Saab 340B, Руководство по эксплуатации

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ELECTRICAL
Description
Aircraft Operations Manual
5.1
PAGE 2
Jun 01/19
In case of fire handle is pulled, the corresponding
generator is de
− energized by its GCU and discon-
nected from the GEN BUS.
After any fault causing a GCU to isolate the af-
fected generator, the field relay can be reset by
cycling the respective GEN switch in RESET posi-
tion.
Applicable without mod 2533 installed.
The GCU can not detect DC generator voltage
low (generator not charging) and subsequently
not disconnect a non
− charging generator. Also
see Abnormal Procedures DC voltage low.
NOTE
Applicable with mod 2533 installed.
The GCU will detect DC generator voltage
low situation and subsequently disconnect a non
−
charging generator.
NOTE
2.3 External power
An external power receptacle on the right hand aft
fuselage wing fairing, allows the aircraft to be sup-
plied on ground with 28 V DC power from a ground
power unit.
A status light on the overhead panel indicates when
external power is available.
2.4 Batteries
There are two 24 V/43 ampere − hours nickel − cad-
mium batteries which are installed in the left and
right wing fairings.
With battery power only, each battery supplies pow-
er to its respective HOT BAT BUS and BAT BUS
via GEN BUS. A number of other buses are then
powered from the BAT BUS, see Fig. 2.
When using the batteries for engine start, they will
be connected in series with the Series/Parallel relay
and thereby supplying 48 V DC to the starter/gener-
ator.
Two thermal switches are installed on each battery
to provide overheat protection. The first thermal
switch closes at 57

C so that a NO BAT START
light on the overhead panel comes on, indicating
that the batteries should not be used for engine
starting. A second thermal switch closes at a tem-
perature of 71

C, thereby disconnecting the battery
from its GEN BUS and the START BUS, indicated
by a BAT HOT light on the overhead panel. In an
emergency situation the 71

C thermal switch can
be overridden by setting the battery switch to
OVRD position to assure battery supply to the GEN
BUS.
One thermal sensor is located on each battery to
measure the battery temperature, which is shown
on the temperature indicator on the overhead panel.
The indicator is shared with the fuel temperature
indication by means of a selector switch.
To improve ventilation on ground, a fan is installed
in each battery compartment. The fan is controlled
by the nose landing gear locked down switch when
airborne ram air is used for ventilation.
2.5 Power Distribution Unit (PDU)
A left and a right power distribution unit controls all
primary switching of the different power sources
which might be connected to the aircraft buses. The
following relays are installed in the distribution units:
L/R Generator Relay (GR)
When the generator relay is closed, the starter/gen-
erator powers the GEN BUS. The following condi-
tions must be met for the generator relay to close:
− External power relay open.
− Engine start completed.
− Generator field current reset.
External Power Overvoltage Relay (right PDU)
An overvoltage protection relay will open the exter-
nal power relay or not allow it to close if external
power voltage should exceed 31 volt.
External Power Relay (EPR) (right PDU)
When the external power relay is closed, the exter-
nal power unit powers the DC buses via the START
BUS.
The L GEN BUS is powered via the de − energized
series/parallel relay and the R GEN BUS via the
closed bus tie relay.
The following condition must be met for the external
power relay to close:
− EXT PWR switch on overhead panel in ON posi-
tion.