Precise Localization of High-Voltage Breakdown Events using $\phi$-Optical Time-Domain Reflectometry on an Optical Ground Wire

We present $\phi$-OTDR for detecting and localising full spark-gap breakdowns by analysing backscattered light phase and frequency-domain signatures during high-voltage discharges synchronised with oscilloscope-recorded events. Measuring sub-kHz confirms clear discharge signatures and acoustic reconstruction over long links with $\approx$ 10 m spatial resolution.