Evaluation of the ZFX 240-kJ parallel-plate water capacitor: lessons learned

The ZFX pulsed-power generator employed a unique intermediate store capacitor; a 0.58-/spl mu/F water-dielectric parallel-plate transfer capacitor (TC) designed for a maximum voltage of 940 kV. To lower the cost and overall size of the TC, plastic field attractors (PFAs) were used to reduce the electric field in the water at the plate edges. The TC was operated successfully at the 750 kV level for several discharges, but a damaging electrical breakdown in the TC ended operations. Electrical stress in the TC was well below the predicted failure level at the time of the breakdown; it was probably caused by debris in the water. Debris was particularly difficult to remove because of the complicated geometry of the TC, a factor which also impeded removal of trapped air bubbles and limited accessibility of the TC interior. PFAs had poor survivability when a fault occurred. The extensive engineering and fabrication effort required to correct these problems would reduce the possible cost savings of the configuration.