how are underwater power cables serviced? and do they require regular maintenance>?

Answer 1

Depending on the situation, they are inspected by divers or manned or remote control submersables. They contain sensors related to leakage and gas pressure, etc.
If they need service, they are almost always pulled to the surface, just like long distance underwater telephone and telegraph line, buy specially designed service ships. They normally do not require a lot of service.

Answer 2

I can tell you that an underwater telephone cable is made to be very reliable and if something fails a ship actually has to go find it and pull it up. Repair the amplifier that failed and then drop the cable back down.

Sometimes they are cut by other ship anchors.

I would think that an underwater power cable would have no parts other than wire and insulation, so it would only fail if cut by an anchor. If it was a short cable, they would just lay a new one, which would be cheaper and easier than finding the broken pieces and splicing them back together. Its all a mater of cost.

Answer 3

Underwater cables are very expensive so it is better to repair a fault than to abandon the cable and lay a new one.

A signal is sent through the cable and is refleted back at the fault and the time to return is used to estimate where the fault is. The cable can the be brought to the surface and the the fault repaired.