Dual-Beam Mach–Zehnder Interferometry for High-Sensitivity Measurement of Impulse Electric Fields in Liquid Dielectrics

Liquid dielectrics are critical insulating materials widely used in high-voltage power equipment. During operation, these insulating liquids are frequently subjected to impulse voltages, posing significant challenges to insulation reliability. Currently, electric-field characteristics under such transient impulses are typically estimated by numerical simulations due to the absence of high-sensitivity experimental measurement techniques. To address this research gap, this research develops a dual-beam Mach-Zehnder interferometric system integrated with a synchronized trigger circuit (67 ns delay) and a high-speed CCD camera to capture real-time fringe displacements induced by lightning impulse waveforms. A comprehensive image processing workflow is proposed, incorporating statistical analysis to identify optimal fringe regions for computation. This method achieves a measurement sensitivity of 0.22 kV/mm, which is 7.2 times higher than that of conventional single-beam methods. Experimental validation using propylene carbonate (Kerr constant 1×10−12m/V²) under impulse voltages demonstrates a relative error between measured and theoretical fields below 10%. This technique offers a non-intrusive, quantitative, and real-time diagnostic capability, providing valuable experimental insights for enhancing insulation design and ensuring reliability in power equipment.