MIL-HDBK-1004/10
where
R=
electrolyte-to-anode resistance for a single
horizontal anode
P=
250-ohm centimeter soil resistivity
L=
5-foot anode length
K=
0.0234 factor for length to diameter (refer to
para. 6.2.1.4)
R=
(250/5) x (0.0234)
R=
1.17
b)
Minimum weight of anodes required for 15-year life (front
side):
W=
YSI
where
W
=
weight of anodes required
Y
=
15 years
S
=
1 lbs/A yr (in this case includes efficiency factor)
I
=
57.13 A
W
=
15 x 1 x 57.13 = 857 pounds
Each anode weighs 44 pounds, thus for the desired system life, the required
number of anodes is:
857/44
= 19.5 (say 20)
c)
Number of anodes required for current output (front side):
N = I/i
where
N
=
number of anodes required
I
=
current requirement (A)
i
=
output per anode (A)
N
=
57.3/1.5
N
=
38.2 (say 40)
Thus, the number of anodes will be limited by the output per anode.
d) Resistance of dc circuit. Resistance of the anodes is
negligible because the 40 anodes, each with a resistance of 1.17 ohms, will be
in parallel. Resistance of the feeder conductor (1,000 feet of HMWPE Size #4)
is 0.254 ohms (refer to Table 10). Resistance of the 1,000-foot #4 bond
header is also 0.254 ohms:
R
= 0.254 ohms
f
R
= 0.254 ohms
n
R
=R
+R
= 0.508 ohms
t
f
n
204
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