Streaming electrification occurs in large power transformers when charge separation takes place at the oil/cellulose interface as the oil is circulated 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 phenomenon. A simplified 1/4-scale shell-form transformer insulation structure was designed and fabricated for testing in an appropriately scaled tank complete with six individual cooling loops. Discrete electrodes along the oil flow path facilitated mapping of the internal streaming current distributions as a function of various operating conditions. The streaming current magnitudes and spatial distributions were found to vary with pump configuration, temperature and moisture. Furthermore, certain pumping arrangements which provided interfering transverse flows were shown to reduce local streaming electrification.
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