Abstract :
A survey of finishes and methods of protection for transformers and chokes used in communication equipment during the war shows that they do not withstand the climatic conditions experienced in different parts of the world. The design of hermetically sealed metal containers and the assembly and sealing of the whole transformer unit is described in considerable detail. This process is developed to cover the sealing of both existing and new transformers. The relative merits of a number of filling media are discussed and practical details of filling with bitumen under pressure are given. X-ray photographs show how difficult it is to obtain satisfactory results with this method of filling. Air-filling is described and it is seen to hold definite advantages, both in ease of production and in the performance of the component, over the original method of bitumen-filling under pressure. Results of tests on unsealed, sealed and bitumen-filled and sealed and air-filled transformers confirm the suitability of the hermetically sealed and air-filled transformer for use in almost every part of the world, both on land and in aircraft.
