CN109991513B - A method and system for calculating the theoretical value of the time constant of the DC component of short-circuit current - Google Patents

A method and system for calculating the theoretical value of the time constant of the DC component of short-circuit current Download PDF

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CN109991513B
CN109991513B CN201910153205.6A CN201910153205A CN109991513B CN 109991513 B CN109991513 B CN 109991513B CN 201910153205 A CN201910153205 A CN 201910153205A CN 109991513 B CN109991513 B CN 109991513B
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circuit current
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CN109991513A (en
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李振强
周沛洪
何慧雯
娄颖
查志鹏
戴敏
周姣
范冕
王磊
李志军
张波
彭庆华
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
State Grid Hebei Electric Power Co Ltd
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China Electric Power Research Institute Co Ltd CEPRI
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Abstract

本发明公开了一种计算短路电流直流分量的时间常数的理论值的方法及系统，包括：确定短路电流的交流分量的峰值；对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线；利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线；确定第一直流分量波形和第二直流分量波形，并分别进行指数拟合，以分别获取第一拟合公式和第二拟合公式；根据所述第一拟合公式和第二拟合公式选取较大的时间常数作为时间常数理论值。本发明根据设置的短路电流直流分量曲线拟合的原则，确定短路电流直流分量的时间常数，可避免拟合公式选取的盲目性；通过对计算的时间常数的准确性进行检验，保证了计算结果的准确性。

Figure 201910153205

The invention discloses a method and system for calculating the theoretical value of the time constant of the DC component of the short-circuit current, including: determining the peak value of the AC component of the short-circuit current; fitting to obtain a first DC component attenuation curve; using a harmonic analysis method to analyze the short-circuit current waveform to obtain a second DC component attenuation curve; determining the first DC component waveform and the second DC component waveform, and performing exponential fitting respectively to obtain a first fitting formula and a second fitting formula; according to the first fitting formula and the second fitting formula, a larger time constant is selected as the theoretical value of the time constant. The present invention determines the time constant of the DC component of the short-circuit current according to the set principle of curve fitting of the DC component of the short-circuit current, which can avoid blindness in the selection of the fitting formula; by checking the accuracy of the calculated time constant, the calculation result is guaranteed accuracy.

Figure 201910153205

Description

一种计算短路电流直流分量的时间常数的理论值的方法及 系统A method for calculating the theoretical value of the time constant of the DC component of short-circuit current and system

技术领域technical field

本发明涉及输电技术领域，并且更具体地，涉及一种计算短路电流直流分量的时间常数的理论值的方法及系统。The present invention relates to the technical field of power transmission, and more specifically, to a method and system for calculating the theoretical value of the time constant of the DC component of the short-circuit current.

背景技术Background technique

与输电线路的工作电流相比，系统的短路电流很大，当线路或母线发生短路故障时，在短路瞬间，系统中的电感元件磁通不能突变，因此短路电流中就会出现直流分量，直流分量的最大值必然等于短路电流周期分量改变量的绝对值。系统在t0时刻发生短路故障时，短路电流IDC中的直流分量iDC可用简单的指数函数的形式表示为：

Figure GDA0002061532570000011
其中，IDC为故障电流在故障时刻t0时的直流分量；t为短路故障开始后的时间；τ为电网的直流时间常数。Compared with the working current of the transmission line, the short-circuit current of the system is very large. When a short-circuit fault occurs in the line or bus, the magnetic flux of the inductive element in the system cannot change suddenly at the moment of short-circuit, so there will be a DC component in the short-circuit current. The maximum value of the component must be equal to the absolute value of the change of the periodic component of the short-circuit current. When a short-circuit fault occurs in the system at time t 0 , the DC component iDC in the short-circuit current IDC can be expressed in the form of a simple exponential function as:
Figure GDA0002061532570000011
Among them, I DC is the DC component of the fault current at fault time t 0 ; t is the time after the short-circuit fault starts; τ is the DC time constant of the power grid.

现有的采用电磁暂态计算出相应故障下的短路电流，对短路电流进行相应的数学处理得到的时间常数更为准确。常用的计算方法有如下两种：The existing method uses the electromagnetic transient state to calculate the short-circuit current under the corresponding fault, and the time constant obtained by corresponding mathematical processing on the short-circuit current is more accurate. There are two commonly used calculation methods as follows:

方法1，对电流波形的包络线拟合，上、下包络线的平均值为直流分量衰减曲线，通过指数曲线拟合求出直流分量的时间常数，如图1所示；其中，(□)表示上包络线和(△)表示下包络线、(×)表示拟合的直流分量。Method 1, for the envelope curve fitting of the current waveform, the average value of the upper and lower envelope curves is the DC component attenuation curve, and the time constant of the DC component is obtained by exponential curve fitting, as shown in Figure 1; among them, ( □) indicates the upper envelope and (△) indicates the lower envelope, and (×) indicates the fitted DC component.

方法2，采用谐波分析方法(通常采用快速傅立叶变换)得出直流分量衰减曲线，通过指数曲线拟合求出直流分量的时间常数，如图2所示；其中，(×)表示交流分量和(△)表示直流分量。Method 2, using the harmonic analysis method (usually using fast Fourier transform) to obtain the attenuation curve of the DC component, and calculating the time constant of the DC component through exponential curve fitting, as shown in Figure 2; where (×) represents the AC component and (△) indicates a DC component.

但是，在拟合的过程中仍存在一些不规范的问题，导致拟合曲线不准确，计算出来的时间常数与实际误差较大，不利于断路器开断短路电流。However, there are still some non-standard problems in the fitting process, which lead to inaccurate fitting curves, and large errors between the calculated time constant and the actual one, which is not conducive to breaking the short-circuit current of the circuit breaker.

因此，需要一种能够准确地确定短路电流直流分量的时间常数的方法。Therefore, there is a need for a method that can accurately determine the time constant of the DC component of the short-circuit current.

发明内容Contents of the invention

本发明提出一种计算短路电流直流分量的时间常数的理论值的方法及系统，以解决如何准确地确定短路电流直流分量的时间常数的问题。The invention proposes a method and system for calculating the theoretical value of the time constant of the DC component of the short-circuit current to solve the problem of how to accurately determine the time constant of the DC component of the short-circuit current.

为了解决上述问题，根据本发明的一个方面，提供一种计算短路电流直流分量的时间常数的理论值的方法，其特征在于，所述方法包括：In order to solve the above problems, according to one aspect of the present invention, a method for calculating the theoretical value of the time constant of the DC component of the short-circuit current is provided, wherein the method includes:

对短路电流波形进行傅里叶分析，以确定所述短路电流的交流分量的峰值；performing Fourier analysis on the short-circuit current waveform to determine the peak value of the AC component of the short-circuit current;

对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线；Fitting the upper envelope and the lower envelope of the short-circuit current waveform to obtain a first DC component decay curve;

利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线；Analyzing the short-circuit current waveform by using a harmonic analysis method to obtain a second DC component attenuation curve;

分别选取所述第一直流分量衰减曲线和第二直流分量衰减曲线在故障开始时，预设时间阈值段内的曲线作为第一直流分量波形和第二直流分量波形；Respectively select the first DC component attenuation curve and the second DC component attenuation curve at the beginning of the fault, and the curves within the preset time threshold period as the first DC component waveform and the second DC component waveform;

分别对所述第一直流分量波形和第二直流分量波形进行指数拟合，以分别获取满足拟合原则的预设格式的第一拟合公式和第二拟合公式；respectively performing exponential fitting on the first DC component waveform and the second DC component waveform to respectively obtain a first fitting formula and a second fitting formula in a preset format satisfying a fitting principle;

当所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差小于等于第一预设误差阈值时，选取较大的时间常数作为时间常数理论值。When the relative error between the first time constant and the second time constant in the first fitting formula and the second fitting formula is less than or equal to the first preset error threshold, a larger time constant is selected as the theoretical value of the time constant.

优选地，其中所述预设时间阈值的取值范围为[60,150)，单位为ms。Preferably, the value range of the preset time threshold is [60, 150), and the unit is ms.

优选地，其中所述预设格式公式为：

Figure GDA0002061532570000021
所述拟合原则为：IDC与I0的相对误差小于等于第二预设误差阈值；Preferably, wherein the preset format formula is:
Figure GDA0002061532570000021
The fitting principle is: the relative error between IDC and I0 is less than or equal to the second preset error threshold;

其中，IDC为故障时刻t0时刻的故障电流的直流分量；t为故障开始后的时刻；τ为时间常数；I0为所述短路电流的交流分量的峰值。Wherein, I DC is the DC component of the fault current at the fault time t 0 ; t is the time after the fault starts; τ is the time constant; I 0 is the peak value of the AC component of the short-circuit current.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

将所述短路电流的直流分量分别和所述第一直流分量波形和第二直流分量波形进行叠加，以获取第一叠加短路电流波形和第二叠加短路电流波形；superimposing the DC component of the short-circuit current with the first DC component waveform and the second DC component waveform respectively to obtain a first superimposed short-circuit current waveform and a second superimposed short-circuit current waveform;

分别将所述第一叠加短路电流波形和第二叠加短路电流波形与所述短路电流波形进行比对，以获取比对结果；其中，若所述比对结果指示所述第一叠加短路电流波形和第二叠加短路电流波形分别与所述短路电流波形重合率大于等于预设重合阈值，则表明确定的时间常数理论值准确。Comparing the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform respectively to obtain a comparison result; wherein, if the comparison result indicates that the first superimposed short-circuit current waveform If the coincidence rate of the second superimposed short-circuit current waveform and the short-circuit current waveform is greater than or equal to a preset coincidence threshold, it indicates that the determined theoretical value of the time constant is accurate.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

当所述比对结果指示所述第一叠加短路电流波形或第二叠加短路电流波形与所述短路电流波形重合率小于预设重合阈值时，表明确定的时间常数理论值不准确，重新选取新的预设时间阈值进行计算。When the comparison result indicates that the coincidence ratio between the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is less than the preset coincidence threshold, it indicates that the determined theoretical value of the time constant is inaccurate, and a new one is selected again. The preset time threshold is calculated.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

当获取的第一拟合公式和第二拟合公式不满足拟合原则；或所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差大于第一预设误差阈值时，重新选取新的预设时间阈值进行计算。When the obtained first fitting formula and the second fitting formula do not satisfy the fitting principle; or the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is greater than the first When a preset error threshold is reached, a new preset time threshold is reselected for calculation.

根据本发明的另一个方面，提供了一种计算短路电流直流分量的时间常数的理论值的系统，其特征在于，所述系统包括：According to another aspect of the present invention, a system for calculating the theoretical value of the time constant of the DC component of the short-circuit current is provided, wherein the system includes:

交流分量的峰值确定单元，用于对短路电流波形进行傅里叶分析，以确定所述短路电流的交流分量的峰值；A peak value determination unit of the AC component, configured to perform Fourier analysis on the short-circuit current waveform to determine the peak value of the AC component of the short-circuit current;

第一直流分量衰减曲线获取单元，用于对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线；A first DC component attenuation curve acquisition unit, configured to fit the upper and lower envelopes of the short-circuit current waveform to obtain a first DC component attenuation curve;

第二直流分量衰减曲线获取单元，用于利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线；The second DC component attenuation curve acquisition unit is configured to analyze the short-circuit current waveform by using a harmonic analysis method to obtain a second DC component attenuation curve;

直流分量波形确定单元，用于分别选取所述第一直流分量衰减曲线和第二直流分量衰减曲线在故障开始时，预设时间阈值段内的曲线作为第一直流分量波形和第二直流分量波形；The DC component waveform determination unit is used to respectively select the first DC component attenuation curve and the second DC component attenuation curve at the beginning of the fault, and the curves within the preset time threshold period as the first DC component waveform and the second DC component waveform component waveform;

拟合公式获取单元，用于分别对所述第一直流分量波形和第二直流分量波形进行指数拟合，以分别获取满足拟合原则的预设格式的第一拟合公式和第二拟合公式；A fitting formula acquisition unit, configured to perform exponential fitting on the first DC component waveform and the second DC component waveform respectively, so as to respectively obtain the first fitting formula and the second fitting formula in a preset format satisfying the fitting principle combined formula;

时间常数理论值确定单元，用于当所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差小于等于第一预设误差阈值时，选取较大的时间常数作为时间常数理论值。A time constant theoretical value determination unit, used to select a larger The time constant of is taken as the theoretical value of the time constant.

优选地，其中所述预设时间阈值的取值范围为[60,150)，单位为ms。Preferably, the value range of the preset time threshold is [60, 150), and the unit is ms.

优选地，其中所述预设格式公式为：

Figure GDA0002061532570000041
所述拟合原则为：IDC与I0的相对误差小于等于第二预设误差阈值；Preferably, wherein the preset format formula is:
Figure GDA0002061532570000041
The fitting principle is: the relative error between IDC and I0 is less than or equal to the second preset error threshold;

其中，IDC为故障时刻t0时刻的故障电流的直流分量；t为故障开始后的时刻；τ为时间常数；I0为所述短路电流的交流分量的峰值。Wherein, I DC is the DC component of the fault current at the fault time t 0 ; t is the time after the fault starts; τ is the time constant; I 0 is the peak value of the AC component of the short-circuit current.

优选地，其中所述系统还包括：Preferably, wherein said system also includes:

校验单元，用于将所述短路电流的直流分量分别和所述第一直流分量波形和第二直流分量波形进行叠加，以获取第一叠加短路电流波形和第二叠加短路电流波形；A verification unit, configured to superimpose the DC component of the short-circuit current with the first DC component waveform and the second DC component waveform respectively, so as to obtain the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform;

所述分别将所述第一叠加短路电流波形和第二叠加短路电流波形与所述短路电流波形进行比对，以获取比对结果；其中，若所述比对结果指示所述第一叠加短路电流波形和第二叠加短路电流波形分别与所述短路电流波形重合率大于等于预设重合阈值，则表明确定的时间常数理论值准确。The first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform are respectively compared with the short-circuit current waveform to obtain a comparison result; wherein, if the comparison result indicates that the first superimposed short-circuit If the coincidence rate of the current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform is greater than or equal to a preset coincidence threshold, it indicates that the determined theoretical value of the time constant is accurate.

优选地，其中所系统还包括：Preferably, wherein the system also includes:

预设时间阈值重置单元，用于当所述比对结果指示所述第一叠加短路电流波形或第二叠加短路电流波形与所述短路电流波形重合率小于预设重合阈值时，表明确定的时间常数理论值不准确，重新选取新的预设时间阈值进行计算；或当获取的第一拟合公式和第二拟合公式不满足拟合原则；或所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差大于第一预设误差阈值时，重新选取新的预设时间阈值，并返回直流分量波形确定单元。The preset time threshold reset unit is used to indicate that when the comparison result indicates that the coincidence rate of the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is less than a preset coincidence threshold The theoretical value of the time constant is inaccurate, and a new preset time threshold is selected for calculation; or when the first fitting formula and the second fitting formula obtained do not meet the fitting principle; or the first fitting formula and the second When the relative error between the first time constant and the second time constant in the fitting formula is greater than the first preset error threshold, reselect a new preset time threshold, and return to the DC component waveform determining unit.

本发明提供了一种计算短路电流直流分量的时间常数的理论值的方法及系统，包括：确定短路电流的交流分量的峰值；对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线；利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线；确定第一直流分量波形和第二直流分量波形，并分别进行指数拟合，以分别获取第一拟合公式和第二拟合公式；根据所述第一拟合公式和第二拟合公式选取较大的时间常数作为时间常数理论值。本发明根据预设时间阈值确定需要拟合的直流分量波形，并根据设置的短路电流直流分量曲线拟合的原则，确定短路电流直流分量的时间常数，可避免拟合公式选取的盲目性；同时提出了对时间常数计算结果正确与否的检验方法，保证了计算结果的准确性。The present invention provides a method and system for calculating the theoretical value of the time constant of the DC component of the short-circuit current, including: determining the peak value of the AC component of the short-circuit current; fitting to obtain a first DC component attenuation curve; using a harmonic analysis method to analyze the short-circuit current waveform to obtain a second DC component attenuation curve; determining the first DC component waveform and the second DC component waveform, and performing exponential fitting respectively to obtain a first fitting formula and a second fitting formula; according to the first fitting formula and the second fitting formula, a larger time constant is selected as the theoretical value of the time constant. The present invention determines the DC component waveform to be fitted according to the preset time threshold, and determines the time constant of the DC component of the short-circuit current according to the set principle of short-circuit current DC component curve fitting, which can avoid the blindness of fitting formula selection; at the same time The method of checking whether the calculation result of time constant is correct or not is proposed to ensure the accuracy of the calculation result.

附图说明Description of drawings

通过参考下面的附图，可以更为完整地理解本发明的示例性实施方式：A more complete understanding of the exemplary embodiments of the present invention can be had by referring to the following drawings:

图1为根据短路电流波形的上包络线和下包络线进行拟合，确定直流分量的时间常数的方法的示意图；Fig. 1 is a schematic diagram of a method for determining the time constant of the DC component by fitting according to the upper and lower envelopes of the short-circuit current waveform;

图2为采用谐波分析方法确定直流分量衰减曲线，并通过直流曲线拟合确定直流分量的时间常数的方法的示意图；Fig. 2 is a schematic diagram of a method for determining the attenuation curve of the DC component by the harmonic analysis method, and determining the time constant of the DC component by DC curve fitting;

图3为根据本发明实施方式的计算短路电流直流分量的时间常数的理论值的方法300的流程图；3 is a flowchart of a method 300 for calculating a theoretical value of the time constant of the DC component of the short-circuit current according to an embodiment of the present invention;

图4为根据本发明实施方式的短路电流波形图；Fig. 4 is a short-circuit current waveform diagram according to an embodiment of the present invention;

图5a为根据本发明实施方式的故障时间为60ms时对直流分量波形进行拟合的示意图；Fig. 5a is a schematic diagram of fitting the DC component waveform when the fault time is 60 ms according to an embodiment of the present invention;

图5b为根据本发明实施方式的故障时间为120ms时对直流分量波形进行拟合的示意图；Fig. 5b is a schematic diagram of fitting the DC component waveform when the fault time is 120 ms according to an embodiment of the present invention;

图5c为根据本发明实施方式的故障时间为160ms时对直流分量波形进行拟合的示意图；Fig. 5c is a schematic diagram of fitting the DC component waveform when the fault time is 160 ms according to an embodiment of the present invention;

图6为根据本发明实施方式的断路器的叠加短路波形与初始的短路电流波形的对比图；以及6 is a comparison diagram of the superimposed short-circuit waveform and the initial short-circuit current waveform of the circuit breaker according to an embodiment of the present invention; and

图7为根据本发明实施方式的计算短路电流直流分量的时间常数的理论值的系统700的结构示意图。FIG. 7 is a schematic structural diagram of a system 700 for calculating the theoretical value of the time constant of the DC component of the short-circuit current according to an embodiment of the present invention.

具体实施方式Detailed ways

现在参考附图介绍本发明的示例性实施方式，然而，本发明可以用许多不同的形式来实施，并且不局限于此处描述的实施例，提供这些实施例是为了详尽地且完全地公开本发明，并且向所属技术领域的技术人员充分传达本发明的范围。对于表示在附图中的示例性实施方式中的术语并不是对本发明的限定。在附图中，相同的单元/元件使用相同的附图标记。Exemplary embodiments of the present invention will now be described with reference to the drawings; however, the present invention may be embodied in many different forms and are not limited to the embodiments described herein, which are provided for the purpose of exhaustively and completely disclosing the present invention. invention and fully convey the scope of the invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings do not limit the present invention. In the figures, the same units/elements are given the same reference numerals.

除非另有说明，此处使用的术语(包括科技术语)对所属技术领域的技术人员具有通常的理解含义。另外，可以理解的是，以通常使用的词典限定的术语，应当被理解为与其相关领域的语境具有一致的含义，而不应该被理解为理想化的或过于正式的意义。Unless otherwise specified, the terms (including scientific and technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it can be understood that terms defined by commonly used dictionaries should be understood to have consistent meanings in the context of their related fields, and should not be understood as idealized or overly formal meanings.

图3为根据本发明实施方式的计算短路电流直流分量的时间常数的理论值的方法300的流程图。如图3所示，本发明的实施方式提供的计算短路电流直流分量的时间常数的理论值的方法，根据预设时间阈值确定需要拟合的直流分量波形，并根据设置的短路电流直流分量曲线拟合的原则，确定短路电流直流分量的时间常数，可避免拟合公式选取的盲目性；同时提出了对时间常数计算结果正确与否的检验方法，保证了计算结果的准确性。本发明的实施方式提供的计算短路电流直流分量的时间常数的理论值的方法300从步骤301处开始，在步骤301对短路电流波形进行傅里叶分析，以确定所述短路电流的交流分量的峰值。FIG. 3 is a flowchart of a method 300 for calculating a theoretical value of a time constant of a DC component of a short-circuit current according to an embodiment of the present invention. As shown in Figure 3, the method for calculating the theoretical value of the time constant of the short-circuit current DC component provided by the embodiment of the present invention determines the DC component waveform to be fitted according to the preset time threshold, and according to the set short-circuit current DC component curve The principle of fitting is to determine the time constant of the DC component of the short-circuit current, which can avoid the blindness of the fitting formula selection; at the same time, a method of checking whether the calculation result of the time constant is correct or not is proposed to ensure the accuracy of the calculation result. The method 300 for calculating the theoretical value of the time constant of the DC component of the short-circuit current provided by the embodiment of the present invention starts at step 301. In step 301, Fourier analysis is performed on the short-circuit current waveform to determine the time constant of the AC component of the short-circuit current. peak.

在步骤302，对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线。In step 302, the upper envelope and the lower envelope of the short-circuit current waveform are fitted to obtain a first DC component attenuation curve.

在本发明的实施方式中，获取第一直流分量衰减曲线的方法与图1所示的方法的原理相同。In the embodiment of the present invention, the principle of the method for obtaining the first DC component attenuation curve is the same as that of the method shown in FIG. 1 .

在步骤303，利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线。In step 303, the waveform of the short-circuit current is analyzed using a harmonic analysis method to obtain a second DC component attenuation curve.

在本发明的实施方式中，获取第二直流分量衰减曲线的方法与图2所示的方法的原理相同。In an embodiment of the present invention, the principle of the method for obtaining the second DC component attenuation curve is the same as that of the method shown in FIG. 2 .

在步骤304，分别选取所述第一直流分量衰减曲线和第二直流分量衰减曲线在故障开始时，预设时间阈值段内的曲线作为第一直流分量波形和第二直流分量波形。优选地，其中所述预设时间阈值的取值范围为[60,150)，单位为ms。In step 304, the first DC component decay curve and the second DC component decay curve are respectively selected as the first DC component waveform and the second DC component waveform within the preset time threshold when the fault starts. Preferably, the value range of the preset time threshold is [60, 150), and the unit is ms.

对于预设时间阈值，可以根据具体的短路电流波形来确定。The preset time threshold can be determined according to the specific short-circuit current waveform.

在本发明的实施方式中，为了保证计算的时间常数的准确性，选取的预设时间阈值的取值范围为[60,150)，即时间轴范围从故障开始时取值，不小于60ms，不大于150ms，并且尽量在80～120ms之间选择。In the embodiment of the present invention, in order to ensure the accuracy of the calculated time constant, the value range of the selected preset time threshold is [60,150), that is, the time axis range takes a value from the beginning of the fault, not less than 60ms, not greater than 150ms, and try to choose between 80~120ms.

例如，若选取预设时间阈值为100，则从所述第一直流分量衰减曲线中选取从故障时刻开始时到时间为100ms时，共100ms的曲线作为第一直流分量波形；从所述第二直流分量衰减曲线中选取从故障时刻开始时到时间为100ms时，共100ms的曲线作为第二直流分量波形。For example, if the preset time threshold is selected to be 100, a curve of 100 ms is selected from the first DC component attenuation curve as the first DC component waveform from the beginning of the fault moment to the time of 100 ms; In the second DC component attenuation curve, a curve with a total of 100 ms from the fault moment to 100 ms is selected as the second DC component waveform.

在步骤305，分别对所述第一直流分量波形和第二直流分量波形进行指数拟合，以分别获取满足拟合原则的预设格式的第一拟合公式和第二拟合公式。In step 305, exponential fitting is performed on the first DC component waveform and the second DC component waveform respectively, so as to respectively obtain a first fitting formula and a second fitting formula in a preset format satisfying a fitting principle.

优选地，其中所述预设格式公式为：

Figure GDA0002061532570000071
所述拟合原则为：IDC与I0的相对误差小于等于第二预设误差阈值；Preferably, wherein the preset format formula is:
Figure GDA0002061532570000071
The fitting principle is: the relative error between IDC and I0 is less than or equal to the second preset error threshold;

其中，IDC为故障时刻t0时刻的故障电流的直流分量；t为故障开始后的时刻；τ为时间常数；I0为所述短路电流的交流分量的峰值。Wherein, I DC is the DC component of the fault current at the fault time t 0 ; t is the time after the fault starts; τ is the time constant; I 0 is the peak value of the AC component of the short-circuit current.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

当获取的第一拟合公式和第二拟合公式不满足拟合原则；或所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差大于第一预设误差阈值时，重新选取新的预设时间阈值返回步骤303进行计算。When the obtained first fitting formula and the second fitting formula do not satisfy the fitting principle; or the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is greater than the first When a preset error threshold is reached, reselect a new preset time threshold and return to step 303 for calculation.

在本发明的实施方式中，第二预设误差阈值可以为5％，拟合原则为：IDC与I0的相对误差小于等于第二预设误差阈值，即保证IDC的值接近交流分量峰值I0，两者之间的差值约等于故障前的线路工作电流峰值。In an embodiment of the present invention, the second preset error threshold may be 5%, and the fitting principle is: the relative error between IDC and I0 is less than or equal to the second preset error threshold, that is, to ensure that the value of IDC is close to the AC component The peak value I 0 , the difference between the two is approximately equal to the peak value of the line operating current before the fault.

若IDC与I0的相对误差大于第二预设误差阈值5％，则表明由此得出的时间常数准确度低，因此需要重新选取预设时间阈值，并返回步骤303重新计算。If the relative error between I DC and I 0 is greater than the second preset error threshold 5%, it indicates that the accuracy of the time constant thus obtained is low, so the preset time threshold needs to be reselected, and return to step 303 for recalculation.

其中，第二预设误差阈值的取值5％也可以替换为其他任一值，例如1％，6％，10％等。Wherein, the value 5% of the second preset error threshold may also be replaced with any other value, such as 1%, 6%, 10% and so on.

在步骤306，当所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差小于等于第一预设误差阈值时，选取较大的时间常数作为时间常数理论值。In step 306, when the relative error between the first time constant and the second time constant in the first fitting formula and the second fitting formula is less than or equal to the first preset error threshold, a larger time constant is selected as the time Constant theoretical value.

在本发明的实施方式中，第一预设误差阈值可以选取为10％，若第一时间常数和第二时间常数的相对误差小于等于第一预设误差阈值10％，则表明由此计算出来的时间常数的准确度满足要求，可以确定时间常数理论值；反之，则表明由此确定的时间常数理论值准确度低，需要重新选取新的预设时间阈值，并返回步骤303重新进行计算。In an embodiment of the present invention, the first preset error threshold can be selected as 10%. If the relative error between the first time constant and the second time constant is less than or equal to the first preset error threshold 10%, it means that the calculated If the accuracy of the time constant meets the requirements, the theoretical value of the time constant can be determined; otherwise, it indicates that the accuracy of the theoretical value of the time constant thus determined is low, and a new preset time threshold needs to be selected again, and return to step 303 for recalculation.

其中，第一预设误差阈值的取值10％也可以替换为其他任一值，例如2％，5％等。Wherein, the value 10% of the first preset error threshold can also be replaced with any other value, such as 2%, 5% and so on.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

将所述短路电流的直流分量分别和所述第一直流分量波形和第二直流分量波形进行叠加，以获取第一叠加短路电流波形和第二叠加短路电流波形；superimposing the DC component of the short-circuit current with the first DC component waveform and the second DC component waveform respectively to obtain a first superimposed short-circuit current waveform and a second superimposed short-circuit current waveform;

分别将所述第一叠加短路电流波形和第二叠加短路电流波形与所述短路电流波形进行比对，以获取比对结果；其中，若所述比对结果指示所述第一叠加短路电流波形和第二叠加短路电流波形分别与所述短路电流波形重合率大于等于预设重合阈值，则表明确定的时间常数理论值准确。Comparing the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform respectively to obtain a comparison result; wherein, if the comparison result indicates that the first superimposed short-circuit current waveform If the coincidence rate of the second superimposed short-circuit current waveform and the short-circuit current waveform is greater than or equal to a preset coincidence threshold, it indicates that the determined theoretical value of the time constant is accurate.

优选地，其中所述方法还包括：Preferably, wherein said method further comprises:

当所述比对结果指示所述第一叠加短路电流波形或第二叠加短路电流波形与所述短路电流波形重合率小于预设重合阈值时，表明确定的时间常数理论值不准确，重新选取新的预设时间阈值返回步骤303进行计算。When the comparison result indicates that the coincidence ratio between the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is less than the preset coincidence threshold, it indicates that the determined theoretical value of the time constant is inaccurate, and a new one is selected again. The preset time threshold returns to step 303 for calculation.

在本发明的实施方式中，还可以根据叠加短路电流波形和原短路电流波形的对比结果对确定的时间常数理论值的准确度进行校验，以从两方面保证计算结果的准确性。In the embodiment of the present invention, the accuracy of the determined theoretical value of the time constant can also be verified according to the comparison result of the superimposed short-circuit current waveform and the original short-circuit current waveform, so as to ensure the accuracy of the calculation result from two aspects.

其中，若两个短路电流波形重合或相近，则计算结果准确，时间常数理论值为第一时间常数和第二时间常数中较大的一个；否则应进行修正，修正的方法是改变拟合的时间轴范围，即重新选取新的预设时间阈值返回步骤303进行计算。Among them, if the two short-circuit current waveforms coincide or are similar, the calculation result is accurate, and the theoretical value of the time constant is the larger one of the first time constant and the second time constant; otherwise, it should be corrected, and the corrected method is to change the fitted The time axis range, that is, reselecting a new preset time threshold returns to step 303 for calculation.

例如，某一系统的短路电流波形如图4所示，故障发生在0.6s，其稳态值为72kA(峰值)。采用步骤303所示的方法利用谐波分析方法对所述短路电流波形进行分析，获取直流分量衰减曲线。然后，分别按照从故障开始时算60ms、120m和160ms，获取直流分量波形，并进行拟合，分别获取如图5a、5b和5c所示的拟合曲线和拟合公式。For example, the short-circuit current waveform of a certain system is shown in Figure 4, the fault occurs at 0.6s, and its steady-state value is 72kA (peak value). Using the method shown in step 303, the harmonic analysis method is used to analyze the short-circuit current waveform to obtain a DC component attenuation curve. Then, according to 60ms, 120m and 160ms from the beginning of the fault, the DC component waveform is obtained and fitted, and the fitting curve and fitting formula shown in Figure 5a, 5b and 5c are respectively obtained.

比较图5a、5b和5c可看出，时间轴范围不同(即选取的预设时间阈值不同)，得到的拟合公式也不同，最大的直流分量为图5a中的84.495kA，最小的为图5c中的70.57kA；最大的时间常数为图5c中的1/12.09＝83ms，最小的时间常数为图5a中的1/16.76＝60ms。可见，时间范围不同，得到的时间差异很大。Comparing Figures 5a, 5b, and 5c, it can be seen that the range of the time axis is different (that is, the selected preset time threshold is different), and the fitting formulas obtained are also different. The largest DC component is 84.495kA in Figure 5a, and the smallest is 70.57kA in 5c; the largest time constant is 1/12.09=83ms in Fig. 5c, and the smallest time constant is 1/16.76=60ms in Fig. 5a. It can be seen that the time ranges are different, and the obtained time varies greatly.

由理论分析，直流分量的最大值必然等于短路电流周期分量改变量的绝对值，因此IDC的值应接近交流分量峰值I0(72kA)。所以，图5b的时间范围取120ms是合理的。According to theoretical analysis, the maximum value of the DC component must be equal to the absolute value of the short-circuit current periodic component change, so the value of I DC should be close to the peak value of the AC component I 0 (72kA). Therefore, it is reasonable to take 120ms as the time range in Fig. 5b.

在对获取的时间常数进行校验时，首先将短路电流的交流分量和直流分量进行叠加，形成叠加短路电流波形，然后将叠加短路电流波形与图2中的原短路电流进行对比，比对结果如图6所示。由图6可以看出，叠加短路电流波形与计算的短路电流波形较比较接近，因此，可以确定获取的时间常数准确。When verifying the obtained time constant, the AC component and the DC component of the short-circuit current are first superimposed to form a superimposed short-circuit current waveform, and then the superimposed short-circuit current waveform is compared with the original short-circuit current in Figure 2, and the comparison results As shown in Figure 6. It can be seen from Figure 6 that the superimposed short-circuit current waveform is relatively close to the calculated short-circuit current waveform, so it can be determined that the obtained time constant is accurate.

图7为根据本发明实施方式的计算短路电流直流分量的时间常数的理论值的系统700的结构示意图。如图7所示，本发明的实施方式提供的计算短路电流直流分量的时间常数的理论值的系统700，包括：交流分量的峰值确定单元701、第一直流分量衰减曲线获取单元702、第二直流分量衰减曲线获取单元703、直流分量波形确定单元704、拟合公式获取单元705和时间常数理论值确定单元706。FIG. 7 is a schematic structural diagram of a system 700 for calculating the theoretical value of the time constant of the DC component of the short-circuit current according to an embodiment of the present invention. As shown in FIG. 7 , the system 700 for calculating the theoretical value of the time constant of the DC component of the short-circuit current provided by the embodiment of the present invention includes: a peak value determination unit 701 of the AC component, a first DC component attenuation curve acquisition unit 702, a second Two DC component attenuation curve acquisition unit 703 , DC component waveform determination unit 704 , fitting formula acquisition unit 705 and time constant theoretical value determination unit 706 .

优选地，所述交流分量的峰值确定单元701，用于对短路电流波形进行傅里叶分析，以确定所述短路电流的交流分量的峰值。Preferably, the peak value determination unit 701 of the AC component is configured to perform Fourier analysis on the short-circuit current waveform to determine the peak value of the AC component of the short-circuit current.

优选地，所述第一直流分量衰减曲线获取单元702，用于对所述短路电流波形的上包络线和下包络线进行拟合，以获取第一直流分量衰减曲线。Preferably, the first DC component attenuation curve acquisition unit 702 is configured to fit the upper and lower envelopes of the short-circuit current waveform to acquire the first DC component attenuation curve.

优选地，所述第二直流分量衰减曲线获取单元703，用于利用谐波分析方法对所述短路电流波形进行分析，以获取第二直流分量衰减曲线。Preferably, the second DC component attenuation curve acquisition unit 703 is configured to analyze the short-circuit current waveform using a harmonic analysis method to acquire a second DC component attenuation curve.

优选地，所述直流分量波形确定单元704，用于分别选取所述第一直流分量衰减曲线和第二直流分量衰减曲线在故障开始时，预设时间阈值段内的曲线作为第一直流分量波形和第二直流分量波形。Preferably, the DC component waveform determining unit 704 is configured to respectively select the first DC component attenuation curve and the second DC component attenuation curve at the beginning of the fault, and the curve within the preset time threshold period as the first DC component component waveform and a second DC component waveform.

优选地，其中所述预设时间阈值的取值范围为[60,150)，单位为ms。Preferably, the value range of the preset time threshold is [60, 150), and the unit is ms.

优选地，所述拟合公式获取单元705，用于分别对所述第一直流分量波形和第二直流分量波形进行指数拟合，以分别获取满足拟合原则的预设格式的第一拟合公式和第二拟合公式。Preferably, the fitting formula obtaining unit 705 is configured to perform exponential fitting on the first DC component waveform and the second DC component waveform respectively, so as to respectively obtain the first fitting formulas in a preset format satisfying the fitting principle. fit formula and the second fit formula.

优选地，其中所述预设格式公式为：

Figure GDA0002061532570000101
所述拟合原则为：IDC与I0的相对误差小于等于第二预设误差阈值；Preferably, wherein the preset format formula is:
Figure GDA0002061532570000101
The fitting principle is: the relative error between IDC and I0 is less than or equal to the second preset error threshold;

其中，IDC为故障时刻t0时刻的故障电流的直流分量；t为故障开始后的时刻；τ为时间常数；I0为所述短路电流的交流分量的峰值。Wherein, I DC is the DC component of the fault current at the fault time t 0 ; t is the time after the fault starts; τ is the time constant; I 0 is the peak value of the AC component of the short-circuit current.

优选地，所述时间常数理论值确定单元706，用于当所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差小于等于第一预设误差阈值时，选取较大的时间常数作为时间常数理论值。Preferably, the time constant theoretical value determination unit 706 is configured to determine when the relative error between the first time constant and the second time constant in the first fitting formula and the second fitting formula is less than or equal to the first preset error When the threshold is set, a larger time constant is selected as the theoretical value of the time constant.

优选地，其中所述系统还包括：校验单元，用于将所述短路电流的直流分量分别和所述第一直流分量波形和第二直流分量波形进行叠加，以获取第一叠加短路电流波形和第二叠加短路电流波形；所述分别将所述第一叠加短路电流波形和第二叠加短路电流波形与所述短路电流波形进行比对，以获取比对结果；其中，若所述比对结果指示所述第一叠加短路电流波形和第二叠加短路电流波形分别与所述短路电流波形重合率大于等于预设重合阈值，则表明确定的时间常数理论值准确。Preferably, the system further includes: a checking unit, configured to superimpose the DC component of the short-circuit current with the first DC component waveform and the second DC component waveform respectively, so as to obtain the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform; the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform are compared with the short-circuit current waveform to obtain the comparison result; wherein, if the comparison The results indicate that the coincidence rate of the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform is greater than or equal to a preset coincidence threshold, which indicates that the determined theoretical value of the time constant is accurate.

优选地，其中所系统还包括：预设时间阈值重置单元，用于当所述比对结果指示所述第一叠加短路电流波形或第二叠加短路电流波形与所述短路电流波形重合率小于预设重合阈值时，表明确定的时间常数理论值不准确，重新选取新的预设时间阈值进行计算；或当获取的第一拟合公式和第二拟合公式不满足拟合原则；或所述第一拟合公式和第二拟合公式中的第一时间常数和第二时间常数的相对误差大于第一预设误差阈值时，重新选取新的预设时间阈值，并返回直流分量波形确定单元。Preferably, the system further includes: a preset time threshold reset unit, used for when the comparison result indicates that the coincidence ratio between the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is less than When the coincidence threshold is preset, it indicates that the determined theoretical value of the time constant is inaccurate, and a new preset time threshold is selected for calculation; or when the obtained first fitting formula and second fitting formula do not satisfy the fitting principle; or the obtained When the relative error between the first time constant and the second time constant in the first fitting formula and the second fitting formula is greater than the first preset error threshold, reselect a new preset time threshold, and return to DC component waveform determination unit.

本发明的实施例的计算短路电流直流分量的时间常数的理论值的系统700与本发明的另一个实施例的计算短路电流直流分量的时间常数的理论值的方法300相对应，在此不再赘述。The system 700 for calculating the theoretical value of the time constant of the DC component of the short-circuit current in the embodiment of the present invention corresponds to the method 300 for calculating the theoretical value of the time constant of the DC component of the short-circuit current in another embodiment of the present invention, which is not repeated here repeat.

已经通过参考少量实施方式描述了本发明。然而，本领域技术人员所公知的，正如附带的专利权利要求所限定的，除了本发明以上公开的其他的实施例等同地落在本发明的范围内。The invention has been described with reference to a small number of embodiments. However, it is clear to a person skilled in the art that other embodiments than the invention disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

通常地，在权利要求中使用的所有术语都根据他们在技术领域的通常含义被解释，除非在其中被另外明确地定义。所有的参考“一个/所述/该[装置、组件等]”都被开放地解释为所述装置、组件等中的至少一个实例，除非另外明确地说明。这里公开的任何方法的步骤都没必要以公开的准确的顺序运行，除非明确地说明。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/the/the [means, component, etc.]" are openly construed to mean at least one instance of said means, component, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims (8)

1. A method of calculating a theoretical value of a time constant of a direct current component of a short circuit current, the method comprising:
fourier analyzing the short circuit current waveform to determine a peak value of an alternating current component of the short circuit current;
fitting an upper envelope curve and a lower envelope curve of the short-circuit current waveform to obtain a first direct-current component attenuation curve;
analyzing the short-circuit current waveform by using a harmonic analysis method to obtain a second direct current component attenuation curve;
respectively selecting curves in a preset time threshold period as a first direct current component waveform and a second direct current component waveform when the first direct current component attenuation curve and the second direct current component attenuation curve start to fail;
respectively performing exponential fitting on the first direct current component waveform and the second direct current component waveform to respectively obtain a first fitting formula and a second fitting formula which meet a preset format of a fitting principle;
when the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is smaller than or equal to a first preset error threshold value, a larger time constant is selected as a theoretical value of the time constant;
wherein the method further comprises:
superposing the direct current component of the short-circuit current with the first direct current component waveform and the second direct current component waveform respectively to obtain a first superposition short-circuit current waveform and a second superposition short-circuit current waveform;
comparing the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform respectively to obtain a comparison result; if the comparison result indicates that the coincidence rate of the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform is greater than or equal to a preset coincidence threshold value, the determined theoretical value of the time constant is accurate;
and when the comparison result indicates that the coincidence rate of the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is smaller than a preset coincidence threshold value, indicating that the determined time constant theoretical value is inaccurate, and reselecting a new preset time threshold value for calculation.
2. The method of claim 1, wherein the preset time threshold has a value in ms in a range of [60,150 ].
3. The method of claim 1, wherein the pre-set format formula is:
Figure FDA0004153587820000021
the fitting principle is as follows: i DC And I 0 The relative error of (2) is less than or equal to a second preset error threshold;
wherein I is DC For the moment of failure t 0 A direct current component of the fault current at the moment; t is the time after the fault begins; τ is a time constant; i 0 Is the peak value of the alternating component of the short-circuit current.
4. The method according to claim 1, wherein the method further comprises:
when the acquired first fitting formula and second fitting formula do not meet the fitting principle; or when the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is larger than a first preset error threshold value, a new preset time threshold value is selected again for calculation.
5. A system for calculating a theoretical value of a time constant of a direct current component of a short circuit current, the system comprising:
a peak value determining unit of alternating current component, which is used for carrying out Fourier analysis on the short circuit current waveform so as to determine the peak value of the alternating current component of the short circuit current;
the first direct current component attenuation curve acquisition unit is used for fitting the upper envelope curve and the lower envelope curve of the short-circuit current waveform to acquire a first direct current component attenuation curve;
the second direct current component attenuation curve acquisition unit is used for analyzing the short circuit current waveform by utilizing a harmonic analysis method so as to acquire a second direct current component attenuation curve;
the direct current component waveform determining unit is used for respectively selecting curves in a preset time threshold period as a first direct current component waveform and a second direct current component waveform when the first direct current component attenuation curve and the second direct current component attenuation curve start to fail;
the fitting formula obtaining unit is used for respectively carrying out exponential fitting on the first direct current component waveform and the second direct current component waveform so as to respectively obtain a first fitting formula and a second fitting formula which meet a preset format of a fitting principle;
the time constant theoretical value determining unit is used for selecting a larger time constant as a time constant theoretical value when the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is smaller than or equal to a first preset error threshold value;
wherein the system further comprises:
the verification unit is used for superposing the direct current component of the short-circuit current with the first direct current component waveform and the second direct current component waveform respectively so as to obtain a first superposition short-circuit current waveform and a second superposition short-circuit current waveform; comparing the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform respectively to obtain a comparison result; if the comparison result indicates that the coincidence rate of the first superimposed short-circuit current waveform and the second superimposed short-circuit current waveform with the short-circuit current waveform is greater than or equal to a preset coincidence threshold value, the determined theoretical value of the time constant is accurate;
and the preset time threshold resetting unit is used for indicating that the determined theoretical value of the time constant is inaccurate when the comparison result indicates that the coincidence rate of the first superimposed short-circuit current waveform or the second superimposed short-circuit current waveform and the short-circuit current waveform is smaller than a preset coincidence threshold value, and re-selecting a new preset time threshold value for calculation.
6. The system of claim 5, wherein the predetermined time threshold has a value in ms in the range of [60,150 ].
7. The system of claim 5, wherein the pre-set format formula is:
Figure FDA0004153587820000031
the fitting principle is as follows: i DC And I 0 The relative error of (2) is less than or equal to a second preset error threshold;
wherein I is DC For the moment of failure t 0 A direct current component of the fault current at the moment; t is the time after the fault begins; τ is a time constant; i 0 Is the peak value of the alternating component of the short-circuit current.
8. The system of claim 5, wherein the system further comprises:
the preset time threshold resetting unit is used for judging whether the acquired first fitting formula and second fitting formula do not meet the fitting principle; or when the relative error of the first time constant and the second time constant in the first fitting formula and the second fitting formula is larger than a first preset error threshold, a new preset time threshold is selected again, and the direct current component waveform determining unit is returned.
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