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Drive upgrade proves a seismic shift for PGS

09 July 2012

A drive upgrade has enhanced the thruster performance on a fleet of seismic survey vessels owned by Petroleum Geophysical Services (PGS) of Norway. A 15-year life cycle extension and improved dynamic performance has been achieved, following upgrades to an original analogue variable-speed drive system.

The project, carried out by engineering specialist, Dynamotive, involved the upgrade of original analogue load commutated inverter (LCI) drive systems to a modern digital control platform, delivering active dynamic load reduction to the vessels’ propulsion systems, while improving the efficiency and utilisation of the generators and the ships’ power management systems. 

The upgrade is claimed to have vastly improved the effectiveness and local ability of the ship board maintenance teams, while adding optional remote support engineering from Dynamotive via a secure Internet connection. This remote engineering tool supports vessels wherever they happen to be operating in the world, providing monitoring, protection and diagnostic display of machines, transformers, choke temperatures, system currents, voltages and alarms.

By retaining and reusing components from the original LCI drive system, such as power thyristors and Brush-manufactured synchronous machines, the ship’s infrastructure was spared a great deal of disruption, while at the same time saving PGS both capital and maintenance costs. The upgrade involved installation of ABB AC 800PEC process control systems, which form 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, saving cost and improving operational efficiency. 

The AC 800PEC is normally deployed on process control tasks, but in this application it is used to provide control and management of the thyristor power devices. In this configuration, it combines a high-speed control capability for dynamic load management, with low-speed process control and information tasks usually carried out by separate programmable logic controllers. The DFE upgrade was installed and commissioned during a 30 day dry dock period alongside other essential vessel maintenance and upgrade works. Dynamotive director, David Bates takes up the story:

“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. 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 a 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 also conducted at the facility.

Complex retrofits face significant challenges when integrating new design components into the retained elements of an existing installation. Dynamotive overcame challenges, such as restricted access, by supplying a mix of new control cabinets and technologies deployed on chassis plates. In this way all components could be integrated seamlessly into the retained elements. While this flexible approach did add a certain degree of complexity to the deployment, it saved both cost and downtime for PGS.

This particular retrofit was considerably aided by the compact, modular nature of the new hardware, which eased on-board system integration, installation, and commissioning. Dynamotive was able both to manage and functionally prove each upgrade prior to site installation, with all design and installation phases engineered specifically to minimise their impact on the vessel infrastructure. David Bates again:

“Retrofits or upgrades are often misunderstood and underestimated in terms of the complex challenges and considerations that they entail. The result can be a disappointed customer who cannot restart his business operations to the agreed schedule. Dynamotive’s approach mitigates this risk through detailed preparation and planning, encompassing all aspects of engineering and logistical risk management considerations, to ensure 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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