Name:- Nisarg AminTopic:- Design Of Field Regulators for

DC Shunt Generators

1

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:

AP

60ZNEg

Eg

NEg

NKEg

• 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

• 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.

• 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.

• 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

• This permits a wide range of control of induced EMF.

• This variable or adjustable resistance is called the shunt field regulator.