ELECTRIC PROPULSION FOR PIPELAY / DIVING SUPPORT … · DP3, however the combination of flexible installation, operating profile, safety, redundancy, maintenance and availability

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pr/acquisitie/electric propulsion pipelay vessels/version D

ELECTRIC PROPULSION FOR PIPELAY / DIVING SUPPORT VESSELS WITH HIGH REDUNDANCY, INTEGRATED AUTOMATION AND POWER ELECTRICS FOR NOTATION DP2 and DP3 Written by: - Mr. Paul Bracké MSc. - Mr. Arie Boer Summary The paper is describing the diesel electric propulsion system for three offshore vessels, built for the Aberdeen based company Subsea 7. The first is a rigged reeled pipe lay vessel named "SEVEN OCEANS" and already in operation. The second is a flexlay pipe lay vessel named "SEVEN SEAS" being in commissioning at the moment and the third a diving support vessel the "SEVEN ATLANTIC" which still is in building process. Already in a very early stage the installations and systems needed for such complex vessels were discussed with the yard, owner, classification societies and suppliers of vital equipment and systems. These items were not related only to the applied techniques, but also to the building process, which gives higher quality and guaranteed delivery(time) of the vessel. The operational, functional, safety, DP and class requirements were the basis for the design of the power plant, propulsion system and automation on board. The complete design inclusive yard delivered auxiliary systems was reviewed in a FMEA analysis and tested in a super FAT as far as practical. The SEVEN OCEANS and SEVEN SEAS have DP2 requirements and all functions of the propulsion drives, power plant, distribution and auxiliary systems are controlled, managed and displayed via a Kongsberg automation system, which was part of the turn-key delivery. Control of the vessel is done through two wheelhouse control desks aft and fore and one controldesk in the ECR. The third vessel, the SEVEN ATLANTIC, is dedicated as a diving support vessel under DP notation 3. Difference between the electrical designs caused by the more stringent DP notations are highlighted. INTRODUCTION Where in the past (steam) diesel-direct propulsed pipelay and cable laying vessels were designed and built the demands on safety and station keeping became so high that more redundant systems were needed, these demands on safety and DP notation were not able to be mechanically solved in a proper way by diesel-direct propulsion installations. Why diesel-electric? When talking about diesel-electric propulsion, the first question to ask is: why? Depending on the type of vessel, its functionality, operating conditions and rules to be fulfilled the reasons can be: • safety, redundancy and availability • noise and vibration requirements • flexible installation possibilities • operating profile / flexibilty / high hotel load or other consumers • reduction of emissions • economic demands • reduction of fuel costs • reduction of down time • reduction of man power In case of pipe laying and diving support vessels we will especially hi-light the safety, redundancy and availability reasons.

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Technically it is not required to select DE propulsion for station keeping according DP2 or DP3, however the combination of flexible installation, operating profile, safety, redundancy, maintenance and availability of the systems make the choice for an electric system technically as well as commercially attractive. The diesel-electric concepts perfect suits the safety and availability requirements applicable for pipe lay and diving support activities because of the possibilities in redundancy and separation in the power generation. One of the mayor benefits of this concept is the flexibility to place components, such as diesel generator sets, switchboards, e-motors, drives etc., at their most efficient location. Besides an efficient layout it's also easy to create separated compartments to fulful safety and redundancy requirements. Together with redundant power and control cabling, to and from all electrical systems an optimal installation fulfilling all necessary requirements will be the results. Because of the above it is possible to design the ship in such a way that in extreme cases like flooding or fire in any compartment, this will not lead to a blackout of the total propulsion system and power supply. There will always be the possibility of controlled specified operation ensuring the safety and availability of the vessel. SEVEN OCEANS - SEVEN SEAS - SEVEN ATLANTIC These three innovative vessels, built for the Aberdeen based offshore company Subsea 7, the first a reeled rigid pipe laying construction vessel, the second a flex lay pipe laying construction vessel and the third a diving support vessel are designed and built at IHC Merwede Shipyard and equipped with Huisman-Itrec pipelay equipment. The vessels are suitable for world wide operations and will be Dynamic Positioned according to the owners requirements.

fig. 1 - SEVEN OCEANS - SEVEN SEAS - SEVEN ATLANTIC

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Rules and standards General design requirement : Lloyd's Register of Shipping (LRoS) Classification notation : +100A1 PipeLaying (Diving)Ship, UD strength for

load of 10 t/m2, Heli Landing Area, +LMC, UMS, CAC(3)

Additional requirements : SOLAS regulations for Cargo Ships FMEA : IMCA M 04/04 S&R App D&E Facts and figures

SEVEN OCEANS

SEVEN SEAS

SEVEN ATLANTIC

Yardnumber

709

710

713

Main dimensions

length 157.31 mtrs. length 151.00 mtrs. length 144,79 mtrs.

breadth 28.40 mtrs. breadth 28.40 mtrs. breadth 26.00 mtrs. depth 12.50 mtrs. depth 12.50 mtrs. depth 12.00 mtrs. Deadweight 10,930 ton 11,800 ton 8,700 ton Speed 15,0 knots 13,0 knots 13,6 knots DP system DP2 DP2 DP3 Pipe lay equipment

lay ramp with 300 ton tensioner, 80 ton A&R winch and 16 ton knuckle boom crane

lay tower with two 200 ton tensioners, 125 ton A&R winch and 16 ton knuckle boom craen

main pipe reel, capacity 3,500 ton

two carousels below deck: 1,250 tonnes, one carousel on deck: 3,000 tonnes, rigid steel pipe lay possibility

piggy back reel A&R winch 360 ton Diving system moonpool 7x7,5 mtrs. two diving moonpools

integrated twin bell diving system capacity for 24 divers (8 diving teams) one tool moonpool maximum operating depth 350 mtrs.

cranes 400 / 40 / 5 ton 400 / 40 / 12 / 5 ton 120 / 10 / 2,5 ton ROV system two fully integrated

cursor launched work ROV's housed in a hangar

two fully integrated cursor launched work ROV's housed in a hangar

two fully integrated cursor moonpool launched observation ROV's one deck ROV

well treatment chemical / acid tanks mixing tanks injection pumps

crew 120 120 150 table 1: facts and figures of 3 Subsea 7 vessels

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Description of the diesel-electric installations on board of the vessels SEVEN OCEANS and SEVEN SEAS (yard numbers 709 and 710) Already in a very early stage the technical installations and systems needed for such complex vessels were discussed by the Bakker Croon Combination with yard, owner, classification societies and suppliers of vital equipment and systems. These items were not related only to the applied techniques, but also to the building process, which gives higher quality and guaranteed delivery time of the vessel. The operational, functional, safety, DP and class requirements were the basis for the design of the power plant, propulsion system and automation on board. The complete design inclusive yard delivered auxiliary systems was pre- and reviewed in a FMEA analysis and tested in a super FAT as far as practical. The DP requirements and all functions of the propulsion drives, power plant, distribution and auxiliary systems are controlled, managed and displayed via a vessel management automation system, which was part of the turn-key delivery. Control of the vessel is done through two wheelhouse control desks one aft and one fore and one control desk in the ECR. All control systems were part of the FMEA analysis as well. The description will mainly highlight the following:

! redundant power generation and distribution ! diesel electric propulsion with azimuthing thrusters and one tunnel thruster ! integrated automation, vessel management and DP system ! controls / overview ! differences with SEVEN ATLANTIC ! harmonics under control ! FMEA ! reels and cranes ! building process

Redundant power generation and distribution Power generation consisting of six Wärtsilä engines fitted with 3600 kVA A. van Kaick generators, which generate a 6,6 kV mains voltage. This power plant provides power for both propulsion pipelay/crane activities and other consumers. High voltage is required since with low voltage the maximum permissible short circuit currents would be exceeded. As the safety and operation demands are high, there are two completely separated engine rooms, each accommodating three of the six diesel generator sets, of course complete with other engine room auxiliaries needed to operate such vessels.

fig. 2 - main generators 4, 5 and 6 PS fig. 3 - HV switchboards PS

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This high voltage power is supplying the main switchboards which are located in two separate rooms directly above the engineroom and connected to each other with an inner- and outer bustie. From the main switchboards all consumers such as main propulsion, thrusters, crane and low voltage distribution transformers are supplied. The distribution transformers are located in the same compartment and are supplying the low voltage switchboards which are located one deck higher. The power is supplied from each main switchboard to a mix of forward and aft thrusters. In this way there is always at least one thruster at the forward end and one at the aft end available in the case of calamities. For domestic use power is still and always available via the low voltage switchboards and transformers, even in extreme calamities (like engine room fire or flooding of one of the engine or switchboard rooms). Regular operations are carried out with minimum three diesel generator sets running (in parallel mode), depending on weather conditions. In extreme conditions other remaining sets can be added. One set is always standby for emergency and maintenance services.

fig. 4 - one-line SEVEN OCEANS / SEVEN SEAS Diesel-electric propulsion with azimuthing thrusters and one tunnel thruster The entire propulsion / thruster package consists of three Wärtsilä fixed pitch propellers in azimuthing nozzles aft each driven by an Indar propulsion squirrel cage motor with a shaft power of 2.950 kW. Each motor is controlled through a Bakker Sliedrecht designed and built direct water cooled frequency drive bases on ABB ACS 800 modules. Forward in the ship two electrical retractable Wärtsilä azimuth thrusters are provided, each with a shaft power of 2.400 kW. Control and power supply are again provided through a similar Bakker frequency drive for each thruster.

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fig. 5 - main propulsion fig. 6 - retractable thruster Additionally there is a transverse tunnel thruster in the bow with a shaft power of 2,200 kW, bringing the total installed propulsion power to a hefty 15,850 kW. The remaining power capacity is used for all electrical systems on board, including the pipe laying, ROV and crane equipment. The entire propulsion plant has been divided, fully separate propulsion/thruster rooms, resulting in a full redundancy for every link of the chain. Integrated automation, vessel management and DP system The integrated Kongsberg vessel management system for alarm, control, monitoring and DP, communicates via digital (LAN-bus system) signals, which are transmitted via a redundant optical cable, including a fully redundant field bus network. Control and monitoring is done by screens and rollerball control, of which 6 operators stations are meant for the vessel management system and 2 operators systems for the DP system. There are several authorisation login-in codes available for the crew, which may vary from allowance to control the ballast system or to the complete control of engine room and wheelhouse equipment.

fig. 7 - ECR controldesk fig. 8 - mimic power & propulsion

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fig.9 - vessel management and DP system (SEVEN OCEANS / SEVEN SEAS) The central and field station computers control all systems on functioning. Several sub-systems can be controlled and monitored via mimic pages on the screen. Historical data can be collected and stored in a separate history station, allowing failure analyses and out trend analyses. Essential in diesel-electric propulsion is Power Management, enabling automatic control, management and monitoring of the power plant. Additionally there is also per thruster a fast frequency detection power reduce system installed in case of unexpected bus connected engine overload. The system features a special module considering the maximum dp/dt which is allowed for diesel engines. In other words, the diesel engines only allow a certain power increase per time unit. This dp/dt module prevents that a too large power increase causes a black-out. Depending of the mains configuration with one or more diesel generator sets in parallel a smaller or larger dp/dt is allowed.

fig. 10 - mimic diesel generator set fig. 11 - mimic propulsion plant

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fig. 12 - wheelhouse SEVEN OCEANS / SEVEN SEAS fig. 13 - ECR SEVEN OCEANS / SEVEN SEAS Controls All functions of the propellers, thrusters, e-motors and frequency drives are controlled, managed and displayed via the integrated system incorporated in the consoles of the wheelhouse. On aft and fore consoles there are two independent steering positions. The vessels can be manually controlled by the thruster controllers or automatically by the DP system. In case of calamities the C-joy system can directly take over all functions and is fully independent. For functions see table 2. a) thruster control system &

vessel control system - alarm management - machinery management

- power management - auxiliary machinery

- fluid management - ballast monitoring and control

b) DP system can control manually tracking and station keeping - duel redundancy - nominal single-point failure - failure detection - fault isolation - switch-over not standby - comparison of sensor data

between components

table 2 - control functions

fig. 14 - DP console wheelhouse fig. 15 - mimic thruster overview

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The system provides a total control of the vessel, with emphasis of control and monitoring in the wheelhouse, the engine control room and the thruster compartments. In the unlikely event of extreme calamities in the computerised control system, it is always possible to control the propellers, thrusters via direct wired non follow up controllers from the consoles, which are independent from the other control systems, control positions are shown in table 3.

fig. 16 - overview navigation console

navigation - lever controls (all thrusters)

- track pilot (thrusters 4 and 5 only) - C-joy via DP system - Non Follow Up (only thrusters 4, 5 and 6)

DP console (PS aft) - lever controls (all thrusters) - 2 DP operator stations - independent C-joy control

wing control PS/SB - C-joy via DP system

ECR - only indicators

propeller / thruster room - local speed control (drive) - local azimuth thruster control

table 3 - overview of thruster and propeller controls SEVEN OCEANS / SEVEN SEAS

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Differences with regard to the diving support vessel SEVEN ATLANTIC (yard number 713): The differences between the SEVEN OCEANS / SEVEN SEAS and the SEVEN ATLANTIC are related to the power generation and distribution system, the automation and DP system and cable routing and separation. These differences will be described as follows: Power generation and distribution The amount of power generation is the same power as yard numbers 709 en 710 through six diesel generatorsets of 3600 kVA. However, the diesel generatorsets are physically located in 3 totally separated enginerooms instead of 2. With regard to the distribution through the main high voltage switchboard there are vital separations between generator field by means of couple circuit breakers. fig. 17 - one-line SEVEN ATLANTIC

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Comparison DP2 / DP3 The pipelaying vessels Seven Seas an Seven Oceans are designed and build according to the DP2 classification. Basicly this rule indicates that no single failure, excluding fire or flooding, will result in loss of position. However the owner had the more stringent specification that one single failure, excluding fire or flooding, will not result in the loss of more than one thruster. This requirement resulted in the application of inner bustie switches in the two HV-switch boards and a much more complex design concerning selectivity on electrical faults. This configuration is shown in fig. 4. fig. 18 - power separation zones SEVEN OCEANS / SEVEN SEAS The diving support vessel Seven Atlantic is designed according to the DP-class DP3. This indicates that one failure, including fire and flooding, will not lead to loss of position. For this ship this has resulted in 3 fire&flooding separated engine rooms, 3 HV-switchboards, all located in fire&flooding separated rooms, a so-called "swop" switch over panel is separately located in thrusterroom 2, additional separated cable trunks&routing and galvanic isolation components in the control and emergency stop circuitry. The one line configuration is shown in fig.17. In addition the DP control system is more complex. A third DP computer installed in a separated room and additional DP sensors. fig. 19 - power and cable separation zones SEVEN ATLANTIC

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Automation, DP system and controls The automation, DP system and controls of the SEVEN ATLANTIC are more complex than the ones of the SEVEN OCEANS / SEVEN SEAS. The main difference can be related to the third DP console, computer and sensors to be located in a different location. The control positions are given in table 4 and the overview in fig. 20. fig. 20 - vessel management and DP system SEVEN ATLANTIC. navigation - lever controls (all thrusters)

- track pilot (thruster 4 an 5 only) - independent C-joy control - Non Follow Up controls (only thrusters 4,5 and 6

DP-console (PS/SB) - lever controls (all thrusters) - 2 DP operating stations

Wing control PS/SB C-joy via independent C-joy control

ECR - lever controls (all thrusters)

Back-up station (separate room) - independent C-joy control - 2 DP operating stations

Propeller / thruster room - local speed control - local azimuth thruster control

table 3 - overview controls SEVEN ATLANTIC

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Harmonics under control To reduce the harmonic disturbances in the (main) supplies within the class requirements the propulsion plant, reel and energy drives are configured in a semi 24-pulse supply system, using so-called double stock transformers (phase shifted). This choice gives an optimum in applied reliable techniques, efficiency, control of lower and higher harmonics. The pre-calculations were based on a THD (Total Hamonic Distortion) of <8 %, the alternator reactances were chosen in such a way that there was a balance between the short circuit current Ik" and the level of the THD. fig. 24 - overview drives and harmonics FMEA Failure Mode Effect Analysis were already discussed in the pre-stage and compiled to figures / dates and were done on: - main, aux. engines - power generation - power / vessel management - power distribution - propellers, steering gear - thrusters - networks - DP control system - essential aux. systems

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fig. 25 - view on the super FAT

table 4 - FMEA topics (red = yard, green - Bakker Croon Combination

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Reels and cranes The supplier for the pipe laying equipment, tower, reel and the cranes is Huisman-Itrec from Schiedam, which are also driven and controlled by Bakker Sliedrecht frequency drives.

fig. 26 - drive motors for reel fig. 27 - 400 ton deepsea crane Building process (general proven facts) The choice for mentioned installations/systems on board of vessels is highly expressed by the availability of techniques and of the people/organisations that dare and are open to implement, and to maintain and service it afterwards. Critical success factors are good and early communication and co-operation between all parties involved such as yard, owner, naval architect, system specialists etc., which should result into a clear package of requirements.

fig. 28 - thruster and propulsion motors fig. 29 - SEVEN OCEANS under construction Furthermore of importance is optimisation of dimensioning with ample freedom in design Thoroughly carried out preliminary studies and designs can prevent unfortunate choices and, in addition, provide more certainty with regard to easy building with only little points of discussion.

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Systems and vessels designed in such a way also provide predictable maintenance, wherein preventive maintenance on regular (planned) base keeps exploitation costs lower and controllable. After trials the complete electrical installation was successfully turn-key delivered, inclusive a previous intensive training program for the crew.

fig. 30 - pipelay trial trip SEVEN OCEANS CONCLUSION After an intensive pre-design , detailed design, FMEA-analysis, component manufacturing and component testing a Super FAT was organised in which the system functionality was thoroughly tested. During the sea trials this approach proved again to be very successful. No major problems occurred and the systems operated fully according the specifications and expectations.

Documents

ELECTRIC PROPULSION FOR PIPELAY / DIVING SUPPORT … · DP3, however the combination of flexible installation, operating profile, safety, redundancy, maintenance and availability