Page 352 - Introduction to Marine Engineering

Instrumentation and control

ship's actual course resulting in a feedback to the controller and
subsequent corrective action. The controller action must be correctly
adjusted for the particular external conditions to ensure that excessive
rudder movement does not occur.

Electrical supply control
The automatic provision of electrical power to meet varying load
demands can be achieved by performing the following functions
automatically:

1. Prime mover start up.
2. Synchronising of incoming machine with bus-bars.
3. Load sharing between alternators,
4. Safety and operational checks on power supply and equipment in
operation.
5. Unloading, stopping and returning to standby of surplus machines.
6. Preferential tripping of non-essential loads under emergency
conditions and their reinstating when acceptable.
A logic flow diagram for such a system is given in Figure 15.47. Each
of three machines is considered able to supply 250 kW. A loading in
excess of this will result in the start up and synchronising of another

>750, 1 .
<500kW ,
>250kW Start up Unload
Machine No.1 1 »» No. 2 No. 3 « j . |kW Preferential
on load machine machine Lo 2r!,,J tripping
^v" I
, r*' *•" T
.... •
Return to Open Close
stand by Synchronise circuit circuit
with supply
condition breaker breaker
t ' 1 » •
Open Close Return to '
circuit circuit stand by Synchronise
breaker breaker condition with supply
t '- v \
'
Unload \-—\ >500 kW *^ - „ Start up
No. 2 « J L oad 1 — »• No. 3
machine machine
<250kW
Figure 15,47 Automatic load control of alternators
machine. Should the load fall to a value where a running machine is
unnecessary it will be unloaded, stopped and returned to the standby
condition. If the system should overload through some fault, such as a
machine not starting, an alarm will be given and preferential tripping
will occur of non-essential loads. Should the system totally fail the
emergency alternator will start up and supply essential services and
lighting through its switchboard.