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Characteristics of DC Shunt Generator


Related Topics
Construction of DC Generator
Types of DC Generators
Losses in DC Machine
Armature Reaction in DC Machines
Compensating Windings and Interpoles
Commutation in DC Machines
DC Generator Characteristics
Characteristics of Separately Excited Generators
Characteristics of DC Series Generator
Characteristics of Shunt DC Generator
Characteristics of Compound DC Generators
Parallel Operation of DC Generators
Parallel Operation of DC Shunt Generators
Parallel Operation of DC Series Generators
Parallel Operation of DC Compound Generators

In a shunt generator, the field winding is connected in parallel with the armature winding so that terminal voltage of the generator is applied across it. 

The shunt field winding has many turns of fine wire having high resistance. Therefore, only a part of armature current flows through shunt field winding and the rest flows through the load.

Figure shows the connections of a shunt wound generator. The armature current Ia splits up into two parts; a small fraction Ish flowing through shunt field winding while the major part IL goes to the external load.

Open circuit characteristic

The O.C.C. of a shunt generator is similar in shape to that of a series generator as shown in Fig. (ii). The line OA represents the shunt field circuit resistance. When the generator is run at normal speed, it will build up a voltage OM. At no-load, the terminal voltage of the generator will be constant (= OM) represented by the horizontal dotted line MC.

Internal characteristic


When the generator is loaded, flux per pole is reduced due to armature reaction. Therefore, e.m.f. E generated on load is less than the e.m.f. generated at no load. As a result, the internal characteristic (E/Ia) drops down slightly as shown in Fig (ii).
Characteristics of Shunt Generator

External or Load characteristic


Curve 2 shows the external characteristic of a shunt generator. It gives the relation between terminal voltage V and load current IL.
V = E - IaRa = E - (IL + Ish)Ra
Therefore, external characteristic curve will lie below the internal characteristic curve by an amount equal to drop in the armature circuit [i.e., (IL + Ish)Ra]as shown in Fig (ii).
Note. It may be seen from the external characteristic that change in terminal voltage from no-load to full load is small. The terminal voltage can always be maintained constant by adjusting the field rheostat R automatically