Alternator Basic TheoryFor generating electricity/induction we require

Magnet Relative motion between the two

Coil

N S

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Bicycle DynamoSimplest & most basic form of alternator is bicycle dynamo.Rotor is a Two Pole Permanent Magnet.

Voltage Speed.

Voltage Strength of the magnet. (Can not be adjusted).

Alternator Basic Theory

Principle

DisadvantagesTwo Carbon brushes are required to be used.

Alternator Basic Theory

Brush SystemPermanent magnet used earlier can be replaced by an electromagnet.Output voltage can be adjusted at the same speed by changing DC supply.

Principle

Alternator Basic TheoryBrushless Separate excitation SystemIn order to avoid use of brushes we have to use a small alternator named ‘Exciter’.Main Field, Rotating Rectifiers & Exciter Armature are mounted on the same shaft.Excitation supply comes from battery to exciter field instead of main field.In this case the DC power required for excitation is much lesser.DisadvantagesThis is an open loop system & input to exciter does not vary for variation in output voltage.

Principle

Alternator Basic Theory

Self Excited & Regulated Shunt SystemIn order to give correction in the exciter input according to the voltage output we have to use AVR.

Different Types of AVR’s are being used in DG sets. The one that is being used currently is

Basler DECS

Principle

MainArmature

MainField

ExciterArmature

RotatingRectifiers

ExciterField

SurgeSuppressor

Short CircuitBack Up CT’s

Rotor

AVR

AVR

BoosterUnit

End

Alternator Basic Theory

Stator

Winding

N

S

MainField

V

ACBack

Alternator Separate ExcitationBrush System

ACDC

SlipRings

Back

Stator

Winding

V

MainField

S

N

+-

Alternator Separate ExcitationBrushless System

Stator

Winding

MainFieldN

S

V

ACDC

ExciterRotatingRectifiers

Back

+-

Alternator Self ExcitationBrushless System

ACDC

RotatingRectifiers

Back

Exciter

Stator

Winding

MainFieldN

S

V

SCM CT’S

N

S

Phase Terminals

Neutral Terminals

ACDC Back

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