Monday, March 23, 2009

Basic Generator


1 Separately Excited Generator

Now that we have learned some basic facts about DC
generators, we can study the various types and their properties.
Thus, instead of using permanent magnets to create the magnetic
field, we can use a pair of electromagnets, called field poles, as
shown in Fig.3.20. When the DC field current in such a generator
is supplied by an independent source (such as a storage battery or
another generator, called an exciter), the generator is said to be
separately excited. Thus, in Fig.3.20 the DC source connected to
terminals a and b causes an exciting current IX to flow. If the
armature is driven by a motor or a diesel engine, a voltage Eo
appears between brush terminals x and y.

1.1Separately Excited Generator Under Load

2 Shunt Generator

A shunt-excited generator is a machine whose shunt field
winding is connected in parallel with the armature terminals, so
that the generator can be self-excited (Fig.3.22). The principal
advantage of this connection is that it eliminates the need for an
external source of excitation.

2.1 Controlling The Voltage Of A Shunt Generator Shunt generator
under load

2.2 Shunt generator under load

3 Compound Generator

A compound generator (Fig.3.28a) is similar to a shunt
generator, except that it has additional field coils connected in
series with the armature. These series field coils are composed of a
few turns of heavy wire, big enough to carry the armature current.
The total resistance of the series coils is, therefore, small.
Fig.3.28b is a schematic diagram showing the shunt and series
field connections.

3.1 Differential Compound Generator

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