Water ingress to subsea electrical cables is the dominant cause of electrical faults. This results in an increase in leakage current and a low insulation resistance (Low IR) alarm. Continual insulation degradation eventually leads to failure of the circuit.
Existing topside located line insulation monitors only display a single IR result for the complete subsea system. When the IR drops, the topsides monitor provides no information on the number of faults or their location. A costly subsea fault finding campaign and possibly a production disruption is required which also carries the risk of introducing new faults in previously good connections. Even if a fault can be found and fixed, the entire process must be repeated each time a new fault occurs providing no long term added value.
Distribution systems that include subsea deployed transformer modules pose an additional integrity management challenge. In these systems a topside located line insulation monitor can typically only monitor up to the primary winding of the transformer, effectively monitoring the main umbilical only. Integrity monitoring of the electrical distribution equipment attached to the secondary side of the transformer, as is now commonly specified by field operators, must be addressed by other means.
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