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The shaft generator system has made significant advances with regard to efficiency, weight, and size with improved functionality being enabled by the development in power electronics technology, generator design including permanent magnet machines, and higher performance control systems. However, it is their inherent simplicity, high efficiency, and energy-saving capability (enabling lower fuel consumption and avoidance of CO2 emissions) that make shaft generators a viable and cost-effective system to help ship owners and designers meet ever-more stringent efficiency and emission limits.
In this article we look in detail at the system structure of shaft generator systems, and why variable speed shaft generators have gradually become the preferred solution (versus direct mechanical connection to the main engine). We describe the unique characteristics of the latest low-voltage frequency converter technology used by ABB in our shaft generator systems, as well as the technical advantages of permanent magnet (PM) generators versus synchronous excitation generators. The frequency converter is configurable to single- or multi-drive enabling auxiliary engines to easily be integrated with alternative power sources such as battery energy storage, fuel cells, solar panels, wind power, or electricity from shore.
The article also explores the different operation modes of speed shaft generators including as a power generator (PTO) for the vessel’s electrical network; booster motor (PTI) for the main propulsion shaft; or alternative propulsion system (PTH) providing redundancy and added safety. In addition, we cover key system performance features including short circuit protection capability in case of faults; managing harmonic distortions to protect the ship’s grid; equalized loading across parallel auxiliary generators; fast compensation capability to handle rapid load changes; encoder-less control of the rotor pole position for motor control purposes; advanced synchronization with the ship’s grid on start-up; and power factor compensation for shore power connection.
