MIL-HDBK-1004/10
where
W
=
weight of anodes required
Y
=
15 years
S
=
1 lbs/A yr (in this case includes efficiency factor)
I
=
8.3 A
W
=
15 x 1 x 8.3 = 124.5 pounds
Each anode weighs 44 pounds, thus for the desired system life, the required
number of anodes is:
124.5/44 = 2.8 (say 3)
h)
Number of anodes required for current output (shore side):
N = I/i
where
N
=
number of anodes required
I
=
current requirement (A)
i
=
output per anode (A
N
=
8.3/1.5
N
=
5.5 (say 6)
Thus, the number of anodes will be limited by the output per anode.
i)
Resistance of dc circuit:
Resistance of six anodes is:
1/R = 1/1.86 + 1/1.86 + 1/1.86 + 1/1.86 + 1/1.86 + 1/1.86
R = 0.310 ohms
Resistance of feeder conductor 1,000 feet of HMWPE Size #4 (0.254 ohms per M
feet) (refer to Table 10):
R = 0.254
Total resistance = 0.254 + 0.310 = 0.564 ohms.
j)
Sizing rectifier (shore side):
Requirements:
dc current - 8.3 A
Anode circuit resistance - 0.564 ohms
dc voltage = IR = 8.3 x 0.564 = 4.68 V
A standard rectifier in this range has an output of 12 A at 6 V.
Typical
installation of this system is shown in Figure 114.
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