Series Generator

Series Generator

AU: Dec.-18

• When the field winding is connected in series with the armature winding while supplying the load then the generator is called series generator. It is shown in the Fig. 3.20.1.

• Field winding, in this case is denoted as S₁ and S₂. The resistance of series field winding is very small and hence naturally it has less number of turns of thick cross-section wire as shown in the Fig. 3.20.1. Let R_se be the resistance of the series field winding.

Voltage and Current Relations

•As all armature, field and load are in series they carry the same current.

ஃ   I_a = I_se = I_L

where I_se = Current through series field winding.

• Now in addition to drop I_aR_a, induced e.m.f. has to supply voltage drop across series field winding too.

This is I_se R_se i.e I_a R_se as I_a = S_se. So Voltage equation can be written as,

Ex. 30.2.1 A d.c. series generator has armature resistance of 0.5 Ω and series field resistance of 0.03Ω. It drives a load of 50 A. If it has 6 turns/coil and total 540 on the armature ans is driven at 1500 r.p.m., calculate the terminal voltage at the load. Assume 4 poles, lap type winding, flux per pole as 2 mWb and total brush drop as 2V. 

Sol. Consider the series generator as shownin Fig 3.30.2.

Ex. 3.20.2 A series generator having a combined armature and field resistance of 0.4 Ω is running at 1000 rpm and delivering 5.5 kW at a terminal voltage of 110 V. If the speed is raised to 1500 rpm and the load adjusted to 10 kW, find the new current and terminal voltage. Assume the machine is working on the straight line portion of the magnetization characteristics.

AU: Dec.-12, 18, Marks 15

Sol :

1. Comparison between Shunt and Series Field Winding

Review Questions

1. Show the connection diagram of d.c. series anil generator and mention its voltage and current relationships.

2. How will you distinguish between series and shunt windings of a d.c. machine?

3. A series generator delivers 100 A at 250 V and the resistance of the series field and armature resistance are 0.055 2 and 0.12 respectively. Calculate the armature current and generated EMF. 

[Ans.: 265.5 V]