In today’s economic and regulatory environment, it’s more important than ever to keep your subsea cables and terminations operating at the highest level. This 5-step plan for marine cable inspection, along with tips for general handling, will help you save on downtime and the cost of replacing gear before the end of its useful life:
- Step 1: Visual Inspection
- Step 2: Electrical Conductor Resistance Testing
- Step 3: Insulation Resistance Testing
In this blog, we will discuss how to test for problems with your cable’s electrical insulation, a frequent cause of subsea cable failure.
Insulation resistance testing
Marine cables should be inspected regularly as part of the operating procedure to ensure your equipment remains in good condition. A visual inspection of the cable can indicate problems with the electrical isolation, but the damage to insulation is not always visible. Moisture in the cable or tight bending or kinking of the cable during handling could weaken the insulation and cause electric current to leak out of the wires. To add to the problem, the insulation may be damaged in more than one place.
Insulation Resistance (I.R.) testing on a regular base is key to maintaining the condition of your cable, as low electrical isolation is one of the main reasons cables fail.
To prevent contact with a live conductor, before any type of testing, inspection, cleaning, connection, or disconnection, the connectors must be de-energized so that there’s no energy flowing through the system. You also need to ensure all connectors at both ends of the cable are clean and dry and that the connectors at the opposite end of the cable are disconnected and the cap replaced.
Using a counter connector is preferred. Otherwise, plug test clips into the cable connector. Ensure that they’re making contact and use a calibrated insulation resistance meter. The meter sends a test voltage down each wire to see if there’s any leakage current.
Proper isolation testing is done by testing each conductor against the complete cable, termination, and deck-end connectors. Basically, this means that the cable, termination, and deck end connectors are shorted to each other and the conductor to be measured is separated out for measurement. Once the value is recorded, the conductor is put back, the next conductor is taken out and tested, and so on until the complete cable has been measured.
The result for each wire is noted on a cable log sheet, which also records the hours of use, faults, maintenance, and inspections. Compare your results to the last results taken and to the manufacturer’s ratings. Electrical insulation resistance and conduction resistance testing together will give you a good indication of the health of the cable core. A digital optical fiber cable will need fiber optic testing as well.
You can trust the experts at DeRegt for all your marine cable needs, beginning with the early stages of design and development and continuing throughout their operational lifetimes. Together we will ensure your equipment works as designed, saving you time and money in the long run.
Practical Guide to extend Cable Lifetime
For a fresh look at how to handle and maintain marine cables in the field to prevent damage to the insulation, download the DeRegt Guide to Seismic Cable Handling.
