The dc series generator has a lot of applications when the appliances needs the voltage boosters. In other words, this type of generator gives output as rising voltage characteristics instead of constant voltage as like as dc shunt generator.
DC series generator
The generator which field winding is connected in series with the armature conductor in known as dc series generators.
The circuit diagram for dc series generator is given below
The equation of dc series generator,
Eg = Vt + Ia*(Ra+Rse) + Armatue Reaction drop + Brush Voltage drop
Just neglect the armature reaction drop and brush drop. So, easier analysis of machine.
Assume the generator is operating constant speed N by the external prime mover or diesel engine. The armature current is equal to the field current and load current because of series connection.
First and fore most step is to conduct the no load test or occ test in dc series generator.
The load on the generator is removed and run the machine under constant speed N the emf generation in the generator is given by the equation,
The emf equation of dc generator Eg = (NՓP/60)*Z/A
The generating emf in directly proportional to the field flux and this field flux is proportional to the armature current Ia.
Magnetization characteristics of dc series generator
If we notice that the magnetizing characteristics
Even though the field current is zero there is some voltage across the terminal because of residual magnetism in the poles.
The curve start rising linearly and saturated at one point because of core saturation.
Load characteristics of dc series generator
Then load is fed into generator and operating at constant speed such that armature current is constant. By varying the field current the load characteristics are plotted between terminal voltage Vt and field current If.
Here, external and internal characteristics are plotted in the same graph.
Nature of voltage rise in DC series generator
The addition of load causes armature current flow through the circuit the effect of armature flux on main field causes armature reaction leads to demagnetization. which reduces the voltage at terminal from no load to full load. The voltage drop at armature conductors is Ia Ra.
As you can see the load increases and Vt is increases and that is why the dc series generator is operated in boosters and when its is need by rising voltage characteristics.
DC series generator is also used in regenerative breaking in locomotives when it is running freely.
Try to solve this problem,
A DC series generator delivers a load current of 50 amps at 500 volts. The resistance of armature is 0.05 ohms and series resistance are 0.03 ohms. Find the induced emf, power developed in armature and power delivered to load, if contact drop is 1 volt per brush. Neglect armature reaction. so, it is ease to work.
Eg = 500 + 50*(0.05+0.03) +(2*1)
induced emf=Eg= 506 volts
Power developed in armature
P armature = Eg*Ia = 506*50 = 25.3KW
P load = Vt*Ia = 500*50 = 25KW
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