WO2014101657A1 - 一种消除煤矿高压电网单端行波故障定位死区的方法 - Google Patents

一种消除煤矿高压电网单端行波故障定位死区的方法 Download PDF

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WO2014101657A1
WO2014101657A1 PCT/CN2013/089156 CN2013089156W WO2014101657A1 WO 2014101657 A1 WO2014101657 A1 WO 2014101657A1 CN 2013089156 W CN2013089156 W CN 2013089156W WO 2014101657 A1 WO2014101657 A1 WO 2014101657A1
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wave
fault
line
traveling wave
head
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French (fr)
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梁睿
王崇林
崔连华
周希伦
刘建华
高列
庞乐乐
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China University of Mining and Technology CUMT
China University of Mining and Technology Beijing CUMTB
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China University of Mining and Technology CUMT
China University of Mining and Technology Beijing CUMTB
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/11Locating faults in cables, transmission lines, or networks using pulse reflection methods
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00Emergency 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
    • H02H7/26Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/265Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured making use of travelling wave theory

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  • the invention relates to a method for single-ended traveling wave fault location of a coal mine high voltage power grid, in particular to a method for eliminating a single-ended traveling wave fault location dead zone in a high voltage power grid of a coal mine.
  • China's coal mine power supply and high voltage power grids are mostly single-ended radial power grids.
  • the common voltage levels are mostly 10kV or 6kV single busbars or double busbars. According to statistics, more than 80% of coal mine power grids are single-phase ground faults.
  • the ranging methods based on fault transient traveling wave analysis mainly have the following two methods: single-ended method and double-end method.
  • the single-ended method calculates the fault according to the time difference between the arrival of the traveling wave head and the wave head of the refraction returning to the detecting end. Distance;
  • the double-end rule calculates the time difference between the fault point and the detection point on both sides of the fault line, and obtains the fault distance.
  • the double-ended traveling wave ranging method has obtained certain applications, but the single-ended method has not been applied due to the difficulty of actually detecting the reflected wave head and the fact that the computer cannot be automatically realized.
  • the cost of the single-ended ranging method is lower than that of the double-ended ranging method. It does not require the GPS time-scale system and data communication at both ends. The real-time measurement result is stronger. Therefore, the single-ended traveling wave fault location is studied. It has important practical significance and has great potential and value in theoretical research.
  • the single-ended traveling wave ranging Due to the complexity of the coal distribution network line and the randomness of the fault distance, the single-ended traveling wave ranging has the possibility of locating the dead zone, that is, the fault distance is exactly equal to a certain outgoing line, causing the traveling wave head to arrive at the same time, and the reaction fault distance is The wave head overlaps with the wave head of the full length of the reaction non-faulty line.
  • the single-ended traveling wave ranging method can be divided into frequency method and time domain method.
  • the extracted characteristic frequency is inversely related to the distance between the fault point and the discontinuity point of the wave impedance to the measuring point.
  • the characteristic frequency of the fault point in the spectrogram will be buried in a certain reaction line.
  • the traveling wave head of the same path length will reach the measuring point at the same time, so that the obtained voltage or current signal is enhanced or weakened to different degrees, which increases the difficulty of its identification.
  • the object of the present invention is to provide a method for eliminating single-ended traveling wave fault locating dead zone in a high-voltage power grid of a coal mine, and to solve the problem that the existing single-ended traveling wave fault location is difficult to distinguish due to fault traveling wave characteristics, and if the fault location matches the basic characteristics of the line It is also a question of judging the lack of dead zones.
  • the object of the present invention is achieved as follows:
  • the method eliminates the wave head reflected by the non-faulty line by comparing the calculated value of the known structure of the line topology parameter with the measured value, and finds the reflected wave head and the fault point reflection of the opposite side bus of the fault line.
  • the wave head is a special wave head; further classifying the special wave head to eliminate the positioning dead zone and achieve accurate fault location;
  • VHF signal avoiding the superposition of the traveling wave signal on the power frequency and its harmonics, reducing the dynamic fluctuation range of the signal, and improving the resolution of data acquisition;
  • the wire with the distributed parameters forms a wave process, and the electromagnetic field approaches the speed of the light to the line two.
  • the electromagnetic field energy of the traveling wave is defined as the instantaneous power
  • the sudden change point is also defined as the arrival time of the traveling wave
  • the voltage signal u(t) and the current signal i(t) in a certain period of time obtained by the observation point are passed through Clark.
  • the time taken by the traveling wave to and from the fault measuring point and the end or branch point of each outgoing line is calculated in advance, which is denoted as t;
  • i indicates the normal running of the line From the point of measurement, the number of discontinuities of the wave impedance, including the branch point and the end point of the line;
  • m denotes the number of actually observable wave heads except the initial traveling wave head, including the branch point, the reflected wave of the line end point and the fault point;
  • the two wave heads cannot correspond to the theoretical values. At this time, the opposite end bus reflected wave and the fault point reflected wave of the fault outgoing line do not overlap with other wave heads;
  • the dead zone problem of the single-ended traveling wave ranging method is generated. This is further divided into: the reflected wave of the fault point coincides with the reflected wave of a certain outgoing line, and the faulty outgoing line The opposite side bus reflected wave coincides with the reflected wave of a certain outgoing line;
  • the reflected wave of the fault point and the reflected wave of the opposite end bus overlap with the reflected wave of the non-faulty line, that is, the extreme case of the single-ended traveling wave ranging dead zone.
  • the traveling wave signal is susceptible to noise interference.
  • the wavelet analysis modulus maximum value is discriminated, the small amplitude of the traveling wave sudden change will inevitably lead to the misjudgment of the traveling wave head, giving the fault
  • the result of the positioning has a great impact.
  • the traveling wave instantaneous current defined by the traveling wave voltage and current, the amplitude of the signal is amplified at a certain sudden change point, and the amplitude of the noise is reduced on the other hand, which effectively enhances the resolution of the weaker wave head in the traveling wave. The degree makes the positioning method more feasible and accurate.
  • the invention has the following advantages:
  • FIG. 1 is a diagram of a single-ended traveling wave ranging algorithm considering wave head overlap in the present invention.
  • FIG. 2 is a schematic diagram of a line topology of the present invention.
  • Figure 3 is a diagram showing the traveling wave current, voltage and instantaneous power after the fault occurs in the present invention.
  • Fig. 4 is a graph showing the results of wavelet analysis based on instantaneous power of the present invention.
  • Embodiment 1 This method eliminates the wave head reflected by the non-faulty line by comparing the calculated value of the known structure of the line topology parameter with the measured value, and finds the reflected wave head of the opposite end bus of the fault line and the reflected wave head of the fault point, that is, the special wave head. Further classify the special wave head to eliminate the positioning dead zone and achieve accurate fault location;
  • the signal needs to be band-pass filtered to suppress the VHF signal in the power system and avoid the superposition of the traveling wave signal on the power frequency and its harmonics. , narrowing the dynamic fluctuation range of the signal and improving the resolution of data acquisition;
  • the wire with the distributed parameters forms a wave process, and the electromagnetic field propagates to both ends of the line at a certain speed.
  • the electromagnetic field energy of the traveling wave ie, the instantaneous power
  • the sudden change point can also be defined as the arrival time of the traveling wave;
  • the time taken by the traveling wave to and from the fault measuring point and the end or branch point of each outgoing line is calculated in advance, which is denoted as t;
  • i indicates the normal running of the line From the point of measurement, the number of discontinuities of the wave impedance, including the branch point and the end point of the line;
  • m denotes the number of actually observable wave heads except the initial traveling wave head, including the branch point, the reflected wave of the line end point and the fault point;
  • the corresponding method is used to calculate the fault distance for the above different situations.
  • the high-speed data acquisition card is used to obtain the current and voltage signals of the CT and PT secondary side at a sampling rate of 10 MHz or higher, respectively, and the Clark transform is decoupled and the line is calculated.
  • the time taken by the traveling wave to and from the fault measuring point and the end or branch point of each outgoing line is calculated in advance, denoted as t;, where i indicates that the line is normal In operation, from the point of measurement, the number of discontinuities of the wave impedance, including the branch point and the end point of the line.
  • the above problem solving method is divided into two cases: the reflected wave of the fault point coincides with the wave head of the reflected wave of a certain outgoing line, and only the wave head of the reflected wave of the opposite end bus line can be found at this time, and the reflected wave is reflected by the fault point.
  • the relationship between the arrival time of the reflected wave head and the arrival time of the opposite side bus is verified to determine the fault distance; the reflected wave of the opposite end bus of the fault outgoing line coincides with the wave head of the reflected wave of a certain outgoing line, and the positioning method is similar to the former case.
  • the wave head outside the initial wave head is calculated one by one.
  • the traveling wave head which reflects the length of the faulty line appears at the coincidence time of the wave head.
  • Embodiment 2 The present invention has high positioning accuracy and high adaptability in a complex distribution network, and the system or system scale of different scales changes, and the present invention can be satisfied.
  • the overhead line and cable use the Frequency Dependent (Phase) Model, which better reflects the transient and harmonic characteristics of the line.
  • the 10kV network has 6 outlets, 3 overhead lines, 2 cable lines, and 1 cable hybrid line (bold line is cable).
  • the parameters of the overhead line are: zero sequence impedance 0.3E-03+j0.1E-02Q / m, positive sequence impedance 0.3E-04+JO.4E-03 ⁇ / m; zero sequence admittance is 0.1E-10+j0 .2E-08 S / m , positive sequence admittance is 0.1E-10+j0.3E-08 S / m.
  • the parameters of the cable are: zero sequence impedance is 0.2E-03+j0.2E-02 Q /m, positive sequence impedance is 0.3E-04+j0.2E-03 Q / m ; zero sequence admittance is j0.2E -07 S / m, positive sequence admittance is j0.2E-07 S / m.
  • the output is terminated with a ⁇ - ⁇ type transformer, the ratio is 35/llkV, the capacity is 31.5MVA, and the load side is connected to the ⁇ - ⁇ type transformer.
  • the transformation ratio is 10 D.66kV, the capacity is 1MVA, and the neutral point is adopted. Not grounded.
  • the load uses the fixed load model and is set to an inductive load. Due to cable faults in the coal mine grid, most of them are single-phase ground faults, and in most cases the grounding resistance is small. Therefore, the simulation is grounded with a phase A through a 100 ohm resistor.
  • the phase-mode transformation In the case of single-phase short-circuit, the phase-mode transformation must be used to decouple the conductors to determine a single wave speed.
  • the actual distribution line is not fully transposed, but the asymmetric line is decoupled using a balanced line-mode transformation matrix.
  • the coupling between the moduli is already small, so it can be simplified as a balanced line for processing, using a real matrix Clark transform.
  • the ⁇ -mode component is passed into a 10 ⁇ 100kHz second-order Butterworth bandpass filter. It became a normal single-ended fault.
  • the positioning principle could not be carried out.
  • the transient voltage and current detected at the busbar are respectively converted by Clark, and the transient waveform of the mode and the voltage and current are calculated as shown in Figure 3.
  • the fault location principle cannot be performed.
  • the waveform of the instantaneous power of the traveling wave is relatively smooth, and the amplitude of the ripple is smaller.
  • the amplitude of the noise is reduced after the signal is filtered, due to data acquisition,
  • the factors such as the filtering link can not avoid the influence of noise on the weak traveling wave signal.
  • the traveling wave instantaneous power defined in this paper can effectively reduce the influence of external noise.
  • the line NO. the line represents the time when the reflected wave at the end of the ith line reaches the measurement point
  • i m represents the arrival time of the reflected wave at the round trip m times
  • 4′ represents the 4th outlet cable mixed with the reflected wave reaching the measurement end.
  • ij indicates that the traveling wave passes through the ith line and is refracted into the j-th line to reflect back to the measuring end or the traveling wave is folded through the j-th line.
  • the db6 wavelet analysis is performed using the wavelet instantaneous power defined above, wherein the analysis result of the dl layer is as shown in FIG.
  • Fig. 4 if the fault is unknown and the fault time is unknown, the initial wave head arrival time in Fig. 4 is used as a reference, and the t ⁇ tu relative t in the graph is respectively read. The coordinates of the moment, and compare with the time in Table 1 to reflect the length of the non-faulty line or other impedance discontinuities.
  • the single-ended traveling wave ranging has the possibility of locating the dead zone, that is, the fault distance is exactly equal to a certain outgoing line, causing the traveling wave head to arrive at the same time.
  • the wave head of the fault distance overlaps with the wave head of the full length of the reactive non-fault line.

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  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
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  • Locating Faults (AREA)

Abstract

一种消除煤矿高压电网单端行波故障定位死区的方法,属于煤矿高压电网单端行波故障定位的方法。通过定义行波瞬时功率(P);利用特殊波头相互印证的方法来辨识故障特征波头,解决定位死区问题;通过对线路拓扑参数已知结构的计算值与测量值的比较,排除非故障线路反射的波头,寻找故障线路对端母线的反射波波头及故障点反射波波头即特殊波头;通过进一步对特殊波头分类计算,实现消除定位死区功能,同时实现故障精确定位;经过大量的仿真及现场数据试验,定位误差在100米以内。

Description

一种消除煤矿高压电网单端行波故障定位死区的方法
技术领域
本发明涉及一种煤矿高压电网单端行波故障定位的方法,尤其是一种消除煤矿高压电 网单端行波故障定位死区的方法。
背景技术:
我国煤矿供电高压电网多为单端辐射状电网, 常见电压等级多为 10kV或 6kV单母线 或双母线供电。 据统计, 煤矿电网的 80%以上均为单相接地故障。
目前基于故障暂态行波分析的测距方法主要有以下两种方法:单端法与双端法,单端 法根据行波波头到达检测端与折返射的波头再次到达检测端的时间差来计算故障距离; 双端法则计算故障点到达故障线路两侧检测点的时刻差, 获取故障距离。 双端行波测距 方法获取了一定的应用, 但单端方法由于实际检测反射波头的困难与计算机无法自动实 现等原因, 尚未得到应用。 单端测距法较双端测距法的成本低一半以上, 不需要 GPS 时 标系统及两端数据通信等, 测距结果的实时性更强, 因此, 对单端行波故障定位的研究 具有重要的实际意义, 理论研究上有很好的潜力与价值。
由于煤矿配电网线路的复杂性与故障距离的随机性,单端行波测距存在定位死区的可 能性, 即故障距离与某条出线恰好相等, 导致行波波头同时到达, 反应故障距离的波头 与反应非故障线路全长的波头重叠。 目前单端行波测距方法又可分为频率法、 时域法。 提取的特征频率与故障点及波阻抗不连续点到测量点的距离有反比关系, 当故障距离与 其它出线或分支长度恰好相等时, 频谱图中的故障点特征频率将埋没于某一反应线路拓 扑的固有的特征频率中, 而时域分析时, 相同路径长度的行波波头将同时到达测量点, 从而使获得的电压或电流信号得到不同程度的增强或削弱, 增加了其识别的难度。
发明内容:
本发明的目的是要提供一种消除煤矿高压电网单端行波故障定位死区的方法, 解决 现有单端行波故障定位由于故障行波特征难于分辨,故障位置若和线路基本特征匹配时, 更是有判断死区不足的问题。
本发明的目的是这样实现的: 该方法通过对线路拓扑参数已知结构的计算值与测量 值的比较, 排除非故障线路反射的波头, 寻找故障线路对端母线的反射波波头及故障点 反射波波头即特殊波头; 进一步对特殊波头分类计算, 消除定位死区, 实现故障精确定 位;
a,定义行波瞬时功率:
行波的特征频段为 f=10〜100kHz, 即在上述频段内, 行波的能量最大; 行波信号经 CT或 PT引入数据采集装置之前,对信号进行带通滤波处理,抑制电力系统中的甚高频信 号, 避免行波信号在工频及其谐波上的迭加, 縮小信号的动态波动范围, 提高数据采集 的分辨率;
由于故障发生后, 具有分布参数的导线形成了波过程, 电磁场以接近光速向线路两 端传播, 定义行波的电磁场能量即瞬时功率, 其突变点同样定义为行波到达时刻; 将观测 点获取的一定时间段内的电压信号 u(t), 电流信号 i(t), 经 Clark变换后, 得到线模分量 ua(t^ ia(t), 并定义行波瞬时功率, p(t) = ua (t) -ia (t) ;
b,特殊波头相互印证:
在线路拓扑参数已知的情况下, 根据行波波速理论值, 预先计算行波往返于故障 测量点与各个出线末端或分支点所用的时间, 记为 t;, 其中, i表示线路正常运行时, 从测量点来看, 波阻抗不连续点的个数, 包括分支点与线路末端点; 观察行波瞬时功 率信号经 db6小波分解后的 dl层, 记录行波初次到达测量点的时刻 t。, 分别计算可 观测波头与初始波头时刻的时间差 tm -t。, 其中, m表示除初始行波波头外, 实际可 观测波头的个数, 包括分支点, 线路末端点与故障点的反射波;
对照计算值与测量值, 排除非故障线路反射的波头, 寻找故障线路对端母线的反 射波波头及故障点反射波波头即特殊波头;
特殊波头存在以下三种情况:
1、 两个波头与理论值均无法对应, 这时故障出线的对端母线反射波与故障点反 射波均未与其他波头重叠;
2、 有一个波头与理论值无法对应, 这时产生了单端行波测距方法的死区问题, 这又分为:故障点的反射波与某条出线的反射波重合,故障出线的对端母线反射波与 某条出线的反射波重合;
3、 故障点反射波与对端母线反射波均与非故障线路的反射波重叠, 即单端行波测距 死区的极端情况。
本发明定义了行波瞬时功率, p(t) = ua(t) .ia (t),由于单一分析电压或电流信号的方法, 易受电网中噪声的干扰, 易出现波头的误判, 而行波瞬时功率有效改善了波头识别对噪 声干扰的适应性。
有益效果, 由于在实际电网运行中, 行波信号易受到噪声的干扰, 小波分析模极大 值辨析时, 幅值较小的行波突变点不可避免的会导致行波波头的误判, 给故障定位的结 果造成很大影响。 利用行波电压、 电流定义的行波瞬时功率, 在某一突变点处放大了信 号的突变幅度, 从另一方面减小了噪声的幅值, 有效增强了行波中较弱波头的分辨程度, 使定位方法更具可行性与精度。
针对单端行波定位方法出现的原理上的测距死区的情况, 根据两个反应故障距离的 特殊波头, 即故障点反射波与故障线路对端母线反射波的数学关系, + ^2 ) = 21^ , 其中, 为故障点反射波与初始波头的时间差, ζ(Γ2为对端母线反射波与初始波头的时 间差, V为行波在某介质中的传播速度, 为故障线路的全长。对每个观测到的行波一一 辨识, 排除非故障线路与分支点的反射波波头, 利用上述特殊波头中的任一到达时刻, 进行故障定位。 该方法应用两个波头的数学关系进行验证, 有效提高了单端行波测距方 法的适应性与可行性, 达到了本发明的目的。
本发明与现有技术相比具有如下优点:
1、 定义了行波瞬时功率, 提高了在实际电网中高噪声下的行波波头分辨程度;
2、 对煤矿电网中, 利用故障出线的两个特殊波头相互验证的方法, 解决了线缆混合 线路中, 波速不一致, 波头难以识别的问题;
附图说明
图 1为本发明考虑波头重叠的单端行波测距算法图。
图 2为本发明的线路拓扑示意图。
图 3 为本发明的故障发生后行波电流、 电压与瞬时功率图。
图 4 为本发明的基于瞬时功率的小波分析结果图。
具体实施方式
实施例 1 :该方法通过对线路拓扑参数已知结构的计算值与测量值的比较,排除非故 障线路反射的波头, 寻找故障线路对端母线的反射波波头及故障点反射波波头即特殊波 头; 进一步对特殊波头分类计算, 消除定位死区, 实现故障精确定位;
1、 定义行波瞬时功率:
行波的特征频段为 f=10〜100kHz, 即在上述频段内, 行波的能量最大。 行波信号经 CT或 PT引入数据采集装置之前, 需要对信号进行带通滤波处理, 目的是抑制电力系统 中的甚高频信号, 并避免行波信号在工频及其谐波上的迭加, 縮小信号的动态波动范围, 提高数据采集的分辨率;
由于故障发生后, 具有分布参数的导线形成了波过程, 电磁场以一定的速度向线路 两端传播, 可以定义行波的电磁场能量即瞬时功率, 其突变点同样可定义为行波到达时 刻; 将观测点获取的一定时间段内的电压信号 u(t), 电流信号 i(t), 经 Clark变换后, 得 到线模分量 (0与^0, 并定义行波瞬时功率, p(t) = ua(t) _ia(t) 。
2、 特殊波头相互印证的方法:
在线路拓扑参数已知的情况下, 根据行波波速理论值, 预先计算行波往返于故障 测量点与各个出线末端或分支点所用的时间, 记为 t;, 其中, i表示线路正常运行时, 从测量点来看, 波阻抗不连续点的个数, 包括分支点与线路末端点; 观察行波瞬时功 率信号经 db6小波分解后的 dl层, 记录行波初次到达测量点的时刻 t。, 分别计算可 观测波头与初始波头时刻的时间差 tm -t。, 其中, m表示除初始行波波头外, 实际可 观测波头的个数, 包括分支点, 线路末端点与故障点的反射波;
对照计算值与测量值,排除非故障线路反射的波头,寻找故障线路对端母线的反 射波波头及故障点反射波波头即特殊波头。 特殊波头存在以下三种情况:
1、 若有二个波头无法与理论值相对应, 说明此两个波头分别是故障点反射波与 对端母线反射波; 2、 若仅有一个波头无法与理论值相对应, 说明出现了单端测距方法的死区, 即 故障点反射波或故障线路对端母线反射波头与非故障线路故障反射波波头重合;利用 反应故障线路全长的两个波头的时间差的关系, 即: 7 +/(7^ = 2£,其中, ^为 故障点反射波与初始波头的时间差, ζ(Γ2为对端母线反射波与初始波头的时间差, V 为行波在某介质中的传播速度, 为故障线路的全长。计算此波头对应的对端母线反 射波或故障点反射波波头, 若计算值与某一理论时刻对应, 则可以确定, 此反射波头 是来自对端母线或故障点;
3、 若波头与理论值均对应, 说明故障出线的对端母线反射波与故障点反射波均 与非故障出线波头重叠, 这是一种极端的情况; 在时间段 T内, 分别对每个波头进行 如 2) 的计算验证, 以此辨别波头。
针对以上不同的情况采用对应的方法计算故障距离。
本方法具体实现流程图如图 1所示,本方法的具体步骤如下:
1、 系统的电缆出线某处发生故障时, 利用高速数据采集卡采用 10MHz或更高的采 样速率获取 CT、 PT二次侧的电流及电压信号, 分别对其进行 Clark变换解耦, 并计算线 模对应的行波瞬时功率;
2、 在线路拓扑参数已知的情况下, 根据行波波速理论值, 预先计算行波往返于故障 测量点与各个出线末端或分支点所用的时间, 记为 t;, 其中, i表示线路正常运行时, 从 测量点来看, 波阻抗不连续点的个数, 包括分支点与线路末端点。
3、 观察行波瞬时功率信号经 db6小波分解后的 dl层, 记录行波初次到达测量点的 时刻 t。, 分别计算可观测波头与初始波头时刻的时间差 tm -t。, 其中, m表示除初始行波 波头外, 实际可观测波头的个数, 包括分支点, 线路末端点与故障点的反射波。
4、 将 3 ) 与 2)对照, 排除非故障线路反射的波头, 若两个波头与理论值无法对应, 则说明故障出线的对端母线反射波与故障点反射波均未出线与其它波头重迭, 可直接计 算故障距离; 若仅有一个波头与理论值对应, 则上述两个波头其一与其它波头发生了重 叠, 即单端行波测距方法的死区问题。
5、 上述问题解决方法又分为两种情况: 故障点的反射波与某条出线的反射波的波头 重合, 此时能找到的只有对端母线反射波的波头, 利用故障点反射波与对端母线反射波 波头到达时刻的关系进行验证, 以此确定故障距离; 故障出线的对端母线的反射波与某 条出线的反射波的波头重合, 定位方法与前一种情况类似。
6、若故障点反射波与对端母线反射波均与非故障线路的反射波重迭, 即单端行波测 距死区的极端情况, 则根据初始波头外的波头一一计算其对应特殊波头的到达时刻, 在 波头重合时刻出现的即为反映故障线路长度的行波波头。
实施例 2: 本发明在复杂配电网具有很高定位精度并且具备很高的适应性, 不同规 模的系统或系统规模发生变化, 本发明均可以满足。 现以一个模型为例: 在图 2中, 架空线路与电缆采用 Frequency Dependent (Phase) Model, 此模型更能反 映线路的暂态及谐波特性。 其中, 10kV网络有 6条出线, 3条架空线路, 2条电缆线路, 1条线缆混合线路(加粗线为电缆)。架空线路的参数为:零序阻抗 0.3E-03+j0.1E-02Q / m, 正序阻抗 0.3E-04+JO.4E-03 Ω / m; 零序导纳为 0.1E-10+j0.2E-08 S / m , 正序导纳为 0.1E-10+j0.3E-08 S / m。 电缆的参数为: 零序阻抗为 0.2E-03+j0.2E-02 Q /m, 正序的阻抗为 0.3E-04+j0.2E-03 Q / m ; 零序导纳为 j0.2E-07 S / m, 正序导纳为 j0.2E-07 S / m。根据线路参 数可以计算得出架空线路的 α模波速 , val =2.994E8m/s, 电缆线路 va2=1.5169E8m/s。 出线 端接 Υ-Δ型连接的变压器, 变比为 35/llkV, 容量为 31.5MVA, 负载侧接 Υ-Δ型连接的变 压器, 变比为 10 D.66kV, 容量为 1MVA, 中性点采用不接地方式。 负载使用 fixed load 模 型, 并设置为感性负载。 由于煤矿电网中出现的电缆故障, 多为单相接地故障, 且大部 分情况下接地电阻小, 所以, 仿真以 A相经 100欧姆电阻接地。
对于单相接地短路的情况,必须使用相模变换对各导线进行解耦,从而确定单一的波 速, 实际的配电线路换位并不充分, 但使用平衡线路模变换矩阵对非对称线路进行解耦 时, 各模量间的耦合已经很小了, 所以可以简化为平衡线路来处理, 使用实数矩阵 Clark 变换。 并将 α模分量通入 10~100kHz二阶的 Butterworth带通滤波器。 成了普通单端故障 定位原理无法进行。 故障发生后 0.1ms的时间段内的, 母线处检测到的暂态电压、 电流 分别经 Clark变换后《模的暂态波形以及由电压、 电流计算出的如图 3所示, 成了普通单 端故障定位原理无法进行。
在图 3中, 相比电压、 电流信号, 行波瞬时功率的波形相对平滑, 纹波的幅值更小, 虽然信号经滤波后, 噪声的幅值会有所减小, 但由于数据采集, 滤波环节等因素, 仍无 法避免噪声对弱行波信号的影响, 尤其是在实际的煤矿电网中, 本文定义的行波瞬时功 率能有效减小受外界噪声影响。
记 t。为初始波头到达时刻, 根据线路长度参数并结合选线结果, 可计算出某条出线 对应的反射波到达时刻与初始波头的时间差, 也就是说, 故障行波到达测量点 (母线) 后, 经其他路径再返回测量点的时间段, 分别记为, …, tu, 结果如下表 1所示。 表 1 根据线路参数计算各个出线对应反射波头到达时刻的理论值
Figure imgf000007_0001
其中, 出线 NO.—行代表第 i条出线末端反射波到达测量点时刻, im表示在出线往返 m次的反射波到达时刻, 4'代表第 4条出线线缆混合出反射波到达测量端的时刻, i-j表 示行波经第 i条出线又折射进入第 j条出线反射回测量端的时刻或行波经第 j条出线又折 射进入第 i条出线反射回测量端的时刻。 利用上文所定义的小波瞬时功率进行 db6小波 分析, 其中, dl层的分析结果如图 4所示。
在图 4中, 若在故障未知, 故障时刻未知的情况下, 利用图 4中初始波头到达时刻作 为基准, 分别读取图中 t^tu相对 t。时刻的坐标, 并与表 1中反应非故障线路全长或其他 阻抗不连续点的时间对比。
对比的结果显示, 在所涉及的 11个波头之中, 仅有 t5 -t =49.94us无法与表 1计算的 波头时差的理论值相近, 而在正常情况下, 由于行波的色散效应, 在所能观察到波头的 有限时间段内, 应至少还有两个波头可明显观察得到, 即故障点的一次反射波与故障线 路负荷端的一次反射波, 但图 4中, 仅观测到了一个可辨识波头。 很明显, 由于煤矿配 电网线路的复杂性与故障距离的随机性, 单端行波测距存在定位死区的可能性, 即故障 距离与某条出线恰好相等, 导致行波波头同时到达, 反应故障距离的波头与反应非故障 线路全长的波头重叠。
此时,本文提出利用单端故障测距导出的故障点的反射波与对端母线反射波波头到达 时间的关系即: ν(ΔΤ1 + ΔΤ2) = 2ί, 确定特殊波头来消除死区的影响, 其中, ΔΊ为故障点 反射波与初始波头的时间差, ΔΤ2为对端母线反射波与初始波头的时间差, V为行波在某 介质中的传播速度, L为故障线路的全长, X为故障点到检测点的距离。 若^ -^ 为故障点反射波到达时刻与初始波头的时间差, 则对应的对端母线反射波到达时刻为
(t5 -t0 y=42.19us;若 -1 =49.94118为对端母线反射波与初始波头的时间差,则对应的故障 点反射波到达时刻为 (t5 -t。)'=28.9us。 从表 1中, 我们可以看到 42.19us介于 与 之间, 而 28.9us与 十分接近, 则可以确定, t5 -t =49.94us为对端母线反射波与初始波头的时 间差, 即可以计算出故障距离为 2.192km, 绝对误差为 8m

Claims

权利要求书
1、 一种消除煤矿高压电网单端行波故障定位死区的方法, 其特征是: 该方法通过对 线路拓扑参数已知结构的计算值与测量值的比较, 排除非故障线路反射的波头, 寻找故 障线路对端母线的反射波波头及故障点反射波波头即特殊波头; 进一步对特殊波头分类 计算, 消除定位死区, 实现故障精确定位;
a,定义行波瞬时功率:
行波的特征频段为 f=l(Tl00kHz, 即在上述频段内, 行波的能量最大; 行波信号经 CT或 PT引入数据采集装置之前, 对信号进行带通滤波处理, 抑制电力系统中的甚高频信 号, 避免行波信号在工频及其谐波上的迭加, 縮小信号的动态波动范围, 提高数据采集 的分辨率;
由于故障发生后, 具有分布参数的导线形成了波过程, 电磁场以接近光速向线路两 端传播, 定义行波的电磁场能量即瞬时功率, 其突变点同样定义为行波到达时刻; 将观测 点获取的一定时间段内的电压信号 u(t), 电流信号 i(t), 经 Clark 变换后, 得到线模分量 (0与^(0, 并定义行波瞬时功率, p(t) = ua(t) .ia(t) ;
b,特殊波头相互印证:
在线路拓扑参数已知的情况下, 根据行波波速理论值, 预先计算行波往返于故障 测量点与各个出线末端或分支点所用的时间, 记为 t;, 其中, i 表示线路正常运行 时, 从测量点来看, 波阻抗不连续点的个数, 包括分支点与线路末端点; 观察行波瞬 时功率信号经 db6 小波分解后的 dl 层, 记录行波初次到达测量点的时刻 t。, 分别计 算可观测波头与初始波头时刻的时间差 tm -t。, 其中, m表示除初始行波波头外, 实 际可观测波头的个数, 包括分支点, 线路末端点与故障点的反射波;
对照计算值与测量值, 排除非故障线路反射的波头, 寻找故障线路对端母线的反 射波波头及故障点反射波波头即特殊波头;
特殊波头存在以下三种情况:
( 1 )、 两个波头与理论值均无法对应, 这时故障出线的对端母线反射波与故障点 反射波均未与其他波头重叠;
( 2 )、 有一个波头与理论值无法对应, 这时产生了单端行波测距方法的死区问 题, 这又分为: 故障点的反射波与某条出线的反射波重合, 故障出线的对端母线反射 波与某条出线的反射波重合;
( 3 )、 故障点反射波与对端母线反射波均与非故障线路的反射波重叠, 即单端行波 测距死区的极端情况。
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