BUS TIE LOGIC
BUS TIE contactor closes if any of the following conditions is met:
• BUS TIE switch = ON
• One GEN = ON-LINE and the other GEN = OFF-LINE
• EXT PWR is connected to helicopter bus bars
STEP 5 – ENGINE 2 STARTING ON BATTERIES
An Engine normal start (AUTO Mode) is initiated by the Engine Electronic
Unit (EEC) when pilot moves the relevant ENG MODE switch on the ENG
control panel to IDLE or FLIGHT.
This causes the GCU to close the relevant Generator contactor so the
starter is fed by the MAIN Battery power via MAIN BUS 2 and cranks the
engine.
Due to the great amount of power required to start the engine, MAIN battery
voltage drops very much (represented with a paler shade of color).
The AUX battery only supplies the ESS BUS 1 and 2, in order to keep a
sufficient high voltage for the pilot Display Units (PFD and MFD): this
ensures pilots can monitor engine parameters during starting.
Engine start sequence is terminated by the EEC when it detects Ng = 49%:
the START signal is removed and the GCU releases the Generator
contactor.
The EEC then accelerates the engine to Nf = 65% (IDLE) or Nf = 100%
(FLIGHT).
NOTE
An Engine Manual Start (MANUAL Mode) is initiated by pressing the
START push-button on the relevant Engine Control Lever (ECL)
which directly sends a control signal to the relevant GCU.
In this case the EEC is not involved and the start sequence is
terminated by the GCU thanks to the Generator speed sensing
signal.