WÄRTSILÄ 46F Series, Product Manual

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In normal operation the load should not be reduced from 100% to 0% in less than 15 seconds.
When absolutely necessary, the load can be reduced as fast as the pitch setting system can
react (overspeed due to windmilling must be considered for high speed ships).
2.2.2 Diesel electric propulsion
Fig 2-3 Maximum load increase rates for engines operating at nominal speed
In normal operation the load should not be reduced from 100% to 0% in less than 15 seconds.
In an emergency situation the full load can be thrown off instantly.
The maximum deviation from steady state speed is less than 10%, when applying load
according to the emergency loading ramp. Load increase according to the normal ramp
correspondingly results in less than 3% speed deviation.
2.2.2.1 Maximum instant load steps
The electrical system must be designed so that tripping of breakers can be safely handled.
This requires that the engines are protected from load steps exceeding their maximum load
acceptance capability. The maximum permissible load step for an engine that has attained
normal operating temperature is 33% MCR. The resulting speed drop is less than 10% and
the recovery time to within 1% of the steady state speed at the new load level is max. 5
seconds.
When electrical power is restored after a black-out, consumers are reconnected in groups,
which may cause significant load steps. The engine must be allowed to recover for at least
10 seconds before applying the following load step, if the load is applied in maximum steps.
2.2.2.2 Start-up time
A diesel generator typically reaches nominal speed in about 25 seconds after the start signal.
The acceleration is limited by the speed control to minimise smoke during start-up.
2.3 Operation at low load and idling
The engine can be started, stopped and operated on heavy fuel under all operating conditions.
Continuous operation on heavy fuel is preferred rather than changing over to diesel fuel at low
load operation and manoeuvring. The following recommendations apply:
Absolute idling (declutched main engine, disconnected generator)
DAAB605814 2-3
2. Operating Ranges Wärtsilä 46F Product Guide