Hi,
Just to clear a couple of things up. I went out on this job, on seaeye marine’s behalf.
When i said the LIM is not reliable, i told your back to back, that, If the LIM shows a fault, there is a 100% chance a fault is on the system. But when the LIM says no fault, there may still be a fault on the system. This has been proved time and time again.
It is wise to put in place the testing procedure into your weekly or monthly checks. This will then give you some knowledge of the intergrity of the system.
I agree with a previous poster who said they have only changed a LIM out once. The LIM is sometimes blamed because no fault has been found. Because it has not been found does’nt mean its not there.
The problem you now have is, if you have tested the system as the procedure i left, then the fault is only subsea. This will be hard to find.
I do have proir knowledge of this system and the operation. I would guess that there is tether damage, as there has been a lot of tether damage in the past.
You could blank off the tether whip and tie the sub into your launch cage. Dive the sub and leave it for a while. Put tension on the tether and unplug the deck lead from the surface unit and megger the tether.
If this passes then it has to be on the sub. You have already found cables that have been cut. Inspect every cable.
Then i suppose you will have to open the e-pod and dissconnect one node at a time, dive the sub and monitor the LIM. Repeat until the LIM is Stable.
Remember the LIM is a protection device not a test instrument.
I will speak to seaeye on monday to see about meggering the system while it is in the water, then you could slowly bring the system up and monitor the insulation resistance as it rises out. I don’t see why you can’t do this but i will speak to nick to be sure.
My gut feeling is the tether, as pressure related faults are less common and from what i saw, damage is the favourite.
Im home now for a few days feel free to contact me. Your company has my details.
