DC Generators are classified on the basis of armature and field winding connection. If armature and field is connected in shunt then this machine is called as shunt generator. When armature and field are connected in series then it is called as series generator.
Types of DC Generators
Que. Classify different types of generators.
Que. Give the classification of DC generator based on their winding connections.
1. D.C Shunt Generator.
2. D.C Series Generator.
3. D.C Compound Generators.
3.1 Cumulative compound generator
3.2 Differential compound Generator
Que. Draw the connection diagrams of different types of DC Generators.
- The current supplied to the field winding can be by two possible way. The way in which the field current of a generator is supplied will decide the type of dc generators.
- The two different ways of supplying the field current are as follows:
- To connect the field winding to an external dc source such as battery called as separately excited generator.
- To use the EMF induced in the armature winding of the generator to supply its own field current called as self-excited generator.
Separately Excited DC Generator
- There is no physical connection between the armature and field windings. The field winding is connected to the external DC source. The armature is driven mechanically by a prime mover.
- The field current produces magnetic flux which is cut by the rotating armature winding and EMF is induced into it. Thus mechanical energy gets converted into electrical energy. This energy is then supplied to the load
Self-Excited DC Generators
- In the self-excited generators, the field winding is not excited from any external energy source. But the induced voltage in the armature itself will excite the field winding of the dc generators.
- But then the question arises that if the field winding is not excited then how can the voltage be induced in the armature winding. And if the armature does not produce any voltage then how can there be any field current?
- The answer to all these questions is the residual magnetism, which is possessed by the field poles under normal operating condition.
- Residual magnetism: magnetization remaining in an electro magnet after a current in the coil is turned off.
Types of Self Excited Generators:
Que. Draw connection circuit diagram of (i) DC shunt generator & (ii) DC series generator
The self-excited dc generators are classified into three types as:
- Shunt type generator.
- Series type generator.
- Compound generators.
The shunt generator is a self-excited generator where the field winding is fed by the armature itself because, the two windings are connected in parallel, and therefore this type of connection machine is called as shunt dc generator.
In a series generator, the field winding is connected in series with the armature winding.
Compound DC Generators
We have discussed the series and shunt dc generators in which the field winding is connected in either series or parallel with the armature winding.
But in the compound generators, there are two independent field windings. One of them is connected in series with the armature and the other one is connected in parallel with the armature winding.
The two types of compound dc generators:
- Long shunt compound dc generator
- Short shunt compound dc generator
Long Shunt Compound Generator
Que. Draw the connection diagram of long shunt differential DC compound generator.
Rse Represents the series field winding and Rsh is the shunt field winding.
The shunt field winding is connected in parallel with the series combination of armature and the series field winding.
Short Shunt Compound DC Generator
Now the shunt field Rsh winding appears directly in parallel with the armature winding and this parallel combination is in series with the series field Rse winding.
Applications of Different Types of Generators
- Lighting loads
- Battery charging.
- For the arc lamps
- As constant current generators
- As boosters on d.c. feeders.
Separately excited generators:
The applications of these generators have limitations, because they need a separate excitation for the field winding. Some of the applications are electro refining of materials or electro-plating.
Cumulative compound generators:
- Used for domestic lighting
- For energy transmission over a long distance.
Differential compound generators:
This type of generators are very rarely used, due to their drooping load characteristics. One of its important applications is electric arc welding.
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