Galloping Vibration Monitoring of Overhead Transmission Lines by Chirped FBG Array

A distributed online fiber sensing system based on the phase-sensitive optical time domain reflectometer(Φ-OTDR)enhanced by the drawing tower fiber Bragg grating(FBG)array is presented and investigated experimentally for monitoring the galloping of overhead transmission lines.The chirped FBG array enhanced Φ-OTDR sensing system can be used to measure the galloping behavior of the overhead transmission lines(optical phase conductor or optical power ground wire),which are helpful for monitoring the frequency response characteristics of the ice-induced galloping,evaluating the motion tendencies of these cables,and avoiding the risk of flashover during galloping.The feasibility of the proposed online monitoring system is demonstrated through a series of experiments at the Special Optical Fiber Cable Laboratory of State Grid Corporation of China(Beijing,China).Results show that the proposed system is effective and reliable for the monitoring of galloping shape and characteristic frequency,which can predict the trend of destructive vibration behavior and avoid the occurrence of cable breaking and tower toppling accidents,and these features are essential for the safety operation in smart grids.

CHARACTERISTICS ANALYSIS OF THE INDUCED OVERCURRENT GENERATED BY CLOSE TRIGGERED LIGHTNING ON THE OVERHEAD TRANSMISSION POWER LINE

Techniques of artificially-triggered lightning have provided a significantly useful means to directly measure various physical parameters of lightning discharge and to conduct research on protection methods of lightning electromagnetic pulses.In this study,using capacitive and resistive dividers,current probes and optical fiber transmission devices,we measured and analyzed the induced overvoltage on the overhead transmission line and the overcurrent through Surge Protective Devices(SPD) when a lightning discharge was artificially triggered nearby on August 12,2008 at Conghua Field Lightning Experiment Site.The triggered lightning discharge contained an initial current stage and eight return strokes whose peak currents ranged from 6.6kA to 26.4kA.We found that overcurrents through SPD were induced on the power line both during the initial continuous current stage and the return stroke processes.During the return strokes,the residual voltage and the current through the SPD lasted up to the ms(millisecond) range,and the overcurrents exhibited a mean waveform up to 22/69μs with a peak value of less than 2kA.Based on the observed data,simple calculations show that the corresponding single discharge energy was much greater than the values of the high voltage pulse generators commonly used in the experiments regulated for SPD.The SPD discharge current peak was not synchronous to that of the residual voltage with the former obviously lagging behind the latter.The SPD discharge current peak was well correlated with the triggered lightning current peak and the wave-front current gradient.The long duration of the SPD current is one of the major reasons why the SPD was damaged even with a big nominal discharge current.