The application of a theorem of electrostatics to insulation problems

The arrangement of conductors so that they shall assist in insulating one another has received but little consideration. The object of this paper is to emphasize a principle of electrostatic theory by which this may be done. A statement of this principle is: “If a region in any particular electric field be isolated or cut out by any number of closed surfaces then the electric field in this region will remain unchanged, whatever change may take place in the external field, if the potentials at all points on the enclosing surfaces are maintained at their original value.” A discussion of the principle follows and illustrations of electrostatic fields produced by its means. Limitations imposed on practical applications of the principle are discussed. Application to core-type transformers is considered. Arrangements suitable for various conditions of service are described and a description is given of a transformer which was built according to this principle, and tested. Application to shell-type transformers and to outlet terminals and insulators is shown. Condenser type terminal affords an example of the advantage obtained by conforming to this principle. Suggestions are made as to its application to line insulators. This principle is capable of wide application and seems to afford a solution of some of the most perplexing problems confronting electrical engineers.