fault is determined as an inter-zone fault, and the protection is not operated.

[0108] The method of the application performs a rotation coordinate system transformation (dq0 transformation) on the measured current and voltage of the outgoing line, and then uses the correlation between active power, reactive power and line parameters to form a protection principle and perform protection, which can be directly applied to an actual device to realize high-sensitivity and high-reliability fault discrimination.

[0109] The following specific examples illustrate the implementation of the application in the application, a simulation model is constructed as shown in Figure 2 The rated voltage U B of the outgoing line is 220 kV, the line length is 100 km, the rated capacity S B of the wind farm is 200 MVA, and the protection is installed at the beginning of the line close to the wind farm side. The line parameters are shown in Table 1, and three-phase short-circuit, two-phase short-circuit and two-phase short-circuit grounding faults are set at 5 km, 50 km and 100 km of the line respectively, and the fault type is metallic grounding. The effectiveness of the new protection principle is tested and analyzed.

[0110] Table 1 Line parameter table

[0111]

[0112] The line protection reactance value (named value) is X set =k×X1×L, wherein X1 is the line positive sequence reactance, L is the line length, L=100 km, and k is the distance I section protection range, which is 80% of the line length, k=0.8. The impedance reference value is

[0113] At this time, X set =k×X1×L=0.8×100×0.31388=25.11 Ω.

[0114] X set * (unit value)=X set / Z B =25.11 / 242=0.1038.

[0115] 1) Intra-zone fault verification

[0116] Taking the ABC three-phase short-circuit at 5 km as an example, the simulation results of the voltage and current dq components are shown in Figure 3 , and the simulation measured results of R and X are shown in Figure 4 .

[0117] According to Figure 3It can be seen that when the fault occurs at 5 km, u d Setting value:

[0118]

[0119] The actual resistance R of the line from the fault point to the measuring point is 0.0178*5 Ω=0.089 Ω, and the simulation measured value is 0.092 Ω; the actual reactance X of the line from the fault point to the measuring point is 0.31388*5 Ω=1.57 Ω, and the simulation measured value is 1.56 Ω. At this time, u d The simulation measured value is 0.007, which is less than u d The setting value is 0.113, which meets the criterion, and the protection reliably acts.

[0120] When the ABC three-phase short circuit, AB two-phase short circuit and ABG two-phase short circuit grounding occur at 5 km and 50 km respectively, u d The measured value, u d The setting value, the measured value of resistance R and reactance X, and the protection action are shown in Table 2.

[0121] Table 2 Protection action table

[0122]

[0123]

[0124] According to Table 2, the new principle of distance protection can accurately act and accurately measure the resistance R and reactance X of the line from the fault point to the protection installation when the three-phase short circuit, two-phase short circuit and two-phase short circuit grounding occur in the area.

[0125] 2) Out-of-area fault verification

[0126] Taking the fault occurring at 100 km of the line as an example, the adaptability of the protection is analyzed. The dq component simulation results of voltage and current are shown in Figure 5 The simulation measured results of R and X at 100 km are shown in Figure 6 When the ABC three-phase fault occurs at 100 km, u d Setting value:

[0127]

[0128] When the ABC three-phase short circuit fault occurs at 100 km, the actual resistance R of the line from the fault point to the measuring point is 0.0178*100 Ω=1.78 Ω, and the simulation measured value is 1.802 Ω; the actual reactance X of the line from the fault point to the measuring point is 0.31388*100 Ω=31.38 Ω, and the simulation measured value is 31.07 Ω. At this time, u d The simulation measured value is 0.139, which is greater than ud The setting value is 0.113, the fault point is outside the protection range, and the protection reliably does not act.

[0129] Similarly, when the AB two-phase short-circuit fault occurs at 100km, the actual resistance R of the line from the fault point to the measuring point is 0.0178*100Ω=1.78Ω, and the simulation measured value is 1.76Ω; the actual reactance X of the line from the fault point to the measuring point is 0.31388*100Ω=31.38Ω, and the simulation measured value is 30.08Ω. At this time, u d The simulation measured value is 0.145, which is greater than u d The setting value is 0.113, the fault point is outside the protection range, and the protection reliably does not act.

[0130] The protection method provided in the application has u d The simulation measured value is 0.145, which is greater than u d The setting value, the measured values of the resistance R and the reactance X, and the protection action are shown in Table 3. The new principle of the distance protection can reliably not act when the three-phase short-circuit fault, the two-phase short-circuit fault and the two-phase short-circuit grounding fault occur outside the range, and can accurately measure the resistance R and the reactance X of the line from the fault point to the protection installation.

[0131] Table 3 protection action table

[0132]

[0133] The method provided in the application only uses local measurement information, solves the problem that the traditional power frequency distance protection is rejected or misoperated due to the limited amplitude after the new energy fault, the non-power frequency, the controlled phase angle and the unstable internal impedance, and simulation data and recorded data prove the effectiveness of the method.

[0134] Figure 7 A schematic diagram of a protection system 700 of an alternating current line according to an embodiment of the application. As shown in the figure, the protection system 700 of the alternating current line provided by the embodiment of the application comprises a fault type acquisition unit 701, a first protection unit 702 and a second protection unit 703. Figure 7 Preferably, the fault type acquisition unit 701 is configured to acquire a power grid fault type.

[0135]

[0136] ​Preferably, the first protection unit 702 is used to acquire the phase voltage measurement value and phase current measurement value of any phase of the line measurement point when the fault type indicates that a symmetrical fault has occurred in the power grid, perform coordinate transformation on the phase voltage measurement value and phase current measurement value to obtain the phase voltage component and phase current component, determine whether the phase voltage component and phase current component meet the first preset criterion, and when the first preset criterion is met, activate the protection.

[0137] Preferably, the first protection unit 702 performs coordinate transformation on the phase voltage measurement value and the phase current measurement value to obtain the phase voltage component and the phase current component, including:

[0138] The phase voltage measurement value is obtained by taking the d-axis component of the phase voltage phase of any phase as the d-axis reference coordinate system, and using it as the phase voltage component.

[0139] The phase current measurement value is obtained by taking the d-axis component of the phase current phase of any phase as the d-axis reference coordinate system, and using it as the phase current component.

[0140] Preferably, the first protection unit 702 determines whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, performs a protection action, including:

[0141] Determine whether the phase voltage component and phase current component satisfy the first preset sub-criteria. Or the second presupposed sub-criteria If either the first or the second preset sub-criteria is met, the fault is determined to be within the zone, and the protection system operates; if neither is met, the fault is determined to be outside the zone, and the protection system does not operate.

[0142] Among them, u d For phase voltage components; I d R is the phase current component; set The first preset setting value; X set θ1 is the second preset setting value; θ1 is the phase angle difference between the measured phase voltage and the measured phase current.

[0143] Preferably, the second protection unit 703 is used to acquire the line voltage measurement value and line current measurement value of any two phases of the line measurement point when the fault type indicates that an asymmetrical fault has occurred in the power grid, perform coordinate transformation on the line voltage measurement value and line current measurement value to obtain the line voltage component and line current component, determine whether the line voltage component and line current component meet the second preset criterion, and when the second preset criterion is met, activate the protection.

[0144] Preferably, the second protection unit 703 performs coordinate transformation on the line voltage measurement value and the line current measurement value to obtain the line voltage component and the line current component, including:

[0145] the line voltage measurement value is taken as a d-axis component in a d-axis reference coordinate system with the phase-to-phase voltage phase of the arbitrary two phases as the d-axis reference coordinate system, as a line voltage component;

[0146] the line current measurement value is taken as a d-axis component in a d-axis reference coordinate system with the phase-to-phase current phase of the arbitrary two phases as the d-axis reference coordinate system, as a line current component.

[0147] Preferably, the second protection unit 703 judges whether the line voltage component and the line current component satisfy a second preset criterion, and when the second preset criterion is satisfied, a protection action is performed, including:

[0148] judging whether the phase voltage component and the phase current component satisfy a third preset sub-criterion or a fourth preset sub-criterion and when the third preset sub-criterion or the fourth preset sub-criterion is satisfied, determining that it is an internal fault, and performing a protection action; if neither is satisfied, determining that it is an external fault, and not performing a protection action;

[0149] wherein u dX is the line voltage component; I dX is the line current component; R set is a first preset setting value; X set is a second preset setting value; and θ2 is a phase angle difference between the line voltage measurement value and the line current measurement value.

[0150] The protection system 700 of the AC line of the embodiment of the present application corresponds to the protection method 100 of the AC line of another embodiment of the present application, and will not be described here again.

[0151] Based on another aspect of the present application, the present application provides a computer readable storage medium, which stores a computer program, and the program is executed by a processor to implement the steps of any one of the protection methods of the AC line.

[0152] Based on another aspect of the present application, the present application provides an electronic device, including:

[0153] the above computer readable storage medium; and

[0154] one or more processors for executing the program in the computer readable storage medium.

[0155] The present application has been described by referring to a small number of embodiments. However, it is well known to those skilled in the art that, as defined in the attached patent claims, other embodiments than the above disclosed embodiments are equivalently within the scope of the present application.

[0156] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined in the patent or patent application to which this disclosure pertains. All references to "a" or "an" means "at least one", unless otherwise clearly indicated by the context of the disclosure. The steps of any methods disclosed herein need not be performed in the precise order disclosed unless explicitly stated.

[0157] Those skilled in the art will appreciate that embodiments of the present application can be devised for a method, a system, or a computer program product. Accordingly, the present application can be embodied in the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code.

[0158] The present application is described herein with reference to the drawings, in which are shown flowcharts and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present application. It will be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processing device or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowcharts and / or block diagrams block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0159] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0160] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0161] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A method of protecting an alternating current line, characterized in that, The method comprises: acquiring a power grid fault type; when the fault type indicates that a symmetric fault occurs in the power grid, acquiring phase voltage measurement values and phase current measurement values of any phase of a line measurement point, performing coordinate transformation on the phase voltage measurement values and the phase current measurement values to acquire phase voltage components and phase current components, judging whether the phase voltage components and the phase current components satisfy a first preset criterion, and when the first preset criterion is satisfied, determining an in-zone fault and performing protection; if none of the first preset criterion is satisfied, determining an out-of-zone fault and not performing protection; when the fault type indicates that an asymmetric fault occurs in the power grid, acquiring line voltage measurement values and line current measurement values of any two phases of the line measurement point, performing coordinate transformation on the line voltage measurement values and the line current measurement values to acquire line voltage components and line current components, judging whether the line voltage components and the line current components satisfy a second preset criterion, and when the second preset criterion is satisfied, performing protection.

2. The method of claim 1, wherein, The coordinate transformation on the phase voltage measurement values and the phase current measurement values to acquire the phase voltage components and the phase current components comprises: acquiring the phase voltage measurement values as d-axis components in a d-axis reference coordinate system with a phase voltage phase of the any phase as the d-axis reference coordinate system; acquiring the phase current measurement values as d-axis components in the d-axis reference coordinate system with a phase current phase of the any phase as the d-axis reference coordinate system.

3. The method of claim 1, wherein, The judgment on whether the phase voltage components and the phase current components satisfy the first preset criterion and the protection when the first preset criterion is satisfied comprise: determining whether the phase voltage component and the phase current component satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, determining an internal fault and performing protection; if neither is satisfied, determining an external fault and not performing protection wherein u d is a phase voltage component; I d is a phase current component; R set is a first preset setting value; X set is a second preset setting value; θ1 is a phase angle difference between the phase voltage measurement value and the phase current measurement value.

4. The method of claim 1, wherein, The coordinate transformation on the line voltage measurement values and the line current measurement values to acquire the line voltage components and the line current components comprises: acquiring the line voltage measurement values as d-axis components in the d-axis reference coordinate system with an inter-phase voltage phase of the any two phases as the d-axis reference coordinate system; acquiring the line current measurement values as d-axis components in the d-axis reference coordinate system with an inter-phase current phase of the any two phases as the d-axis reference coordinate system.

5. The method of claim 1, wherein, The judgment on whether the line voltage components and the line current components satisfy the second preset criterion and the protection when the second preset criterion is satisfied comprise: determining whether the phase voltage component and the phase current component satisfy a third preset sub-criterion or a fourth preset sub-criterion and when the third preset sub-criterion or the fourth preset sub-criterion is satisfied, determining an internal fault and performing protection; if neither is satisfied, determining an external fault and not performing protection wherein u dX is a line voltage component; I dX is a line current component; R set is a first preset setting value; X set is a second preset setting value; and θ2is a phase angle difference between the line voltage measurement and the line current measurement.

6. An AC line protection system characterized by, The system comprises: a fault type acquisition unit configured to acquire a power grid fault type; a first protection unit configured to, when the fault type indicates that a symmetric fault occurs in the power grid, acquire phase voltage measurement values and phase current measurement values of any phase of a line measurement point, perform coordinate transformation on the phase voltage measurement values and the phase current measurement values to acquire phase voltage components and phase current components, judge whether the phase voltage components and the phase current components satisfy a first preset criterion, and when the first preset criterion is satisfied, determine an in-zone fault and perform protection; if none of the first preset criterion is satisfied, determine an out-of-zone fault and not perform protection; a second protection unit configured to, when the fault type indicates that an asymmetric fault occurs in the power grid, acquire line voltage measurement values and line current measurement values of any two phases of the line measurement point, perform coordinate transformation on the line voltage measurement values and the line current measurement values to acquire line voltage components and line current components, judge whether the line voltage components and the line current components satisfy a second preset criterion, and when the second preset criterion is satisfied, perform protection.

7. The system of claim 6, wherein, The first protection unit performs coordinate transformation on the phase voltage measurement value and the phase current measurement value to obtain a phase voltage component and a phase current component, comprising: obtaining the phase voltage measurement value as a d-axis component in a d-axis reference coordinate system with the phase voltage phase of the any phase as the d-axis reference, as the phase voltage component; obtaining the phase current measurement value as a d-axis component in the d-axis reference coordinate system with the phase current phase of the any phase as the d-axis reference, as the phase current component.

8. The system of claim 6, wherein, The first protection unit judges whether the phase voltage component and the phase current component satisfy a first preset criterion, and when the first preset criterion is satisfied, performs a protection action, comprising: determining whether the phase voltage component and the phase current component satisfy a first preset sub-criterion or a second preset sub-criterion and when the first preset sub-criterion or the second preset sub-criterion is satisfied, determining an internal fault and performing protection; if neither is satisfied, determining an external fault and not performing protection wherein u d is a phase voltage component; I d is a phase current component; R set is a first preset setting value; X set is a second preset setting value; θ1is a phase angle difference between the phase voltage measurement value and the phase current measurement value.

9. The system of claim 6, wherein, The second protection unit performs coordinate transformation on the line voltage measurement value and the line current measurement value to obtain a line voltage component and a line current component, comprising: obtaining the line voltage measurement value as a d-axis component in a d-axis reference coordinate system with the phase-to-phase voltage phase of the any two phases as the d-axis reference, as the line voltage component; obtaining the line current measurement value as a d-axis component in the d-axis reference coordinate system with the phase-to-phase current phase of the any two phases as the d-axis reference, as the line current component.

10. The system of claim 6, wherein, The second protection unit judges whether the line voltage component and the line current component satisfy a second preset criterion, and when the second preset criterion is satisfied, performs a protection action, comprising: determining whether the phase voltage component and the phase current component satisfy a third preset sub-criterion or a fourth preset sub-criterion and when the third preset sub-criterion or the fourth preset sub-criterion is satisfied, determining an internal fault and performing protection; if neither is satisfied, determining an external fault and not performing protection wherein u dX is a line voltage component; I dX is a line current component; R set is a first preset setting value; X set is a second preset setting value; and θ2is a phase angle difference between the line voltage measurement and the line current measurement.

11. A computer readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the steps of the method in any one of claims 1-5.

12. An electronic device, comprising: comprising: the computer readable storage medium in claim 11; and one or more processors for executing the program in the computer readable storage medium.

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