Electrical Machine Design

Item 01. Number of poles, p
Use: p = 120 × f / N
The frequency should be either 25hz or 60 hz.
Commonly used is 60 hz for modern machines.

Item 02. Voltage per phase, E
Use: E = Vt /
Vt is the given terminal voltage. Round-off E to the nearest whole number.

Item 03 & 04. Full Load Characteristics: Power Factor, cos q , Efficiency , h
Use the Table of Performace Data on page 268-269 for respective Output: HP, number of poles: p, terminal voltage: Vt, and nearest synchronous speed: N.

Item 05. Full Load Current in Stator WInding, I_c
Use: I_c = HP × 746 / 3 × E × cos q × h .
Round-off to nearest tenth place.

Item 06. Average Air Gap Flux Density, B"g
For computational design, use the following trial values (see table)

HP	B"g	q_LO	q_HI
10	26,000	400	540
30	27,000	500	640
40	27500	530	660
50	28,000	550	680
75	28,750	600	730
100	29,000	620	750
125	29,250	650	760
150	30,000	665	775
200	32,500	675	785
250	35,000	695	800

Use: B"g_final =B"g_ave =F /la t
Where:
F = Flux per pole, item 21
la = Gross Armature Length, item 13
t = pole pitch, item 12.

Use: B"g_max = (p /2) ×B"g_ave
B"g_ave ranges from 23,000 to 38,000 lines/sq.in.
for 60-hz. modern machines
Round-off B"g to nearest 100s.

Item 07. Specific Loading, q
Use: q _trial =q_LO + ½ (q_HI - q_LO )
Use: q _final = Cs_final ×I_c / l_final
The final value of specific loading, q_final , should be within the values of the upper limit, q_HI , and the lower limit, q_LO.

Item 08. Distribution Factor, k
For induction motors, usually k = 0.96, and the pitch factor, k' = 1. Thus winding factor, d = 0.96.

Item 09. Output Factor, D²la
Use: D²la = (4.07 ×HP ×10¹¹ ) / (B"g_trial ×q_trial ×N × d × h × cos q )
Output per pole =HP /p.
Make D²la a whole number for ease of computation. The output factor should NOT be exceeded by any combination of D and la.

Item 10. Internal Stator Diameter, D
Use: D = p ×t /p
Rounded to the nearest multiple of 1/8".

Item 11. Peripheral Velocity, v
Use: v = 10 × f ×t
Should not exceed 7,000 feet per minute for modern machines at 60-hz.

Armature Design: Items 12 - 17