Method And System Of Power Cable Fault Location Based On Characteristics Of Surge Discharge

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.