Wartsila ?31DF Series Product Manual page 178

14. Automation System
Immediately after the engine stop signal is activated in gas operating mode, the GVU performs
gas shut-off and ventilation. The pilot injection is active during the first part of the deceleration
in 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 exhaust
gas system is ventilated to discharge any unburned gas.
14.2.3.2 Shutdown mode
Shutdown 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 be
investigated and corrected before re-start.
14.2.3.3 Emergency stop mode
The 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 emergency
stop 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 control
14.2.4.1 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 also
possible to select an operating mode in which the speed reference can be adjusted with
increase/decrease signals.
The electronic speed control handles load sharing between parallel engines, fuel limiters, and
various other control functions (e.g. ready to open/close clutch, speed filtering). Overload
protection and control of the load increase rate must however be included in the propulsion
control as described in the chapter
14.2.4.2 Generating sets
The electronic speed control is integrated in the engine automation system.
The load sharing can be based on traditional speed droop, or handled independently by the
speed control units without speed droop. The later load sharing principle is commonly referred
to as isochronous load sharing. With isochronous load sharing there is no need for load
balancing, frequency adjustment, or generator loading/unloading control in the external control
system.
In a speed droop system each individual speed control unit decreases its internal speed
reference when it senses increased load on the generator. Decreased network frequency with
higher system load causes all generators to take on a proportional share of the increased total
load. Engines with the same speed droop and speed reference will share load equally. Loading
and unloading of a generator is accomplished by adjusting the speed reference of the individual
speed control unit. The speed droop is typically 4%, which means that the difference in
frequency between zero load and maximum load is 4%.
In isochronous mode the speed reference remains constant regardless of load level. Both
isochronous load sharing and traditional speed droop are standard features in the speed
control and either mode can be easily selected. If the ship has several switchboard sections
14-10
Operating Ranges.
Wärtsilä 31DF Product Guide
DBAE248994