R = 0.032 ohm.

(b) Find the voltage drop in riser anode feeder by

E = IR,

where I = 3.62 amperes and R = 0.032 ohm. Thus,

E = 3.62 A 0.032 ohm

E = 0.116 V.

(c) Find the voltage drop in the riser anode suspension cables for wire size No.2 AWG, 0.159 ohm

per 1000 feet rating, and estimated length 130 feet;

130 ft

0.159 ohm

R'

1000 ft

1000 ft

R = 0.02 ohm.

E = IR

where 1=3.62/2=1.81 amperes average (single current does not flow the full length of the anode string) and

R = 0.02 ohm. Thus,

E = 1.81 A x 0.02 ohm

E = 0.04 V.

(d) Find the voltage drop through riser anodes:

E = IR,

where I = 3.62 amperes and R = 2.63 ohms. Thus,

E = 3.62 A x 2.63 ohms

E = 9.52 V.

(e) Find the total voltage drop in the riser anode circuit:

ET = 0.116V + 0.04V + 9.52V

ET = 9.68 volts.

(21) Select the riser anode circuit variable resistor.

(a) Criteria for the variable resistor are the same as given for the stub anode resistor.

(b) Riser anode circuit data -- rectifier output = 80 volts, anode current = 3.62 amperes, anode

resistance = 2.63 + 0.032+0.02 = 2.68 ohms.

(c) Variable resistor rating (resistor should reduce anode current by one-half when full rectifier

voltage is applied)

r = E/I,

where E = 80 volts and I = 3.62/2 = 1.81 amperes. Thus,

R = 80 V - l.18 A

R = 44.2 ohms.

Resistor ohmic value = 44.2 ohms -2.68 ohms = 41.5 ohms.

Resistor wattage rating = (3.62 A)2 x 41.5 ohms = 543.8 W.

(d) The commercially available resistor that nearest meets the size requirements is a 750-watt, 50-

ohm, 3.87-ampere model. This rheostat is 10 inches in diameter and 3 inches deep and is fairly expensive. It