Alpha Technologies AlphaGen PN-6x-T 7.5kW 48Vdc - Manual (Page 73)

042-288-B0-001, Rev. A2 73
6.0 Operation
6.1 Normal Operating Condition
Under normal operating conditions (no alarms) the ECM’s RAS switch is in the AUTO
position. The ECM has control over the APU while in Auto mode. Each time the RAS switch
is moved from the STOP position to the AUTO position, the ECM, after a short delay, runs
the APU for one minute. This indicates that the ECM is in the Auto mode, and is capable of
starting and stopping the APU automatically. The APU can be controlled manually by placing
the RAS switch in the RUN or STOP positions. In Auto mode, the ECM continuously monitors
the AC line voltage, DC bus voltage, enclosure sensors, and APU status. If a fault occurs, the
ECM determines whether to start or inhibit the APU based on the type of fault.
6.1.1 AC Line Fail
Standby Operating Condition Less Than Three Minutes
If an AC line disturbance or outage is less than three minutes, the ECM will not start
the APU unless the battery bus voltage drops below a programmable threshold (Low
DC Bus Level). The default is 49V. The ECM will notify the system operator of a line
failure via the front panel LEDs, and through the AC Fail Relay located on Terminal
Block 2 (see Table 3-1).
Standby Operating Condition More Than Three Minutes
If an AC line disturbance or outage is longer than three minutes, the ECM start delay
timer expires and the ECM starts the APU. The ECM starts and runs the APU until
either a normal shutdown or major alarm occurs. If the APU fails to start, the ECM
attempts to start the engine up to nine times, with either 30 or 60 second intervals
between attempts. If the engine will not start, the ECM reports an Engine Over-crank
alarm.
6.1.2 Low DC Bus Level
If the DC bus voltage level drops to 49Vdc, or below, the APU will start. The APU
continues to run until the ECM DC Sense Voltage increases to 53.5Vdc or higher.
Once the ECM DC Sense Voltage level is reached, and the 12-minute cool-down
period expires, the APU will stop.
The 53.5Vdc threshold is set to assure rectifiers are supporting the DC bus before
the generator goes into cool down and shuts off. The level assumes a rectifier set
point of 54.5Vdc at 25°C and a battery temperature compensation of -70mV/c.
** Note: Under very hot battery temperature conditions the voltage threshold may not
be eclipsed by rectifier output until temperatures cool.