ELECTRICAL
Description
Aircraft Operations Manual
5.1
PAGE
4
Jun 01/19
position or in AUTO position with both generators
on line.
L/R MAIN START BUS relay
When a MAIN START BUS relay is closed, it con-
nects the MAIN START BUS to its BAT BUS.
To close a MAIN START BUS relay, the respective
generator relay or the external power relay must be
closed.
L/R MAIN BUS relay
When a MAIN BUS relay is closed, it connects the
MAIN BUS to the GEN BUS.
To close a MAIN BUS relay the following conditions
must be met:
−
The corresponding BAT BUS powered.
−
The corresponding MAIN START BUS relay
closed.
−
No engine starting in progress.
Overcurrent relay
To protect the main distribution system in case of a
short circuit, there is a bus tie overcurrent relay
installed.
Should the current over the relay exceed 800 am-
pere the overcurrent relay trips, causing the bus tie
relay to open.
Manual reset of the overcurrent relay can be done
by the RESET BUS TIE pushbutton (K
−
1) on the
forward part of left pilot’s circuit breaker panel.
Automatic override of the bus tie overcurrent
protection is performed during an engine start.
2.6
DC Buses
Remote Controlled Circuit Breakers (RCCB) are
used to switch high current and are controlled either
by a switch or by an electric bus via a small current
CB. The RCCB will open for an overcurrent. The
respective GEN BUS supplies power to its respec-
tive BAT BUS and to respective MAIN BUS via the
MAIN BUS relay. The respective MAIN BUS sup-
plies its AVIONIC BUS visa a RCCB. The RCCB
will close when respective AVIONIC switch is set to
ON provided the respective MAIN BUS is powered.
The R MAIN BUS also supplies the UTILITY BUS
via a RCCB. If the R MAIN BUS is powered the
RCCB will close and supply power to the UTILITY
BUS provided both generators are on line or exter-
nal power is switched on.
The respective BAT BUS supplies the L/R MAIN
START BUS via its main start bus relay and L/R
ESS BUS via its ESS BUS relay. The ESS BUS
relays are open during engine start.
The L/R MAIN START BUS supplies its respective
AVIONIC START BUS when the L/R AVION switch
is ON.
When the ESS AVION switch is ON the ESS
AVIONIC BUS is supplied from the L ESS BUS and
the EMER AVIONIC BUS from the EMERGENCY
BUS.
2.7
Emergency power supply
Emergency power is supplied by the emergency
power supply unit which contains the emergency
battery and a battery heater. The battery is a 24 V/5
ampere
−
hours lead
−
acid battery. The battery heater
will be activated automatically in cold temperatures.
The heater warms up the battery for best battery
efficiency.
When the L BAT BUS is powered from generator or
external power, the emergency battery is charged
from this bus. The emergency battery begins to
supply power to the EMERGENCY BUS when the L
BAT BUS voltage goes below 24 V.
If the emergency battery voltage drops below 24 V,
the EMER PWR light on the overhead panel comes
on. This light also comes on if the EMERGENCY
BUS is not powered, provide the warning electronic
unit (WEU) is powered.
2.8
DC/AC inverter system
Applicable with a main and a standby inverter
installed
There are two 400 Hz inverters, one main inverter
and one standby inverter. With the MAIN INV 115V
26V switch in ON and the 26V inverter switch in
MAIN INV, the main inverter supplies power to:
−
L and R INV BUS 115V AC
−
L and R INV BUS 26V AC
If the DC supply from the L MAIN BUS to the main
inverter is interrupted, or the main inverter fails, the
