Interpoles in synchronous converters

Synchronous converters with interpoles have been used but little in this country, but they have been built to some extent in England and on the continent of Europe, principally by companies which are either directly connected with or very closely allied to the companies which have manufactured the great bulk of the converter apparatus installed in this country. Considering that interpole generators and motors came into extensive use in this country at about the same time as in Europe, the question would naturally be raised why interpole converters have not come into similarly extensive use, especially as the principal designers of converters in this country are in direct touch with the designers of the commutating pole converters in Europe. The reply might be that the introduction of any new type of apparatus is a relatively slow process; but, on the other hand, interpoles on direct current generators and motors came into general use in a relatively short time, especially so in railway motors. This indicates that there has been a more or less pressing need for interpoles in certain classes of apparatus and the greater the need for the change the quicker was the change made. Any important change in design or type must be justified by engineering and commercial reasons, such as improved performance greater economy, or lower cost. In the railway motor, placed under the car, and more or less inaccessible, improved operation at the brushes and commutator, when equipped with interpoles, represented a pressing reason for the change in type, although the cost and efficiency were not appreciably changed. In the direct-current generator with the modern tendency toward higher speeds with lower cost, the interpoles represented a practical necessity. This has been recognized for several years and the change to the interpole type has been made as rapidly as circumstances will permit. Also, in variable-speed direct-current motors interpoles have been in general use for a number of years, simply because the interpoles represent a very definite improvement in a number of ways.