Drives power novel electric trimaran warship

FKI drive systems are proving their reliability on the new Research Vessel (RV) Triton, the world's first largest motor powered trimaran fitted with a medium voltage, full electric propulsion system.

FKI drive systems are proving their reliability on the new Research Vessel (RV) Triton, the world's first largest motor powered trimaran fitted with a medium voltage, full electric propulsion system.

Seen as the future of warship design, the RV Triton is capable of pivotal turning and speeds of 20 knots thanks to its unique propulsion system, which relies on FKI's high power FID convertors.

Offering vector control for constant torque, and full regenerative capability, the FID drives provide a compact, reliable solution - and deliver the energy saving and low harmonic qualities necessary to make the project a success.

RV Triton is the first of its type - a trimaran warship demonstrator that may be the model for the British Navy's Future Surface Combat Combatant Design.

The ship is unique, in that it is the first trimaran of truly ocean-going size to put to sea, the vessel demonstrating its capabilities by crossing the Atlantic in May 2001.

Built at a cost of GBP 13 million, by Southampton-based shipbuilder Vosper Thornycroft, the RV Triton is notable not only for its three hull design, but also for the fact that its propulsion system is fully electrical, providing what is possibly a stepping stone to the world's first all-electric warship.

The ship's propulsion system is based on two 2MW (6600V) diesel generators, converted by switchboards fitted with FKI's FID 5000 drives to supply a 3.5MW motor used for powering the central thrust shaft in the main hull of the vessel.

Further FKI drives - FID 4000 units - have also been supplied to convert power from an auxiliary 400kW (440V) generator to two 350kW motors that drive side steering thrusters, either in tandem or independently.

These provide unrivalled levels of speed control and manoeuvring capability where it is needed most, when entering or leaving harbour.

The FID 5000 drive on the ships main propulsion system is a voltage source frequency convertor based on the well-proven pulsewidth modulation (PWM) principle.

The unit reduces the incoming supplies from 6600V (or up to 90% of the ship's main generating capacity) to the optimum 955V whilst helping keep harmonics levels within the 10% total harmonic distortion required.

The FID 5000 was chosen for its high power capabilities (4100kVA) and excellent performance in emergency-stop and zero shaft speed situations.

Designed with a series of integrated gate-turn-off thyristors (GTOs), the drives can provide dynamic braking via a chopper to direct excess energy into a naturally air cooled resistor.

This feature enables the RV Triton to reduce its crash stopping distance from ten to five lengths when running at full speed (20 knots).

In addition, the FID 5000 provided the perfect solution for use in a ship's control room, as it is equipped with a direct water-cooling system, which replaces the traditional bulky air to water heat exchangers, increasing operational space.

The FKI drives specified on the two auxiliary 350kW thruster motors (rated at 1200rev/min) are FID 4000, 600kVA units.

These inverters - being lower power, are connected directly to the ship's low voltage switchboard.

Both are vector controlled, active front-end types.

Vector control optimises motor performance, ensuring maximum torque across the power range and excellent step responses to improve manoeuvring accuracy and efficiency.

Also aiding efficiency - via energy saving - is the drive's active front end.

It allows full regenerative energy from the thruster motors to be fed back directly into the mains without the need for braking resistors.

The same feature also ensures extremely low harmonic current distortion without the need for bulky phase shift transformers.

As a result, cabinet volume and weight are much reduced, enabling two key objectives in the overall RV Triton design to be achieved.

All the FKI drives used on the RV Triton were specified not only for their performance, but also due to their well-proven operation in marine environments.

Traditionally used in demanding applications such as traction, crane and other marine systems, the high power FKI convertors have provided the reliable operation required for the RV Triton to successfully complete a rigorous 18-month trial period conducted by both British and American Navies.

The ability of the drives to maximise energy efficiency and reduce harmonics has also been instrumental in helping to prove to the US Defence Research Agency that an electric propulsion system is not only a viable option, but may also be the future for warship design.

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