Bruce developed a series of electrode shapes that approximated an ideal uniform field. In practice, breakdown measurements are made with spherical electrodes, because small changes in the surface of a uniform field electrode can cause field irregularities which in turn dramatically affects the breakdown voltages. Also, a deviation from parallelism of the opposing electrode faces can cause significant deviations from a large uniform field area. Spheres are easier to make and keep smooth, even though there isn't a "nice" analytical solution to the field between the electrodes. Furthermore, if there is a misalignment between the spheres, the region between the spheres is still geometrically the same.
The Bruce profile is a figure of revolution, starting with a flat plane in the center, with a sine curve used as a transition to a circular section at the edge. The idea is to have a large area of uniform field (2 flat plates) with a gradually increasing radius of curvature to the edge. The Bruce profile apparently wasn't originally developed with the intention of finding an analytically nice E field, but was an empirically derived method to reduce the edge effects.
Copyright 1998, Jim Lux / bruce.htm / 8 March 1998 / Back to HV Home / Back to home page / Mail to Jim
