Cathodic Protection Training Course

Module 4

Equivalent circuits.

Many books on cathodic protection try to substantiate theories by showing electrical drawings of equivalent circuits.

This is fine for the parts of the cathodic protection circuits that pass through conductors that are designed for the purpose.

Cathodic Protection Network is different.... we not only draw equivalent circuits... we make them. Our equivalent circuits have to work!

Equivalent Circuit of a groundbed and three pipelines.

Equivalent Circuit of three CP test posts and a coating fault.

The drawing of equivalent circuits fails to be useful when the circuits do not function as described when actually constructed.

The problem is that the path of the electrical current passes through 'mass earth' and that cannot be accurately expressed by the
symbolism used by convention in the electrical industry.

A dry cell battery is a corrosion cell and can be incorporated into a working model of an equivalent circuit.

Corrosion cells can happen to be in parallel or in series and the equivalent circuits of these situations can be achieved
very simply using battery holders as shown.

By using a length of steel pipe and a thick copper wire, we can pruduce an equivalent circuit of several corrosion cells on a pipeline.

We then balance the battery outputs with a transformer rectifier and we have the equivalent circuit of a single cathodic protection
system applied to a single pipeline.

This is a useful aid to study cathodic protection in the field as we can now visualise the electrical balance.

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