STADT - STEALTH AC Propulsion Technology for the All-Electric Naval Ships

STADT is a Norwegian drive specialist company that revolutionised the naval industry by introducing STEALTH AC electric propulsion technology. The technology has been on the civil marine market for several years and has already proven its reliability and low noise characteristics. STADT provides the fully integrated scope of electric propulsion, from main switchboards via the STEALTH AC drive and the electric propulsion motors.

The system has a unique set of valuable characteristics not seen in any other electric propulsion systems so far, such as negligible losses in the drive itself, compact design without big transformers, and use of highly reliable technology throughout the system.

Sine-wave technology for warships

STADT offers a real sine-wave technology that is very different from the more known pulse width modulation (PWM) type of AC motor drives. The sine-wave motor control does not generate any electromagnetic interference; instead the noise is fully eliminated. Thus, complex screening of power cables for the propulsion drives is not needed any more. Another advantage is the possibility for a medium-voltage grid, up to 15kV system voltage for this new system, giving minimal electric field from the ship's systems.

Electric propulsion AC drives

The STEALTH AC drive pulls linear power from the generators, so no disturbances are generated. The ship grid will operate with a pure undistorted voltage within all of the main switchboards. This eliminates any overheating of power components and eliminates malfunctions of any kind.

Up until now, electric propulsion systems have used heavy propulsion transformers to cancel harmonic distortion from the PWM drives. The STADT STEALTH AC drive does not need filtering in this way, which makes the transformers obsolete.

Lower fuel consumption and emission

In practical terms, the STADT STEALTH AC drive does not generate any excessive heat during operation, except from electric losses in alternator and electric propulsion motors. This leads to additional system benefits such as:

• Less fuel consumption: up to 8% improvement compared to other types of electric systems due to the patented No-Loss technology
• Longer endurance for the ship
• Lowered emissions of COx, NOx, SOx etc
• Less wild heat dissipation: reduced need for air condition systems
• Increased reliability, and 30 years designed liftetime

This also leads to the elimination of intricate water cooling systems within the AC drive, again leading to improved reliability. The new drive saves space due to the eliminated need for big transformers, and due to a major reduction in the number of components in the inverter topology. The compact design and vast reduction in space can lead to improvements of more than 50% in weight and volume.

Rugged electric propulsion technology for the naval fleet

Throughout the years of development, STADT has focused on how to improve reliability in electric drives for propulsion. Vulnerable components such as capacitors have a modest role to play in the new STEALTH drive. Our insulation strategy has improved dramatically, and the robust thyristors also play an important role in parallel with the IGBT switching and bypassing element operating in sequence.

The drive topology takes advantage of the best features in each component's type, and utilises them in the most effective way, giving a solution with the desired new features mentioned. The STEALTH drive also operates in conjunction with CP propeller systems to perform optimal manoeuvrability and energy efficiency for the vessel.

To avoid a situation where a tiny component failure might stop the ship's propulsion, STADT has implemented a redundant concept from generators via MSB, drives and electric propulsion motors that takes redundancy into account in each level of the system.

Electric ship propulsion motors, generators and switchboards

STADT drive systems can be supplied with custom-built AC propulsion motors in different technologies, such as navy approved with water cooling, as well as new designs based on superconducting elements to reach the most compact design with highest efficiency.

STEALTH AC drives are available from 100kW and up to 100MW in different configurations and a full range of voltage classes - 230V to 15kV.

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