DC Machine winding

Classification of winding

• Concentrated WdgIn case of concentrated winding all the conductor under a

pole is placed in one slot . If the emf is not sinusoidal , this type of wdg has the following demerits.i) Design calculations because of complicated equation becomes

complicated.ii) Core loss due to harmonics will be high and therefore efficiency

will be less.iii) High frequency components leads to communication interference.

Cont…

• Distributed Wdg To overcome the disadvantage of concentrate winding a distributed

winding is used.

It is classified into two groups

i) Single layer winding

ii) Double layer winding

• Both the groups again classified in to

1) Lap winding

2) Wave winding

Yb & Yf

Some important points

• Irrespective of the number of turns of the coil, -- no. of commutator segment = no. of coils

• No. of parallel path A= P ( for simplex lap) = 2 (for simplex wave)

. No. of brushes or brush arm = P(for simplex lap) = 2(for simplex wave)

Minimum brush width = 1 segment width for simplex lap or wave wdg = 2 segment width for duplex lap or wave wdg = 3 segment width for triplex lap or wave wdg

Pole enclosure,Ψ = pole Arc(PQ) / pole pitch < 1.0 ( lies between 0.6 to 0.8)where pole pitch (AB) =Slot/pole or Z/P (conductor /pole)

Direction of induced e. m. f or current- Flemings right hand rule

• Generally the generators are assumed to be rotating in the anti – clockwise direction.

Direction of rotation of conductors

Q1. Double layer for 24 conductors 4 pole progressive simplex lap winding

• Soln

Given Z= 24 therefore C=12 =Slot (since double layer)

Pole pitch =Z/Pole =24/4 = 6( for calculating Yb & Yf)

Pole pitch = Slot/pole =12/4 =3 (for pole arc calculation)

Yb=Z/P±k (must be a odd number)

+ for progressive , - for retrogressive

= 6+1=7

Yb-Yf= ±2m( + for progressive , - for retrogressive)

m=1 (for simplex) m=2 (for duplex) m=3 (for triplex) so on

Pole arc calculation

• Pole arc/ pole pitch =(0.6 to 0.8)

• Pole arc= 0.8* 3=2.4

• Distance between adjacent poles=3-2.4=0.6

• Length of the conductor =5cm

• Distance between slots=1cm

Calculations for wave winding

» C ±1m

• Yc (commutator pitch)=------------» P/2

m=1 (for simplex) m=2 (for duplex) m=3 (for triplex) so on

( + for progressive , - for retrogressive)

1) If Yc is odd then Yc=Yb=Yf

2) If Yc is even then Yb=Yc ±1, Yf=Yb 2

3) If Yc is fraction 1 coil will be made mechanically present but not electrically connected i.e one dummy coil will be present.

Q2 Double layer for 26 conductors 4 pole

progressive simplex wave winding.

• Given Z=26 C=13=S

• Yc=7=Yb=Yf

• S/p=13/4=3.25

• Pole arc=0.8*S/P=2.6

Q3. Double layer 3 phase 24 conductors 4 pole full pitched lap winding

• Let us consider phase seq= RYB

• m=slot/pote/phase=24/12=2

• Β=180/(3*m)=30

• mB=60

• Coil seq=RBY