Does anyone have any experience with using armoured cable with any surface to subsea power supplies? I see there are a few of these power supply systems kicking around now from Outland technologies, SubseaLED and Bluelink. We are looking at using something but with an armoured cable and 2 pairs. My main initial question, is whether it would be ok to use the steel armouring as the protective earth/gnd for the high voltage… the armouring would have an equivalent CSA upward of 8mm^2, but obviously less conductive than copper.
Hello Nick,
it’s a good question but did you considered also that in case of current leakage to earth, your main lift can become polarized relative to the surrounding seawater and act as anode which can accelerate corrosion of the steel?
Yes always a consideration. From what i can see all the systems i’ve looked at have current leakage monitoring for safety, so we’d have constant monitoring of any leakage current. In my experience with these cables, working in salt water, we often experience some form of leakage at the wet end terminations/connectors that isn’t detected until the signal degradation affects the towed equipment, the cables tend to hold up quite well to corrosion. This aside, what are your thoughts on using the armouring as an earth?
From what i’ve experienced with these cables over the years the corrosion affect from current leakage isn’t a big deal, leakage almost always occurs at the tow vehicle end (termination/connector breakdown) this bottom 10-20m always fatigues quicker, we keep an eye on it and chop it back when necessary.
Hi Nick,
I need to be cautious with my response since this is a public forum and the information could be easily misinterpreted by individuals without proper training. Generally speaking, the answer is “No, don’t do this.” It would be best to add another copper conductor INSIDE the armored cable rather than using the armor as a conductor.
The OTPS system and all high voltage power supply systems made by Outland adhere to stringent safety guidelines derived from our experience, military, and industry publications. Our systems are designed to be extremely conservative to maximize safety. We utilize the most reliable methods to monitor safety faults with reference to ground. For a system to become unsafe, multiple faults must occur simultaneously. A good earth ground is one crucial aspect of this safety.
That being said, hypothetically, the armor COULD be used as a ground as long as there are no corrosion issues that could limit conductivity. You would also need to rearrange our topside and bottle topology to allow for connection to the armor jacket and ensure connectivity to the armor jacket (e.g., attach a wire to the armor with a clamp and pot it). Seems like that would be a ton of work though…
Thanks for the response, all understood. If possible we’d source an Armoured cable with sufficient pairs to mimic the configuration used in the OTPS high power tether, but at the minute i’m not having much luck! i’ll keep searching. Much appreciated your feedback.
If you’re looking to adapt to a supply you already have, then having the manufacture spec the cable would be the way to go. If you already have a cable in mind, then it is possible to adapt the supply to the application, provided it’s done within the limits of the cable and you don’t compromise safety.
We’ve modified our power supplies to run on coax armored umbilicals, such as those used for higher power side scan sonar (SSS) tow fish. The advantage is that they are very strong and easily available with a winch and slipring. They work by putting power (300-1,000VDC) down a coax cable along with an RF signal. The earth connection is typically the cable armor itself. There are some challenges, and please do not plug a FathomX board into a power supply without appropriate modifications. However, it is easy enough and if you ever need a power supply just for that, please let us know.
Your quickest and simplest bet is to buy an existing system from Outland or any of us, and spec the right cable for it.
Yes essentially already have a couple of winches of our own set up with armoured cable and as you’re probably aware they are quite common in the survey industry for SSS and ROTV etc. so a good option for us.
That’s great news to hear you have modified systems before to work over coax. I’d be keen to ask you a few more questions about this and maybe get an informal quote if i can give you a rough spec of what we’re after, happy to take this off the forum if i can contact you via e-mail?
