What is IR and what does it do?
A subsea cable can have multiple copper conductors that carry electrical current in the form of power or communication signals, and an insulating layer which isolates the conductors from other conductors and electrical earth.
When the cable is new and the IR is high, power cables deliver the voltage and current needed by the equipment on the seabed without tripping overcurrent circuit breakers, or letting the voltage drop to a point where the Subsea Control Module (SCM) can no longer function properly.
Damaged and faulty cables will eventually allow seawater to ingress onto the conductors, causing low IR and leakage currents which can be hazardous to personnel and will eventually lead to system shutdown. The salt water also acts as an electrolyte, promoting a chemical reaction that can erode and weaken the copper conductors, which may accelerate the time taken for a fault condition to occur.
Although no insulator is ever completely perfect, cable IR – the ability to resist flow of leakage currents from the conductor into surrounding sea water, cable armour or other conductors – is vital to safe and compliant subsea operations.