The Diseases Of Electrical Machinery

4 THE DISEASES OF this case also the only remedy is to turn down the commutator. Carborundum for Grinding Commutators.—It may here be mentioned that recently for the purpose of grinding down the commutator surface, carbor- undum is used instead of glass-paper. This can now be obtained in the form of carborundum-paper in different degrees of fineness. With this material it is possible to do something that one cannot do with glass-paper, that is, to grind down those commutators that have the insulation between the segments made of too hard material. This is rendered possible by the hardness of carborundum. The author now uses carborundum exclusively in his practices. On no account must emery be used. Wrong Placing of the Brush.es.—A cause of sparking is often the wrong position of the brushes, since the segments are so burnt by the sparks that afterwards, when the brushes are correctly adj usted, sparkless working is still impossible. Since in different modern types of machines various types of armature winding are employed, it is of no use giving a general rule for the position of the brushes, and it could lead very easily to the wrong result. While one could formerly say that at no-load the brushes might stand exactly in the middle between two pole shoes, and must be rocked forward with increasing loads, this is nowadays not the case. Modern machines are more and more so wound that with a two-pole drum arma-