44 
DIRECT-CURRENT DYNAMOS AND MOTORS. 
therefore, by (19): 
550 X 3.X 10° 
ls = 3365 x 40,000 — 2/°? feet, 
and by (20): 
_ 12x 1,750 _ : 
L. = 1,200 = 17.5 inches. 
The total flux is obtained from (21), thus: 
@ — 6X 10° xX 3 X 550 
1,200 X 200 
Taking the average value of B, for multipolar dynamos 
given in Table 17, namely B, = 60,000, the required 
radial depth is found by formula (23): 
41,200,000 x ; 
| Bs = S175 x 60,000 = 6.5 inches. 
Subtracting twice this depth from the external diameter, 
the internal diameter of the given armature is found to 
be 45 — 13 = 32 inches. 
41,200,000 lines of force. 
838. Total Length of Armature Conductor.—The active 
or inductive length, J,, of the armature conductor being 
known by (19), the total length of wire on the armature 
may be obtained approximately by making due allow- 
ances for the inactive length required to join the active 
portions of the armature conductors into continuous 
turns, or convolutions. 
In a drum armature the total length of wire, /,, depends 
upon the ratio of diameter tolength of armature core and 
is given approximately, in feet, by the formula: 
tte x (14 SP) eee, (24) 
Since the total active length is more accurately obtained 
by multiplying the number of conductors by the active 
length of one conductor, formula (24) can also be written 
in the form 
te kx D:\ N : 
L= Nxix(1+ my ~7_=+) =F [La + (kx D,)], -.(25) 
