A High Reliability Compact Lightweight High Voltage Transformer

This paper describes the design, testing and performance of a new high voltage transformer. An existing compact lightweight high voltage transformer was re-designed to improve its reliability and maintainability. The transformer is used in a dc power supply which is nominally rated at 100 kV and 1.5 Amperes. The entire supply is located within a pressure vessel with Sulphur Hexafluoride ( S F g ) gas for insulation and cooling. The original design encompassed a delta-wye transformation with zig-zag secondaries to provide 12 pulse rectification. The windings were configured in concentric coil pairs with the small (zag) secondary mounted outside the main (zig) windings with molded-in-place silicone rubber spacers. The unit performed well except for a relatively high failure rate due primarily to insulation breakdown between the zig and the zag windings. The transformer was re-designed by changing the mechanical configuration of the windings to sectional, side-by-side windings or "pies." This new winding configuration simplifies the implementation of the zig-zag connections and reduces voltage stress between windings. Added advantages are that it is easier to manufacture and also much easier to repair. The design reduces the major manufacturing steps by approximately 50 percent. The expected lifetime or mean-time-between-failure (MTBF) of this transformer has been increased by a calculated factor of ten.