WO2021047568A1 - Method for automatically adjusting malfunction protection delay by means of tail current identification - Google Patents

Abstract

Disclosed is a method for restraining a tail current and preventing malfunction protection maloperation. A fault current is processed by means of a differential filtering algorithm to acquire first current data; the fault current is processed by means of a full-cycle Fourier algorithm to acquire second current data; the first current data is processed by means of half-wave integration to acquire third current data; and whether the third current data and the second current data both satisfy a malfunction action threshold is determined, and if the two both satisfy the malfunction action threshold, a malfunction protection action is started. The present invention is suitable for a scenario in which a relay protection secondary current transformer has a "tail current" after a short-circuit fault occurs in a power system, the effect of the tail current can be effectively reduced, and malfunction protection maloperation can be prevented.

Description

A Method for Automatically Adjusting Failure Protection Delay Through Tail Current Identification Technical field

The invention relates to a method for automatically adjusting the failure protection delay time through the identification of the trailing current, and belongs to the relay protection of the electric power system.

current technology

Circuit breaker failure protection is a kind of backup protection widely used in power systems. According to the principle of circuit breaker failure protection, the delay setting of circuit breaker failure protection should consider the sum of circuit breaker action time, current element protection return time, and time coordination margin. When the system fails, the relay protection detects the failure and the action outlet trips. After the circuit breaker is opened, the CT current may be tailed due to the attenuated DC component. At this time, the CT current is not zero, but gradually decays to zero according to a certain time constant. It may cause the return time of the current element to be too long. When the failure protection delay setting is small, it may cause the failure protection to malfunction. In order to prevent malfunction of the failure protection, the current setting of the circuit breaker failure protection action time is generally set to 200-250ms, which is used to avoid the possible excessive tripping time of the circuit breaker and the CT tail current when the fault is removed, which causes the current element to return too much. Wait for things slowly. But the problem is that when the switch fails, the isolation fault time is too long, the typical time can reach 370ms ~ 405ms.

When the power system fails and the switch failure fault isolation time is too long, there may be system instability problems for some circuit breakers. For UHV multi-circuit DC concentrated feed into the nearby area, the switch failure fault isolation time is too long, and it may also cause the multi-circuit DC to have multiple consecutive commutation failures at the same time, resulting in DC blocking, resulting in a huge load transfer, and the transmission and receiving The end-to-end power grid has a serious impact, and there is even a risk of network collapse.

再结合全周傅氏算法(其中，

为第n点 电流采样值，

为第n-1点电流采样值，

为差分算法后电流值)，该算法对故障电流中的恒定直流分量有良好的抑制作用，对图4所示的衰减直流分量也有一定的抑制效果。 In order to suppress the DC component in the fault current, the prior art proposes to perform differential filtering on the original current collected by the secondary CT.

Combined with the full-week Fourier algorithm (where,

Is the current sampling value at the nth point,

Is the current sampling value at point n-1,

It is the current value after the differential algorithm). The algorithm has a good suppression effect on the constant DC component in the fault current, and also has a certain suppression effect on the attenuated DC component shown in Figure 4.

The existing attenuated DC component suppression algorithm (differential filtering algorithm) has obvious suppression effect on the constant DC component in the fault current, but the suppression effect on the attenuated DC component is limited. The full-cycle Fourier algorithm needs to use the full-cycle data (20ms), which prolongs the time for judging the return of the fault current. In order to solve the problem that some circuit breakers may have system instability when the switch failure fault isolation time is too long, and may cause multiple commutation failures of multiple DCs at the same time, it is necessary to shorten the failure protection action time, thereby increasing The attenuation of the DC component leads to the risk of malfunction of the failure protection.

Summary of the invention

In view of the above-mentioned shortcomings in the existing research, the purpose of the present invention is to provide a method for suppressing the trailing current and preventing the malfunction of the malfunction protection, so as to solve the problem of the risk of malfunction of the malfunction protection in the prior art.

In order to solve the above technical problems, the technical solutions adopted by the present invention are:

A method for suppressing trailing current and preventing malfunction of failure protection, the method includes the following steps:

Process the fault current through a differential filtering algorithm to obtain the first current data;

Process the fault current through the full-cycle Fourier algorithm to obtain the second current data;

Processing the first current data by half-wave integration to obtain third current data;

It is determined whether the third current data and the second current data meet the failure action threshold at the same time, and if the failure action threshold is met at the same time, a failure protection action start instruction is sent.

Further, the method for acquiring the first current data includes:

The first current data is obtained by the following formula:

为第一电流数据，

为第n点故障电流采样值，

为第n-1点故障电流采样值，

表示各相电流，k为电流离散采样值的比值。 among them,

Is the first current data,

Is the sampling value of the fault current at the nth point,

Is the sampling value of fault current at point n-1,

Indicates the current of each phase, and k is the ratio of the discrete sampling values of the current.

Further, the method for acquiring the third current data includes:

Integral algorithm for fault current:

Among them, i(t) is the fault current, S is the integral value of the fault current function, and T is the data sampling period;

Put the first current data into formula (1) to obtain the third current data:

Wherein: i _s a third current data, n represents the discrete sample position.

Further, the method for acquiring the second current data includes:

Fourier decomposition of the fault current function:

In the formula, i(t) is the fault current, I _m is the peak value of each integral harmonic component, α _{m is} the initial phase angle of each integral harmonic component, ω is the angular frequency, and n represents the position of the discrete sampling point;

Let m=1, and obtain the coefficient of the fundamental component according to the orthogonality of the trigonometric function as:

Among them, X ₁ is the amplitude of the second current data, α ₁ is the phase of the second current data, a ₁ is the real part _{of the fundamental wave current, b 1} is the imaginary part of the fundamental wave current, and x ₁ (t) is the base Wave current function, T is the data sampling period.

Further, the length of the data window of the half-wave integration algorithm is 10 ms; the length of the data window of the full-cycle Fourier algorithm is 20 ms.

Further, the method further includes: if the processed current cannot meet the failure action threshold at the same time, sending a failure protection return instruction.

Further, the method further includes:

Judging whether there is a tail current in the first current data and the second current data;

If there is no trailing current, the failure protection start command will be sent according to the setting delay;

If there is a trailing current, send an instruction to extend the failure protection action time.

Further, the method for judging the trailing current includes:

If the fault current sampling value is continuously greater than zero or continuously less than zero within the time of more than one cycle data window, there is a phenomenon of current tailing.

Further, the time of the one cycle data window is 20 ms.

A computer-readable storage medium has a computer program stored thereon, and when the program is executed by a processor, the steps of the above-mentioned method are realized.

Compared with the prior art, the beneficial effects achieved by the present invention are:

The invention shortens the return time of the protection judgment fault current when there is an attenuated DC component through the new differential algorithm; the invention uses the full-cycle Fourier algorithm combined with the half-wave integral algorithm to shorten the judgment failure under the premise of ensuring the accuracy of the failure protection action The fault current return time reduces the risk of malfunction of the failure protection; through the identification of the tail current, the current tail phenomenon can be reliably identified, and the failure protection action time can be dynamically adjusted to prevent the failure protection from malfunctioning under the premise of shortening the failure protection action time.

Description of the drawings

Figure 1 is a diagram of the method of dynamically adjusting the failure protection action time and failure quick return;

Figure 2 is a comparison diagram of no-flow return time;

[Corrected according to Rule 91 on 17.12.2020]
Figure 3a is a fault current diagram;
Figure 3b is a comparison diagram of the amplitude of the trailing current;

Figure 4 shows the "tailing" diagram of the CT secondary current.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

Failure protection is an important part of power grid security protection. When the failure protection fails to operate, the fault point will still not be able to be effectively removed, which will cause further damage to the equipment and further deterioration of the stability of the grid operation. However, if the failure protection malfunctions, that is, the circuit breaker has correctly isolated the fault point, but due to the malfunction protection malfunction, all adjacent circuit breakers still have to be tripped, which will inevitably cause the increase of the power outage range of the power grid.

In addition, in order to solve the problem that the switch failure fault isolation time is too long, there may be system instability for some circuit breakers, and may cause multiple DCs to occur at the same time for multiple consecutive commutation failures. It is necessary to shorten the failure protection action time.

In order to solve the contradiction between the shortening of the failure protection action time and the failure protection anti-misoperation (the shortening of the failure action time setting may not be able to escape the influence of the trailing current and increase the risk of the failure protection misoperation), the present invention proposes a long data window combined with a short The data window algorithm shortens the return time of the protection judgment fault current; an improved differential algorithm is proposed to further shorten the return time of the protection judgment fault current when there is an attenuated DC component; a trailing current identification method is proposed, which can reliably identify Current tailing phenomenon dynamically adjusts the failure protection action time, the failure protection operates quickly when there is no current tail, and the failure protection delays the action when there is current tail. It prevents the failure protection from malfunctioning under the premise of shortening the failure protection action time.

The specific process of the present invention is as follows:

A method for suppressing trailing current and preventing malfunction of failure protection, the method includes the following steps:

Process the fault current through a differential filtering algorithm to obtain the first current data;

Process the fault current through the full-cycle Fourier algorithm to obtain the second current data;

The method for acquiring the first current data includes: the first current data is acquired by the following formula:

为第一电流数据，

为第n点故障电流采样值，

为第n-1点故障电流采样值，

表示各相电流，k值根据衰减直流分量的衰减指数函数确定，为电流离散采样值(当前值/前一点)的比值，根据每周波24点采样建议k取0.998，差分算法能可靠滤除故障电流中的恒定直流分量； among them,

Is the first current data,

Is the sampling value of the fault current at the nth point,

Is the sampling value of fault current at point n-1,

Represents the current of each phase, the value of k is determined according to the attenuation exponential function of the attenuated DC component, and is the ratio of the current discrete sampling value (current value/previous point). According to the 24-point sampling of the weekly wave, it is recommended to take 0.998 for k. The differential algorithm can reliably filter out the fault The constant DC component in the current;

The first current data is processed by half-wave integration to obtain the third current data. The method for obtaining the third current data includes:

Integral algorithm for fault current:

引入公式(1)得到第三电流数据： Among them: i(t) is the fault current, S is the integral value of the fault current function, and T is the data sampling period. Take the 24 points sampling of the data sampling period as an example. After the data is discretized, the difference filtered data

Introduce formula (1) to obtain the third current data:

Wherein: i _s a third half-wave current data integration process.

The method for processing the fault current through the full-cycle Fourier algorithm to obtain the second current data includes: performing Fourier decomposition on the fault current:

Let b _m =I _m sinα _m , a _m =I _m cosα _m

In the formula, i(t) is the fault current, I _m is the peak value of each integral harmonic component, α _{m is} the initial phase angle of each integral harmonic component, ω is the angular frequency, and m represents the DC component contained in the current signal ( m=0), fundamental wave component (m=1) and other harmonic components (m>1).

Let m=1, and obtain the coefficient of the fundamental component according to the orthogonality of the trigonometric function as:

Among them, X ₁ is the amplitude of the second current data, α ₁ is the phase of the second current data, a ₁ is the real part _{of the fundamental wave current, b 1} is the imaginary part of the fundamental wave current, and x ₁ (t) is the base Wave current function, T is the data sampling period.

Let m=0 in formula 3, the discretized DC component i(n)=b ₀ (n) in the current signal, for the attenuated DC component, |b ₀ (0)|>|b ₀ (1)|>| b ₀ (2)|＞......＞|b ₀ (n-1)|＞|b ₀ (n)|, compare the improved differential filter value |i′(n)=|i(n) -0.998*i(n-1)|=|b ₀ (n)-0.998*b ₀ (n-1)|and the conventional differential filter value |i″(n)|=|i(n)-i(n -1)|=|b ₀ (n)-b ₀ (n-1)|, we get |i″(n)|＞|i′(n)|, combined with formula (2) to get the improved difference algorithm The half-wave integral value is less than the half-wave integral value of the conventional integral algorithm, which is more conducive to judging the failure current return.

The semi-integral algorithm only needs a 10ms data window, and the algorithm itself has a certain function of filtering out high-frequency components. Because in the process of integration, the positive and negative half cycles of the harmonic components cancel each other out, and the proportion of the remaining parts that are not completely canceled out is much smaller. However, the semi-integral algorithm cannot filter out the DC component, and the calculation accuracy is low; the full-cycle Fourier algorithm can not only completely filter out various integral harmonics and pure DC components, but also for non-integral high-frequency components and exponentially attenuated The low-frequency components contained in the aperiodic components also have a certain ability to suppress, but it requires a data window length of one cycle (20ms).

The invention shortens the return time of the protection judgment fault current by combining the long data window with the short data window algorithm;

Determine whether the second current data and the third current data processed by the full-cycle Fourier algorithm and half-wave integration meet the failure action threshold at the same time; if the failure action threshold is met at the same time, send the failure protection action start instruction.

If the processed current can meet the failure action threshold at the same time and there is no tail current, the failure protection start command will be sent according to the setting delay. If there is tail current, the failure protection action time extension command will be sent; if the processed current If the failure action threshold cannot be met at the same time, the failure protection return command will be sent.

As shown in Figure 1, when the failure protection receives the external protection tripping input signal, the value of the fault current after half-wave integration and the full-cycle Fourier algorithm all meets the failure action threshold (using AND logic), and meets other failures The protection action condition, after the failure protection delay time, the failure protection action; when any one of the calculated values of the fault current after the half-wave integration and the full-cycle Fourier algorithm is less than the failure current threshold, or the external protection tripping input signal returns, It is considered that the fault current is completely isolated (using OR logic), and the failure protection returns.

As shown in Figure 2, after 7A fault current removal with PSCD simulation, after standard differential filtering algorithm, the full-cycle Fourier algorithm and half-wave integral algorithm are compared with the no-current return time; the fault current is isolated at about 510ms, after the entire cycle After the Fourier algorithm, the no-flow condition is met at about 530ms; after the half-wave integration algorithm, the no-flow condition is met at about 520ms; the failure protection is used as a backup protection element, without considering the rapidity of the protection action, and the full data window is adopted. Zhou Fu's algorithm has good filtering characteristics and calculation accuracy, which can improve the sensitivity of failure protection actions. When the fault current returns, the fastness of the algorithm needs to be considered. The half-cycle integral algorithm has a short data window, which can quickly meet the current return threshold and reduce the risk of malfunction protection. The present invention uses a long data window (full-cycle Fourier algorithm) combined with a short data window. (Half-wave integral algorithm) method, under the premise of ensuring the accuracy of the failure protection action, shortens the return time of the failure fault current judgment, and reduces the risk of the failure protection malfunction.

As shown in Figure 3, PSCD is used to simulate the attenuated DC component. Comparison method one: standard differential filtering + half-wave integral algorithm and method two: improved differential filtering (differential filtering method in the present invention) + half-wave integral algorithm calculated Current value, the fault current is isolated from 280ms, and a tail current appears. The tail current is not zero for a long time. Compare the calculation amplitude of the tail current between method 1 and method 2. The value of k is the calculated value of 0.998 (the solid line in the figure). The value of k is 1.00 (the dotted line in the figure) is generally too small; for the attenuated DC component that may exist after the fault is removed, the improved differential filtering second half-wave integration algorithm combined with the full-cycle Fourier algorithm is used to calculate the failure return current, method two (improved differential Filtered half-wave integration algorithm + full-cycle Fourier algorithm) than method 1 (standard differential filtering after half-wave integration algorithm + full-cycle Fourier algorithm), the amplitude of the trailing current calculated by the method is smaller, which can quickly identify the fault current return status.

Comparing the simulation results of Fig. 2 and Fig. 3, the following conclusions are drawn:

From Figure 2: The half-wave integral algorithm has a short data window, which can quickly identify the no-current state of the current;

From Figure 3, it can be concluded that the second half-wave integral after improved differential filtering has a smaller amplitude of the trailing current calculated by the first method, which can quickly identify the no-current state of the trailing current;

或者持续小于零

利用该特征，首先用拖尾电流“过零点判别法”识别故障电流是否存在拖尾现象，即根据衰减直流分量在一定时间内偏向坐标轴一侧，不过零点的特征，当保护启动后，每周波实时检测电流过零情况，检测某一段时间内电流没有过零就可以认为是拖尾电流； As shown in Figure 4, a typical waveform of current tailing after fault removal is given. The real-time sampling value of tailing current is obviously skewed to the "0" side of the abscissa axis, that is, when there is more than one cycle data window (greater than 20ms) The original sample value continues to be greater than zero within the time period

Or continuously less than zero

Using this feature, first use the trailing current "zero-crossing point discrimination method" to identify whether the fault current has trailing phenomenon, that is, according to the attenuated DC component to one side of the coordinate axis within a certain period of time, but the zero point, when the protection is activated, every time Cycle real-time detection of the current zero-crossing situation, detecting that the current does not cross zero within a certain period of time can be considered as a tail current;

When the tail current is detected, the failure protection action delay time is automatically extended to avoid the slow return time of the current caused by the tail current; if the tail current is not detected, the failure protection will act quickly according to the failure protection delay after the setting is shortened.

A system for suppressing trailing current and preventing malfunction of malfunction protection, the system including a processor and a storage medium;

The storage medium is used to store instructions;

The processor is configured to operate according to the instruction to execute the steps of the above-mentioned method.

A computer-readable storage medium has a computer program stored thereon, and when the program is executed by a processor, the steps of the above-mentioned method are realized.

Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, this application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt 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 codes.

This application is described with reference to flowcharts and/or block diagrams of methods, devices (systems), and computer program products according to embodiments of this application. It should be understood that each process and/or block in the flowchart and/or block diagram, and 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 the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing equipment to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing equipment are generated It is a device that realizes the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device. The device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment. The instructions provide steps for implementing the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: Modifications or equivalent replacements of specific implementation manners without departing from the spirit and scope of the present invention shall be covered by the scope of protection of the claims of the present invention.

Claims (10)

A method for suppressing tail current and preventing malfunction of malfunction protection, characterized in that the method includes the following steps: Process the fault current through a differential filtering algorithm to obtain the first current data; Process the fault current through the full-cycle Fourier algorithm to obtain the second current data; Processing the first current data by half-wave integration to obtain third current data; It is determined whether the third current data and the second current data meet the failure action threshold at the same time, and if the failure action threshold is met at the same time, a failure protection action start instruction is sent. The method for suppressing the trailing current and preventing the malfunction of the failure protection according to claim 1, wherein the method for acquiring the first current data comprises: The first current data is obtained by the following formula:

among them,

Is the first current data,

Is the sampling value of the fault current at the nth point,

Is the sampling value of fault current at point n-1,

Indicates the current of each phase, and k is the ratio of the discrete sampling values of the current. The method for suppressing trailing current and preventing malfunction of failure protection according to claim 1, wherein the method for acquiring the third current data comprises: Integral algorithm for fault current:

Among them, i(t) is the fault current, S is the integral value of the fault current function, and T is the data sampling period; Put the first current data into formula (1) to obtain the third current data:

Wherein: i _s a third current data, n represents the discrete sample position. The method for suppressing the trailing current and preventing malfunction of the failure protection according to claim 1, wherein the method for acquiring the second current data comprises: Fourier decomposition of the fault current function:

Let b _m =I _m sinα _m , a _m =I _m cosα _m

In the formula, i(t) is the fault current, I _m is the peak value of each integral harmonic component, α _{m is} the initial phase angle of each integral harmonic component, ω is the angular frequency, and n represents the position of the discrete sampling point; Let m=1, and obtain the coefficient of the fundamental component according to the orthogonality of the trigonometric function as:

Among them, X ₁ is the amplitude of the second current data, α ₁ is the phase of the second current data, a ₁ is the real part _{of the fundamental wave current, b 1} is the imaginary part of the fundamental wave current, and x ₁ (t) is the base Wave current function, T is the data sampling period. The method for suppressing tail current and preventing malfunction of failure protection according to claim 1, wherein the length of the data window of the half-wave integral algorithm is 10 ms; the length of the data window of the full-cycle Fourier algorithm Is 20ms. The method for suppressing the trailing current and preventing malfunction of the failure protection according to claim 1, wherein the method further comprises: if the processed current cannot meet the failure operation threshold at the same time, sending a failure protection return instruction . The method for suppressing tail current and preventing malfunction of failure protection according to claim 1, wherein the method further comprises: Judging whether there is a tail current in the first current data and the second current data; If there is no trailing current, the failure protection start command will be sent according to the setting delay; If there is a trailing current, send an instruction to extend the failure protection action time. The method for suppressing the trailing current and preventing the malfunction of the failure protection according to claim 7, wherein the method for judging the trailing current includes: If the fault current sampling value is continuously greater than zero or continuously less than zero within the time of more than one cycle data window, there is a phenomenon of current tailing. The method for suppressing the trailing current and preventing the malfunction of the failure protection according to claim 8, wherein the time of the one cycle data window is 20 ms. A computer-readable storage medium having a computer program stored thereon is characterized in that the program implements the steps of the method according to any one of claims 1-9 when the program is executed by a processor.

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