How to Calculate the Number of Poles in a DC Generator

Where have you looked, so far?

Why do you want to know?

I have tried many google searchs and even read through the text book supplied with my course but there is to example for me to go of. I need to no the formuala to calculte how many poles in a DC generator.

Read this: Synchronous Generators

Thanks I think I found the formula that I need. Many THANKS

That formula I dont thik will work as I dont no the number of ploes to use,The formula was f =pn/120. I dont have the poles so how can I use this?

I think each pole would have 2 conductors, hence 80/2 = 40 poles.

(Synchronous applies to AC rather than DC.)

Now I am just more confused...sorry :)

Hello jesseryanwarren ,

The formula for generated voltage in a generator is given as

WHERE Eg is the generated voltage
Ø is the flux per pole
Z is the total number of conductors
N is the speed in rpm
P is the number of poles
A is the number of parallel paths

In a simplex wave winding A is 2

and in a simplex lap winding A is same as the number of poles


Let us assume the above generator to be a simplex wave wound one .

Hence Eg = ( ØZNP )/(2*60)

substituting the value we get P = 4 poles

SIBIN

As Sibin already explained

the DC machine number of poles is not related directly to machine velocity [rpm].

Indeed the EMF=N*p/a*n*Fi where:

N=total number of turns ;p= pole pair number a=the rotor current parallel ways and Fi=the single turn magnetic flux.

But the number of poles is chosen according to technological reasons [heating-cooling, ventilation and so on].

For rotor diameter less then 40 cm -4 poles is usually recommended.

For rotor diameter less then 70 cm will be 6 poles

For up to 120 mm 8 poles and for more 10 poles.

Then Fi=pi*D/2/p*li*B where pi=3.1414….D=rotor diameter; li=rotor length; B=Magnetic Flux Density in the machine gap.

The AC machine frequency could be [usually] 50 or 60 Hz. But DC machine frequency is [usually] 25 up 75 Hz -for small diameter up 75, for large diameter only 25-in order to reduce the laminate losses

Correction:

Sibin formula is correct. In my relation N it is number of active conductors [and not the number of turns as I said] and n=rpm/60 [rps] of course. Since EMF could be 5-10% more than generator terminal voltage p= (approx.) 2 and 2p=4.

That 'N' is just for an indication