Experiments on non-destructive testing of grounding grids using SH0 guided wave

Abstract

Grounding grids are widely used in substations to maintain the safe operation of operators and power apparatus. In this paper, an electromagnetic ultrasonic technique is proposed to diagnose the degradation of grounding grids. Firstly, the propagation of guided waves in an infinite plate is studied. It is shown that the lower shear horizontal wave (SH0) has several unique features that are attractive for long-range non-destructive testing (NDT). Secondly, the propagation of guided waves in a rectangular section bar is investigated experimentally. It is found that the SH0 wave excited by an electromagnetic acoustic transducer (EMAT), compared to a Lamb wave excited by a piezoelectric transducer, has a more powerful transmission capability in a rectangular section bar. Thirdly, SH0 wave experiments are conducted on plates with different widths; it is found that the variation in width has little influence on the propagation of the SH0 wave when the width of the plates is greater than the width of the EMAT transducers. Fourthly, experiments are conducted on a rectangular section bar in the laboratory to investigate the sensitivity of the SH0 wave to defects and the surrounding environment. It is found that SH0 wave testing offers an effective way to evaluate the health condition of a rectangular section bar. Finally, the proposed technique is applied to the NDT of a grounding grid in the field.