# DC Motor - Flux Per Pole

Discussion in 'Homework Help' started by Zaraphrax, Nov 1, 2009.

1. ### Zaraphrax Thread Starter Active Member

Mar 21, 2009
47
3
Hi there,

I'm studying for finals and can't quite get this question out.

For a DC machine:

Average air-gap flux density - B = 389 mT
Effective length of rotor slots - L=0.2 m
Rotor diamater D=0.2m
Number of poles P=4
number of parallel paths in armature winding - alpha=4
Required rotational back EMF E = 220V
Rotational speed N = 1500 r/min

Calculate the flux per pole and the number of turns on the rotor winding.

I'd be able to do it if I knew how many slots there were (because one could then find the number of conductors).

Becuase in that case you could just rearrange

E = (pz/alpha) * phi * N

to

phi = (alpha*E)/(pzN)

However since I can't find Z (number of conductors), I'm lost.

Any help is muchly appreciated. Thanks

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Would this be correct?

Ec=BLv

where
B=0.389,
L=0.2,
v=n$\pi$D/60=1500x$\pi$x0.2/60=15.708 m/s

Ec=0.389x0.2x15.708=1.222 volts

E=ZxEc/a

Z=axE/Ec=4x220/1.222=720 turns

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Clearly I forgot the number of poles (4) - so I guess Z=720/4=180 ...????

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Sorry about the confusion between number of conductors Z and turns ...?