UFC 3-570-06
JANUARY 31 2003
operational checkouts to ensure proper operation. Impressed current system anode
leads must have a special insulation to preclude the copper lead wire from becoming
part of the anode system. Since the power source is forcing everything connected to
the positive terminal to act as an anode (and corrode) any defect or nick in the
insulation of the anode lead wire would result in copper metal loss ending in failure of
the anode system.
Figure 2-24. Impressed Current Cathodic Protection System
(-) (+)
Rectifier
(or other DC Power Source)
Test Lead
TANK
Anode
Anode
(Cathode)
Current Flow in the Earth
Current Flow in the Earth
Metallic Anode Selected for low weight loss (Usually Graphite or HSCI)
Impressed current systems are fundamentally the same as galvanic anode
systems in their operation, except that in impressed current systems a rectifier or other
direct current power source is used to increase the potential of the electrons from the
anodes to provide the desired protective current. Thus, as shown in Figure 2-24, in
addition to an anode and a connection to the structure being protected, an impressed
current cathodic protection system uses a rectifier or other power source. A battery,
solar cell, direct current generator, or thermoelectric generator may be used as a power
source. However, nearly all impressed current cathodic protection systems use
alternating current or solar powered rectifiers as a power source.
2-7.1
Impressed Current Rectifiers. Rectifiers used for cathodic protection
commonly use an adjustable step down transformer, rectifier stacks, a shunt to measure
output current, meters to indicate output current and voltage, circuit breakers, lightning
arresters, and transformer tap connections, all in one case. The function of the rectifier
is to convert alternating current into controlled (pulsating) direct current. A typical pole
mounted rectifier for cathodic protection service is shown in Figure 2-25.
2-7.1.1
Rectifier Stacks are of two general types: selenium plates or silicon diodes.
2-42
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