Streaming electrification measurements in a 1/4-scale transformer model

Streaming electrification occurs in large power transformers when charge se paration takes place at the oil/cellulose interface as the oil is circulate d for cooling and can cause catastrophic failures. This study was performed with practical emphasis to examine the impact of cooling loop orientation and operation in the transformer lower plenum upon the electrification phen omenon. A simplified 1/4-scale shell-form transformer insulation structure was designed and fabricated for testing in an appropriately scaled tank com plete with six individual cooling loops. Discrete electrodes along the oil flow path facilitated mapping of the internal streaming current distributio ns as a function of various operating conditions. The streaming current mag nitudes and spatial distributions were found to vary with pump configuratio n, temperature and moisture. Furthermore, certain pumping arrangements whic h provided interfering transverse flows were shown to reduce local streamin g electrification.