CN109507533B - A kind of single-ended quick-action main protection method of HVDC transmission line - Google Patents
A kind of single-ended quick-action main protection method of HVDC transmission line Download PDFInfo
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Abstract
Description
技术领域technical field
本发明涉及一种高压直流输电线路的单端速动主保护方法。The invention relates to a single-end quick-acting main protection method for a high-voltage direct current transmission line.
背景技术Background technique
我国一次能源与电力负荷的逆向分布特性决定了高压输电将在我国电网结构中占据日益重要的地位。高压输电中，相比于高压交流输电，高压直流输电的电压恒定、没有集肤效应、传输的功率更大、经济效益更好，使其在远距离输电中脱颖而出。目前，中国电网共建成并投运高压直流输电工程29个，包含7个±800kV特高压直流输电工程，形成大规模“西电东送”、“北电南送”的能源配置格局。到2020年跨区、跨国电网输送容量将达到4.1亿kW，西北地区到东部的输送距离达2000～3000km以上。The reverse distribution characteristics of my country's primary energy and power load determine that high-voltage transmission will occupy an increasingly important position in my country's power grid structure. In high-voltage transmission, compared with high-voltage AC transmission, high-voltage direct current transmission has constant voltage, no skin effect, greater transmission power, and better economic benefits, making it stand out in long-distance power transmission. At present, China Power Grid has built and put into operation 29 high-voltage DC transmission projects, including 7 ±800kV UHVDC transmission projects, forming a large-scale "West-to-East Power Transmission" and "North-to-South Power Transmission" energy allocation pattern. By 2020, the transregional and transnational power grid transmission capacity will reach 410 million kW, and the transmission distance from the northwest region to the east will reach more than 2000-3000km.
由于输电距离远，输电线路长且周围环境恶劣，容易出现区内短路等故障。根据现场运行经验，区内线路故障约占直流输电系统全部故障的50％，区内线路故障发生后线路主保护正确动作、断开故障线路的只有50％，另一半的区内线路故障由直流控制系统响应动作，直流闭锁，关闭整个输电系统的送端，引起不必要的系统停运，造成巨大的设备损耗和经济损失。Due to the long transmission distance, long transmission lines and harsh surrounding environment, faults such as short circuits in the area are prone to occur. According to field operation experience, line faults in the area account for about 50% of all faults in the DC transmission system, and only 50% of the line main protections operate correctly and disconnect the faulty line after the line fault occurs in the area, and the other half of the line faults in the area are caused by DC The control system responds to the action, DC blocking, shutting down the sending end of the entire power transmission system, causing unnecessary system outage, resulting in huge equipment loss and economic loss.
理想的直流输电线路主保护对位于线路两侧电流测点之间的线路区内故障进行动作，而对测点之外的区外故障应当不动作而由控制系统响应动作。我国高压直流输电线路主保护广泛采用ABB和西门子公司的保护装置，其主保护配置行波保护，行波保护以故障后线路出口侧电流中的行波波头电压、电流变化量和变化率为判据，进行线路故障检测，当计算值超过整定值，输出主保护动作信号。实际工程运行经验表明，现有行波主保护方案存在一定缺陷：1)行波保护无法动作于线路远端接地电阻大于100Ω的区内高阻接地故障；2)行波保护会对线路远端区外非高阻接地故障尤其是金属性接地故障误动。其拒动和误动的原因如下：当发生区内远端高阻接地故障时，由于接地电阻大和故障距离远，使行波保护计算采用的电参量(行波波头电压、电流变化量和变化率)在时域上的变化量显著减小，以致无法满足主动作判据，不能进行主保护动作；而发生区外金属性接地故障时，由于接地电阻极小，会使行波保护计算值满足保护动作判据，发生区内主保护误动。因此，行波主保护无法正确区分线路远端区内的高阻接地故障和远端区外的金属性接地故障，其可靠性低。The ideal main protection of HVDC transmission line will act on the line fault located between the current measuring points on both sides of the line, and should not act on the external fault outside the measuring point, and the control system should act in response. The protection devices of ABB and Siemens are widely used in the main protection of HVDC transmission lines in my country. The main protection is equipped with traveling wave protection. Traveling wave protection is based on the traveling wave head voltage, current variation and rate of change in the line outlet side current after a fault. , for line fault detection, when the calculated value exceeds the set value, the main protection action signal is output. Actual engineering operation experience shows that the existing traveling wave main protection scheme has certain defects: 1) traveling wave protection cannot act on high-impedance grounding faults in the area where the remote grounding resistance of the line is greater than 100Ω; 2) traveling wave protection will Non-high-resistance ground faults outside the area, especially metallic ground faults, malfunction. The reasons for its refusal and malfunction are as follows: When a remote high-resistance grounding fault occurs in the area, due to the large grounding resistance and the long distance of the fault, the electrical parameters (traveling wave head voltage, current variation and rate of change) used in the calculation of traveling wave protection ) in the time domain is significantly reduced, so that the main action criterion cannot be satisfied, and the main protection action cannot be performed; and when an external metallic ground fault occurs, due to the extremely small grounding resistance, the calculated value of the traveling wave protection will satisfy Criterion of protection action, the main protection in the zone is malfunctioning. Therefore, the traveling wave main protection cannot correctly distinguish the high-impedance ground fault in the far-end area of the line and the metallic ground fault outside the remote area, and its reliability is low.
发明内容Contents of the invention
本发明的目的是提供一种高压直流输电线路的单端速动主保护方法，该方法对高压直流输电线路的远距离及高阻接地故障的检出率高、且对区外故障的误检出率低，能更好地保障高压直流输电系统的安全稳定和高效运行。The purpose of the present invention is to provide a single-ended quick-acting main protection method for high-voltage direct current transmission lines, which has a high detection rate for long-distance and high-resistance grounding faults of high-voltage direct current transmission lines, and can detect false detections of external faults The output rate is low, which can better guarantee the safe, stable and efficient operation of the HVDC transmission system.
本发明实现其发明目的所采用的技术方案是，一种高压直流输电线路的单端速动主保护方法，其步骤如下：The technical solution adopted by the present invention to realize the purpose of the invention is a single-ended quick-acting main protection method for a high-voltage direct current transmission line, the steps of which are as follows:
A、数据采集A. Data collection
高压直流输电系统的保护装置以100kHz的采样频率，实时采集直流输电线路整流器出口侧的电流和直流滤波器出口侧的电流，分别得到当前时刻t的整流电流离散值ia(t)和当前时刻t的滤波后电流离散值ib(t)；The protection device of the HVDC transmission system collects the current at the outlet side of the rectifier of the DC transmission line and the current at the outlet side of the DC filter in real time at a sampling frequency of 100 kHz, and obtains the rectified current discrete value i a (t) at the current time t and the current time Filtered current discrete value i b (t) of t;
B、整流电流信号的处理B. Processing of rectified current signal
将之前的299个时刻和当前时刻t的整流电流离散值ia(t-299)、ia(t-298)、ia(t-297)…ia(t-2)、ia(t-1)、ia(t),构成当前时刻t的整流电流序列Ia(t),Ia(t)＝[ia(t-299)、ia(t-298)、ia(t-297)…ia(t-2)、ia(t-1)、ia(t)]；The rectified current discrete values i a (t-299), i a (t-298), i a (t-297)...i a (t-2), i a ( t-1), i a (t), constitute the rectified current sequence I a (t) at the current moment t, I a (t) = [i a (t-299), i a (t-298), i a (t-297)...i a (t-2), i a (t-1), i a (t)];
对当前时刻t的整流电流序列Ia(t)进行10层小波分解并重构，得到当前时刻t的10个频段的整流电流序列，记录其中的：Perform 10-level wavelet decomposition and reconstruction on the rectified current sequence I a (t) at the current moment t, and obtain the rectified current sequence of 10 frequency bands at the current moment t, and record the following:
频率范围为12.5～6.25kHz的第三频段整流小波分解电流序列 其中为当前时刻t的第三频段整流小波分解电流值；The third frequency band rectified wavelet decomposition current sequence in the frequency range of 12.5～6.25kHz in is the third frequency band rectification wavelet decomposition current value at the current moment t;
频率范围为6.25～3.12kHz的第四频段整流小波分解电流序列 其中为当前时刻t的第四频段整流小波分解电流值；The fourth frequency band rectified wavelet decomposition current sequence in the frequency range of 6.25 ~ 3.12kHz in is the fourth frequency band rectification wavelet decomposition current value at the current moment t;
频率范围为3.12～1.56kHz的第五频段整流小波分解电流序列 其中为当前时刻t的第五频段整流小波分解电流值；The fifth frequency band rectified wavelet decomposition current sequence with frequency range of 3.12～1.56kHz in is the fifth frequency band rectification wavelet decomposition current value at the current moment t;
将当前时刻t的第三频段整流小波分解电流序列中的所有整流小波分解电流值，第四频段整流小波分解电流序列中的所有整流小波分解电流值和第五频段整流小波分解电流序列中的所有整流小波分解电流值累加，得到当前时刻t的次高频段整流小波分解电流总和A(t)， Decompose the current sequence of the third frequency band rectified wavelet at the current moment t All rectified wavelet-decomposed current values in the fourth band rectified wavelet-decomposed current sequence All rectified wavelet-decomposed current values and fifth-band rectified wavelet-decomposed current sequences in Accumulate all the rectified wavelet decomposition current values in the current time t to obtain the sum A(t) of the sub-high frequency band rectification wavelet decomposition current at the current moment t,
C、滤波电流信号的处理C. Processing of filtered current signal
将之前的299个时刻和当前时刻t的滤波后电流离散值ib(t-299)、ib(t-298)、ib(t-297)…ib(t-2)、ib(t-1)、ib(t)，构成当前时刻t的滤波后电流序列Ib(t),Ib(t)＝[ib(t-299)、ib(t-298)、ib(t-297)…ib(t-2)、ib(t-1)、ib(t)]；The filtered current discrete values i b (t-299), i b (t-298), i b (t-297)...i b (t-2), i b of the previous 299 moments and the current moment t (t-1), i b (t), constitute the filtered current sequence I b (t) at the current moment t, I b (t) = [i b (t-299), i b (t-298), i b (t-297)...i b (t-2), i b (t-1), i b (t)];
对当前时刻t的滤波后电流序列I2(t)进行10层小波分解并重构，得到当前时刻t的10个频段的滤波后电流序列，记录其中的：Perform 10-level wavelet decomposition and reconstruction on the filtered current sequence I 2 (t) at the current moment t, and obtain the filtered current sequence of 10 frequency bands at the current moment t, and record the following:
频率范围为12.5～6.25kHz的第三频段滤波后小波分解电流序列 其中为当前时刻t的第三频段滤波后小波分解电流值；Wavelet decomposed current sequence after filtering in the third frequency band in the frequency range of 12.5～6.25kHz in is the wavelet-decomposed current value after filtering in the third frequency band at the current moment t;
频率范围为6.25～3.12kHz的第四频段滤波后小波分解电流序列 其中为当前时刻t的第四频段滤波后小波分解电流值；Wavelet decomposed current sequence after filtering in the fourth frequency band with a frequency range of 6.25 ~ 3.12kHz in is the wavelet-decomposed current value after filtering in the fourth frequency band at the current moment t;
频率范围为3.12～1.56kHz的第五频段滤波后小波分解电流序列 其中为当前时刻t的第五频段滤波后小波分解电流值；The wavelet decomposed current sequence after filtering in the fifth frequency band with a frequency range of 3.12～1.56kHz in is the wavelet-decomposed current value after filtering in the fifth frequency band at the current moment t;
将当前时刻t的第三频段滤波后小波分解电流序列中的所有滤波后小波分解电流值，第四频段滤波后小波分解电流序列中的所有滤波后小波分解电流值和第五频段滤波后小波分解电流序列中的所有滤波后小波分解电流值累加，得到当前时刻t的次高频段滤波后小波分解电流总和B(t)， Decompose the wavelet current sequence after filtering the third frequency band at the current moment t All filtered wavelet-decomposed current values in the fourth frequency band filtered wavelet-decomposed current sequence All filtered wavelet-decomposed current values and the fifth-band filtered wavelet-decomposed current series in All the filtered wavelet-decomposed current values in are accumulated to obtain the sub-high frequency band filtered wavelet-decomposed current sum B(t) at the current moment t,
D、电流信号差值的计算D. Calculation of current signal difference
将C步的当前时刻t的次高频段滤波后小波分解电流总和B(t)，减去B步的当前时刻t的次高频段整流小波分解电流总和A(t)，得到当前时刻t的次高频段电流信号差值D(t)，D(t)＝B(t)－A(t)；Subtract the sub-high band rectified wavelet decomposition current sum A(t) of sub-high band rectification at the current time t of step B from the sub-high frequency band filtered current sum B(t) at the current time t of step C to obtain the sub-high band rectification current sum A(t) at the current time t. High-frequency current signal difference D(t), D(t)=B(t)-A(t);
将当前时刻t和之前的99个时刻的次高频段电流信号差值D(t)进行平均，得到当前时刻t的次高频段电流信号差平均值 Average the sub-high frequency current signal difference D(t) at the current time t and the previous 99 moments to obtain the average value of the sub high frequency current signal difference at the current time t
E、保护动作E. Protection action
如当前时刻t的次高频段电流信号差平均值大于次高频段电流信号差设定值Dset，则判定线路区内存在故障，输出主保护信号，线路主保护动作；否则，判定线路区内不存在故障，不输出主保护信号。For example, the average value of the current signal difference in the sub-high frequency band at the current time t If it is greater than the set value D set of the current signal difference in the sub-high frequency band, it is determined that there is a fault in the line area, and the main protection signal is output, and the line main protection operates; otherwise, it is determined that there is no fault in the line area, and the main protection signal is not output.
本发明方法的原理如下：The principle of the inventive method is as follows:
输电线路故障电流蕴含着丰富的暂态信息，不同故障位置尤其是区内、外故障受直流线路两侧电抗器和滤波器的影响，传输到测点处的暂态信息区别很大。相比于传统行波保护只利用线路故障电流的时域特征进行故障识别，本发明采用滤波前后两个故障电流来识别区内外故障，且提取其中最能反应区内故障的暂态信息，其准确性更高。Transmission line fault current contains rich transient information. Different fault locations, especially internal and external faults, are affected by the reactors and filters on both sides of the DC line, and the transient information transmitted to the measuring point is very different. Compared with the traditional traveling wave protection, which only uses the time-domain characteristics of the line fault current for fault identification, the present invention uses two fault currents before and after filtering to identify faults inside and outside the zone, and extracts the transient information that can best reflect the fault in the zone. Accuracy is higher.
当故障未发生时，线路处于正常运行工况下，此时，直流滤波器对其两侧的12k次基波电流(k＝1,2,3…，基波频率50Hz)有过滤作用，这几个频点仅占本发明所选频段很小一部分，滤波器对其余电流分量影响很小，故线路正常工作时，电流ib(t)、ia(t)的特定频段差较小，只体现了滤波器两侧电流的自然差异。When the fault does not occur, the line is under normal operating conditions. At this time, the DC filter has a filtering effect on the 12k-order fundamental current (k=1,2,3..., fundamental frequency 50Hz) on both sides of it. Several frequency points only account for a very small part of the selected frequency band of the present invention, and the filter has little influence on the remaining current components, so when the line works normally, the specific frequency band difference of current i b (t), i a (t) is small, Only the natural difference in current on both sides of the filter is represented.
当线路区内发生接地故障时，故障点产生的大量暂态高频信号迅速传输到线路侧电流测点，因此线路侧电流信号ib(t)所含高频分量丰富，而经过滤波器传输到整流侧后，ia(t)的高频分量大大衰减，计算所得特定频段差远远大于系统正常工作及区外接地故障。因此，计算出的两电流信号在所选频段差值很大，能进行可靠的主保护。When a ground fault occurs in the line area, a large number of transient high-frequency signals generated by the fault point are quickly transmitted to the line side current measuring point, so the line side current signal i b (t) contains rich high frequency components, and the transmission through the filter After reaching the rectifier side, the high-frequency component of i a (t) is greatly attenuated, and the calculated specific frequency band difference is far greater than the normal operation of the system and the ground fault outside the area. Therefore, the difference between the two calculated current signals in the selected frequency band is very large, and reliable main protection can be carried out.
当线路末端区外发生接地故障时，故障点同样产生大量暂态信号，但由于暂态信号的传播经过逆变侧滤波器及整个线路，使ia(t)和ib(t)所含高频分量较之区内故障大大减少，而整流器侧电流ia(t)所含高频分量又在经过整流侧滤波器后衰减，故线路侧直流电流ib(t)所含高频分量仍多于整流器侧直流电流ia(t)所含高频分量，且所得特定频段差大于系统正常工作值，但又小于区内故障产生的特定频段差。因此，计算出的两电流信号在所选频段差较小，不会产生主保护误动作。When a ground fault occurs outside the line end area, a large number of transient signals are also generated at the fault point, but because the transient signal propagates through the inverter side filter and the entire line, the values contained in ia (t) and ib (t) The high-frequency components are greatly reduced compared with the internal faults, and the high-frequency components contained in the rectifier-side current i a (t) are attenuated after passing through the rectifier-side filter, so the high-frequency components contained in the line-side DC current i b (t) It is still more than the high-frequency component contained in the DC current ia (t) on the rectifier side, and the obtained specific frequency band difference is greater than the normal operating value of the system, but smaller than the specific frequency band difference caused by the fault in the area. Therefore, the difference between the two calculated current signals in the selected frequency band is small, and there will be no misoperation of the main protection.
根据以上特点，本发明对高压输电线路高阻故障及远端区内外故障具有较强的识别能力和快速的动作能力。According to the above characteristics, the present invention has strong identification ability and fast action ability for high-resistance faults of high-voltage transmission lines and faults inside and outside the remote area.
与现有技术相比，本发明的有益效果是：Compared with prior art, the beneficial effect of the present invention is:
一、当线路区内发生接地故障时，故障点产生的大量暂态高频信号迅速传输到线路侧电流测点，因此线路侧电流信号ib(t)所含高频分量丰富，而经过滤波器传输到整流侧后，ia(t)的高频分量大大衰减，计算所得特定频段差远远大于系统正常工作及区外接地故障。因此，计算出的两电流信号在所选频段差值很大，能进行可靠的主保护。总之，本发明不采用易受故障距离和故障电阻影响的电流的时域特征，而是选择了三个能够反应接地故障特征的频段，所选的频段受故障电阻和故障位置的影响小，使之对故障电阻和故障位置的耐受能力增强，提高了对区内故障的识别能力，保护动作不受故障距离的影响，能够可靠地保护线路全长。1. When a ground fault occurs in the line area, a large number of transient high-frequency signals generated at the fault point are quickly transmitted to the current measuring point on the line side, so the current signal i b (t) on the line side contains rich high-frequency components, and after filtering After the converter is transmitted to the rectifier side, the high-frequency component of i a (t) is greatly attenuated, and the calculated specific frequency band difference is far greater than the normal operation of the system and the ground fault outside the area. Therefore, the difference between the two calculated current signals in the selected frequency band is very large, and reliable main protection can be carried out. In a word, the present invention does not use the time-domain characteristics of the current that are easily affected by the fault distance and fault resistance, but selects three frequency bands that can reflect the characteristics of the ground fault. The selected frequency bands are less affected by the fault resistance and fault location, so that The tolerance to fault resistance and fault location is enhanced, the ability to identify faults in the area is improved, the protection action is not affected by the fault distance, and the entire length of the line can be reliably protected.
二、当线路末端区外发生接地故障时，故障点同样产生大量暂态信号，但由于暂态信号的传播经过逆变侧滤波器及整个线路，使ia(t)和ib(t)所含高频分量较之区内故障大大减少，而整流器侧电流ia(t)所含高频分量又在经过整流侧滤波器后衰减，故线路侧直流电流ib(t)所含高频分量仍多于整流器侧直流电流ia(t)所含高频分量，且所得特定频段差大于系统正常工作值，但又小于区内故障产生的特定频段差。因此，对区外故障不会产生主保护误动作。其主保护准确、可靠、误动率低。2. When a ground fault occurs outside the line end area, the fault point also generates a large number of transient signals, but because the transient signal propagates through the inverter side filter and the entire line, i a (t) and i b (t) Compared with the faults in the area, the high-frequency components contained in the rectifier-side current i a (t) are greatly reduced, and the high-frequency components contained in the rectifier-side current i a (t) are attenuated after passing through the rectifier-side filter, so the high-frequency components contained in the line-side DC current i b (t) The frequency component is still more than the high frequency component contained in the DC current ia (t) on the rectifier side, and the obtained specific frequency band difference is greater than the normal operating value of the system, but smaller than the specific frequency band difference caused by the fault in the area. Therefore, there will be no misoperation of the main protection for external faults. Its main protection is accurate, reliable, and has a low malfunction rate.
三、本发明在一次计算中使用4ms内所有数据，并利用逐点滑动窗提高了数据采样的精确性，减少了瞬时干扰信号对识别、保护的干扰、影响，进一步提高了其可靠性；同时，仅使用线路单端电参量，无需在线路两侧进行数据交换，减少了保护动作延迟；在故障发生后4ms内即可识别区内故障，保护动作速度快。Three, the present invention uses all data in 4ms in one calculation, and utilizes the point-by-point sliding window to improve the accuracy of data sampling, reduces the interference and influence of instantaneous interference signal on identification and protection, and further improves its reliability; , only use the single-end electrical parameters of the line, without data exchange on both sides of the line, which reduces the protection action delay; the fault in the zone can be identified within 4ms after the fault occurs, and the protection action speed is fast.
四、本发明无需改变高压直流输电系统的结构和硬件，只需基于系统现有的保护点，实时采集电气量信号，速度快，实时性好，适于工程应用。4. The present invention does not need to change the structure and hardware of the high-voltage direct current transmission system, and only needs to collect electrical quantity signals in real time based on the existing protection points of the system. The speed is fast, the real-time performance is good, and it is suitable for engineering applications.
进一步，本发明的次高频段电流信号差设定值Dset的取值为2。Further, the set value D set of the sub-high frequency band current signal difference in the present invention is 2.
下面结合附图和具体实施方式对本发明作进一步的详细说明。The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.
附图说明Description of drawings
图1为本发明仿真实验中线路末端区内发生高阻接地故障所在时间段的次高频段电流信号差值D(t)变化图；Fig. 1 is the change diagram of the sub-high frequency band current signal difference D (t) of the time period where a high-impedance ground fault occurs in the line end area in the simulation experiment of the present invention;
图2为本发明仿真实验中线路末端区外发生金属性接地故障所在时间段的次高频段电流信号差值D(t)变化图。Fig. 2 is a variation diagram of the sub-high frequency current signal difference D(t) in the time period when a metallic ground fault occurs outside the line end area in the simulation experiment of the present invention.
具体实施方式Detailed ways
实施例Example
本发明的一种具体实施方式是，一种高压直流输电线路的单端速动主保护方法，其步骤如下：A specific embodiment of the present invention is a single-ended quick-acting main protection method for a high-voltage direct current transmission line, the steps of which are as follows:
A、数据采集A. Data collection
高压直流输电系统的保护装置以100kHz的采样频率，实时采集直流输电线路整流器出口侧的电流和直流滤波器出口侧的电流，分别得到当前时刻t的整流电流离散值ia(t)和当前时刻t的滤波后电流离散值ib(t)；The protection device of the HVDC transmission system collects the current at the outlet side of the rectifier of the DC transmission line and the current at the outlet side of the DC filter in real time at a sampling frequency of 100 kHz, and obtains the rectified current discrete value i a (t) at the current time t and the current time Filtered current discrete value i b (t) of t;
B、整流电流信号的处理B. Processing of rectified current signal
将之前的299个时刻和当前时刻t的整流电流离散值ia(t-299)、ia(t-298)、ia(t-297)…ia(t-2)、ia(t-1)、ia(t),构成当前时刻t的整流电流序列Ia(t),Ia(t)＝[ia(t-299)、ia(t-298)、ia(t-297)…ia(t-2)、ia(t-1)、ia(t)]；The rectified current discrete values i a (t-299), i a (t-298), i a (t-297)...i a (t-2), i a ( t-1), i a (t), constitute the rectified current sequence I a (t) at the current moment t, I a (t) = [i a (t-299), i a (t-298), i a (t-297)...i a (t-2), i a (t-1), i a (t)];
对当前时刻t的整流电流序列Ia(t)进行10层小波分解并重构，得到当前时刻t的10个频段的整流电流序列，记录其中的：Perform 10-level wavelet decomposition and reconstruction on the rectified current sequence I a (t) at the current moment t, and obtain the rectified current sequence of 10 frequency bands at the current moment t, and record the following:
频率范围为12.5～6.25kHz的第三频段整流小波分解电流序列 其中为当前时刻t的第三频段整流小波分解电流值；The third frequency band rectified wavelet decomposition current sequence in the frequency range of 12.5～6.25kHz in is the third frequency band rectification wavelet decomposition current value at the current moment t;
频率范围为6.25～3.12kHz的第四频段整流小波分解电流序列 其中为当前时刻t的第四频段整流小波分解电流值；The fourth frequency band rectified wavelet decomposition current sequence in the frequency range of 6.25 ~ 3.12kHz in is the fourth frequency band rectification wavelet decomposition current value at the current moment t;
频率范围为3.12～1.56kHz的第五频段整流小波分解电流序列 其中为当前时刻t的第五频段整流小波分解电流值；The fifth frequency band rectified wavelet decomposition current sequence with frequency range of 3.12～1.56kHz in is the fifth frequency band rectification wavelet decomposition current value at the current moment t;
将当前时刻t的第三频段整流小波分解电流序列中的所有整流小波分解电流值，第四频段整流小波分解电流序列中的所有整流小波分解电流值和第五频段整流小波分解电流序列中的所有整流小波分解电流值累加，得到当前时刻t的次高频段整流小波分解电流总和A(t)， Decompose the current sequence of the third frequency band rectified wavelet at the current moment t All rectified wavelet-decomposed current values in the fourth band rectified wavelet-decomposed current sequence All rectified wavelet-decomposed current values and fifth-band rectified wavelet-decomposed current sequences in Accumulate all the rectified wavelet decomposition current values in the current time t to obtain the sum A(t) of the sub-high frequency band rectification wavelet decomposition current at the current moment t,
C、滤波电流信号的处理C. Processing of filtered current signal
将之前的299个时刻和当前时刻t的滤波后电流离散值ib(t-299)、ib(t-298)、ib(t-297)…ib(t-2)、ib(t-1)、ib(t)，构成当前时刻t的滤波后电流序列Ib(t),Ib(t)＝[ib(t-299)、ib(t-298)、ib(t-297)…ib(t-2)、ib(t-1)、ib(t)]；The filtered current discrete values i b (t-299), i b (t-298), i b (t-297)...i b (t-2), i b of the previous 299 moments and the current moment t (t-1), i b (t), constitute the filtered current sequence I b (t) at the current moment t, I b (t) = [i b (t-299), i b (t-298), i b (t-297)...i b (t-2), i b (t-1), i b (t)];
对当前时刻t的滤波后电流序列I2(t)进行10层小波分解并重构，得到当前时刻t的10个频段的滤波后电流序列，记录其中的：Perform 10-level wavelet decomposition and reconstruction on the filtered current sequence I 2 (t) at the current moment t, and obtain the filtered current sequence of 10 frequency bands at the current moment t, and record the following:
频率范围为12.5～6.25kHz的第三频段滤波后小波分解电流序列 其中为当前时刻t的第三频段滤波后小波分解电流值；Wavelet decomposed current sequence after filtering in the third frequency band in the frequency range of 12.5～6.25kHz in is the wavelet-decomposed current value after filtering in the third frequency band at the current moment t;
频率范围为6.25～3.12kHz的第四频段滤波后小波分解电流序列 其中为当前时刻t的第四频段滤波后小波分解电流值；Wavelet decomposed current sequence after filtering in the fourth frequency band with a frequency range of 6.25 ~ 3.12kHz in is the wavelet-decomposed current value after filtering in the fourth frequency band at the current moment t;
频率范围为3.12～1.56kHz的第五频段滤波后小波分解电流序列 其中为当前时刻t的第五频段滤波后小波分解电流值；The wavelet decomposed current sequence after filtering in the fifth frequency band with a frequency range of 3.12～1.56kHz in is the wavelet-decomposed current value after filtering in the fifth frequency band at the current moment t;
将当前时刻t的第三频段滤波后小波分解电流序列中的所有滤波后小波分解电流值，第四频段滤波后小波分解电流序列中的所有滤波后小波分解电流值和第五频段滤波后小波分解电流序列中的所有滤波后小波分解电流值累加，得到当前时刻t的次高频段滤波后小波分解电流总和B(t)， Decompose the wavelet current sequence after filtering the third frequency band at the current moment t All filtered wavelet-decomposed current values in the fourth frequency band filtered wavelet-decomposed current sequence All filtered wavelet-decomposed current values and the fifth-band filtered wavelet-decomposed current series in All the filtered wavelet-decomposed current values in are accumulated to obtain the sub-high frequency band filtered wavelet-decomposed current sum B(t) at the current moment t,
D、电流信号差值的计算D. Calculation of current signal difference
将C步的当前时刻t的次高频段滤波后小波分解电流总和B(t)，减去B步的当前时刻t的次高频段整流小波分解电流总和A(t)，得到当前时刻t的次高频段电流信号差值D(t)，D(t)＝B(t)－A(t)；Subtract the sub-high band rectified wavelet decomposition current sum A(t) of sub-high band rectification at the current time t of step B from the sub-high frequency band filtered current sum B(t) at the current time t of step C to obtain the sub-high band rectification current sum A(t) at the current time t. High-frequency current signal difference D(t), D(t)=B(t)-A(t);
将当前时刻t和之前的99个时刻的次高频段电流信号差值D(t)进行平均，得到当前时刻t的次高频段电流信号差平均值 Average the sub-high frequency current signal difference D(t) at the current time t and the previous 99 moments to obtain the average value of the sub high frequency current signal difference at the current time t
E、保护动作E. Protection action
如当前时刻t的次高频段电流信号差平均值大于次高频段电流信号差设定值Dset，则判定线路区内存在故障，输出主保护信号，线路主保护动作；否则，判定线路区内不存在故障，不输出主保护信号。For example, the average value of the current signal difference in the sub-high frequency band at the current time t If it is greater than the set value D set of the current signal difference in the sub-high frequency band, it is determined that there is a fault in the line area, and the main protection signal is output, and the line main protection operates; otherwise, it is determined that there is no fault in the line area, and the main protection signal is not output.
本例的次高频段电流信号差设定值Dset的取值为2。In this example, the set value D set of the current signal difference in the sub-high frequency band is 2.
仿真实验Simulation
为验证本发明的保护方法的线路区内故障检测的准确性，采用PSCAD/EMTDC建立高压直流输电系统仿真模型；设置不同距离、不同接地电阻的区内故障和区外故障，来对比说明本方法对于区内故障的可靠动作以及对区外故障的可靠不动作；用Matlab处理故障信号，得到在行波保护无法正确动作的故障情况下的特定频段差的平均值及保护动作情况，如表1所示。In order to verify the accuracy of fault detection in the line area of the protection method of the present invention, a high-voltage direct current transmission system simulation model is established by using PSCAD/EMTDC; the internal faults and external faults of different distances and different grounding resistances are set to compare and illustrate this method Reliable action for internal faults and reliable non-action for external faults; use Matlab to process the fault signal, and obtain the average value of the specific frequency band difference and the protection action situation in the case of faults where the traveling wave protection cannot operate correctly, as shown in Table 1. shown.
表1各种故障情况下保护动作情况(均为行波保护无法正确动作的故障)Table 1 Protection actions under various fault conditions (all are faults where traveling wave protection cannot operate correctly)
表1表明，对于行波保护无法正确动作的接地电阻为100Ω、500Ω，故障距离在1000-2500km的接地故障，本发明方法保护均可准确、快速识别；也即本发明可有效识别线路末端区内发生的高阻接地故障。图1为本发明仿真实验中线路末端区内发生高阻接地故障所在时间段的次高频段电流信号差值D(t)变化图；图1说明，区内线路远端高阻故障发生时，本发明方法得到的次高频段电流信号差值D(t)值明显大于保护整定值，能快速识别并保护动作。说明本发明对于区内的线路远端高阻故障识别能力强。Table 1 shows that for the grounding resistance of 100Ω, 500Ω and the fault distance of 1000-2500km for the grounding resistance that the traveling wave protection cannot operate correctly, the protection method of the present invention can be accurately and quickly identified; that is, the present invention can effectively identify the line end area A high-resistance ground fault occurs within the Fig. 1 is the change diagram of the sub-high frequency band current signal difference D (t) of the time period where the high-impedance ground fault occurs in the line end area in the simulation experiment of the present invention; The value D(t) of the sub-high frequency current signal difference obtained by the method of the invention is obviously greater than the protection setting value, and can quickly identify and protect the action. It shows that the present invention has a strong ability to identify high-resistance faults at the remote end of the line in the area.
表2还表明，对区外(大于2500km)接地电阻为0.1Ω的金属性接地故障，本发明方法也不会识别并动作，也即本发明对于任何区外故障均能能够可靠不动作(不发生主保护误动作)，符合区内保护的基本原理和要求。图2为本发明仿真实验中线路末端区外发生金属性接地故障所在时间段的次高频段电流信号差值D(t)变化图；图2说明，区外线路发生金属性(低阻)接地故障故障时，本发明方法得到的次高频段电流信号差值D(t)值小于保护设定值，不会识别并进行主保护动作。也说明本发明对于任何区外故障均能能够可靠不动作，符合区内保护的基本原理和要求。Table 2 also shows that the metallic grounding fault of 0.1 Ω to the grounding resistance outside the area (greater than 2500km), the method of the present invention will not identify and act, that is to say, the present invention can reliably not act for any out-of-area fault (no Maloperation of the main protection occurs), which conforms to the basic principles and requirements of protection in the area. Fig. 2 is the change diagram of the sub-high frequency band current signal difference D (t) of the time period where a metallic grounding fault occurs outside the line end area in the simulation experiment of the present invention; Fig. 2 illustrates that metallic (low resistance) grounding occurs in the line outside the area When a fault occurs, the sub-high frequency current signal difference D(t) value obtained by the method of the present invention is less than the protection setting value, and the main protection action will not be identified and performed. It also shows that the present invention can reliably not act for any fault outside the zone, and conforms to the basic principles and requirements of the protection in the zone.
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