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Wartsila ?31DF Series Product Manual
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Immediately after the engine stop signal is activated in gas operating mode, the GVU performsgas shut-off and ventilation. The pilot injection is active during the first part of the decelerationin order to ensure that all gas remaining in engine is burned.In case the engine has been running on gas within two minutes prior to the stop the exhaustgas system is ventilated to discharge any unburned gas.14.2.3.2 Shutdown modeShutdown mode is initiated automatically as a response to measurement signals.In shutdown mode the clutch/generator breaker is opened immediately without unloading.The actions following a shutdown are similar to normal engine stop.Shutdown mode must be reset by the operator and the reason for shutdown must beinvestigated and corrected before re-start.14.2.3.3 Emergency stop modeThe sequence of engine stopping in emergency stop mode is similar to shutdown mode,except that also the pilot fuel injection is de-activated immediately upon stop signal.Emergency stop is the fastest way of manually shutting down the engine. In case the emergencystop push-button is pressed, the button is automatically locked in pressed position.To return to normal operation the push button must be pulled out and alarms acknowledged.14.2.4 Speed control14.2.4.1 Main engines (mechanical propulsion)The electronic speed control is integrated in the engine automation system.The remote speed setting from the propulsion control is an analogue 4-20 mA signal. It is alsopossible to select an operating mode in which the speed reference can be adjusted withincrease/decrease signals.The electronic speed control handles load sharing between parallel engines, fuel limiters, andvarious other control functions (e.g. ready to open/close clutch, speed filtering). Overloadprotection and control of the load increase rate must however be included in the propulsioncontrol as described in the chapter Operating Ranges.14.2.4.2 Generating setsThe electronic speed control is integrated in the engine automation system.The load sharing can be based on traditional speed droop, or handled independently by thespeed control units without speed droop. The later load sharing principle is commonly referredto as isochronous load sharing. With isochronous load sharing there is no need for loadbalancing, frequency adjustment, or generator loading/unloading control in the external controlsystem.In a speed droop system each individual speed control unit decreases its internal speedreference when it senses increased load on the generator. Decreased network frequency withhigher system load causes all generators to take on a proportional share of the increased totalload. Engines with the same speed droop and speed reference will share load equally. Loadingand unloading of a generator is accomplished by adjusting the speed reference of the individualspeed control unit. The speed droop is typically 4%, which means that the difference infrequency between zero load and maximum load is 4%.In isochronous mode the speed reference remains constant regardless of load level. Bothisochronous load sharing and traditional speed droop are standard features in the speedcontrol and either mode can be easily selected. If the ship has several switchboard sections14-10 DBAE248994Wärtsilä 31DF Product Guide14. Automation System |
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