Design of field regulators for dc shunt generators

1. Name:- Nisarg Amin
Topic:- Design Of Field Regulators for
DC Shunt Generators
1

2. Function
• The function of field regulators in case of DC shunt
generators is to control the value of field current
thereby controlling the terminal voltage of the
generator.
• The generated EMF in a DC generator is:







A
P
60
ZN
Eg
Eg
NEg 
NKEg 

4. • From the above equation, it is clear that the
generated EMF is directly proportional to the
product of flux per pole and speed.
• If generator runs at constant speed then the
generated EMF is directly proportional to the
flux per pole and hence to the field current If.
• The terminal voltage on load:
V = E - IaRa

5. • With the increase in load current, terminal
voltage will slightly decrease due to the ohmic
drop in the armature and due to armature
reaction.
• This decrease in terminal voltage under load
can easily be neutralized by increasing field
current slightly and therefore constant
terminal voltage can be maintained.

6. • A D.C. shunt generator should maintain a
constant voltage across its terminals
irrespective of the magnitude of load being
supplied by it.
• It is not easy to control the speed of armature
in a D.C. shunt generator except by varying the
speed of the prime mover.

7. • So, it I s undesirable to regulate the terminal
voltage of a generator by variation of speed.
• Therefore it is customary to vary the magnetic
flux for this purpose.
• This can be easily by inserting a variable or
adjustable resistance in series with the main
field circuit as shown in figure

8. • This permits a wide range of control of
induced EMF.
• This variable or adjustable resistance is called
the shunt field regulator.