Nov 22, 2014

Self Excited Generator



A DC generator whose field magnet windings are supplied current from the generator output itself is termed as self-excited generator. Self-Excited generator can be categorized into three types relying upon the design in which the field windings are coupled to the armature winding. They are
  1. Series Generator
  2. Compound Generator

Series Generator:

Series Generator
The fig above shows the connection of a series wound generator. In a series generator, the field winding is connected in series with armature winding in order that whole armature current flows through the field winding likewise because the load. Since the field winding carries the entire load current, it's some turns of thick wire having low resistance. Series generators are seldom used aside from special functions e.g., Voltage boosters.

Terminal Voltage V = Eg-I(Ra+Rse)
Armature Current Ia = Ise = IL = I
Power developed in armature = EgIa
Power delivered to load = EgIa-Ia2(Ra+Rse)
                                       = I[Eg-IaRa-IaRse
                                       = VIa or VIL

Shunt Generator:

Shunt Generator
The fig shows that the field winding connected is in parallel with the armature winding in order that supply voltage of the generator is applied across it. Generally in shunt generator the shunt coil has large number of turns with fine wire having high resistance. As a result, solely a part of armature current flows through shunt winding and also the rest flows through the load.

Terminal Voltage V=Eg-IaRa
Armature Current Ia=IL+Ish
Shunt field current Ish = V/Rsh
Power Developed in armature = EgIa
Power delivered to load = VIL

Compound Generator:

In a compound generator, there are 2 sets of field winding on every pole—one is in series and also the different in parallel with the armature. This generator can be classified into two:

(a) Short Shunt during which solely shunt winding is connected in parallel with the armature winding which is shown in the figure.
Short shunt compound Generator
(b) Another one is long Shunt during which shunt winding is connected in parallel with each series field winding and armature winding as shown in the figure.
Long Shunt Compound Generator
Short Shunt Compound Generator
Terminal Voltage V = Eg – (IaRa) – (IseRse)
Series field current Ise = IL
Shunt field current Ish = (V+IseRse) / Rsh
Power developed in armature = EgIa
Power delivered to load = VIL

Long shunt Compound Generator
Terminal voltage, V = Eg - Ia(Ra + Rse)
Series field current, Ise = Ia = IL + Ish
Shunt field current, Ish = V/Rsh
Power developed in armature = EgIa
Power delivered to load = VIL


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