Relation between No. of poles and output voltage

The no. of poles is directly related with the speed of the generator and not with the output voltage. The following formula could be used: f x 60 = n x p, where f is the frequency in Hz or c/s, n is the speed in rpm and p is the number of poles pairs. The output voltage is related with the winding diagram and depends directly of the number of elementar parallel wire/turns.

How the no of poles affect the speed or rpm of the generator.Does increasing the no of poles increases the speed.

Theabove formula instead of 60, it should be 120

Seed in RPM=(120 x frequency)/# of poles

so the speed is invesely proportional to the # of poles

eg. if #of poles is 2, the speed of the generator is 3600rpm

if # of poles is 4, the speed of the generator is 1800 RPM

The initial formula is correct with the value of 60. Is the conversion of c/s to c/min.

Please note that p is the # of poles pairs and not the # of poles.

No, it may remain 60 but P would be (number of pair of poles)

In electric motors (converting input energy into mechanical rotation) and generators (converting input rotational energy into electrical energy), the shaft rotational speed in revolutions per minute (RPM), the frequency of the alternating current (Hz), and the number of poles are all directly related. There have been good discussions of this in other threads on CR4. If you are dealing with a generator, and hold the shaft speed constant, then increasing the number of poles increases the frequency by a corresponding ratio. If you want a constant output frequency, using a generator with a larger number of poles necessitates its being turned at a correspondingly slower shaft RPM.

The relationships between these in motors is similar. As was well-stated in post #2 above, the voltage used or produced is determined by the number of turns in the windings of the generator or motor, and not by the speed.

-JMM

- According to SMCTR's formula: f x 60 = n x p: When frequency is fix, the smaller P is, the larger n should be.

- According to Faraday's formula: E = V x B x D (E= Potential generated in the conductor, related to voltage; V=the velocity of the conductor, related to n; B= Megnetic field strenth, related to winding diagram and E (in case of rectified excitation); D= the length of the conductor, related to winding diagram). When winding diagram (or D) remains the same, the larger V (or n) is, the larger E would be.

According to the above, the smaller P is, the larger E is.

I see numerous "generic reference answers" to the original question ... e.g.:

"voltage is related with the winding diagram and depends directly of the number of elementar parallel wire/turns" ... but nothing specific, so here's a rule-of-thumb from the rewinding shop point-of-view:

If the windings on the armature consist of 80 turns per coil of #15 AWG wire and the unit is rated to put out 120 volts, but you want to rewind it so that it puts out 240 volts , you would wind new coils of 160 turns each using #18 AWG wire (going 3 wire gauges down gives approx 1/2 the cross-sectional area in size , making it "do-able", fit-wise.

You now have twice the turns of wire cutting the field flux with each pass ... thus, you'll get twice the voltage, BUT don't forget that the original design only provided "X" amount of iron for "Z" amount of flux in the first place, so you won't get any more *power* (total watts) ... those extra volts become available at a sacrifice in the ampreres that can be delivered ... one-half.

Hope this helps ~

A lot of discussion, but only few ideas from the practical point-of-view, from the service point-of-view.

I agree with the previous comments of ndt-tom and add the following comment.

A synchronous generator is driven by a prime-mover at a specific and constant speed - the synchronous speed, which is related with the # of poles and with the output frequency.
So, from this point-of-view does not exist any relation between the # of poles and the output voltage. The value of the output voltage is then fixed by the field current (excitation).

The output voltage also could simple be changed by changing the connection of the winding, from parallel to series (reduces the output voltage to the half) or from series to parallel (increases the output voltage to the double).