Advantage and Disadvantage of DC Generator
DC Generators are the devices which convert the mechanical energy into the Electrical Energy of Direct Current form.
I am going to talk about the generators at the power system scale. Smaller machines my have advantages like simple windings, construction and control, but at the larger scale, things are different.
Advantages:
Advantages of the DC generators are very few like ease of parallel operation, simple design and construction and lesser system stability issues unlike the alternators.
Disadvantages:
Inherently, both AC and DC generators work on the Faraday's law of electromagnetic induction. When the conductor cuts the magnetic field, emf is induced in it. Now, the voltage induced in the armature of the DC generator is AC, but that is converted to the Dc form through the Commutator. So, basically that converted voltage is supplied to the load through the brush and slip ring assembly.
Now, we don't need any stats for the discussion, as we can conclude by the qualitative analysis that DC generators are less efficient than the AC generators due to the reason that is basically is an AC generator, but it converts the produced energy into the direct current form, which obviously includes the losses and hence decreases the efficiency.
Now, as the DC generator has brushes and commutators, there is a sparking in the assembly and also due to the friction between the brush and commutator, there is more requirement of maintenance. Hence, they are not robust and need the frequent maintenance, unlike the AC generators, which don't have any such parts and the power is directly taken from the steady windings of the stator.
Commutation phenomena limits the ratings of the generators from going above some Megawatts. Since the current is very higher, arcing takes place and rapid changes in the commutator segments limits the speed of the machine.
Also, the armature reaction increases, which requires use of the compensating windings and the needs the compensation for the self inductance of windings.
Also, due to the sparking at the commutators due to the current switching, it produces the electromagnetic noise.
Conclusion:
Disadvantages of the DC generator overweights its advantages at the large power ratings which makes them lesser economic, reliable and efficient to use.