CN ES Technology Manager, ABB Marine & Ports China
General introduction – shaft generator
In the marine segment, “shaft generator” is defined as the rotation electrical machine that takes power from the main propulsion diesel engine to produce electricity. A shaft generator is not state-of-the-art technology in the marine industry, but it is decades old.
Due to the differences in fuel consumption of the two-stroke low speed propulsion engine and the medium-speed genset four-stroke engine, the shaft generator solution can offer significant fuel savings. It is widely applied in various ship types, especially fishing vessels, Ro-Ro ships, container ships and oil tankers.
ABB Mariine & Ports has been active in the shaft generator segment since the 2010s, focusing on delivering qualified variable speed shaft generator solutions. ABB shaft generator solutions offer advanced performance verified in project after project. The ABB shaft generator solution demonstrates:
- High qualified voltage output: Total voltage harmonic is very low, even to less than 2% in some cases
- Powerful short circuit ability: Controllable short circuit magnitude and durations
- Strong dynamic performance: Support the starting up of a motor with high power rating;
- Fast synchronous: Built-in fast synchronous meets variable application
- Harmonic compensation: Provides optional harmonic compensation function to help increase ship grid quality
Besides ‘traditional’ shaft generator solutions, European owners are incresingly asking for more environmentally friendly and flexible solutions such as battery integrated shaft generator drive systems that require deep insight into various components including the main engine, propeller, shaft generator, auxiliary generator, battery and other consumers. Knowledge of how these components work together and compensate each other to achieve the target set by customer is also required.
Advanced application – shaft generator plus energy storage
With the development of power electronics and energy storage systems, the market is demanding advanced systems able to perform complex functions. The below diagram shows the system in a modern Ro-Ro ship, featuring shaft generator together with energy storage, and offering variable operational profiles to enhance system benefits.
In addition to the well known benefits of onboard energy storage systems, like zero emissions in port, there are more functions when a shaft generator works with energy storage:
Dynamic support for Power Take Off (PTO): Rapid hotel load changes with AC grid can cause mechanical impact at the main propulsion shaft when the shaft generator is working at Power Take Off (PTO) mode, increasing the wear of mechanical components. Energy storage systems enable dynamic support to mitigate mechanical wear and sustain steady shaft generator loads for improved efficiency.
Dynamic support for main propulsion engine: Propeller characteristics fluctuate when sailing in heavy weather, which may cause the propulsion loads to change dramatically with variations of tide and wind. To ensure that the main engine is working at optimal efficiency, a control system needs to tune pitch accordingly to prevent main engine overload. The consequences of tuning pitch are increased mechanical wear and impact on ship speed. The energy storage system and shaft generator work together to sustain the propeller load variations instead of tuning mechanical propeller pitch.
Future hybrid solutions
Onboard electrical power systems are shifting to hybridization, where variable energy sources co-exist on vessels. Shaft generators offer possibilities to achieve hybrid requirements and help shipowners to achieve enhanced benefits.