excavating the seabedReference Story

A sophisticated motor control system supplied by Vacon is central to the operation of the revolutionary UT-1 submersible ultra-trencher, which was built by underwater engineering specialist SMD and is owned and operated by CTC Marine*.

The UT-1, the world’s most powerful jetting remote operated vehicle (ROV), uses hydraulic jets to cut trenches in the sea bed to allow the rapid and cost-effective installation of, for example, flexible flow lines and cables. The Vacon drive sys-tem, which uses active front-end (AFE) technology in a com-mon DC bus configuration with modular inverters, controls the pumps that power the trenching jets.

Versatility, proven reliability and low level of harmonics

The engineers at SMD chose Vacon AC drive systems for this prestigious project because of their versatility and their prov-en reliability in marine applications. In addition, the intrinsi-cally low level of harmonics associated with AFE drives was an important benefit as the UT-1 derives its supplies from a shipboard generator.

The jetting pump drive system developed by Vacon and SMD for CTC Marine’s UT-1 submersible comprises four drive pan-els, each equipped with a 750 A LCL filter and a 750 A AFE module to provide power for the common DC bus. The bus supplies four 460 A INU inverter modules, which deliver their output via sine filters to transformers which step up the volt-age to the 3.3 kV needed by the two 375 kW medium voltage pump motors.

All of the key items for this system, except the transform-ers, were selected from Vacon’s extensive range of standard products.

Compact construction and easy integration important benefits

Despite their high current ratings, the power modules used in the UT-1 jetting pump drive system feature very compact construction, an important benefit given the very restricted space available to accommodate them on the ROV. All the modules are also air-cooled, thereby eliminating the ad-ditional complexity that would have been involved in imple-menting a liquid-cooled solution.

Monitoring and supervisory control of the AFE modules and the INU inverter modules are provided via a common fieldbus system, making the drives easy to integrate with the other systems on board the UT-1.

Ultra-trencher with a variety of roles

Permanently installed on the multi-role subsea construction vessel Volantis, the UT-1 ultra-trencher ROV is currently be-ing used in a variety of roles to service the offshore oil and gas, life-of-field seismic, telecommunications, e-field, power and renewables market sectors.

The innovative design of the UT-1 permits deployment and of-fers unparalleled flexibility in even the most severe weather conditions. However, in spite of the huge demands operating

Vacon Drives UK Ltd.18 Maizefield, Hinckley Fields Industrial Estate Hinckley Leicestershire, LE10 1YF, UKTel. +44 (0)1455 611 515Fax. +44 (0)1455 611 517E-mail: sales@vacon.co.ukWeb: http://www.vacon.co.uk R

S00

0152

A

in these conditions places on its onboard systems, it is de-livering exceptional levels of availability, an achievement to which the Vacon drive system has made no small contribu-tion.

Boosting DC link voltage by up to 35% above nominal

The Vacon AFE units used in this project are regenerative modules that have been specifically developed for common DC bus applications. In addition to their excellent harmonic performance, these modules can also boost the DC link volt-age by up to 35% above nominal. The INU inverter units are also bidirectional, and are available with integral DC supply systems in ratings up to 75 kW. Higher ratings, such as those featured in this in project, are exclusively for use with exter-nal DC supply systems.

*Headquartered in Darlington, UK, CTC Marine Projects (CTC) is a leading provider of subsea, installation, cable lay and trenching services for the international offshore construc-tion industry. CTC operates some of the world’s largest fleet of high technology marine trenching and burial equipment, which is supported by a fleet of DP2 multi-role construction vessels, flexible installation and shallow water spreads.

A sophisticated motor control system supplied by Vacon is central to the operation of the revolutionary UT-1 sub-mersible ultra-trencher, which was built by underwater engineering specialist SMD and is owned and operated by CTC Marine*.

Ultra-trencher images courtesy of CTC Marine.