ELECTRICAL POWER – SIMPLIFIED SCHEMATIC
DIAGRAM
A simplified schematic diagram is used to describe the operation of the
electrical power as follows:
• Normal procedures:
• Engine starting on batteries (BATTERY Starting)
• Engine starting on external power (EXT PWR Starting)
• In-flight normal operation
• Emergency procedures:
• Single Generator Failure
• Single DC Bus Failure
• Dual Generator Failure
BATTERY STARTING
The following diagrams represent the sequence of actions for a normal
battery starting of the engines (steps 1 to 8 on the simplified schematic
diagram). In this example engine no. 2 is started first.
Refer to AW139-RFM-4D – Section 2 for Normal Procedures.
STEP 1
Helicopter is parked and ready for flight. All switches are in the safe position.
STEPS 2 TO 3
When BATTERY MASTER switch is set to ON, Main and Aux Batteries are
connected to ESS BUS 1 and ESS BUS 2 thus providing power to the
rotorcraft essential loads.
The BATTERY MASTER switch at ON also enables the BATTERY MAIN
and the BATTERY AUX switches.
When BATTERY MAIN switch is set to ON, the Main Battery is connected to
MAIN BUS 1 (Main Battery contactor K3 closes) which is then also powered.
When BATTERY AUX switch is set to ON, the Auxiliary Battery is connected
to MAIN BUS 2 (Aux Battery contactor K4 closes), but MAIN BUS 2 is not
powered because of the reverse biased diode (CR5) which only permits
recharging of the Auxiliary battery from MAIN BUS 2.
When GEN 1 and GEN 2 switches are set to ON they give an input to the
relevant GCU so that the GCU will put the relevant generator on-line as soon
as conditions permit.
23 VOLT CHECK
Before attempting starting the engine on batteries, the pilot has to check that
the involved MAIN BUS voltage is not less than 23 V.
STEP 4
As in this example the engine no 2 is started first, the BUS TIE switch must
be set to ON to power MAIN BUS 2.
BUS TIE Contactor closes thus connecting MAIN BUS 1 and MAIN BUS 2.