Measurement of voltage resulting from single-phase switching of a high-voltage 3-phase transformer

Single-phase switching of small high-voltage transformers with large turns ratios can result in excessive secondary voltages and damage to connected equipment unless these conditions are recognized and measures taken to mitigate these phenomena. Failure of switchgear connected to the low side of a 66,000/480 500-kva delta-delta transformer prompted investigation and measurement of voltages attained on two similar installations. Measurements were found to be in reasonable agreement with those determined analytically.