Armature Windings The mean­ing of the following terms used in connection with armature winding should be clearly kept in mind. Pole-pitch It may be variously defined as : i) The periphery of the armature divided by the number of poles of the generator i.e. the distance between two adjacent poles. ii) It is equal to the number of armature conductors (or armature slots) per pole. If there are 48 conductors and 4 poles, the pole pitch is 48/4 = 12. Conductor The length of a wire lying in the magnetic field and in which an e.m.f. is induced, is called a conductor (or inductor) as. for example, length AB or CO in Fig. 26.21 Coil and Winding Element With reference lo Fig. 26.21. the two conductors AB and CD along with their end connections constitute one coil of the armature winding. The read more

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For small machines roller bearings are used at both ends. For large machines roller bearings are used at driving end and ball bearings at non driving or commutative end.Sometimes pedastal bearings are also used for large machines.The bearings are housed in the endshield.The figure below shows a pedestal bearing. read more

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Usually we use box type brush holders in all D.C. machines.At the outer end of arm a brush box is provided which is open at top and the bottom is attached.The brush is pressed to the commutator by means of a clock spring and this pressure could be adjusted by a level arrangement in the spring.The brush is connected to a flexible conductor called pigtail.The flexible conductor may be attached to the brush by a screw or may be soldered. Brush boxes are generally made of bronze casting or sheet brass.For small machines working on low voltage commutation conditions are easy and galvanized steel boxes are employed.There are individual and multiple brush holders available on the market.In multiple brush holders a number of single brush holders are built into one long assembly. Brush read more

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The brushes used for machines are divided into five classes according to the material with which it is made they are Metal Graphite brush Carbon Graphite brush Graphite brush Electro – Graphite brush Copper brush The maximum current density at brush contact varies from 0.5A/sq.cm to 23A/sq.cm for copper.For large current machines working at low voltage copper brushes are employed.Lubrication should be done properly else it may cut the commutator rapidly leading to high wear and tear.Graphite and carbon graphite brushes are self lubricating and therefore it is used very widely. Even for soft brushes there is wear but it takes place gradually.Though the mica segments between the commutator doesn’t wear easily but it reduces the effective contact with the segments and it may read more

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We use brush gear to collect or feed current from a rotating commutator.A brush gear consists of following parts. Brushes Brush Holders Brush studs or Brush holder arm Brush Rocker Current collecting busbars read more

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