ALTERNATOR (GENERATOR) - ETO

ALTERNATOR

In electricity generation, an alternator is a device that converts mechanical energy to electrical energy for use in an external circuit. the course of mechanical energy may vary widely from a hand crank to an engine. a prime mover of the alternator can be a diesel engine or a turbo engine in case design of the ship. the basic working principle related to FARADAY'S LAWS OF ELECTRO-MAGNETISM and direction of the current found by FLEMINGS RIGHT-HAND RULE.

PRINCIPLE OF WORKING

Whenever the conductor kept in the magnetic field and if it is allowed to rotate the MMF can be converted to EMF by Faraday's law Electro-magnetic induction. If this EMF uses the direction of the current can be found by Fleming Right-Hand rule.

TYPES OF ALTERNATOR

• Static alternator
• Conventional alternator
• Brush-less alternator

PARTS OF ALTERNATOR

Yoke - complete body, for accommodating all other parts
Stator - From where the output is obtained ( Stationary Armature )
Rotor - To produce the MMF ( Field )
Slip rings - rotating along with the rotor
Brushes and assembly - Used to carry output from the slip rings
Supporting bearing - To reduce friction loss (DE - Driven end, NDE - Non driven end)

TYPES OF ROTOR WINDING
Two types

• Salient pole
• Non-salient pole

TYPES OF STATOR WINDING

• Single Layer
• Double Layer

Arrangement of stator winding- Full pitch and Frictional pitch

ADVANTAGES OF STATIONARY ARMATURE

It is easily to insulated stationary winding for high voltage
The three-phase alternator is can directly connect to the lead by providing a solid connection
Simple and rust construction


f = NP/120

where

N =  Speed of rotor in RPM
P = no.of.poles

No.of cycles/revolution = no.of.pair of poles P|2

No.of.rev / sec = N/60

No. of cycles / sec = (P/2).(N/60) = NP/120

No.of cycles of EMF per sec of the frequency = F.NP/120


EMF EQUATION  OF ALTERNATOR

Let,

Z = no of conductor
Φ   = Flux per pole
P = no of rotor pole
N = Rotor speed in rpm

in one rev ( is 60/N sec ) each stator conductor cuts by P (wb)

dΦ  = PΦ , 
dt = 60/N

Therefore average EMF induced in one conductor = dΦ/dt = PΦ/(60/N) =  PΦN/60 Volts

since Z conductors in series = ( PΦN/60 )Z

                                              = PΦZ/60 *120f/P = 2fΦZ volts


   RMS value of EMF/Phase = Average value * Kf

                          2fΦZ * 1.11 = 2.22fΦZ volts

                         Erms / Phase = 2.22fΦZ volts

Kp and Kd are pitch and distribution of the armature winding, then

                                Ermf/Phase = 2.22 Kp Kd fΦ Z volts


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