Drive upgrade enhances thruster performance on seismic survey vessels

Paul Boughton
A 15-year life cycle extension and improved dynamic performance is being achieved on a fleet of seismic survey vessels, following the upgrade of a variable-speed drive system by engineering specialist, Dynamotive.
The fleet, owned by Petroleum Geophysical Services (PGS) of Norway, has had its original analogue load commutated inverter (LCI) drive systems upgraded to a digital control platform. The upgrade delivers active dynamic load reduction to the vessels propulsion systems, while improving the efficiency and utilisation of the generators and the ships power management system.
The upgrade vastly improves the effectiveness and local ability of the ship board maintenance teams, with the added reassurance of optional remote support engineering from Dynamotive, via a secure internet connection. The remote engineering tool provides support to vessels anywhere in the world, thereby providing clients with more assured business continuity, via rapid monitoring, protection and diagnostic display of machines, transformers, choke temperatures, system currents, voltages and alarms.
The overall project upgrade delivers a high performance, robust and reliable propulsion drive system with extended life cycle and with vastly reduced overall project costs. By retaining and re-using components from the original LCI drive system – such as power thyristors and Brush-manufactured synchronous machines - the ship’s infrastructure faced minimum intrusion and disruption, saving money and reducing downtime.
Dynamotive’s upgrade system features the high speed ABB AC 800PEC controller which forms the heart of the digital front end (DFE) design. The DFE brings a faster and more dynamic response to the propulsion systems relative to available ship power. This leads to cost savings and improved operation efficiency.
The AC 800PEC is a high performance process control system that provides the control and management of the thyristor power devices. It combines high-speed control capability for dynamic load management, with low-speed process control and information tasks usually carried out by separate PLC units.
The DFE upgrade was installed and commissioned during a 30 day dry dock period alongside other essential vessel maintenance and upgrade works.
“The old analogue drives are, by design, slower to react and as such the generators were not fully loaded and utilised to protect against potential black outs on the vessel,” explains David Bates, Commercial and Marketing Director, Dynamotive. “As such the upgrade has allowed the client to better optimise the generator loading, improving the vessel efficiency and performance while bringing significant energy saving and associated carbon dioxide emission reductions.”
Using its proof of concept test rig, at its UK facility, Dynamotive designed and tested the digital control system prior to vessel installation. Client and maritime classification tests were conducted at the facility.
Complex retrofits face significant challenges when integrating new design components into retained elements of an existing installation. Dynamotive overcame these challenges, such as restricted access, by supplying a mix of new control cabinets and technologies deployed on chassis plates. This way all components could be integrated seamlessly into the retained elements of the vessel’s control system. This flexible approach adds complexity to the deployment, but saves the client money and downtime.
An important aspect of the retrofit design is the smaller, more compact modular hardware which assists the ease of the on-board system integration, installation, commissioning and any subsequent maintenance by on-board personnel.
With its extensive upgrade experience, Dynamotive can project manage and functionally prove any upgrade, prior to site installation. The design and installation phases are engineered specifically to minimise the impact and intrusion to the vessel infrastructure, thereby reducing cost and overall project timelines.
“Retrofit or upgrade solutions are often misunderstood and underestimated in terms of the complex challenges and considerations required,” says Bates. “The result can be disappointed customers who do not restart business operations on time. Dynamotive’s expertise and approach mitigates this risk via detailed preparation and planning, encompassing all aspects of engineering and logistical risk management considerations. This ensures ensuring projects are delivered on time and within budget.”
Dynamotive continues to manage and maintain the fleet’s original analogue drive system along with the new digital drive system, in partnership with Wilhelmsen Ship Management, which acts on behalf of the vessel owners, PGS.
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