【作者】 李峰；

【导师】 徐科军；

【作者基本信息】 合肥工业大学 ， 仪器科学与技术， 2015， 博士

【摘要】 电力电缆故障定位技术广泛用于城市电网地下电缆故障的查找,在保障城市电网安全可靠运行中具有重要的作用。目前,电力电缆故障定位技术已经得到了广泛的应用,然而这项技术在故障测距和故障定点两个方面仍然存在一些关键问题没有解决,造成电缆故障查找费时、费力,影响了电缆及时恢复供电。本文针对这些问题展开研究,具体研究内容如下：在只考虑暂态低频分量信号的条件下,采用均匀传输线电路模型的T形等效网络,建立电力电缆故障冲闪测试放电回路模型,分析冲闪放电过程中的电压、电流响应规律。分析了放电电容、初始放电电压、电缆长度、串联电阻等关键参数与放电电压、电流响应的关系。现场实验结果表明,本文建立的电力电缆故障冲闪测试放电回路模型及电路分析是正确的,所得结论为电缆故障定位研究和设备研制提供了理论依据。在电弧反射故障测距设备中,受电弧起弧时刻、燃弧时间长短等因素变化的影响,准确选择故障测距脉冲发射时刻存在困难,这严重影响了设备的故障测距功能的实现,造成设备不易操作,测试准备时间延长。针对这一问题,本文提出根据故障电弧放电电流的整定值确定脉冲发射时刻的方法。根据电缆故障冲闪测试放电规律,首先选取直流电弧放电阶段作为脉冲发射时段,然后根据冲闪放电电流的变化规律和电弧的伏安特性,由冲闪放电电流的整定值算出脉冲的发射时刻。实验结果说明这种方法可以避免手动选取故障测距脉冲发射时刻的盲目性,有较好的实用意义。针对电弧反射故障测距脉冲信号易受电弧电压波动干扰,影响准确计算故障距离的问题,提出基于经验模态分解的脉冲信号提取方法。通过对受扰脉冲信号进行经验模态分解,分析了脉冲信号和干扰的时频分布规律,然后根据受扰脉冲信号特定时段的均值特性,用经验模态滤波的方法提取出脉冲信号,用于故障距离计算。实验结果说明这种方法可以有效地消除电弧电压干扰的影响,有利于故障位置判断和距离计算。针对电力电缆单相低阻接地故障难于定点的问题,提出一种基于电缆故障测试冲闪放电特征的电缆故障定点方法。分析了冲闪放电过程中电缆全径电流和故障点泄漏电流的分布和特征,根据故障泄漏电流在故障点附近地面上形成的电位差信号与冲闪放电电流信号特征相同,并且故障点前和故障点后电位差的极性相反的特性,利用金属探针探测大地电位差的方法实现故障定点。这种方法利用短时脉冲信号定点故障,具有抗大地直流和低频电场干扰能力强的优点,适合直埋电力电缆单相低阻接地故障定点。研制了电力电缆故障定位系统,系统包括高压信号发生器、电力电缆故障测距仪和电力电缆故障定点仪三部分。高压信号发生器具有-8kv/64μF、-16kv/16μF、-32 kV/4μF三种组合形式的电力电缆故障冲闪测试放电功能。与高压信号发生器的冲闪测试放电功能相配合,电力电缆故障测距仪能够进行低压脉冲法、脉冲电流法和电弧反射法电缆故障测距,计算出电缆故障的距离。与高压信号发生器的冲闪测试放电功能相配合,电力电缆故障定点仪能够通过探测大地电位差的冲闪放电信号特征,进行故障定点。分析了系统的故障定位精度,通过实验验证了系统的功能和性能。更多还原

【Abstract】 Power cable fault-locating techniques are used extensively in urban distribution network for finding out underground cable fault. These cable fault-locating techniques have played an increasingly important role in ensuring the safe and reliable operation of the urban power network. Although cable fault-locating techniques have been widely used at present, there are still some key problems on fault locating and fault pinpointing unresolved. This will make cable fault locating spents more time and manpower. For this reason power supply can not be restored in time, and the supply reliability is influenced. In the paper, fault locating and fault pinpointing are studied. The main research contents in this paper include:When only low frequency transient components are considered, the circuit model of the surge discharge system for power cable fault testing is constructed based on the T-type equivalent network of uniform transmission line. The response laws of the voltage and current of this circuit model are analyzed. It also analyses the relationships of surge discharge voltage and current to capacitance value of the discharge capacitor, initial voltage of the discharge capacitor, cable length and resistance value of system series resistor. Field experimental results show that the proposed circuit model of the surge discharge system for power cable fault testing is validated. And the response analyses to this model consist with the experimental datas. These results present a theoretical base for cable fault-locating techniques research and cable fault-locating devices designing.Pulse emitting time selection of cable fault locator using arc reflection method is influenced by arc start time and arc duration time etc. Thus it is difficult to choose exact time for test pulse emitting into the cable during cable fault arcing. For this reseason the fault-locating function of cable fault location systems is badly affected. It can lead to cable fault locator is difficult to operate. The test preparative time of cable fault testing devices is prolonged. In response to this problem, this paper gives a method of determining pulse emitting time based on set value of arc current. According to the arc current changes, the period of DC arc discharge can be chosen as the pulse emitting time window, then pulse emitting time can be worked out using set value of arc current associated to arc current changes and arc voltage-current characteristic. The experiments show that this method avoids blindness of traditional method of manually choosing pulse emitting time. It has considerable practical significance in cable fault location.During cable fault locating using the arc reflection method, the fault arc voltage fluctuation interferes with echo pulses. It may influence the accuracy of fault location. In this paper a new pulse signals extraction algorithm is proposed based on empirical mode decomposition (EMD). The time-frequency distribution of the disturbed pulse signal is analyzed using EMD. This method can extract pulse signals using EMD filter based on arithmetical mean characteristic of the disturbed pulse signals over a specific period time. The influence of fault arc voltage fluctuation interferes can be eliminated effectively. Extracted pulse signals can be used to calculate cable fault distance.The experimental results have shown the effectiveness of the proposed method.Because breakdown sound of underground power cable fault is quite weak, single-phase earth fault with low-resistance is difficult to be pinpointed acoustically. In this paper a new fault pinpointing method is proposed based on identifying the characteristics of surge discharge current. The discharge current is produced by high voltage generator during cable fault testing. Current distribution and characteristics in full path as well as around fault site of undergroung cable are analysed. The results show that earth voltage gradient produced by fault leakage current has the same characteristics with surge discharge current, and the polarity of earth voltage gradient around fault site is opposite each other in front of fault and behind fault. Thus, underground power cable fault can be pinpointed in accordance with the previous explained rules. While a pair of metal probes can be used during detecting earth voltage gradient. It is also because surge discharge current with high frequency characteristic is applied, earth DC and low frequency disturb signals can be easily eliminated by fault pinpointing device. The proposed method is extremely useful for pinpointing single-phase earth fault with low-resistance of underground power cable.A power cable fault location systems are developed. The systems are consisted of high voltage generator, cable fault locator and fault pinpointing device. The high voltage generator can produces surge discharge for cable fault test as-8kV/64μF,-16kV/16μF and-32kV/4μF. Cooperating with high voltage generator, cable fault locator can locate fault and calculate fault distance using TDR method, impulse current method, arc reflection method respectively. Using surge discharge function of high voltage generator, fault pinpointing device can find out the exact site of cable fault according to detect earth voltage gradient produced by surge discharge. Because earth voltage gradient waveform has the same characteristics with surge discharge current waveform, fault pinpointing device can easily identify and pinpoint the cable fault. The locating accuracy of systems is analyzed. Systems performance is verified by experiments.更多还原