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Class 13 DCGenerator types

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									  Types of D.C. Generators

According to the way in which their fields
are excited, generators are classified into :
 i) Separately excited D.C. Generator
 ii) Self- excited D.C. Generator




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i)   Separately excited D.C. Generators are those whose field
     magnets are energized from an independent source of D.C. Current

                          If                              I
                                        Brush
                                                      +
                                                              L
                                                 Eg           O   V
                                                              A
                        Field Winding                         D

                                                      -
                                         Brush

                    R




                  V  E g  IR a  Brush Drops
                  Ra = Armature Resistance

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ii) Self excited D.C. Generators are those whose field
   magnets are energized by the currents produced by the generators
   themselves.

There are 3 types of self-excited D.C. Generators named according to
the manner in which their field coils are connected to the armature.

These are :

•   Shunt wound D.C. Generator
•   Series wound D.C. Generator
•   Compound wound D.C. Generator




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i)   Shunt wound D.C. Generator

                                 Ish                  I
                                             +
                                       Ia
                                                 Ra       L
            Shunt Field                                   O   V
                                        Eg                A
                 Rsh                                      D

                                             -


               Rsh – Shunt Field Resistance
               Ra - Armature Resistance
                I a  I  I sh
                V  E g  I a R a  Brush Drops
                 V  I sh R sh
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ii) Series wound D.C. Generator

                        Ia=Ise=I   Rse

                             Series Field
                    +
                                            L
                                            O   V
               Eg
                                            A
                                            D




   V  E g  I a ( R a  R se )  Brush Drops



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iii) Compound wound D.C. Generator

                                           I


                      Series Field

                             Ish
                                               L   V
                                      Ia       O
                                               A
                                               D
        Shunt Field                  Eg




                            Short Shunt




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                      Ish                I



                               Series Field

                                    Ia
        Shunt Field                           L   V
                                              O
                               Eg             A
                                              D




                            Long Shunt



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Ex.1 A D.C. Shunt Generator delivers 450A at 230V and the
resistance of the shunt field and armature are 50Ω and 0.03 Ω
respectively. Calculate the generated EMF.




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Ex.2 An 8 - pole D.C. Shunt Generator with 778 wave
wound armature conductors running at 500 rpm supplies
a load of 12.5Ω resistance at terminal voltage of 250V.
The armature resistance is 0.24Ω and the field resistance is 250Ω .
Find the armature current, the generated EMF and the flux per pole.




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