Parameters of an alternator

@zaveri-5TD6Sk • Oct 17, 2024

Oct 17, 2024

1.3K

What factor decides the voltage output of an alternator. ? is it always fixed for a particular machine ?

Second : for an alternator,

input mechanical power = output electrical power (ignoring the efficiency)

angular velocity of shaft * torque applied = voltage obtained * current

now considering that the voltage is fixed, then can the current flow be varied by varying the RPM of the shaft ?

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grsalvi

@grsalvi-7IhIh1 • Dec 9, 2012

EMF induced in transformer (voltage output of transformer)
The theoretical equation is
E(phase)=4.44*(frequency)*(flux per pole)*(total number of coils).

Though above equation tells what will be the emf induced in each phase of an alternator, lets see what is practically deciding the voltage generated.

You know an alternator works on principle that "when ever the flux linking with a coil is changed ,an emf is induced in the coil".

That's it , the parameters which decide the emf induced in Alternator are :
a]the flux per pole
b]number of coils ,since more coils more conductors cut flux ,hence more emf induced.
c]rate of change of flux, which directly dependent on the RPM on alternator.
Jeffrey Arulraj

@jeffrey-xA7lUP • Dec 9, 2012

Alternator has input DC source which generates a mechanical work Which is converted back into AC source

DC is converted into AC in an alternator right pure mech energy is not transferred directly in an alternator

Always the load current is determined by speed in motors not sure about that in an alternator
grsalvi

@grsalvi-7IhIh1 • Dec 9, 2012

And yes the second part the current flow of alternator is dependent on the load you apply to alternator.
Increase load ,current increases .As in motors ,mentioned by Conqueror above.
lal

@lal-R60Xjx • Dec 9, 2012

Conqueror
Alternator has input DC source which generates a mechanical work Which is converted back into AC source

DC is converted into AC in an alternator right pure mech energy is not transferred directly in an alternator

Always the load current is determined by speed in motors not sure about that in an alternator
I would like to disagree. Infact mechanical energy is what gets converted to alternating electrical energy in an alternator. The DC source used in alternators is just used to energise the field. By just energising the field an alternator cannot provide an AC output. For that, the field is rotated to make a varying flux by means of mechanical energy. So actually, its completely the mechanical energy that gets converted to electrical energy at the output.

Current and voltage are dependent to each other. The ratio of voltage and current is a constant, V/I = Z (impedance). When one varies, the other follows to keep the ratio constant for a particular load (impedance). Higher load means lower impedance and vice-versa.
Jeffrey Arulraj

@jeffrey-xA7lUP • Dec 9, 2012

Thanks for clearing it out #-Link-Snipped-# now pretty clear about alternator
ABCD ABCD

@abcd-2NEyMb • Dec 10, 2012

nice question zaveri, had the same time ago. But, number of coils will be three for 3-phase alternator. Err?
But, what is responsible for frequency of the AC generated?
lal

@lal-R60Xjx • Dec 10, 2012

Frequency of the generated AC is goverened by the number of poles and speed of rotor.

f = NP/120
N = speed in rpm
P = number of poles

Once a machine is made, its poles will not be changed. So it is safe to say, speed controls the frequency.
ABCD ABCD

@abcd-2NEyMb • Dec 11, 2012

lal
Frequency of the generated AC is goverened by the number of poles and speed of rotor.

f = NP/120
N = speed in rpm
P = number of poles

Once a machine is made, its poles will not be changed. So it is safe to say, speed controls the frequency.
Thanks, can you give the source(or book) of this information? I'm interested in reading more about this.
lal

@lal-R60Xjx • Dec 11, 2012

mreccentric
Thanks, can you give the source(or book) of this information? I'm interested in reading more about this.
Refer any book on electrical machines. Or try the vast web. There are numerous quality sources available on the internet.
ABCD ABCD

@abcd-2NEyMb • Dec 11, 2012

lal
Refer any book on electrical machines. Or try the vast web. There are numerous quality sources available on the internet.
BTW, which book did you refer? I have one will go and check if this is there.
lal

@lal-R60Xjx • Dec 11, 2012

I use 'Theory and Performance of Electrical Machines' by J. B. Gupta.

Any text book on Electrical Machines sure will have that theory.
pinank

@pinank-6TUo5O • Dec 12, 2012

mreccentric
BTW, which book did you refer? I have one will go and check if this is there.
you can use Electrical Machines by PS Bhimbra...