Answer / piyush kumar

1. Frequency is given by Ns(rpm) divided by 60 to make it "per second"
2. This is due to one pair of poles so needs to be divided by 2.
3. There are P no of such pole pairs so needs to be multiplied by P.
4. So we get f = (Ns/60)*(1/2)*P
or Ns = (120*f)/P

Hope this explains it !!!

Answer / subhasish(rimo) sengupta

f=1/T. when,T = time period for one full cycle.
in T seconds, 1 revolution is completed.
So, in 1 second,1/T revolutions or f full waves is formed.

If there are P no. of poles,then P/2 no. of full waves will be formed in one full revolution of the field.
Now, if n=rotation of the field in 1 second,
then f=(P/2)*n
or,n=2f/p.
So, N=(60*2*f)/P , (when N= rotation per min.)
or, N=120f/P.

Answer / k.prakashchandra

It is N (RPM)and not Ns(RPS) which is =N/60. One south pole
and one north pole produce a cycle. So in one second f= N/60
x P/2 = NP/120. Hence N = 120f/P

Answer / lokeshraj

the Ns is the speed in rpm so there is a facter 60 is
there. then two poles makes a magnet or passing over two
poles one cycle of output is completed. combining both
there is a 120 factor.....

Answer / tandel jinal

Here,
If there is 2 Pole rotor then 1 cycle completed in one revolution,

And if 4 Pole rotor then 2 cycles completed in one revolution,

Number of poles increased then cycles also will increased as half of number of poles.

So, 1 rev.- P/2 cycles complete

Now, N = Speed in rpm ( rev. per minute )
N/60 = Speed in rps ( rev. per second )
If,
1 rev. = P/2 cycles
Then, N/60 rev. = ?

P/2*N/60 = f in Hz
f = PN/120 cycle/sec.

So, N = 120N/P.

Answer / parth

Ns=120*f/p
There are no of pair of pole then p/2.
Ns=1/T in rpm then convert in to rps.
1/T=f.
Ns=60*2*f/p.

Answer / shriram.n

speed=2*60f/p
where
2=?
60=min.
f=frequency
p=pole

we can find speed of motor through below fprmula also
i.e
speed=60f/p
where
60=min.
f=frequency
p=pairs of poles.

example
s=120*50/4=1500rpm

like s=60*50/2(4pole have 2 pairs)=1500rpm

Answer / uday

Ns is nothing but the no. of revolutions indirectly seen by
any pole pair( i.e. created or wound inside). so that will
be 50 cycles per sec per pole, in case of 2 pole machine and
it is 3000RPM)

Answer / aditi

Ns=2f/p rev/s

Multipying by 60 gives Ns in rev/min
and 2 accounts for pole pairs.

Answer / jigneshchaudhari2006

it is phase difference

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