Understanding the discharge activity across GFRP material due to salt deposit under transient voltages by adopting OES and LIBS technique

Abstract

In the present study, breakdown characteristics of a glass fiber reinforced plastic (GFRP) with different salt deposit densities (SDD) under standard lightning impulse (LI)/ switching impulse (SI) voltages are studied. Optical emission during discharge process and the discharge current are measured simultaneously. It is observed that flashover voltage (FOV) reduces with increase in salt deposit density on GFRP material under LI/SI (irrespective of the polarity of applied voltage) voltages. It is also observed that irrespective of level of SDD, the FOV is less with SIV compared with LIV. FOV under negative SIV is less compared with positive SIV. Optical emission corresponding to Na I emission at 589 nm in discharge plasma follows the discharge current profile and also the lifetime of Na I emission is high under switching impulse compared with lightning impulse voltages. Na I emission in the discharge plasma sustains for a longer period in case of negative switching impulse voltages. Plasma temperature is estimated using emission lines and it is observed that the local temperature during discharge process is high under negative switching impulse voltage. With increase in salt deposit density, the optical emission spectrum of GFRP material in addition of Na I line at 589 nm is observed. Laser induced breakdown spectroscopy (LIBS) technique is proposed and demonstrated for the detection of a salt deposit on a GFRP material from a standoff distance of 1 m. In addition, temporal and spatial profile of laser induced plasma on the polluted GFRP material is used to quantify the salt deposit. Laser fluence less than 5 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is ideally suited to rank the severity of a salt deposit on GFRP material at an incident laser wavelength of 1064 nm.