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Propulsion Update A side view diagram of the pipe laying SEMAC 1 barge. Siemens Outfits Pipe-Laying Barge With Electric Drive System When the pipe lay barge SEMAC 1 underwent a conversion from a hydraulic to an electric drive sys- tem, with a power increase, for its tensioners and A/R winch, owner European Marine Contractors (EMC) chose Siemens Electric Ltd. of Montreal, Canada for the job. The 145-meter long semi-sub- mersible barge lays gas and oil pipe lines under the sea. Prefabricated joints are welded to the pipeline in round-the-clock operation. Anchor winches move the barge forward in the rhythm of the welding opera- tion, and the barge can lay pipe at a top speed of 2.5 miles per day. The barge's high cost of operation and tight schedules demand that pipe handling equipment be reli- able, efficient and operator friendly; all conditions which are satisfied with state-of-the-art electrical drive systems. For the complex project, Siemens supplied DC motors, con- verter- and control-cubicles, opera- tor consoles, low- and medium-volt- age switchgear and dry-type power transformers. For the tensioners, three cater- pillar-type drives hold the pipe at a constant tension, regardless ofbarge movements. The tensioners are rated 75 tons each and are designed for a maximum pipe laying speed of 36 meters per minute. The upper and the lower tracks of the tensioners are each driven by a 290 kW DC, blower ventilated motor. The double-drum abandonment/ retrieval winch is driven by four DC motors of 320 kW each, and operates in conjunction with a 250 kW spooling winch. Rated at 275 tons, the winch can handle wires up to four inches at a maximum speed of 44 meters per minute. It serves for the laydown and the re- covery of the pipeline on the sea floor. The tensioners and the winches can be operated in tension- and in speed-control mode from local con- trol stations and from two main operator desks. For the tensioners, an additional position control mode is implemented, which achieves in- creased pipeline stability, impor- tant at rough sea conditions. The common control system for the tensioners and A/R is a closed- loop system built-up with a modu- lar analog system, located in 19- inch racks. This type of control makes it possible to smoothly trans- fer the pipe from one system to the other, without applying the brakes and losing control over the holding tension in the pipeline. This proves an important feature, especially at bad weather conditions, which of- ten dictates the laydown of the pipe. All digital signals are processed by a centralized programmable con- troller system, which is interfaced with the analog controls. Because control cubicles and desks are dis- tributed all over the ship, electronic terminators for local input/output signals are used which are connected by a two-wire ring cable to the cen- tral controller. This configuration requires a minimum of cabling and reduces installation, engineering and commissioning costs. The flexibility of the program- mable controller with regard to implementation of modifications, commissioning procedure^etc.^s an advantage over conventional hard- wired controls. Due to the flexibility of the con- trols the drives could be commis- sioned within a very short period of time. The barge resumed operation in spring of 1991, after going in for conversion in late 1990, and has layed hundreds of kilometers of pipe- line of different sizes since. A further advantage of electric drives is their energy-efficiency. Higher amounts of active power, which result in increased fuel con- sumption on the diesel power plant, are only required during the short intervals ofbarge movement. As a matter of fact, energy is even regen- erated by the tensioner drives when the barge is pulled ahead. 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