Sections: Armature | Commutator | Questions

Armature Winding and Core

Item 1. Number of poles, p
When frequency and speed is given, use 120f ¸ N
Number of poles is usually limited to the speed of the dynamo. This is usually a multiple of 2. See guide in selecting a suitable number of poles for a preliminary design.
When frequency is not given, it is safe to use 60 Hz, to solve for the number of poles.

Frequency, f
When number of poles are assumed, use (p/2) X (N/60)
Between 30 and 60 cycles per second in ac generators.
Assume 60 Hz, the permissible limit, when not given.

Item 2. Ratio of pole arc to pole pitch, r
Usually given.
For all rotating machines: 0.6 to 0.8, With interpoles: 0.6 to 0.64.
common value 0.7.

Item 3. Specific Loading, q
When, the number of conductors, Z, are known, use: ZI_c ¸ pD.
Subject for correction when, number of conductors, Z, is finalized.
For noninterpole machines: 350 to 650,
for those with commutating poles: 400 to 1,300.
When Output is known, use the table of approximate values of specific loading for interpole dynamos.

Item 4. App. air gap flux density (open circuit), B"g
When armature length is a final value, use: F ¸ l_a x t x r
Dependent on the Output, KW, usually from 37,000 up to 67,500.
When Output is known, use the table of Approximate Values of Apparent Air-Gap Density.

Item 5. Line current (full load), I
Use the high-end voltage of the given range, this I = KW ¸ V.
Current per path not to exceed 250 to 300 Amps.

Item 6. Type of winding
Number of parallel paths: lap winding: p x plex, wave winding: 2 x plex.
Lap winding: not to exceed 250 to 300 amps per path.

Exciting current % of rated current, I_sc
Given the Output, KW, use one-step below value from the table for shunt field currents expressed as percentages of the full-load rated currents of machine.
From 0.3 to 3.0, depending on the output of the amchine.

Item 7. Armature current per circuit, I_c
Dependent on the Exciting current, use: (I/p) x (1 + % @item6).

Item 8. Output factor, r
Use l_aD² = (W/N)(6.06 x 10⁸)/(B"_gqr).
l_a, B"_g, q and r are usually assumed, thus subject for correction.

Item 9. Armature diameter, in, D
From the Output factor, or for a square pole face for interpole machines, D = pl_a/2 or when peripheral velocity is determined: D = 12v / N
Reducing the diameter, D, will increase the specific loading, q.
When the ratio of pole arc and armature length, k and the number of poles, p are known, use: D = l_apk / p r

Item 10. Peripheral velocity, fpm, v
When diameter and speed are given, use (p DN) /12
Between 3,000 and 10,000 fpm.
Assumed when speed of rotation N is not specified.

Armature Ampere-conductor per pole, ZI_c/p
Use p Dq/p.
Refer to the table for approximate values of Ampere-conductors per pole. Maximum is 25,000.

Items 11 - 18

---

Home | EMD | Sites | ABdA | Help | E-mail