0103im.jpg)
ETL 1110-9-10(FR)
5 Jan 91
b)
Summarize each circuit's resistance,
current
requirement and voltage requirement:
Circuit
Current Resistance
Voltage Required
(amp)
(ohm)
(V)
Main anodes
17.7
1.46
25.8
Stub anodes
1.3
21.16
27.5
Riser anodes
14.5
1.28
18.6
Total current
requirement
33.5
c)
Determine the rectifier voltage (VREC) based on
the largest circuit voltage requirement of 27.5
V, because voltage requirement varies for all
three circuits. With a 120 percent safety factor
as in equation 1-17, the rectifier voltage is
calculated:
27.5 x (120%) = 33 V
Total current required = 33.5 amp.
c.
Select rectifier
1)
Rectifier capacity.
A commercially available rectifier having a rated
output of 40 V, 42 amp is selected.
Because of the different circuit resistances, separate
control of each circuit is required.
This is best
handled by a rectifier having three separate output
circuits.
2)
Automatic potential control
To prevent over or under protection as the water level
varies, automatic potential control is specified. The
tank and riser-to-water potentials are maintained by
the controller through permanent copper-copper sulfate
reference electrodes suspended within the bowl and
riser. The reference electrodes should have a life of
at least 15 years.
The automatic controller is located in the rectifier
unit. The controller must be capable of sensing the
potential accurately and free of IR (voltage) drop
error.
The control does this by turning off the
101
Previous Page
