Item 01. Number of poles, frequency, p, f
p = 120 x f / N
The frequency should be either 25hz or 60 hz.
Commonly used is 60 hz for modern machines.
Item 02. Peripheral Speed (fpm), v
v = pDr N / 12
Initially assume this value to be 18,000 fpm. On this basis, a reasonable diameter of the rotor, Dr will have been generated.
Item 03. Diameter of rotor, Dr
Dr = (18,000 x 12) / (Np)
This dimension limits the internal diameter of the armature D, because the air gap, d, doesn't usually exceed one (1.0) inch.
For correction later when the air gap, d have been finalized. This value should at least be a multiple of 1/8".
Item 04. Line current (full load), I
I = KVA /
x KV.
Where:
KVA is the Rated Output, and
KV is the Terminal Voltage.
Item 05. Phase connection (star or delta)
For computational design, assume that a star connection of phases is employed, thus I would also equal to the current per phase winding.
Item 06. Volts per phase, vector OEt
Vector OEt = KV /
See item 05, above.
Output of
AC Gen
kVA
| Average
Values
Specific
loading
|
50
| 450- 500
|
100
| 480- 550
|
200
| 530- 600
|
500
| 620- 700
|
1,000
| 700- 800
|
5,000
| 800- 900
|
10,000
| 900-1,000
|
Item 07. Specific Loading, q
q final = Cs x Ic / l
The following are average values of q for commercial machines:
Refer also to item 03 of General Design Considerations and Article 71, page 178. For the trial value of Specific Loading, by interpolation, use the low value within the range of the respective kVA. The final value of Specific Loading should be within the range of the low and high values so that the current density should be within the limits.
Item 08. Current in Armature Conductor, Ic
Refer to item 05.
Item 09. Armature ampere-turns per pole, (TI)a
(TI)a = (½p × D/p)(Z'Ic/pxD) = Z' Ic / 2p
(TI)a = (tq)/2.
The limit is 12,000 Ampere-turns per pole.
Where Specific Loading, q, is the final value as computed in Item No. 07, above.
Item 10. Length of air gap at center
d = 1.25 qt/B"g
This value is usually between 3/4" to 1", for machines greater than 1,000 kVA. If found later that the B"g leads to unduly high flux density at the teeth, it should be modified.
Assume for 60hz, B"gtrial = 0.585 of B"g, rounded to the nearest 100, to the respective output in the table found below.
Output
| B"g
| Output
| B"g
|
5
| 37,000
| 750
| 61,000
|
10
| 42,000
| 1,000
| 62,000
|
20
| 45,000
| 1,500
| 62,500
|
30
| 47,000
| 2,000
| 63,000
|
40
| 48,500
| 2,500
| 63,500
|
50
| 50,000
| 3,000
| 64,000
|
100
| 53,000
| 4,000
| 65,000
|
200
| 56,500
| 5,000
| 65,500
|
300
| 57,500
| 7,500
| 66,500
|
400
| 58,500
| 1,000
| 67,000
|
500
| 59,000
| Larger
| 67,500
|
Items 11 - 17
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