The Diseases Of Electrical Machinery

ELECTRICAL MACHINERY. 53 winding laid in slots or tunnels on the internal peri- phery, and the windings are brought out to two fixed terminals. Unless special circumstances, e.g. heavy current output, call for a departure from the usual practice, all the armature coils are connected in series ; although, naturally, for machines of low volt- age and large output, it is easily possible, in order to obtain a manageable section for the copper, to arrange for several parallel circuits. Break in. the Winding.—If the turns are all in series, on the occurrence of a break the machine will naturally give no current. Such a fault can easily be found, but will rarely occur, since a cause for the breaking of the fixed armature winding is very un- usual. Short-Circnits in the Windings.—If a short- circuit between the windings of a machine is present (by which we mean an undesired electrical connection of two points of the winding), the seriousness of the fault depends greatly upon the position of the short- circuit. If the short-circuit occurs in one coil only, it naturally affects that coil only. It is as if the coil were short-circuited, and then the internally-generated voltage produces an immense current Such a fault is therefore soon noticed, by reason of the dangerous heating of the damaged coil. In addition to this, the voltage of thewhole machine will be lowered,(i)because the voltage of the defective coil is no longer available, and (2) because the heavy current in the faulty coil