Protection method and system of AC line, storage medium and electronic equipment

Abstract

The invention discloses an AC line protection method and system, a storage medium and electronic equipment. 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, a phase voltage measurement value and a phase current measurement value of any phase of a line measurement point are obtained, coordinate transformation is carried out to obtain a phase voltage component and a phase current component, whether the phase voltage component and the phase current component meet a first preset criterion or not is judged, and when the first preset criterion is met, the fault type of the power grid is determined to be the symmetric fault type. Determining an internal fault, and performing protection action; if the conditions are not met, determining that the fault is an external fault, and performing protection without action; when the fault type indicates that the power grid has an asymmetric fault, line voltage measurement values and line current measurement values of any two phases of a line measurement point are obtained, coordinate transformation is performed to obtain a line voltage component and a line current component, whether the line voltage component and the line current component meet a second preset criterion is judged, and when the second preset criterion is met, the fault type of the power grid is determined. And protection action.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection, and more specifically, to an AC line protection method, system, storage medium and electronic equipment. Background Art

[0002] Safe operation is an important foundation and prerequisite for building a new power system. 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 that relies on the characteristics of synchronous power sources is threatened. This is mainly reflected in the following aspects: after a power grid fault, the power electronic device will quickly change the control strategy and related parameters, and the fault current, voltage and sequence component characteristics are quite different from those of the traditional synchronous motor system. Characteristics such as limited amplitude and controlled phase angle have led to a serious decrease in protection reliability.

[0003] In order to adapt to the fault characteristics of new power systems, domestic and foreign scholars have also made certain progress in the research on distance protection of new energy station transmission lines. In response to the problem of large errors in power frequency impedance calculation, some scholars proposed a differential equation solution algorithm for fault distance iterative calculation based on digital low-pass filtering and fault point voltage reconstruction, constructed a distance protection scheme suitable for wind farm transmission lines and conducted simulation verification. In view of the problem that the traditional time domain differential equation algorithm is difficult to correctly identify the fault direction for faults at the outlet of the wind farm transmission line, some scholars analyzed the transient voltage of the double-fed wind turbine fault and proposed a time domain distance protection algorithm that can quickly identify the fault direction under zero voltage fault conditions based on the difference coefficient between the memory voltage drop and the actual voltage drop under different fault conditions. The calculation accuracy of the above time domain distance protection scheme is theoretically not affected by the fault current characteristics of new energy, and can be well applied to new energy transmission lines. However, none of the above related schemes fully considers the model error caused by the line concentrated parameter model ignoring the distributed capacitance, that is, no analysis is made on the adaptability of time domain distance protection to the length of the transmission line. As the scale of new energy in my country continues to expand, it has gradually become a reality to absorb new energy with ultra-high voltage and long-distance transmission. Therefore, the errors caused by ignoring the distributed capacitance of the line will become increasingly important. Some scholars pointed out that due to the constantly changing measurement impedance trajectory, distance protection cannot be used as a remote backup for the lower-level line. At the same time, the document proposed an improved permissive longitudinal protection strategy to solve this problem. Some scholars allow the station-side distance protection to delay the action, allowing the system-side circuit breaker to trip first. At this time, the weak feed effect disappears, and the station-side distance protection can operate correctly, but this method increases the fault isolation time. In addition, some scholars have changed the power frequency variable distance protection setting value to prevent the protection from malfunctioning when a reverse fault occurs when the impedance behind is capacitive. However, the impedance characteristics of new energy change with control strategies, fault conditions and other factors, and the method of modifying the setting value is difficult to apply to new energy transmission lines.

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

[0005] Therefore, a new AC line protection method is needed. Summary of the invention

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

[0007] In order to solve the above problem, according to one aspect of the present invention, a method for protecting an AC line is provided, the method comprising:

[0008] Get the type of power grid fault;

[0009] When the fault type indicates that a symmetrical fault occurs in the power grid, a phase voltage measurement value and a 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 a phase voltage component and a phase current component, and it is determined whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, it is determined to be an in-zone fault and protection is actuated; if both are not met, it is determined to be an out-of-zone fault and protection is not actuated;

[0010] When the fault type indicates that an asymmetric fault occurs in the power grid, the line voltage measurement values ​​and the line current measurement values ​​of any two phases of the line measurement point are obtained, the line voltage measurement values ​​and the line current measurement values ​​are transformed into coordinates to obtain the line voltage components and the line current components, and it is determined whether the line voltage components and the line current components meet a second preset criterion, and when the second preset criterion is met, protection is activated.

[0011] Preferably, the step of performing 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 comprises:

[0012] The phase voltage measurement value is obtained by taking the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component;

[0013] The phase current measurement value is obtained by taking the phase current phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase current component.

[0014] Preferably, determining whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, a protection action is performed, including:

[0015] Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0016] Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

[0017] Preferably, the step of performing 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 comprises:

[0018] The line voltage measurement value is obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component;

[0019] The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

[0020] Preferably, determining whether the line voltage component and the line current component meet a second preset criterion, and performing a protection action when the second preset criterion is met, comprises:

[0021] Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0022] Among them, 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; 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 invention, there is provided an AC line protection system, the system comprising:

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

[0025] a first protection unit, configured to obtain a phase voltage measurement value and a phase current measurement value of any phase of a line measurement point when the fault type indicates that a symmetrical fault occurs in the power grid, perform 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, determine whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, determine that it is an in-zone fault and the protection is activated; if both are not satisfied, determine that it is an out-of-zone fault and the protection is not activated;

[0026] The second protection unit is used to obtain the line voltage measurement values ​​and line current measurement values ​​of any two phases of the line measurement point when the fault type indicates that an asymmetric fault occurs in the power grid, perform coordinate transformation on the line voltage measurement values ​​and the line current measurement values ​​to obtain the line voltage component and the line current component, determine whether the line voltage component and the line current component meet the second preset criterion, and perform protection action when the second preset criterion is met.

[0027] Preferably, the first protection unit 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:

[0028] The phase voltage measurement value is obtained by taking the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component;

[0029] The phase current measurement value is obtained by taking the phase current phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase current component.

[0030] Preferably, the first protection unit determines whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, the protection action includes:

[0031] Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0032] Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

[0033] Preferably, the second protection unit 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:

[0034] The line voltage measurement value is obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component;

[0035] The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

[0036] Preferably, the second protection unit determines whether the line voltage component and the line current component meet a second preset criterion, and when the second preset criterion is met, the protection action includes:

[0037] Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0038] Among them, 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; θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

[0039] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, and when the program is executed by a processor, the program implements any step of a method for protecting an AC line.

[0040] According to another aspect of the present invention, the present invention provides an electronic device, including:

[0041] The computer-readable storage medium described above; and

[0042] One or more processors are used to execute the program in the computer-readable storage medium.

[0043] The present invention provides a protection method, system, storage medium and electronic device for an AC line. The method comprises: obtaining a power grid fault type; when the fault type indicates that a symmetrical 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, judging whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, determining that it is an in-zone fault and the protection is activated; if both are not met, determining that it is an out-of-zone fault and the protection is not activated; when the fault type indicates that an asymmetrical 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, judging whether the line voltage component and the line current component meet a second preset criterion, and when the second preset criterion is met, the protection is activated. The method of the present invention is adaptable to various scenarios of access and transmission of new energy power sources, has high reliability, and has important engineering significance for the future high-proportion consumption of new energy and safe operation of power grids. It can provide the premise and guarantee for the further development of a high-proportion new energy power electronic system in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0045] Figure 1is a flow chart of an AC line protection method 100 according to an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of a PSCAD simulation verification model of a protection principle according to an embodiment of the present invention;

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

[0048] Figure 4 Schematic diagram of R and X simulation measurement results when a fault occurs at 5 km according to an embodiment of the present invention;

[0049] Figure 5 Schematic diagram of simulation results of voltage and current dq components when an out-of-zone fault occurs according to an embodiment of the present invention;

[0050] Figure 6 Schematic diagram of simulation results of R and X when a fault occurs at 100 km according to an embodiment of the present invention;

[0051] Figure 7 FIG. 7 is a schematic structural diagram of an AC line protection system 700 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0053] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0054] New energy power sources, flexible DC converter stations and other power electronic devices have completely changed the system fault characteristics, and the traditional backup relay protection principle that relies on the characteristics of synchronous power sources is threatened. This is mainly reflected in the following aspects: after a power grid fault, the power electronic device will quickly change the control strategy and related parameters. The fault current, voltage and sequence component characteristics are quite different from those of the traditional synchronous motor system. The characteristics of limited amplitude and controlled phase angle lead to a serious decrease in protection reliability. Therefore, the present invention proposes a new principle of AC line protection based on electrical quantity decoupling, and provides a protection method for AC lines. Its main feature is that it is based on the perspective of the new energy control system, and the measured current and voltage of the transmission line can be transformed into a rotating coordinate system (dq0 transformation). Then, the correlation between active power, reactive power and line parameters is used to form a protection principle, so as to reliably judge the faults inside and outside the zone. This method only uses local measurement information, and solves the problem of refusal / misoperation of traditional power frequency distance protection due to limited amplitude, non-power frequency, controlled phase angle and unstable internal impedance after new energy faults.

[0055] Figure 1 FIG. 1 is a flow chart of a protection method 100 for an AC line according to an embodiment of the present invention. Figure 1 As shown, the AC line protection method provided by the embodiment of the present invention is suitable for the scenarios of access and transmission of various new energy power sources, has high reliability, has important engineering significance for the future high-proportion consumption of new energy and safe operation of the power grid, and can provide the premise and guarantee for the further development of a high-proportion new energy power electronic system in the future. The AC line protection method 100 provided by the embodiment of the present invention 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 the phase voltage component and the phase current component, and it is determined whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, the protection action is taken.

[0057] Preferably, the step of performing 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 comprises:

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

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

[0060] Preferably, determining whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, a protection action is performed, including:

[0061] Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0062] Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

[0063] When a symmetrical fault occurs in the power grid, since most new energy sources use independent control with power decoupling to achieve low voltage ride-through, that is, the active and reactive output of the new energy source during the fault is determined by the control system. Therefore, for the protection of the new energy transmission line, from the perspective of the control system, the measured current and voltage can be transformed by the rotating coordinate system (dq0 transformation), and then the correlation between active power, reactive power and line parameters can be used to form the protection principle. Therefore, according to the instantaneous power balance, the active power under symmetrical faults can be:

[0064]

[0065] In the formula, u d 、i d They are the measured phase voltage and the measured phase current at the line measurement point, respectively, with the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system. d It is the d-axis component of the measured phase current at the line measurement point in the d-axis reference coordinate system with the A-phase current phase as the reference coordinate system; R is 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, θ is the phase angle difference between the measured voltage and the measured current at the line measurement point, so it can be simplified:

[0068]

[0069] In normal operation, θ is the power factor angle, that is, the R value is very large, which can be regarded as the resistance component of the load impedance when the system is operating normally. When a fault occurs within the forward protection range, 0≤R≤R set . R set =0.8×R1, which is the protection setting of section I. R1 is the positive sequence resistance of the entire length of the protected line, that is, after the fault, it can be expressed as:

[0070]

[0071] Simplification can get the first preset protection sub-criterion:

[0072]

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

[0074]

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

[0076]

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

[0078]

[0079] In normal operation, θ can be understood as the power factor angle, that is, the X value is very large, which can be regarded as the reactance component of the load impedance when the system is operating normally. When a fault occurs within the forward protection range, 0≤X≤X set .X set =0.8×X1, which is the setting value of protection stage I. X1 is the positive sequence reactance value of the entire length of the protected line, that is, after the fault, it can be expressed as:

[0080]

[0081] Simplification can get the second preset protection sub-criterion:

[0082]

[0083] Therefore, in the present invention, when the fault type indicates that a symmetrical fault occurs in the power grid, firstly, the phase voltage measurement value and the phase current measurement value of any phase at the line measurement point are obtained; then, the coordinate transformation of the phase voltage measurement value and the phase current measurement value is performed, and the phase voltage measurement value is obtained with the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component, and the phase current measurement value is obtained with the phase current phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase current component; finally, it is determined whether the phase voltage component and the phase current component meet the first preset criterion, and when the first preset criterion is met, the protection action is taken. Specifically, it includes: determining whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an in-zone fault and the protection is activated; otherwise, if neither is met, it is determined to be an out-of-zone fault and the protection is not activated.

[0084] In step 103, when the fault type indicates that an asymmetric fault occurs in the power grid, the line voltage measurement values ​​and the line current measurement values ​​of any two phases of the line measurement point are obtained, the line voltage measurement values ​​and the line current measurement values ​​are coordinate transformed to obtain the line voltage components and the line current components, and it is determined whether the line voltage components and the line current components meet a second preset criterion, and when the second preset criterion is met, the protection action is taken.

[0085] Preferably, the step of performing 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 comprises:

[0086] The line voltage measurement value is obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component;

[0087] The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

[0088] Preferably, determining whether the line voltage component and the line current component meet a second preset criterion, and performing a protection action when the second preset criterion is met, comprises:

[0089] Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0090] Among them, u dX is the 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; θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

[0091] When an asymmetric fault occurs in the power grid, there are double frequency components after direct dq0 transformation, which is not suitable for distance protection construction. Therefore, a virtual rotating coordinate system method is proposed to reconstruct the spatial rotational symmetric system for dq0 transformation, that is, the virtual construction method is used for calculation under asymmetric faults. The three-phase symmetrical system is constructed based on the line voltage (current) measured at the line measurement points AB, BC, and CA, that is, there are three groups of three-phase symmetrical components in the calculation process, and the instantaneous value functions of voltage and current can be respectively:

[0092]

[0093] In the formula, * represents the virtual phase, U and I represent the amplitude of the function, cos is the cosine function, w represents the angular frequency, t represents the 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 As can be seen from the formula, the frequency-doubled component is eliminated at this time, while still satisfying the energy conservation. Therefore, according to the instantaneous power balance, the active power and reactive power under asymmetric faults can be:

[0094]

[0095]

[0096] Due to the existence of virtual phases during the calculation process, the three groups of symmetric components are calculated separately. dX It can be the two-phase current difference (i.e. line current) at the line measurement point, with the AB, BC or CA phase voltage phase as the d-axis component in the d-axis reference coordinate system. dX The line voltage at the line measurement point can be the d-axis component of the AB, BC or CA phase-to-phase voltage in the d-axis reference coordinate system. qX It can be the two-phase current difference (line current) of the line measurement point with the AB, BC or CA phase voltage phase as the q-axis component in the d-axis reference coordinate system. Therefore, I dX The two-phase current difference (i.e., line current) at the line measurement point can be the d-axis component in the AB, BC, or CA phase current phase in the d-axis reference coordinate system. That is, R and X can be expressed as:

[0097]

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

[0099]

[0100] In normal operation, θ can be understood as the power factor angle, that is, the R value is large, which can be regarded as the resistance component of the load impedance when the system is operating normally. The X value is large, which can be regarded as the reactance component of the load impedance when the system is operating normally.

[0101] When a fault occurs within the forward protection range, 0≤R≤R set , 0≤X≤X set The constant value of section I is R set =0.8×R1, R1 is the positive sequence resistance value of the entire length of the protected line, and the I section constant is X set =0.8×X1, X1 is the positive sequence reactance value of the entire length of the protected line, that is, after the fault, it can be expressed as:

[0102]

[0103] Simplification can get the third preset protection sub-criterion:

[0104]

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

[0106]

[0107] Therefore, in the present invention, when the fault type indicates that an asymmetric fault occurs in the power grid, first, the line voltage measurement values ​​and line current measurement values ​​of any two phases at the line measurement point are obtained; then, the line voltage measurement values ​​and line current measurement values ​​are subjected to coordinate transformation, and the line voltage measurement values ​​are obtained with the phase-to-phase voltage phase of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component, and the line current measurement values ​​are obtained with the phase-to-phase current phase of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component; finally, it is determined whether the line voltage component and the line current component meet the second preset criterion, and when the second preset criterion is met, the protection action is taken. Specifically, it includes: determining whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criterion or the fourth preset sub-criterion is met, it is determined to be an in-zone fault and the protection is activated; otherwise, if neither is met, it is determined to be an out-of-zone fault and the protection is not activated.

[0108] The method of the present invention transforms the measured current and voltage of the transmission line into a rotating coordinate system (dq0 transformation), and then uses the correlation between active power, reactive power and line parameters to form a protection principle and perform protection based on it. It can be directly applied to actual devices to achieve high-sensitivity and high-reliability fault identification.

[0109] The following specifically illustrates the embodiments of the present invention. Figure 2 The simulation model shown in Figure 1. Among them, the rated voltage of the transmission line is U B =220kV, line length 100km, wind farm rated capacity S B =200MVA, the protection is installed at the beginning of the line near the wind farm side. The line parameters are shown in Table 1. Three-phase short circuit, two-phase short circuit and two-phase short circuit grounding faults are set at 5km, 50km and 100km of the line respectively. The fault type is metallic grounding. The effectiveness of the proposed new protection principle is tested and analyzed.

[0110] Table 1 Line parameters

[0111]

[0112] Line protection reactance setting value (nominal value): X set =k×X1×L, where: X1 is the positive sequence reactance of the line; L is the line length, L=100km; k is the protection range of section I, which is 80% of the total length of the line, k=0.8. Impedance reference value

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

[0114] X set * (Per Unit Value) = X set / Z B =25.11 / 242=0.1038.

[0115] 1) In-area fault verification

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

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

[0118]

[0119] The actual resistance of the line from the fault point to the measurement point is R = 0.0178 × 5Ω = 0.089Ω, and the simulated measured value is 0.092Ω; the actual reactance of the line from the fault point to the measurement point is X = 0.31388 × 5Ω = 1.57Ω, and the simulated measured value is 1.56Ω. At this time, u d The simulation measured value is 0.007, which is less than u d The set value is 0.113, which meets the judgment criteria and the protection operates reliably.

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

[0121] Table 2 Protection action status table

[0122]

[0123]

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

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

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

[0127]

[0128] When a three-phase ABC short circuit fault occurs at 100km, the actual line resistance from the fault point to the measurement point is R = 0.0178 × 100Ω = 1.78Ω, and the simulated measured value is 1.802Ω; the actual line reactance from the fault point to the measurement point is X = 0.31388 × 100Ω = 31.38Ω, and the simulated measured value is 31.07Ω. 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 is reliable and does not operate.

[0129] Similarly, when a two-phase AB short circuit fault occurs at 100 km, the actual line resistance from the fault point to the measurement point is R = 0.0178 × 100Ω = 1.78Ω, and the simulated measured value is 1.76Ω; the actual line reactance from the fault point to the measurement point is X = 0.31388 × 100Ω = 31.38Ω, and the simulated 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 is reliable and does not operate.

[0130] The protection method proposed in the present invention is used for the case where ABC three-phase short circuit, AB two-phase short circuit and ABG two-phase short circuit to ground are respectively caused at 100km (outside the zone). d Measurement value, u d The setting value, measured values ​​of resistance R and reactance X, setting value, and protection action are shown in Table 3. When three-phase short circuit, two-phase short circuit, and two-phase short circuit grounding metallic fault occur outside the zone, the proposed new distance protection principle can reliably prevent the protection from action, and can accurately measure the resistance R and reactance X of the line from the fault point to the protection installation.

[0131] Table 3 Protection action status table

[0132]

[0133] The method of the present invention only uses local measurement information, which solves the problem of refusal / false operation of traditional power frequency distance protection due to limited amplitude, non-power frequency, controlled phase angle and unstable internal impedance after new energy faults. Both simulation data and recorded data have confirmed the effectiveness of this method.

[0134] Figure 7 FIG. 7 is a schematic diagram of the structure of an AC line protection system 700 according to an embodiment of the present invention. Figure 7 As shown, the AC line protection system 700 provided in the embodiment of the present invention includes: a fault type acquisition unit 701 , a first protection unit 702 and a second protection unit 703 .

[0135] Preferably, the fault type acquisition unit 701 is used to acquire a power grid fault type.

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

[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 phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component;

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

[0140] Preferably, the first protection unit 702 determines whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, the protection action includes:

[0141] Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0142] Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

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

[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 obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component;

[0146] The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

[0147] Preferably, the second protection unit 703 determines whether the line voltage component and the line current component meet a second preset criterion, and when the second preset criterion is met, the protection action includes:

[0148] Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated;

[0149] Among them, 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; θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

[0150] The AC line protection system 700 of the embodiment of the present invention corresponds to the AC line protection method 100 of another embodiment of the present invention, which will not be described in detail herein.

[0151] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, and when the program is executed by a processor, the program implements any step of a method for protecting an AC line.

[0152] According to another aspect of the present invention, the present invention provides an electronic device, including:

[0153] The computer-readable storage medium described above; and

[0154] One or more processors are used to execute the program in the computer-readable storage medium.

[0155] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0156] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of said means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0157] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0158] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0159] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0160] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for protecting an AC line, characterized in that: The method comprises: Get the type of power grid fault; When the fault type indicates that a symmetrical fault occurs in the power grid, a phase voltage measurement value and a 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 a phase voltage component and a phase current component, and it is determined whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, it is determined to be an in-zone fault and protection is actuated; if both are not met, it is determined to be an out-of-zone fault and protection is not actuated; When the fault type indicates that an asymmetric fault occurs in the power grid, the line voltage measurement values ​​and the line current measurement values ​​of any two phases of the line measurement point are obtained, the line voltage measurement values ​​and the line current measurement values ​​are transformed into coordinates to obtain the line voltage components and the line current components, and it is determined whether the line voltage components and the line current components meet a second preset criterion, and when the second preset criterion is met, protection is activated.

2. The method according to claim 1, characterized in that 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 includes: The phase voltage measurement value is obtained by taking the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component; The phase current measurement value is obtained by taking the phase current phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase current component.

3. The method according to claim 1, characterized in that Determining whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, performing a protection action, including: Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated; Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

4. The method according to claim 1, characterized in that The step of performing 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 comprises: The line voltage measurement value is obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component; The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

5. The method according to claim 1, characterized in that Determining whether the line voltage component and the line current component meet a second preset criterion, and performing a protection action when the second preset criterion is met, includes: Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated; Among them, 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; θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

6. A protection system for an AC line, characterized in that: The system comprises: A fault type acquisition unit, used to acquire a power grid fault type; a first protection unit, configured to obtain a phase voltage measurement value and a phase current measurement value of any phase of a line measurement point when the fault type indicates that a symmetrical fault occurs in the power grid, perform 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, determine whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, determine that it is an in-zone fault and the protection is activated; if both are not satisfied, determine that it is an out-of-zone fault and the protection is not activated; The second protection unit is used to obtain the line voltage measurement values ​​and line current measurement values ​​of any two phases of the line measurement point when the fault type indicates that an asymmetric fault occurs in the power grid, perform coordinate transformation on the line voltage measurement values ​​and the line current measurement values ​​to obtain the line voltage component and the line current component, determine whether the line voltage component and the line current component meet the second preset criterion, and perform protection action when the second preset criterion is met.

7. The system according to claim 6, characterized in that The first protection unit 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: The phase voltage measurement value is obtained by taking the phase voltage phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase voltage component; The phase current measurement value is obtained by taking the phase current phase of any phase as the d-axis component in the d-axis reference coordinate system as the phase current component.

8. The system according to claim 6, characterized in that The first protection unit determines whether the phase voltage component and the phase current component meet a first preset criterion, and when the first preset criterion is met, a protection action is performed, including: Determine whether the phase voltage component and the phase current component meet the first preset sub-criterion Or the second preset sub-criterion When the first preset sub-criteria or the second preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated; Among them, 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; θ1 is the phase angle difference between the phase voltage measurement value and the phase current measurement value.

9. The system according to claim 6, characterized in that The second protection unit 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: The line voltage measurement value is obtained by taking the phase between the phase voltages of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line voltage component; The line current measurement value is obtained by taking the phase between the phase currents of the arbitrary two phases as the d-axis component in the d-axis reference coordinate system as the line current component.

10. The system according to claim 6, characterized in that The second protection unit determines whether the line voltage component and the line current component meet a second preset criterion, and when the second preset criterion is met, performs a protection action, including: Determine whether the phase voltage component and the phase current component meet the third preset sub-criterion Or the fourth preset sub-criterion When the third preset sub-criteria or the fourth preset sub-criteria is met, it is determined to be an internal fault and the protection is activated; if neither is met, it is determined to be an external fault and the protection is not activated; Among them, 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; θ2 is the phase angle difference between the line voltage measurement value and the line current measurement value.

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

12. An electronic device, characterized in that: include: The computer readable storage medium as claimed in claim 11; as well as One or more processors are used to execute the program in the computer-readable storage medium.

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