IK) THE DESIGN OF STATIC TRANSFORMERS 



keeping the oil clean, and free from impurities or moisture. 

 Many insulating materials which can be employed with great 

 advantage in air-immersed transformers must not be used in 

 oil-immersed transformers, as not only will the oil destroy 

 their good properties, but the presence of these insulating 

 materials will destroy the good properties of the oil. That 



Output in KM. 



FIG. 73. Curve showing the time taken for transformers of various outputs to 

 reach final temperature at full load. 



there can still exist prejudices against the oil-immersed type 

 of transformer is very remarkable, and such a state of affairs 

 is not likely to long continue. Some ten years ago these 

 same strong prejudices existed in certain large electrical manu- 

 facturing firms in Germany, but they have long since been 

 overcome, and the appropriateness of the oil-immersed type 

 for a wide range of work is now almost universally admitted. 



