WO2022022751A1 - 不同类型电流互感器混用线路的微分电流差动保护方法 - Google Patents

不同类型电流互感器混用线路的微分电流差动保护方法 Download PDF

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WO2022022751A1
WO2022022751A1 PCT/CN2021/118408 CN2021118408W WO2022022751A1 WO 2022022751 A1 WO2022022751 A1 WO 2022022751A1 CN 2021118408 W CN2021118408 W CN 2021118408W WO 2022022751 A1 WO2022022751 A1 WO 2022022751A1
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current
rogowski coil
differential
different types
differential protection
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PCT/CN2021/118408
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English (en)
French (fr)
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李宝伟
石欣
王莉
朱云峰
陈�光
王耀武
席颖颖
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许继集团有限公司
许继电气股份有限公司
许昌许继软件技术有限公司
国家电网有限公司
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Publication of WO2022022751A1 publication Critical patent/WO2022022751A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means

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  • the invention relates to a differential current differential protection method suitable for mixed lines of different types of current transformers, and belongs to the technical field of power system relay protection.
  • the present invention proposes a differential current differential protection method suitable for mixed circuits of different types of current transformers, which eliminates the influence of the integrator link and improves the The reliability of differential protection is improved.
  • the purpose of the present invention is to provide a differential current differential protection method suitable for mixed circuits of different types of current transformers, so as to adapt to the mixed use of electronic current transformers and electromagnetic current transformers in the process of digitalization of substations, and avoid traditional Rogowski coils.
  • the influence of the integrator link of the current type transformer on the differential protection improves the reliability of the differential protection.
  • the present invention provides a differential current differential protection method for mixed circuits of different types of current transformers to solve the above problems, and the method includes the following steps:
  • the continuous transfer function of the Rogowski coil model in the step 1) is:
  • s is the complex variable
  • M is the mutual inductance between the coil and the primary wire
  • R s is the total resistance of the coil winding and lead wire
  • L is the inductance of the coil
  • C 0 is the stray capacitance of the coil
  • R a is the load resistance.
  • T is the sampling period
  • ⁇ 0 is a specific angular velocity
  • z is the z transform operator.
  • z is the z transform operator
  • a 1 , a 2 , a 3 , b 1 , b 2 , and b 3 are coefficients obtained by discretizing the continuous transfer function of the Rogowski coil through pre-correction bilinear transform.
  • ⁇ 0 is an angular velocity corresponding to a frequency of 50 Hz.
  • step 1) virtual digital Rogowski coil model is:
  • n is the sampling number
  • X is the input signal of the virtual Rogowski coil
  • Y is the output signal of the virtual Rogowski coil
  • a 1 , a 2 , a 3 , b 1 , b 2 , b 3 are the continuous transfer function of the Rogowski coil Discrete coefficients by pre-correcting bilinear transformation.
  • i cd ' is the differential current
  • i re ' is the braking current
  • i' m is the measured value of the M-side current through the Rogowski coil
  • i' n is the value of the N-side current after passing through the virtual digital Rogowski coil. coil.
  • i' c is the capacitive current through the virtual digital Rogowski coil
  • u' c is the measured phase voltage through the virtual digital Rogowski coil
  • u' c0 is the zero-sequence voltage through the virtual digital Rogowski coil
  • C 1 and C 0 are respectively Positive-sequence capacitance and zero-sequence capacitance over the full length of the line.
  • i 'm is the measured value of the M-side current through the Rogowski coil
  • i'n is the value of the N-side current after passing through the virtual digital Rogowski coil
  • u'm and u'n are the measured voltages on the M-side and N-side respectively after the virtual digital Rogowski coil.
  • the value after the digital Rogowski coil; u' m0 and u' n0 are the value of the zero-sequence voltage measured on the M side and the N side after the virtual digital Rogowski coil;
  • k c is the zero-sequence current compensation coefficient of the capacitor
  • i cd ′ is the differential current
  • i re ′ is the braking current
  • i set is the fixed value of the traditional differential protection
  • K is the braking coefficient
  • k is the amplitude response coefficient of the Rogowski coil.
  • the braking coefficient K takes a value of 0.7.
  • the present invention provides a current differential protection method for a mixed circuit of different types of current transformers.
  • the method first analyzes and models the physical model of the Rogowski coil without an integral loop, and discretizes the transfer function of the model to obtain its digital transfer model and construct a virtual digital Rogowski coil;
  • the signal collected by the transformer is processed by the virtual digital Rogowski coil.
  • the differential current is constructed by using the current collected by the Rogowski coil and the opposite side current collected by the electromagnetic current transformer through the virtual digital Rogowski coil. Protect.
  • the present invention based on the analysis of the shortcomings of the Rogowski coil integral link of a typical electronic current transformer in the process of signal transmission, and the idea of inheriting the advantages and improving the shortcomings, proposes a method suitable for different types of current transformers. Differential current differential protection method for the mixed use of the device.
  • the differential current differential protection method proposed by the invention is suitable for the mixed connection of different types of current transformers, and solves the problem of the influence of different types of current transformers on both sides of the line on differential protection during the promotion of intelligent substations.
  • the scheme can omit the integral link of the electronic transformer in the field engineering application, reduce the cost, reduce the delay of the intermediate link, and avoid the influence of the damage of the integrator on the protection.
  • the present invention is a differential current differential protection method suitable for the mixed connection of different types of current transformers.
  • the Rogowski coil electronic current transformer sampling circuit used does not contain an integral link, which avoids the traditional Rogowski coil integrator link to the accuracy of Influence.
  • the invention is suitable for lines in the case of mixed use of different types of current transformers, reliable action in the area of faults, reliable non-operation in the out-of-area faults.
  • FIG. 1 is a flowchart of a differential current differential protection method for a mixed circuit of different types of current transformers according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram of a data processing link of a differential current differential protection method for a mixed circuit of different types of current transformers according to an embodiment of the present invention
  • FIG. 3 is a circuit diagram of a Rogowski coil according to an embodiment of the present invention.
  • the present invention provides a differential current differential protection method suitable for mixed lines of different types of current transformers.
  • the method establishes a digital model of virtual digital Rogowski coil by analyzing the structure of Rogowski coil, and constructs differential protection by passing the sampling signal of electromagnetic current transformer through the virtual digital Rogowski coil.
  • the original voltage signal is also passed through the virtual digital Rogowski coil to calculate the capacitive current, and the capacitive current is used to compensate the differential current and braking current.
  • the current on both sides and the capacitive current related to the differential protection pass through the Rogowski coil or the virtual digital Rogowski coil, so that they pass through the same transmission link, thereby reducing the transient link of the Rogowski coil transfer function. Influence, improve the accuracy of differential protection.
  • the present invention is a differential current differential protection method suitable for mixed lines of different types of current transformers.
  • the steps of the method are shown in Figure 1, and the schematic diagram 2 of its data processing link is shown in Figure 2.
  • the specific content is:
  • s is the complex variable
  • M is the mutual inductance between the coil and the primary wire
  • R s is the total resistance of the coil winding and lead wire
  • L is the inductance of the coil
  • C 0 is the stray capacitance of the coil
  • R a is the load resistance.
  • the transfer function is discretized by pre-modified bilinear transformation, and the specific method is as follows: the following formula is brought into the continuous transfer function to realize.
  • T is the sampling period
  • ⁇ 0 is a specific angular velocity
  • z is the z transform operator. Discretization in this way can ensure that the amplitude response and phase response at the frequency corresponding to ⁇ 0 are the same as the continuous transfer function.
  • ⁇ 0 in the present invention is the angular velocity corresponding to a frequency of 50 Hz.
  • the z transfer function corresponding to the continuous transfer function of the Rogowski coil is obtained as:
  • z is the z transform operator
  • a 1 , a 2 , a 3 , b 1 , b 2 , and b 3 are coefficients obtained by discretizing the continuous transfer function of the Rogowski coil through pre-correction bilinear transform.
  • the virtual digital Rogowski coil is:
  • n is the sampling number
  • X is the input signal of the virtual Rogowski coil
  • Y is the output signal of the virtual Rogowski coil
  • a 1 , a 2 , a 3 , b 1 , b 2 , b 3 are the continuous transfer function of the Rogowski coil Discrete coefficients by pre-correcting bilinear transformation.
  • the virtual digital Rogowski coil is used to process the sampling signal of the electromagnetic current transformer, so that the signal collected by the electromagnetic current transformer also becomes the current signal in the differential domain;
  • i cd ′ is the differential current
  • i re ′ is the braking current
  • i′ m is the measured value of the M-side current through the Rogowski coil
  • i′ n is the value of the N-side current after the virtual digital Rogowski coil
  • i' c is the capacitive current through the virtual digital Rogowski coil
  • u' c is the measured phase voltage through the virtual digital Rogowski coil
  • u' c0 is the zero-sequence voltage through the virtual digital Rogowski coil
  • C 1 and C 0 are respectively Positive-sequence capacitance and zero-sequence capacitance over the full length of the line.
  • i 'm is the measured value of the M-side current through the Rogowski coil
  • i'n is the value of the N-side current after passing through the virtual digital Rogowski coil
  • u'm and u'n are the measured voltages on the M-side and N-side respectively after the virtual digital Rogowski coil.
  • the value after the digital Rogowski coil; u' m0 and u' n0 are the value of the zero-sequence voltage measured on the M side and the N side after the virtual digital Rogowski coil;
  • k c is the zero-sequence current compensation coefficient of the capacitor
  • the Rogowski coil is a transfer function in the differential domain.
  • the voltage through the virtual digital Rogowski coil is differentiated.
  • the differentiation will cause the higher harmonics to be amplified. Therefore, a low-pass filter must be added.
  • the calculated differential current and braking current are passed through a low-pass filter to reduce the impact of higher harmonics on the protection performance.
  • the present invention selects a Butterworth low-pass filter with a smaller window length, which can not only filter high-order harmonics, but also does not bring excessive delay to affect the action time of the differential protection.
  • i cd ′ is the differential current
  • i re ′ is the braking current
  • i set is the fixed value of the traditional differential protection
  • K is the braking coefficient, generally 0.7
  • k is the amplitude response coefficient of the Rogowski coil.
  • the present invention provides a differential current differential protection method for a mixed circuit of different types of current transformers.
  • the method first analyzes and models the physical model of the Rogowski coil without an integral loop, and discretizes the transfer function of the model to obtain its digital transfer model and construct a virtual digital Rogowski coil;
  • the signal collected by the transformer is processed by the virtual digital Rogowski coil.
  • the differential current is constructed by using the current collected by the Rogowski coil and the opposite side current collected by the electromagnetic current transformer through the virtual digital Rogowski coil. Protect.
  • the capacitance current in the differential domain on both sides is calculated, and the capacitance current is used to compensate the differential current, thereby improving the Accuracy of differential protection.
  • the present invention is a differential current differential protection method suitable for the mixed connection of different types of current transformers.
  • the Rogowski coil electronic current transformer sampling circuit used does not contain an integral link, which avoids the traditional Rogowski coil integrator link to the accuracy of Influence.
  • the invention is suitable for lines in the case of mixed use of different types of current transformers, reliable action in the area of faults, reliable non-operation in the out-of-area faults.
  • the invention studies the mathematical model of the Rogowski coil without an integral loop, constructs a virtual digital Rogowski coil, uses the virtual Rogowski coil to perform differential domain processing on the current collected by the conventional current transformer, and compares the processed current with the current collected by the actual Rogowski coil.
  • the differential protection is constructed for the opposite side current, which avoids the influence of time delay, phase shift, and poor low-frequency transmission characteristics caused by the Rogowski coil integral loop, and improves the reliability of the differential protection.
  • the scheme can omit the integral link of the electronic transformer in the field engineering application, which reduces the cost, reduces the delay of the intermediate link, and avoids the influence of the damage of the integrator on the protection.

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Abstract

一种不同类型电流互感器混用线路的微分电流差动保护方法，包括：对不带积分回路的罗氏线圈进行分析和建模，并将其模型的传递函数进行离散化，从而获取其数字传变模型，构造虚拟数字罗氏线圈；对电磁式电流互感器采集的信号经虚拟数字罗氏线圈，进行等传变处理；用经罗氏线圈采集的本侧电流和经电磁式电流互感器采集后经虚拟数字罗氏线圈的对侧电流，构造差动保护。同时，为了减小分布电容电流对差动保护的影响，将两侧的电压信号经虚拟数字罗氏线圈处理后，计算两侧微分域的电容电流，以此电容电流对差流进行补偿，从而提高差动保护的精度。该方法适用于不同类型电流互感器混用情况下的线路，在区内故障可靠动作，在区外故障可靠不动作。

Description

不同类型电流互感器混用线路的微分电流差动保护方法 技术领域
本发明涉及一种适用于不同类型电流互感器混用线路的微分电流差动保护方法，属于电力系统继电保护技术领域。
背景技术
随着智能变电站逐渐得到广泛应用，传统变电站将向智能化变电站过渡。在数字化变电站在建设过程中势必会出现线路两侧电磁型电流互感器与电子式电流互感器混用的情况。根据《智能变电站继电保护技术规范》要求：“线路纵联保护、母线差动保护、变压器差动保护应适应常规互感器和电子式互感器混合使用的情况。”电磁式电流互感器输出的电流和一次电流呈现比例关系。以罗氏线圈为主的电子式电流互感器(ECT)工作原理为法拉第电磁感应原理和安培环路定理，其输出为输入电流信号的微分，为得到原始电流信号，需要增加积分环节，由此会带来一定的时间延迟和相位偏移，降低了频响带宽，增加了功耗。特别是采用数字积分器的ECT在采样环节发生高频混叠时，又会造成低频信号传变放大，增大了传变误差。
因此，为了避免罗氏线圈电流型互感器积分环节传变信号的不利影响，本发明提出了一种适用于不同类型电流互感器混用线路的微分电流差动保护方法，消除了积分器环节影响，提高了差动保护的可靠性。
发明内容
本发明的目的是提供一种适用于不同类型电流互感器混用线路的微分电流差动保护方法，以适应变电站数字化过程中电子式电流互感器和电磁式电流互感器混用的情况，避免传统罗氏线圈电流型互感器积分器环节对差动保护的影响，提高差动保护的可靠性。
本发明为解决上述问题提供了一种不同类型电流互感器混用线路的微分电流差动保护方法，该方法包括以下步骤：
1)对不含积分回路的罗氏线圈的传变电路进行等值建模分析，构建虚拟数字罗氏线圈模型；
2)采用虚拟数字罗氏线圈对电磁式电流互感器的采样信号进行处理；
3)用经罗氏线圈采集的本侧电流和经电磁式电流互感器采集、并经虚拟数字罗氏线圈的对侧电流，用于计算差动电流和制动电流，以构造差动保护；
4)将不同类型电流互感器混用线路两侧的电压信号经虚拟数字罗氏线圈处理后，计算两侧微分域的电容电流，以此电容电流对差动电流和制动电流进行补偿；
5)将差动电流分别和一预定值以及制动电流进行比较，差动电流大于该预定值且大于制动电流，则差动保护动作。
所述步骤1)中罗氏线圈模型的连续传递函数为：
Figure PCTCN2021118408-appb-000001
其中：s为复变量，M为线圈与一次导线的互感，R s为线圈绕组和引线总电阻；L为线圈的电感；C 0为线圈的杂散电容；R a为负载电阻。
进一步的，对所述传递函数采用预修正双线性变换进行离散化处理，将下式(2)带入公式(1)中：
Figure PCTCN2021118408-appb-000002
其中，T为采样周期，ω 0为某一特定的角速度，z为z变换算子。
公式(2)带入公式(1)后，得到罗氏线圈连续传递函数对应的z传递函数形式为：
Figure PCTCN2021118408-appb-000003
其中，z为z变换算子，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
进一步的，所述ω 0为对应50Hz频率的角速度。
进一步的，所述步骤1)虚拟数字罗氏线圈模型为：
Figure PCTCN2021118408-appb-000004
其中，n为采样序号，X为虚拟罗氏线圈的输入信号，Y为虚拟罗氏线圈的输出信号，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
进一步的，所述步骤3)中差动电流和制动电流的计算公式如下：
Figure PCTCN2021118408-appb-000005
其中，i cd′为差动电流；i re′为制动电流；i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值虚拟数字罗氏线圈。
进一步的，所述步骤4)中电容电流的计算公式为：
Figure PCTCN2021118408-appb-000006
其中：i′ c为经虚拟数字罗氏线圈的电容电流；u′ c为经虚拟数字罗氏线圈的测量相电压；u′ c0为经虚拟数字罗氏线圈的零序电压；C 1和C 0分别为线路全长的正序电容和零序电容。
进一步的，经所述电容电流补偿的微分差动电流和制动电流的计算公式如下：
Figure PCTCN2021118408-appb-000007
其中，i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值；u′ m和u′ n分别为M侧和N侧测量电压经虚拟数字罗氏线圈后的值；u′ m0和u′ n0分别为M侧和N侧测量的零序电压经虚拟数字罗氏线圈后的值；k c为电容的零序电流补偿系数，
Figure PCTCN2021118408-appb-000008
进一步的，所述步骤5)中差动保护动作的判别条件为：
Figure PCTCN2021118408-appb-000009
其中，i cd′为差动电流；i re′为制动电流；i set为传统差动保护的定值；K为制动系数；k为罗氏线圈的幅值响应系数。
进一步的，制动系数K取值为0.7。
综上所述，本发明提供了一种不同类型电流互感器混用线路的电流差动保护方法。该方法首先对不带积分回路的罗氏线圈物理模型进行分析和建模，并将其模型的传递函数进行离散化，从而获取其数字传变模型，构造虚拟数字罗氏线圈；其次，对电磁式电流互感器采集的信号经虚拟数字罗氏线圈，进行等传变处理；最后，用经罗氏线圈采集的本侧电流和经电磁式电流互感器采集后经虚拟数字罗氏线圈的对侧电流，构造差动保护。同时，为了减小分布电容电流对差动保护的影响，将两侧的电压信号经虚拟数字罗氏线圈处理后，计算两侧微分域的电容电流，以此电容电流对差流进行补偿，从而提高差动保护的精度。本发明的有益效果是：本发明在分析了典型的电子式电流互感器罗氏线圈积分环节在信号传变过程中的缺点基础上，按继承优点改进缺点的思路，提出了适用于不同类型电流互感器混用情况的微分电流差动保护方法。本发明提出的微分电流差动保护方法适用于不同类型电流互感器混联的情况，解决了智能变电站推广过程中，线路两侧电流互感器类型不同对差动保护的影响的问题。同时，该方案在现场工程应用中可省略电子互感器的积分环节，降低了成本，减小中间环节的延时，并避免了积分器损坏对保护的影响。本发明的一种适用于不同类型电流互感器混联的微分电 流差动保护方法，所使用的罗氏线圈电子式电流互感器采样回路不含积分环节，避免了传统罗氏线圈积分器环节对精度的影响。该发明适用于不同类型电流互感器混用情况下的线路，在区内故障可靠动作，在区外故障可靠不动作。
附图说明
图1是本发明实施例的一种不同类型电流互感器混用线路的微分电流差动保护方法流程图；
图2是本发明实施例的一种不同类型电流互感器混用线路的微分电流差动保护方法的数据处理环节示意图；
图3是本发明实施例的罗氏线圈电路图。
具体实施方式
下面结合附图对本发明的具体实施方式做进一步的说明。
变电站智能化改造过程会出现线路两侧分别使用不同类型电流互感器的情况，分别为电磁式电流互感器与电子式电流互感器。鉴于典型电子式电流互感器罗氏线圈的积分环节存在的问题，本发明提供了一种适用于不同类型电流互感器混用线路的微分电流差动保护方法。该方法通过分析罗氏线圈结构，建立虚拟数字罗氏线圈数字模型，将电磁式电流互感器的采样信号经虚拟数字罗氏线圈后，构造差动保护。为提高精度，将原始电压信号也经虚拟数字罗氏线圈后计算电容电流，用该电容电流对差动电流和制动电流进行补偿。因此，差动保护相关的两侧电流、电容电流均经罗氏线圈或者虚拟数字罗氏线圈，使其经过了相同的传变环节，从而降低了罗氏线圈的传递函数的暂态环节对差动保护的影响，提高了差动保护的精度。
本发明一种适用于不同类型电流互感器混用线路的微分电流差动保护方法，该方法的步骤如图1所示，其数据处理环节示意图2所示，其具体内容为：
1)对不含积分回路的罗氏线圈的传变电路进行等值建模分析，不含积分回路的罗氏线圈的电路图如图3所示，其传递函数为：
Figure PCTCN2021118408-appb-000010
其中：s为复变量，M为线圈与一次导线的互感，R s为线圈绕组和引线总电阻；L为线圈的电感；C 0为线圈的杂散电容；R a为负载电阻。
将该传递函数用预修正双线性变换进行离散化处理，具体方法为：将下式带入连续传递函数实现。
Figure PCTCN2021118408-appb-000011
其中，T为采样周期，ω 0为某一特定的角速度，z为z变换算子。以该方法进行离散化，可以保证在ω 0对应的频率下的幅值响应和相位响应和连续传递函数相同。本发明中的ω 0为对应50Hz频率的角速度。
得到罗氏线圈连续传递函数对应的z传递函数形式为：
Figure PCTCN2021118408-appb-000012
其中，z为z变换算子，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
虚拟数字罗氏线圈为：
Figure PCTCN2021118408-appb-000013
其中，n为采样序号，X为虚拟罗氏线圈的输入信号，Y为虚拟罗氏线圈的输出信号，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
2)采用虚拟数字罗氏线圈，对电磁式电流互感器的采样信号进行处理，从而使得经电磁式电流互感器采集的信号也变为微分域的电流信号；
3)不同类型电流互感器混用线路两侧为不同类型电流互感器，假设本侧为罗氏线圈，对侧为电磁式电流互感器。将经罗氏线圈采集的本侧电流和经电磁式 电流互感器采集，再经虚拟数字罗氏线圈的对侧电流用于计算差动电流和制动电流。公式为：
Figure PCTCN2021118408-appb-000014
其中，i cd′为差动电流；i re′为制动电流；i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值；
4)将线路两侧电压经虚拟数字罗氏线圈后得到微分域的电压，以此电压计算微分域的电容电流，电容电流计算公式为：
Figure PCTCN2021118408-appb-000015
其中：i′ c为经虚拟数字罗氏线圈的电容电流；u′ c为经虚拟数字罗氏线圈的测量相电压；u′ c0为经虚拟数字罗氏线圈的零序电压；C 1和C 0分别为线路全长的正序电容和零序电容。
经电容电流补偿的微分差动电流和制动电流的计算公式如下：
Figure PCTCN2021118408-appb-000016
其中，i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值；u′ m和u′ n分别为M侧和N侧测量电压经虚拟数字罗氏线圈后的值；u′ m0和u′ n0分别为M侧和N侧测量的零序电压经虚拟数字罗氏线圈后的值；k c为电容的零序电流补偿系数，
Figure PCTCN2021118408-appb-000017
罗氏线圈是微分域的传递函数，同时，计算电容电流的过程中把经虚拟数字罗氏线圈的电压进行微分，微分会导致高次谐波被放大，因此须增加低通滤波器，将按照以上公式计算的差动电流和制动电流经低通滤波器，降低高次谐波对保护性能的影响。本发明选择窗长较小的巴特沃斯低通滤波器，既可过滤高次谐波， 也不会带来过大延时影响差动保护的动作时间。
5)将差动电流分别和差动保护电流定值以及制动电流进行比较，差动电流大于差动保护电流定值且大于制动电流，则差动保护动作。差动保护动作的具体判别条件为：
Figure PCTCN2021118408-appb-000018
其中，i cd′为差动电流；i re′为制动电流；i set为传统差动保护的定值；K为制动系数，一般取0.7；k为罗氏线圈的幅值响应系数。
综上所述，本发明提供了一种不同类型电流互感器混用线路的微分电流差动保护方法。该方法首先对不带积分回路的罗氏线圈物理模型进行分析和建模，并将其模型的传递函数进行离散化，从而获取其数字传变模型，构造虚拟数字罗氏线圈；其次，对电磁式电流互感器采集的信号经虚拟数字罗氏线圈，进行等传变处理；最后，用经罗氏线圈采集的本侧电流和经电磁式电流互感器采集后经虚拟数字罗氏线圈的对侧电流，构造差动保护。同时，为了减小分布电容电流对差动保护的影响，将两侧的电压信号经虚拟数字罗氏线圈处理后，计算两侧微分域的电容电流，以此电容电流对差流进行补偿，从而提高差动保护的精度。
本发明的一种适用于不同类型电流互感器混联的微分电流差动保护方法，所使用的罗氏线圈电子式电流互感器采样回路不含积分环节，避免了传统罗氏线圈积分器环节对精度的影响。该发明适用于不同类型电流互感器混用情况下的线路，在区内故障可靠动作，在区外故障可靠不动作。本发明研究不含积分回路的罗氏线圈数学模型，构造虚拟数字罗氏线圈，并利用虚拟的罗氏线圈对常规电流互感器采集的电流进行微分域处理，将处理后的电流和经实际罗氏线圈采集的对侧电流构造差动保护，避免了罗氏线圈积分回路带来的时间延时、相位偏移、低频传变特性差等影响，提高了差动保护的可靠性。同时，该方案在现场工程应用中可省略电子互感器的积分环节，降低了成本，减小中间环节的延时，并避免了 积分器损坏对保护的影响。
应当理解的是，本发明的上述具体实施方式仅仅用于示例性说明或解释本发明的原理，而不构成对本发明的限制。因此，在不偏离本发明的精神和范围的情况下所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。此外，本发明所附权利要求旨在涵盖落入所附权利要求范围和边界、或者这种范围和边界的等同形式内的全部变化和修改例。

Claims (10)

  1. 一种不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，该方法包括以下步骤：
    1)对不含积分回路的罗氏线圈的传变电路进行等值建模分析，构建出虚拟数字罗氏线圈模型；
    2)采用虚拟数字罗氏线圈对电磁式电流互感器的采样信号进行处理；
    3)用经罗氏线圈采集的本侧电流和经电磁式电流互感器采集、并经虚拟数字罗氏线圈的对侧电流，计算差动电流和制动电流，以构造差动保护；
    4)将不同类型电流互感器混用线路两侧的电压信号经虚拟数字罗氏线圈处理后，计算两侧微分域的电容电流，以此电容电流对差动电流和制动电流进行补偿；
    5)将差动电流分别和一预定值以及制动电流进行比较，差动电流大于该预定值且大于制动电流，则差动保护动作。
  2. 根据权利要求1所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述步骤1)中罗氏线圈模型的连续传递函数为：
    Figure PCTCN2021118408-appb-100001
    其中：s为复变量，M为线圈与一次导线的互感，R s为线圈绕组和引线总电阻；L为线圈的电感；C 0为线圈的杂散电容；R a为负载电阻。
  3. 根据权利要求2所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，对所述传递函数采用预修正双线性变换对罗氏线圈的连续传递函数进行离散化处理，将下式(2)带入罗氏线圈的连续传递函数中：
    Figure PCTCN2021118408-appb-100002
    其中，T为采样周期，ω 0为某一特定的角速度，z为z变换算子，s为罗氏线圈的连续传递函数中的复变量；
    得到罗氏线圈连续传递函数对应的z传递函数形式为：
    Figure PCTCN2021118408-appb-100003
    其中，z为z变换算子，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
  4. 根据权利要求3所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述ω 0为对应50Hz频率的角速度。
  5. 根据权利要求1所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述虚拟数字罗氏线圈模型为：
    Figure PCTCN2021118408-appb-100004
    其中，n为采样序号，X为虚拟罗氏线圈的输入信号，Y为虚拟罗氏线圈的输出信号，a 1、a 2、a 3、b 1、b 2、b 3为将罗氏线圈的连续传递函数通过预修正双线性变换离散后的系数。
  6. 根据权利要求1所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述步骤3)中差动电流和制动电流的计算公式如下：
    Figure PCTCN2021118408-appb-100005
    其中，i cd′为差动电流；i re′为制动电流；i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值。
  7. 根据权利要求1所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述步骤4)中电容电流的计算公式为：
    Figure PCTCN2021118408-appb-100006
    其中：i′ c为经虚拟数字罗氏线圈的电容电流；u′ c为经虚拟数字罗氏线圈的测 量相电压；u′ c0为经虚拟数字罗氏线圈的零序电压；C 1和C 0分别为线路全长的正序电容和零序电容。
  8. 根据权利要求7所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，经所述电容电流补偿的微分差动电流和制动电流的计算公式如下：
    Figure PCTCN2021118408-appb-100007
    其中，i′ m为M侧电流经罗氏线圈的测量值；i′ n为N侧电流经虚拟数字罗氏线圈后的值；u′ m和u′ n分别为M侧和N侧测量电压经虚拟数字罗氏线圈后的值；u′ m0和u′ n0分别为M侧和N侧测量的零序电压经虚拟数字罗氏线圈后的值；k c为电容的零序电流补偿系数，
    Figure PCTCN2021118408-appb-100008
  9. 根据权利要求1-8任一项所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，所述步骤5)中差动保护动作的判别条件为：
    Figure PCTCN2021118408-appb-100009
    其中，i cd′为差动电流；i re′为制动电流；i set为传统差动保护的定值；K为制动系数；k为罗氏线圈的幅值响应系数。
  10. 根据权利要求9所述的不同类型电流互感器混用线路的微分电流差动保护方法，其特征在于，制动系数K取值为0.7。
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