ABB Industri has introduced a Compact Azipod electric propulsion system designed to output 0.4-5 MW for series applications with typical ranges from 10-20 MW. The new system has already attracted the attention of the offshore industry, and ABB has been contracted by Søviknes Verft, an Aker Yards company, to supply two Compact Azipod units, each outputting 2.3 MW, for a new multi-function supply vessel for Island Offshore, Norway.
This order represents the first delivery of its kind to a supply vessel and forms part of a complete package solution from ABB that includes the generators, switchboards, thruster drives, power management, and dynamic positioning.
The new supply vessel, which is due for delivery in November 2001, is a Rolls-Royce UT 745E design, a development of the UT 745. The two Compact Azipod units will comprise an electric AC motor mounted in a 360-degree azimuthing pod and a fixed pitch propeller mounted directly on the motor shaft. This eliminates the need for long shaftlines, reduction gears, rudders, and stern thrusters, leading to space and weight savings.
According to ABB, the Compact Azipod system provides enhanced maneuverability and safety as well as significant fuel and emission reductions. Since the system is located underwater, it has low noise and vibration characteristics compared with conventional electric drive systems, and the space otherwise taken up by the propulsion motors is freed for other uses.
The Compact Azipod system, which is available in five size groups, is being manufactured using standardized modules that can be assembled and installed quickly and easily. There are three main modules: a steering module and a mounting block, a housing module, and a motor module and propeller. This modular construction results in lower production costs and enables yard costs and schedules to be optimized.
The Compact Azipod's permanent magnet electric motor is controlled by a new water-cooled ACS600 marine drive. The latter, launched by ABB last year, uses a Direct Torque Control (DTC), 690V variable-speed drive which gives full nominal torque, smoothly and steplessly in both directions over the entire speed range, including standstill. The DTC's control dynamics are such that the motor speed encoder and angle encoder become redundant. Propeller speed is monitored directly from the motor current and can be optimized according to requirements.
The motor modules are available in five diameters, each with two or three length choices. Propulsion power demands can be satisfied by optimizing the propeller rpm and size according to the hydrodynamics of each project. Some 3 MW of power can be attained with a single motor construction whereas a dual motor uses up to 5 MW.
Permanent magnet technology in the electric motor and direct cooling in the sea allows slimmer motor and pod dimensions to be achieved and also improves hydrodynamics. The absence of an exciter also reduces power losses and results in greater efficiency. Water cooling lessens the need for high-power filtered air cooling in the electrical compartments and enables effective heat transfer without the problems often associated with air filters.
The ACS600 marine drive has also been designed for use on thrusters, oil drilling machinery, compressors, winches, and pumps. Incorporated into a closed cubicle structure up to IP54 with a footprint almost 50% less than an equivalent air-cooled drive, the unit is approved for high levels of vibration and is made of flame-retardant materials with halogen free wiring and cable ducts. ACS600 marine drive units have already been delivered to Wagenborg Kazakhstan for two icebreaking vessels which have been operating in the Caspian Sea since 1998.