Compensating Current Limitation Unit
On long distance pipeline routes several pipelines are often running parallel in one pipeline corridor which is cathodically protected by one common CP-unit having individual cathode cable connections for every pipeline.
Depending on the age and quality of pipeline coating the current demand of the various pipelines differs in a wide range, which can results in an extremely high potential difference at the drain point.
This can not only lead to “Under Protection” for poor coated pipelines and “Over Protection” for well coated pipelines but also result in the circulation of uncontrolled currents between the pipelines and thereby make the cathodic protection system insufficient and can cause corrosion.
The compensating current limitation unit which facilitates the adjustment of current in each pipeline circuit, prevents the flow of uncontrolled circulating currents between pipelines and uniform potential levels, can be provided in the transformer rectifier or supplied separately depending on site conditions and purchaser’s specification.
The unit mainly consists of several current paths depending on the number of pipelines to be connected.
Each current path may consist of :
- Blocking Diode to prevent the flow of current between pipelines
- Variable Resistor to adjust the magnitude of current for each pipeline
- Surge Protection Cascade to protect the components against over voltage
- Shunts & Meters for the total and individual current measurements
- Terminals for cable connections
The enclosure for the unit can be made of sheet steel, stainless steel, cast aluminium or non metallic such as glass fibre reinforced polyester with weather proof protection up to IP 66 and suitable for pole, wall or plinth mounting.