More than 470 system installations underlines Wärtsilä’s position as the world leader in this market segment.”
Shaft generators on board ships are driven by the main engine to supply power to the mains. The mains have to be supplied with constant voltage and frequency by the shaft generator whilst the speed of the main engine changes, i.e. when the vessel travels at different speeds or if the propeller speed strongly varies in heavy seas.
On ships with fixed pitch propellers, the speed is set via the propeller speed. If using controllable pitch propellers, the shaft speed and the propeller pitch are adjusted simultaneously in order to achieve optimum propeller efficiency in this so-called combinator mode. Even with this type of propeller, it is thus economical to use shaft generator systems with frequency converter for variable speed in order to permit combinator mode from pier to pier.
All requirements of a ship‘s mains are met unrestrictedly while the shaft generator is operating:
Wärtsilä’s shaft generator systems are designed with PWM frequency converters using modern IGBT technology. An additional synchronous compensator is no longer needed to generate the reactive power or the short circuit current, and is not required for the voltage control or for the filter circuits in order to lower the harmonics to admissible levels. This configuration has the following features and benefits:
The monitoring, test and simulation display integrated in the shaft generator panel permits monitoring of the system during normal operations. However, even with the main engine out of operation, the system can still be tested and virtually all system functions can be simulated. For monitoring, test and simulation, a colour display with a touch screen provides different mimic screens, such as OVERVIEW, STATUS, VALUES, ALARM, TEST and SETUP.
The shaft generator systems are equipped with a central, microprocessor-based computer for fully digitalized closed-loop and open-loop control and for test and simulation. Compared to earlier versions, numerous PC boards with relays for logic operations and elements for analogue and digital functions, are no longer required and have been eliminated. This drastic reduction in the number of components results in a substantial improvement in reliability and availability.
The harmonic content at the output of the shaft generator system has to be effectively reduced to admissible levels according to the classification. Wärtsilä SAM Electronics’ shaft generator systems are designed with a PWM frequency converter with a high IGBT pulse frequency, resulting in a higher than required mains quality without any measures, such as a filter circuit or duplex reactor. The THD in the mains voltage is below 5% in all operational states.
Shaft generator systems are a valuable technical solution for ship owners who are looking for economical and cleaner electrical power generation during their sea voyage.”
Shaft generator systems with frequency converters supply a three-phase current of constant voltage and frequency to the mains at variable main engine speeds. The useful speed range of the shaft generator can be defined from the ship’s operational requirements. For example, it is possible to select a shaft generator speed range of 60% to 100% of the main engine speed with a constant system output.
All shaft generator systems have one thing in common: The active power required for the mains is generated by the main engine. However, the shaft generator can be arranged and driven by the main engine in various configurations.
For additional shaft motor operation the diode rectifier is replaced by a PWM rectifier similar to the PWM inverter and the system control is adapted accordingly. With this configuration motor operation is provided as follows:
For shore connection with 50 Hz or 60 Hz the frequency converter of the shaft generator system can be used to adapt the shore frequency to the ship’s mains frequency. For that purpose the connection between shaft generator and converter is switched off and the converter is supplied (via cable reel, circuit breaker and transformer) from the shore. With this configuration the ship is full flexible for shore connection worldwide.
One of the latest features is the patented integration of the shaft generator converter into a Waste Heat Recovery System (WHRS). In conjunction with our partners, our Waste Heat Recovery System further enhances overall operational efficiency and cost savings for our customers.
Shaft Generators lower fuel costs, and reduce both maintenance and lubricant costs – for more profit and nature friendly benefits.”
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Wärtsilä is a global leader in advanced technologies and complete lifecycle solutions for the marine and energy markets. By emphasising sustainable innovation and total efficiency, Wärtsilä maximises the environmental and economic performance of the vessels and power plants of its customers.
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