excavating the seabed Reference 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