Multi-particles detection in transformer oil based on lens-free digital holography and transport of intensity equation

Abstract

Transformer oil quality plays an important role in health condition monitoring of a transformer. In order to better monitor the quality of transformer oil, a hybrid method combining lens-free digital holography and transport of intensity equation is proposed. We take a single-shot hologram of sample oil with a large field of view, and then reconstruct intensity images with different distances, which are necessary inputs of transport of intensity equation. After that, we can get relatively high-resolution image of oil. Via experiments, we compare the results from basic lens-free digital holography reconstruction and hybrid method reconstruction. The results show that, the hybrid method can effectively improve the image reconstruction accuracy and achieve a resolution of 2.67 μm across a large field-of-view of 60.35 mm2, which means that we can get high-resolution zoom-in oil image with more details and quantitative parameters in real time, which is a breakthrough for quick transformer oil testing.