Page 154 - Applied Photovoltaics

Figure 8.3. Typical pipe potential distribution for a sunny day (curve 1), and at
night following a cloudy day (curve 2) (Tanasescqu et al, 1988, Used with kind
permission from Springer Science and Business Media).

8.5.2 Controllers

During operation, a controller is virtually essential in a CP system, to adjust the
current so as to keep the reference voltage on the metal structure constant (i.e. control
the current to overcome the varying electrochemical potential). Different types of
controllers are available.
1. To control the current, DC-to-DC conversion can be used to provide superior
protection at high efficiency.
2. Rather than using DC-to-DC conversion, the controller may simply, though
less efficiently, incorporate a rheostat to effectively control the voltage and
hence current applied to the structure.

8.5.3 Power sources

Past CP systems
In grid-connected areas, power rectifiers were used on cathodic protection devices. In
remote areas, diesel or natural gas driven motor generators (or even thermoelectric
generators) have been used. However, fuel and maintenance costs were a severe
problem, particularly for small loads, while line extensions to connect to the main
grid were generally too expensive.

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