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Foam ceramics have excellent properties such as high porosity, high temperature resistance, chemical corrosion resistance and good thermal stability, and are widely used as metal liquid filter, high temperature gas and ion exchange filter, catalyst carrier, environmental material, heat insulation material, sound absorption material, biological material and so on. In this paper, the preparation technology of porous ceramic materials is investigated firstly. Then the foam ceramic samples with different porosity of Al2O3 and SiC materials were manufactured, and their acoustic properties were tested, and the influence of material and porosity on sound absorption performance was analyzed.

In order to investigate the influence of load conditions on the noise characteristics of distribution power transformers, a platform in semi-anechoic room is designed for on-site transformer noise simulation. Transformer noises in balanced, unbalanced and harmonic load conditions are tested, respectively. The spectral distributions and A-weight sound pressure levels (SPLs) are compared to investigate the discrepancy caused by various load conditions. The result shows that the transformer noise is relevant with unbalanced load. Harmonic content is found to have obvious influence on the noise level of distribution power transformer. When harmonic load current is applied, the noise level of distribution power transformer increase obviously. The results can be referenced for the field noise and vibration control of distribution power transformers.

Power transformer vibration and noise not only affect the equipment life, but also seriously pollute the environment. The noise is proportional to the surface vibration velocity of transformer. The objective of this work is to measure vibration velocity distributions on oil-tank surfaces of a power transformer and to investigate relationship of vibrations between different points. No-load test and load test were conducted on a single-phase transformer respectively. The oil-tank surfaces were divided with small grids and a portable digital vibrometer (PDV) was conducted to measure the vibration velocity on every point. The experimental results show that the velocity on a specific point is steady and periodic. The frequencies of vibration mostly converge from 100–500 Hz while the amplitude of vibration reach maximal at 100 Hz. Velocities of different measure points on a surface are quasi-synchronous and have same phases or reversed phases so that the velocity distribution presents as a wave shape. The positions with maximum vibration amplitude at different frequencies are different. This can provide the guidance for the application of vibration method in monitoring the condition of transformer winding.

A high-precision calibrator for metal-oxide surge arrester on-line monitor based on DSP and CPLD was developed to verify the accuracy of on-line monitor. This calibrator can generate standard voltage and current to simulate the actual leakage current of metal-oxide surge arrester. The high spatial resolution digital phase-shifting technology and feedback control technology are utilized in design of the calibrator to achieve high precision. The calibrator was tested by mid-south national center of metrology, and the result shows that it can meet the requirements for verifying metal-oxide surge arrester on-line monitor with 0.1% output amplitude error of voltage and current signals and 0.04°phase error between voltage and current signals.