Page 278 - Offshore Electrical Engineering Manual

CHAPTER
8
Power Management

GENERATOR CONTROLS
With any electrical system, the importance of ergonomically designed controls can-
not be overstressed. The following controls and instrumentation are considered to be
the basis for a generator control panel. The logic of a typical generator control panel
is shown in Fig. 4.8.1.

START AND STOP BUTTONS

The start control normally has the function of initiating the engine automatic start
sequence and, depending on the control philosophy adopted, may automatically syn-
chronise the generator with any generators already on load. An ‘auto/manual’ selector
switch may also be provided. This is useful during commissioning to allow an individual
to check each step in the sequence to be made. Two stop controls are often provided, a
normal stop button which initiates a timed run down of the generator load and allows the
engine to cool down before it is stopped. In the case of large gas turbines, a ratcheting
sequence will also be required. This is a facility whereby the engine is rotated at intervals
to prevent hot spots developing which may cause the misalignment of the main shaft.

AUTOMATIC VOLTAGE REGULATOR AND GOVERNOR
RAISE/LOWER SWITCHES
These controls are used to set the voltage and frequency of the generator and, when
in parallel with another generator, allow the sharing of reactive and real power to be
adjusted, respectively. It is an advantage to group these controls and associated elec-
trical metering such as voltmeters, kW and kVAr meters so that manual adjustment of
real and reactive power can be carried out by one operator. If the controls are spread
across four or five panels, each associated with an individual machine, adjustment
can be difficult. If there are only two machines, then controls can be ‘mirrored’ so that
raise/lower controls are located close together in the area on the panels near where
they butt together. An auto/manual voltage control selector switch is also required,
so that commissioning and routine checks may be carried out on the excitation sys-
tem. In some systems, it may not be possible to switch easily from auto to manual
voltage control or vice versa. As automatic voltage regulators (AVRs) are now solid-
state devices and take up very little room in the control panel, a dual AVR system is

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