Unmanned Offshore Platform Power Supply

[JLuc]

Hi all,

do you have any suggestion for the power supply of an unmanned offshore platform:

distance from shore: 100km
load: 50kw

How about using DC with a rectifer/inverter combination?

Thanks !

 

[rcw retired EE]

With only 60 kW load, the micro turbine & UPS assembly with a small wind turbine providing some extra battery charging capability may be a viable answer, despite my making fun of it. The political benefits and tax exemptions may help with the added costs. The technical challenge will be to put a complicated, sophisticated system together with reasonable reliability in a remote area.

How are the maintenance costs on the micro turbines? Do they provide an advantage over standard diesel piston units because they have fewer moving parts? There was a lot of press on them a few years ago.

 

[MikeHalloran]

The micro turbine mfgr claims low maintenance costs, because of alleged simplicity.

The air compressor for the bearings adds some complexity.

The battery bank and high power four quadrant inverter add more complexity.

You may have noticed that microturbines are not, e.g., arrayed so as to cover every bit of available land in the USA.



Mike Halloran
Pembroke Pines, FL, USA

 

[catserveng]

Several years ago I worked on a project for some offshore environmental monitoring instrument platforms. PV was not a cost effective option at the time, the maximum load was 45 ekW, but there was a fairly large change in demand depending on what was running. The systems installed ended up having a 25 ekW diesel unit, a 45 ekW diesel unit, and four small wind generators with a total capacity of about 22-24 ekW. There was a large battery bank that could be charged by the wind gens or a set of chargers (rectifiers and alternators).

The platforms had a scheduled visit every 30 days, but the design required unattended operation for up to 90 days, in case someone could not get to the platform because of weather or sea conditions.

We installed external sumps with bypass filtration, and a rather elaborate fuel supply system. We sized everything for quarterly services, and the engines we selected had an average 12,000 between major service.

We had to develop a load management system because of the type of sampling the platforms did, they started and ran some fairly large pumps periodically.

Before you make a decision on what type of power source you're going to use I'd suggest you'd understand the types of loads and load profiles you're going to deal with, how often between visits, type of monitoring and emergency response the system will require, and since it's offshore, what regulatory requirements do you face?

We provided the generators, control and fuel module, the shipyard in Japan assembled the platforms and they were positioned offshore, I spent about 8 weeks getting the first one ironed out, the last one I spent 4 days on.

The control system was based on three Allen Bradley SLC500 plc platforms, and redundent HMI platforms using Rockwell's RSView32, generator controls were Woodward and Basler based.
The platform sampling control system was controlled by a Toshiba PLC, all the interface was digital, a lot of wiring but we had a good working relationship with the owners controls vendor and it was a solid system. The platform transmitted data twice a day and had redundent tape backups.

I made a visit to two of the platforms two years later, at the expiration of the system warranty, for an inspection by the owner and a marine safety agency. There were no reported operational problems except for an oil leak on one unit contained by the secondary containment and the unit shutdown by the control system. The small units had about 6500 hours, the large units had about 4000. We determined the engines would likely go the recommended overhaul interval of 12,000 hours based on the inspection, oil sample reports, and fuel and oil consumption records. Two of the wind generators required bearing replacements, and some of the batteries did not test well and were replaced. In general the end user felt it was a success. I don't know if the platforms are still operating.

As I remember the overall power system price, including genertor units, power system module, battery module, wind generators, and monitoring and control system was about $350,000 in 1999.

Hope that helps.

 

[itsmoked]

I have a hard time thinking of what monitoring you would need 50kW for. A lot of my experience has been attributed to remote sensing while achieving low average power consumption. 1W avg can do a whole lot of sensing. With a 100W I can't think what couldn't be sensed. And 50kW?!?

As you get these larger drains I bet the wastage sky rockets due to the ensuing mentality, "we can add this and that too". Waste like using a PLC. Gawh!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

"Waste like using a PLC. Gawh!"

Standard interface, readily available spares, (I nearly said cheap, but someone mentioned A-B ), maintainable by field technicians...


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[MikeHalloran]

The mentality of offshore is not so much "we can add this and that", as it is, "Wal-Mart is not ten minutes, or even a day, away."

Beyond the actual sensors, some loads are unavoidable:
Navigation lights.
Redundant navigation lights.
Anticondensation heaters for idle generator.
Anticondensation heaters for sensor electronics.
Floodlights for boarding.
Signal recording equipment.
Satcom equipment.

Some loads may not be unavoidable, but would not be surprising:
Air conditioning for sensor electronics.
Surveillance cameras and:
Remote positioners.
Washer/Wipers.
Surveillance recording equipment, armored.
Satcom equipment.

Some loads would only be needed during maintenance, but are best left aboard:
Hoist.
Seawater wash pump.
Desalination system for fresh water wash and/or survival.




Mike Halloran
Pembroke Pines, FL, USA

 

[jomamh]

Clearly the most economical answer in this case is the local generation in any of the several possible ways. Only as a theoretical exercise, we can try an a.c. solution with underwater cable. At 50Hz it happens approximately as follows:

1) 10kV, 3x120mm2 Cu, 100kW + 40kvar load, 2 reactors of 560kvar at the beginning and the end of the line, du=2.5%, DP=25kW, Scc=5MVA

2) 30kV, 3x120mm2 Cu, 1MW + 0.4Mvar load, 2 reactors of 2.6Mvar at the beginning and the end of the line, du=2.7%, DP=90kW, Scc=42MVA

Data for cables are taken from underground types. It is only an approximation.

JMM (Spain)

 

[JLuc]

Thanks a lot guys for all your inputs !

JL

 

[MikeHalloran]

Because of the disparity between peak demand and minimum demand, a hybrid system actually can make sense.
E.g.
2 x xxkW gensets
plus
nn kWh of batteries + inverter + charger
...
where the battery bank and charger would be sized to keep either of the gensets very busy charging, for a relatively short time at relatively infrequent intervals, and the gensets would be sized so that either one can run everything continuously, and the inverter would be sized to run just the steady loads, and to start a generator when it couldn't keep up.







Mike Halloran
Pembroke Pines, FL, USA

 

[catserveng]

You know, a term like "offshore platform" can bring to mind anything from a small instrument platform operated by a research or regulatory agency, to a really big oil and gas production platform. Is it a jack-up, floater, flip, or what?

Also depending on where someone wants to put it can bring all kinds of issues up, as pointed out, redundent running lights, security and intrusion prevention systems, lighting and housekeeping loads like ballast and bilge pumps.

As for the PLC's, well it was the best solution I could come up with based on customer requirements, and frankly in that time frame I did a lot of projects with AB SLC's and Woodward/Basler controls and I never had issues with the hardware, I could respond to customer demands for customization or site changes, and the support in my area at the time for the AB products was excellent. So with all that the difference in hardware price really wasn't all that great, of course now days I'm not the fan I was of AB, but isn't that evolution?

Mike, your list is near dead on, except we also had two sets of collision avoidance radars with automated messaging and the anchor handling system. These were floaters with four point anchoring. These platforms were actually pretty interesting, as they sampled water from various depths, looked for oil slicks and floating debris, and also did some air quality monitoring.

Maybe the OP can provide some details on the platform, like what it's doing, types of loads, expected load profiles, etc?

 

[itsmoked]

Yeah Mike thanks for the list.

I was envisioning something like the buoys around here. Solar panels and batteries add a semi-custom computer and the needed sensors. Oh well.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Genex]

Hi Folks
I am new to the forum, but saw your question re unmanned platform power generation.

If you go to

http://www.genexdesign.com

you will see some information there which might be of help.

we deal with this type of equipment based on a high specification enclosures designed for offshore environments.

the diesel drive units are modified to accommodate extended sumps to lengthen standard service intervals to 2000 hours.

Machines are usually configured in dual or triple configuration to provide back up, and allow cycling of the duty unit to further extend platform attendance periods.

Microturbines are a good solution with advertised service intervals of up to 8000 hours, however they require very specfic operating conditions, mainly good stable gas supply, with set gas pressures.

Solar Sytems are effective but require large footprint areas to produce low outputs.

I am not too experienced in wind power systems, but again at 60kVA thats going to be a large footprint area.

The Ormat System mentioned in another reply is very efficient, but only prodcues low power output, I think they have just released an upgraded unit from 500W to 2000W, so you would require multiple arrays.

The footprint of a typical 60kVA Diesel set in a High IP rated enclosure with extended sump to 2000 hours service intervals would be approximately 3.2 mtrs long, by 2 metres wide, by 2.4 mtrs high.

Catserveng,s comments on the diesel system with Allen Bradley PLC etc was correct in my view, and Gen Ex can provide such a system.

Hope this helps.