Skip to main content

Compound Generator

In this type, the part of the field winding is connected in parallel with armature and part in series with the armature. Both series and shunt field windings are mounted on the same poles. Depending upon the connection of shunt and series field winding, compound generator is further classified as : i) Long shunt compound generator, ii) Short shunt compound generator.
1.1 Long Shunt Compound Generator
       In this type, shunt field winding is connected across the series combination of armature and series field winding as shown in the Fig. 1.
Fig. 1 Long shunt compound generator
       Voltage and current relations are as follows.
       From the Fig. 1.
       Ia = Ise 
       and  Ia = Ish +  IL
       Voltage across shunt field winding is Vt.
       Ish = Vt /Rsh
      where Rsh = Resistance of shunt field winding
       And voltage equation is,
       E = Vt + Ia Ra + Ia Rse + Vbrush
       Where Rse = Resistance of series field winding
1.2 Short Shunt Compound Generator
       In this type, shunt field winding is connected, only across the armature, excluding series field winding as shown in the Fig. 2.
Fig. 2  Short shunt compound generator
      Voltage and current relations are as follows.
       For the Fig. 2, Ia =  Ise + Ish 
       and Ise = IL
...    Ia =  IL + Ish 
       The drop across shunt field winding is drop across the armature only and not the total Vt, in this case. So drop across shunt field winding is E -Ia Ra .
        Ish   = (E - Ia Ra ) / ( Rsh)
        Now the voltage equation is E = Vt + Ia Ra + Ise Rse + Vbrush
...      Ise = IL
...      E = Vt + Ia Ra + IL Rse + Vbrush
       Neglecting Vbrush , we can write,
       E = Vt + Ia Ra + IL Rse
       E - Ia Ra = Vt + IL Rse
       Ish = (Vt + IL Rse) / ( Rsh)
       Any of the two above expression of Ish can be used, depending on the quantities known while solving the problems.
1.3  Cumulative and Differential Compound Generator
       It is mentioned earlier that the two windings, shunt and series field are wound on the same pole. Depending on the direction of winding on the pole, two fluxes produced by shunt and series field may help or may oppose each other. This facts decides whether generator is cumulative or differential compound. If the two fluxes help each other as shown in Fig. 3 the generator is called cumulative compound generator.
Fig. 3 Cumulative compound generator
       ΦT = Φsh + Φse
      Where  Φsh = Flux producd by shunt
                 Φse = Flux produced by series, field winding
       If the two windings are wound in such a direction that the fluxes produced by them oppose each other then the generator is called differential compound generator. This is shown in the Fig. 4.
       ΦT = Φsh - Φse
       Where   Φsh = Flux produced by shunt field winding.
                    Φse = Flux produced by series field winding.
Fig. 4  Differential compound generator
Labels:

Comments

Post a Comment

Comment Policy
We’re eager to see your comment. However, Please Keep in mind that all comments are moderated manually by our human reviewers according to our comment policy, and all the links are nofollow. Using Keywords in the name field area is forbidden. Let’s enjoy a personal and evocative conversation.

Popular posts from this blog

Practical Commutation

The e.m.f. induced in each coil of armature is alternating in nature. If load is connected, the current flowing will also be alternating. But the flow of current in a d.c. generator must be undirectional. This can be achieved by the use of commutator. When the armature conductors are under the influence of one pole they carry current in one direction whereas the current is reversed when the conductors are under the influence of other pole. This reversal of current takes place along the magnetic neutral axis. Fig. 1 Note : The reversal of current is likely to take place in short interval when a coil is short circuited by a brush so that transfer of current from one direction to other is carried out without any sparking. This process is called commutation.        Thus a process by which current in the short circuited coil is reversed while it crosses the MNA is called commutation. The time during which the coil remains short circuited is known as...
1 comment
Read more

Demagnetising and Cross Magnetizing Conductors

The conductors which are responsible for producing demagnetizing and distortion effects are shown in the Fig.1. Fig. 1        The brushes are lying along the new position of MNA which is at angle θ  from GNA. The conductors in the region AOC = BOD = 2θ  at the top and bottom of the armature are carrying current in such a direction as to send the flux in armature from right to left. Thus these conductors are in direct opposition to main field and called demagnetizing armature conductors.         The remaining armature conductors which are lying in the region AOD and BOC carry current in such a direction as to send the flux pointing vertically downwards i.e. at right angles to the main field flux. Hence these conductors are called cross magnetizing armature conductors which will cause distortion in main field flux.        These conductors are shown in the Fig. 2 Fig. 2  ...
Post a Comment
Read more

Armature Voltage Control Method or Rheostatic Control of dc motor

Speed Control of D.C. Shunt Motor (Part2)  2. Armature Voltage Control Method or Rheostatic Control        The speed is directly proportional to the voltage applied across the armature. As the supply voltage is normally constant, the voltage across the armature can be controlled by adding a variable resistance in series with the armature as shown in the Fig. 1. Fig. 1 Rheostat control of shunt motor        The field winding is excited by the normal voltage hence I sh is rated and constant in this method. Initially the reheostat position is minimum and rated voltage gets applied across the armature. So speed is also rated. For a given load, armature current is fixed. So when extra resistance is added in the armature circuit, I a remains same and there is voltage drop across the resistance added ( I a R). Hence voltage across the armature decreases, decreasing the speed below normal value. By varyi...
Post a Comment
Read more