Application of ultrasound to the inspection of insulation

Ultrasonic methods have been employed for the inspection of electrical insulation, using both the NDT approach (pulse echo techniques) and by acoustic emission. The NDT approach used a commercial ultrasonic flaw detector to produce A-scans of the insulation system under investigation. A PC scanner system has been developed so that the insulation could be mapped according to the signal depth or amplitude. The acoustic emission equipment was also a standard commercial system with a 1 MHz probe. A fibre-optic link was built to isolate the probe and its pre-amp from the rest of the equipment. Fast Fourier transformation of the signals into the frequency domain allowed the use of neural networks for signal recognition. The systems have been utilised to inspect bushings, transformers, switchgear and cables for internal flaws, dimensional integrity, partial discharges and water trees