Influence of ultrasonic homogenization on particle counts and dielectric strength measurements of transformer oil samples

It is shown that particle deposition in transformer oil samples taken in power equipment operated under service conditions is relatively rapid. The particle counts, the metal-in-oil contents and the breakdown voltage of such samples vary significantly with the deposition time of particles. A simple and inexpensive homogenization method based on ultrasonic agitation is proposed. It is shown that 25 min. of ultrasonic agitation is sufficient to restore the original particle distribution in oil samples. This also leads to a modified and more realistic breakdown voltage value.