WO2013086944A1 - 一种利用直流滤波器电流的高压直流输电全线速度保护方法 - Google Patents

一种利用直流滤波器电流的高压直流输电全线速度保护方法 Download PDF

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Publication number
WO2013086944A1
WO2013086944A1 PCT/CN2012/086076 CN2012086076W WO2013086944A1 WO 2013086944 A1 WO2013086944 A1 WO 2013086944A1 CN 2012086076 W CN2012086076 W CN 2012086076W WO 2013086944 A1 WO2013086944 A1 WO 2013086944A1
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Prior art keywords
filter
current
specific frequency
transmission line
electrical quantity
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PCT/CN2012/086076
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English (en)
French (fr)
Inventor
宋国兵
褚旭
高淑萍
索南·加乐
靳幸福
冉孟兵
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西安交通大学
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Publication of WO2013086944A1 publication Critical patent/WO2013086944A1/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
    • H02H7/22—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 for distribution gear, e.g. bus-bar systems; for switching devices
    • H02H7/226—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 for distribution gear, e.g. bus-bar systems; for switching devices for wires or cables, e.g. heating wires
    • 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
    • H02H7/268—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 for dc systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead

Definitions

  • the invention belongs to the technical field of power system relay protection, and specifically relates to a full-line quick-action protection method for a high-voltage direct current transmission line using a DC filter current.
  • High-voltage direct current (HVDC) transmission has an increasingly important position in long-distance and high-power transmission because of its large transmission power, low line cost and good control performance. It is used by large developed countries as a large-capacity and long-distance distance.
  • the main means of power transmission and heterogeneous networking has become a hot spot in power construction in China due to "West-to-East Power Transmission, North-South Mutual Supply, and National Networking". Since the introduction of DC transmission from Gezhouba to Shanghai in 1989, the number of DC transmission projects in China has been among the best in the world.
  • HVDC transmission lines are generally used as the communication line for large-area networking. Its safety and reliability are not only related to the stability of the system, but also directly affect the stable operation of the regional power grid connected to it and even the entire power grid. Since the DC line is long and the probability of failure is high, improving the operation level of the relay protection of the DC transmission line is of great significance for ensuring the safety and reliability of the DC transmission system. In a sense, the performance of the primary protection of the DC transmission line marks the operating level of the relay protection of the DC system.
  • traveling wave protection has the advantage of fast action speed, but in order to effectively utilize the rate of change of voltage and current, traveling wave protection requires extremely high sampling rate. In order to ensure the selectivity of protection in the case of lightning interference, it is forced to reduce the sensitivity of protection and increase the complexity of the protection criteria.
  • Research at home and abroad shows that: traveling wave protection is not only susceptible to lightning and interference, but also can not identify high-resistance faults, easy to malfunction, and low reliability of motion.
  • the main protection of the DC transmission line generally has problems such as incomplete theory, no universally applicable setting principle, and tuning only relying on simulation results. Therefore, the DC line relay protection device has high sampling rate requirements, and has poor selectivity and low sensitivity. The problem of low dependency.
  • the object of the present invention is to provide a single-ended electric quantity full-line quick-action protection method for high-voltage direct current transmission line faults with high sensitivity, good selectivity, fast action speed and high reliability. Thereby providing relay protection for the DC transmission line.
  • the present invention provides a single-ended electric quantity full-line quick-motion protection method for identifying faults in a high-voltage direct current transmission line region, which utilizes a specific value of a specific frequency electric quantity in a single-ended DC filter branch. Identification of internal faults and out-of-zone faults.
  • a full-line quick-acting protection method for a high-voltage direct current transmission line using a DC filter current the high-voltage transmission line includes a direct current transmission line and a converter station at both ends thereof, and the converter station includes a direct current filter link;
  • Step 2 calculating the sudden change of the current per unit time according to the current in the above signal, when the threshold is greater than the starting threshold, performing step 3;
  • Step 3 using the digital filter Filtering the electrical quantity signal obtained from the first step to obtain a specific frequency electrical quantity;
  • Step 4 calculating the amplitude of the specific frequency electrical quantity; and step 5, comparing the amplitude of the specific frequency electrical quantity with the set threshold value, when greater than the set threshold value, determining that it is an out-of-zone fault; If it is less than the set threshold value, it is judged to be a zone failure.
  • the converter station includes a DC filter link, the DC filter link includes a smoothing reactor and a DC filter, and the DC filter is provided with the transformer; the set threshold value in the step 5 is determined by the flat When a metal fault occurs outside the wave reactor, the electrical quantity that the transformer can feel is set. The value is determined by the parameters of the smoothing reactor, the parameters of the DC filter, and the line parameters.
  • the set threshold value is greater than the worst-case fault outside the smoothing reactor. Calculating the magnitude of the specific frequency electrical quantity, and the set threshold value is less than the magnitude of the specific frequency electrical quantity obtained by the fourth step when the fault occurs in the slightest area on the direct current transmission line side.
  • the electrical quantity signal in the third step is a current signal
  • the specific frequency in the third step is a specific frequency point or a specific frequency segment
  • the specific frequency point is a tuning frequency point of the DC filter, which is a power frequency communication. 12, 24, or 36 times the frequency; the specific frequency segment is 300 Hz or more.
  • the specific frequency segment is 400 Hz to 550 Hz.
  • the impedance amplitude of the minimum input impedance is more than 10 times or more than the impedance amplitude of the maximum input impedance.
  • the frequency band is a specific frequency point or a specific frequency band.
  • the method for calculating the amplitude of the specific frequency electrical quantity obtained by the filtering in the fourth step comprises a Fourier algorithm, a least squares method, and an integral method.
  • the invention has the following beneficial effects -
  • This method uses the single-ended electrical quantity as the original information of the criterion. It is only necessary to extract the single-ended specific frequency point of the direct current transmission line or the electrical quantity of the specific frequency band to realize the identification of the regional and external faults. Compared with the protection of the double-ended electric quantity, it is not affected by the communication channel, and has high reliability and fast action speed;
  • the invention is based on the difference of the impedance characteristics of the DC filter link in the fault zone of the DC transmission line, and proposes a single-end quantity protection method for the DC transmission line.
  • the structure of the relay protection theory is complete and selective. Good, high sensitivity;
  • the method of the invention has low requirements on the sampling frequency of the protection device and is easy to implement. It overcomes the problems of high sampling frequency, poor selectivity, low sensitivity and low reliability of traveling wave protection of existing DC transmission lines. Moreover, the operation reliability and sensitivity of the single-ended full-line quick-action protection using the electric current signal in the side transformer of the direct current transmission line are improved, and the hardware cost is reduced. It can replace the existing traveling wave protection as the main protection of the DC transmission line, and is especially suitable for realizing full-line quick-action protection of the special/UHV DC transmission line by using single-ended electric quantity;
  • Figure 1 is a schematic structural view of a bipolar direct current transmission system
  • FIG. 2 is a circuit diagram of a DC filter section formed by a smoothing reactor and a DC filter of the bipolar direct current transmission system shown in FIG. 1;
  • Figure 3 shows the minimum input impedance of the DC filter link from the converter station side when the faulty DC filter branch is outside the line;
  • Figure 4 is the maximum input impedance of the DC filter link from the DC line side when the DC filter branch is faulty in the line area;
  • FIG. 5 is a frequency characteristic of the minimum input impedance of FIG. 3 and the maximum input impedance of FIG. 4;
  • FIG. 6 is a simulation diagram of a fault in the current discrimination region (point metal ground contact of a DC transmission line) according to a specific frequency band;
  • Figure 7 is a simulation diagram of a fault in the current region (point metal ground at the DC transmission line) according to a specific frequency point current;
  • FIG. 8 is a simulation diagram of a fault in a current frequency determination zone (a point in a DC transmission line is grounded via a 500 ohm transition resistor);
  • Figure 9 is a simulation diagram of the fault in the current discrimination region (the point in the DC transmission line is grounded via a 500 ohm transition resistor) according to a specific frequency point;
  • Figure 10 is a simulation diagram of the external fault (the metallic grounding occurs on the rectification side) according to the current frequency segment of the specific frequency segment;
  • Figure 11 is a simulation diagram of the out-of-zone fault (metal grounding on the rectification side) based on the current at a specific frequency point;
  • Figure 12 is a simulation diagram of the out-of-zone fault (metal grounding on the inverter side) based on the current of a particular frequency segment;
  • FIG. 13 is a simulation diagram of determining an out-of-zone fault (metal grounding on the inverter side) according to a specific frequency point current;
  • Figure 1 is a schematic diagram of the structure of a bipolar DC transmission system.
  • the direct current transmission system is composed of a converter station 1, 2 and a direct current transmission line 3.
  • the converter stations 1 and 2 are equipped with a converter valve 4.
  • a converter valve 4 In the picture,
  • / 2 is the fault point, which occurs on the DC transmission line 3, called the zone fault point; / 2 and
  • the dotted line in Fig. 1 is a filtering section 5 composed of a smoothing reactor and a DC filter.
  • the DC transmission system further includes a control protection system 6 disposed on both sides of the DC transmission line 3, and the control protection system 6 can obtain a digital signal of the local pole electric quantity through an A/D converter (not shown) provided therein.
  • the filter section 5 is composed of a smoothing reactor 51 and a DC filter 52.
  • the DC filter 52 is provided with a transformer 8.
  • Filtering section 5 and converter valve 4 of converter station 1 It is connected by a shunt 11 and a voltage divider 12.
  • i x is the voltage and current of the DC filter branch of the converter valve 4 side of the converter station 1 respectively
  • 2 and 2 are the voltage and current of the DC transmission line 3 side, respectively. It can be seen from the filtering link 5 of Fig. 2: When a fault occurs outside the DC transmission line 3, due to the blocking action of the smoothing reactor 51, the higher frequency current felt by the transformer 8 of the DC filter branch is felt.
  • the component is small; when there is a fault in the DC transmission line 3, since there is no blocking effect of the smoothing reactor 51, the higher frequency current component felt by the transformer 8 of the DC filter branch is large, and this characteristic can be used. To distinguish between DC and transmission line faults, and has high sensitivity and selectivity.
  • Fig. 3 shows the minimum input impedance Z m of the DC filter 52 when an out-of-zone fault occurs, and the current sensed by the transformer 8 of the DC filter branch is maximum at the minimum input impedance.
  • Figure 4 shows the maximum input impedance ⁇ ⁇ of the DC filter 52 in the event of a fault in the line region, in which case the current sensed by the DC filter branch transformer 8 is minimal.
  • Figure 5 shows the comparison of the impedance frequency characteristics of the circuits of Figure 3 and Figure 4 under the DC filter parameters of a DC project.
  • the smoothing reactor 51 has a blocking effect on the high frequency, and the higher the frequency, the more obvious the blocking effect, that is, the component with a higher frequency is difficult to obtain from the DC line.
  • the signal is transmitted to the DC filter branch; when the fault occurs in the DC transmission line, the impedance characteristic of the filter link 5 at both ends of the line has a band-pass property, wherein the signals of the three frequencies of 600 Hz, 1200 Hz and 1800 Hz have no blocking effect. That is, the current at these three frequencies will not be blocked, and the amplitudes of the three frequency components sensed by the DC filter 52 will be larger.
  • the comparison shows that the impedance characteristics of the impedance characteristics at the above three frequencies are much larger than l kQ. That is to say, in the case of an out-of-zone fault, the current component of the DC filter branch at the above three frequencies is much smaller than the fault condition in the zone. Therefore, the faults in the DC transmission line can be distinguished based on the content of the above three frequency components. It can also be seen from Fig. 5 that for the frequency signal above 300 Hz, the blocking capacity of Fig. 4 is more than 100 times higher than that of Fig. 6.
  • the DC filter 52 tuning frequency has the least effect on the signal, and the current component of the tuning frequency point will be large, which can reliably determine the faults in the area and outside.
  • the energy of the fault signal is mainly concentrated in the low frequency band, and the distribution characteristics of the transmission line parameters and the frequency filtering characteristics increase the filtering and blocking effects of the high frequency signal, the content of the high frequency component is actually small when the transmission line is faulty.
  • the conclusion is also confirmed from the recording of DC transmission line faults. Therefore, although the above analysis of signals above 300 Hz has the ability to distinguish between internal and external faults, from the perspective of reliability and the relationship between signal processing capability and hardware devices, fault diagnosis is performed using low-frequency bands of frequency components above 300 Hz. It has a more significant technical effect on improving operational reliability and reducing hardware costs.
  • Example 1 Example 1:
  • the single-ended electric quantity full-line quick-acting protection method for identifying faults in the high-voltage direct current transmission line is mainly based on the amplitude of the specific frequency electrical quantity of the single-ended DC filter branch to realize the fault in the area and the fault outside the area.
  • the local current signal is obtained from the transformer 8 of the branch of the local DC filter 52;
  • step 1) filtering the local current obtained from step 1) by using a digital filter in the control protection system 6 to obtain a specific frequency current amount;
  • Step 2) can be carried out as follows:
  • the current of the DC filter branch current is used to calculate the sudden change of current in unit time, which is greater than the starting threshold value.
  • the left side of the formula is the DC filter branch current sudden change and the right side is the start threshold value;
  • N is the number of sampling points per unit time, that is, the number of sampling points corresponding to the data window of the starting component, and the length of the data window can be 5 ⁇ 10ms
  • I set 0.U n , /iller is the rated current of the DC transmission line.
  • the specific frequency used includes a specific frequency segment and a specific frequency point.
  • the specific frequency point is a tuning frequency point of the DC filter, which is 12, 24, or 36 times of the power frequency AC frequency (i.e., 600 Hz, 1200 Hz, and 1800 Hz); the specific frequency segment is 300 Hz or more.
  • the fault identification in the low frequency band of the frequency component above 300 Hz has a more significant technical effect on improving the operational reliability and reducing the hardware cost, and a specific frequency range of 400 Hz to 550 Hz is preferred.
  • the method for calculating the specific frequency current amplitude obtained by filtering in step 4) includes Fourier algorithm, least squares method, integral method, and other algorithms for obtaining signal amplitude.
  • the set threshold value described in step 5) is set by the electrical quantity that the DC filter branch transformer can feel when a metal fault occurs outside the smoothing reactor (away from the DC line side), and the value is set by the flat wave. Reactor parameters, DC filter parameters, and line parameters are determined.
  • the set threshold value is greater than a magnitude of a specific frequency current calculated by the step 4) when the most severe out-of-zone fault (such as a metallic ground) occurs outside the smoothing reactor, and the set threshold is less than the direct current transmission line. Side occurs most The magnitude of the specific frequency current obtained from step 4) in a minor zone fault (eg 500 ohm transition resistor ground).
  • FIG. 6 and FIG. 7 verify the midpoint metal ground fault in the DC transmission line region
  • FIG. 8 and FIG. 9 show the 500 ohm excessive resistance ground fault in the midpoint of the DC transmission line region.
  • Figure 10 and Figure 11 show the verification results of metallic ground faults outside the DC transmission line and on the rectifier side.
  • Figure 12 and Figure 13 show the verification results of metallic ground faults outside the DC transmission line and on the inverter side. .
  • Fig. 6, Fig. 8, Fig. 10, and Fig. 12 are the results of discrimination based on the current of a specific frequency range of 400 Hz to 550 Hz.
  • the starting threshold is O.lln, and the threshold of the signal in the specific frequency band is set to 0.01 In.
  • Figure 7, Figure 9, Figure 11, and Figure 13 are the results of the discrimination based on the current at a specific frequency point of 600 Hz.
  • the starting threshold is O.lln, and the threshold of the specific frequency signal is set to 0.01 In.
  • the method of the present invention has high sensitivity, good selectivity, fast action speed, and high reliability for regional and out-of-area fault discrimination. This provides reliable relay protection for DC transmission lines.

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Abstract

一种识别高压直流输电线路区内、外故障的单端电气量全线速动保护方法，其利用单端直流滤波器支路中特定频率电气量的幅值实现区内故障、区外故障的判别。该保护方法仅需要采用单端电气量，对采样频率要求不高，算法简单，灵敏度高，在工程上易于实现；不仅具有动作速度快，选择性好，可靠性高的优点，而且理论完备易于整定，可以取代现有的行波保护作为直流输电线路的主保护，尤其适合于利用单端电气量实现特/超高压直流输电线路的全线速动保护。

Description

一种利用直流滤波器电流的高压直流输电全线速度保护方法 技术领域
本发明属于电力系统继电保护技术领域， 具体来说， 是一种利用直流滤 波器电流的高压直流输电线路全线速动保护方法。
背景技术
高压直流 (HVDC)输电以其传输功率大，线路造价低，控制性能好等优点， 在远距离、 大功率输电中占有越来越重要的地位， 世界发达国家都把它作为 大容量、 远距离送电和异歩联网的主要手段， 在我国也因 "西电东送， 南北 互供， 全国联网"而成为电力建设的热点。 自 1989年葛洲坝至上海采用直流 输电以来， 我国直流输电工程数量在世界上已名列前茅。
高压直流输电线路一般作为大区域联网的联络线， 它的安全性和可靠性 不仅关系到本系统的稳定性， 而且将直接影响与其连接的区域电网甚至整个 电网的稳定运行。 由于直流线路长， 发生故障的概率高， 因此提高直流输电 线路继电保护的运行水平对保证直流输电系统的安全性与可靠性具有重要意 义。 而从某种意义上来讲， 直流输电线路主保护的性能标志了直流系统继电 保护的运行水平。
目前， 运行中的直流线路多以行波保护作为主保护。 行波保护具有动作 速度快的优点， 但为了有效利用电压、 电流的变化率， 行波保护对采样率要 求极高。为了保证雷电干扰情况下保护的选择性，被迫降低了保护的灵敏度， 也增加了保护判据的复杂性。 国内外研究表明： 行波保护不但易受雷电和干 扰的影响， 而且不能够识别高阻故障， 易误动， 动作的可靠性低。综上所述， 国内外投运的直流输电工程， 其直流输电线路的主保护普遍存在着理论不完 备、 没有普遍适用的整定原则、 整定仅依赖于仿真结果等问题。 从而导致了 直流线路继电保护装置对采样率要求高， 且存在着选择性差、 灵敏度低、 可 靠性不高的问题。
对于专利 201110209681.9中所述的单端电气量全线速动保护， 其利用直 流输电线路侧传感器中电气量信号构成保护。 由于线路运行电流大， 对故障 时电气量的变化反应不灵敏， 使得保护灵敏度低。
发明内容
本发明的目的在于提供一种灵敏度高、 选择性好、 动作速度快、 可靠性 高的高压直流输电线路区内、 外故障的单端电气量全线速动保护方法。 从而 为直流输电线路提供继电保护。
为达到上述目的， 本发明提供一种识别高压直流输电线路区内、 外故障 的单端电气量全线速动保护方法， 其利用单端直流滤波器支路中特定频率电 气量的幅值实现区内故障、 区外故障的判别。
一种利用直流滤波器电流的高压直流输电线路全线速动保护方法， 高压 输电线路包括直流输电线路及其两端的换流站， 换流站包括一直流滤波器环 节； 歩骤一， 从本极直流滤波器环节的互感器中获得电气量信号； 歩骤二， 根据上述信号中的电流计算单位时间内的电流突变， 大于起动门槛值时， 执 行歩骤三； 歩骤三， 利用数字滤波器对从歩骤一中获得的电气量信号进行滤 波， 获得特定频率电气量；
歩骤四， 计算所述特定频率电气量的幅值； 歩骤五， 比较特定频率电气 量的幅值与设定门槛值的大小， 当大于设定门槛值时， 判定为区外故障； 当 小于设定门槛值时， 判定为区内故障。
所述换流站包含直流滤波环节， 所述直流滤波环节包含平波电抗器和直 流滤波器、 直流滤波器设有所述互感器； 所述歩骤五中的设定门槛值由所述 平波电抗器外侧发生金属性故障时， 互感器所能感受的电气量进行整定， 其 值由平波电抗器参数、 直流滤波器参数以及线路参数确定。
所述设定门槛值大于平波电抗器外侧发生最严重区外故障时由歩骤四计 算得到的特定频率电气量的幅值， 并且该设定门槛值小于直流输电线路侧发 生最轻微区内故障时由歩骤四得到的特定频率电气量的幅值。
所述歩骤三中的电气量信号为电流信号， 所述歩骤三中的特定频率为特 定频率点或特定频率段， 所述特定频率点为直流滤波器的调谐频率点， 为工 频交流频率的 12、 24、 或 36倍； 所述特定频率段为 300Hz以上。 所述特定 频率段为 400Hz〜550Hz。
所述特定频率按照以下方法获得：
获得线路区外故障时直流滤波器的最小输入阻抗， 并获得该最小输入阻 抗在不同频率下的阻抗幅值， 在此情况下流过直流滤波器支路分流器的电流 最大；
获得线路区内故障时直流滤波器的最大输入阻抗， 并获得该最大输入阻 抗在不同频率下的阻抗幅值， 在该情况下流过直流滤波器支路互感器的电流 最小；
将获得的上述最小输入阻抗的阻抗幅值与最大输入阻抗的阻抗幅值进行 对比， 最小输入阻抗的阻抗幅值比最大输入阻抗的阻抗幅值大 10 倍以上或 100倍以上所对应的频点或频带即为特定频率点或特定频率带。
根据权利要求 2所述的方法， 其特征在于： 所述歩骤四中计算滤波得到 的特定频率电气量幅值的方法包括傅氏算法、 最小二乘法、 积分法。 本发明具有以下有益效果-
1、本方法采用单端电气量作为判据的原始信息，仅需提取直流输电线路 的单端特定频率点或特定频率带的电气量即可实现区内、 外故障的判别。 与 利用双端电气量的保护相比， 不受通信通道的影响可靠性高、 动作速度快；
2、本发明是基于直流输电线路区内、外故障时直流滤波环节阻抗特性差 异， 提出直流输电线路单端量保护方法， 构造的继电保护理论完备、 选择性 好、 灵敏度高；
3、与现有方法相比， 本发明方法对保护装置的采样频率要求低、 易于实 现。 克服了现有直流输电线路行波保护对采样频率要求高、 选择性差、 灵敏 度低、 可靠性不高等问题。 且进一歩提高了利用直流输电线路侧互感器中电 气量信号构成单端量全线速动保护的动作可靠性和灵敏度，降低了硬件成本。 可以取代现有的行波保护作为直流输电线路的主保护， 尤其适合于利用单端 电气量实现特 /超高压直流输电线路的全线速动保护；
4、 利用与平波电抗器和直流滤波器有关的特征频率信号进行故障识别， 由于这些信号频率相对较低， 且具有幅值高、 能量大的特点， 因此利用该频 率信号的继电保护将具有对采样率低、 可靠性高的特点。
附图说明
图 1为双极直流输电系统结构示意图；
图 2是图 1所示的双极直流输电系统的平波电抗器和直流滤波器构成的 直流滤波环节的电路图；
图 3是线路区外故障直流滤波器支路时从换流站侧看直流滤波环节的最 小输入阻抗；
图 4是线路区内故障时直流滤波器支路从直流线路侧看直流滤波环节的 最大输入阻抗；
图 5是图 3中的最小输入阻抗及图 4中的最大输入阻抗的频率特性； 图 6是根据特定频率段电流判别区内故障 （直流输电线路中点金属性接 地） 的仿真图；
图 7是根据特定频率点电流判别区内故障 （直流输电线路中点金属性接 地） 的仿真图；
图 8是根据特定频率段电流判别区内故障 （直流输电线路中点经 500欧 姆过渡电阻接地） 的仿真图； 图 9是根据特定频率点电流判别区内故障 （直流输电线路中点经 500欧 姆过渡电阻接地） 的仿真图；
图 10是根据特定频率段电流判别区外故障（整流侧发生金属性接地）的 仿真图；
图 11是根据特定频率点电流判别区外故障（整流侧发生金属性接地）的 仿真图；
图 12是根据特定频率段电流判别区外故障（逆变侧发生金属性接地）的 仿真图；
图 13是根据特定频率点电流判别区外故障（逆变侧发生金属性接地）的 仿真图； 具体实施方式
请参照图 1， 图 1为双极直流输电系统的结构简图。 直流输电系统由换 流站 1、 2和直流输电线路 3构成。 换流站 1、 2都装设有换流阀 4。 图中 、
/2、 /3为故障点， 其中 发生在直流输电线路 3上， 称为区内故障点； /2和
/3发生换流站侧， 称为区外故障点。 jp、 jp分别是换流站 1 的正极直流电 压和直流电流； wjn、 jn分别是换流站 1的负极直流电压和直流电流； kp、 分别是换流站 2 的正极直流电压和直流电流； 、 ^分别是换流站 2 的负极直流电压和直流电流。 图 1中虚线部分为平波电抗器和直流滤波器组 成的滤波环节 5。 该直流输电系统还包括设置在直流输电线路 3两侧的控制 保护系统 6， 该控制保护系统 6通过其中设有的 A/D转换器 （未图示） 可获 得本端极电气量的数字信号， 并进行数字信号的处理、判别， 实现保护功能。 图 2是滤波环节 5的电路图。滤波环节 5由平波电抗器 51和直流滤波器 52构成。 直流滤波器 52设有互感器 8。 滤波环节 5与换流站 1 的换流阀 4 通过分流器 11和分压器 12连接。 图中 、 ix分别是换流站 1换流阀 4侧直 流滤波器支路的电压和电流， 2、 2分别是直流输电线路 3侧的电压和电流。 从图 2的滤波环节 5可以看出： 当直流输电线路 3区外发生故障时， 由于平 波电抗器 51的阻滞作用，使得直流滤波器支路的互感器 8感受到的较高频电 流分量很小； 当直流输电线路 3 区内发生故障时， 由于没有平波电抗器 51 的阻挡作用， 直流滤波器支路的互感器 8感受到的较高频电流分量很大， 该 特性可以用来区分直流输电线路区内、 外故障， 且具有较高的灵敏度和选择 性。
为了充分利用滤波环节 5在直流输电线路 3区内、 区外故障时所表现出 的这种差异性， 构造具有绝对选择性的继电保护原理， 需要分析在哪些频带 中， 直流输电线路 3区外故障时互感器 8所感受到的最大电流还远远小于直 流输电线路 3区内故障的最小短路电流。 为此图 3给出了发生区外故障时直 流滤波器 52的最小输入阻抗 Zm， 在最小输入阻抗时直流滤波器支路的互感 器 8感受到的电流最大。图 4给出了线路区内故障时直流滤波器 52的最大输 入阻抗 Ζιη， 该情况下直流滤波器支路互感器 8感受到的电流最小。 图 5给出 了某直流工程的直流滤波器参数下图 3及图 4电路的阻抗频率特性比较。
从图 5的阻抗频率特性可知， 在直流线路区外故障时， 由平波电抗器 51 对高频具有阻滞作用， 频率越高阻滞效果越明显， 即频率较高的分量难以从 直流线路区外传到直流滤波器支路上； 而在直流输电线路区内故障情况时， 线路两端的滤波环节 5的阻抗特性具有带通性质， 其中对 600Hz、 1200Hz和 1800Hz三个频率的信号没有阻滞作用，也就是说这三个频率下的电流将不会 受到阻滞，直流滤波器 52感受到的这三个频率分量的幅值会较大。对比可知， 阻抗特性在以上三个频点所表现的阻抗远大于 l kQ。 也就是说， 在区外故障 情况下， 直流滤波器支路在以上三个频率的电流分量远小于区内故障情况。 因此，可以根据以上三个频率分量的含量来区分直流输电线路区内、外故障。 从图 5还可以看出， 对于 300Hz以上频率信号， 图 4的阻滞能力则比图 6高出 100倍以上。
考虑到直流输电线路 3区内故障时，直流滤波器 52调谐频率对信号的阻 滞作用最小， 调谐频率点的电流分量将较大， 可以可靠的进行区内、 外故障 的判别。 考虑到故障信号的能量主要集中在低频带， 以及输电线路参数的分 布特性和频变特性对高频信号的滤波和阻滞作用增加等因素， 输电线路故障 时高频分量含量其实较小， 该结论从直流输电线路故障的录波中也得到了证 实。 因此， 虽然前面分析了 300Hz以上的信号都具有区内、 外故障的区分能 力， 但从可靠性的角度和信号处理能力与硬件装置关系的角度考虑， 利用 300Hz以上频率分量中低频带进行故障判别， 对提高动作可靠性和降低硬件 成本有更为显著的技术效果。 实施例 1：
识别高压直流输电线路区内、 外故障的单端电气量全线速动保护方法， 主要利用单端直流滤波器支路特定频率电气量的幅值实现区内故障、 区外故 障的判别。
按照以下歩骤进行：
1 ) 在换流站中， 从本极直流滤波器 52支路的互感器 8中获得本极电流 信号；
2) 根据所述电流信号计算单位时间内的电流突变， 大于起动门槛值时， 系统发生故障；
3 )利用控制保护系统 6中的数字滤波器对从歩骤 1 )中获得的本极电流 进行滤波， 获得特定频率电流量；
4) 计算滤波得到的特定频率电流的幅值；
5 )比较特定频率电流的幅值与设定门槛值的大小，当大于设定门槛值时， 判定为区外故障； 当小于设定门槛值时， 判定为区内故障； 实现直流输电线 路区内故障、 区外故障判别。
其中歩骤 2) 可按照以下方法进行：
根据公式 （1 ) 用本极直流滤波器支路电流计算单位时间内的电流突变， 大于起动门槛值时起动保护， 公式左边为直流滤波器支路电流突变、 右边为 起动门槛值；
N
^M > krNIset ( 1 ) 其中： m=l， 2， …， N; N为单位时间内采样点数， 也就是起动元件数 据窗所对应的采样点数，数据窗长度可取 5〜10ms; 电流突变 Δ/ = / - /„， i为 本极当前电流采样值， ^为本极故障前正常运行电流值； 为可靠系数， Κ > 1 , 一般可取 1.2〜1.5； Iset = 0.Un , /„为直流输电线路的额定电流。
歩骤 4) 所采用的特定频率包括特定频率段和特定频率点。 所述特定频 率点为直流滤波器的调谐频率点， 为工频交流频率的 12、 24、 或 36倍 （即 600Hz, 1200Hz和 1800Hz); 所述特定频率段为 300Hz以上。
若从可靠性的角度和信号处理能力与硬件装置关系的角度考虑， 利用
300Hz以上频率分量中低频带进行故障判别， 对提高动作可靠性和降低硬件 成本有更为显著的技术效果， 则采用特定频率段 400Hz〜550Hz为优选方案。
歩骤 4) 中计算滤波得到的特定频率电流幅值的方法包括傅氏算法、 最 小二乘法、 积分法、 以及其它求取信号幅值的算法。
歩骤 5 ) 中所述的设定门槛值由平波电抗器外侧 （远离直流线路侧） 发 生金属性故障时直流滤波器支路互感器所能感受的电气量进行整定， 其值由 平波电抗器参数、 直流滤波器参数以及线路参数确定。 所述设定门槛值大于 平波电抗器外侧发生最严重区外故障 （例如金属性接地） 时由歩骤 4) 计算 得到的特定频率电流的幅值， 并且该设定门槛值小于直流输电线路侧发生最 轻微区内故障 （例如 500欧姆过渡电阻接地） 时由歩骤 4) 得到的特定频率 电流的幅值。
本实施例中对不同的区内、 区外故障进行了仿真验证。 请参照图 6至图 13， 其中图 6和图 7对直流输电线路区内中点金属性接地故障进行了验证； 图 8和图 9对直流输电线路区内中点经 500欧姆过度电阻接地故障进行了验 证； 图 10和图 11是直流输电线路区外、 整流侧发生金属性接地故障的验证 结果； 图 12和图 13是直流输电线路区外、 逆变侧发生金属性接地故障的验 证结果。其中图 6、图 8、图 10、图 12均是是根据特定频率段为 400Hz-550Hz 的电流所作出的判别结果。其中起动门槛值为 O.lln, 特定频段信号的门槛值 设定为 0.01 In。 图 7、 图 9、 图 11及图 13均是根据特定频率点 600Hz的电 流所作出的判别结果。其中起动门槛值为 O.lln, 特定频点信号的门槛值设定 为 0.01 In。
根据图 6至图 13的验证结果， 可以显著地显示本发明的方法对于区内、 区外故障判别的灵敏度高、 选择性好、 动作速度快、 可靠性高。 从而为直流 输电线路提供可靠的继电保护。

Claims

1、 一种利用直流滤波器电流的高压直流输电线路全线速动保护方法， 高压 输电线路包括直流输电线路及其两端的换流站， 换流站包括一直流滤波器环 节； 其特征在于：
歩骤一， 从本极直流滤波器环节的互感器中获得电气量信号；
歩骤二， 根据上述信号中的电流计算单位时间内的电流突变， 大于起动 门槛值时， 执行歩骤三；
歩骤三， 利用数字滤波器对从歩骤一中获得的电气量信号进行滤波， 获 得特定频率电气量；
歩骤四， 计算所述特定频率电气量的幅值；
歩骤五， 比较特定频率电气量的幅值与设定门槛值的大小， 当大于设定 门槛值时， 判定为区外故障； 当小于设定门槛值时， 判定为区内故障。
2、 根据权利要求 1 所述的方法， 其特征在于： 所述换流站包含直流滤波环 节， 所述直流滤波环节包含平波电抗器和直流滤波器、 直流滤波器设有所述 互感器； 所述歩骤五中的设定门槛值由所述平波电抗器外侧发生金属性故障 时， 互感器所能感受的电气量进行整定， 其值由平波电抗器参数、 直流滤波 器参数以及线路参数确定。
3、 根据权利要求 2所述的方法， 其特征在于： 所述设定门槛值大于平波电 抗器外侧发生最严重区外故障时由歩骤四计算得到的特定频率电气量的幅 值， 并且该设定门槛值小于直流输电线路侧发生最轻微区内故障时由歩骤四 得到的特定频率电气量的幅值。
4、 根据权利要求 2所述的方法， 其特征在于： 所述歩骤三中的电气量信号 为电流信号， 所述歩骤三中的特定频率为特定频率点或特定频率段， 所述特 定频率点为直流滤波器的调谐频率点， 为工频交流频率的 12、 24、 或 36倍; 所述特定频率段为 300Hz以上。
5、 根据权利要求 4 所述的方法， 其特征在于： 所述特定频率段为 ■Hz〜550Hz。
6、 根据权利要求 2-5任一项所述的方法， 其特征在于： 所述特定频率按照以 下方法获得：
1)获得线路区外故障时直流滤波器的最小输入阻抗， 并获得该最小输入阻抗 在不同频率下的阻抗幅值，在此情况下流过直流滤波器支路分流器的电流 最大；
2)获得线路区内故障时直流滤波器的最大输入阻抗， 并获得该最大输入阻抗 在不同频率下的阻抗幅值，在该情况下流过直流滤波器支路互感器的电流 最小；
3)将获得的上述最小输入阻抗的阻抗幅值与最大输入阻抗的阻抗幅值进行 对比， 最小输入阻抗的阻抗幅值比最大输入阻抗的阻抗幅值大 10倍以上 或 100倍以上所对应的频点或频带即为特定频率点或特定频率带。
7、 根据权利要求 2所述的方法， 其特征在于： 所述歩骤四中计算滤波得到 的特定频率电气量幅值的方法包括傅氏算法、 最小二乘法、 积分法。
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