<-- Back Items 01 - 10

Item 11. Internal Diameter of Stator, D
This is limited by the Diameter of the Rotor, item 03, plus the initial calculated air gap, item 10.
Trial D = Dr + 2", which assumes that the d is equal to not less than 1 inch.. This value should at least be a multiple of 1/8".

Item 12. Pole Pitch, t
t = p × D / p.
For 60-hz machines running at moderate speeds, this value lies between 6 to 12 inches. A pitch of 8 to 10 inches, or more being very common for alternators rated above 1,000 kVA.

Item 13. Pole arc, tr
Assume, Distributed winding.

Item 14. Percentage of armature covered by poles
Assume, Distributed winding.

Item 15. Number of inductors per phase, Z
Z_trial = (1/3)(pDq/I_c).
Z_final = n_s x C_s x p.
For the trial value of Z, use the initial value of q. When the value of q, item 07 have been finalized, the number of inductors per phase, Z should be changed accordingly. Also, take into consideration that the final Z, a whole number, should be at least nearer to the computed trial, else the trial current density will not fall within the limits.

Item 16. Total number of inductors, Z'
Z' = Z × n.
Where n = 3, for three-phase, n = 2, for two-phase, and n = 1, for single-phase. At with Z, the Z' should be a whole number.

Item 17. No. of armature slots per pole per phase, n_s
n_s is selected arbitrarily.
Possible numbers: 1, 2, 3, 4, 5, 6
For n_s greater than 6, compute manually for the slots per pole: S/p, the angle of spread: b°, the coil span angle: g°, the distribution factor: k, and the pitch factor: k'.

Electrical degrees between adjacent slots, b°
b° = 180 / S/p.
For the relationship of Slots per pole, number of armature slots per pole per phase, n_s see table for three-phase below:

Slot per pole	ns	b°	k
3	1	60	1.000
6	2	30	0.966
9	3	20	0.960
12	4	15	0.958
15	5	12	0.956
18	6	10	0.955

Distribution Factor, k
Use: k = sin (n_sb/2) / n_s sin (b/2)

Coil Span, g°
Use: g° = 180° - b°

Pitch Factor, k'
Use: k' = sin (g/Z) or
k' = sin [(p/2) x (coil pitch/pole pitch)] or
k' = sin [(p/2) x (S/p - 1)/S/p], using radians.
Where Z = 2 for the number of adjacent inductors between 180 electrical degrees.

S/p	Coil span, g °
	180°	168°	165°	160°	156°	150°	144°	140°	135°	132°	120°
3	1.000	-	-	-	-	-	-	-	-	-	0.866
6	1.000	-	-	-	-	0.966	-	-	-	-	0.866
9	1.000	-	-	0.985	-	-	-	0.940	-	-	0.866
12	1.000	-	0.991	-	-	0.966	-	-	0.924	-	0.866
15	1.000	0.995	-	-	0.978	-	0.951	-	-	0.914	0.866

Winding Factor, d
Use: d = k' x k

Items 18 - 26

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