Observational Study Of Lightning Induced Voltage On Buried Cables

The paper is committed to studying characteristics of lightning induced voltage on buried cables. We have designed a set of observation records systems which are used to measure lightning induced voltage on buried cables. Meanwhile, we discuss the time-frequency characteristics of lightning induced voltage on buried cables. During the summer of 2008 and 2009, we conducted observations of natural and artificial triggered lightning flashes at"Guangzhou Field Experiment Site for Lightning Research and Testing"and preliminary data of lightning induced voltage on buried cables was obtained.We use power cables and signal cables of wind speed measurement, which are commonly used by automatic weather stations of PW3103 type, as well as control cable as test object. Oscilloscope (DL708 / DL750P) whose sampling rate is 10M/s is used to record data of lightning induced voltage and data of△E. The magnitude of△E is used as a trigger for the whole system. Detailed information of natural lightning such as latitude and longitude, current is provided by lightning Location system (LLS).The multi-channel recording system has high sampling rate, large capacity, synchronous recording and other advantages.Using the data of lightning induced voltage on buried power cable and△E, the paper analyzes typical characteristics of lightning induced voltage on buried power cable, which happens during discharge phase in Cloud-lightning flashes, initial breakdown, Stepped leader and strokes in cloud-to-ground lightning flashes. Results show that strokes discharge process produces greater amplitude of lightning induced voltage than other types of lightning discharge process. Through the spectrum analysis, lightning induced voltage amplitude of the spectrum on buried power cable is always lower than that of power on the ground, and the amplitude attenuation of 905.5KHz ~ 1.535MHz band is particularly evident. The results indicate that the soil has a decay effect on the lightning electromagnetic pulse. As the frequency increases, the soil increase the absorption of the incident electromagnetic energy. In addition, we propose a method to calculate the shielding effectiveness of the soil around the test sites, and the average value is 5.49dB.We make full use of the advantages of multi-channel recording to study the waveform and amplitude-frequency characteristics of lightning induced voltage on different types of buried cables. Spectral analysis shows that the frequency bands of lightning induced voltage on buried cables are mainly below 1MHz. Steel shielding layer can effectively reduce the role of the higher frequency components in lightning electromagnetic pulse, So 400kHz~1MHz frequency components of lightning induced voltage on buried control cable are significantly reduced. The shielding layer which is made of braided copper belt reduces 0~50kHz frequency components of lightning induced voltage on signal cable. Compared with other cables, the shielding effect of braided copper belt is better.