[time-nuts] sub cables

[Jim Lux]

At 06:05 PM 4/30/2008, Didier Juges wrote:
>Interestingly, my company just received an RFQ for DC/DC converters 
>for trans-oceanic cables. Interesting specification. Among other 
>things, 2,000,000 hours MTBF (the converters are multi-redundant) 
>and, I like that part, 100% altitude tested :-) Something else you 
>might find interesting: all repeaters are daisy chained. The power 
>comes from two current limited 1A 10,000V supplies, a positive one 
>at one end, and a negative one at the other end, so that if the 
>cable is grounded accidentally in the middle (say, by a boat anchor, 
>just a guess...) all the repeaters still get power. One supply can 
>power the entire cable. Two grounds, and you can lay another cable. 
>The power return is through the earth. Don't swim near a head-end 
>cable... The capacitance of the cable is measured in Farads, and it 
>takes several hours to charge the cable at power up. Some time ago, 
>we bid on the head-end power supplies (we did not get that job). It 
>is interesting to observe that high reliability has a different 
>meaning in the under-sea cable business and in the military airborne 
>business. We do the latter. Didier KO4BB


I would think that the undersea cable and the deep space robotic 
exploration business have similar philosophies.  Long life, 
inaccessibility for repair, etc.

Jim Lux