Design of field regulators for dc shunt generators
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The field regulator in a DC shunt generator controls the field current to regulate the terminal voltage. The generated EMF is directly proportional to the field current and flux per pole. As load increases, the terminal voltage decreases slightly due to armature resistance and reaction. However, by increasing the field current, the terminal voltage can be maintained constant regardless of load. A shunt field regulator, which is a variable resistance in the field circuit, allows control of the induced EMF to regulate the terminal voltage without varying the generator speed.
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.