Page 281 - Offshore Electrical Engineering Manual

268 CHAPTER 8 Power Management

operator more confidence during paralleling operations. An auto-synch unit and a
check-synch relay should be provided; the auto-synch being used normally with
automatic sequencing and the check synch when any paralleling is being carried
out manually. The function of both devices is to provide a ‘close permissive’ signal
to the generator circuit breaker when voltage and frequency conditions are suitable
for paralleling. If the signal is not present, circuit breaker closing is prevented by
the control logic.

INSTRUMENTATION
Metering
The control panel should provide at-a-glance information to allow the operator to
carry out his work. Voltage and frequency displays should be digital and preferably
to no more than two decimal places for fast reading. If the generator nominal volt-
age is more than 1 kV, the display should also be in kilovolts, again for fast reading.
Although this means that the operator only sees changes in steps of 10 V, this is
better than seeing in an equivalent analogue panel meter and is compatible with the
accuracy of the transducer. Real and reactive power meters should preferably be ana-
logue, as they are used mainly for balancing loads between machines and the pointer
‘semaphore’ effect is more quickly appreciated by the operator. A power factor meter
should be provided of either digital or analogue type. However, in either case, the
words ‘leading’ and ‘lagging’ should be displayed rather than ‘+’ and ‘−’.

Synchronising Indicators
The indication provided by a particular instrument should preferably be duplicated
by another for safety and operator confidence. For instance, a synchroscope should
be supplemented by synchronising lamps (preferably three) for manual synchronis-
ing. Lamps should also be provided to indicate that check- and auto-synch permis-
sive signals are present during circuit breaker closing. Where generator controls
cannot be grouped conveniently, it will be necessary to provide busbar voltage and
frequency meters as an aid to the operator during paralleling. If there are more than
two generators in the system, a mimic panel is recommended. The mimic should
show the electrical system in diagrammatic form. The various controls and indi-
cators for each machine should be located on the mimic at positions where they
are clearly associated with the machine whose parameters they are displaying or
controlling.

Alarm Annunciator
As with any machinery, it is necessary to monitor each generator for faults and failures
and bring them quickly to the attention of the operator. This is usually accomplished
by using a matrix of windows, each engraved with a particular fault or failure. Each
of these windows will be lit when a particular fault is sensed by a transducer located
on the engine or generator. The transducers may be level switches, for example,
monitoring lube oil level and operating on low oil level to light up the annunciator