subsea cable : ground fault problem

[PAP]

Hi all,
Not sure that anybody experienced subsea umbilical cable ground fault problem?
It is 1 phase LV cable (service Vmax 600Vac) and monitored with Bender IRDH375 and relay said low insulation value (600kOhm for trip setting).
From theory with ungrounded system, it should be able to power up the unit by bypass such insulation protection device. Let say this is first fault then it should be no problem to keep it run with 1 side grounded in the water.
In case of both side grounded so the upstream CB will trip out due to high current. However, I'm not sure that are there any requirements that is not allow to do so, or any possibility to destroy supply or load equipment?

Furthermore, anybody may suggest the possibility that we'll apply insulation monitoring relay (IRDH375) to check the cable connected to communication equipment e.g. electronic module or modem in subsea (working voltage 12Vdc).Will source voltage from Bender relay harm to those devices?

Thank for your helps

 

[7anoter4]

The cable resistance may be compared with the calculated according IEC 60502-1 ch.17.1.2 Calculations.
For instance for XLPE insulation at 90oC the Ki=>3.67 Mohm.km
Let’s take 240 sqr.mm conductor dia 19 mm ins dia=2.2*2.1+19=24 mm 620 m length.
ki=length[cm]*R[ohm]/10^11/log(D/d)
D=24; d=19; length=620*100=6.2*10^4 cm; R=600*1000=6*10^5 ohm
ki=6.2*10^4*6*10^5/10^11/log(24/19)=3.67
However, in my opinion, the insulation resistance after installation -and mainly-after a long time in operation- could be less but still good [in my opinion 400 kOhm could be still good.]
If your instruments comply or not with the voltage supplied by the relay, In my opinion, you have to contact Bender. See-for instance:

http://bender.org/Product_PDF/IRDH375.pdf