Onb DC

JAN-FREDRIK HANSEN, Think of a Mac from

The newest power and

are designs that are cl ing element and create onboard DC grid for el power and propulsion throughout the vessel thereby eliminating the converter transformers DC components and s lectivity and equipmen tion up to 20 MW, and ABBs onboard DC grid and reduces the electr

n designing the n looked at the enti chain of energy co rine vessels and id using DC distribution r ditional AC system.

Onboard DC Grid
28

Two longstanding and have been carried ove tional AC distribution s framework of the onbo losophy: Equipment sh case of failures and p shall be ensured in suc operation is maintaine failure.

The newest design for marine power and propulsion systems

JAN FREDRIK HANSEN, JOHN OLAV LINDTJRN, TOR-ARNE MYKLEBUST, KLAUS VNSK Think of a Mac from Apple, a Le Corbusier chair, a Frank Lloyd Wright house. All are designs that are clean, elegant, streamlined. All are also designs that took an existing element and created something innovative. ABB has done just that with its Onboard DC Grid for electric power distribution, creating the most flexible marine power and propulsion system to date. The system merges the various DC links throughout the vessel and distributes power through a single 1,000 V DC circuit, thereby eliminating

the need for main AC switchboards, distributed rectifiers and converter transformers. The Onboard DC Grid combines the best of both AC and DC components and systems, is fully compliant with rules and regulations for selectivity and equipment protection, can be used for any electrical marine application up to 20 MW, and operates at a nominal voltage of 1,000 V DC. The best part: ABBs Onboard DC Grid increases a vessels energy efficiency by up to 20 percent and reduces the electrical equipment footprint and weight by up to 30 percent.

n designing the new system, ABB looked at the entire power delivery chain of energy conversions on marine vessels and identified a case for using DC distribution rather than the traditional AC system. Two longstanding and crucial principles have been carried over from the traditional AC distribution system to form the framework of the Onboard DC Grid philosophy: equipment shall be protected in case of failures and proper selectivity1 shall be ensured in such a way that safe operation is maintained after any single failure. Advantages of DC distribution in certain cases include lower overall losses and fewer problems with 1a Platform supply vessel with onboard DC grid harmonic distortion. Yet historically there have been challenges with DC distribution, primarily revolving around how full selectivity and equipment protection can be achieved in ways that are similar to AC distribution. AC currents are by nature simpler to interrupt because of their natural zero crossing every half cycle. DC circuit breakers exist but are more complex, larger and more expensive than comparable AC circuit breakers. ABB overcame these challenges by breaking with the classic protection philosophy, where selectivity is achieved through an arrangement of coordinated circuit breakers, and instead capitalizing on the opportunities afforded by power electronic components in the Onboard DC Grid system. Power distribution and configurations In traditional electrical propulsion systems, variable frequency drives typically account for more than 80 percent of the installed power. At its simplest level, the Onboard DC Grid concept is a reworked and distributed multidrive system where distributed rectifiers are eliminated (Figure 1).

1a Platform supply vessel witn Onboard DC Grid 1a Platform supply vessel with onboard DC grid

1b AC

1b AC AC to to DC DC transformation transformation ofof aa generic electric propulsion system 1b generic electric propulsion system

The new syst merges the v DC links arou the vessel an distributes po through a sin 1,000V CD c

The new system merges the The new system various DC links around the merges the various DC links around vessel and distributes powers the vessel and through a single 1,000 V DC distributes power circuit. The new system merges the various DCthrough links around a single the vessel and distributes power through a single CD circuit. 1,000V
1,000 V DC circuit, thereby eliminating the need for main AC switchboards, distributed rectifiers and ABB overcame these challenges by converter transformers (Figure 2). All electric power breaking with the classic protection phigenerated is fed either directly or via alosophy rectifierwhere into a selectivity is achieved common DC bus that distributes the electrical energy through an arrangement of coordinated

ABB overcame these ch breaking with the classic p losophy where selectivity through an arrangement o rectly or via a rectifier into abreakers commonand DC instea circuit bus that distributes on the the electrical energy afford opportunities to the onboard consumers. main electronicEach components in consumer is then fed a system. separate inDCby grid verter unit. When an AC distribution network is still needed, for example with aand co Power distribution fed using electrical island 230V hotel load, 2 itInis traditional pro converters, developed by variable ABB tofrequency feed tems, d clean power to these more sensitive account for more cirthan 80 p cuits. Additional converters for energy installed power. At its si storage in the form the of batteries orDC super onboard grid con capacitors for leveling out power variaworked and distributed m tions can be added to the where DC grid. tem distributed r

Title picture Marine offshore support vessels are excellent candidates for the Onboard DC Grid Power distribution and configurations

circuit breakers and instead capitalizing on the opportunities afforded by power electronic components in the onboard DC grid system.

eliminated 1a, 1b. The system has been remodeled in such a way that most of the well-proven prodThe new system merges th ucts used in todays electric ships such links around the vessel an as AC generators, inverter power modules, through aand single 1, AC motors can still be used. cuit, thereby eliminating t

30 ABB review 2|12 In traditional electrical propulsion systems, variable frequency drives typically account for more than 80 percent of the installed power. At its simplest level,

main AC switchboards, dis The onboard DC grid can be converter configuredtransfo fiers and in several different ways. With electric a centralgenerated power is ized approach all converter modules are located in one or multiple lineups within the same space that the main AC switchboards used to occupy 3. With a distributed approach, the various

AC toDC DCtransformation transformation ofof a generic electric propulsion system 2 2AC to a generic electric propulsion system
690 Vac @ 60 Hz Switchboard G AC Concept for an island network 1000 Vdc BUS DUCT DC Concept for an island network

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the vessel functionality and value. Protection and safety With the main AC switchboard, AC circuit breakers and protection relays omitted from the new design, a new protection philosophy that fulfills regulatory requirements for selectivity and equipment protection is essential. Proper protection of the onboard DC grid is achieved through a combination of fuses, isolating switches and controlled turn-off of semiconductor power devices. Since all energy-producing components have controllable switching devices, the fault current can be interrupted much faster than would be possible with traditional circuit breakers with associated protection relays. In case of a serious fault in a module, fuses are used to protect and isolate inverter modules just as with current LV frequency converters. In addition, input circuits separate the inverter modules from the main DC bus and afford full control of reverse power, both in fault and normal conditions (as for example in propeller braking mode). This means that faults on a single consumer will not affect other consumers on the main DC distribution system. In the event of severe faults on the distributed DC bus, the system is protected with generators by means of a controllable thyristor rectifier, which also doubles as a protection device for the generator. Isolator switches are installed in each circuit branch in order to automatically isolate faulty sections from the healthy system.

Proper protection of the Onboard DC Grid is achieved through a combination of fuses, isolating switches and controlled turn-off semiconductor power devices.

In close cooperation with Det Norske to the onboard consumers. Each main consumer Veritas, a global organization that prois then fed by a separate inverter unit. When an AC vides classification and risk assessment distribution is still needed, for example with services to the maritime industry, network ABB has ensured that the DC grid a onboard 230 V hotel load, it is fed using island converters, system philosophy meets or exceeds developed by the ABB to feed clean power to these more demands of current rules and regulasensitive circuits. Additional converters for energy tions. Fault currents can be controlled in storage in the of batteries or super capacitors as little as 10 to 20ms. This results in form a for leveling power variations can be added to the drastic reduction in the DC gridsout fault energy levels as compared with traditionDC Grid. al AC protection circuits where fault durations can reach up to 1s. This low-enThe system has been remodeled in such a way that ergy fault protection scheme, combined most of thegenwell-proven products used in todays with the new flexibility in designing erator parameters, allows the ships onboardsuch as AC generators, inverter electric DC grid system to be used for and installed modules AC motors can still be used. power up to 20MW.

Proper protection of the onboard DC grid is achieved through a combination of fuses, isolating switches and controlled turn-off semiconductor power devices.

Thespace Onboard DC Grid can be configured in several Efficiency with fuel and ways. With a centralized approach all The DC grid concept different utilizes well-proven AC generators and motors, but modules allows converter are located in one or multiple for increased efficiency because the syslineups within the same space that the main AC tem is no longer locked to a specific freswitchboards used to occupy (Figure 3). quency (usually 60Hz on ships), even though any 60Hz power source may still be used. The new freedom controlling approach, the various converters With of a distributed each power consumer independently can be placed where it suits the vessel operation or opens up numerous ways of optimizing design best (Figure 4). The AC generators can have fuel consumption. cabinets. As a result of the novel approach to protecWhen operating marine combustion engines at constant speed, con- of components that, by law, must be tion, the the fuel volume sumption is lowest at a very small operinstalled in the main switchboard room is drastically ating window, typically around 85 percent reduced. This affords the vessel designer a new level of rated load. With the introduction of of freedom in designing the electrical power system variable-speed operation of the engine, this window of optimal efficiency can be around the vessel function, increasing the vessel extended as far downfunctionality as 50 percent,and de- value. pending on the engine 5. If the engine Protection and safety grid 31 With the main AC switchboard, AC Onboard circuit DC breakers and protection relays omitted from the new design, either integrated or stand-alone rectifiers installed in

3 3 Onboard Onboard DC DC grid; grid; multidrive multidrive approach approach

3 Onboard DC Grid, multidrive approach

4 4 Onboard Onboard DC DC grid; grid; distributed distributed approach approach

4 Onboard DC Grid, distributed approach

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AC ACBus Bus

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a new protection philosophy that fulfills regulatory requirements for selectivity and equipment protection is essential. Proper protection of the Onboard DC Grid is achieved through a combination of fuses, isolating switches and controlled turn-off of semiconductor power devices. Since all energy-producing components have controllable switching devices, the fault current can be interrupted much faster than would be possible with traditional circuit breakers and their associated protection relays.

several diesel diesel generators in in parallel parallel due due frequency (usually several 60 Hz on generators ships), even though is operated operated at loads loads below below this, this, the enen- source to to redundancy redundancy considerations. considerations. This This any 60 Hzthe power may still be used. The new In case of a serious fault in a module,is fuses are at used gine gine efficiency efficiency remains remains significantly significantly highhigh- means means that that the the connected connected diesel diesel engines engines freedom of controlling each power consumer indeto protect and isolate inverter modules just as with er er than than that that of of the the traditional traditional fixed-speed fixed-speed spend spend most most of of their their running running hours hours at at relrelcurrent LV frequency converters. In addition, input pendently opens up numerous ways of optimizing equivalent. equivalent. The The end end result result is is that that a a typitypi- atively atively low low loads, loads, where where fuel fuel efficiency efficiency is is fuel consumption. circuits separate the inverter modules from the main cal cal offshore offshore support support vessel vessel can can achieve achieve significantly significantly lower lower at, at, eg, eg, 85 85 to to 90 90 perperDC bus and afford full control of reverse power, both 6. 6. fuel fuel savings savings of of up up to to 20 20 percent percent cent cent load. load. in fault and normal conditions (as, for example, in When operating marine combustion engines at By By eliminating eliminating bulky converter transformtransformDP DPfuel is is when when the the propellers propellers (thrusters (thrusters or constant speed, the consumption is lowest inor propeller braking mode). This means that faults bulky on converter ers ers and and main main switchboards switchboards previously previously main main propulsion propulsion or or both) both) are are used used to to stay stay a single consumer will not affect other consumers a very small operating window, typically around 85 needed needed with with the the traditional traditional AC AC system, system, at at a a given given geographical geographical position position (+/(+/- a a percent of rated With the introduction of varion the main DC distribution system.the In the event ofgrid the onboard onboard DC DC grid also also reduces reduces the the load. few few meters) meters) and and heading heading (to (to minimize minimize the the able-speed operation of the engine, this window of severe faults on the distributed DC bus, the system footprint footprint of of the the electrical electrical equipment equipment impact impact of of wind, wind, current current and and wave wave action action 7. 7. This This creates creates more more space space and and can used used on on the the vessel hull). hull).as This This is sometimes sometimes optimal efficiency be vessel extended faris down as is protected with generators by means of a controlprovides greater greater flexibility in in the the positionpositionused used for for work work orders orders close close to to a a drill drill ship ship 5 percent, depending on the engine (Figure 5). If the lable thyristor rectifier, which also provides doubles as flexibility a ing ing of of system system components components in in the the vessel. vessel. or or when performing performing operations operations like like loadloadengine is operated atwhen loads below this, the engine protection device for the generator. Isolator switches In In addition, addition, the the system system enables enables simpler simpler ing/unloading ing/unloading close close to to an an installation installation (eg, (eg, are installed in each circuit branch in order to isolate efficiency remains significantly higher than that of the integration integration of of supplementary supplementary DC DC energy energy a a drillship drillship or or platform). platform). In In severe severe DP DP opoptraditional fixed-speed equivalent. The end in result is faulty sections automatically from the sources healthy system. sources such such as as solar solar panels, panels, fuel fuel cells, cells, erations erations for for example, example, in extreme extreme a typical offshore support vessel can achieve fuel or or batteries batteries into into the the that ships ships DC DC electric electric weather weather or or in in critical critical operations operations where where systems, systems, creating creating scope for for further further fuel loss of of propulsion propulsion power power could could cause cause savings of up fuel to 20 loss percent (Figure 6). In close cooperation with Det Norske Veritas, a scope savings. savings. significant significant damage damage to to the the vessel, vessel, other other global organization that provides classification and installations, installations, or or personnel personnel the the electrielectririsk assessment services to the maritime industry, By eliminating the bulky converter transformers and The The reduced reduced weight weight and and footprint footprint of of the the cal cal plant plant is is split split into into a a minimum minimum of of two two main switchboards previously needed with the a tradiABB has ensured that the Onboard DC Grid electrical system installed installed electrical equipment equipment will will vary vary separate separate sections sections to to achieve achieve a higher higher tional AC applicasystem, Onboard DC Grid also reduces philosophy meets or exceeds the demands of ship depending depending on on the the ship type type and and applica- the level level of of redundancy redundancy in in the the power power system. system. tion. tion. One One comparison comparison using using a a distributed distributed By doing doing so, so, the the vessel vessel used can can maintain maintain its footprint of the By electrical equipment (Figureits current rules and regulations. Fault currents can be the variant variant of the the onboard onboard DC grid grid system system more position position even even if if one one side side of of the the power power 7).DC This creates space and provides greater controlled in as little as 10 ms to 20 ms, of resulting instead instead of of the the traditional traditional AC AC system system for for a a plant plant fails. fails. However, However, running running in in split split flexibility in the positioning of system components in in a drastic reduction in the DC Grids fault energy levels when compared with traditional AC protection the vessel. In addition, the system enables simpler
32 32 ABB ABB review review 2|12 2|12

the the weight weight of of the the electric electric system system compocircuits where fault durations can reach up to 1 s.compoThis The The new new concept concept nents nents by by 25 25 percent percent from from 115 115 to to 86 86 tons. tons. low-energy fault protection scheme, combined with helps helps solve solve the the the new flexibility in designing generator parameters, Dynamic Dynamic positioning positioning vessels vessels traditional traditional allows fuel fuelthe Onboard DC Grid system to be usedof for The The variable variable power power consumption consumption of ananinstalled power up to 20 MW. chor chor handling handling vessels vessels and and offshore offshore supsupefficiency efficiency challenge challenge port port vessels vessels make make them them very very good good cancanfaced faced in in dynamic dynamic didates didates for for the the onboard onboard DC DC grid grid Efficiency with fuel and space 8. 8. The The new new concept concept helps helps system system The DC Grid concept utilizes well-proven AC generapositioning positioning operaopera- solve solve the the traditional traditional fuel fuel efficiency efficiency chalchaltors and motors, but allows for increased efficiency lenge lenge faced faced in in dynamic dynamic positioning positioning (DP) (DP) tion. tion. because the system is no longer locked to aneed specific operation. operation. DP DP vessels vessels often often need to to run run

platform platform supply supply vessel vessel (PSV), (PSV), reduced reduced

5 Engine fuel tests at variable speed (color scheme indicates such as solar panels, fuel cells or batteries specific fuel oil consumption (8FOC) in g/kWh. University 5 Engine fuel tests at variable speed (color scheme indicates speci6 Engine fuel characteristics at variable speed (color scheme test engine
fic fuel oil consumption (SFOC) in g/kWh. University test engine.
100 90 80 Torque (%) 70 60 202 50 40 30 820 840 860 880 900 920 940 960 980 1000 (rpm) Operation with fixed frequency (Traditional AC) 200 198 196 Operation with variable frequency (Onboard DC Grid) 212 210 208 206 204 SFOC (g/kWh)

integration of supplementary DC energy sources into the ships DC fuel electric systems, creating indicates specific oil consumption (SFOC) in g/kWh scope for further fuel savings. 270
Fixed Speed SFOC Variable Speed (full range) SFOC The reduced weight and footprint of the installed Variable Speed (limited range) 230 electrical equipment will vary depending on the ship type and application. One comparison using a 210 distributed variant of the Onboard DC Grid system 190 instead of the traditional AC system for a platform 170 supply vessel (PSV) reduced the weight of the electric system components by 25 percent from 115 to 86 150 0 20 40 60 80 100 120 metric tons. 250 Load (%MCR)

Test results are of fuel consumption as a function of applied torque Further analysis has been done, in cooperation with an independent Testand results area of fuel consumption as aUniversity. function Results of applied RPM for small test engine at Helsinki showtorque engine manufacturer, on a medium speed engine range typically used andthat RPM for a small test engine at Helsinki University. Results show it is possible to run this type of engine with the lowest possible in OSV vessel powerplants. thatfuel it isconsumtion possible to run this type of engine with the lowest possible at least down to 50 percent loading.

es speciengine.

212 210 208 206 204 202 200

SFOC (g/kWh)

Dynamic positioning vessels The variable power consumption of anchor handling fuel comsumtion at least down to 50 percent leading. vessels and offshore support vessels make them very good candidates for the Onboard DC Grid system 7 Benefits of the onboard DC grid 8 New order (Figure 8). The new concept helps solve the traditional 6 6 Engine fuelcharacteristics characteristics at variable (color scheme Engine fuel at variable speedspeed (color scheme fuel efficiency challenge faced in dynamic positioning More functional vessel layout through ABB will equip a newbuild platform support indicates specific fuel oil oil consumption consumption (SFOC) in g/kWh indicates specific fuel (SFOC) in g/kWh (DP) operations. DP vessels often need to run several more flexible placement of electrical vessel (PSV), owned by Myklebusthaug Macomponents nagement and located at the Klevan shipyard 270 diesel generators in parallel due to redundancy in Ulsteinvik, Norway, with a full onboard DC Reduced maintenance of engines by Fixed Speed SFOC considerations. This means that the connected diesel more efficient operation grid system, including all power, propulsion 250 Variable Speed (full range) SFOC and automation systems. Improved dynamic response and engines spend most of their running hours at relaJan-Fredrik Hansen Variable Speed (limited range) maneuverability 230 John Olav Lindtjrn, low loads, where fuel efficiency is significantly The 93m long, 4,800gt type MTtively 6015 PSV, Increased space for payload through lower ABB Process Automation, Marine Systems a multipurpose oil field supply and constelectrical footprint and more flexible lower than atBillingstad, the optimal load, which is typically at 85 210placement of electrical components Norway ruction vessel designed by the Norwegian company Marin Teknikk, is due to for delivery in jan-fredrik.hansen@no.abb.com 90 percent load. A system platform that allows plug and
190play retrofitting possibilities to adapt

the first quarter of 2013. The vessel has five variable-speed diesel generators, four rated

john.o.lindtjorn@no.abb.com

DP is when the propellers (thrusters or main propulTor-Arne Myklebust 198 main propulsion units and three additional ABB Process Automation, Marine sion or both) are used to stay at aSystems given position (+/- a thrusters for DP operation. 196 150 Ulsteinvik, Norway 0 20 40 60 80 100 120 few meters) tor-arne.myklebust@no.abb.com and heading (to minimize the impact of 00 Load (%MCR) wind, current and wave action on the vessel hull). It Klaus Vanska que Further analysis has been done, in cooperation with an independent is sometimes used for work orders close to a drillFurther analysis has been done, in cooperation with an independent how engine manufacturer, on a medium speed engine range typically used mode generally does utilize the full ABB Processs Automation, Marine and Cranes engine manufacturer, on a not medium speed engine range typically ship or when performing operations like loading/ ible in benefits OSV vessel powerplants. electric propulsion because Helsinki, Finland used in OSV of vessel powerplants. unloading close to an installation (eg, a drillship or total optimization of running engines is klaus.vanska@fi.abb.com not possible. Fuel efficiency has thereplatform). In severe DP operations for example, in fore often been sacrificed in favor of Footnotes extreme weather or inofcritical 1 In the event a fault on a operations component or sub-where loss safety. With the onboard DC grid the split er system, selectivity means (on a functional level) mode operation can run more efficiently 7 Benefits of the Onboard DC Grid of propulsion power could cause significant damage that only the faulty component or subsystem is as the engine speed can be adjusted and affected and taken out of operation. to the vessel, other installations or personnel the equip a newbuildoptimized platform support to the required load without 2 The term hotel load is used with respect to electrical plant ships is split intotheir a minimum two separate SV), owned by Myklebusthaug Mato describe non-propulsion of energy the need functional for changing the number ofthrough more More vessel layout requirements, such as lights, air conditioning, and located at the Klevan shipyard generators sections to achieve a higher level of redundancy in the flexibleonline. placement of electrical components computers, water purifiers, radios, etc. vik, Norway, with a full onboard DC power system. m, including all power, propulsion maintenance of engines by more Reduced
170 Up to 20 percent fuel savings

to future energy sources

at 2,300kW and one at 920kW, two 2,200kW

mation systems.

Jan-Fredrik Hansen efficient operation

space for payload through lower jan-fredrik.hansen@no.abb.com uarter of 2013. The vessel has five footprint john.o.lindtjorn@no.abb.com electrical and more flexible placement peed diesel generators, four rated of electrical components platform that allows plug and play ABB Process Automation, Marine Systems retrofitting possibilities to adapt to future Ulsteinvik, Norway energy sources tor-arne.myklebust@no.abb.com
Klaus Vanska Tor-Arne Myklebust

ssel designed by the Norwegian

dynamic response and ABB Process Automation, Marine Systems pose oil field supply and constmaneuverability
John Olav Lindtjrn, Billingstad, Norway

ong, 4,800gt type MT 6015 PSV, Improved

Increased Marin Teknikk, is due for delivery in

pulsion units and three additional A system

W and one at 920kW, two 2,200kW

for DP operation.

Up to 20 percent fuel savings

By doing so, October). the vessel maintain Onboardcan DC Grid for enhancedits DP position even in ships. Paper presented at the Dynamic if one side ofoperation the power plant fails. However, running Positioning Conference, Houston, TX, United in split modeStates. generally does not utilize the full benefits of electric propulsion because total optimization of Onboard DC grid 33 running engines is not possible. Fuel efficiency has therefore often been sacrificed in favor of safety. With the Onboard DC Grid the split mode operation can run more efficiently as the engine speed can be adjusted and optimized to the required load without the need for changing the number of generators online.

Further reading Hansen, J. F., Lindtjrn, J. O., Vanska, K. (2011,

Footnotes

In particular, when considering the DP operation, integration of energy storage to the Onboard DC Grid, will set a new standard for response time of the thrust and station keeping accuracy. The energy storage allows main engines to run with a relatively constant power load by charging and discharging the energy storage device depending on the needed thrust to keep vessels position. Thus, the vessels ability to keep its position will be less dependent on the engines response time for load transients. Positioning performance can be improved, and the engines can operate even closer to their optimal load conditions. Also, as the throttling of the engine is more constant, tear and wear of the mechanical actuators could also be reduced. Yachts One day, a yacht may be transferred to a new port at its maximum speed to be ready to welcome quests, while next day, it is quietly sailing while there is party on board. Whatever the propulsion need should be, the Onboard DC Grid helps to provide the best efficiency and comfort with a reduced use of valuable space. Ferries Some ferries carry trains; others carry cars, trucks or passengers. What is common for almost all ferries is that they operate on scheduled routes between two or more terminals. Most of the terminals are located in densly populated areas and even in the middle of cities. The visibility of these ships and their direct effect to the quality of life for so many people create a strengthened awareness and attention to the environmental emissions by ferry owners and operators. Certain new technologies, such as liquefied natural gas (LNG) engines are being introduced in ferries, and the Onboard DC Grid is particularly well-suited for integrating the LNG power plant with the propulsion, as it gives the possibility to operate the engines at more stable loads with higher efficiency and less methane slip. The Onboard DC Grid is easily compatible with energy storage devices such as batteries either as a source of energy that is supplementary to the combustion engines or even as the only source if adequate charging can be supplied at the terminal.

8 New order

ABB will equip a newbuild platform support vessel (PSV), owned by Myklebusthaug and located at the Klevan shipyard in Ulsteinvik, Norway, with a full Onboard DC Grid system, including all power, propulsion and automation systems. The 93 meters long, 4,800 GT type MT 6015 PSV, a multipurpose oil field supply and construction vessel designed by the Norwegian company Marin Teknikk, is due for delivery in the first quarter of 2013. The vessel has five variable-speed diesel generators, four rated at 2,300 kW and one at 920 kW, two 2,200 kW main propulsion units and three additional thrusters for DP operation.

Jan Fredrik Hansen ABB jan-fredrik.hansen@no.abb.com John Olav Lindtjrn ABB john.o.lindtjorn@no.abb.com Tor Arne Myklebust ABB tor-arne.myklebust@no.abb.com Klaus Vnsk ABB klaus.vanska@fi.abb.com Footnotes 1 In the event of a fault on a component or subsystem, selectivity means (on a functional level) that only the faulty component or subsystem is affected and taken out of operation. 2 The term hotel load is used with respect to ships to describe their non-propulsion energy requirements, such as lights, air conditioning, computers, water purifiers, radios, etc.. Further reading Hansen, J. F., Lindtjrn, J. O., Vanska, K. (October 2011). Onboard DC Grid for enhanced DP operation in ships. Paper presented at the Dynamic Positioning Conference, Houston, TX, United States.